Rust Editor Configuration

Generating Cargo.toml files for use by editors

Many editors require Cargo.toml files in order to understand how your Rust project is structured. 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:

you@computer:/path/to/fuchsia $ fx build garnet/foo/path/to/target:some_label
you@computer:/path/to/fuchsia $ 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") {


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

The VS Code plugin uses the RLS (Rust language server) so you'll need to first 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:

fuchsia_rusty_component.code-workspace javascript { "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.