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 (LSP) 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 supported version

Currently, use the latest version of rust-analyzer.

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)

Note: This is the rust-analyzer extension, not the rust extension that VSCode may recommend for Rust files.

You can install the rust-analyzer extension directly from the VSCode marketplace.

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

Note: To access the VS Code Workspace settings, click the View menu, then Command Palette, and select Preferences: Open Workspace Settings (JSON).

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

In addition, the following settings may provide a smoother experience:

  // optional: only show summary docs for functions (keeps tooltips small)
  "rust-analyzer.callInfo.full": false,
  // optional: don't activate parameterHints automatically
  "editor.parameterHints.enabled": false,

Enabling rustfmt in the rust-analyzer extension

The rust-analyzer extension relies on the rustup tool to choose the right toolchain for invoking rustfmt, so you need to tell rustup about your Fuchsia checkout and its toolchain:

$ rustup toolchain link fuchsia-tools $FUCHSIA_DIR/prebuilt/third_party/rust_tools/<host os>

For instance, on linux, you would use linux-x64, or on MacOS you would use mac-x64 (there should only be one option in your Fuchsia directory, set up correctly for your host development system):

$ rustup toolchain link fuchsia-tools $FUCHSIA_DIR/prebuilt/third_party/rust_tools/linux-x64/

Having done that, the rust-analyzer extension can be configured to use this toolchain and the Fuchsia rustfmt.toml. Open Workspace settings as above, and add:

    // use fuchsia-tools toolchain and fuchsia's rules for rustfmt:
    "rust-analyzer.rustfmt.extraArgs": [
        "--config-path=<path to $FUCHSIA_DIR>/rustfmt.toml"

A note on rust-analyzer and symlinked Fuchsia directories

If your Fuchsia workspace is symlinked from elsewhere (such as another mountpoint), the rust-analyzer extension may not be able to properly locate the files for analysis as they are opened in VSCode.

rust-analyzer, and the rust-project.json file, contain absolute paths to your source files. As such, if you open the Fuchsia directory via the symlink'd location, it will not match those absolute paths, and the rust-analyzer VSCode extension will not be able to align the opened files in VSCode with the files that the rust-analyzer LSP is parsing and analyzing.

Instead, open the actual path to the Fuchsia source in VSCode, so that the LSP and the editor see the same paths to all source files.

Troubleshooting issues with rust-analyzer

If you notice that rust-analyzer is not working correctly, it could be due to a breaking change in the rust-project.json file. The first thing to try in this case is to jiri update, rebase, and re-run fx gen, and see if the issue goes away:

$ jiri update
$ git rebase
$ fx gen


If not, you may need to manually downgrade rust-analyzer to the currently-supported version if it's not the latest, or to a previous version you were using if the currently supported version is listed as “latest”.


For basic support, instructions on rust-lang/rust.vim.

For IDE support, see the vim section of the rust-analyzer manual.

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



See the rust-analyzer manual for instructions.

Check on save

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.

Note that this workflow is based on cargo, which is more likely to break than rust-analyzer based workflows.

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, follow the rust-analyzer setup instructions for Sublime.


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.

Intellij (Custom code completion)

See instructions on the Intellij Rust site. Finally, follow these steps to generate a Cargo.toml file for use by Intellij. Note that cargo-based workflows are more likely to break than rust-analyzer based ones.