rust-analyzer

At its core, rust-analyzer is a library for semantic analysis of Rust code as it changes over time. This manual focuses on a specific usage of the library -- running it as part of a server that implements the Language Server Protocol (LSP). The LSP allows various code editors, like VS Code, Emacs or Vim, to implement semantic features like completion or goto definition by talking to an external language server process.

To improve this document, send a pull request: https://github.com/rust-lang/rust-analyzer

The manual is written in markdown and includes some extra files which are generated from the source code. Run cargo test and cargo xtask codegen to create these.

If you have questions about using rust-analyzer, please ask them in the "IDEs and Editors" topic of Rust users forum.

Installation

To use rust-analyzer, you need a rust-analyzer binary, a text editor that supports LSP, and the source code of the Rust standard library.

If you're using VS Code, the extension bundles a copy of the rust-analyzer binary. For other editors, you'll need to install the binary and configure your editor.

Rust Standard Library

rust-analyzer will attempt to install the standard library source code automatically. You can also install it manually with rustup.

$ rustup component add rust-src

Only the latest stable standard library source is officially supported for use with rust-analyzer. If you are using an older toolchain or have an override set, rust-analyzer may fail to understand the Rust source. You will either need to update your toolchain or use an older version of rust-analyzer that is compatible with your toolchain.

If you are using an override in your project, you can still force rust-analyzer to use the stable toolchain via the environment variable RUSTUP_TOOLCHAIN. For example, with VS Code or coc-rust-analyzer:

{ "rust-analyzer.server.extraEnv": { "RUSTUP_TOOLCHAIN": "stable" } }

Crates

There is a package named ra_ap_rust_analyzer available on crates.io, for people who want to use rust-analyzer programmatically.

For more details, see the publish workflow.

VS Code

This is the best supported editor at the moment. The rust-analyzer plugin for VS Code is maintained in tree.

You can install the latest release of the plugin from the marketplace.

Note that the plugin may cause conflicts with the previous official Rust plugin. The latter is no longer maintained and should be uninstalled.

The server binary is stored in the extension install directory, which starts with rust-lang.rust-analyzer- and is located under:

• Linux: ~/.vscode/extensions

• Linux (Remote, such as WSL): ~/.vscode-server/extensions

• macOS: ~/.vscode/extensions

• Windows: %USERPROFILE%\.vscode\extensions

As an exception, on NixOS, the extension makes a copy of the server and stores it under ~/.config/Code/User/globalStorage/rust-lang.rust-analyzer.

Note that we only support the two most recent versions of VS Code.

Updates

The extension will be updated automatically as new versions become available. It will ask your permission to download the matching language server version binary if needed.

Nightly

We ship nightly releases for VS Code. To help us out by testing the newest code, you can enable pre-release versions in the Code extension page.

Manual installation

Alternatively, download a VSIX corresponding to your platform from the releases page.

Install the extension with the Extensions: Install from VSIX command within VS Code, or from the command line via:

$ code --install-extension /path/to/rust-analyzer.vsix

If you are running an unsupported platform, you can install rust-analyzer-no-server.vsix and compile or obtain a server binary. Copy the server anywhere, then add the path to your settings.json, for example:

{ "rust-analyzer.server.path": "~/.local/bin/rust-analyzer-linux" }

Building From Source

Both the server and the Code plugin can be installed from source:

$ git clone https://github.com/rust-lang/rust-analyzer.git && cd rust-analyzer
$ cargo xtask install

You’ll need Cargo, nodejs (matching a supported version of VS Code) and npm for this.

Note that installing via xtask install does not work for VS Code Remote, instead you’ll need to install the .vsix manually.

If you’re not using Code, you can compile and install only the LSP server:

$ cargo xtask install --server

Make sure that .cargo/bin is in $PATH and precedes paths where rust-analyzer may also be installed. Specifically, rustup includes a proxy called rust-analyzer, which can cause problems if you’re planning to use a source build or even a downloaded binary.

VS Code or VSCodium in Flatpak

Setting up rust-analyzer with a Flatpak version of Code is not trivial because of the Flatpak sandbox. While the sandbox can be disabled for some directories, /usr/bin will always be mounted under /run/host/usr/bin. This prevents access to the system’s C compiler, a system-wide installation of Rust, or any other libraries you might want to link to. Some compilers and libraries can be acquired as Flatpak SDKs, such as org.freedesktop.Sdk.Extension.rust-stable or org.freedesktop.Sdk.Extension.llvm15.

If you use a Flatpak SDK for Rust, it must be in your PATH:

• install the SDK extensions with flatpak install org.freedesktop.Sdk.Extension.{llvm15,rust-stable}//23.08
• enable SDK extensions in the editor with the environment variable FLATPAK_ENABLE_SDK_EXT=llvm15,rust-stable (this can be done using flatseal or flatpak override)

If you want to use Flatpak in combination with rustup, the following steps might help:

• both Rust and rustup have to be installed using https://rustup.rs. Distro packages will not work.

• you need to launch Code, open a terminal and run echo $PATH

• using Flatseal, you must add an environment variable called PATH. Set its value to the output from above, appending :~/.cargo/bin, where ~ is the path to your home directory. You must replace ~, as it won’t be expanded otherwise.

• while Flatseal is open, you must enable access to "All user files"

A C compiler should already be available via org.freedesktop.Sdk. Any other tools or libraries you will need to acquire from Flatpak.

rust-analyzer Binary

Text editors require the rust-analyzer binary to be in $PATH. You can download pre-built binaries from the releases page. You will need to uncompress and rename the binary for your platform, e.g. from rust-analyzer-aarch64-apple-darwin.gz on Mac OS to rust-analyzer, make it executable, then move it into a directory in your $PATH.

On Linux to install the rust-analyzer binary into ~/.local/bin, these commands should work:

$ mkdir -p ~/.local/bin
$ curl -L https://github.com/rust-lang/rust-analyzer/releases/latest/download/rust-analyzer-x86_64-unknown-linux-gnu.gz | gunzip -c - > ~/.local/bin/rust-analyzer
$ chmod +x ~/.local/bin/rust-analyzer

Make sure that ~/.local/bin is listed in the $PATH variable and use the appropriate URL if you’re not on a x86-64 system.

You don’t have to use ~/.local/bin, any other path like ~/.cargo/bin or /usr/local/bin will work just as well.

Alternatively, you can install it from source using the command below. You’ll need the latest stable version of the Rust toolchain.

$ git clone https://github.com/rust-lang/rust-analyzer.git && cd rust-analyzer
$ cargo xtask install --server

If your editor can’t find the binary even though the binary is on your $PATH, the likely explanation is that it doesn’t see the same $PATH as the shell, see this issue. On Unix, running the editor from a shell or changing the .desktop file to set the environment should help.

rustup

rust-analyzer is available in rustup:

$ rustup component add rust-analyzer

Arch Linux

The rust-analyzer binary can be installed from the repos or AUR (Arch User Repository):

• rust-analyzer (built from latest tagged source)

• rust-analyzer-git (latest Git version)

Install it with pacman, for example:

$ pacman -S rust-analyzer

Gentoo Linux

rust-analyzer is installed when the rust-analyzer use flag is set for dev-lang/rust or dev-lang/rust-bin. You also need to set the rust-src use flag.

macOS

The rust-analyzer binary can be installed via Homebrew.

$ brew install rust-analyzer

Windows

It is recommended to install the latest Microsoft Visual C++ Redistributable prior to installation. Download links can be found here.

Other Editors

rust-analyzer works with any editor that supports the Language Server Protocol.

This page assumes that you have already installed the rust-analyzer binary.

• Emacs
  • Eglot
  • LSP Mode
• Vim/Neovim
  • coc-rust-analyzer
  • LanguageClient-neovim
  • YouCompleteMe
  • ALE
  • nvim-lsp
  • vim-lsp
• Sublime Text
  • Sublime Text 4:
  • Sublime Text 3:
• GNOME Builder
• Eclipse IDE
• Kate Text Editor
• juCi++
• Kakoune
• Helix
• Visual Studio 2022
  • rust-analyzer.vs
  • VS RustAnalyzer
  • SourceGear Rust
• Lapce
• Zed

Emacs

To use rust-analyzer, you need to install and enable one of the two popular LSP client implementations for Emacs, Eglot or LSP Mode. Both enable rust-analyzer by default in Rust buffers if it is available.

Eglot

Eglot is the more minimalistic and lightweight LSP client for Emacs, integrates well with existing Emacs functionality and is built into Emacs starting from release 29.

After installing Eglot, e.g. via M-x package-install (not needed from Emacs 29), you can enable it via the M-x eglot command or load it automatically in rust-mode via

(add-hook 'rust-mode-hook 'eglot-ensure)

To enable clippy, you will need to configure the initialization options to pass the check.command setting.

(add-to-list 'eglot-server-programs
             '((rust-ts-mode rust-mode) .
               ("rust-analyzer" :initializationOptions (:check (:command "clippy")))))

For more detailed instructions and options see the Eglot manual (also available from Emacs via M-x info) and the Eglot readme.

Eglot does not support the rust-analyzer extensions to the language-server protocol and does not aim to do so in the future. The eglot-x package adds experimental support for those LSP extensions.

LSP Mode

LSP-mode is the original LSP-client for emacs. Compared to Eglot it has a larger codebase and supports more features, like LSP protocol extensions. With extension packages like LSP UI it offers a lot of visual eyecandy. Further it integrates well with DAP mode for support of the Debug Adapter Protocol.

You can install LSP-mode via M-x package-install and then run it via the M-x lsp command or load it automatically in rust buffers with

(add-hook 'rust-mode-hook 'lsp-deferred)

For more information on how to set up LSP mode and its extension package see the instructions in the LSP mode manual. Also see the rust-analyzer section for rust-analyzer specific options and commands, which you can optionally bind to keys.

Note the excellent guide from @rksm on how to set-up Emacs for Rust development with LSP mode and several other packages.

Vim/Neovim

There are several LSP client implementations for Vim or Neovim:

coc-rust-analyzer

1. Install coc.nvim by following the instructions at coc.nvim (Node.js required)

2. Run :CocInstall coc-rust-analyzer to install coc-rust-analyzer, this extension implements most of the features supported in the VSCode extension:

   • automatically install and upgrade stable/nightly releases

   • same configurations as VSCode extension, rust-analyzer.server.path, rust-analyzer.cargo.features etc.

   • same commands too, rust-analyzer.analyzerStatus, rust-analyzer.ssr etc.

   • inlay hints for variables and method chaining, Neovim Only

Note: coc-rust-analyzer is capable of installing or updating the rust-analyzer binary on its own.

Note: for code actions, use coc-codeaction-cursor and coc-codeaction-selected; coc-codeaction and coc-codeaction-line are unlikely to be useful.

LanguageClient-neovim

1. Install LanguageClient-neovim by following the instructions here

   • The GitHub project wiki has extra tips on configuration

2. Configure by adding this to your Vim/Neovim config file (replacing the existing Rust-specific line if it exists):

   let g:LanguageClient_serverCommands = {
   \ 'rust': ['rust-analyzer'],
   \ }
   

YouCompleteMe

Install YouCompleteMe by following the instructions here.

rust-analyzer is the default in ycm, it should work out of the box.

ALE

To use the LSP server in ale:

let g:ale_linters = {'rust': ['analyzer']}

nvim-lsp

Neovim 0.5 has built-in language server support. For a quick start configuration of rust-analyzer, use neovim/nvim-lspconfig. Once neovim/nvim-lspconfig is installed, use lua require'lspconfig'.rust_analyzer.setup({}) in your init.vim.

You can also pass LSP settings to the server:

lua << EOF
local lspconfig = require'lspconfig'

local on_attach = function(client)
    require'completion'.on_attach(client)
end

lspconfig.rust_analyzer.setup({
    on_attach = on_attach,
    settings = {
        ["rust-analyzer"] = {
            imports = {
                granularity = {
                    group = "module",
                },
                prefix = "self",
            },
            cargo = {
                buildScripts = {
                    enable = true,
                },
            },
            procMacro = {
                enable = true
            },
        }
    }
})
EOF

If you're running Neovim 0.10 or later, you can enable inlay hints via on_attach:

lspconfig.rust_analyzer.setup({
    on_attach = function(client, bufnr)
        vim.lsp.inlay_hint.enable(true, { bufnr = bufnr })
    end
})

Note that the hints are only visible after rust-analyzer has finished loading and you have to edit the file to trigger a re-render.

See https://sharksforarms.dev/posts/neovim-rust/ for more tips on getting started.

Check out https://github.com/mrcjkb/rustaceanvim for a batteries included rust-analyzer setup for Neovim.

vim-lsp

vim-lsp is installed by following the plugin instructions. It can be as simple as adding this line to your .vimrc:

Plug 'prabirshrestha/vim-lsp'

Next you need to register the rust-analyzer binary. If it is avim.lspvailable in $PATH, you may want to add this to your .vimrc:

if executable('rust-analyzer')
  au User lsp_setup call lsp#register_server({
        \   'name': 'Rust Language Server',
        \   'cmd': {server_info->['rust-analyzer']},
        \   'whitelist': ['rust'],
        \ })
endif

There is no dedicated UI for the server configuration, so you would need to send any options as a value of the initialization_options field, as described in the Configuration section. Here is an example of how to enable the proc-macro support:

if executable('rust-analyzer')
  au User lsp_setup call lsp#register_server({
        \   'name': 'Rust Language Server',
        \   'cmd': {server_info->['rust-analyzer']},
        \   'whitelist': ['rust'],
        \   'initialization_options': {
        \     'cargo': {
        \       'buildScripts': {
        \         'enable': v:true,
        \       },
        \     },
        \     'procMacro': {
        \       'enable': v:true,
        \     },
        \   },
        \ })
endif

Sublime Text

Sublime Text 4:

• Follow the instructions in LSP-rust-analyzer.

Install LSP-file-watcher-chokidar to enable file watching (workspace/didChangeWatchedFiles).

Sublime Text 3:

• Install the LSP package.

• From the command palette, run LSP: Enable Language Server Globally and select rust-analyzer.

If it worked, you should see "rust-analyzer, Line X, Column Y" on the left side of the status bar, and after waiting a bit, functionalities like tooltips on hovering over variables should become available.

If you get an error saying No such file or directory: 'rust-analyzer', see the rust-analyzer binary installation section.

GNOME Builder

GNOME Builder 3.37.1 and newer has native rust-analyzer support. If the LSP binary is not available, GNOME Builder can install it when opening a Rust file.

Eclipse IDE

Support for Rust development in the Eclipse IDE is provided by Eclipse Corrosion. If available in PATH or in some standard location, rust-analyzer is detected and powers editing of Rust files without further configuration. If rust-analyzer is not detected, Corrosion will prompt you for configuration of your Rust toolchain and language server with a link to the Window > Preferences > Rust preference page; from here a button allows to download and configure rust-analyzer, but you can also reference another installation. You’ll need to close and reopen all .rs and Cargo files, or to restart the IDE, for this change to take effect.

Kate Text Editor

Support for the language server protocol is built into Kate through the LSP plugin, which is included by default. It is preconfigured to use rust-analyzer for Rust sources since Kate 21.12.

To change rust-analyzer config options, start from the following example and put it into Kate’s "User Server Settings" tab (located under the LSP Client settings):

{
    "servers": {
        "rust": {
            "initializationOptions": {
                "cachePriming": {
                    "enable": false
                },
                "check": {
                    "allTargets": false
                },
                "checkOnSave": false
            }
        }
    }
}

Then click on apply, and restart the LSP server for your rust project.

juCi++

juCi++ has built-in support for the language server protocol, and since version 1.7.0 offers installation of both Rust and rust-analyzer when opening a Rust file.

Kakoune

Kakoune supports LSP with the help of kak-lsp. Follow the instructions to install kak-lsp. To configure kak-lsp, refer to the configuration section which is basically about copying the configuration file in the right place (latest versions should use rust-analyzer by default).

Finally, you need to configure Kakoune to talk to kak-lsp (see Usage section). A basic configuration will only get you LSP but you can also activate inlay diagnostics and auto-formatting on save. The following might help you get all of this.

eval %sh{kak-lsp --kakoune -s $kak_session}  # Not needed if you load it with plug.kak.
hook global WinSetOption filetype=rust %{
    # Enable LSP
    lsp-enable-window

    # Auto-formatting on save
    hook window BufWritePre .* lsp-formatting-sync

    # Configure inlay hints (only on save)
    hook window -group rust-inlay-hints BufWritePost .* rust-analyzer-inlay-hints
    hook -once -always window WinSetOption filetype=.* %{
        remove-hooks window rust-inlay-hints
    }
}

Helix

Helix supports LSP by default. However, it won’t install rust-analyzer automatically. You can follow instructions for installing the rust-analyzer binary.

Visual Studio 2022

There are multiple rust-analyzer extensions for Visual Studio 2022 on Windows:

rust-analyzer.vs

(License: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International)

Visual Studio Marketplace

GitHub

Support for Rust development in the Visual Studio IDE is enabled by the rust-analyzer package. Either click on the download link or install from IDE’s extension manager. For now Visual Studio 2022 is required. All editions are supported viz. Community, Professional & Enterprise. The package aims to provide 0-friction installation and therefore comes loaded with most things required including rust-analyzer binary. If anything it needs is missing, appropriate errors / warnings will guide the user. E.g. cargo.exe needs to be in path and the package will tell you as much. This package is under rapid active development. So if you encounter any issues please file it at rust-analyzer.vs.

VS RustAnalyzer

(License: GPL)

Visual Studio Marketplace

GitHub

SourceGear Rust

(License: closed source)

Visual Studio Marketplace

GitHub (docs, issues, discussions)

• Free (no-cost)

• Supports all editions of Visual Studio 2022 on Windows: Community, Professional, or Enterprise

Lapce

Lapce has a Rust plugin which you can install directly. Unfortunately, it downloads an old version of rust-analyzer, but you can set the server path under Settings.

Zed

Zed has native rust-analyzer support. If the rust-analyzer binary is not available, Zed can install it when opening a Rust file.

Troubleshooting

Start with looking at the rust-analyzer version. Try rust-analyzer: Show RA Version in VS Code (using Command Palette feature typically activated by Ctrl+Shift+P) or rust-analyzer --version in the command line. If the date is more than a week ago, it’s better to update rust-analyzer version.

The next thing to check would be panic messages in rust-analyzer’s log. Log messages are printed to stderr, in VS Code you can see them in the Output > Rust Analyzer Language Server tab of the panel. To see more logs, set the RA_LOG=info environment variable, this can be done either by setting the environment variable manually or by using rust-analyzer.server.extraEnv, note that both of these approaches require the server to be restarted.

To fully capture LSP messages between the editor and the server, run the rust-analyzer: Toggle LSP Logs command and check Output > Rust Analyzer Language Server Trace.

The root cause for many "nothing works" problems is that rust-analyzer fails to understand the project structure. To debug that, first note the rust-analyzer section in the status bar. If it has an error icon and red, that’s the problem (hover will have somewhat helpful error message). rust-analyzer: Status prints dependency information for the current file. Finally, RA_LOG=project_model=debug enables verbose logs during project loading.

If rust-analyzer outright crashes, try running rust-analyzer analysis-stats /path/to/project/directory/ on the command line. This command type checks the whole project in batch mode bypassing LSP machinery.

When filing issues, it is useful (but not necessary) to try to minimize examples. An ideal bug reproduction looks like this:

$ git clone https://github.com/username/repo.git && cd repo && git switch --detach commit-hash
$ rust-analyzer --version
rust-analyzer dd12184e4 2021-05-08 dev
$ rust-analyzer analysis-stats .
💀 💀 💀

It is especially useful when the repo doesn’t use external crates or the standard library.

If you want to go as far as to modify the source code to debug the problem, be sure to take a look at the dev docs!

Configuration

Source: config.rs

The Installation section contains details on configuration for some of the editors. In general rust-analyzer is configured via LSP messages, which means that it’s up to the editor to decide on the exact format and location of configuration files.

Some clients, such as VS Code or COC plugin in Vim provide rust-analyzer specific configuration UIs. Others may require you to know a bit more about the interaction with rust-analyzer.

For the later category, it might help to know that the initial configuration is specified as a value of the initializationOptions field of the InitializeParams message, in the LSP protocol. The spec says that the field type is any?, but rust-analyzer is looking for a JSON object that is constructed using settings from the list below. Name of the setting, ignoring the rust-analyzer. prefix, is used as a path, and value of the setting becomes the JSON property value.

For example, a very common configuration is to enable proc-macro support, can be achieved by sending this JSON:

{
  "cargo": {
    "buildScripts": {
      "enable": true,
    },
  },
  "procMacro": {
    "enable": true,
  }
}

Please consult your editor’s documentation to learn more about how to configure LSP servers.

To verify which configuration is actually used by rust-analyzer, set RA_LOG environment variable to rust_analyzer=info and look for config-related messages. Logs should show both the JSON that rust-analyzer sees as well as the updated config.

This is the list of config options rust-analyzer supports:

rust-analyzer.assist.emitMustUse (default: false)

Whether to insert #[must_use] when generating as_ methods for enum variants.

rust-analyzer.assist.expressionFillDefault (default: "todo")

Placeholder expression to use for missing expressions in assists.

rust-analyzer.assist.termSearch.borrowcheck (default: true)

Enable borrow checking for term search code assists. If set to false, also there will be more suggestions, but some of them may not borrow-check.

rust-analyzer.assist.termSearch.fuel (default: 1800)

Term search fuel in "units of work" for assists (Defaults to 1800).

rust-analyzer.cachePriming.enable (default: true)

Warm up caches on project load.

rust-analyzer.cachePriming.numThreads (default: "physical")

How many worker threads to handle priming caches. The default 0 means to pick automatically.

rust-analyzer.cargo.allTargets (default: true)

Pass --all-targets to cargo invocation.

rust-analyzer.cargo.autoreload (default: true)

Automatically refresh project info via cargo metadata on Cargo.toml or .cargo/config.toml changes.

rust-analyzer.cargo.buildScripts.enable (default: true)

Run build scripts (build.rs) for more precise code analysis.

rust-analyzer.cargo.buildScripts.invocationStrategy (default: "per_workspace")

Specifies the invocation strategy to use when running the build scripts command. If per_workspace is set, the command will be executed for each Rust workspace with the workspace as the working directory. If once is set, the command will be executed once with the opened project as the working directory. This config only has an effect when #rust-analyzer.cargo.buildScripts.overrideCommand# is set.

rust-analyzer.cargo.buildScripts.overrideCommand (default: null)

Override the command rust-analyzer uses to run build scripts and build procedural macros. The command is required to output json and should therefore include --message-format=json or a similar option.

If there are multiple linked projects/workspaces, this command is invoked for each of them, with the working directory being the workspace root (i.e., the folder containing the Cargo.toml). This can be overwritten by changing #rust-analyzer.cargo.buildScripts.invocationStrategy#.

By default, a cargo invocation will be constructed for the configured targets and features, with the following base command line:

cargo check --quiet --workspace --message-format=json --all-targets --keep-going

.

rust-analyzer.cargo.buildScripts.rebuildOnSave (default: true)

Rerun proc-macros building/build-scripts running when proc-macro or build-script sources change and are saved.

rust-analyzer.cargo.buildScripts.useRustcWrapper (default: true)

Use RUSTC_WRAPPER=rust-analyzer when running build scripts to avoid checking unnecessary things.

rust-analyzer.cargo.cfgs

Default:

  "debug_assertions",
  "miri"
]

List of cfg options to enable with the given values.

To enable a name without a value, use "key". To enable a name with a value, use "key=value". To disable, prefix the entry with a !.

rust-analyzer.cargo.extraArgs (default: [])

Extra arguments that are passed to every cargo invocation.

rust-analyzer.cargo.extraEnv (default: {})

Extra environment variables that will be set when running cargo, rustc or other commands within the workspace. Useful for setting RUSTFLAGS.

rust-analyzer.cargo.features (default: [])

List of features to activate.

Set this to "all" to pass --all-features to cargo.

rust-analyzer.cargo.noDefaultFeatures (default: false)

Whether to pass --no-default-features to cargo.

rust-analyzer.cargo.sysroot (default: "discover")

Relative path to the sysroot, or "discover" to try to automatically find it via "rustc --print sysroot".

Unsetting this disables sysroot loading.

This option does not take effect until rust-analyzer is restarted.

rust-analyzer.cargo.sysrootSrc (default: null)

Relative path to the sysroot library sources. If left unset, this will default to {cargo.sysroot}/lib/rustlib/src/rust/library.

This option does not take effect until rust-analyzer is restarted.

rust-analyzer.cargo.target (default: null)

Compilation target override (target tuple).

rust-analyzer.cargo.targetDir (default: null)

Optional path to a rust-analyzer specific target directory. This prevents rust-analyzer's cargo check and initial build-script and proc-macro building from locking the Cargo.lock at the expense of duplicating build artifacts.

Set to true to use a subdirectory of the existing target directory or set to a path relative to the workspace to use that path.

rust-analyzer.cfg.setTest (default: true)

Set cfg(test) for local crates. Defaults to true.

rust-analyzer.checkOnSave (default: true)

Run the check command for diagnostics on save.

rust-analyzer.check.allTargets (default: null)

Check all targets and tests (--all-targets). Defaults to #rust-analyzer.cargo.allTargets#.

rust-analyzer.check.command (default: "check")

Cargo command to use for cargo check.

rust-analyzer.check.extraArgs (default: [])

Extra arguments for cargo check.

rust-analyzer.check.extraEnv (default: {})

Extra environment variables that will be set when running cargo check. Extends #rust-analyzer.cargo.extraEnv#.

rust-analyzer.check.features (default: null)

List of features to activate. Defaults to #rust-analyzer.cargo.features#.

Set to "all" to pass --all-features to Cargo.

rust-analyzer.check.ignore (default: [])

List of cargo check (or other command specified in check.command) diagnostics to ignore.

For example for cargo check: dead_code, unused_imports, unused_variables,...

rust-analyzer.check.invocationStrategy (default: "per_workspace")

Specifies the invocation strategy to use when running the check command. If per_workspace is set, the command will be executed for each workspace. If once is set, the command will be executed once. This config only has an effect when #rust-analyzer.check.overrideCommand# is set.

rust-analyzer.check.noDefaultFeatures (default: null)

Whether to pass --no-default-features to Cargo. Defaults to #rust-analyzer.cargo.noDefaultFeatures#.

rust-analyzer.check.overrideCommand (default: null)

Override the command rust-analyzer uses instead of cargo check for diagnostics on save. The command is required to output json and should therefore include --message-format=json or a similar option (if your client supports the colorDiagnosticOutput experimental capability, you can use --message-format=json-diagnostic-rendered-ansi).

If you're changing this because you're using some tool wrapping Cargo, you might also want to change #rust-analyzer.cargo.buildScripts.overrideCommand#.

If there are multiple linked projects/workspaces, this command is invoked for each of them, with the working directory being the workspace root (i.e., the folder containing the Cargo.toml). This can be overwritten by changing #rust-analyzer.check.invocationStrategy#.

If $saved_file is part of the command, rust-analyzer will pass the absolute path of the saved file to the provided command. This is intended to be used with non-Cargo build systems. Note that $saved_file is experimental and may be removed in the future.

An example command would be:

cargo check --workspace --message-format=json --all-targets

.

rust-analyzer.check.targets (default: null)

Check for specific targets. Defaults to #rust-analyzer.cargo.target# if empty.

Can be a single target, e.g. "x86_64-unknown-linux-gnu" or a list of targets, e.g. ["aarch64-apple-darwin", "x86_64-apple-darwin"].

Aliased as "checkOnSave.targets".

rust-analyzer.check.workspace (default: true)

Whether --workspace should be passed to cargo check. If false, -p <package> will be passed instead if applicable. In case it is not, no check will be performed.

rust-analyzer.completion.addSemicolonToUnit (default: true)

Whether to automatically add a semicolon when completing unit-returning functions.

In match arms it completes a comma instead.

rust-analyzer.completion.autoAwait.enable (default: true)

Toggles the additional completions that automatically show method calls and field accesses with await prefixed to them when completing on a future.

rust-analyzer.completion.autoIter.enable (default: true)

Toggles the additional completions that automatically show method calls with iter() or into_iter() prefixed to them when completing on a type that has them.

rust-analyzer.completion.autoimport.enable (default: true)

Toggles the additional completions that automatically add imports when completed. Note that your client must specify the additionalTextEdits LSP client capability to truly have this feature enabled.

rust-analyzer.completion.autoimport.exclude

Default:

  {
    "path": "core::borrow::Borrow",
    "type": "methods"
  },
  {
    "path": "core::borrow::BorrowMut",
    "type": "methods"
  }
]

A list of full paths to items to exclude from auto-importing completions.

Traits in this list won't have their methods suggested in completions unless the trait is in scope.

You can either specify a string path which defaults to type "always" or use the more verbose form { "path": "path::to::item", type: "always" }.

For traits the type "methods" can be used to only exclude the methods but not the trait itself.

This setting also inherits #rust-analyzer.completion.excludeTraits#.

rust-analyzer.completion.autoself.enable (default: true)

Toggles the additional completions that automatically show method calls and field accesses with self prefixed to them when inside a method.

rust-analyzer.completion.callable.snippets (default: "fill_arguments")

Whether to add parenthesis and argument snippets when completing function.

rust-analyzer.completion.excludeTraits (default: [])

A list of full paths to traits whose methods to exclude from completion.

Methods from these traits won't be completed, even if the trait is in scope. However, they will still be suggested on expressions whose type is dyn Trait, impl Trait or T where T: Trait.

Note that the trait themselves can still be completed.

rust-analyzer.completion.fullFunctionSignatures.enable (default: false)

Whether to show full function/method signatures in completion docs.

rust-analyzer.completion.hideDeprecated (default: false)

Whether to omit deprecated items from autocompletion. By default they are marked as deprecated but not hidden.

rust-analyzer.completion.limit (default: null)

Maximum number of completions to return. If None, the limit is infinite.

rust-analyzer.completion.postfix.enable (default: true)

Whether to show postfix snippets like dbg, if, not, etc.

rust-analyzer.completion.privateEditable.enable (default: false)

Enables completions of private items and fields that are defined in the current workspace even if they are not visible at the current position.

rust-analyzer.completion.snippets.custom

Default:

  "Ok": {
    "postfix": "ok",
    "body": "Ok(${receiver})",
    "description": "Wrap the expression in a `Result::Ok`",
    "scope": "expr"
  },
  "Box::pin": {
    "postfix": "pinbox",
    "body": "Box::pin(${receiver})",
    "requires": "std::boxed::Box",
    "description": "Put the expression into a pinned `Box`",
    "scope": "expr"
  },
  "Arc::new": {
    "postfix": "arc",
    "body": "Arc::new(${receiver})",
    "requires": "std::sync::Arc",
    "description": "Put the expression into an `Arc`",
    "scope": "expr"
  },
  "Some": {
    "postfix": "some",
    "body": "Some(${receiver})",
    "description": "Wrap the expression in an `Option::Some`",
    "scope": "expr"
  },
  "Err": {
    "postfix": "err",
    "body": "Err(${receiver})",
    "description": "Wrap the expression in a `Result::Err`",
    "scope": "expr"
  },
  "Rc::new": {
    "postfix": "rc",
    "body": "Rc::new(${receiver})",
    "requires": "std::rc::Rc",
    "description": "Put the expression into an `Rc`",
    "scope": "expr"
  }
}

Custom completion snippets.

rust-analyzer.completion.termSearch.enable (default: false)

Whether to enable term search based snippets like Some(foo.bar().baz()).

rust-analyzer.completion.termSearch.fuel (default: 1000)

Term search fuel in "units of work" for autocompletion (Defaults to 1000).

rust-analyzer.diagnostics.disabled (default: [])

List of rust-analyzer diagnostics to disable.

rust-analyzer.diagnostics.enable (default: true)

Whether to show native rust-analyzer diagnostics.

rust-analyzer.diagnostics.experimental.enable (default: false)

Whether to show experimental rust-analyzer diagnostics that might have more false positives than usual.

rust-analyzer.diagnostics.remapPrefix (default: {})

Map of prefixes to be substituted when parsing diagnostic file paths. This should be the reverse mapping of what is passed to rustc as --remap-path-prefix.

rust-analyzer.diagnostics.styleLints.enable (default: false)

Whether to run additional style lints.

rust-analyzer.diagnostics.warningsAsHint (default: [])

List of warnings that should be displayed with hint severity.

The warnings will be indicated by faded text or three dots in code and will not show up in the Problems Panel.

rust-analyzer.diagnostics.warningsAsInfo (default: [])

List of warnings that should be displayed with info severity.

The warnings will be indicated by a blue squiggly underline in code and a blue icon in the Problems Panel.

rust-analyzer.files.exclude (default: [])

These paths (file/directories) will be ignored by rust-analyzer. They are relative to the workspace root, and globs are not supported. You may also need to add the folders to Code's files.watcherExclude.

rust-analyzer.files.watcher (default: "client")

Controls file watching implementation.

rust-analyzer.highlightRelated.breakPoints.enable (default: true)

Enables highlighting of related references while the cursor is on break, loop, while, or for keywords.

rust-analyzer.highlightRelated.closureCaptures.enable (default: true)

Enables highlighting of all captures of a closure while the cursor is on the | or move keyword of a closure.

rust-analyzer.highlightRelated.exitPoints.enable (default: true)

Enables highlighting of all exit points while the cursor is on any return, ?, fn, or return type arrow (->).

rust-analyzer.highlightRelated.references.enable (default: true)

Enables highlighting of related references while the cursor is on any identifier.

rust-analyzer.highlightRelated.yieldPoints.enable (default: true)

Enables highlighting of all break points for a loop or block context while the cursor is on any async or await keywords.

rust-analyzer.hover.actions.debug.enable (default: true)

Whether to show Debug action. Only applies when #rust-analyzer.hover.actions.enable# is set.

rust-analyzer.hover.actions.enable (default: true)

Whether to show HoverActions in Rust files.

rust-analyzer.hover.actions.gotoTypeDef.enable (default: true)

Whether to show Go to Type Definition action. Only applies when #rust-analyzer.hover.actions.enable# is set.

rust-analyzer.hover.actions.implementations.enable (default: true)

Whether to show Implementations action. Only applies when #rust-analyzer.hover.actions.enable# is set.

rust-analyzer.hover.actions.references.enable (default: false)

Whether to show References action. Only applies when #rust-analyzer.hover.actions.enable# is set.

rust-analyzer.hover.actions.run.enable (default: true)

Whether to show Run action. Only applies when #rust-analyzer.hover.actions.enable# is set.

rust-analyzer.hover.actions.updateTest.enable (default: true)

Whether to show Update Test action. Only applies when #rust-analyzer.hover.actions.enable# and #rust-analyzer.hover.actions.run.enable# are set.

rust-analyzer.hover.documentation.enable (default: true)

Whether to show documentation on hover.

rust-analyzer.hover.documentation.keywords.enable (default: true)

Whether to show keyword hover popups. Only applies when #rust-analyzer.hover.documentation.enable# is set.

rust-analyzer.hover.dropGlue.enable (default: true)

Whether to show drop glue information on hover.

rust-analyzer.hover.links.enable (default: true)

Use markdown syntax for links on hover.

rust-analyzer.hover.maxSubstitutionLength (default: 20)

Whether to show what types are used as generic arguments in calls etc. on hover, and what is their max length to show such types, beyond it they will be shown with ellipsis.

This can take three values: null means "unlimited", the string "hide" means to not show generic substitutions at all, and a number means to limit them to X characters.

The default is 20 characters.

rust-analyzer.hover.memoryLayout.alignment (default: "hexadecimal")

How to render the align information in a memory layout hover.

rust-analyzer.hover.memoryLayout.enable (default: true)

Whether to show memory layout data on hover.

rust-analyzer.hover.memoryLayout.niches (default: false)

How to render the niche information in a memory layout hover.

rust-analyzer.hover.memoryLayout.offset (default: "hexadecimal")

How to render the offset information in a memory layout hover.

rust-analyzer.hover.memoryLayout.size (default: "both")

How to render the size information in a memory layout hover.

rust-analyzer.hover.show.enumVariants (default: 5)

How many variants of an enum to display when hovering on. Show none if empty.

rust-analyzer.hover.show.fields (default: 5)

How many fields of a struct, variant or union to display when hovering on. Show none if empty.

rust-analyzer.hover.show.traitAssocItems (default: null)

How many associated items of a trait to display when hovering a trait.

rust-analyzer.imports.granularity.enforce (default: false)

Whether to enforce the import granularity setting for all files. If set to false rust-analyzer will try to keep import styles consistent per file.

rust-analyzer.imports.granularity.group (default: "crate")

How imports should be grouped into use statements.

rust-analyzer.imports.group.enable (default: true)

Group inserted imports by the following order. Groups are separated by newlines.

rust-analyzer.imports.merge.glob (default: true)

Whether to allow import insertion to merge new imports into single path glob imports like use std::fmt::*;.

rust-analyzer.imports.preferNoStd (default: false)

Prefer to unconditionally use imports of the core and alloc crate, over the std crate.

rust-analyzer.imports.preferPrelude (default: false)

Whether to prefer import paths containing a prelude module.

rust-analyzer.imports.prefix (default: "plain")

The path structure for newly inserted paths to use.

rust-analyzer.imports.prefixExternPrelude (default: false)

Whether to prefix external (including std, core) crate imports with ::. e.g. "use ::std::io::Read;".

rust-analyzer.inlayHints.bindingModeHints.enable (default: false)

Whether to show inlay type hints for binding modes.

rust-analyzer.inlayHints.chainingHints.enable (default: true)

Whether to show inlay type hints for method chains.

rust-analyzer.inlayHints.closingBraceHints.enable (default: true)

Whether to show inlay hints after a closing } to indicate what item it belongs to.

rust-analyzer.inlayHints.closingBraceHints.minLines (default: 25)

Minimum number of lines required before the } until the hint is shown (set to 0 or 1 to always show them).

rust-analyzer.inlayHints.closureCaptureHints.enable (default: false)

Whether to show inlay hints for closure captures.

rust-analyzer.inlayHints.closureReturnTypeHints.enable (default: "never")

Whether to show inlay type hints for return types of closures.

rust-analyzer.inlayHints.closureStyle (default: "impl_fn")

Closure notation in type and chaining inlay hints.

rust-analyzer.inlayHints.discriminantHints.enable (default: "never")

Whether to show enum variant discriminant hints.

rust-analyzer.inlayHints.expressionAdjustmentHints.enable (default: "never")

Whether to show inlay hints for type adjustments.

rust-analyzer.inlayHints.expressionAdjustmentHints.hideOutsideUnsafe (default: false)

Whether to hide inlay hints for type adjustments outside of unsafe blocks.

rust-analyzer.inlayHints.expressionAdjustmentHints.mode (default: "prefix")

Whether to show inlay hints as postfix ops (.* instead of *, etc).

rust-analyzer.inlayHints.genericParameterHints.const.enable (default: true)

Whether to show const generic parameter name inlay hints.

rust-analyzer.inlayHints.genericParameterHints.lifetime.enable (default: false)

Whether to show generic lifetime parameter name inlay hints.

rust-analyzer.inlayHints.genericParameterHints.type.enable (default: false)

Whether to show generic type parameter name inlay hints.

rust-analyzer.inlayHints.implicitDrops.enable (default: false)

Whether to show implicit drop hints.

rust-analyzer.inlayHints.implicitSizedBoundHints.enable (default: false)

Whether to show inlay hints for the implied type parameter Sized bound.

rust-analyzer.inlayHints.lifetimeElisionHints.enable (default: "never")

Whether to show inlay type hints for elided lifetimes in function signatures.

rust-analyzer.inlayHints.lifetimeElisionHints.useParameterNames (default: false)

Whether to prefer using parameter names as the name for elided lifetime hints if possible.

rust-analyzer.inlayHints.maxLength (default: 25)

Maximum length for inlay hints. Set to null to have an unlimited length.

rust-analyzer.inlayHints.parameterHints.enable (default: true)

Whether to show function parameter name inlay hints at the call site.

rust-analyzer.inlayHints.rangeExclusiveHints.enable (default: false)

Whether to show exclusive range inlay hints.

rust-analyzer.inlayHints.reborrowHints.enable (default: "never")

Whether to show inlay hints for compiler inserted reborrows. This setting is deprecated in favor of #rust-analyzer.inlayHints.expressionAdjustmentHints.enable#.

rust-analyzer.inlayHints.renderColons (default: true)

Whether to render leading colons for type hints, and trailing colons for parameter hints.

rust-analyzer.inlayHints.typeHints.enable (default: true)

Whether to show inlay type hints for variables.

rust-analyzer.inlayHints.typeHints.hideClosureInitialization (default: false)

Whether to hide inlay type hints for let statements that initialize to a closure. Only applies to closures with blocks, same as #rust-analyzer.inlayHints.closureReturnTypeHints.enable#.

rust-analyzer.inlayHints.typeHints.hideClosureParameter (default: false)

Whether to hide inlay parameter type hints for closures.

rust-analyzer.inlayHints.typeHints.hideNamedConstructor (default: false)

Whether to hide inlay type hints for constructors.

rust-analyzer.interpret.tests (default: false)

Enables the experimental support for interpreting tests.

rust-analyzer.joinLines.joinAssignments (default: true)

Join lines merges consecutive declaration and initialization of an assignment.

rust-analyzer.joinLines.joinElseIf (default: true)

Join lines inserts else between consecutive ifs.

rust-analyzer.joinLines.removeTrailingComma (default: true)

Join lines removes trailing commas.

rust-analyzer.joinLines.unwrapTrivialBlock (default: true)

Join lines unwraps trivial blocks.

rust-analyzer.lens.debug.enable (default: true)

Whether to show Debug lens. Only applies when #rust-analyzer.lens.enable# is set.

rust-analyzer.lens.enable (default: true)

Whether to show CodeLens in Rust files.

rust-analyzer.lens.implementations.enable (default: true)

Whether to show Implementations lens. Only applies when #rust-analyzer.lens.enable# is set.

rust-analyzer.lens.location (default: "above_name")

Where to render annotations.

rust-analyzer.lens.references.adt.enable (default: false)

Whether to show References lens for Struct, Enum, and Union. Only applies when #rust-analyzer.lens.enable# is set.

rust-analyzer.lens.references.enumVariant.enable (default: false)

Whether to show References lens for Enum Variants. Only applies when #rust-analyzer.lens.enable# is set.

rust-analyzer.lens.references.method.enable (default: false)

Whether to show Method References lens. Only applies when #rust-analyzer.lens.enable# is set.

rust-analyzer.lens.references.trait.enable (default: false)

Whether to show References lens for Trait. Only applies when #rust-analyzer.lens.enable# is set.

rust-analyzer.lens.run.enable (default: true)

Whether to show Run lens. Only applies when #rust-analyzer.lens.enable# is set.

rust-analyzer.lens.updateTest.enable (default: true)

Whether to show Update Test lens. Only applies when #rust-analyzer.lens.enable# and #rust-analyzer.lens.run.enable# are set.

rust-analyzer.linkedProjects (default: [])

Disable project auto-discovery in favor of explicitly specified set of projects.

Elements must be paths pointing to Cargo.toml, rust-project.json, .rs files (which will be treated as standalone files) or JSON objects in rust-project.json format.

rust-analyzer.lru.capacity (default: null)

Number of syntax trees rust-analyzer keeps in memory. Defaults to 128.

rust-analyzer.lru.query.capacities (default: {})

Sets the LRU capacity of the specified queries.

rust-analyzer.notifications.cargoTomlNotFound (default: true)

Whether to show can't find Cargo.toml error message.

rust-analyzer.numThreads (default: null)

How many worker threads in the main loop. The default null means to pick automatically.

rust-analyzer.procMacro.attributes.enable (default: true)

Expand attribute macros. Requires #rust-analyzer.procMacro.enable# to be set.

rust-analyzer.procMacro.enable (default: true)

Enable support for procedural macros, implies #rust-analyzer.cargo.buildScripts.enable#.

rust-analyzer.procMacro.ignored (default: {})

These proc-macros will be ignored when trying to expand them.

This config takes a map of crate names with the exported proc-macro names to ignore as values.

rust-analyzer.procMacro.server (default: null)

Internal config, path to proc-macro server executable.

rust-analyzer.references.excludeImports (default: false)

Exclude imports from find-all-references.

rust-analyzer.references.excludeTests (default: false)

Exclude tests from find-all-references and call-hierarchy.

rust-analyzer.runnables.command (default: null)

Command to be executed instead of 'cargo' for runnables.

rust-analyzer.runnables.extraArgs (default: [])

Additional arguments to be passed to cargo for runnables such as tests or binaries. For example, it may be --release.

rust-analyzer.runnables.extraTestBinaryArgs

Default:

  "--show-output"
]

Additional arguments to be passed through Cargo to launched tests, benchmarks, or doc-tests.

Unless the launched target uses a custom test harness, they will end up being interpreted as options to rustc’s built-in test harness (“libtest”).

rust-analyzer.rustc.source (default: null)

Path to the Cargo.toml of the rust compiler workspace, for usage in rustc_private projects, or "discover" to try to automatically find it if the rustc-dev component is installed.

Any project which uses rust-analyzer with the rustcPrivate crates must set [package.metadata.rust-analyzer] rustc_private=true to use it.

This option does not take effect until rust-analyzer is restarted.

rust-analyzer.rustfmt.extraArgs (default: [])

Additional arguments to rustfmt.

rust-analyzer.rustfmt.overrideCommand (default: null)

Advanced option, fully override the command rust-analyzer uses for formatting. This should be the equivalent of rustfmt here, and not that of cargo fmt. The file contents will be passed on the standard input and the formatted result will be read from the standard output.

rust-analyzer.rustfmt.rangeFormatting.enable (default: false)

Enables the use of rustfmt's unstable range formatting command for the textDocument/rangeFormatting request. The rustfmt option is unstable and only available on a nightly build.

rust-analyzer.semanticHighlighting.doc.comment.inject.enable (default: true)

Inject additional highlighting into doc comments.

When enabled, rust-analyzer will highlight rust source in doc comments as well as intra doc links.

rust-analyzer.semanticHighlighting.nonStandardTokens (default: true)

Whether the server is allowed to emit non-standard tokens and modifiers.

rust-analyzer.semanticHighlighting.operator.enable (default: true)

Use semantic tokens for operators.

When disabled, rust-analyzer will emit semantic tokens only for operator tokens when they are tagged with modifiers.

rust-analyzer.semanticHighlighting.operator.specialization.enable (default: false)

Use specialized semantic tokens for operators.

When enabled, rust-analyzer will emit special token types for operator tokens instead of the generic operator token type.

rust-analyzer.semanticHighlighting.punctuation.enable (default: false)

Use semantic tokens for punctuation.

When disabled, rust-analyzer will emit semantic tokens only for punctuation tokens when they are tagged with modifiers or have a special role.

rust-analyzer.semanticHighlighting.punctuation.separate.macro.bang (default: false)

When enabled, rust-analyzer will emit a punctuation semantic token for the ! of macro calls.

rust-analyzer.semanticHighlighting.punctuation.specialization.enable (default: false)

Use specialized semantic tokens for punctuation.

When enabled, rust-analyzer will emit special token types for punctuation tokens instead of the generic punctuation token type.

rust-analyzer.semanticHighlighting.strings.enable (default: true)

Use semantic tokens for strings.

In some editors (e.g. vscode) semantic tokens override other highlighting grammars. By disabling semantic tokens for strings, other grammars can be used to highlight their contents.

rust-analyzer.signatureInfo.detail (default: "full")

Show full signature of the callable. Only shows parameters if disabled.

rust-analyzer.signatureInfo.documentation.enable (default: true)

Show documentation.

rust-analyzer.typing.triggerChars (default: "=.")

Specify the characters allowed to invoke special on typing triggers.

• typing = after let tries to smartly add ; if = is followed by an existing expression
• typing = between two expressions adds ; when in statement position
• typing = to turn an assignment into an equality comparison removes ; when in expression position
• typing . in a chain method call auto-indents
• typing { or ( in front of an expression inserts a closing } or ) after the expression
• typing { in a use item adds a closing } in the right place
• typing > to complete a return type -> will insert a whitespace after it
• typing < in a path or type position inserts a closing > after the path or type.

rust-analyzer.vfs.extraIncludes (default: [])

Additional paths to include in the VFS. Generally for code that is generated or otherwise managed by a build system outside of Cargo, though Cargo might be the eventual consumer.

rust-analyzer.workspace.discoverConfig (default: null)

Enables automatic discovery of projects using [DiscoverWorkspaceConfig::command].

[DiscoverWorkspaceConfig] also requires setting progress_label and files_to_watch. progress_label is used for the title in progress indicators, whereas files_to_watch is used to determine which build system-specific files should be watched in order to reload rust-analyzer.

Below is an example of a valid configuration:

"rust-analyzer.workspace.discoverConfig": {
    "command": [
        "rust-project",
        "develop-json"
    ],
    "progressLabel": "rust-analyzer",
    "filesToWatch": [
        "BUCK"
    ]
}

On DiscoverWorkspaceConfig::command

Warning: This format is provisional and subject to change.

[DiscoverWorkspaceConfig::command] must return a JSON object corresponding to DiscoverProjectData::Finished:

#[derive(Debug, Clone, Deserialize, Serialize)]
#[serde(tag = "kind")]
#[serde(rename_all = "snake_case")]
enum DiscoverProjectData {
    Finished { buildfile: Utf8PathBuf, project: ProjectJsonData },
    Error { error: String, source: Option<String> },
    Progress { message: String },
}

As JSON, DiscoverProjectData::Finished is:

{
    // the internally-tagged representation of the enum.
    "kind": "finished",
    // the file used by a non-Cargo build system to define
    // a package or target.
    "buildfile": "rust-analyzer/BUILD",
    // the contents of a rust-project.json, elided for brevity
    "project": {
        "sysroot": "foo",
        "crates": []
    }
}

It is encouraged, but not required, to use the other variants on DiscoverProjectData to provide a more polished end-user experience.

DiscoverWorkspaceConfig::command may optionally include an {arg}, which will be substituted with the JSON-serialized form of the following enum:

#[derive(PartialEq, Clone, Debug, Serialize)]
#[serde(rename_all = "camelCase")]
pub enum DiscoverArgument {
   Path(AbsPathBuf),
   Buildfile(AbsPathBuf),
}

The JSON representation of DiscoverArgument::Path is:

{
    "path": "src/main.rs"
}

Similarly, the JSON representation of DiscoverArgument::Buildfile is:

{
    "buildfile": "BUILD"
}

DiscoverArgument::Path is used to find and generate a rust-project.json, and therefore, a workspace, whereas DiscoverArgument::buildfile is used to to update an existing workspace. As a reference for implementors, buck2's rust-project will likely be useful: https://github.com/facebook/buck2/tree/main/integrations/rust-project.

rust-analyzer.workspace.symbol.search.kind (default: "only_types")

Workspace symbol search kind.

rust-analyzer.workspace.symbol.search.limit (default: 128)

Limits the number of items returned from a workspace symbol search (Defaults to 128). Some clients like vs-code issue new searches on result filtering and don't require all results to be returned in the initial search. Other clients requires all results upfront and might require a higher limit.

rust-analyzer.workspace.symbol.search.scope (default: "workspace")

Workspace symbol search scope.

Non-Cargo Based Projects

rust-analyzer does not require Cargo. However, if you use some other build system, you’ll have to describe the structure of your project for rust-analyzer in the rust-project.json format:

interface JsonProject {
    /// Path to the sysroot directory.
    ///
    /// The sysroot is where rustc looks for the
    /// crates that are built-in to rust, such as
    /// std.
    ///
    /// https://doc.rust-lang.org/rustc/command-line-arguments.html#--sysroot-override-the-system-root
    ///
    /// To see the current value of sysroot, you
    /// can query rustc:
    ///
    /// ```
    /// $ rustc --print sysroot
    /// /Users/yourname/.rustup/toolchains/stable-x86_64-apple-darwin
    /// ```
    sysroot?: string;
    /// Path to the directory with *source code* of
    /// sysroot crates.
    ///
    /// By default, this is `lib/rustlib/src/rust/library`
    /// relative to the sysroot.
    ///
    /// It should point to the directory where std,
    /// core, and friends can be found:
    ///
    /// https://github.com/rust-lang/rust/tree/master/library.
    ///
    /// If provided, rust-analyzer automatically adds
    /// dependencies on sysroot crates. Conversely,
    /// if you omit this path, you can specify sysroot
    /// dependencies yourself and, for example, have
    /// several different "sysroots" in one graph of
    /// crates.
    sysroot_src?: string;
    /// List of groups of common cfg values, to allow
    /// sharing them between crates.
    ///
    /// Maps from group name to its cfgs. Cfg follow
    /// the same format as `Crate.cfg`.
    cfg_groups?: { [key: string]: string[]; };
    /// The set of crates comprising the current
    /// project. Must include all transitive
    /// dependencies as well as sysroot crate (libstd,
    /// libcore and such).
    crates: Crate[];
    /// Configuration for CLI commands.
    ///
    /// These are used for running and debugging binaries
    /// and tests without encoding build system-specific
    /// knowledge into rust-analyzer.
    ///
    /// # Example
    ///
    /// Below is an example of a test runnable. `{label}` and `{test_id}`
    /// are explained in `Runnable::args`'s documentation below.
    ///
    /// ```json
    /// {
    ///     "program": "buck",
    ///     "args": [
    ///         "test",
    ///          "{label}",
    ///          "--",
    ///          "{test_id}",
    ///          "--print-passing-details"
    ///     ],
    ///     "cwd": "/home/user/repo-root/",
    ///     "kind": "testOne"
    /// }
    /// ```
    runnables?: Runnable[];
}

interface Crate {
    /// Optional crate name used for display purposes,
    /// without affecting semantics. See the `deps`
    /// key for semantically-significant crate names.
    display_name?: string;
    /// Path to the root module of the crate.
    root_module: string;
    /// Edition of the crate.
    edition: '2015' | '2018' | '2021' | '2024';
    /// The version of the crate. Used for calculating
    /// the correct docs.rs URL.
    version?: string;
    /// Dependencies
    deps: Dep[];
    /// Should this crate be treated as a member of
    /// current "workspace".
    ///
    /// By default, inferred from the `root_module`
    /// (members are the crates which reside inside
    /// the directory opened in the editor).
    ///
    /// Set this to `false` for things like standard
    /// library and 3rd party crates to enable
    /// performance optimizations (rust-analyzer
    /// assumes that non-member crates don't change).
    is_workspace_member?: boolean;
    /// Optionally specify the (super)set of `.rs`
    /// files comprising this crate.
    ///
    /// By default, rust-analyzer assumes that only
    /// files under `root_module.parent` can belong
    /// to a crate. `include_dirs` are included
    /// recursively, unless a subdirectory is in
    /// `exclude_dirs`.
    ///
    /// Different crates can share the same `source`.
    ///
    /// If two crates share an `.rs` file in common,
    /// they *must* have the same `source`.
    /// rust-analyzer assumes that files from one
    /// source can't refer to files in another source.
    source?: {
        include_dirs: string[];
        exclude_dirs: string[];
    };
    /// List of cfg groups this crate inherits.
    ///
    /// All cfg in these groups will be concatenated to
    /// `cfg`. It is impossible to replace a value from
    /// the groups.
    cfg_groups?: string[];
    /// The set of cfgs activated for a given crate, like
    /// `["unix", "feature=\"foo\"", "feature=\"bar\""]`.
    cfg: string[];
    /// Target tuple for this Crate.
    ///
    /// Used when running `rustc --print cfg`
    /// to get target-specific cfgs.
    target?: string;
    /// Environment variables, used for
    /// the `env!` macro
    env: { [key: string]: string; };

    /// Whether the crate is a proc-macro crate.
    is_proc_macro: boolean;
    /// For proc-macro crates, path to compiled
    /// proc-macro (.so file).
    proc_macro_dylib_path?: string;

    /// Repository, matching the URL that would be used
    /// in Cargo.toml.
    repository?: string;

    /// Build-specific data about this crate.
    build?: BuildInfo;
}

interface Dep {
    /// Index of a crate in the `crates` array.
    crate: number;
    /// Name as should appear in the (implicit)
    /// `extern crate name` declaration.
    name: string;
}

interface BuildInfo {
    /// The name associated with this crate.
    ///
    /// This is determined by the build system that produced
    /// the `rust-project.json` in question. For instance, if buck were used,
    /// the label might be something like `//ide/rust/rust-analyzer:rust-analyzer`.
    ///
    /// Do not attempt to parse the contents of this string; it is a build system-specific
    /// identifier similar to `Crate::display_name`.
    label: string;
    /// Path corresponding to the build system-specific file defining the crate.
    build_file: string;
    /// The kind of target.
    ///
    /// This information is used to determine what sort
    /// of runnable codelens to provide, if any.
    target_kind: 'bin' | 'lib' | 'test';
}

interface Runnable {
    /// The program invoked by the runnable.
    ///
    /// For example, this might be `cargo`, `buck`, or `bazel`.
    program: string;
    /// The arguments passed to `program`.
    args: string[];
    /// The current working directory of the runnable.
    cwd: string;
    /// Used to decide what code lens to offer.
    ///
    /// `testOne`: This runnable will be used when the user clicks the 'Run Test'
    /// CodeLens above a test.
    ///
    /// The args for testOne can contain two template strings:
    /// `{label}` and `{test_id}`. `{label}` will be replaced
    /// with the `Build::label` and `{test_id}` will be replaced
    /// with the test name.
    kind: 'testOne' | string;
}

This format is provisional and subject to change. Specifically, the roots setup will be different eventually.

There are three ways to feed rust-project.json to rust-analyzer:

• Place rust-project.json file at the root of the project, and rust-analyzer will discover it.

• Specify "rust-analyzer.linkedProjects": [ "path/to/rust-project.json" ] in the settings (and make sure that your LSP client sends settings as a part of initialize request).

• Specify "rust-analyzer.linkedProjects": [ { "roots": […​], "crates": […​] }] inline.

Relative paths are interpreted relative to rust-project.json file location or (for inline JSON) relative to rootUri.

You can set the RA_LOG environment variable to rust_analyzer=info to inspect how rust-analyzer handles config and project loading.

Note that calls to cargo check are disabled when using rust-project.json by default, so compilation errors and warnings will no longer be sent to your LSP client. To enable these compilation errors you will need to specify explicitly what command rust-analyzer should run to perform the checks using the rust-analyzer.check.overrideCommand configuration. As an example, the following configuration explicitly sets cargo check as the check command.

{ "rust-analyzer.check.overrideCommand": ["cargo", "check", "--message-format=json"] }

check.overrideCommand requires the command specified to output json error messages for rust-analyzer to consume. The --message-format=json flag does this for cargo check so whichever command you use must also output errors in this format. See the Configuration section for more information.

Security

At the moment, rust-analyzer assumes that all code is trusted. Here is a non-exhaustive list of ways to make rust-analyzer execute arbitrary code:

• proc macros and build scripts are executed by default

• .cargo/config can override rustc with an arbitrary executable

• rust-toolchain.toml can override rustc with an arbitrary executable

• VS Code plugin reads configuration from project directory, and that can be used to override paths to various executables, like rustfmt or rust-analyzer itself.

• rust-analyzer’s syntax trees library uses a lot of unsafe and hasn’t been properly audited for memory safety.

Privacy

The LSP server performs no network access in itself, but runs cargo metadata which will update or download the crate registry and the source code of the project dependencies. If enabled (the default), build scripts and procedural macros can do anything.

The Code extension does not access the network.

Any other editor plugins are not under the control of the rust-analyzer developers. For any privacy concerns, you should check with their respective developers.

For rust-analyzer developers, cargo xtask release uses the GitHub API to put together the release notes.

Features

Annotations

Source: annotations.rs

Provides user with annotations above items for looking up references or impl blocks and running/debugging binaries.

Auto Import

Source: auto_import.rs

Using the auto-import assist it is possible to insert missing imports for unresolved items. When inserting an import it will do so in a structured manner by keeping imports grouped, separated by a newline in the following order:

• std and core
• External Crates
• Current Crate, paths prefixed by crate
• Current Module, paths prefixed by self
• Super Module, paths prefixed by super

Example:

use std::fs::File;

use itertools::Itertools;
use syntax::ast;

use crate::utils::insert_use;

use self::auto_import;

use super::AssistContext;

Import Granularity

It is possible to configure how use-trees are merged with the imports.granularity.group setting. It has the following configurations:

• crate: Merge imports from the same crate into a single use statement. This kind of nesting is only supported in Rust versions later than 1.24.
• module: Merge imports from the same module into a single use statement.
• item: Don't merge imports at all, creating one import per item.
• preserve: Do not change the granularity of any imports. For auto-import this has the same effect as item.
• one: Merge all imports into a single use statement as long as they have the same visibility and attributes.

In VS Code the configuration for this is rust-analyzer.imports.granularity.group.

Import Prefix

The style of imports in the same crate is configurable through the imports.prefix setting. It has the following configurations:

• crate: This setting will force paths to be always absolute, starting with the crate prefix, unless the item is defined outside of the current crate.
• self: This setting will force paths that are relative to the current module to always start with self. This will result in paths that always start with either crate, self, super or an extern crate identifier.
• plain: This setting does not impose any restrictions in imports.

In VS Code the configuration for this is rust-analyzer.imports.prefix.

Completion With Autoimport

Source: flyimport.rs

When completing names in the current scope, proposes additional imports from other modules or crates, if they can be qualified in the scope, and their name contains all symbols from the completion input.

To be considered applicable, the name must contain all input symbols in the given order, not necessarily adjacent. If any input symbol is not lowercased, the name must contain all symbols in exact case; otherwise the containing is checked case-insensitively.

fn main() {
    pda$0
}
# pub mod std { pub mod marker { pub struct PhantomData { } } }

->

use std::marker::PhantomData;

fn main() {
    PhantomData
}
# pub mod std { pub mod marker { pub struct PhantomData { } } }

Also completes associated items, that require trait imports. If any unresolved and/or partially-qualified path precedes the input, it will be taken into account. Currently, only the imports with their import path ending with the whole qualifier will be proposed (no fuzzy matching for qualifier).

mod foo {
    pub mod bar {
        pub struct Item;

        impl Item {
            pub const TEST_ASSOC: usize = 3;
        }
    }
}

fn main() {
    bar::Item::TEST_A$0
}

->

use foo::bar;

mod foo {
    pub mod bar {
        pub struct Item;

        impl Item {
            pub const TEST_ASSOC: usize = 3;
        }
    }
}

fn main() {
    bar::Item::TEST_ASSOC
}

NOTE: currently, if an assoc item comes from a trait that's not currently imported, and it also has an unresolved and/or partially-qualified path, no imports will be proposed.

Fuzzy search details

To avoid an excessive amount of the results returned, completion input is checked for inclusion in the names only (i.e. in HashMap in the std::collections::HashMap path). For the same reasons, avoids searching for any path imports for inputs with their length less than 2 symbols (but shows all associated items for any input length).

Import configuration

It is possible to configure how use-trees are merged with the imports.granularity.group setting. Mimics the corresponding behavior of the Auto Import feature.

LSP and performance implications

The feature is enabled only if the LSP client supports LSP protocol version 3.16+ and reports the additionalTextEdits (case-sensitive) resolve client capability in its client capabilities. This way the server is able to defer the costly computations, doing them for a selected completion item only. For clients with no such support, all edits have to be calculated on the completion request, including the fuzzy search completion ones, which might be slow ergo the feature is automatically disabled.

Feature toggle

The feature can be forcefully turned off in the settings with the rust-analyzer.completion.autoimport.enable flag. Note that having this flag set to true does not guarantee that the feature is enabled: your client needs to have the corresponding capability enabled.

Debug ItemTree

Source: view_item_tree.rs

Displays the ItemTree of the currently open file, for debugging.

Expand Macro Recursively

Source: expand_macro.rs

Shows the full macro expansion of the macro at the current caret position.

Expand and Shrink Selection

Source: extend_selection.rs

Extends or shrinks the current selection to the encompassing syntactic construct (expression, statement, item, module, etc). It works with multiple cursors.

File Structure

Source: file_structure.rs

Provides a tree of the symbols defined in the file. Can be used to

• fuzzy search symbol in a file (super useful)
• draw breadcrumbs to describe the context around the cursor
• draw outline of the file

Find All References

Source: references.rs

Shows all references of the item at the cursor location

Folding

Source: folding_ranges.rs

Defines folding regions for curly braced blocks, runs of consecutive use, mod, const or static items, and region / endregion comment markers.

Format String Completion

Source: format_like.rs

"Result {result} is {2 + 2}" is expanded to the "Result {} is {}", result, 2 + 2.

The following postfix snippets are available:

• format -> format!(...)
• panic -> panic!(...)
• println -> println!(...)
• log: ** logd -> log::debug!(...) ** logt -> log::trace!(...) ** logi -> log::info!(...) ** logw -> log::warn!(...) ** loge -> log::error!(...)

Go to Declaration

Source: goto_declaration.rs

Navigates to the declaration of an identifier.

This is the same as Go to Definition with the following exceptions:

• outline modules will navigate to the mod name; item declaration
• trait assoc items will navigate to the assoc item of the trait declaration as opposed to the trait impl
• fields in patterns will navigate to the field declaration of the struct, union or variant

Go to Definition

Source: goto_definition.rs

Navigates to the definition of an identifier.

For outline modules, this will navigate to the source file of the module.

Go to Implementation

Source: goto_implementation.rs

Navigates to the impl items of types.

Go to Type Definition

Source: goto_type_definition.rs

Navigates to the type of an identifier.

Highlight Related

Source: highlight_related.rs

Highlights constructs related to the thing under the cursor:

1. if on an identifier, highlights all references to that identifier in the current file
   • additionally, if the identifier is a trait in a where clause, type parameter trait bound or use item, highlights all references to that trait's assoc items in the corresponding scope
2. if on an async or await token, highlights all yield points for that async context
3. if on a return or fn keyword, ? character or -> return type arrow, highlights all exit points for that context
4. if on a break, loop, while or for token, highlights all break points for that loop or block context
5. if on a move or | token that belongs to a closure, highlights all captures of the closure.

Note: ?, | and -> do not currently trigger this behavior in the VSCode editor.

Hover

Source: hover.rs

Shows additional information, like the type of an expression or the documentation for a definition when "focusing" code. Focusing is usually hovering with a mouse, but can also be triggered with a shortcut.

Inlay Hints

Source: inlay_hints.rs

rust-analyzer shows additional information inline with the source code. Editors usually render this using read-only virtual text snippets interspersed with code.

rust-analyzer by default shows hints for

• types of local variables
• names of function arguments
• names of const generic parameters
• types of chained expressions

Optionally, one can enable additional hints for

• return types of closure expressions
• elided lifetimes
• compiler inserted reborrows
• names of generic type and lifetime parameters

Note: inlay hints for function argument names are heuristically omitted to reduce noise and will not appear if any of the following criteria are met:

• the parameter name is a suffix of the function's name
• the argument is a qualified constructing or call expression where the qualifier is an ADT
• exact argument<->parameter match(ignoring leading underscore) or parameter is a prefix/suffix of argument with _ splitting it off
• the parameter name starts with ra_fixture
• the parameter name is a well known name in a unary function
• the parameter name is a single character in a unary function

Interpret A Function, Static Or Const.

Source: interpret.rs

Join Lines

Source: join_lines.rs

Join selected lines into one, smartly fixing up whitespace, trailing commas, and braces.

See this gif for the cases handled specially by joined lines.

Magic Completions

Source: lib.rs

In addition to usual reference completion, rust-analyzer provides some ✨magic✨ completions as well:

Keywords like if, else while, loop are completed with braces, and cursor is placed at the appropriate position. Even though if is easy to type, you still want to complete it, to get { } for free! return is inserted with a space or ; depending on the return type of the function.

When completing a function call, () are automatically inserted. If a function takes arguments, the cursor is positioned inside the parenthesis.

There are postfix completions, which can be triggered by typing something like foo().if. The word after . determines postfix completion. Possible variants are:

• expr.if -> if expr {} or if let ... {} for Option or Result
• expr.match -> match expr {}
• expr.while -> while expr {} or while let ... {} for Option or Result
• expr.ref -> &expr
• expr.refm -> &mut expr
• expr.let -> let $0 = expr;
• expr.lete -> let $1 = expr else { $0 };
• expr.letm -> let mut $0 = expr;
• expr.not -> !expr
• expr.dbg -> dbg!(expr)
• expr.dbgr -> dbg!(&expr)
• expr.call -> (expr)

There also snippet completions:

Expressions

• pd -> eprintln!(" = {:?}", );
• ppd -> eprintln!(" = {:#?}", );

Items

• tfn -> #[test] fn feature(){}
• tmod ->

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_name() {}
}

And the auto import completions, enabled with the rust-analyzer.completion.autoimport.enable setting and the corresponding LSP client capabilities. Those are the additional completion options with automatic use import and options from all project importable items, fuzzy matched against the completion input.

Matching Brace

Source: matching_brace.rs

If the cursor is on any brace (<>(){}[]||) which is a part of a brace-pair, moves cursor to the matching brace. It uses the actual parser to determine braces, so it won't confuse generics with comparisons.

Memory Usage

Source: apply_change.rs

Clears rust-analyzer's internal database and prints memory usage statistics.

Move Item

Source: move_item.rs

Move item under cursor or selection up and down.

On Enter

Source: on_enter.rs

rust-analyzer can override Enter key to make it smarter:

• Enter inside triple-slash comments automatically inserts ///
• Enter in the middle or after a trailing space in // inserts //
• Enter inside //! doc comments automatically inserts //!
• Enter after { indents contents and closing } of single-line block

This action needs to be assigned to shortcut explicitly.

Note that, depending on the other installed extensions, this feature can visibly slow down typing. Similarly, if rust-analyzer crashes or stops responding, Enter might not work. In that case, you can still press Shift-Enter to insert a newline.

VS Code

Add the following to keybindings.json:

{
  "key": "Enter",
  "command": "rust-analyzer.onEnter",
  "when": "editorTextFocus && !suggestWidgetVisible && editorLangId == rust"
}

When using the Vim plugin:

{
  "key": "Enter",
  "command": "rust-analyzer.onEnter",
  "when": "editorTextFocus && !suggestWidgetVisible && editorLangId == rust && vim.mode == 'Insert'"
}

On Typing Assists

Source: typing.rs

Some features trigger on typing certain characters:

• typing let = tries to smartly add ; if = is followed by an existing expression
• typing = between two expressions adds ; when in statement position
• typing = to turn an assignment into an equality comparison removes ; when in expression position
• typing . in a chain method call auto-indents
• typing { or ( in front of an expression inserts a closing } or ) after the expression
• typing { in a use item adds a closing } in the right place
• typing > to complete a return type -> will insert a whitespace after it

VS Code

Add the following to settings.json:

"editor.formatOnType": true,

Open Docs

Source: doc_links.rs

Retrieve a links to documentation for the given symbol.

The simplest way to use this feature is via the context menu. Right-click on the selected item. The context menu opens. Select Open Docs.

Parent Module

Source: parent_module.rs

Navigates to the parent module of the current module.

Related Tests

Source: runnables.rs

Provides a sneak peek of all tests where the current item is used.

The simplest way to use this feature is via the context menu. Right-click on the selected item. The context menu opens. Select Peek Related Tests.

Rename

Source: rename.rs

Renames the item below the cursor and all of its references

Run

Source: runnables.rs

Shows a popup suggesting to run a test/benchmark/binary at the current cursor location. Super useful for repeatedly running just a single test. Do bind this to a shortcut!

Semantic Syntax Highlighting

Source: syntax_highlighting.rs

rust-analyzer highlights the code semantically. For example, Bar in foo::Bar might be colored differently depending on whether Bar is an enum or a trait. rust-analyzer does not specify colors directly, instead it assigns a tag (like struct) and a set of modifiers (like declaration) to each token. It's up to the client to map those to specific colors.

The general rule is that a reference to an entity gets colored the same way as the entity itself. We also give special modifier for mut and &mut local variables.

Token Tags

Rust-analyzer currently emits the following token tags:

• For items:

• For literals:

• For operators:

• For punctuation:

Token Modifiers

Token modifiers allow to style some elements in the source code more precisely.

Rust-analyzer currently emits the following token modifiers:

Show Dependency Tree

Source: fetch_crates.rs

Shows a view tree with all the dependencies of this project

Show Syntax Tree

Source: view_syntax_tree.rs

Shows a tree view with the syntax tree of the current file

Status

Source: status.rs

Shows internal statistic about memory usage of rust-analyzer.

Structural Search and Replace

Source: lib.rs

Search and replace with named wildcards that will match any expression, type, path, pattern or item. The syntax for a structural search replace command is <search_pattern> ==>> <replace_pattern>. A $<name> placeholder in the search pattern will match any AST node and $<name> will reference it in the replacement. Within a macro call, a placeholder will match up until whatever token follows the placeholder.

All paths in both the search pattern and the replacement template must resolve in the context in which this command is invoked. Paths in the search pattern will then match the code if they resolve to the same item, even if they're written differently. For example if we invoke the command in the module foo with a pattern of Bar, then code in the parent module that refers to foo::Bar will match.

Paths in the replacement template will be rendered appropriately for the context in which the replacement occurs. For example if our replacement template is foo::Bar and we match some code in the foo module, we'll insert just Bar.

Inherent method calls should generally be written in UFCS form. e.g. foo::Bar::baz($s, $a) will match $s.baz($a), provided the method call baz resolves to the method foo::Bar::baz. When a placeholder is the receiver of a method call in the search pattern (e.g. $s.foo()), but not in the replacement template (e.g. bar($s)), then *, & and &mut will be added as needed to mirror whatever autoderef and autoref was happening implicitly in the matched code.

The scope of the search / replace will be restricted to the current selection if any, otherwise it will apply to the whole workspace.

Placeholders may be given constraints by writing them as ${<name>:<constraint1>:<constraint2>...}.

Supported constraints:

Available via the command rust-analyzer.ssr.

// Using structural search replace command [foo($a, $b) ==>> ($a).foo($b)]

// BEFORE
String::from(foo(y + 5, z))

// AFTER
String::from((y + 5).foo(z))

Also available as an assist, by writing a comment containing the structural search and replace rule. You will only see the assist if the comment can be parsed as a valid structural search and replace rule.

// Place the cursor on the line below to see the assist 💡.
// foo($a, $b) ==>> ($a).foo($b)

User Snippet Completions

Source: snippet.rs

rust-analyzer allows the user to define custom (postfix)-snippets that may depend on items to be accessible for the current scope to be applicable.

A custom snippet can be defined by adding it to the rust-analyzer.completion.snippets.custom object respectively.

{
  "rust-analyzer.completion.snippets.custom": {
    "thread spawn": {
      "prefix": ["spawn", "tspawn"],
      "body": [
        "thread::spawn(move || {",
        "\t$0",
        "});",
      ],
      "description": "Insert a thread::spawn call",
      "requires": "std::thread",
      "scope": "expr",
    }
  }
}

In the example above:

• "thread spawn" is the name of the snippet.

• prefix defines one or more trigger words that will trigger the snippets completion. Using postfix will instead create a postfix snippet.

• body is one or more lines of content joined via newlines for the final output.

• description is an optional description of the snippet, if unset the snippet name will be used.

• requires is an optional list of item paths that have to be resolvable in the current crate where the completion is rendered.

View Crate Graph

Source: view_crate_graph.rs

Renders the currently loaded crate graph as an SVG graphic. Requires the dot tool, which is part of graphviz, to be installed.

Only workspace crates are included, no crates.io dependencies or sysroot crates.

View Hir

Source: view_hir.rs

View Memory Layout

Source: view_memory_layout.rs

Displays the recursive memory layout of a datatype.

View Mir

Source: view_mir.rs

Workspace Symbol

Source: symbol_index.rs

Uses fuzzy-search to find types, modules and functions by name across your project and dependencies. This is the most useful feature, which improves code navigation tremendously. It mostly works on top of the built-in LSP functionality, however # and * symbols can be used to narrow down the search. Specifically,

• Foo searches for Foo type in the current workspace
• foo# searches for foo function in the current workspace
• Foo* searches for Foo type among dependencies, including stdlib
• foo#* searches for foo function among dependencies

That is, # switches from "types" to all symbols, * switches from the current workspace to dependencies.

Note that filtering does not currently work in VSCode due to the editor never sending the special symbols to the language server. Instead, you can configure the filtering via the rust-analyzer.workspace.symbol.search.scope and rust-analyzer.workspace.symbol.search.kind settings. Symbols prefixed with __ are hidden from the search results unless configured otherwise.

Assists

Assists, or code actions, are small local refactorings, available in a particular context. They are usually triggered by a shortcut or by clicking a light bulb icon in the editor. Cursor position or selection is signified by ┃ character.

add_braces

Source: add_braces.rs

Adds braces to lambda and match arm expressions.

Before

fn foo(n: i32) -> i32 {
    match n {
        1 =>┃ n + 1,
        _ => 0
    }
}

After

fn foo(n: i32) -> i32 {
    match n {
        1 => {
            n + 1
        },
        _ => 0
    }
}

add_explicit_enum_discriminant

Source: add_explicit_enum_discriminant.rs

Adds explicit discriminant to all enum variants.

Before

enum TheEnum┃ {
    Foo,
    Bar,
    Baz = 42,
    Quux,
}

After

enum TheEnum {
    Foo = 0,
    Bar = 1,
    Baz = 42,
    Quux = 43,
}

add_explicit_type

Source: add_explicit_type.rs

Specify type for a let binding.

Before

fn main() {
    let x┃ = 92;
}

After

fn main() {
    let x: i32 = 92;
}

add_hash

Source: raw_string.rs

Adds a hash to a raw string literal.

Before

fn main() {
    r#"Hello,┃ World!"#;
}

After

fn main() {
    r##"Hello, World!"##;
}

add_impl_default_members

Source: add_missing_impl_members.rs

Adds scaffold for overriding default impl members.

Before

trait Trait {
    type X;
    fn foo(&self);
    fn bar(&self) {}
}

impl Trait for () {
    type X = ();
    fn foo(&self) {}┃
}

After

trait Trait {
    type X;
    fn foo(&self);
    fn bar(&self) {}
}

impl Trait for () {
    type X = ();
    fn foo(&self) {}

    ┃fn bar(&self) {}
}

add_impl_missing_members

Source: add_missing_impl_members.rs

Adds scaffold for required impl members.

Before

trait Trait<T> {
    type X;
    fn foo(&self) -> T;
    fn bar(&self) {}
}

impl Trait<u32> for () {┃

}

After

trait Trait<T> {
    type X;
    fn foo(&self) -> T;
    fn bar(&self) {}
}

impl Trait<u32> for () {
    ┃type X;

    fn foo(&self) -> u32 {
        todo!()
    }
}

add_label_to_loop

Source: add_label_to_loop.rs

Adds a label to a loop.

Before

fn main() {
    loop┃ {
        break;
        continue;
    }
}

After

fn main() {
    'l: loop {
        break 'l;
        continue 'l;
    }
}

add_lifetime_to_type

Source: add_lifetime_to_type.rs

Adds a new lifetime to a struct, enum or union.

Before

struct Point {
    x: &┃u32,
    y: u32,
}

After

struct Point<'a> {
    x: &'a u32,
    y: u32,
}

add_missing_match_arms

Source: add_missing_match_arms.rs

Adds missing clauses to a match expression.

Before

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        ┃
    }
}

After

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } => ${1:todo!()},
        Action::Stop => ${2:todo!()},┃
    }
}

add_return_type

Source: add_return_type.rs

Adds the return type to a function or closure inferred from its tail expression if it doesn't have a return type specified. This assists is useable in a functions or closures tail expression or return type position.

Before

fn foo() { 4┃2i32 }

After

fn foo() -> i32 { 42i32 }

add_turbo_fish

Source: add_turbo_fish.rs

Adds ::<_> to a call of a generic method or function.

Before

fn make<T>() -> T { todo!() }
fn main() {
    let x = make┃();
}

After

fn make<T>() -> T { todo!() }
fn main() {
    let x = make::<${0:_}>();
}

apply_demorgan

Source: apply_demorgan.rs

Apply De Morgan's law. This transforms expressions of the form !l || !r into !(l && r). This also works with &&. This assist can only be applied with the cursor on either || or &&.

Before

fn main() {
    if x != 4 ||┃ y < 3.14 {}
}

After

fn main() {
    if !(x == 4 && y >= 3.14) {}
}

apply_demorgan_iterator

Source: apply_demorgan.rs

Apply De Morgan's law to Iterator::all and Iterator::any.

This transforms expressions of the form !iter.any(|x| predicate(x)) into iter.all(|x| !predicate(x)) and vice versa. This also works the other way for Iterator::all into Iterator::any.

Before

fn main() {
    let arr = [1, 2, 3];
    if !arr.into_iter().┃any(|num| num == 4) {
        println!("foo");
    }
}

After

fn main() {
    let arr = [1, 2, 3];
    if arr.into_iter().all(|num| num != 4) {
        println!("foo");
    }
}

auto_import

Source: auto_import.rs

If the name is unresolved, provides all possible imports for it.

Before

fn main() {
    let map = HashMap┃::new();
}

After

use std::collections::HashMap;

fn main() {
    let map = HashMap::new();
}

bind_unused_param

Source: bind_unused_param.rs

Binds unused function parameter to an underscore.

Before

fn some_function(x: i32┃) {}

After

fn some_function(x: i32) {
    let _ = x;
}

change_visibility

Source: change_visibility.rs

Adds or changes existing visibility specifier.

Before

┃fn frobnicate() {}

After

pub(crate) fn frobnicate() {}

comment_to_doc

Source: convert_comment_from_or_to_doc.rs

Converts comments to documentation.

Before

// Wow what ┃a nice module
// I sure hope this shows up when I hover over it

After

//! Wow what a nice module
//! I sure hope this shows up when I hover over it

convert_bool_then_to_if

Source: convert_bool_then.rs

Converts a bool::then method call to an equivalent if expression.

Before

fn main() {
    (0 == 0).then┃(|| val)
}

After

fn main() {
    if 0 == 0 {
        Some(val)
    } else {
        None
    }
}

convert_bool_to_enum

Source: convert_bool_to_enum.rs

This converts boolean local variables, fields, constants, and statics into a new enum with two variants Bool::True and Bool::False, as well as replacing all assignments with the variants and replacing all usages with == Bool::True or == Bool::False.

Before

fn main() {
    let ┃bool = true;

    if bool {
        println!("foo");
    }
}

After

#[derive(PartialEq, Eq)]
enum Bool { True, False }

fn main() {
    let bool = Bool::True;

    if bool == Bool::True {
        println!("foo");
    }
}

convert_closure_to_fn

Source: convert_closure_to_fn.rs

This converts a closure to a freestanding function, changing all captures to parameters.

Before

fn main() {
    let mut s = String::new();
    let closure = |┃a| s.push_str(a);
    closure("abc");
}

After

fn main() {
    let mut s = String::new();
    fn closure(a: &str, s: &mut String) {
        s.push_str(a)
    }
    closure("abc", &mut s);
}

convert_for_loop_with_for_each

Source: convert_iter_for_each_to_for.rs

Converts a for loop into a for_each loop on the Iterator.

Before

fn main() {
    let x = vec![1, 2, 3];
    for┃ v in x {
        let y = v * 2;
    }
}

After

fn main() {
    let x = vec![1, 2, 3];
    x.into_iter().for_each(|v| {
        let y = v * 2;
    });
}

convert_from_to_tryfrom

Source: convert_from_to_tryfrom.rs

Converts a From impl to a TryFrom impl, wrapping returns in Ok.

Before

impl ┃From<usize> for Thing {
    fn from(val: usize) -> Self {
        Thing {
            b: val.to_string(),
            a: val
        }
    }
}

After

impl TryFrom<usize> for Thing {
    type Error = ${0:()};

    fn try_from(val: usize) -> Result<Self, Self::Error> {
        Ok(Thing {
            b: val.to_string(),
            a: val
        })
    }
}

convert_if_to_bool_then

Source: convert_bool_then.rs

Converts an if expression into a corresponding bool::then call.

Before

fn main() {
    if┃ cond {
        Some(val)
    } else {
        None
    }
}

After

fn main() {
    cond.then(|| val)
}

convert_integer_literal

Source: convert_integer_literal.rs

Converts the base of integer literals to other bases.

Before

const _: i32 = 10┃;

After

const _: i32 = 0b1010;

convert_into_to_from

Source: convert_into_to_from.rs

Converts an Into impl to an equivalent From impl.

Before

impl ┃Into<Thing> for usize {
    fn into(self) -> Thing {
        Thing {
            b: self.to_string(),
            a: self
        }
    }
}

After

impl From<usize> for Thing {
    fn from(val: usize) -> Self {
        Thing {
            b: val.to_string(),
            a: val
        }
    }
}

convert_iter_for_each_to_for

Source: convert_iter_for_each_to_for.rs

Converts an Iterator::for_each function into a for loop.

Before

fn main() {
    let iter = iter::repeat((9, 2));
    iter.for_each┃(|(x, y)| {
        println!("x: {}, y: {}", x, y);
    });
}

After

fn main() {
    let iter = iter::repeat((9, 2));
    for (x, y) in iter {
        println!("x: {}, y: {}", x, y);
    }
}

convert_let_else_to_match

Source: convert_let_else_to_match.rs

Converts let-else statement to let statement and match expression.

Before

fn main() {
    let Ok(mut x) = f() else┃ { return };
}

After

fn main() {
    let mut x = match f() {
        Ok(x) => x,
        _ => return,
    };
}

convert_match_to_let_else

Source: convert_match_to_let_else.rs

Converts let statement with match initializer to let-else statement.

Before

fn foo(opt: Option<()>) {
    let val┃ = match opt {
        Some(it) => it,
        None => return,
    };
}

After

fn foo(opt: Option<()>) {
    let Some(val) = opt else { return };
}

convert_named_struct_to_tuple_struct

Source: convert_named_struct_to_tuple_struct.rs

Converts struct with named fields to tuple struct, and analogously for enum variants with named fields.

Before

struct Point┃ { x: f32, y: f32 }

impl Point {
    pub fn new(x: f32, y: f32) -> Self {
        Point { x, y }
    }

    pub fn x(&self) -> f32 {
        self.x
    }

    pub fn y(&self) -> f32 {
        self.y
    }
}

After

struct Point(f32, f32);

impl Point {
    pub fn new(x: f32, y: f32) -> Self {
        Point(x, y)
    }

    pub fn x(&self) -> f32 {
        self.0
    }

    pub fn y(&self) -> f32 {
        self.1
    }
}

convert_nested_function_to_closure

Source: convert_nested_function_to_closure.rs

Converts a function that is defined within the body of another function into a closure.

Before

fn main() {
    fn fo┃o(label: &str, number: u64) {
        println!("{}: {}", label, number);
    }

    foo("Bar", 100);
}

After

fn main() {
    let foo = |label: &str, number: u64| {
        println!("{}: {}", label, number);
    };

    foo("Bar", 100);
}

convert_to_guarded_return

Source: convert_to_guarded_return.rs

Replace a large conditional with a guarded return.

Before

fn main() {
    ┃if cond {
        foo();
        bar();
    }
}

After

fn main() {
    if !cond {
        return;
    }
    foo();
    bar();
}

convert_tuple_return_type_to_struct

Source: convert_tuple_return_type_to_struct.rs

This converts the return type of a function from a tuple type into a tuple struct and updates the body accordingly.

Before

fn bar() {
    let (a, b, c) = foo();
}

fn foo() -> (┃u32, u32, u32) {
    (1, 2, 3)
}

After

fn bar() {
    let FooResult(a, b, c) = foo();
}

struct FooResult(u32, u32, u32);

fn foo() -> FooResult {
    FooResult(1, 2, 3)
}

convert_tuple_struct_to_named_struct

Source: convert_tuple_struct_to_named_struct.rs

Converts tuple struct to struct with named fields, and analogously for tuple enum variants.

Before

struct Point┃(f32, f32);

impl Point {
    pub fn new(x: f32, y: f32) -> Self {
        Point(x, y)
    }

    pub fn x(&self) -> f32 {
        self.0
    }

    pub fn y(&self) -> f32 {
        self.1
    }
}

After

struct Point { field1: f32, field2: f32 }

impl Point {
    pub fn new(x: f32, y: f32) -> Self {
        Point { field1: x, field2: y }
    }

    pub fn x(&self) -> f32 {
        self.field1
    }

    pub fn y(&self) -> f32 {
        self.field2
    }
}

convert_two_arm_bool_match_to_matches_macro

Source: convert_two_arm_bool_match_to_matches_macro.rs

Convert 2-arm match that evaluates to a boolean into the equivalent matches! invocation.

Before

fn main() {
    match scrutinee┃ {
        Some(val) if val.cond() => true,
        _ => false,
    }
}

After

fn main() {
    matches!(scrutinee, Some(val) if val.cond())
}

convert_while_to_loop

Source: convert_while_to_loop.rs

Replace a while with a loop.

Before

fn main() {
    ┃while cond {
        foo();
    }
}

After

fn main() {
    loop {
        if !cond {
            break;
        }
        foo();
    }
}

destructure_struct_binding

Source: destructure_struct_binding.rs

Destructures a struct binding in place.

Before

struct Foo {
    bar: i32,
    baz: i32,
}
fn main() {
    let ┃foo = Foo { bar: 1, baz: 2 };
    let bar2 = foo.bar;
    let baz2 = &foo.baz;
}

After

struct Foo {
    bar: i32,
    baz: i32,
}
fn main() {
    let Foo { bar, baz } = Foo { bar: 1, baz: 2 };
    let bar2 = bar;
    let baz2 = &baz;
}

destructure_tuple_binding

Source: destructure_tuple_binding.rs

Destructures a tuple binding in place.

Before

fn main() {
    let ┃t = (1,2);
    let v = t.0;
}

After

fn main() {
    let (┃_0, _1) = (1,2);
    let v = _0;
}

desugar_async_into_impl_future

Source: toggle_async_sugar.rs

Rewrites asynchronous function from async fn into -> impl Future. This action does not touch the function body and therefore 0 block does not transform to async { 0 }.

Before

pub as┃ync fn foo() -> usize {
    0
}

After

pub fn foo() -> impl core::future::Future<Output = usize> {
    0
}

desugar_doc_comment

Source: desugar_doc_comment.rs

Desugars doc-comments to the attribute form.

Before

/// Multi-line┃
/// comment

After

#[doc = r"Multi-line
comment"]

expand_glob_import

Source: expand_glob_import.rs

Expands glob imports.

Before

mod foo {
    pub struct Bar;
    pub struct Baz;
}

use foo::*┃;

fn qux(bar: Bar, baz: Baz) {}

After

mod foo {
    pub struct Bar;
    pub struct Baz;
}

use foo::{Bar, Baz};

fn qux(bar: Bar, baz: Baz) {}

expand_glob_reexport

Source: expand_glob_import.rs

Expands non-private glob imports.

Before

mod foo {
    pub struct Bar;
    pub struct Baz;
}

pub use foo::*┃;

After

mod foo {
    pub struct Bar;
    pub struct Baz;
}

pub use foo::{Bar, Baz};

expand_record_rest_pattern

Source: expand_rest_pattern.rs

Fills fields by replacing rest pattern in record patterns.

Before

struct Bar { y: Y, z: Z }

fn foo(bar: Bar) {
    let Bar { ..┃ } = bar;
}

After

struct Bar { y: Y, z: Z }

fn foo(bar: Bar) {
    let Bar { y, z  } = bar;
}

expand_tuple_struct_rest_pattern

Source: expand_rest_pattern.rs

Fills fields by replacing rest pattern in tuple struct patterns.

Before

struct Bar(Y, Z);

fn foo(bar: Bar) {
    let Bar(..┃) = bar;
}

After

struct Bar(Y, Z);

fn foo(bar: Bar) {
    let Bar(_0, _1) = bar;
}

extract_constant

Source: extract_variable.rs

Extracts subexpression into a constant.

Before

fn main() {
    ┃(1 + 2)┃ * 4;
}

After

fn main() {
    const ┃VAR_NAME: i32 = 1 + 2;
    VAR_NAME * 4;
}

extract_expressions_from_format_string

Source: extract_expressions_from_format_string.rs

Move an expression out of a format string.

Before

fn main() {
    print!("{var} {x + 1}┃");
}

After

fn main() {
    print!("{var} {}"┃, x + 1);
}

extract_function

Source: extract_function.rs

Extracts selected statements and comments into new function.

Before

fn main() {
    let n = 1;
    ┃let m = n + 2;
    // calculate
    let k = m + n;┃
    let g = 3;
}

After

fn main() {
    let n = 1;
    fun_name(n);
    let g = 3;
}

fn ┃fun_name(n: i32) {
    let m = n + 2;
    // calculate
    let k = m + n;
}

extract_module

Source: extract_module.rs

Extracts a selected region as separate module. All the references, visibility and imports are resolved.

Before

┃fn foo(name: i32) -> i32 {
    name + 1
}┃

fn bar(name: i32) -> i32 {
    name + 2
}

After

mod modname {
    pub(crate) fn foo(name: i32) -> i32 {
        name + 1
    }
}

fn bar(name: i32) -> i32 {
    name + 2
}

extract_static

Source: extract_variable.rs

Extracts subexpression into a static.

Before

fn main() {
    ┃(1 + 2)┃ * 4;
}

After

fn main() {
    static ┃VAR_NAME: i32 = 1 + 2;
    VAR_NAME * 4;
}

extract_struct_from_enum_variant

Source: extract_struct_from_enum_variant.rs

Extracts a struct from enum variant.

Before

enum A { ┃One(u32, u32) }

After

struct One(u32, u32);

enum A { One(One) }

extract_type_alias

Source: extract_type_alias.rs

Extracts the selected type as a type alias.

Before

struct S {
    field: ┃(u8, u8, u8)┃,
}

After

type ┃Type = (u8, u8, u8);

struct S {
    field: Type,
}

extract_variable

Source: extract_variable.rs

Extracts subexpression into a variable.

Before

fn main() {
    ┃(1 + 2)┃ * 4;
}

After

fn main() {
    let ┃var_name = 1 + 2;
    var_name * 4;
}

fix_visibility

Source: fix_visibility.rs

Makes inaccessible item public.

Before

mod m {
    fn frobnicate() {}
}
fn main() {
    m::frobnicate┃();
}

After

mod m {
    ┃pub(crate) fn frobnicate() {}
}
fn main() {
    m::frobnicate();
}

flip_binexpr

Source: flip_binexpr.rs

Flips operands of a binary expression.

Before

fn main() {
    let _ = 90 +┃ 2;
}

After

fn main() {
    let _ = 2 + 90;
}

flip_comma

Source: flip_comma.rs

Flips two comma-separated items.

Before

fn main() {
    ((1, 2),┃ (3, 4));
}

After

fn main() {
    ((3, 4), (1, 2));
}

flip_or_pattern

Source: flip_or_pattern.rs

Flips two patterns in an or-pattern.

Before

fn foo() {
    let (a |┃ b) = 1;
}

After

fn foo() {
    let (b | a) = 1;
}

flip_trait_bound

Source: flip_trait_bound.rs

Flips two trait bounds.

Before

fn foo<T: Clone +┃ Copy>() { }

After

fn foo<T: Copy + Clone>() { }

generate_constant

Source: generate_constant.rs

Generate a named constant.

Before

struct S { i: usize }
impl S { pub fn new(n: usize) {} }
fn main() {
    let v = S::new(CAPA┃CITY);
}

After

struct S { i: usize }
impl S { pub fn new(n: usize) {} }
fn main() {
    const CAPACITY: usize = ┃;
    let v = S::new(CAPACITY);
}

generate_default_from_enum_variant

Source: generate_default_from_enum_variant.rs

Adds a Default impl for an enum using a variant.

Before

enum Version {
 Undefined,
 Minor┃,
 Major,
}

After

enum Version {
 Undefined,
 Minor,
 Major,
}

impl Default for Version {
    fn default() -> Self {
        Self::Minor
    }
}

generate_default_from_new

Source: generate_default_from_new.rs

Generates default implementation from new method.

Before

struct Example { _inner: () }

impl Example {
    pub fn n┃ew() -> Self {
        Self { _inner: () }
    }
}

After

struct Example { _inner: () }

impl Example {
    pub fn new() -> Self {
        Self { _inner: () }
    }
}

impl Default for Example {
    fn default() -> Self {
        Self::new()
    }
}

generate_delegate_methods

Source: generate_delegate_methods.rs

Generate delegate methods.

Before

struct Age(u8);
impl Age {
    fn age(&self) -> u8 {
        self.0
    }
}

struct Person {
    ag┃e: Age,
}

After

struct Age(u8);
impl Age {
    fn age(&self) -> u8 {
        self.0
    }
}

struct Person {
    age: Age,
}

impl Person {
    ┃fn age(&self) -> u8 {
        self.age.age()
    }
}

generate_delegate_trait

Source: generate_delegate_trait.rs

Generate delegate trait implementation for StructFields.

Before

trait SomeTrait {
    type T;
    fn fn_(arg: u32) -> u32;
    fn method_(&mut self) -> bool;
}
struct A;
impl SomeTrait for A {
    type T = u32;

    fn fn_(arg: u32) -> u32 {
        42
    }

    fn method_(&mut self) -> bool {
        false
    }
}
struct B {
    a┃: A,
}

After

trait SomeTrait {
    type T;
    fn fn_(arg: u32) -> u32;
    fn method_(&mut self) -> bool;
}
struct A;
impl SomeTrait for A {
    type T = u32;

    fn fn_(arg: u32) -> u32 {
        42
    }

    fn method_(&mut self) -> bool {
        false
    }
}
struct B {
    a: A,
}

impl SomeTrait for B {
    type T = <A as SomeTrait>::T;

    fn fn_(arg: u32) -> u32 {
        <A as SomeTrait>::fn_(arg)
    }

    fn method_(&mut self) -> bool {
        <A as SomeTrait>::method_(&mut self.a)
    }
}

generate_deref

Source: generate_deref.rs

Generate Deref impl using the given struct field.

Before

struct A;
struct B {
   ┃a: A
}

After

struct A;
struct B {
   a: A
}

impl core::ops::Deref for B {
    type Target = A;

    fn deref(&self) -> &Self::Target {
        &self.a
    }
}

generate_derive

Source: generate_derive.rs

Adds a new #[derive()] clause to a struct or enum.

Before

struct Point {
    x: u32,
    y: u32,┃
}

After

#[derive(┃)]
struct Point {
    x: u32,
    y: u32,
}

generate_doc_example

Source: generate_documentation_template.rs

Generates a rustdoc example when editing an item's documentation.

Before

/// Adds two numbers.┃
pub fn add(a: i32, b: i32) -> i32 { a + b }

After

/// Adds two numbers.
///
/// # Examples
///
/// ```
/// use ra_test_fixture::add;
///
/// assert_eq!(add(a, b), );
/// ```
pub fn add(a: i32, b: i32) -> i32 { a + b }

generate_documentation_template

Source: generate_documentation_template.rs

Adds a documentation template above a function definition / declaration.

Before

pub struct S;
impl S {
    pub unsafe fn set_len┃(&mut self, len: usize) -> Result<(), std::io::Error> {
        /* ... */
    }
}

After

pub struct S;
impl S {
    /// Sets the length of this [`S`].
    ///
    /// # Errors
    ///
    /// This function will return an error if .
    ///
    /// # Safety
    ///
    /// .
    pub unsafe fn set_len(&mut self, len: usize) -> Result<(), std::io::Error> {
        /* ... */
    }
}

generate_enum_as_method

Source: generate_enum_projection_method.rs

Generate an as_ method for this enum variant.

Before

enum Value {
 Number(i32),
 Text(String)┃,
}

After

enum Value {
 Number(i32),
 Text(String),
}

impl Value {
    fn as_text(&self) -> Option<&String> {
        if let Self::Text(v) = self {
            Some(v)
        } else {
            None
        }
    }
}

generate_enum_is_method

Source: generate_enum_is_method.rs

Generate an is_ method for this enum variant.

Before

enum Version {
 Undefined,
 Minor┃,
 Major,
}

After

enum Version {
 Undefined,
 Minor,
 Major,
}

impl Version {
    /// Returns `true` if the version is [`Minor`].
    ///
    /// [`Minor`]: Version::Minor
    #[must_use]
    fn is_minor(&self) -> bool {
        matches!(self, Self::Minor)
    }
}

generate_enum_try_into_method

Source: generate_enum_projection_method.rs

Generate a try_into_ method for this enum variant.

Before

enum Value {
 Number(i32),
 Text(String)┃,
}

After

enum Value {
 Number(i32),
 Text(String),
}

impl Value {
    fn try_into_text(self) -> Result<String, Self> {
        if let Self::Text(v) = self {
            Ok(v)
        } else {
            Err(self)
        }
    }
}

generate_enum_variant

Source: generate_enum_variant.rs

Adds a variant to an enum.

Before

enum Countries {
    Ghana,
}

fn main() {
    let country = Countries::Lesotho┃;
}

After

enum Countries {
    Ghana,
    Lesotho,
}

fn main() {
    let country = Countries::Lesotho;
}

generate_fn_type_alias_named

Source: generate_fn_type_alias.rs

Generate a type alias for the function with named parameters.

Before

unsafe fn fo┃o(n: i32) -> i32 { 42i32 }

After

type ${0:FooFn} = unsafe fn(n: i32) -> i32;

unsafe fn foo(n: i32) -> i32 { 42i32 }

generate_fn_type_alias_unnamed

Source: generate_fn_type_alias.rs

Generate a type alias for the function with unnamed parameters.

Before

unsafe fn fo┃o(n: i32) -> i32 { 42i32 }

After

type ${0:FooFn} = unsafe fn(i32) -> i32;

unsafe fn foo(n: i32) -> i32 { 42i32 }

generate_from_impl_for_enum

Source: generate_from_impl_for_enum.rs

Adds a From impl for this enum variant with one tuple field.

Before

enum A { ┃One(u32) }

After

enum A { One(u32) }

impl From<u32> for A {
    fn from(v: u32) -> Self {
        Self::One(v)
    }
}

generate_function

Source: generate_function.rs

Adds a stub function with a signature matching the function under the cursor.

Before

struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    bar┃("", baz());
}

After

struct Baz;
fn baz() -> Baz { Baz }
fn foo() {
    bar("", baz());
}

fn bar(arg: &str, baz: Baz) ${0:-> _} {
    todo!()
}

generate_getter

Source: generate_getter_or_setter.rs

Generate a getter method.

Before

struct Person {
    nam┃e: String,
}

After

struct Person {
    name: String,
}

impl Person {
    fn ┃name(&self) -> &str {
        &self.name
    }
}

generate_getter_mut

Source: generate_getter_or_setter.rs

Generate a mut getter method.

Before

struct Person {
    nam┃e: String,
}

After

struct Person {
    name: String,
}

impl Person {
    fn ┃name_mut(&mut self) -> &mut String {
        &mut self.name
    }
}

generate_impl

Source: generate_impl.rs

Adds a new inherent impl for a type.

Before

struct Ctx┃<T: Clone> {
    data: T,
}

After

struct Ctx<T: Clone> {
    data: T,
}

impl<T: Clone> Ctx<T> {┃}

generate_is_empty_from_len

Source: generate_is_empty_from_len.rs

Generates is_empty implementation from the len method.

Before

struct MyStruct { data: Vec<String> }

impl MyStruct {
    #[must_use]
    p┃ub fn len(&self) -> usize {
        self.data.len()
    }
}

After

struct MyStruct { data: Vec<String> }

impl MyStruct {
    #[must_use]
    pub fn len(&self) -> usize {
        self.data.len()
    }

    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }
}

generate_mut_trait_impl

Source: generate_mut_trait_impl.rs

Adds a IndexMut impl from the Index trait.

Before

pub enum Axis { X = 0, Y = 1, Z = 2 }

impl<T> core::ops::Index┃<Axis> for [T; 3] {
    type Output = T;

    fn index(&self, index: Axis) -> &Self::Output {
        &self[index as usize]
    }
}

After

pub enum Axis { X = 0, Y = 1, Z = 2 }

┃impl<T> core::ops::IndexMut<Axis> for [T; 3] {
    fn index_mut(&mut self, index: Axis) -> &mut Self::Output {
        &self[index as usize]
    }
}

impl<T> core::ops::Index<Axis> for [T; 3] {
    type Output = T;

    fn index(&self, index: Axis) -> &Self::Output {
        &self[index as usize]
    }
}

generate_new

Source: generate_new.rs

Adds a fn new for a type.

Before

struct Ctx<T: Clone> {
     data: T,┃
}

After

struct Ctx<T: Clone> {
     data: T,
}

impl<T: Clone> Ctx<T> {
    fn ┃new(data: T) -> Self {
        Self { data }
    }
}

generate_setter

Source: generate_getter_or_setter.rs

Generate a setter method.

Before

struct Person {
    nam┃e: String,
}

After

struct Person {
    name: String,
}

impl Person {
    fn ┃set_name(&mut self, name: String) {
        self.name = name;
    }
}

generate_trait_from_impl

Source: generate_trait_from_impl.rs

Generate trait for an already defined inherent impl and convert impl to a trait impl.

Before

struct Foo<const N: usize>([i32; N]);

macro_rules! const_maker {
    ($t:ty, $v:tt) => {
        const CONST: $t = $v;
    };
}

impl<const N: usize> Fo┃o<N> {
    // Used as an associated constant.
    const CONST_ASSOC: usize = N * 4;

    fn create() -> Option<()> {
        Some(())
    }

    const_maker! {i32, 7}
}

After

struct Foo<const N: usize>([i32; N]);

macro_rules! const_maker {
    ($t:ty, $v:tt) => {
        const CONST: $t = $v;
    };
}

trait ${0:NewTrait}<const N: usize> {
    // Used as an associated constant.
    const CONST_ASSOC: usize = N * 4;

    fn create() -> Option<()>;

    const_maker! {i32, 7}
}

impl<const N: usize> ${0:NewTrait}<N> for Foo<N> {
    // Used as an associated constant.
    const CONST_ASSOC: usize = N * 4;

    fn create() -> Option<()> {
        Some(())
    }

    const_maker! {i32, 7}
}

generate_trait_impl

Source: generate_impl.rs

Adds a new trait impl for a type.

Before

struct ┃Ctx<T: Clone> {
    data: T,
}

After

struct Ctx<T: Clone> {
    data: T,
}

impl<T: Clone> ${1:_} for Ctx<T> {┃}

inline_call

Source: inline_call.rs

Inlines a function or method body creating a let statement per parameter unless the parameter can be inlined. The parameter will be inlined either if it the supplied argument is a simple local or if the parameter is only accessed inside the function body once.

Before

fn foo(name: Option<&str>) {
    let name = name.unwrap┃();
}

After

fn foo(name: Option<&str>) {
    let name = match name {
            Some(val) => val,
            None => panic!("called `Option::unwrap()` on a `None` value"),
        };
}

inline_const_as_literal

Source: inline_const_as_literal.rs

Evaluate and inline const variable as literal.

Before

const STRING: &str = "Hello, World!";

fn something() -> &'static str {
    STRING┃
}

After

const STRING: &str = "Hello, World!";

fn something() -> &'static str {
    "Hello, World!"
}

inline_into_callers

Source: inline_call.rs

Inline a function or method body into all of its callers where possible, creating a let statement per parameter unless the parameter can be inlined. The parameter will be inlined either if it the supplied argument is a simple local or if the parameter is only accessed inside the function body once. If all calls can be inlined the function will be removed.

Before

fn print(_: &str) {}
fn foo┃(word: &str) {
    if !word.is_empty() {
        print(word);
    }
}
fn bar() {
    foo("안녕하세요");
    foo("여러분");
}

After

fn print(_: &str) {}

fn bar() {
    {
        let word: &str = "안녕하세요";
        if !word.is_empty() {
            print(word);
        }
    };
    {
        let word: &str = "여러분";
        if !word.is_empty() {
            print(word);
        }
    };
}

inline_local_variable

Source: inline_local_variable.rs

Inlines a local variable.

Before

fn main() {
    let x┃ = 1 + 2;
    x * 4;
}

After

fn main() {
    (1 + 2) * 4;
}

inline_macro

Source: inline_macro.rs

Takes a macro and inlines it one step.

Before

macro_rules! num {
    (+$($t:tt)+) => (1 + num!($($t )+));
    (-$($t:tt)+) => (-1 + num!($($t )+));
    (+) => (1);
    (-) => (-1);
}

fn main() {
    let number = num┃!(+ + + - + +);
    println!("{number}");
}

After

macro_rules! num {
    (+$($t:tt)+) => (1 + num!($($t )+));
    (-$($t:tt)+) => (-1 + num!($($t )+));
    (+) => (1);
    (-) => (-1);
}

fn main() {
    let number = 1+num!(+ + - + +);
    println!("{number}");
}

inline_type_alias

Source: inline_type_alias.rs

Replace a type alias with its concrete type.

Before

type A<T = u32> = Vec<T>;

fn main() {
    let a: ┃A;
}

After

type A<T = u32> = Vec<T>;

fn main() {
    let a: Vec<u32>;
}

inline_type_alias_uses

Source: inline_type_alias.rs

Inline a type alias into all of its uses where possible.

Before

type ┃A = i32;
fn id(x: A) -> A {
    x
};
fn foo() {
    let _: A = 3;
}

After

fn id(x: i32) -> i32 {
    x
};
fn foo() {
    let _: i32 = 3;
}

into_to_qualified_from

Source: into_to_qualified_from.rs

Convert an into method call to a fully qualified from call.

Before

//- minicore: from
struct B;
impl From<i32> for B {
    fn from(a: i32) -> Self {
       B
    }
}

fn main() -> () {
    let a = 3;
    let b: B = a.in┃to();
}

After

struct B;
impl From<i32> for B {
    fn from(a: i32) -> Self {
       B
    }
}

fn main() -> () {
    let a = 3;
    let b: B = B::from(a);
}

introduce_named_lifetime

Source: introduce_named_lifetime.rs

Change an anonymous lifetime to a named lifetime.

Before

impl Cursor<'_┃> {
    fn node(self) -> &SyntaxNode {
        match self {
            Cursor::Replace(node) | Cursor::Before(node) => node,
        }
    }
}

After

impl<'a> Cursor<'a> {
    fn node(self) -> &SyntaxNode {
        match self {
            Cursor::Replace(node) | Cursor::Before(node) => node,
        }
    }
}

introduce_named_type_parameter

Source: introduce_named_type_parameter.rs

Replaces impl Trait function argument with the named generic.

Before

fn foo(bar: ┃impl Bar) {}

After

fn foo<┃B: Bar>(bar: B) {}

invert_if

Source: invert_if.rs

This transforms if expressions of the form if !x {A} else {B} into if x {B} else {A} This also works with !=. This assist can only be applied with the cursor on if.

Before

fn main() {
    if┃ !y { A } else { B }
}

After

fn main() {
    if y { B } else { A }
}

line_to_block

Source: convert_comment_block.rs

Converts comments between block and single-line form.

Before

   // Multi-line┃
   // comment

After

  /*
  Multi-line
  comment
  */

make_raw_string

Source: raw_string.rs

Adds r# to a plain string literal.

Before

fn main() {
    "Hello,┃ World!";
}

After

fn main() {
    r#"Hello, World!"#;
}

make_usual_string

Source: raw_string.rs

Turns a raw string into a plain string.

Before

fn main() {
    r#"Hello,┃ "World!""#;
}

After

fn main() {
    "Hello, \"World!\"";
}

merge_imports

Source: merge_imports.rs

Merges neighbor imports with a common prefix.

Before

use std::┃fmt::Formatter;
use std::io;

After

use std::{fmt::Formatter, io};

merge_match_arms

Source: merge_match_arms.rs

Merges the current match arm with the following if their bodies are identical.

Before

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        ┃Action::Move(..) => foo(),
        Action::Stop => foo(),
    }
}

After

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move(..) | Action::Stop => foo(),
    }
}

merge_nested_if

Source: merge_nested_if.rs

This transforms if expressions of the form if x { if y {A} } into if x && y {A} This assist can only be applied with the cursor on if.

Before

fn main() {
   i┃f x == 3 { if y == 4 { 1 } }
}

After

fn main() {
   if x == 3 && y == 4 { 1 }
}

move_arm_cond_to_match_guard

Source: move_guard.rs

Moves if expression from match arm body into a guard.

Before

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } => ┃if distance > 10 { foo() },
        _ => (),
    }
}

After

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } if distance > 10 => foo(),
        _ => (),
    }
}

move_bounds_to_where_clause

Source: move_bounds.rs

Moves inline type bounds to a where clause.

Before

fn apply<T, U, ┃F: FnOnce(T) -> U>(f: F, x: T) -> U {
    f(x)
}

After

fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
    f(x)
}

move_const_to_impl

Source: move_const_to_impl.rs

Move a local constant item in a method to impl's associated constant. All the references will be qualified with Self::.

Before

struct S;
impl S {
    fn foo() -> usize {
        /// The answer.
        const C┃: usize = 42;

        C * C
    }
}

After

struct S;
impl S {
    /// The answer.
    const C: usize = 42;

    fn foo() -> usize {
        Self::C * Self::C
    }
}

move_from_mod_rs

Source: move_from_mod_rs.rs

Moves xxx/mod.rs to xxx.rs.

Before

//- /main.rs
mod a;
//- /a/mod.rs
┃fn t() {}┃

After

fn t() {}

move_guard_to_arm_body

Source: move_guard.rs

Moves match guard into match arm body.

Before

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } ┃if distance > 10 => foo(),
        _ => (),
    }
}

After

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } => if distance > 10 {
            foo()
        },
        _ => (),
    }
}

move_module_to_file

Source: move_module_to_file.rs

Moves inline module's contents to a separate file.

Before

mod ┃foo {
    fn t() {}
}

After

mod foo;

move_to_mod_rs

Source: move_to_mod_rs.rs

Moves xxx.rs to xxx/mod.rs.

Before

//- /main.rs
mod a;
//- /a.rs
┃fn t() {}┃

After

fn t() {}

normalize_import

Source: normalize_import.rs

Normalizes an import.

Before

use┃ std::{io, {fmt::Formatter}};

After

use std::{fmt::Formatter, io};

promote_local_to_const

Source: promote_local_to_const.rs

Promotes a local variable to a const item changing its name to a SCREAMING_SNAKE_CASE variant if the local uses no non-const expressions.

Before

fn main() {
    let foo┃ = true;

    if foo {
        println!("It's true");
    } else {
        println!("It's false");
    }
}

After

fn main() {
    const ┃FOO: bool = true;

    if FOO {
        println!("It's true");
    } else {
        println!("It's false");
    }
}

pull_assignment_up

Source: pull_assignment_up.rs

Extracts variable assignment to outside an if or match statement.

Before

fn main() {
    let mut foo = 6;

    if true {
        ┃foo = 5;
    } else {
        foo = 4;
    }
}

After

fn main() {
    let mut foo = 6;

    foo = if true {
        5
    } else {
        4
    };
}

qualify_method_call

Source: qualify_method_call.rs

Replaces the method call with a qualified function call.

Before

struct Foo;
impl Foo {
    fn foo(&self) {}
}
fn main() {
    let foo = Foo;
    foo.fo┃o();
}

After

struct Foo;
impl Foo {
    fn foo(&self) {}
}
fn main() {
    let foo = Foo;
    Foo::foo(&foo);
}

qualify_path

Source: qualify_path.rs

If the name is unresolved, provides all possible qualified paths for it.

Before

fn main() {
    let map = HashMap┃::new();
}

After

fn main() {
    let map = std::collections::HashMap::new();
}

reformat_number_literal

Source: number_representation.rs

Adds or removes separators from integer literal.

Before

const _: i32 = 1012345┃;

After

const _: i32 = 1_012_345;

remove_dbg

Source: remove_dbg.rs

Removes dbg!() macro call.

Before

fn main() {
    let x = ┃dbg!(42 * dbg!(4 + 2));┃
}

After

fn main() {
    let x = 42 * (4 + 2);
}

remove_hash

Source: raw_string.rs

Removes a hash from a raw string literal.

Before

fn main() {
    r#"Hello,┃ World!"#;
}

After

fn main() {
    r"Hello, World!";
}

remove_mut

Source: remove_mut.rs

Removes the mut keyword.

Before

impl Walrus {
    fn feed(&mut┃ self, amount: u32) {}
}

After

impl Walrus {
    fn feed(&self, amount: u32) {}
}

remove_parentheses

Source: remove_parentheses.rs

Removes redundant parentheses.

Before

fn main() {
    _ = ┃(2) + 2;
}

After

fn main() {
    _ = 2 + 2;
}

remove_unused_imports

Source: remove_unused_imports.rs

Removes any use statements in the current selection that are unused.

Before

struct X();
mod foo {
    use super::X┃;
}

After

struct X();
mod foo {
}

remove_unused_param

Source: remove_unused_param.rs

Removes unused function parameter.

Before

fn frobnicate(x: i32┃) {}

fn main() {
    frobnicate(92);
}

After

fn frobnicate() {}

fn main() {
    frobnicate();
}

reorder_fields

Source: reorder_fields.rs

Reorder the fields of record literals and record patterns in the same order as in the definition.

Before

struct Foo {foo: i32, bar: i32};
const test: Foo = ┃Foo {bar: 0, foo: 1}

After

struct Foo {foo: i32, bar: i32};
const test: Foo = Foo {foo: 1, bar: 0}

reorder_impl_items

Source: reorder_impl_items.rs

Reorder the items of an impl Trait. The items will be ordered in the same order as in the trait definition.

Before

trait Foo {
    type A;
    const B: u8;
    fn c();
}

struct Bar;
┃impl Foo for Bar┃ {
    const B: u8 = 17;
    fn c() {}
    type A = String;
}

After

trait Foo {
    type A;
    const B: u8;
    fn c();
}

struct Bar;
impl Foo for Bar {
    type A = String;
    const B: u8 = 17;
    fn c() {}
}

replace_arith_with_checked

Source: replace_arith_op.rs

Replaces arithmetic on integers with the checked_* equivalent.

Before

fn main() {
  let x = 1 ┃+ 2;
}

After

fn main() {
  let x = 1.checked_add(2);
}

replace_arith_with_saturating

Source: replace_arith_op.rs

Replaces arithmetic on integers with the saturating_* equivalent.

Before

fn main() {
  let x = 1 ┃+ 2;
}

After

fn main() {
  let x = 1.saturating_add(2);
}

replace_arith_with_wrapping

Source: replace_arith_op.rs

Replaces arithmetic on integers with the wrapping_* equivalent.

Before

fn main() {
  let x = 1 ┃+ 2;
}

After

fn main() {
  let x = 1.wrapping_add(2);
}

replace_char_with_string

Source: replace_string_with_char.rs

Replace a char literal with a string literal.

Before

fn main() {
    find('{┃');
}

After

fn main() {
    find("{");
}

replace_derive_with_manual_impl

Source: replace_derive_with_manual_impl.rs

Converts a derive impl into a manual one.

Before

#[derive(Deb┃ug, Display)]
struct S;

After

#[derive(Display)]
struct S;

impl Debug for S {
    ┃fn fmt(&self, f: &mut Formatter) -> Result<()> {
        f.debug_struct("S").finish()
    }
}

replace_if_let_with_match

Source: replace_if_let_with_match.rs

Replaces a if let expression with a match expression.

Before

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    ┃if let Action::Move { distance } = action {
        foo(distance)
    } else {
        bar()
    }
}

After

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move { distance } => foo(distance),
        _ => bar(),
    }
}

replace_is_some_with_if_let_some

Source: replace_is_method_with_if_let_method.rs

Replace if x.is_some() with if let Some(_tmp) = x or if x.is_ok() with if let Ok(_tmp) = x.

Before

fn main() {
    let x = Some(1);
    if x.is_som┃e() {}
}

After

fn main() {
    let x = Some(1);
    if let Some(${0:x1}) = x {}
}

replace_let_with_if_let

Source: replace_let_with_if_let.rs

Replaces let with an if let.

Before

fn main(action: Action) {
    ┃let x = compute();
}

fn compute() -> Option<i32> { None }

After

fn main(action: Action) {
    if let Some(x) = compute() {
    }
}

fn compute() -> Option<i32> { None }

replace_match_with_if_let

Source: replace_if_let_with_match.rs

Replaces a binary match with a wildcard pattern and no guards with an if let expression.

Before

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    ┃match action {
        Action::Move { distance } => foo(distance),
        _ => bar(),
    }
}

After

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    if let Action::Move { distance } = action {
        foo(distance)
    } else {
        bar()
    }
}

replace_named_generic_with_impl

Source: replace_named_generic_with_impl.rs

Replaces named generic with an impl Trait in function argument.

Before

fn new<P┃: AsRef<Path>>(location: P) -> Self {}

After

fn new(location: impl AsRef<Path>) -> Self {}

replace_qualified_name_with_use

Source: replace_qualified_name_with_use.rs

Adds a use statement for a given fully-qualified name.

Before

fn process(map: std::collections::┃HashMap<String, String>) {}

After

use std::collections::HashMap;

fn process(map: HashMap<String, String>) {}

replace_string_with_char

Source: replace_string_with_char.rs

Replace string literal with char literal.

Before

fn main() {
    find("{┃");
}

After

fn main() {
    find('{');
}

replace_try_expr_with_match

Source: replace_try_expr_with_match.rs

Replaces a try expression with a match expression.

Before

fn handle() {
    let pat = Some(true)┃?;
}

After

fn handle() {
    let pat = match Some(true) {
        Some(it) => it,
        None => return None,
    };
}

replace_turbofish_with_explicit_type

Source: replace_turbofish_with_explicit_type.rs

Converts ::<_> to an explicit type assignment.

Before

fn make<T>() -> T { ) }
fn main() {
    let a = make┃::<i32>();
}

After

fn make<T>() -> T { ) }
fn main() {
    let a: i32 = make();
}

replace_with_eager_method

Source: replace_method_eager_lazy.rs

Replace unwrap_or_else with unwrap_or and ok_or_else with ok_or.

Before

fn foo() {
    let a = Some(1);
    a.unwra┃p_or_else(|| 2);
}

After

fn foo() {
    let a = Some(1);
    a.unwrap_or(2);
}

replace_with_lazy_method

Source: replace_method_eager_lazy.rs

Replace unwrap_or with unwrap_or_else and ok_or with ok_or_else.

Before

fn foo() {
    let a = Some(1);
    a.unwra┃p_or(2);
}

After

fn foo() {
    let a = Some(1);
    a.unwrap_or_else(|| 2);
}

sort_items

Source: sort_items.rs

Sorts item members alphabetically: fields, enum variants and methods.

Before

struct ┃Foo┃ { second: u32, first: String }

After

struct Foo { first: String, second: u32 }

Before

trait ┃Bar┃ {
    fn second(&self) -> u32;
    fn first(&self) -> String;
}

After

trait Bar {
    fn first(&self) -> String;
    fn second(&self) -> u32;
}

Before

struct Baz;
impl ┃Baz┃ {
    fn second(&self) -> u32;
    fn first(&self) -> String;
}

After

struct Baz;
impl Baz {
    fn first(&self) -> String;
    fn second(&self) -> u32;
}

There is a difference between sorting enum variants:

Before

enum ┃Animal┃ {
  Dog(String, f64),
  Cat { weight: f64, name: String },
}

After

enum Animal {
  Cat { weight: f64, name: String },
  Dog(String, f64),
}

and sorting a single enum struct variant:

Before

enum Animal {
  Dog(String, f64),
  Cat ┃{ weight: f64, name: String }┃,
}

After

enum Animal {
  Dog(String, f64),
  Cat { name: String, weight: f64 },
}

split_import

Source: split_import.rs

Wraps the tail of import into braces.

Before

use std::┃collections::HashMap;

After

use std::{collections::HashMap};

sugar_impl_future_into_async

Source: toggle_async_sugar.rs

Rewrites asynchronous function from -> impl Future into async fn. This action does not touch the function body and therefore async { 0 } block does not transform to just 0.

Before

pub fn foo() -> impl core::future::F┃uture<Output = usize> {
    async { 0 }
}

After

pub async fn foo() -> usize {
    async { 0 }
}

toggle_ignore

Source: toggle_ignore.rs

Adds #[ignore] attribute to the test.

Before

┃#[test]
fn arithmetics {
    assert_eq!(2 + 2, 5);
}

After

#[test]
#[ignore]
fn arithmetics {
    assert_eq!(2 + 2, 5);
}

toggle_macro_delimiter

Source: toggle_macro_delimiter.rs

Change macro delimiters in the order of ( -> { -> [ -> (.

Before

macro_rules! sth {
    () => {};
}

sth!┃( );

After

macro_rules! sth {
    () => {};
}

sth!{ }

unmerge_match_arm

Source: unmerge_match_arm.rs

Splits the current match with a | pattern into two arms with identical bodies.

Before

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move(..) ┃| Action::Stop => foo(),
    }
}

After

enum Action { Move { distance: u32 }, Stop }

fn handle(action: Action) {
    match action {
        Action::Move(..) => foo(),
        Action::Stop => foo(),
    }
}

unmerge_use

Source: unmerge_use.rs

Extracts single use item from use list.

Before

use std::fmt::{Debug, Display┃};

After

use std::fmt::{Debug};
use std::fmt::Display;

unnecessary_async

Source: unnecessary_async.rs

Removes the async mark from functions which have no .await in their body. Looks for calls to the functions and removes the .await on the call site.

Before

pub asy┃nc fn foo() {}
pub async fn bar() { foo().await }

After

pub fn foo() {}
pub async fn bar() { foo() }

unqualify_method_call

Source: unqualify_method_call.rs

Transforms universal function call syntax into a method call.

Before

fn main() {
    std::ops::Add::add┃(1, 2);
}

After

use std::ops::Add;

fn main() {
    1.add(2);
}

unwrap_block

Source: unwrap_block.rs

This assist removes if...else, for, while and loop control statements to just keep the body.

Before

fn foo() {
    if true {┃
        println!("foo");
    }
}

After

fn foo() {
    println!("foo");
}

unwrap_option_return_type

Source: unwrap_return_type.rs

Unwrap the function's return type.

Before

fn foo() -> Option<i32>┃ { Some(42i32) }

After

fn foo() -> i32 { 42i32 }

unwrap_result_return_type

Source: unwrap_return_type.rs

Unwrap the function's return type.

Before

fn foo() -> Result<i32>┃ { Ok(42i32) }

After

fn foo() -> i32 { 42i32 }

unwrap_tuple

Source: unwrap_tuple.rs

Unwrap the tuple to different variables.

Before

fn main() {
    ┃let (foo, bar) = ("Foo", "Bar");
}

After

fn main() {
    let foo = "Foo";
    let bar = "Bar";
}

wrap_return_type_in_option

Source: wrap_return_type.rs

Wrap the function's return type into Option.

Before

fn foo() -> i32┃ { 42i32 }

After

fn foo() -> Option<i32> { Some(42i32) }

wrap_return_type_in_result

Source: wrap_return_type.rs

Wrap the function's return type into Result.

Before

fn foo() -> i32┃ { 42i32 }

After

fn foo() -> Result<i32, ${0:_}> { Ok(42i32) }

wrap_unwrap_cfg_attr

Source: wrap_unwrap_cfg_attr.rs

Wraps an attribute to a cfg_attr attribute or unwraps a cfg_attr attribute to the inner attributes.

Before

#[derive┃(Debug)]
struct S {
   field: i32
}

After

#[cfg_attr(┃, derive(Debug))]
struct S {
   field: i32
}

Diagnostics

While most errors and warnings provided by rust-analyzer come from the cargo check integration, there’s a growing number of diagnostics implemented using rust-analyzer’s own analysis. Some of these diagnostics don’t respect #[allow] or #[deny] attributes yet, but can be turned off using the rust-analyzer.diagnostics.enable, rust-analyzer.diagnostics.experimental.enable or rust-analyzer.diagnostics.disabled settings.

Clippy

To run cargo clippy instead of cargo check, you can set "rust-analyzer.check.command": "clippy".

attribute-expansion-disabled

Source: macro_error.rs

This diagnostic is shown for attribute proc macros when attribute expansions have been disabled.

await-outside-of-async

Source: await_outside_of_async.rs

This diagnostic is triggered if the await keyword is used outside of an async function or block

break-outside-of-loop

Source: break_outside_of_loop.rs

This diagnostic is triggered if the break keyword is used outside of a loop.

cast-to-unsized

Source: invalid_cast.rs

This diagnostic is triggered when casting to an unsized type

expected-function

Source: expected_function.rs

This diagnostic is triggered if a call is made on something that is not callable.

generic-args-prohibited

Source: generic_args_prohibited.rs

This diagnostic is shown when generic arguments are provided for a type that does not accept generic arguments.

inactive-code

Source: inactive_code.rs

This diagnostic is shown for code with inactive #[cfg] attributes.

incoherent-impl

Source: incoherent_impl.rs

This diagnostic is triggered if the targe type of an impl is from a foreign crate.

incorrect-ident-case

Source: incorrect_case.rs

This diagnostic is triggered if an item name doesn't follow Rust naming convention.

invalid-cast

Source: invalid_cast.rs

This diagnostic is triggered if the code contains an illegal cast

invalid-derive-target

Source: invalid_derive_target.rs

This diagnostic is shown when the derive attribute is used on an item other than a struct, enum or union.

macro-def-error

Source: macro_error.rs

This diagnostic is shown for macro expansion errors.

macro-error

Source: macro_error.rs

This diagnostic is shown for macro expansion errors.

malformed-derive

Source: malformed_derive.rs

This diagnostic is shown when the derive attribute has invalid input.

mismatched-arg-count

Source: mismatched_arg_count.rs

This diagnostic is triggered if a function is invoked with an incorrect amount of arguments.

mismatched-tuple-struct-pat-arg-count

Source: mismatched_arg_count.rs

This diagnostic is triggered if a function is invoked with an incorrect amount of arguments.

missing-fields

Source: missing_fields.rs

This diagnostic is triggered if record lacks some fields that exist in the corresponding structure.

Example:

struct A { a: u8, b: u8 }

let a = A { a: 10 };

missing-match-arm

Source: missing_match_arms.rs

This diagnostic is triggered if match block is missing one or more match arms.

missing-unsafe

Source: missing_unsafe.rs

This diagnostic is triggered if an operation marked as unsafe is used outside of an unsafe function or block.

moved-out-of-ref

Source: moved_out_of_ref.rs

This diagnostic is triggered on moving non copy things out of references.

need-mut

Source: mutability_errors.rs

This diagnostic is triggered on mutating an immutable variable.

no-such-field

Source: no_such_field.rs

This diagnostic is triggered if created structure does not have field provided in record.

non-exhaustive-let

Source: non_exhaustive_let.rs

This diagnostic is triggered if a let statement without an else branch has a non-exhaustive pattern.

parenthesized-generic-args-without-fn-trait

Source: parenthesized_generic_args_without_fn_trait.rs

This diagnostic is shown when a Fn-trait-style generic parameters (Trait(A, B) -> C) was used on non-Fn trait/type.

private-assoc-item

Source: private_assoc_item.rs

This diagnostic is triggered if the referenced associated item is not visible from the current module.

private-field

Source: private_field.rs

This diagnostic is triggered if the accessed field is not visible from the current module.

proc-macro-disabled

Source: macro_error.rs

This diagnostic is shown for proc macros that have been specifically disabled via rust-analyzer.procMacro.ignored.

remove-trailing-return

Source: remove_trailing_return.rs

This diagnostic is triggered when there is a redundant return at the end of a function or closure.

remove-unnecessary-else

Source: remove_unnecessary_else.rs

This diagnostic is triggered when there is an else block for an if expression whose then branch diverges (e.g. ends with a return, continue, break e.t.c).

replace-filter-map-next-with-find-map

Source: replace_filter_map_next_with_find_map.rs

This diagnostic is triggered when .filter_map(..).next() is used, rather than the more concise .find_map(..).

trait-impl-incorrect-safety

Source: trait_impl_incorrect_safety.rs

Diagnoses incorrect safety annotations of trait impls.

trait-impl-missing-assoc_item

Source: trait_impl_missing_assoc_item.rs

Diagnoses missing trait items in a trait impl.

trait-impl-orphan

Source: trait_impl_orphan.rs

Only traits defined in the current crate can be implemented for arbitrary types

trait-impl-redundant-assoc_item

Source: trait_impl_redundant_assoc_item.rs

Diagnoses redundant trait items in a trait impl.

type-mismatch

Source: type_mismatch.rs

This diagnostic is triggered when the type of an expression or pattern does not match the expected type.

typed-hole

Source: typed_hole.rs

This diagnostic is triggered when an underscore expression is used in an invalid position.

undeclared-label

Source: undeclared_label.rs

unimplemented-builtin-macro

Source: unimplemented_builtin_macro.rs

This diagnostic is shown for builtin macros which are not yet implemented by rust-analyzer

unlinked-file

Source: unlinked_file.rs

This diagnostic is shown for files that are not included in any crate, or files that are part of crates rust-analyzer failed to discover. The file will not have IDE features available.

unnecessary-braces

Source: useless_braces.rs

Diagnostic for unnecessary braces in use items.

unreachable-label

Source: unreachable_label.rs

unresolved-assoc-item

Source: unresolved_assoc_item.rs

This diagnostic is triggered if the referenced associated item does not exist.

unresolved-extern-crate

Source: unresolved_extern_crate.rs

This diagnostic is triggered if rust-analyzer is unable to discover referred extern crate.

unresolved-field

Source: unresolved_field.rs

This diagnostic is triggered if a field does not exist on a given type.

unresolved-ident

Source: unresolved_ident.rs

This diagnostic is triggered if an expr-position ident is invalid.

unresolved-import

Source: unresolved_import.rs

This diagnostic is triggered if rust-analyzer is unable to resolve a path in a use declaration.

unresolved-macro-call

Source: unresolved_macro_call.rs

This diagnostic is triggered if rust-analyzer is unable to resolve the path to a macro in a macro invocation.

unresolved-method

Source: unresolved_method.rs

This diagnostic is triggered if a method does not exist on a given type.

unresolved-module

Source: unresolved_module.rs

This diagnostic is triggered if rust-analyzer is unable to discover referred module.

unused-mut

Source: mutability_errors.rs

This diagnostic is triggered when a mutable variable isn't actually mutated.

unused-variables

Source: unused_variables.rs

This diagnostic is triggered when a local variable is not used.

Editor Features

VS Code

Color configurations

It is possible to change the foreground/background color and font family/size of inlay hints. Just add this to your settings.json:

{
  "editor.inlayHints.fontFamily": "Courier New",
  "editor.inlayHints.fontSize": 11,

  "workbench.colorCustomizations": {
    // Name of the theme you are currently using
    "[Default Dark+]": {
      "editorInlayHint.foreground": "#868686f0",
      "editorInlayHint.background": "#3d3d3d48",

      // Overrides for specific kinds of inlay hints
      "editorInlayHint.typeForeground": "#fdb6fdf0",
      "editorInlayHint.parameterForeground": "#fdb6fdf0",
    }
  }
}

Semantic style customizations

You can customize the look of different semantic elements in the source code. For example, mutable bindings are underlined by default and you can override this behavior by adding the following section to your settings.json:

{
  "editor.semanticTokenColorCustomizations": {
    "rules": {
      "*.mutable": {
        "fontStyle": "", // underline is the default
      },
    }
  },
}

Most themes doesn’t support styling unsafe operations differently yet. You can fix this by adding overrides for the rules operator.unsafe, function.unsafe, and method.unsafe:

{
   "editor.semanticTokenColorCustomizations": {
         "rules": {
             "operator.unsafe": "#ff6600",
             "function.unsafe": "#ff6600",
             "method.unsafe": "#ff6600"
         }
    },
}

In addition to the top-level rules you can specify overrides for specific themes. For example, if you wanted to use a darker text color on a specific light theme, you might write:

{
   "editor.semanticTokenColorCustomizations": {
         "rules": {
             "operator.unsafe": "#ff6600"
         },
         "[Ayu Light]": {
            "rules": {
               "operator.unsafe": "#572300"
            }
         }
    },
}

Make sure you include the brackets around the theme name. For example, use "[Ayu Light]" to customize the theme Ayu Light.

Special when clause context for keybindings.

You may use inRustProject context to configure keybindings for rust projects only. For example:

{
    "key": "ctrl+alt+d",
    "command": "rust-analyzer.openDocs",
    "when": "inRustProject"
}

More about when clause contexts here.

Setting runnable environment variables

You can use "rust-analyzer.runnables.extraEnv" setting to define runnable environment-specific substitution variables. The simplest way for all runnables in a bunch:

"rust-analyzer.runnables.extraEnv": {
    "RUN_SLOW_TESTS": "1"
}

Or it is possible to specify vars more granularly:

"rust-analyzer.runnables.extraEnv": [
    {
        // "mask": null, // null mask means that this rule will be applied for all runnables
        "env": {
                "APP_ID": "1",
                "APP_DATA": "asdf"
        }
    },
    {
        "mask": "test_name",
        "env": {
                "APP_ID": "2", // overwrites only APP_ID
        }
    }
]

You can use any valid regular expression as a mask. Also note that a full runnable name is something like run bin_or_example_name, test some::mod::test_name or test-mod some::mod, so it is possible to distinguish binaries, single tests, and test modules with this masks: "^run", "^test " (the trailing space matters!), and "^test-mod" respectively.

If needed, you can set different values for different platforms:

"rust-analyzer.runnables.extraEnv": [
    {
        "platform": "win32", // windows only
        "env": {
                "APP_DATA": "windows specific data"
        }
    },
    {
        "platform": ["linux"],
        "env": {
                "APP_DATA": "linux data",
        }
    },
    { // for all platforms
        "env": {
                "APP_COMMON_DATA": "xxx",
        }
    }
]

Compiler feedback from external commands

Instead of relying on the built-in cargo check, you can configure Code to run a command in the background and use the $rustc-watch problem matcher to generate inline error markers from its output.

To do this you need to create a new VS Code Task and set "rust-analyzer.checkOnSave": false in preferences.

For example, if you want to run cargo watch instead, you might add the following to .vscode/tasks.json:

{
    "label": "Watch",
    "group": "build",
    "type": "shell",
    "command": "cargo watch",
    "problemMatcher": "$rustc-watch",
    "isBackground": true
}

Live Share

VS Code Live Share has partial support for rust-analyzer.

Live Share requires the official Microsoft build of VS Code, OSS builds will not work correctly.

The host’s rust-analyzer instance will be shared with all guests joining the session. The guests do not have to have the rust-analyzer extension installed for this to work.

If you are joining a Live Share session and do have rust-analyzer installed locally, commands from the command palette will not work correctly since they will attempt to communicate with the local server.

Contributing Quick Start

rust-analyzer is an ordinary Rust project, which is organized as a Cargo workspace, builds on stable and doesn't depend on C libraries. So, just

$ cargo test

should be enough to get you started!

To learn more about how rust-analyzer works, see Architecture. It also explains the high-level layout of the source code. Do skim through that document.

We also publish rustdoc docs to pages: https://rust-lang.github.io/rust-analyzer/ide/. Note though, that the internal documentation is very incomplete.

Various organizational and process issues are discussed in this document.

Getting in Touch

rust-analyzer is a part of the RLS-2.0 working group. Discussion happens in this Zulip stream:

https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frust-analyzer

• Issue Labels
• Code Style & Review Process
• Cookbook
  • CI
  • Launching rust-analyzer
  • TypeScript Tests
  • How to ...
  • Logging
  • Profiling
  • Release Process
  • Permissions

Issue Labels

• good-first-issue are good issues to get into the project.
• E-has-instructions issues have links to the code in question and tests.
• Broken Window are issues which are not necessarily critical by themselves, but which should be fixed ASAP regardless, to avoid accumulation of technical debt.
• E-easy, E-medium, E-hard, E-unknown, labels are estimates for how hard would be to write a fix. Each triaged issue should have one of these labels.
• S-actionable and S-unactionable specify if there are concrete steps to resolve or advance an issue. Roughly, actionable issues need only work to be fixed, while unactionable ones are blocked either on user feedback (providing a reproducible example), or on larger architectural work or decisions. This classification is descriptive, not prescriptive, and might be wrong: Any unactionable issue might have a simple fix that we missed. Each triaged issue should have one of these labels.
• fun is for cool, but probably hard stuff.
• C-Architecture is for moderate/large scale architecture discussion. Also a kind of fun. These issues should generally include a link to a Zulip discussion thread.

Code Style & Review Process

See the Style Guide.

Cookbook

CI

We use GitHub Actions for CI. Most of the things, including formatting, are checked by cargo test. If cargo test passes locally, that's a good sign that CI will be green as well. The only exception is that some long-running tests are skipped locally by default. Use env RUN_SLOW_TESTS=1 cargo test to run the full suite.

We use bors to enforce the not rocket science rule.

Launching rust-analyzer

Debugging the language server can be tricky. LSP is rather chatty, so driving it from the command line is not really feasible, driving it via VS Code requires interacting with two processes.

For this reason, the best way to see how rust-analyzer works is to find a relevant test and execute it. VS Code & Emacs include an action for running a single test.

Launching a VS Code instance with a locally built language server is also possible. There's "Run Extension (Debug Build)" launch configuration for this in VS Code.

In general, I use one of the following workflows for fixing bugs and implementing features:

If the problem concerns only internal parts of rust-analyzer (i.e. I don't need to touch the rust-analyzer crate or TypeScript code), there is a unit-test for it. So, I use rust-analyzer: Run action in VS Code to run this single test, and then just do printf-driven development/debugging. As a sanity check after I'm done, I use cargo xtask install --server and Reload Window action in VS Code to verify that the thing works as I expect.

If the problem concerns only the VS Code extension, I use Run Installed Extension launch configuration from launch.json. Notably, this uses the usual rust-analyzer binary from PATH. For this, it is important to have the following in your settings.json file:

{
    "rust-analyzer.server.path": "rust-analyzer"
}

After I am done with the fix, I use cargo xtask install --client to try the new extension for real.

If I need to fix something in the rust-analyzer crate, I feel sad because it's on the boundary between the two processes, and working there is slow. I usually just cargo xtask install --server and poke changes from my live environment. Note that this uses --release, which is usually faster overall, because loading stdlib into debug version of rust-analyzer takes a lot of time. To speed things up, sometimes I open a temporary hello-world project which has "rust-analyzer.cargo.sysroot": null in .code/settings.json. This flag causes rust-analyzer to skip loading the sysroot, which greatly reduces the amount of things rust-analyzer needs to do, and makes printf's more useful. Note that you should only use the eprint! family of macros for debugging: stdout is used for LSP communication, and print! would break it.

If I need to fix something simultaneously in the server and in the client, I feel even more sad. I don't have a specific workflow for this case.

Additionally, I use cargo run --release -p rust-analyzer -- analysis-stats path/to/some/rust/crate to run a batch analysis. This is primarily useful for performance optimizations, or for bug minimization.

TypeScript Tests

If you change files under editors/code and would like to run the tests and linter, install npm and run:

cd editors/code
npm ci
npm run lint

How to ...

• ... add an assist? #7535
• ... add a new protocol extension? #4569
• ... add a new configuration option? #7451
• ... add a new completion? #6964
• ... allow new syntax in the parser? #7338

Logging

Logging is done by both rust-analyzer and VS Code, so it might be tricky to figure out where logs go.

Inside rust-analyzer, we use the tracing crate for logging, and tracing-subscriber for logging frontend. By default, log goes to stderr, but the stderr itself is processed by VS Code. --log-file <PATH> CLI argument allows logging to file. Setting the RA_LOG_FILE=<PATH> environment variable will also log to file, it will also override --log-file.

To see stderr in the running VS Code instance, go to the "Output" tab of the panel and select rust-analyzer. This shows eprintln! as well. Note that stdout is used for the actual protocol, so println! will break things.

To log all communication between the server and the client, there are two choices:

• You can log on the server side, by running something like

  env RA_LOG=lsp_server=debug code .
  

• You can log on the client side, by the rust-analyzer: Toggle LSP Logs command or enabling "rust-analyzer.trace.server": "verbose" workspace setting. These logs are shown in a separate tab in the output and could be used with LSP inspector. Kudos to @DJMcNab for setting this awesome infra up!

There are also several VS Code commands which might be of interest:

• rust-analyzer: Status shows some memory-usage statistics.

• rust-analyzer: View Hir shows the HIR expressions within the function containing the cursor.

• If rust-analyzer.showSyntaxTree is enabled in settings, Rust Syntax Tree: Focus on Rust Syntax Tree View shows the syntax tree of the current file.

  You can click on nodes in the rust editor to go to the corresponding syntax node.

  You can click on Reveal Syntax Element next to a syntax node to go to the corresponding rust code and highlight the proper text range.

  If you trigger Go to Definition in the inspected Rust source file, the syntax tree view should scroll to and select the appropriate syntax node token.

  You can click on Copy next to a syntax node to copy a text representation of the node.

  

Profiling

We have a built-in hierarchical profiler, you can enable it by using RA_PROFILE env-var:

RA_PROFILE=*             // dump everything
RA_PROFILE=foo|bar|baz   // enabled only selected entries
RA_PROFILE=*@3>10        // dump everything, up to depth 3, if it takes more than 10 ms

Some rust-analyzer contributors have export RA_PROFILE='*>10' in my shell profile.

For machine-readable JSON output, we have the RA_PROFILE_JSON env variable. We support filtering only by span name:

RA_PROFILE=* // dump everything
RA_PROFILE_JSON="vfs_load|parallel_prime_caches|discover_command" // dump selected spans

We also have a "counting" profiler which counts number of instances of popular structs. It is enabled by RA_COUNT=1.

To measure time for from-scratch analysis, use something like this:

$ cargo run --release -p rust-analyzer -- analysis-stats ../chalk/

For measuring time of incremental analysis, use either of these:

$ cargo run --release -p rust-analyzer -- analysis-bench ../chalk/ --highlight ../chalk/chalk-engine/src/logic.rs
$ cargo run --release -p rust-analyzer -- analysis-bench ../chalk/ --complete ../chalk/chalk-engine/src/logic.rs:94:0

Look for fn benchmark_xxx tests for a quick way to reproduce performance problems.

Release Process

Release process is handled by release, dist, publish-release-notes and promote xtasks, release being the main one.

release assumes that you have checkouts of rust-analyzer, rust-analyzer.github.io, and rust-lang/rust in the same directory:

./rust-analyzer
./rust-analyzer.github.io
./rust-rust-analyzer  # Note the name!

The remote for rust-analyzer must be called upstream (I use origin to point to my fork). In addition, for xtask promote (see below), rust-rust-analyzer must have a rust-analyzer remote pointing to this repository on GitHub.

release calls the GitHub API calls to scrape pull request comments and categorize them in the changelog. This step uses the curl and jq applications, which need to be available in PATH. Finally, you need to obtain a GitHub personal access token and set the GITHUB_TOKEN environment variable.

Release steps:

1. Set the GITHUB_TOKEN environment variable.
2. Inside rust-analyzer, run cargo xtask release. This will:
   • checkout the release branch
   • reset it to upstream/nightly
   • push it to upstream. This triggers GitHub Actions which:
     • runs cargo xtask dist to package binaries and VS Code extension
     • makes a GitHub release
     • publishes the VS Code extension to the marketplace
   • call the GitHub API for PR details
   • create a new changelog in rust-analyzer.github.io
3. While the release is in progress, fill in the changelog.
4. Commit & push the changelog.
5. Run cargo xtask publish-release-notes <CHANGELOG> -- this will convert the changelog entry in AsciiDoc to Markdown and update the body of GitHub Releases entry.
6. Tweet.
7. Make a new branch and run cargo xtask rustc-pull, open a PR, and merge it. This will pull any changes from rust-lang/rust into rust-analyzer.
8. Switch to master, pull, then run cargo xtask rustc-push --rust-path ../rust-rust-analyzer --rust-fork matklad/rust. Replace matklad/rust with your own fork of rust-lang/rust. You can use the token to authenticate when you get prompted for a password, since josh will push over HTTPS, not SSH. This will push the rust-analyzer changes to your fork. You can then open a PR against rust-lang/rust.

Note: besides the rust-rust-analyzer clone, the Josh cache (stored under ~/.cache/rust-analyzer-josh) will contain a bare clone of rust-lang/rust. This currently takes about 3.5 GB.

This HackMD has details about how josh syncs work.

If the GitHub Actions release fails because of a transient problem like a timeout, you can re-run the job from the Actions console. If it fails because of something that needs to be fixed, remove the release tag (if needed), fix the problem, then start over. Make sure to remove the new changelog post created when running cargo xtask release a second time.

We release "nightly" every night automatically and promote the latest nightly to "stable" manually, every week.

We don't do "patch" releases, unless something truly egregious comes up. To do a patch release, cherry-pick the fix on top of the current release branch and push the branch. There's no need to write a changelog for a patch release, it's OK to include the notes about the fix into the next weekly one. Note: we tag releases by dates, releasing a patch release on the same day should work (by overwriting a tag), but I am not 100% sure.

Permissions

There are two sets of people with extra permissions:

• The rust-lang team t-rust-analyzer. This team has write access to the repository and merge queue permissions (note the repo itself is managed by infra admins). It's ok to self-approve if you think you know what you are doing! Feel free to request a review or assign any PR to a reviewer with the relevant expertise to bring the work to their attention. Don't feel pressured to review assigned PRs though. If you don't feel like reviewing for whatever reason, someone else will pick the review up (but please speak up if you don't feel like it)!
• The rust-lang team t-rust-analyzer-contributors. This team has general triaging permissions allowing to label, close and re-open issues.

Architecture

This document describes the high-level architecture of rust-analyzer. If you want to familiarize yourself with the code base, you are just in the right place!

You might also enjoy "Explaining Rust Analyzer" series on YouTube. It goes deeper than what is covered in this document, but will take some time to watch.

See also these implementation-related blog posts:

• https://rust-analyzer.github.io/blog/2019/11/13/find-usages.html
• https://rust-analyzer.github.io/blog/2020/07/20/three-architectures-for-responsive-ide.html
• https://rust-analyzer.github.io/blog/2020/09/16/challeging-LR-parsing.html
• https://rust-analyzer.github.io/blog/2020/09/28/how-to-make-a-light-bulb.html
• https://rust-analyzer.github.io/blog/2020/10/24/introducing-ungrammar.html

For older, by now mostly outdated stuff, see the guide and another playlist.

Bird's Eye View

• Entry Points
• Code Map
  • xtask
  • editors/code
  • lib/
  • crates/parser
  • crates/syntax
  • crates/base-db
  • crates/hir-expand, crates/hir-def, crates/hir_ty
  • crates/hir
  • crates/ide, crates/ide-db, crates/ide-assists, crates/ide-completion, crates/ide-diagnostics, crates/ide-ssr
  • crates/rust-analyzer
  • crates/toolchain, crates/project-model, crates/flycheck
  • crates/mbe, crates/tt, crates/proc-macro-api, crates/proc-macro-srv, crates/proc-macro-srv-cli
  • crates/cfg
  • crates/vfs, crates/vfs-notify, crates/paths
  • crates/stdx
  • crates/profile
  • crates/intern
  • crates/load-cargo
  • crates/rustc-dependencies
  • crates/span
• Cross-Cutting Concerns
  • Stability Guarantees
  • Code generation
  • Cancellation
  • Testing
  • Performance Testing
  • Error Handling
  • Observability
  • Configurability
  • Serialization

On the highest level, rust-analyzer is a thing which accepts input source code from the client and produces a structured semantic model of the code.

More specifically, input data consists of a set of test files ((PathBuf, String) pairs) and information about project structure, captured in the so called CrateGraph. The crate graph specifies which files are crate roots, which cfg flags are specified for each crate and what dependencies exist between the crates. This is the input (ground) state. The analyzer keeps all this input data in memory and never does any IO. Because the input data is source code, which typically measures in tens of megabytes at most, keeping everything in memory is OK.

A "structured semantic model" is basically an object-oriented representation of modules, functions and types which appear in the source code. This representation is fully "resolved": all expressions have types, all references are bound to declarations, etc. This is derived state.

The client can submit a small delta of input data (typically, a change to a single file) and get a fresh code model which accounts for changes.

The underlying engine makes sure that model is computed lazily (on-demand) and can be quickly updated for small modifications.

Entry Points

crates/rust-analyzer/src/bin/main.rs contains the main function which spawns LSP. This is the entry point, but it front-loads a lot of complexity, so it's fine to just skim through it.

crates/rust-analyzer/src/handlers/request.rs implements all LSP requests and is a great place to start if you are already familiar with LSP.

Analysis and AnalysisHost types define the main API for consumers of IDE services.

Code Map

This section talks briefly about various important directories and data structures. Pay attention to the Architecture Invariant sections. They often talk about things which are deliberately absent in the source code.

Note also which crates are API Boundaries. Remember, rules at the boundary are different.

xtask

This is rust-analyzer's "build system". We use cargo to compile rust code, but there are also various other tasks, like release management or local installation. They are handled by Rust code in the xtask directory.

editors/code

VS Code plugin.

lib/

rust-analyzer independent libraries which we publish to crates.io. It's not heavily utilized at the moment.

crates/parser

It is a hand-written recursive descent parser, which produces a sequence of events like "start node X", "finish node Y". It works similarly to kotlin's parser, which is a good source of inspiration for dealing with syntax errors and incomplete input. Original libsyntax parser is what we use for the definition of the Rust language. TreeSink and TokenSource traits bridge the tree-agnostic parser from grammar with rowan trees.

Architecture Invariant: the parser is independent of the particular tree structure and particular representation of the tokens. It transforms one flat stream of events into another flat stream of events. Token independence allows us to parse out both text-based source code and tt-based macro input. Tree independence allows us to more easily vary the syntax tree implementation. It should also unlock efficient light-parsing approaches. For example, you can extract the set of names defined in a file (for typo correction) without building a syntax tree.

Architecture Invariant: parsing never fails, the parser produces (T, Vec<Error>) rather than Result<T, Error>.

crates/syntax

Rust syntax tree structure and parser. See RFC and ./syntax.md for some design notes.

• rowan library is used for constructing syntax trees.
• ast provides a type safe API on top of the raw rowan tree.
• ungrammar description of the grammar, which is used to generate syntax_kinds and ast modules, using cargo test -p xtask command.

Tests for ra_syntax are mostly data-driven. test_data/parser contains subdirectories with a bunch of .rs (test vectors) and .txt files with corresponding syntax trees. During testing, we check .rs against .txt. If the .txt file is missing, it is created (this is how you update tests). Additionally, running the xtask test suite with cargo test -p xtask will walk the grammar module and collect all // test test_name comments into files inside test_data/parser/inline directory.

To update test data, run with UPDATE_EXPECT variable:

env UPDATE_EXPECT=1 cargo qt

After adding a new inline test you need to run cargo test -p xtask and also update the test data as described above.

Note api_walkthrough in particular: it shows off various methods of working with syntax tree.

See #93 for an example PR which fixes a bug in the grammar.

Architecture Invariant: syntax crate is completely independent from the rest of rust-analyzer. It knows nothing about salsa or LSP. This is important because it is possible to make useful tooling using only the syntax tree. Without semantic information, you don't need to be able to build code, which makes the tooling more robust. See also https://mlfbrown.com/paper.pdf. You can view the syntax crate as an entry point to rust-analyzer. syntax crate is an API Boundary.

Architecture Invariant: syntax tree is a value type. The tree is fully determined by the contents of its syntax nodes, it doesn't need global context (like an interner) and doesn't store semantic info. Using the tree as a store for semantic info is convenient in traditional compilers, but doesn't work nicely in the IDE. Specifically, assists and refactors require transforming syntax trees, and that becomes awkward if you need to do something with the semantic info.

Architecture Invariant: syntax tree is built for a single file. This is to enable parallel parsing of all files.

Architecture Invariant: Syntax trees are by design incomplete and do not enforce well-formedness. If an AST method returns an Option, it can be None at runtime, even if this is forbidden by the grammar.

crates/base-db

We use the salsa crate for incremental and on-demand computation. Roughly, you can think of salsa as a key-value store, but it can also compute derived values using specified functions. The base-db crate provides basic infrastructure for interacting with salsa. Crucially, it defines most of the "input" queries: facts supplied by the client of the analyzer. Reading the docs of the base_db::input module should be useful: everything else is strictly derived from those inputs.

Architecture Invariant: particularities of the build system are not the part of the ground state. In particular, base-db knows nothing about cargo. For example, cfg flags are a part of base_db, but features are not. A foo feature is a Cargo-level concept, which is lowered by Cargo to --cfg feature=foo argument on the command line. The CrateGraph structure is used to represent the dependencies between the crates abstractly.

Architecture Invariant: base-db doesn't know about file system and file paths. Files are represented with opaque FileId, there's no operation to get an std::path::Path out of the FileId.

crates/hir-expand, crates/hir-def, crates/hir_ty

These crates are the brain of rust-analyzer. This is the compiler part of the IDE.

hir-xxx crates have a strong ECS flavor, in that they work with raw ids and directly query the database. There's little abstraction here. These crates integrate deeply with salsa and chalk.

Name resolution, macro expansion and type inference all happen here. These crates also define various intermediate representations of the core.

ItemTree condenses a single SyntaxTree into a "summary" data structure, which is stable over modifications to function bodies.

DefMap contains the module tree of a crate and stores module scopes.

Body stores information about expressions.

Architecture Invariant: these crates are not, and will never be, an api boundary.

Architecture Invariant: these crates explicitly care about being incremental. The core invariant we maintain is "typing inside a function's body never invalidates global derived data". i.e., if you change the body of foo, all facts about bar should remain intact.

Architecture Invariant: hir exists only in context of particular crate instance with specific CFG flags. The same syntax may produce several instances of HIR if the crate participates in the crate graph more than once.

crates/hir

The top-level hir crate is an API Boundary. If you think about "using rust-analyzer as a library", hir crate is most likely the façade you'll be talking to.

It wraps ECS-style internal API into a more OO-flavored API (with an extra db argument for each call).

Architecture Invariant: hir provides a static, fully resolved view of the code. While internal hir-* crates compute things, hir, from the outside, looks like an inert data structure.

hir also handles the delicate task of going from syntax to the corresponding hir. Remember that the mapping here is one-to-many. See Semantics type and source_to_def module.

Note in particular a curious recursive structure in source_to_def. We first resolve the parent syntax node to the parent hir element. Then we ask the hir parent what syntax children does it have. Then we look for our node in the set of children.

This is the heart of many IDE features, like goto definition, which start with figuring out the hir node at the cursor. This is some kind of (yet unnamed) uber-IDE pattern, as it is present in Roslyn and Kotlin as well.

crates/ide, crates/ide-db, crates/ide-assists, crates/ide-completion, crates/ide-diagnostics, crates/ide-ssr

The ide crate builds on top of hir semantic model to provide high-level IDE features like completion or goto definition. It is an API Boundary. If you want to use IDE parts of rust-analyzer via LSP, custom flatbuffers-based protocol or just as a library in your text editor, this is the right API.

Architecture Invariant: ide crate's API is build out of POD types with public fields. The API uses editor's terminology, it talks about offsets and string labels rather than in terms of definitions or types. It is effectively the view in MVC and viewmodel in MVVM. All arguments and return types are conceptually serializable. In particular, syntax trees and hir types are generally absent from the API (but are used heavily in the implementation). Shout outs to LSP developers for popularizing the idea that "UI" is a good place to draw a boundary at.

ide is also the first crate which has the notion of change over time. AnalysisHost is a state to which you can transactionally apply_change. Analysis is an immutable snapshot of the state.

Internally, ide is split across several crates. ide-assists, ide-completion, ide-diagnostics and ide-ssr implement large isolated features. ide-db implements common IDE functionality (notably, reference search is implemented here). The ide contains a public API/façade, as well as implementation for a plethora of smaller features.

Architecture Invariant: ide crate strives to provide a perfect API. Although at the moment it has only one consumer, the LSP server, LSP does not influence its API design. Instead, we keep in mind a hypothetical ideal client -- an IDE tailored specifically for rust, every nook and cranny of which is packed with Rust-specific goodies.

crates/rust-analyzer

This crate defines the rust-analyzer binary, so it is the entry point. It implements the language server.

Architecture Invariant: rust-analyzer is the only crate that knows about LSP and JSON serialization. If you want to expose a data structure X from ide to LSP, don't make it serializable. Instead, create a serializable counterpart in rust-analyzer crate and manually convert between the two.

GlobalState is the state of the server. The main_loop defines the server event loop which accepts requests and sends responses. Requests that modify the state or might block user's typing are handled on the main thread. All other requests are processed in background.

Architecture Invariant: the server is stateless, a-la HTTP. Sometimes state needs to be preserved between requests. For example, "what is the edit for the fifth completion item of the last completion edit?". For this, the second request should include enough info to re-create the context from scratch. This generally means including all the parameters of the original request.

reload module contains the code that handles configuration and Cargo.toml changes. This is a tricky business.

Architecture Invariant: rust-analyzer should be partially available even when the build is broken. Reloading process should not prevent IDE features from working.

crates/toolchain, crates/project-model, crates/flycheck

These crates deal with invoking cargo to learn about project structure and get compiler errors for the "check on save" feature.

They use crates/paths heavily instead of std::path. A single rust-analyzer process can serve many projects, so it is important that server's current directory does not leak.

crates/mbe, crates/tt, crates/proc-macro-api, crates/proc-macro-srv, crates/proc-macro-srv-cli

These crates implement macros as token tree -> token tree transforms. They are independent from the rest of the code.

tt crate defined TokenTree, a single token or a delimited sequence of token trees. mbe crate contains tools for transforming between syntax trees and token tree. And it also handles the actual parsing and expansion of declarative macro (a-la "Macros By Example" or mbe).

For proc macros, the client-server model are used. We start a separate process (proc-macro-srv-cli) which loads and runs the proc-macros for us. And the client (proc-macro-api) provides an interface to talk to that server separately.

And then token trees are passed from client, and the server will load the corresponding dynamic library (which built by cargo). And due to the fact the api for getting result from proc macro are always unstable in rustc, we maintain our own copy (and paste) of that part of code to allow us to build the whole thing in stable rust.

Architecture Invariant: Bad proc macros may panic or segfault accidentally. So we run it in another process and recover it from fatal error. And they may be non-deterministic which conflict how salsa works, so special attention is required.

crates/cfg

This crate is responsible for parsing, evaluation and general definition of cfg attributes.

crates/vfs, crates/vfs-notify, crates/paths

These crates implement a virtual file system. They provide consistent snapshots of the underlying file system and insulate messy OS paths.

Architecture Invariant: vfs doesn't assume a single unified file system. i.e., a single rust-analyzer process can act as a remote server for two different machines, where the same /tmp/foo.rs path points to different files. For this reason, all path APIs generally take some existing path as a "file system witness".

crates/stdx

This crate contains various non-rust-analyzer specific utils, which could have been in std, as well as copies of unstable std items we would like to make use of already.

crates/profile

This crate contains utilities for CPU and memory profiling.

crates/intern

This crate contains infrastructure for globally interning things via Arc.

crates/load-cargo

This crate exposes several utilities for loading projects, used by the main rust-analyzer crate and other downstream consumers.

crates/rustc-dependencies

This crate wraps the rustc_* crates rust-analyzer relies on and conditionally points them to mirrored crates-io releases such that rust-analyzer keeps building on stable.

crates/span

This crate exposes types and functions related to rust-analyzer's span for macros.

A span is effectively a text range relative to some item in a file with a given SyntaxContext (hygiene).

Cross-Cutting Concerns

This sections talks about the things which are everywhere and nowhere in particular.

Stability Guarantees

One of the reasons rust-analyzer moves relatively fast is that we don't introduce new stability guarantees. Instead, as much as possible we leverage existing ones.

Examples:

• The ide API of rust-analyzer are explicitly unstable, but the LSP interface is stable, and here we just implement a stable API managed by someone else.
• Rust language and Cargo are stable, and they are the primary inputs to rust-analyzer.
• The rowan library is published to crates.io, but it is deliberately kept under 1.0 and always makes semver-incompatible upgrades

Another important example is that rust-analyzer isn't run on CI, so, unlike rustc and clippy, it is actually ok for us to change runtime behavior.

At some point we might consider opening up APIs or allowing crates.io libraries to include rust-analyzer specific annotations, but that's going to be a big commitment on our side.

Exceptions:

• rust-project.json is a de-facto stable format for non-cargo build systems. It is probably ok enough, but was definitely stabilized implicitly. Lesson for the future: when designing API which could become a stability boundary, don't wait for the first users until you stabilize it. By the time you have first users, it is already de-facto stable. And the users will first use the thing, and then inform you that now you have users. The sad thing is that stuff should be stable before someone uses it for the first time, or it should contain explicit opt-in.
• We ship some LSP extensions, and we try to keep those somewhat stable. Here, we need to work with a finite set of editor maintainers, so not providing rock-solid guarantees works.

Code generation

Some components in this repository are generated through automatic processes. Generated code is updated automatically on cargo test. Generated code is generally committed to the git repository.

In particular, we generate:

• API for working with syntax trees (syntax::ast, the ungrammar crate).

• Various sections of the manual:

  • features
  • assists
  • config

• Documentation tests for assists

See the xtask\src\codegen\assists_doc_tests.rs module for details.

Architecture Invariant: we avoid bootstrapping. For codegen we need to parse Rust code. Using rust-analyzer for that would work and would be fun, but it would also complicate the build process a lot. For that reason, we use syn and manual string parsing.

Cancellation

Let's say that the IDE is in the process of computing syntax highlighting, when the user types foo. What should happen? rust-analyzers answer is that the highlighting process should be cancelled -- its results are now stale, and it also blocks modification of the inputs.

The salsa database maintains a global revision counter. When applying a change, salsa bumps this counter and waits until all other threads using salsa finish. If a thread does salsa-based computation and notices that the counter is incremented, it panics with a special value (see Canceled::throw). That is, rust-analyzer requires unwinding.

ide is the boundary where the panic is caught and transformed into a Result<T, Cancelled>.

Testing

rust-analyzer has three interesting system boundaries to concentrate tests on.

The outermost boundary is the rust-analyzer crate, which defines an LSP interface in terms of stdio. We do integration testing of this component, by feeding it with a stream of LSP requests and checking responses. These tests are known as "heavy", because they interact with Cargo and read real files from disk. For this reason, we try to avoid writing too many tests on this boundary: in a statically typed language, it's hard to make an error in the protocol itself if messages are themselves typed. Heavy tests are only run when RUN_SLOW_TESTS env var is set.

The middle, and most important, boundary is ide. Unlike rust-analyzer, which exposes API, ide uses Rust API and is intended for use by various tools. A typical test creates an AnalysisHost, calls some Analysis functions and compares the results against expectation.

The innermost and most elaborate boundary is hir. It has a much richer vocabulary of types than ide, but the basic testing setup is the same: we create a database, run some queries, assert result.

For comparisons, we use the expect crate for snapshot testing.

To test various analysis corner cases and avoid forgetting about old tests, we use so-called marks. See the cov_mark crate documentation for more.

Architecture Invariant: rust-analyzer tests do not use libcore or libstd. All required library code must be a part of the tests. This ensures fast test execution.

Architecture Invariant: tests are data driven and do not test the API. Tests which directly call various API functions are a liability, because they make refactoring the API significantly more complicated. So most of the tests look like this:

#[track_caller]
fn check(input: &str, expect: expect_test::Expect) {
    // The single place that actually exercises a particular API
}

#[test]
fn foo() {
    check("foo", expect![["bar"]]);
}

#[test]
fn spam() {
    check("spam", expect![["eggs"]]);
}
// ...and a hundred more tests that don't care about the specific API at all.

To specify input data, we use a single string literal in a special format, which can describe a set of rust files. See the Fixture its module for fixture examples and documentation.

Architecture Invariant: all code invariants are tested by #[test] tests. There's no additional checks in CI, formatting and tidy tests are run with cargo test.

Architecture Invariant: tests do not depend on any kind of external resources, they are perfectly reproducible.

Performance Testing

TBA, take a look at the metrics xtask and #[test] fn benchmark_xxx() functions.

Error Handling

Architecture Invariant: core parts of rust-analyzer (ide/hir) don't interact with the outside world and thus can't fail. Only parts touching LSP are allowed to do IO.

Internals of rust-analyzer need to deal with broken code, but this is not an error condition. rust-analyzer is robust: various analysis compute (T, Vec<Error>) rather than Result<T, Error>.

rust-analyzer is a complex long-running process. It will always have bugs and panics. But a panic in an isolated feature should not bring down the whole process. Each LSP-request is protected by a catch_unwind. We use always and never macros instead of assert to gracefully recover from impossible conditions.

Observability

rust-analyzer is a long-running process, so it is important to understand what's going on inside. We have several instruments for that.

The event loop that runs rust-analyzer is very explicit. Rather than spawning futures or scheduling callbacks (open), the event loop accepts an enum of possible events (closed). It's easy to see all the things that trigger rust-analyzer processing, together with their performance

rust-analyzer includes a simple hierarchical profiler (hprof). It is enabled with RA_PROFILE='*>50' env var (log all (*) actions which take more than 50 ms) and produces output like:

85ms - handle_completion
    68ms - import_on_the_fly
        67ms - import_assets::search_for_relative_paths
             0ms - crate_def_map:wait (804 calls)
             0ms - find_path (16 calls)
             2ms - find_similar_imports (1 calls)
             0ms - generic_params_query (334 calls)
            59ms - trait_solve_query (186 calls)
         0ms - Semantics::analyze_impl (1 calls)
         1ms - render_resolution (8 calls)
     0ms - Semantics::analyze_impl (5 calls)

This is cheap enough to enable in production.

Similarly, we save live object counting (RA_COUNT=1). It is not cheap enough to enable in prod, and this is a bug which should be fixed.

Configurability

rust-analyzer strives to be as configurable as possible while offering reasonable defaults where no configuration exists yet. The rule of thumb is to enable most features by default unless they are buggy or degrade performance too much. There will always be features that some people find more annoying than helpful, so giving the users the ability to tweak or disable these is a big part of offering a good user experience. Enabling them by default is a matter of discoverability, as many users don't know about some features even though they are presented in the manual. Mind the code--architecture gap: at the moment, we are using fewer feature flags than we really should.

Serialization

In Rust, it is easy (often too easy) to add serialization to any type by adding #[derive(Serialize)]. This easiness is misleading -- serializable types impose significant backwards compatibility constraints. If a type is serializable, then it is a part of some IPC boundary. You often don't control the other side of this boundary, so changing serializable types is hard.

For this reason, the types in ide, base_db and below are not serializable by design. If such types need to cross an IPC boundary, then the client of rust-analyzer needs to provide a custom, client-specific serialization format. This isolates backwards compatibility and migration concerns to a specific client.

For example, rust-project.json is its own format -- it doesn't include CrateGraph as is. Instead, it creates a CrateGraph by calling appropriate constructing functions.

Debugging VSCode plugin and the language server

Prerequisites

• Install LLDB and the LLDB Extension.

• Open the root folder in VSCode. Here you can access the preconfigured debug setups.

  

• Install all TypeScript dependencies

  cd editors/code
  npm ci
  

Common knowledge

• All debug configurations open a new [Extension Development Host] VSCode instance where only the rust-analyzer extension being debugged is enabled.
• To activate the extension you need to open any Rust project folder in [Extension Development Host].

Debug TypeScript VSCode extension

• Run Installed Extension - runs the extension with the globally installed rust-analyzer binary.
• Run Extension (Debug Build) - runs extension with the locally built LSP server (target/debug/rust-analyzer).

TypeScript debugging is configured to watch your source edits and recompile. To apply changes to an already running debug process, press Ctrl+Shift+P and run the following command in your [Extension Development Host]

> Developer: Reload Window

Debug Rust LSP server

• When attaching a debugger to an already running rust-analyzer server on Linux you might need to enable ptrace for unrelated processes by running:

  echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope
  

• By default, the LSP server is built without debug information. To enable it, you'll need to change Cargo.toml:

    [profile.dev]
    debug = 2
  

• Select Run Extension (Debug Build) to run your locally built target/debug/rust-analyzer.

• In the original VSCode window once again select the Attach To Server debug configuration.

• A list of running processes should appear. Select the rust-analyzer from this repo.

• Navigate to crates/rust-analyzer/src/main_loop.rs and add a breakpoint to the on_request function.

• Go back to the [Extension Development Host] instance and hover over a Rust variable and your breakpoint should hit.

If you need to debug the server from the very beginning, including its initialization code, you can use the --wait-dbg command line argument or RA_WAIT_DBG environment variable. The server will spin at the beginning of the try_main function (see crates\rust-analyzer\src\bin\main.rs)

    let mut d = 4;
    while d == 4 { // set a breakpoint here and change the value
        d = 4;
    }

However for this to work, you will need to enable debug_assertions in your build

RUSTFLAGS='--cfg debug_assertions' cargo build --release

Demo

• Debugging TypeScript VScode extension.
• Debugging Rust LSP server.

Troubleshooting

Can't find the rust-analyzer process

It could be a case of just jumping the gun.

The rust-analyzer is only started once the onLanguage:rust activation.

Make sure you open a rust file in the [Extension Development Host] and try again.

Can't connect to rust-analyzer

Make sure you have run echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope.

By default this should reset back to 1 every time you log in.

Breakpoints are never being hit

Check your version of lldb. If it's version 6 and lower, use the classic adapter type. It's lldb.adapterType in settings file.

If you're running lldb version 7, change the lldb adapter type to bundled or native.

Guide to rust-analyzer

About the guide

This guide describes the current state of rust-analyzer as of the 2024-01-01 release (git tag 2024-01-01). Its purpose is to document various problems and architectural solutions related to the problem of building IDE-first compiler for Rust. There is a video version of this guide as well - however, it's based on an older 2019-01-20 release (git tag guide-2019-01): https://youtu.be/ANKBNiSWyfc.

• The big picture
• IDE API
• Inputs
• Source roots (a.k.a. "Filesystems are horrible")
• Language Server Protocol
• Salsa
• Salsa Input Queries
• From text to semantic model
• Syntax trees
• Building a Module Tree
• Location Interner pattern
• Macros and recursive locations
• Name resolution
• Source Map pattern
• Type inference
• Tying it all together: completion

The big picture

On the highest possible level, rust-analyzer is a stateful component. A client may apply changes to the analyzer (new contents of foo.rs file is "fn main() {}") and it may ask semantic questions about the current state (what is the definition of the identifier with offset 92 in file bar.rs?). Two important properties hold:

• Analyzer does not do any I/O. It starts in an empty state and all input data is provided via apply_change API.

• Only queries about the current state are supported. One can, of course, simulate undo and redo by keeping a log of changes and inverse changes respectively.

IDE API

To see the bigger picture of how the IDE features work, let's take a look at the AnalysisHost and Analysis pair of types. AnalysisHost has three methods:

• default() for creating an empty analysis instance
• apply_change(&mut self) to make changes (this is how you get from an empty state to something interesting)
• analysis(&self) to get an instance of Analysis

Analysis has a ton of methods for IDEs, like goto_definition, or completions. Both inputs and outputs of Analysis' methods are formulated in terms of files and offsets, and not in terms of Rust concepts like structs, traits, etc. The "typed" API with Rust specific types is slightly lower in the stack, we'll talk about it later.

The reason for this separation of Analysis and AnalysisHost is that we want to apply changes "uniquely", but we might also want to fork an Analysis and send it to another thread for background processing. That is, there is only a single AnalysisHost, but there may be several (equivalent) Analysis.

Note that all of the Analysis API return Cancellable<T>. This is required to be responsive in an IDE setting. Sometimes a long-running query is being computed and the user types something in the editor and asks for completion. In this case, we cancel the long-running computation (so it returns Err(Cancelled)), apply the change and execute request for completion. We never use stale data to answer requests. Under the cover, AnalysisHost "remembers" all outstanding Analysis instances. The AnalysisHost::apply_change method cancels all Analysises, blocks until all of them are Dropped and then applies changes in-place. This may be familiar to Rustaceans who use read-write locks for interior mutability.

Next, let's talk about what the inputs to the Analysis are, precisely.

Inputs

rust-analyzer never does any I/O itself, all inputs get passed explicitly via the AnalysisHost::apply_change method, which accepts a single argument, a Change. Change is a wrapper for FileChange that adds proc-macro knowledge. FileChange is a builder for a single change "transaction", so it suffices to study its methods to understand all the input data.

The change_file method controls the set of the input files, where each file has an integer id (FileId, picked by the client) and text (Option<Arc<str>>). Paths are tricky; they'll be explained below, in source roots section, together with the set_roots method. The "source root" is_library flag along with the concept of durability allows us to add a group of files which are assumed to rarely change. It's mostly an optimization and does not change the fundamental picture.

The set_crate_graph method allows us to control how the input files are partitioned into compilation units -- crates. It also controls (in theory, not implemented yet) cfg flags. CrateGraph is a directed acyclic graph of crates. Each crate has a root FileId, a set of active cfg flags and a set of dependencies. Each dependency is a pair of a crate and a name. It is possible to have two crates with the same root FileId but different cfg-flags/dependencies. This model is lower than Cargo's model of packages: each Cargo package consists of several targets, each of which is a separate crate (or several crates, if you try different feature combinations).

Procedural macros are inputs as well, roughly modeled as a crate with a bunch of additional black box dyn Fn(TokenStream) -> TokenStream functions.

Soon we'll talk how we build an LSP server on top of Analysis, but first, let's deal with that paths issue.

Source roots (a.k.a. "Filesystems are horrible")

This is a non-essential section, feel free to skip.

The previous section said that the filesystem path is an attribute of a file, but this is not the whole truth. Making it an absolute PathBuf will be bad for several reasons. First, filesystems are full of (platform-dependent) edge cases:

• It's hard (requires a syscall) to decide if two paths are equivalent.
• Some filesystems are case-sensitive (e.g. macOS).
• Paths are not necessarily UTF-8.
• Symlinks can form cycles.

Second, this might hurt the reproducibility and hermeticity of builds. In theory, moving a project from /foo/bar/my-project to /spam/eggs/my-project should not change a bit in the output. However, if the absolute path is a part of the input, it is at least in theory observable, and could affect the output.

Yet another problem is that we really really want to avoid doing I/O, but with Rust the set of "input" files is not necessarily known up-front. In theory, you can have #[path="/dev/random"] mod foo;.

To solve (or explicitly refuse to solve) these problems rust-analyzer uses the concept of a "source root". Roughly speaking, source roots are the contents of a directory on a file system, like /home/matklad/projects/rustraytracer/**.rs.

More precisely, all files (FileIds) are partitioned into disjoint SourceRoots. Each file has a relative UTF-8 path within the SourceRoot. SourceRoot has an identity (integer ID). Crucially, the root path of the source root itself is unknown to the analyzer: A client is supposed to maintain a mapping between SourceRoot IDs (which are assigned by the client) and actual PathBufs. SourceRoots give a sane tree model of the file system to the analyzer.

Note that mod, #[path] and include!() can only reference files from the same source root. It is of course possible to explicitly add extra files to the source root, even /dev/random.

Language Server Protocol

Now let's see how the Analysis API is exposed via the JSON RPC based language server protocol. The hard part here is managing changes (which can come either from the file system or from the editor) and concurrency (we want to spawn background jobs for things like syntax highlighting). We use the event loop pattern to manage the zoo, and the loop is the GlobalState::run function initiated by main_loop after GlobalState::new does a one-time initialization and tearing down of the resources.

Let's walk through a typical analyzer session!

First, we need to figure out what to analyze. To do this, we run cargo metadata to learn about Cargo packages for current workspace and dependencies, and we run rustc --print sysroot and scan the "sysroot" (the directory containing the current Rust toolchain's files) to learn about crates like std. This happens in the GlobalState::fetch_workspaces method. We load this configuration at the start of the server in GlobalState::new, but it's also triggered by workspace change events and requests to reload the workspace from the client.

The ProjectModel we get after this step is very Cargo and sysroot specific, it needs to be lowered to get the input in the form of Change. This happens in GlobalState::process_changes method. Specifically

• Create SourceRoots for each Cargo package(s) and sysroot.
• Schedule a filesystem scan of the roots.
• Create an analyzer's Crate for each Cargo target and sysroot crate.
• Setup dependencies between the crates.

The results of the scan (which may take a while) will be processed in the body of the main loop, just like any other change. Here's where we handle:

• File system changes
• Changes from the editor

After a single loop's turn, we group the changes into one Change and apply it. This always happens on the main thread and blocks the loop.

To handle requests, like "goto definition", we create an instance of the Analysis and schedule the task (which consumes Analysis) on the threadpool. The task calls the corresponding Analysis method, while massaging the types into the LSP representation. Keep in mind that if we are executing "goto definition" on the threadpool and a new change comes in, the task will be canceled as soon as the main loop calls apply_change on the AnalysisHost.

This concludes the overview of the analyzer's programing interface. Next, let's dig into the implementation!

Salsa

The most straightforward way to implement an "apply change, get analysis, repeat" API would be to maintain the input state and to compute all possible analysis information from scratch after every change. This works, but scales poorly with the size of the project. To make this fast, we need to take advantage of the fact that most of the changes are small, and that analysis results are unlikely to change significantly between invocations.

To do this we use salsa: a framework for incremental on-demand computation. You can skip the rest of the section if you are familiar with rustc's red-green algorithm (which is used for incremental compilation).

It's better to refer to salsa's docs to learn about it. Here's a small excerpt:

The key idea of salsa is that you define your program as a set of queries. Every query is used like a function K -> V that maps from some key of type K to a value of type V. Queries come in two basic varieties:

• Inputs: the base inputs to your system. You can change these whenever you like.

• Functions: pure functions (no side effects) that transform your inputs into other values. The results of queries are memoized to avoid recomputing them a lot. When you make changes to the inputs, we'll figure out (fairly intelligently) when we can re-use these memoized values and when we have to recompute them.

For further discussion, its important to understand one bit of "fairly intelligently". Suppose we have two functions, f1 and f2, and one input, z. We call f1(X) which in turn calls f2(Y) which inspects i(Z). i(Z) returns some value V1, f2 uses that and returns R1, f1 uses that and returns O. Now, let's change i at Z to V2 from V1 and try to compute f1(X) again. Because f1(X) (transitively) depends on i(Z), we can't just reuse its value as is. However, if f2(Y) is still equal to R1 (despite i's change), we, in fact, can reuse O as result of f1(X). And that's how salsa works: it recomputes results in reverse order, starting from inputs and progressing towards outputs, stopping as soon as it sees an intermediate value that hasn't changed. If this sounds confusing to you, don't worry: it is confusing. This illustration by @killercup might help:

Salsa Input Queries

All analyzer information is stored in a salsa database. Analysis and AnalysisHost types are essentially newtype wrappers for RootDatabase -- a salsa database.

Salsa input queries are defined in SourceDatabase and SourceDatabaseExt (which are a part of RootDatabase). They closely mirror the familiar Change structure: indeed, what apply_change does is it sets the values of input queries.

From text to semantic model

The bulk of the rust-analyzer is transforming input text into a semantic model of Rust code: a web of entities like modules, structs, functions and traits.

An important fact to realize is that (unlike most other languages like C# or Java) there is not a one-to-one mapping between the source code and the semantic model. A single function definition in the source code might result in several semantic functions: for example, the same source file might get included as a module in several crates or a single crate might be present in the compilation DAG several times, with different sets of cfgs enabled. The IDE-specific task of mapping source code into a semantic model is inherently imprecise for this reason and gets handled by the source_analyzer.

The semantic interface is declared in the semantics module. Each entity is identified by an integer ID and has a bunch of methods which take a salsa database as an argument and returns other entities (which are also IDs). Internally, these methods invoke various queries on the database to build the model on demand. Here's the list of queries.

The first step of building the model is parsing the source code.

Syntax trees

An important property of the Rust language is that each file can be parsed in isolation. Unlike, say, C++, an include can't change the meaning of the syntax. For this reason, rust-analyzer can build a syntax tree for each "source file", which could then be reused by several semantic models if this file happens to be a part of several crates.

The representation of syntax trees that rust-analyzer uses is similar to that of Roslyn and Swift's new libsyntax. Swift's docs give an excellent overview of the approach, so I skip this part here and instead outline the main characteristics of the syntax trees:

• Syntax trees are fully lossless. Converting any text to a syntax tree and back is a total identity function. All whitespace and comments are explicitly represented in the tree.

• Syntax nodes have generic (next|previous)_sibling, parent, (first|last)_child functions. You can get from any one node to any other node in the file using only these functions.

• Syntax nodes know their range (start offset and length) in the file.

• Syntax nodes share the ownership of their syntax tree: if you keep a reference to a single function, the whole enclosing file is alive.

• Syntax trees are immutable and the cost of replacing the subtree is proportional to the depth of the subtree. Read Swift's docs to learn how immutable + parent pointers + cheap modification is possible.

• Syntax trees are build on best-effort basis. All accessor methods return Options. The tree for fn foo will contain a function declaration with None for parameter list and body.

• Syntax trees do not know the file they are built from, they only know about the text.

The implementation is based on the generic rowan crate on top of which a rust-specific AST is generated.

The next step in constructing the semantic model is ...

Building a Module Tree

The algorithm for building a tree of modules is to start with a crate root (remember, each Crate from a CrateGraph has a FileId), collect all mod declarations and recursively process child modules. This is handled by the crate_def_map_query, with two slight variations.

First, rust-analyzer builds a module tree for all crates in a source root simultaneously. The main reason for this is historical (module_tree predates CrateGraph), but this approach also enables accounting for files which are not part of any crate. That is, if you create a file but do not include it as a submodule anywhere, you still get semantic completion, and you get a warning about a free-floating module (the actual warning is not implemented yet).

The second difference is that crate_def_map_query does not directly depend on the SourceDatabase::parse query. Why would calling the parse directly be bad? Suppose the user changes the file slightly, by adding an insignificant whitespace. Adding whitespace changes the parse tree (because it includes whitespace), and that means recomputing the whole module tree.

We deal with this problem by introducing an intermediate block_def_map_query. This query processes the syntax tree and extracts a set of declared submodule names. Now, changing the whitespace results in block_def_map_query being re-executed for a single module, but because the result of this query stays the same, we don't have to re-execute crate_def_map_query. In fact, we only need to re-execute it when we add/remove new files or when we change mod declarations.

We store the resulting modules in a Vec-based indexed arena. The indices in the arena becomes module IDs. And this brings us to the next topic: assigning IDs in the general case.

Location Interner pattern

One way to assign IDs is how we've dealt with modules: Collect all items into a single array in some specific order and use the index in the array as an ID. The main drawback of this approach is that these IDs are not stable: Adding a new item can shift the IDs of all other items. This works for modules, because adding a module is a comparatively rare operation, but would be less convenient for, for example, functions.

Another solution here is positional IDs: We can identify a function as "the function with name foo in a ModuleId(92) module". Such locations are stable: adding a new function to the module (unless it is also named foo) does not change the location. However, such "ID" types ceases to be a Copyable integer and in general can become pretty large if we account for nesting (for example: "third parameter of the foo function of the bar impl in the baz module").

Intern and Lookup traits allows us to combine the benefits of positional and numeric IDs. Implementing both traits effectively creates a bidirectional append-only map between locations and integer IDs (typically newtype wrappers for salsa::InternId) which can "intern" a location and return an integer ID back. The salsa database we use includes a couple of interners. How to "garbage collect" unused locations is an open question.

For example, we use Intern and Lookup implementations to assign IDs to definitions of functions, structs, enums, etc. The location, ItemLoc contains two bits of information:

• the ID of the module which contains the definition,
• the ID of the specific item in the module's source code.

We "could" use a text offset for the location of a particular item, but that would play badly with salsa: offsets change after edits. So, as a rule of thumb, we avoid using offsets, text ranges or syntax trees as keys and values for queries. What we do instead is we store "index" of the item among all of the items of a file (so, a positional based ID, but localized to a single file).

One thing we've glossed over for the time being is support for macros. We have only proof of concept handling of macros at the moment, but they are extremely interesting from an "assigning IDs" perspective.

Macros and recursive locations

The tricky bit about macros is that they effectively create new source files. While we can use FileIds to refer to original files, we can't just assign them willy-nilly to the pseudo files of macro expansion. Instead, we use a special ID, HirFileId to refer to either a usual file or a macro-generated file:

enum HirFileId {
    FileId(FileId),
    Macro(MacroCallId),
}

MacroCallId is an interned ID that identifies a particular macro invocation. Simplifying, it's a HirFileId of a file containing the call plus the offset of the macro call in the file.

Note how HirFileId is defined in terms of MacroCallId which is defined in terms of HirFileId! This does not recur infinitely though: any chain of HirFileIds bottoms out in HirFileId::FileId, that is, some source file actually written by the user.

Note also that in the actual implementation, the two variants are encoded in a single u32, which are differentiated by the MSB (most significant bit). If the MSB is 0, the value represents a FileId, otherwise the remaining 31 bits represent a MacroCallId.

Now that we understand how to identify a definition, in a source or in a macro-generated file, we can discuss name resolution a bit.

Name resolution

Name resolution faces the same problem as the module tree: if we look at the syntax tree directly, we'll have to recompute name resolution after every modification. The solution to the problem is the same: We lower the source code of each module into a position-independent representation which does not change if we modify bodies of the items. After that we loop resolving all imports until we've reached a fixed point.

And, given all our preparation with IDs and a position-independent representation, it is satisfying to test that typing inside function body does not invalidate name resolution results.

An interesting fact about name resolution is that it "erases" all of the intermediate paths from the imports: in the end, we know which items are defined and which items are imported in each module, but, if the import was use foo::bar::baz, we deliberately forget what modules foo and bar resolve to.

To serve "goto definition" requests on intermediate segments we need this info in the IDE, however. Luckily, we need it only for a tiny fraction of imports, so we just ask the module explicitly, "What does the path foo::bar resolve to?". This is a general pattern: we try to compute the minimal possible amount of information during analysis while allowing IDE to ask for additional specific bits.

Name resolution is also a good place to introduce another salsa pattern used throughout the analyzer:

Source Map pattern

Due to an obscure edge case in completion, IDE needs to know the syntax node of a use statement which imported the given completion candidate. We can't just store the syntax node as a part of name resolution: this will break incrementality, due to the fact that syntax changes after every file modification.

We solve this problem during the lowering step of name resolution. Along with the ItemTree output, the lowering query additionally produces an AstIdMap via an ast_id_map query. The ItemTree contains imports, but in a position-independent form based on AstId. The AstIdMap contains a mapping from position-independent AstIds to (position-dependent) syntax nodes.

Type inference

First of all, implementation of type inference in rust-analyzer was spearheaded by @flodiebold. #327 was an awesome Christmas present, thank you, Florian!

Type inference runs on per-function granularity and uses the patterns we've discussed previously.

First, we lower the AST of a function body into a position-independent representation. In this representation, each expression is assigned a positional ID. Alongside the lowered expression, a source map is produced, which maps between expression ids and original syntax. This lowering step also deals with "incomplete" source trees by replacing missing expressions by an explicit Missing expression.

Given the lowered body of the function, we can now run type inference and construct a mapping from ExprIds to types.

Tying it all together: completion

To conclude the overview of the rust-analyzer, let's trace the request for (type-inference powered!) code completion!

We start by receiving a message from the language client. We decode the message as a request for completion and schedule it on the threadpool. This is the place where we catch canceled errors if, immediately after completion, the client sends some modification.

In the handler, we deserialize LSP requests into rust-analyzer specific data types (by converting a file url into a numeric FileId), ask analysis for completion and serialize results into the LSP.

The completion implementation is finally the place where we start doing the actual work. The first step is to collect the CompletionContext -- a struct which describes the cursor position in terms of Rust syntax and semantics. For example, expected_name: Option<NameOrNameRef> is the syntactic representation for the expected name of what we're completing (usually the parameter name of a function argument), while expected_type: Option<Type> is the semantic model for the expected type of what we're completing.

To construct the context, we first do an "IntelliJ Trick": we insert a dummy identifier at the cursor's position and parse this modified file, to get a reasonably looking syntax tree. Then we do a bunch of "classification" routines to figure out the context. For example, we find an parent fn node, get a semantic model for it (using the lossy source_analyzer infrastructure) and use it to determine the expected type at the cursor position.

The second step is to run a series of independent completion routines. Let's take a closer look at complete_dot, which completes fields and methods in foo.bar|. First we extract a semantic receiver type out of the DotAccess argument. Then, using the semantic model for the type, we determine if the receiver implements the Future trait, and add a .await completion item in the affirmative case. Finally, we add all fields & methods from the type to completion.

LSP Extensions

This document describes LSP extensions used by rust-analyzer. It's a best effort document, when in doubt, consult the source (and send a PR with clarification ;-) ). We aim to upstream all non Rust-specific extensions to the protocol, but this is not a top priority. All capabilities are enabled via the experimental field of ClientCapabilities or ServerCapabilities. Requests which we hope to upstream live under experimental/ namespace. Requests, which are likely to always remain specific to rust-analyzer are under rust-analyzer/ namespace.

If you want to be notified about the changes to this document, subscribe to #4604.

• Configuration in initializationOptions
• Snippet TextEdit
  • Example
  • Unresolved Questions
• CodeAction Groups
  • Example
  • Unresolved Questions
• Parent Module
  • Example
  • Unresolved Question
• Join Lines
  • Example
  • Unresolved Question
• On Enter
  • Example
  • Unresolved Question
• Structural Search Replace (SSR)
  • Example
  • Unresolved Question
• Matching Brace
  • Example
  • Unresolved Question
• Runnables
• Test explorer
• Open External Documentation
• Local Documentation
• Analyzer Status
• Reload Workspace
• Rebuild proc-macros
• Server Status
  • Controlling Flycheck
• Syntax Tree
• View Syntax Tree
• View Hir
• View Mir
• Interpret Function
• View File Text
• View ItemTree
• View Crate Graph
• Expand Macro
• Hover Actions
• Open Cargo.toml
  • Example
• Related tests
• Hover Range
  • Example
• Move Item
• Workspace Symbols Filtering
• Client Commands
• Colored Diagnostic Output
• Dependency Tree
• View Recursive Memory Layout
  • Unresolved questions:

Configuration in initializationOptions

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/567

The initializationOptions field of the InitializeParams of the initialization request should contain the "rust-analyzer" section of the configuration.

rust-analyzer normally sends a "workspace/configuration" request with { "items": ["rust-analyzer"] } payload. However, the server can't do this during initialization. At the same time some essential configuration parameters are needed early on, before servicing requests. For this reason, we ask that initializationOptions contains the configuration, as if the server did make a "workspace/configuration" request.

If a language client does not know about rust-analyzer's configuration options it can get sensible defaults by doing any of the following:

• Not sending initializationOptions
• Sending "initializationOptions": null
• Sending "initializationOptions": {}

Snippet TextEdit

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/724

Experimental Client Capability: { "snippetTextEdit": boolean }

If this capability is set, WorkspaceEdits returned from codeAction requests and TextEdits returned from textDocument/onTypeFormatting requests might contain SnippetTextEdits instead of usual TextEdits:

interface SnippetTextEdit extends TextEdit {
    insertTextFormat?: InsertTextFormat;
    annotationId?: ChangeAnnotationIdentifier;
}

export interface TextDocumentEdit {
    textDocument: OptionalVersionedTextDocumentIdentifier;
    edits: (TextEdit | SnippetTextEdit)[];
}

When applying such code action or text edit, the editor should insert snippet, with tab stops and placeholders. At the moment, rust-analyzer guarantees that only a single TextDocumentEdit will have edits which can be InsertTextFormat.Snippet. Any additional TextDocumentEdits will only have edits which are InsertTextFormat.PlainText.

Example

"Add derive" code action transforms struct S; into #[derive($0)] struct S;

Unresolved Questions

• Where exactly are SnippetTextEdits allowed (only in code actions at the moment)?
• Can snippets span multiple files (so far, no)?

CodeAction Groups

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/994

Experimental Client Capability: { "codeActionGroup": boolean }

If this capability is set, CodeActions returned from the server contain an additional field, group:

interface CodeAction {
    title: string;
    group?: string;
    ...
}

All code-actions with the same group should be grouped under single (extendable) entry in lightbulb menu. The set of actions [ { title: "foo" }, { group: "frobnicate", title: "bar" }, { group: "frobnicate", title: "baz" }] should be rendered as

💡
  +-------------+
  | foo         |
  +-------------+-----+
  | frobnicate >| bar |
  +-------------+-----+
                | baz |
                +-----+

Alternatively, selecting frobnicate could present a user with an additional menu to choose between bar and baz.

Example

fn main() {
    let x: Entry/*cursor here*/ = todo!();
}

Invoking code action at this position will yield two code actions for importing Entry from either collections::HashMap or collection::BTreeMap, grouped under a single "import" group.

Unresolved Questions

• Is a fixed two-level structure enough?
• Should we devise a general way to encode custom interaction protocols for GUI refactorings?

Parent Module

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/1002

Experimental Server Capability: { "parentModule": boolean }

This request is sent from client to server to handle "Goto Parent Module" editor action.

Method: experimental/parentModule

Request: TextDocumentPositionParams

Response: Location | Location[] | LocationLink[] | null

Example

// src/main.rs
mod foo;
// src/foo.rs

/* cursor here*/

experimental/parentModule returns a single Link to the mod foo; declaration.

Unresolved Question

• An alternative would be to use a more general "gotoSuper" request, which would work for super methods, super classes and super modules. This is the approach IntelliJ Rust is taking. However, experience shows that super module (which generally has a feeling of navigation between files) should be separate. If you want super module, but the cursor happens to be inside an overridden function, the behavior with single "gotoSuper" request is surprising.

Join Lines

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/992

Experimental Server Capability: { "joinLines": boolean }

This request is sent from client to server to handle "Join Lines" editor action.

Method: experimental/joinLines

Request:

interface JoinLinesParams {
    textDocument: TextDocumentIdentifier,
    /// Currently active selections/cursor offsets.
    /// This is an array to support multiple cursors.
    ranges: Range[],
}

Response: TextEdit[]

Example

fn main() {
    /*cursor here*/let x = {
        92
    };
}

experimental/joinLines yields (curly braces are automagically removed)

fn main() {
    let x = 92;
}

Unresolved Question

• What is the position of the cursor after joinLines? Currently, this is left to editor's discretion, but it might be useful to specify on the server via snippets. However, it then becomes unclear how it works with multi cursor.

On Enter

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/1001

Experimental Server Capability: { "onEnter": boolean }

This request is sent from client to server to handle the Enter key press.

Method: experimental/onEnter

Request:: TextDocumentPositionParams

Response:

SnippetTextEdit[]

Example

fn main() {
    // Some /*cursor here*/ docs
    let x = 92;
}

experimental/onEnter returns the following snippet

fn main() {
    // Some
    // $0 docs
    let x = 92;
}

The primary goal of onEnter is to handle automatic indentation when opening a new line. This is not yet implemented. The secondary goal is to handle fixing up syntax, like continuing doc strings and comments, and escaping \n in string literals.

As proper cursor positioning is raison d'être for onEnter, it uses SnippetTextEdit.

Unresolved Question

• How to deal with synchronicity of the request? One option is to require the client to block until the server returns the response. Another option is to do a operational transforms style merging of edits from client and server. A third option is to do a record-replay: client applies heuristic on enter immediately, then applies all user's keypresses. When the server is ready with the response, the client rollbacks all the changes and applies the recorded actions on top of the correct response.
• How to deal with multiple carets?
• Should we extend this to arbitrary typed events and not just onEnter?

Structural Search Replace (SSR)

Experimental Server Capability: { "ssr": boolean }

This request is sent from client to server to handle structural search replace -- automated syntax tree based transformation of the source.

Method: experimental/ssr

Request:

interface SsrParams {
    /// Search query.
    /// The specific syntax is specified outside of the protocol.
    query: string,
    /// If true, only check the syntax of the query and don't compute the actual edit.
    parseOnly: boolean,
    /// The current text document. This and `position` will be used to determine in what scope
    /// paths in `query` should be resolved.
    textDocument: TextDocumentIdentifier;
    /// Position where SSR was invoked.
    position: Position;
    /// Current selections. Search/replace will be restricted to these if non-empty.
    selections: Range[];
}

Response:

WorkspaceEdit

Example

SSR with query foo($a, $b) ==>> ($a).foo($b) will transform, eg foo(y + 5, z) into (y + 5).foo(z).

Unresolved Question

• Probably needs search without replace mode
• Needs a way to limit the scope to certain files.

Matching Brace

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/999

Experimental Server Capability: { "matchingBrace": boolean }

This request is sent from client to server to handle "Matching Brace" editor action.

Method: experimental/matchingBrace

Request:

interface MatchingBraceParams {
    textDocument: TextDocumentIdentifier,
    /// Position for each cursor
    positions: Position[],
}

Response:

Position[]

Example

fn main() {
    let x: Vec<()>/*cursor here*/ = vec![];
}

experimental/matchingBrace yields the position of <. In many cases, matching braces can be handled by the editor. However, some cases (like disambiguating between generics and comparison operations) need a real parser. Moreover, it would be cool if editors didn't need to implement even basic language parsing

Unresolved Question

• Should we return a nested brace structure, to allow paredit-like actions of jump out of the current brace pair? This is how SelectionRange request works.
• Alternatively, should we perhaps flag certain SelectionRanges as being brace pairs?

Runnables

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/944

Experimental Server Capability: { "runnables": { "kinds": string[] } }

This request is sent from client to server to get the list of things that can be run (tests, binaries, cargo check -p).

Method: experimental/runnables

Request:

interface RunnablesParams {
    textDocument: TextDocumentIdentifier;
    /// If null, compute runnables for the whole file.
    position?: Position;
}

Response: Runnable[]

interface Runnable {
    label: string;
    /// If this Runnable is associated with a specific function/module, etc., the location of this item
    location?: LocationLink;
    /// Running things is necessary technology specific, `kind` needs to be advertised via server capabilities,
    // the type of `args` is specific to `kind`. The actual running is handled by the client.
    kind: string;
    args: any;
}

rust-analyzer supports two kinds of runnables, "cargo" and "shell". The args for "cargo" look like this:

{
    /**
     * Environment variables to set before running the command.
     */
    environment?: Record<string, string>;
    /**
     * The working directory to run the command in.
     */
    cwd: string;
    /**
     * The workspace root directory of the cargo project.
     */
    workspaceRoot?: string;
    /**
     * The cargo command to run.
     */
    cargoArgs: string[];
    /**
     * Arguments to pass to the executable, these will be passed to the command after a `--` argument.
     */
    executableArgs: string[];
    /**
     * Command to execute instead of `cargo`.
     */
    overrideCargo?: string;
}

The args for "shell" look like this:

{
    /**
     * Environment variables to set before running the command.
     */
    environment?: Record<string, string>;
    /**
     * The working directory to run the command in.
     */
    cwd: string;
    kind: string;
    program: string;
    args: string[];
}

Test explorer

Experimental Client Capability: { "testExplorer": boolean }

If this capability is set, the experimental/discoveredTests notification will be sent from the server to the client.

Method: experimental/discoverTest

Request: DiscoverTestParams

interface DiscoverTestParams {
    // The test that we need to resolve its children. If not present,
    // the response should return top level tests.
    testId?: string | undefined;
}

Response: DiscoverTestResults

interface TestItem {
    // A unique identifier for the test
    id: string;
    // The file containing this test
    textDocument?: lc.TextDocumentIdentifier | undefined;
    // The range in the file containing this test
    range?: lc.Range | undefined;
    // A human readable name for this test
    label: string;
    // The kind of this test item. Based on the kind,
	// an icon is chosen by the editor.
    kind: "package" | "module" | "test";
    // True if this test may have children not available eagerly
    canResolveChildren: boolean;
    // The id of the parent test in the test tree. If not present, this test
    // is a top level test.
    parent?: string | undefined;
    // The information useful for running the test. The client can use `runTest`
    // request for simple execution, but for more complex execution forms
    // like debugging, this field is useful.
    // Note that this field includes some information about label and location as well, but
    // those exist just for keeping things in sync with other methods of running runnables
    // (for example using one consistent name in the vscode's launch.json) so for any propose
    // other than running tests this field should not be used.
    runnable?: Runnable | undefined;
};

interface DiscoverTestResults {
    // The discovered tests.
    tests: TestItem[];
    // For each test which its id is in this list, the response
    // contains all tests that are children of this test, and
    // client should remove old tests not included in the response.
    scope: string[] | undefined;
    // For each file which its uri is in this list, the response
    // contains all tests that are located in this file, and
    // client should remove old tests not included in the response.
    scopeFile: lc.TextDocumentIdentifier[] | undefined;
}

Method: experimental/discoveredTests

Notification: DiscoverTestResults

This notification is sent from the server to the client when the server detect changes in the existing tests. The DiscoverTestResults is the same as the one in experimental/discoverTest response.

Method: experimental/runTest

Request: RunTestParams

interface RunTestParams {
    // Id of the tests to be run. If a test is included, all of its children are included implicitly. If
    // this property is undefined, then the server should simply run all tests.
    include?: string[] | undefined;
    // An array of test ids the user has marked as excluded from the test included in this run; exclusions
    // should apply after inclusions.
    // May be omitted if no exclusions were requested. Server should not run excluded tests or
    // any children of excluded tests.
    exclude?: string[] | undefined;
}

Response: void

Method: experimental/endRunTest

Notification:

This notification is sent from the server to the client when the current running session is finished. The server should not send any run notification after this.

Method: experimental/abortRunTest

Notification:

This notification is sent from the client to the server when the user is no longer interested in the test results. The server should clean up its resources and send a experimental/endRunTest when is done.

Method: experimental/changeTestState

Notification: ChangeTestStateParams

type TestState = { tag: "passed" }
    | {
        tag: "failed";
        // The standard error of the test, containing the panic message. Clients should
        // render it similar to a terminal, and e.g. handle ansi colors.
        message: string;
    }
    | { tag: "started" }
    | { tag: "enqueued" }
    | { tag: "skipped" };

interface ChangeTestStateParams {
    testId: string;
    state: TestState;
}

Method: experimental/appendOutputToRunTest

Notification: string

This notification is used for reporting messages independent of any single test and related to the run session in general, e.g. cargo compiling progress messages or warnings.

Open External Documentation

This request is sent from the client to the server to obtain web and local URL(s) for documentation related to the symbol under the cursor, if available.

Method: experimental/externalDocs

Request: TextDocumentPositionParams

Response: string | null

Local Documentation

Experimental Client Capability: { "localDocs": boolean }

If this capability is set, the Open External Documentation request returned from the server will have the following structure:

interface ExternalDocsResponse {
    web?: string;
    local?: string;
}

Analyzer Status

Method: rust-analyzer/analyzerStatus

Request:

interface AnalyzerStatusParams {
    /// If specified, show dependencies of the current file.
    textDocument?: TextDocumentIdentifier;
}

Response: string

Returns internal status message, mostly for debugging purposes.

Reload Workspace

Method: rust-analyzer/reloadWorkspace

Request: null

Response: null

Reloads project information (that is, re-executes cargo metadata).

Rebuild proc-macros

Method: rust-analyzer/rebuildProcMacros

Request: null

Response: null

Rebuilds build scripts and proc-macros, and runs the build scripts to reseed the build data.

Server Status

Experimental Client Capability: { "serverStatusNotification": boolean }

Method: experimental/serverStatus

Notification:

interface ServerStatusParams {
    /// `ok` means that the server is completely functional.
    ///
    /// `warning` means that the server is partially functional.
    /// It can answer correctly to most requests, but some results
    /// might be wrong due to, for example, some missing dependencies.
    ///
    /// `error` means that the server is not functional. For example,
    /// there's a fatal build configuration problem. The server might
    /// still give correct answers to simple requests, but most results
    /// will be incomplete or wrong.
    health: "ok" | "warning" | "error",
    /// Is there any pending background work which might change the status?
    /// For example, are dependencies being downloaded?
    quiescent: boolean,
    /// Explanatory message to show on hover.
    message?: string,
}

This notification is sent from server to client. The client can use it to display persistent status to the user (in modline). It is similar to the showMessage, but is intended for stares rather than point-in-time events.

Note that this functionality is intended primarily to inform the end user about the state of the server. In particular, it's valid for the client to completely ignore this extension. Clients are discouraged from but are allowed to use the health status to decide if it's worth sending a request to the server.

Controlling Flycheck

The flycheck/checkOnSave feature can be controlled via notifications sent by the client to the server.

Method: rust-analyzer/runFlycheck

Notification:

interface RunFlycheckParams {
    /// The text document whose cargo workspace flycheck process should be started.
    /// If the document is null or does not belong to a cargo workspace all flycheck processes will be started.
    textDocument: lc.TextDocumentIdentifier | null;
}

Triggers the flycheck processes.

Method: rust-analyzer/clearFlycheck

Notification:

interface ClearFlycheckParams {}

Clears the flycheck diagnostics.

Method: rust-analyzer/cancelFlycheck

Notification:

interface CancelFlycheckParams {}

Cancels all running flycheck processes.

Syntax Tree

Method: rust-analyzer/syntaxTree

Request:

interface SyntaxTreeParams {
    textDocument: TextDocumentIdentifier,
    range?: Range,
}

Response: string

Returns textual representation of a parse tree for the file/selected region. Primarily for debugging, but very useful for all people working on rust-analyzer itself.

View Syntax Tree

Method: rust-analyzer/viewSyntaxTree

Request:

interface ViewSyntaxTreeParams {
    textDocument: TextDocumentIdentifier,
}

Response: string

Returns json representation of the file's syntax tree. Used to create a treeView for debugging and working on rust-analyzer itself.

View Hir

Method: rust-analyzer/viewHir

Request: TextDocumentPositionParams

Response: string

Returns a textual representation of the HIR of the function containing the cursor. For debugging or when working on rust-analyzer itself.

View Mir

Method: rust-analyzer/viewMir

Request: TextDocumentPositionParams

Response: string

Returns a textual representation of the MIR of the function containing the cursor. For debugging or when working on rust-analyzer itself.

Interpret Function

Method: rust-analyzer/interpretFunction

Request: TextDocumentPositionParams

Response: string

Tries to evaluate the function using internal rust analyzer knowledge, without compiling the code. Currently evaluates the function under cursor, but will give a runnable in future. Highly experimental.

View File Text

Method: rust-analyzer/viewFileText

Request: TextDocumentIdentifier

Response: string

Returns the text of a file as seen by the server. This is for debugging file sync problems.

View ItemTree

Method: rust-analyzer/viewItemTree

Request:

interface ViewItemTreeParams {
    textDocument: TextDocumentIdentifier,
}

Response: string

Returns a textual representation of the ItemTree of the currently open file, for debugging.

View Crate Graph

Method: rust-analyzer/viewCrateGraph

Request:

interface ViewCrateGraphParams {
    full: boolean,
}

Response: string

Renders rust-analyzer's crate graph as an SVG image.

If full is true, the graph includes non-workspace crates (crates.io dependencies as well as sysroot crates).

Expand Macro

Method: rust-analyzer/expandMacro

Request:

interface ExpandMacroParams {
    textDocument: TextDocumentIdentifier,
    position: Position,
}

Response:

interface ExpandedMacro {
    name: string,
    expansion: string,
}

Expands macro call at a given position.

Hover Actions

Experimental Client Capability: { "hoverActions": boolean }

If this capability is set, Hover request returned from the server might contain an additional field, actions:

interface Hover {
    ...
    actions?: CommandLinkGroup[];
}

interface CommandLink extends Command {
    /**
     * A tooltip for the command, when represented in the UI.
     */
    tooltip?: string;
}

interface CommandLinkGroup {
    title?: string;
    commands: CommandLink[];
}

Such actions on the client side are appended to a hover bottom as command links:

  +-----------------------------+
  | Hover content               |
  |                             |
  +-----------------------------+
  | _Action1_ | _Action2_       |  <- first group, no TITLE
  +-----------------------------+
  | TITLE _Action1_ | _Action2_ |  <- second group
  +-----------------------------+
  ...

Open Cargo.toml

Upstream Issue: https://github.com/rust-lang/rust-analyzer/issues/6462

Experimental Server Capability: { "openCargoToml": boolean }

This request is sent from client to server to open the current project's Cargo.toml

Method: experimental/openCargoToml

Request: OpenCargoTomlParams

Response: Location | null

Example

// Cargo.toml
[package]
// src/main.rs

/* cursor here*/

experimental/openCargoToml returns a single Link to the start of the [package] keyword.

Related tests

This request is sent from client to server to get the list of tests for the specified position.

Method: rust-analyzer/relatedTests

Request: TextDocumentPositionParams

Response: TestInfo[]

interface TestInfo {
    runnable: Runnable;
}

Hover Range

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/377

Experimental Server Capability: { "hoverRange": boolean }

This extension allows passing a Range as a position field of HoverParams. The primary use-case is to use the hover request to show the type of the expression currently selected.

interface HoverParams extends WorkDoneProgressParams {
    textDocument: TextDocumentIdentifier;
    position: Range | Position;
}

Whenever the client sends a Range, it is understood as the current selection and any hover included in the range will show the type of the expression if possible.

Example

fn main() {
    let expression = $01 + 2 * 3$0;
}

Triggering a hover inside the selection above will show a result of i32.

Move Item

Upstream Issue: https://github.com/rust-lang/rust-analyzer/issues/6823

This request is sent from client to server to move item under cursor or selection in some direction.

Method: experimental/moveItem

Request: MoveItemParams

Response: SnippetTextEdit[]

export interface MoveItemParams {
    textDocument: TextDocumentIdentifier,
    range: Range,
    direction: Direction
}

export const enum Direction {
    Up = "Up",
    Down = "Down"
}

Workspace Symbols Filtering

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/941

Experimental Server Capability: { "workspaceSymbolScopeKindFiltering": boolean }

Extends the existing workspace/symbol request with ability to filter symbols by broad scope and kind of symbol. If this capability is set, workspace/symbol parameter gains two new optional fields:

interface WorkspaceSymbolParams {
    /**
     * Return only the symbols defined in the specified scope.
     */
    searchScope?: WorkspaceSymbolSearchScope;
    /**
     * Return only the symbols of specified kinds.
     */
    searchKind?: WorkspaceSymbolSearchKind;
    ...
}

const enum WorkspaceSymbolSearchScope {
    Workspace = "workspace",
    WorkspaceAndDependencies = "workspaceAndDependencies"
}

const enum WorkspaceSymbolSearchKind {
    OnlyTypes = "onlyTypes",
    AllSymbols = "allSymbols"
}

Client Commands

Upstream Issue: https://github.com/microsoft/language-server-protocol/issues/642

Experimental Client Capability: { "commands?": ClientCommandOptions }

Certain LSP types originating on the server, notably code lenses, embed commands. Commands can be serviced either by the server or by the client. However, the server doesn't know which commands are available on the client.

This extensions allows the client to communicate this info.

export interface ClientCommandOptions {
    /**
     * The commands to be executed on the client
     */
    commands: string[];
}

Colored Diagnostic Output

Experimental Client Capability: { "colorDiagnosticOutput": boolean }

If this capability is set, the "full compiler diagnostics" provided by checkOnSave will include ANSI color and style codes to render the diagnostic in a similar manner as cargo. This is translated into --message-format=json-diagnostic-rendered-ansi when flycheck is run, instead of the default --message-format=json.

The full compiler rendered diagnostics are included in the server response regardless of this capability:

// https://microsoft.github.io/language-server-protocol/specifications/specification-current#diagnostic
export interface Diagnostic {
    ...
    data?: {
        /**
         * The human-readable compiler output as it would be printed to a terminal.
         * Includes ANSI color and style codes if the client has set the experimental
         * `colorDiagnosticOutput` capability.
         */
        rendered?: string;
    };
}

Dependency Tree

Method: rust-analyzer/fetchDependencyList

Request:

export interface FetchDependencyListParams {}

Response:

export interface FetchDependencyListResult {
    crates: {
        name: string;
        version: string;
        path: string;
    }[];
}

Returns all crates from this workspace, so it can be used create a viewTree to help navigate the dependency tree.

View Recursive Memory Layout

Method: rust-analyzer/viewRecursiveMemoryLayout

Request: TextDocumentPositionParams

Response:

export interface RecursiveMemoryLayoutNode = {
    /// Name of the item, or [ROOT], `.n` for tuples
    item_name: string;
    /// Full name of the type (type aliases are ignored)
    typename: string;
    /// Size of the type in bytes
    size: number;
    /// Alignment of the type in bytes
    alignment: number;
    /// Offset of the type relative to its parent (or 0 if its the root)
    offset: number;
    /// Index of the node's parent (or -1 if its the root)
    parent_idx: number;
    /// Index of the node's children (or -1 if it does not have children)
    children_start: number;
    /// Number of child nodes (unspecified it does not have children)
    children_len: number;
};

export interface RecursiveMemoryLayout = {
    nodes: RecursiveMemoryLayoutNode[];
};

Returns a vector of nodes representing items in the datatype as a tree, RecursiveMemoryLayout::nodes[0] is the root node.

If RecursiveMemoryLayout::nodes::length == 0 we could not find a suitable type.

Generic Types do not give anything because they are incomplete. Fully specified generic types do not give anything if they are selected directly but do work when a child of other types this is consistent with other behavior.

Unresolved questions:

• How should enums/unions be represented? currently they do not produce any children because they have multiple distinct sets of children.
• Should niches be represented? currently they are not reported.
• A visual representation of the memory layout is not specified, see the provided implementation for an example, however it may not translate well to terminal based editors or other such things.

Setup Guide

This guide gives a simplified opinionated setup for developers contributing to rust-analyzer using Visual Studio Code to make changes and Visual Studio Code Insiders to test those changes. This guide will assume you have Visual Studio Code and Visual Studio Code Insiders installed.

Prerequisites

Since rust-analyzer is a Rust project, you will need to install Rust. You can download and install the latest stable version of Rust here.

Step-by-Step Setup

Step 01: Fork the rust-analyzer repository and clone the fork to your local machine.

Step 02: Open the project in Visual Studio Code.

Step 03: Open a terminal and run cargo build to build the project.

Step 04: Install the language server locally by running the following command:

# Install only the language server  
cargo xtask install --server \  
    --code-bin code-insiders \  # Target a specific editor (code, code-exploration, code-insiders, codium, or code-oss)  
    --dev-rel  # Build in release mode with debug info level 2  

In the output of this command, there should be a file path provided to the installed binary on your local machine. It should look something like the following output below:

Installing <path-to-rust-analyzer-binary>
Installed package `rust-analyzer v0.0.0 (<path-to-rust-analyzer-binary>)` (executable `rust-analyzer.exe`)

In Visual Studio Code Insiders, you will want to open your User Settings (JSON) from the Command Palette. From there you should ensure that the rust-analyzer.server.path key is set to the <path-to-rust-analyzer-binary>. This will tell Visual Studio Code Insiders to use the locally installed version that you can debug.

The User Settings (JSON) file should contain the following:

{
    "rust-analyzer.server.path": "<path-to-rust-analyzer-binary>"
}

Now you should be able to make changes to rust-analyzer in Visual Studio Code and then view the changes in Visual Studio Code Insiders.

Debugging rust-analyzer

The simplest way to debug rust-analyzer is to use the eprintln! macro. The reason why we use eprintln! instead of println! is because the language server uses stdout to send messages. So instead we will debug using stderr.

An example debugging statement could go into the main_loop.rs file which can be found at crates/rust-analyzer/src/main_loop.rs. Inside the main_loop we will add the following eprintln! to test debugging rust-analyzer:

eprintln!("Hello, world!");

Now, run the following commands to check the project and reinstall the server:

cargo check  
cargo xtask install --server --code-bin code-insiders --dev-rel  

Now on Visual Studio Code Insiders, we should be able to open the Output tab on our terminal and switch to Rust Analyzer Language Server to see the eprintln! statement we just wrote.

If you are able to see your output, you now have a complete workflow for debugging rust-analyzer.

Style

Our approach to "clean code" is two-fold:

• We generally don't block PRs on style changes.
• At the same time, all code in rust-analyzer is constantly refactored.

It is explicitly OK for a reviewer to flag only some nits in the PR, and then send a follow-up cleanup PR for things which are easier to explain by example, cc-ing the original author. Sending small cleanup PRs (like renaming a single local variable) is encouraged.

When reviewing pull requests prefer extending this document to leaving non-reusable comments on the pull request itself.

General

Scale of Changes

Everyone knows that it's better to send small & focused pull requests. The problem is, sometimes you have to, eg, rewrite the whole compiler, and that just doesn't fit into a set of isolated PRs.

The main things to keep an eye on are the boundaries between various components. There are three kinds of changes:

1. Internals of a single component are changed. Specifically, you don't change any pub items. A good example here would be an addition of a new assist.

2. API of a component is expanded. Specifically, you add a new pub function which wasn't there before. A good example here would be expansion of assist API, for example, to implement lazy assists or assists groups.

3. A new dependency between components is introduced. Specifically, you add a pub use reexport from another crate or you add a new line to the [dependencies] section of Cargo.toml. A good example here would be adding reference search capability to the assists crates.

For the first group, the change is generally merged as long as:

• it works for the happy case,
• it has tests,
• it doesn't panic for the unhappy case.

For the second group, the change would be subjected to quite a bit of scrutiny and iteration. The new API needs to be right (or at least easy to change later). The actual implementation doesn't matter that much. It's very important to minimize the amount of changed lines of code for changes of the second kind. Often, you start doing a change of the first kind, only to realize that you need to elevate to a change of the second kind. In this case, we'll probably ask you to split API changes into a separate PR.

Changes of the third group should be pretty rare, so we don't specify any specific process for them. That said, adding an innocent-looking pub use is a very simple way to break encapsulation, keep an eye on it!