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rust-lang-nursery / rls


Repository for the Rust Language Server (aka RLS)


Build Status Build status

Rust Language Server (RLS)

This project is in the alpha stage of development. It is likely to be buggy in some situations; proceed with caution.

The RLS provides a server that runs in the background, providing IDEs, editors, and other tools with information about Rust programs. It supports functionality such as 'goto definition', symbol search, reformatting, and code completion, and enables renaming and refactorings.

The RLS gets its source data from the compiler and from Racer. Where possible it uses data from the compiler which is precise and complete. Where its not possible, (for example for code completion and where building is too slow), it uses Racer.

Since the Rust compiler does not yet support end-to-end incremental compilation, we can't offer a perfect experience. However, by optimising our use of the compiler and falling back to Racer, we can offer a pretty good experience for small to medium sized crates. As the RLS and compiler evolve, we'll offer a better experience for larger and larger crates.

The RLS is designed to be frontend-independent. We hope it will be widely adopted by different editors and IDEs. To seed development, we provide a reference implementation of an RLS frontend for Visual Studio Code.


Step 1: Install rustup

You can install rustup on many platforms. This will help us quickly install the rls and its dependencies.

Step 2: Switch to nightly

Switch to the nightly compiler:

rustup default nightly
rustup update nightly

Step 3: Install the RLS

Once you have rustup installed, run the following commands:

rustup component add rls
rustup component add rust-analysis
rustup component add rust-src

If you've never set up Racer before, you may also need follow the Racer configuration steps


Though the RLS is built to work with many IDEs and editors, we currently use VSCode to test the RLS.

To run with VSCode, you'll need a recent VSCode version installed.

Next, you'll need to run the VSCode extension (for this step, you'll need a recent node installed:

git clone
cd rls_vscode
npm install
code .

VSCode will open into the rls_vscode project. From here, click the Debug button on the left-hand side (a bug with a line through it). Next, click the green triangle at the top. This will launch a new instance of VSCode with the rls_vscode plugin enabled. From there, you can open your Rust projects using the RLS.

You'll know it's working when you see this in the status bar at the bottom, with a spinning indicator:

RLS analysis: working /

Once you see:

RLS analysis: done

Then you have the full set of capabilities available to you. You can goto def, find all refs, rename, goto type, etc. Completions are also available using the heuristics that Racer provides. As you type, your code will be checked and error squiggles will be reported when errors occur. You can hover these squiggles to see the text of the error.


The RLS can be configured on a per-project basis by adding a file called rls.toml to the project root (i.e., next to Cargo.toml). Entries in this file will affect how the RLS operates and how it builds your project.

Currently we accept the following options:

  • build_lib (bool, defaults to false) checks the project as if you passed the --lib argument to cargo.
  • cfg_test (bool, defaults to true) checks the project as if you were running cargo test rather than cargo build. I.e., compiles (but does not run) test code.
  • unstable_features (bool, defaults to false) enables unstable features. Currently, this includes renaming and formatting.
  • sysroot (String, defaults to "") if the given string is not empty, use the given path as the sysroot for all rustc invocations instead of trying to detect the sysroot automatically


You can look in the in this repo to learn more about contributing to this project.