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.

Various organizational and process issues are discussed here.

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.
E-fun is for cool, but probably hard stuff.

CI

We use Travis 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. We use bors-ng to enforce the not rocket science rule.

You can run cargo format-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 plugins for VS Code (in typescript) and Emacs (in elisp). The docs top-level directory contains both developer and user documentation.

We have some automation infra in Rust in the crates/tool package. It contains stuff like formatting checking, code generation and powers cargo install-code. 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 even a VS Code task for this, so just F5 should work (thanks, @andrew-w-ross!).

I often just install development version with cargo jinstall-lsp and restart the host VS Code.

See ./debugging.md for how to attach to rust-analyzer with debugger, and don't forget that rust-analyzer has useful pd snippet and dbg postfix completion for printf debugging :-)

Working With VS Code Extension

To work on the VS Code extension, launch code inside editors/code and use F5 to launch/debug. To automatically apply formatter and linter suggestions, use npm run fix.

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 flexi_logger for logging frotend. By default, log goes to stderr (the same as with env_logger), but the stderr itself is processed by VS Code. To mirror logs to a ./log directory, set RA_INTERNAL_MODE=1 environmental variable.

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 jinstall-lsp.
Rust Analyzer: Syntax Tree shows syntax tree of the current file/selection.

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