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jonathandturner / rls


Repository for the Rust Language Server (aka RLS)


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Rust Language Server (RLS)

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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.

If you already have rustup installed, be sure to run self update to ensure you have the latest rustup:

rustup self update

If you're going to use the VSCode extension, you can skip steps 2 and 3.

Step 2: Update nightly

Update the nightly compiler. You don't have to use it as your default compiler, but it needs to be on your system:

rustup update nightly

Step 3: Install the RLS

Once you have rustup installed, run the following commands:

rustup component add rls-preview --toolchain nightly
rustup component add rust-analysis --toolchain nightly
rustup component add rust-src --toolchain nightly

If you've never set up Racer before, you'll need to set up your RUST_SRC_PATH variable. To do so, you can 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. VSCode setting "window.openFoldersInNewWindow" cannot be set to "on". 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, using the official Visual Studio Code extension this will be done via the workspace settings file settings.json.

Other editors will have their own way of sending the workspace/DidChangeConfiguration method.

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. Mutually exclusive with, and preferred over build_bin.
  • build_bin (String, defaults to "") checks the project as if you passed -- bin <build_bin> argument to cargo. Mutually exclusive with build_lib.
  • 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 range formatting and workspace_mode, analyze_package options.
  • 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
  • target (String, defaults to "") if the given string is not empty, use the given target triple for all rustc invocations
  • wait_to_build (u64, defaults to 500) time in milliseconds between receiving a change notification and starting build
  • workspace_mode (bool, defaults to false) Experimental mode, requires unstable_features turned on. When turned on, RLS will try to scan current workspace and analyze every package in it.
  • analyze_package (String, defaults to "") When workspace_mode is enabled, analysis will be only provided for the specified package (runs as if -p <analyze_package> was passed).


For tips on debugging and troubleshooting, see


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

If you want to implement RLS support in an editor, see