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 setup rust-analyzer on VS Code, see the VS Code guide Additional Vs Code extensions for Fuchsia.

Vim

Install rust-lang/rust.vim, which also integrates with:

  • Tagbar: universal-ctags is strongly recommended, but other ctags implementations are also supported.

  • Syntastic: rust.vim automatically registers cargo as a syntax checker for Rust. Yet it will fail unless you set up cargo. If you want to disable the integration (or use rust-analyzer to check the code, e.g. via YouCompleteMe), add the following to your ~/.vimrc:

    let g:syntastic_rust_checkers = []

  • Auto formatting: to run rustfmt on save (disabled by default), add the following to ~./vimrc:

    let g:rustfmt_command = 'FUCHSIA_DIR/prebuilt/third_party/rust/HOST_OS/bin/rustfmt'
let g:rustfmt_autosave = 1

For IDE support, see the vim section of the rust-analyzer manual. For YouCompleteMe, add --rust-completer (or --all) if you are installing from source, and it should work out of the box. You can also specify the path to a standalone rust-analyzer in your ~/.vimrc (this is not guaranteed to work due to version compatibility); here is an example assuming it is installed to ~/.local/bin/rust-analyzer (note the intentional absence of /bin in the path):

let g:ycm_rust_toolchain_root = $HOME . '/.local'

emacs

Completion

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. If you haven't already, install rustup. Then, from your Fuchsia root, type:

rustup toolchain link fuchsia FUCHSIA_DIR/prebuilt/third_party/rust/HOST_OS
rustup default fuchsia

Finally, follow the steps 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 instructions to generate Cargo.toml and .cargo/config, 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

Setup

First, install the LSP package for Sublime. Then, follow the rust-analyzer setup instructions for Sublime.

Usage

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.