rust/docs/dev/README.md

Contributing Quick Start

Rust Analyzer is just a usual 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 document.

We also publish rustdoc docs to pages:

https://rust-analyzer.github.io/rust-analyzer/ra_ide/

Various organizational and process issues are discussed in this document.

Getting in Touch

Rust Analyzer is a part of RLS-2.0 working group. 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 are good issues to get into the project.
• E-mentor issues have links to the code in question and tests.
• E-easy, E-medium, E-hard, labels are estimates for how hard would be to write a fix.
• fun is for cool, but probably hard stuff.

CI

We use GitHub Actions for CI. Most of the things, including formatting, are checked by cargo test so, 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 rule.

You can run cargo xtask install-pre-commit-hook to install git-hook to run rustfmt on commit.

Code organization

All Rust code lives in the crates top-level directory, and is organized as a single Cargo workspace. The editors top-level directory contains code for integrating with editors. Currently, it contains the plugin for VS Code (in typescript). The docs top-level directory contains both developer and user documentation.

We have some automation infra in Rust in the xtask package. It contains stuff like formatting checking, code generation and powers cargo xtask install. The latter syntax is achieved with the help of cargo aliases (see .cargo directory).

Launching rust-analyzer

Debugging 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 includes an action for running a single test).

However, launching a VS Code instance with locally build language server is possible. There's "Run Extension (Dev Server)" launch configuration for this.

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 (ie, I don't need to touch ra_lsp_server 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 sanity check that the thing works as I expect.

If the problem concerns only the VS Code extension, I use Run Extension launch configuration from launch.json. Notably, this uses the usual ra_lsp_server binary from PATH. For this it is important to have the following in setting.json file:

{
    "rust-analyzer.raLspServerPath": "ra_lsp_server"
}

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

If I need to fix something in the ra_lsp_server 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 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 ra_lsp_server -- analysis-stats path/to/some/rust/crate to run a batch analysis. This is primarily useful for performance optimizations, or for bug minimization.

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.

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 RUST_LOG=gen_lsp_server=trace 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 for setting this awesome infra up!

There's also two VS Code commands which might be of interest:

• Rust Analyzer: Status shows some memory-usage statistics. To take full advantage of it, you need to compile rust-analyzer with jemalloc support:

  $ cargo install --path crates/ra_lsp_server --force --features jemalloc
  

  There's an alias for this: cargo xtask install --server --jemalloc.

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

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.

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

$ cargo run --release -p ra_lsp_server -- analysis-stats ../chalk/

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

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