Contributing - rust-analyzer

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# Contributing Quick Start

rust-analyzer is an ordinary Rust project, which is organized as a Cargo workspace, builds on stable and doesn’t depend on C libraries. So, just

    $ cargo test

should be enough to get you started!

To learn more about how rust-analyzer works, see Architecture. It also explains the high-level layout of the source code. Do skim through that document.

We also publish rustdoc docs to https://rust-lang.github.io/rust-analyzer/ide/. Note though, that the internal documentation is very incomplete.

Various organizational and process issues are discussed in this document.

# Getting in Touch

rust-analyzer is a part of the RLS-2.0 working group. Discussion happens in this Zulip stream:

https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frust-analyzer

# Issue Labels

- good-first-issue are good issues to get into the project.
- E-has-instructions issues have links to the code in question and tests.
- Broken Window are issues which are not necessarily critical by themselves, but which should be fixed ASAP regardless, to avoid accumulation of technical debt.
- E-easy, E-medium, E-hard, E-unknown, labels are estimates for how hard would be to write a fix. Each triaged issue should have one of these labels.
- S-actionable and S-unactionable specify if there are concrete steps to resolve or advance an issue. Roughly, actionable issues need only work to be fixed, while unactionable ones are blocked either on user feedback (providing a reproducible example), or on larger architectural work or decisions. This classification is descriptive, not prescriptive, and might be wrong: Any unactionable issue might have a simple fix that we missed. Each triaged issue should have one of these labels.
- fun is for cool, but probably hard stuff.
- C-Architecture is for moderate/large scale architecture discussion. Also a kind of fun. These issues should generally include a link to a Zulip discussion thread.

# Code Style & Review Process

See the Style Guide.

# Cookbook

## CI

We use GitHub Actions for CI. Most of the things, including formatting, are checked by `cargo test`. If `cargo test` passes locally, that’s a good sign that CI will be green as well. The only exception is that some long-running tests are skipped locally by default. Use `env RUN_SLOW_TESTS=1 cargo test` to run the full suite.

We use bors to enforce the not rocket science rule.

## Launching rust-analyzer

Debugging the language server can be tricky. LSP is rather chatty, so driving it from the command line is not really feasible, driving it via VS Code requires interacting with two processes.

For this reason, the best way to see how rust-analyzer works is to find a relevant test and execute it. VS Code & Emacs include an action for running a single test.

Launching a VS Code instance with a locally built language server is also possible. There’s “Run Extension (Debug Build)” launch configuration for this in VS Code.

In general, I use one of the following workflows for fixing bugs and implementing features:

If the problem concerns only internal parts of rust-analyzer (i.e. I don’t need to touch the `rust-analyzer` crate or TypeScript code), there is a unit-test for it. So, I use rust-analyzer: Run action in VS Code to run this single test, and then just do printf-driven development/debugging. As a sanity check after I’m done, I use `cargo xtask install --server` and Reload Window action in VS Code to verify that the thing works as I expect.

If the problem concerns only the VS Code extension, I use Run Installed Extension launch configuration from `launch.json`. Notably, this uses the usual `rust-analyzer` binary from `PATH`. For this, it is important to have the following in your `settings.json` file:

    {
        "rust-analyzer.server.path": "rust-analyzer"
    }

After I am done with the fix, I use `cargo xtask install --client` to try the new extension for real.

If I need to fix something in the `rust-analyzer` crate, I feel sad because it’s on the boundary between the two processes, and working there is slow. I usually just `cargo xtask install --server` and poke changes from my live environment. Note that this uses `--release`, which is usually faster overall, because loading stdlib into debug version of rust-analyzer takes a lot of time. To speed things up, sometimes I open a temporary hello-world project which has `"rust-analyzer.cargo.sysroot": null` in `.code/settings.json`. This flag causes rust-analyzer to skip loading the sysroot, which greatly reduces the amount of things rust-analyzer needs to do, and makes printf’s more useful. Note that you should only use the `eprint!` family of macros for debugging: stdout is used for LSP communication, and `print!` would break it.

If I need to fix something simultaneously in the server and in the client, I feel even more sad. I don’t have a specific workflow for this case.

Additionally, I use `cargo run --release -p rust-analyzer -- analysis-stats path/to/some/rust/crate` to run a batch analysis. This is primarily useful for performance optimizations, or for bug minimization.

## TypeScript Tests

If you change files under `editors/code` and would like to run the tests and linter, install npm and run:

    cd editors/code
    npm ci
    npm run lint

## How to …

- … add an assist? #7535
- … add a new protocol extension? #4569
- … add a new configuration option? #7451
- … add a new completion? #6964
- … allow new syntax in the parser? #7338

## Logging

Logging is done by both rust-analyzer and VS Code, so it might be tricky to figure out where logs go.

Inside rust-analyzer, we use the `tracing` crate for logging, and `tracing-subscriber` for logging frontend. By default, log goes to stderr, but the stderr itself is processed by VS Code. `--log-file <PATH>` CLI argument allows logging to file. Setting the `RA_LOG_FILE=<PATH>` environment variable will also log to file, it will also override `--log-file`.

To see the server stderr output in the running VS Code instance, go to the “Output” tab of the panel and select `rust-analyzer Language Server`. This shows `eprintln!` as well. Note that `stdout` is used by LSP messages, so using `println!`—or anything that writes to `stdout`—will break rust-analyzer!

To log all communication between the server and the client, there are two choices:

- You can log on the server side, by running something like

      env RA_LOG=lsp_server=debug code .

- You can log on the client side, by the `rust-analyzer: Toggle LSP Logs` command or enabling `"rust-analyzer.trace.server": "verbose"` workspace setting. These logs are shown in a separate tab named `rust-analyzer LSP Trace` in the output and could be used with LSP inspector. Kudos to @DJMcNab for setting this awesome infra up!

Finally there are the logs of the VSCode extension itself which go into the `rust-analyzer Extension` output tab.

There are also several VS Code commands which might be of interest:

- `rust-analyzer: Status` shows some memory-usage statistics.

- `rust-analyzer: View Hir` shows the HIR expressions within the function containing the cursor.

- If `rust-analyzer.showSyntaxTree` is enabled in settings, `Rust Syntax Tree: Focus on Rust Syntax Tree View` shows the syntax tree of the current file.

  You can click on nodes in the rust editor to go to the corresponding syntax node.

  You can click on `Reveal Syntax Element` next to a syntax node to go to the corresponding rust code and highlight the proper text range.

  If you trigger Go to Definition in the inspected Rust source file, the syntax tree view should scroll to and select the appropriate syntax node token.

  You can click on `Copy` next to a syntax node to copy a text representation of the node.

## Profiling

We have a built-in hierarchical profiler, you can enable it by using `RA_PROFILE` env-var:

    RA_PROFILE=*             // dump everything
    RA_PROFILE=foo|bar|baz   // enabled only selected entries
    RA_PROFILE=*@3>10        // dump everything, up to depth 3, if it takes more than 10 ms

Some rust-analyzer contributors have `export RA_PROFILE='*>10'` in my shell profile.

For machine-readable JSON output, we have the `RA_PROFILE_JSON` env variable. We support filtering only by span name:

    RA_PROFILE=* // dump everything
    RA_PROFILE_JSON="vfs_load|parallel_prime_caches|discover_command" // dump selected spans

We also have a “counting” profiler which counts number of instances of popular structs. It is enabled by `RA_COUNT=1`.

To measure time for from-scratch analysis, use something like this:

    $ cargo run --release -p rust-analyzer -- analysis-stats ../chalk/

For measuring time of incremental analysis, use either of these:

    $ cargo run --release -p rust-analyzer -- analysis-bench ../chalk/ --highlight ../chalk/chalk-engine/src/logic.rs
    $ cargo run --release -p rust-analyzer -- analysis-bench ../chalk/ --complete ../chalk/chalk-engine/src/logic.rs:94:0

Look for `fn benchmark_xxx` tests for a quick way to reproduce performance problems.

## Release Process

Release process is handled by `release`, `dist`, `publish-release-notes` and `promote` xtasks, `release` being the main one.

`release` assumes that you have checkouts of `rust-analyzer`, `rust-analyzer.github.io`, and `rust-lang/rust` in the same directory:

    ./rust-analyzer
    ./rust-analyzer.github.io
    ./rust-rust-analyzer  # Note the name!

The remote for `rust-analyzer` must be called `upstream` (I use `origin` to point to my fork). In addition, for `xtask promote` (see below), `rust-rust-analyzer` must have a `rust-analyzer` remote pointing to this repository on GitHub.

`release` calls the GitHub API calls to scrape pull request comments and categorize them in the changelog. This step uses the `curl` and `jq` applications, which need to be available in `PATH`. Finally, you need to obtain a GitHub personal access token and set the `GITHUB_TOKEN` environment variable.

Release steps:

1. Set the `GITHUB_TOKEN` environment variable.
2. Inside rust-analyzer, run `cargo xtask release`. This will:
   - checkout the `release` branch
   - reset it to `upstream/nightly`
   - push it to `upstream`. This triggers GitHub Actions which:
     - runs `cargo xtask dist` to package binaries and VS Code extension
     - makes a GitHub release
     - publishes the VS Code extension to the marketplace
   - call the GitHub API for PR details
   - create a new changelog in `rust-analyzer.github.io`
3. While the release is in progress, fill in the changelog.
4. Commit & push the changelog.
5. Run `cargo xtask publish-release-notes <CHANGELOG>` – this will convert the changelog entry in AsciiDoc to Markdown and update the body of GitHub Releases entry.
6. Tweet.
7. Perform a subtree pull.
8. Perform a subtree push.

If the GitHub Actions release fails because of a transient problem like a timeout, you can re-run the job from the Actions console. If it fails because of something that needs to be fixed, remove the release tag (if needed), fix the problem, then start over. Make sure to remove the new changelog post created when running `cargo xtask release` a second time.

We release “nightly” every night automatically and promote the latest nightly to “stable” manually, every week.

We don’t do “patch” releases, unless something truly egregious comes up. To do a patch release, cherry-pick the fix on top of the current `release` branch and push the branch. There’s no need to write a changelog for a patch release, it’s OK to include the notes about the fix into the next weekly one. Note: we tag releases by dates, releasing a patch release on the same day should work (by overwriting a tag), but I am not 100% sure.

## Permissions

There are two sets of people with extra permissions:

- The rust-lang team t-rust-analyzer. This team has write access to the repository and merge queue permissions (note the repo itself is managed by infra admins). It’s ok to self-approve if you think you know what you are doing! Feel free to request a review or assign any PR to a reviewer with the relevant expertise to bring the work to their attention. Don’t feel pressured to review assigned PRs though. If you don’t feel like reviewing for whatever reason, someone else will pick the review up (but please speak up if you don’t feel like it)!
- The rust-lang team t-rust-analyzer-contributors. This team has general triaging permissions allowing to label, close and re-open issues.

## Synchronizing subtree changes

`rust-analyzer` is a josh subtree of the rust-lang/rust repository. We use the rustc-josh-sync tool to perform synchronization between these two repositories. You can find documentation of the tool here.

You can install the synchronization tool using the following commands:

    cargo install --locked --git https://github.com/rust-lang/josh-sync

Both pulls (synchronizing changes from rust-lang/rust into rust-analyzer) and pushes (synchronizing changes from rust-analyzer into rust-lang/rust) are performed from this repository. changes from rust-analyzer to rust-lang/rust) are performed from this repository.

Usually we first perform a pull, wait for it to be merged, and then perform a push.

### Performing a pull

1. Checkout a new branch that will be used to create a PR against rust-analyzer
2. Run the pull command

       rustc-josh-sync pull

3. Push the branch to your fork of `rust-analyzer` and create a PR

- If you have the `gh` CLI installed, `rustc-josh-sync` can create the PR for you.

### Performing a push

Wait for the previous pull to be merged.

1. Switch to `master` and pull
2. Run the push command to create a branch named `<branch-name>` in a `rustc` fork under the `<gh-username>` account

       rustc-josh-sync push <branch-name> <gh-username>

   - The push will ask you to download a checkout of the `rust-lang/rust` repository.
   - If you get prompted for a password, see this.
3. Create a PR from `<branch-name>` into `rust-lang/rust`

> Besides the `rust` checkout, the Josh cache (stored under `~/.cache/rustc-josh`) will contain a bare clone of `rust-lang/rust`. This currently takes several GBs.