rust-analyzer/docs/dev/README.md

# 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.md](./architecture.md) document.
It also explains the high-level layout of the source code.
Do skim through that document.

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

Various organizational and process issues are discussed in this document.

# Getting in Touch

Rust Analyzer is a part of [RLS-2.0 working
group](https://github.com/rust-lang/compiler-team/tree/6a769c13656c0a6959ebc09e7b1f7c09b86fb9c0/working-groups/rls-2.0).
Discussion happens in this Zulip stream:

https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0

# Issue Labels

* [good-first-issue](https://github.com/rust-analyzer/rust-analyzer/labels/good%20first%20issue)
  are good issues to get into the project.
* [E-has-instructions](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-has-instructions)
  issues have links to the code in question and tests.
* [E-easy](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-easy),
  [E-medium](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-medium),
  [E-hard](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-hard),
  [E-unknown](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-unknown),
  labels are *estimates* for how hard would be to write a fix. Each triaged issue should have one of these labels.
* [S-actionable](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AS-actionable) and
  [S-unactionable](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AS-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 effectively wont-fix. Each triaged issue should have one of these labels.
* [fun](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3Afun)
  is for cool, but probably hard stuff.
* [Design](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%Design)
  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

Do see [./style.md](./style.md).

# 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-ng to enforce the [not rocket science](https://graydon2.dreamwidth.org/1597.html) 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:
```json
{
    "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.withSysroot": false` 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:

```bash
cd editors/code
npm ci
npm run lint
```
## How to ...

* ... add an assist? [#7535](https://github.com/rust-analyzer/rust-analyzer/pull/7535)
* ... add a new protocol extension? [#4569](https://github.com/rust-analyzer/rust-analyzer/pull/4569)
* ... add a new configuration option? [#7451](https://github.com/rust-analyzer/rust-analyzer/pull/7451)
* ... add a new completion? [#6964](https://github.com/rust-analyzer/rust-analyzer/pull/6964)
* ... allow new syntax in the parser? [#7338](https://github.com/rust-analyzer/rust-analyzer/pull/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 standard `log` crate for logging, and `env_logger` 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.

To see stderr in the running VS Code instance, go to the "Output" tab of the panel and select `rust-analyzer`.
This shows `eprintln!` as well.
Note that `stdout` is used for the actual protocol, so `println!` will break things.

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 enabling `"rust-analyzer.trace.server": "verbose"` workspace setting.
  These logs are shown in a separate tab in the output and could be used with LSP inspector.
  Kudos to [@DJMcNab](https://github.com/DJMcNab) for setting this awesome infra up!


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

* `Rust Analyzer: Status` shows some memory-usage statistics.

* `Rust Analyzer: Syntax Tree` shows syntax tree of the current file/selection.

* `Rust Analyzer: View Hir` shows the HIR expressions within the function containing the cursor.

  You can hover over syntax nodes in the opened text file to see the appropriate
  rust code that it refers to and the rust editor will also highlight the proper
  text range.

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

  ![demo](https://user-images.githubusercontent.com/36276403/78225773-6636a480-74d3-11ea-9d9f-1c9d42da03b0.png)

## 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
```

In particular, I have `export RA_PROFILE='*>10'` in my shell profile.

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` 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!
```

Additionally, it assumes that remote for `rust-analyzer` is called `upstream` (I use `origin` to point to my fork).

Release steps:

1. 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
     * pushes VS Code extension to the marketplace
   * create new changelog in `rust-analyzer.github.io`
2. While the release is in progress, fill in the changelog
3. Commit & push the changelog
4. Tweet
5. Inside `rust-analyzer`, run `cargo xtask promote` -- this will create a PR to rust-lang/rust updating rust-analyzer's submodule.
   Self-approve the PR.

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.

## Permissions

There are three sets of people with extra permissions:

* rust-analyzer GitHub organization **admins** (which include current t-compiler leads).
  Admins have full access to the org.
* **review** team in the organization.
  Reviewers have `r+` access to all of organization's repositories and publish rights on crates.io.
  They also have direct commit access, but all changes should via bors queue.
  It's ok to self-approve if you think you know what you are doing!
  bors should automatically sync the permissions.
* **triage** team in the organization.
  This team can label and close issues.