This manual focuses on a specific usage of the library -- running it as part of a server that implements the
https://microsoft.github.io/language-server-protocol/[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.
The manual is written in https://asciidoc.org[AsciiDoc] and includes some extra files which are generated from the source code. Run `cargo test` and `cargo xtask codegen` to create these and then `asciidoctor manual.adoc` to create an HTML copy.
If you have questions about using rust-analyzer, please ask them in the https://users.rust-lang.org/c/ide/14["`IDEs and Editors`"] topic of Rust users forum.
In theory, one should be able to just install the <<rust-analyzer-language-server-binary,`rust-analyzer` binary>> and have it automatically work with any editor.
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`.
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.
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 `$PATH`.
If your editor can't find the binary even though the binary is on your `$PATH`, the likely explanation is that it doesn't see the same `$PATH` as the shell, see https://github.com/rust-lang/rust-analyzer/issues/1811[this issue].
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`)
To use `rust-analyzer`, you need to install and enable one of the two popular LSP client implementations for Emacs, https://github.com/joaotavora/eglot[Eglot] or https://github.com/emacs-lsp/lsp-mode[LSP Mode]. Both enable `rust-analyzer` by default in rust buffers if it is available.
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
Eglot does not support the rust-analyzer extensions to the language-server protocol and does not aim to do so in the future. The https://github.com/nemethf/eglot-x#rust-analyzer-extensions[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 https://github.com/emacs-lsp/lsp-mode[LSP UI] it offers a lot of visual eyecandy.
Further it integrates well with https://github.com/emacs-lsp/dap-mode[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
[source,emacs-lisp]
----
(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 https://emacs-lsp.github.io/lsp-mode/page/installation[LSP mode manual].
Also see the https://emacs-lsp.github.io/lsp-mode/page/lsp-rust-analyzer/[rust-analyzer section] for `rust-analyzer` specific options and commands, which you can optionally bind to keys.
Note the excellent https://robert.kra.hn/posts/2021-02-07_rust-with-emacs/[guide] from https://github.com/rksm[@rksm] on how to set-up Emacs for Rust development with LSP mode and several other packages.
Note: for code actions, use `coc-codeaction-cursor` and `coc-codeaction-selected`; `coc-codeaction` and `coc-codeaction-line` are unlikely to be useful.
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,Configuration>> section.
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-language-server-binary,`rust-analyzer` binary>> section on installing the language server binary.
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.
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):
https://gitlab.com/cppit/jucipp[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.
https://kakoune.org/[Kakoune] supports LSP with the help of https://github.com/kak-lsp/kak-lsp[`kak-lsp`].
Follow the https://github.com/kak-lsp/kak-lsp#installation[instructions] to install `kak-lsp`.
To configure `kak-lsp`, refer to the https://github.com/kak-lsp/kak-lsp#configuring-kak-lsp[configuration section] which is basically about copying the https://github.com/kak-lsp/kak-lsp/blob/master/kak-lsp.toml[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 https://github.com/kak-lsp/kak-lsp#usage[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.
[source,txt]
----
eval %sh{kak-lsp --kakoune -s $kak_session} # Not needed if you load it with plug.kak.
Support for Rust development in the Visual Studio IDE is enabled by the link:https://marketplace.visualstudio.com/items?itemName=kitamstudios.RustAnalyzer[rust-analyzer] package. Either click on the download link or install from IDE's extension manager.
For now link:https://visualstudio.microsoft.com/downloads/[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 link:https://github.com/kitamstudios/rust-analyzer/[rust-analyzer.vs].
https://lapce.dev/[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.
=== Crates
There is a package named `ra_ap_rust_analyzer` available on https://crates.io/crates/ra_ap_rust-analyzer[crates.io], for someone who wants to use it programmatically.
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.
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.
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,VS Code>> or <<coc-rust-analyzer,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 https://microsoft.github.io/language-server-protocol/specifications/specification-current/#initialize[`InitializeParams` message, in the LSP protocol].
Please consult your editor's documentation to learn more about how to configure https://microsoft.github.io/language-server-protocol/[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:
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:
* 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).
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.
* 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.
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.
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.
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.
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`:
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:
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.
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 https://code.visualstudio.com/docs/editor/tasks[VS Code Task] and set `"rust-analyzer.checkOnSave": false` in preferences.
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.
