Rust editor configuration

As there is no specific editor for Rust development on Fuchsia, vim and VS Code are the most popular options. However, documentation for setting up any editor is welcome in this document.

rust-analyzer setup

rust-analyzer is a Language Server Protocol implementation for Rust. This is the recommended workflow and will work with minimal editor setup.

rust-analyzer uses a file in the out/ directory called rust-project.json that is generated based on the build graph at gn gen time. A symlink to the rust-project.json is located in the root directory of the Fuchsia tree.

The rust-project.json file format is currently unstable. Sometimes this can cause an unexpected version mismatch where GN produces a rust-project.json that rust-analyzer is not expecting, causing rust-analyzer to not work correctly.

Currently, use the latest version of rust-analyzer.

Alternative setup with Cargo.toml files

This is a volunteer-maintained workflow that exists because many tools in the Rust ecosystem assume cargo integration. GN and Cargo have some design mismatches that may result in manual tweaks being needed for the generated Cargo.tomls.

Generating Cargo.toml files for use by editors

In order to generate the cargo files based on the build graph of GN, add --cargo-toml-gen to the fx set and fx args commands. This adds a few seconds at gn gen time. For example:

fx set --cargo-toml-gen <normal fx args>

Most editors require the Cargo.toml file to be in a location that is adjacent to the src/ directory. Symlinks to these files can be generated using the following commands, where //garnet/foo/path/to/target:label is the GN target that you want to work on:

fx gen-cargo garnet/foo/path/to/target:some_label

Note that this label must point to a rustc_... GN template (not a Fuchsia package or other GN target). For example:

rustc_binary("some_label") {

Generating .cargo/config files for use by editor

Some plugins require a .cargo/config file to allow cargo to operate correctly for Fuchsia (e.g. to run cargo check). To easily generate this file, use the fargo tool.

  1. Install rustup

  2. Configure rustup to use the Fuchsia Rust toolchain by running:

    rustup toolchain link fuchsia $($FUCHSIA_DIR/scripts/youcompleteme/ VSCODE_RUST_TOOLCHAIN)
    rustup default fuchsia
  3. Clone and install the fargo tool within your $FUCHSIA_DIR by following the getting started instructions for fargo.

  4. Create your config:

    cd $FUCHSIA_DIR && fargo write-config
    # Note the caveats about changing architecture in the fargo readme

Intellij (Custom code completion)

See instructions on the Intellij Rust site. Finally, follow the steps above to generate a Cargo.toml file for use by Intellij.


See instructions on rust-lang/rust.vim.

If you use Tagbar, see this post for instructions on making it work better with Rust.

Visual Studio Code

To use rust-analyzer with VSCode, use the latest stable version of VSCode since rust-analyzer frequently depends on recent language server features. VSCode can be downloaded from the official VSCode website. It is recommended to:

rust-analyzer VSCode extension (supported workflow)

You can install the rust-analyzer extension directly from the VSCode marketplace. If you notice that rust-analyzer is broken, it could be due to a breaking change in the rust-project.json file. You may need to manually downgrade rust-analyzer to a currently supported version.

Once you have installed the rust-analyzer extension, add the following configurations to your settings.json file:

Note: To access the VS Code settings, click the Code menu, then Preferences, then Settings. Scroll and click on Edit in settings.json.

  // disable cargo check on save
  "rust-analyzer.checkOnSave.enable": false,
  "rust-analyzer.checkOnSave.allTargets": false,

RLS (Alternative setup with Cargo)

install rustup. Next, install this VS Code plugin. You need to configure rustup to use the Fuchsia Rust toolchain. Run this command from your Fuchsia source code root directory.

rustup toolchain link fuchsia $(scripts/youcompleteme/ VSCODE_RUST_TOOLCHAIN)
rustup default fuchsia

Follow the steps above to generate a Cargo.toml file for use by VS Code.

Open VS Code and ensure that the directory where the generated Cargo.toml file resides is added as a directory in your workspace (even though you probably have its ancestor fuchsia directory already in your workspace). For example:

you@computer:/path/to/fuchsia $ fx build src/rusty/component:bin
you@computer:/path/to/fuchsia $ fx gen-cargo src/rusty/component:bin

In a new VS Code workspace, in this example, add both /path/to/fuchsia and /path/to/fuchsia/src/rusty/component to the workspace. Saving the workspace would yield something like:


  "folders": [
      "path": "/path/to/fuchsia"
      "path": "/path/to/fuchsia/src/rusty/component"

Next, take note of the paths output by the following:

you@computer:/path/to/fuchsia $ ./scripts/youcompleteme/ FUCHSIA_ROOT
you@computer:/path/to/fuchsia $ ./scripts/youcompleteme/ VSCODE_RUST_TOOLCHAIN

Open VS Code settings

  • MacOS X: Code>Preferences>Settings
  • Linux: File>Preferences>Settings

Note there are different settings defined for each environment (for example, user vs remote development server). In the upper right corner, click an icon whose mouse-over balloon tip says “Open Settings (JSON)”. Add the following settings:

  // General rust and RLS configuration.
  "": "x86_64-fuchsia",
  "rust.target_dir": "<FUCHSIA_ROOT>/out/cargo_target",
  "rust.unstable_features": true,
  "rust-client.rlsPath": "<VS_CODE_TOOLCHAIN>/bin/rls",
  "rust-client.disableRustup": true,
  "rust.mode": "rls",

  // Read `Cargo.toml` from innermost root workspace directory.
  "rust-client.nestedMultiRootConfigInOutermost": false,

  // Optional extras:

  // Log RLS info/warning/error messages to a VSCode Output Panel.
  "rust-client.revealOutputChannelOn": "info",

  // Create `rls[numeric-id].log` in your project directory. Errors from RLS
  // will be logged there.
  "rust-client.logToFile": true,



You will be using flycheck to compile your Rust files when you save them. flycheck will parse those outputs and highlight errors. You'll also use flycheck-rust so that it will compile with cargo and not with rustc. Both are available from melpa.


If you don't yet have melpa, follow the instructions here.

Install flycheck and flycheck-rust in M-x list-packages. Type i to queue for installation what you are missing and then x to execute.

Next, make sure that flycheck-rust is run at startup. Put this in your .emacs files:

(with-eval-after-load 'rust-mode
  (add-hook 'flycheck-mode-hook #'flycheck-rust-setup))

You'll want cargo to run “check” and not “test” so set flycheck-rust-check-tests to nil. You can do this by typing C-h v flycheck-rust-check-tests<RET> and then customizing the variable in the normal way.

Now, you'll want to make sure that the default cargo and rustc that you are using are Fuchsia versions of those. From your fuchsia root, type:

rustup toolchain link fuchsia $PWD/prebuilt/third_party/rust/linux-x64 && rustup default fuchsia

Finally, follow the steps at the top of this page to generate a Cargo.toml for the GN target that you want to work on.

You can read about adjusting flycheck to display your errors as you like. Type C-h v flycheck-highlighting-mode<RET> and customize it. Also customize C-h v flycheck-indiation-mode<RET>.

Now restart emacs and try it out.

Test and debug

To test that it works, you can run M-x flycheck-compile and see the command-line that flycheck is using to check syntax. It ought to look like one of these depending on whether you are in a lib or bin:

cargo check --lib --message-format\=json
cargo check --bin recovery_netstack --message-format\=json

If it runs rustc instead of cargo, that‘s because you didn’t fx gen-cargo.

Note that it might report errors on the first line of the current file. Those are actually errors from a different file. The error's comment will name the problematic file.

Sublime Text

Using Rust-Enhanced for syntax checking

Follow the steps above to generate a Cargo.toml file and also the steps to generate a cargo/config file, which will also setup cargo to use the Fuchsia Rust toolchain.

Then, install the Rust Enhanced plugin. Now, you should have syntax checking on save and be able to run cargo check from the context menu / command palette. Thanks to fargo, some tests also appear to run OK, but this hasn't been thoroughly tested.

Using a language server for intellisense / hover tooltips / go-to-definition


First, install the LSP package for Sublime. Then, you have two choices for the language server, pick one:

  1. rust-analyzer (recommended): Follow the [rust-analyzer setup instructions] ( for Sublime.
  2. RLS: Just enable rls in the LSP: Enable Language Server options from the Sublime command palette.


In order for the language server to work, you need to open a folder that contains a Cargo.toml as the root of your Sublime project. There are two ways you can do this:

  1. Open a new Sublime window for the folder that contains the Cargo.toml (e.g. garnet/foo/path/to/target)
  2. Or, go to the top menu bar -> Project -> Add Folder to Project. This will keep all your files inside one Sublime window, and works even if you have the broader fuchsia folder also open.

You may need to restart Sublime after these steps.