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Contributing Quick Start

Rust Analyzer is just a usual 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 ./ document.

We also publish rustdoc docs to pages:

Various organizational and process issues are discussed in this document.

Getting in Touch

Rust Analyzer is a part of RLS-2.0 working group. Discussion happens in this Zulip stream:

Work List

We have this "work list" paper document:

It shows what everyone is working on right now. If you want to (this is not mandatory), add yourself to the list!

Issue Labels

  • good-first-issue are good issues to get into the project.
  • E-mentor issues have links to the code in question and tests.
  • E-easy, E-medium, E-hard, labels are estimates for how hard would be to write a fix.
  • fun is for cool, but probably hard stuff.


We use Travis for CI. Most of the things, including formatting, are checked by cargo test so, if cargo test passes locally, that's a good sign that CI will be green as well. We use bors-ng to enforce the not rocket science rule.

You can run cargo xtask install-pre-commit-hook to install git-hook to run rustfmt on commit.

Code organization

All Rust code lives in the crates top-level directory, and is organized as a single Cargo workspace. The editors top-level directory contains code for integrating with editors. Currently, it contains plugins for VS Code (in typescript) and Emacs (in elisp). The docs top-level directory contains both developer and user documentation.

We have some automation infra in Rust in the xtask package. It contains stuff like formatting checking, code generation and powers cargo xtask install. The latter syntax is achieved with the help of cargo aliases (see .cargo directory).

Launching rust-analyzer

Debugging 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 includes an action for running a single test).

However, launching a VS Code instance with locally build language server is possible. There's even a VS Code task for this, so just F5 should work (thanks, @andrew-w-ross!).

I often just install development version with cargo xtask install --server --jemalloc and restart the host VS Code.

See ./ for how to attach to rust-analyzer with debugger, and don't forget that rust-analyzer has useful pd snippet and dbg postfix completion for printf debugging :-)

Working With VS Code Extension

To work on the VS Code extension, launch code inside editors/code and use F5 to launch/debug. To automatically apply formatter and linter suggestions, use npm run fix.

Tests are located inside src/test and are named *.test.ts. They use the Mocha test framework and the builtin Node assert module. Unlike normal Node tests they must be hosted inside a VS Code instance. This can be done in one of two ways:

  1. When F5 debugging in VS Code select the Extension Tests configuration from the drop-down at the top of the Debug View. This will launch a temporary instance of VS Code. The test results will appear in the "Debug Console" tab of the primary VS Code instance.

  2. Run npm test from the command line. Although this is initiated from the command line it is not headless; it will also launch a temporary instance of VS Code.

Due to the requirements of running the tests inside VS Code they are not run on CI. When making changes to the extension please ensure the tests are not broken locally before opening a Pull Request.

To install only the VS Code extension, use cargo xtask install --client-code.


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 standard log crate for logging, and env_logger for logging frontend. By default, log goes to stderr, but the stderr itself is processed by VS Code.

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 RUST_LOG=gen_lsp_server=trace code .
  • you can log on the client side, by 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's also two VS Code commands which might be of interest:

  • Rust Analyzer: Status shows some memory-usage statistics. To take full advantage of it, you need to compile rust-analyzer with jemalloc support:

    $ cargo install --path crates/ra_lsp_server --force --features jemalloc

    There's an alias for this: cargo xtask install --server --jemalloc.

  • Rust Analyzer: Syntax Tree shows syntax tree of the current file/selection.


We have a built-in hierarchical profiler, you can enable it by using RA_PROF 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

In particular, I have `export RA_PROFILE='*>10' in my shell profile.

To measure time for from-scratch analysis, use something like this:

$ cargo run --release -p ra_cli -- analysis-stats ../chalk/

For measuring time of incremental analysis, use either of these:

$ cargo run --release -p ra_cli -- analysis-bench ../chalk/ --highlight ../chalk/chalk-engine/src/
$ cargo run --release -p ra_cli -- analysis-bench ../chalk/ --complete ../chalk/chalk-engine/src/
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