444 lines
16 KiB
Markdown
444 lines
16 KiB
Markdown
# Contributing Quick Start
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Rust Analyzer is an ordinary Rust project, which is organized as a Cargo
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workspace, builds on stable and doesn't depend on C libraries. So, just
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```
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$ cargo test
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```
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should be enough to get you started!
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To learn more about how rust-analyzer works, see
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[./architecture.md](./architecture.md) document.
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We also publish rustdoc docs to pages:
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https://rust-analyzer.github.io/rust-analyzer/ra_ide/
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Various organizational and process issues are discussed in this document.
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# Getting in Touch
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Rust Analyzer is a part of [RLS-2.0 working
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group](https://github.com/rust-lang/compiler-team/tree/6a769c13656c0a6959ebc09e7b1f7c09b86fb9c0/working-groups/rls-2.0).
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Discussion happens in this Zulip stream:
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https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0
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# Issue Labels
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* [good-first-issue](https://github.com/rust-analyzer/rust-analyzer/labels/good%20first%20issue)
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are good issues to get into the project.
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* [E-has-instructions](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-has-instructions)
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issues have links to the code in question and tests.
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* [E-easy](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-easy),
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[E-medium](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-medium),
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[E-hard](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3AE-hard),
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labels are *estimates* for how hard would be to write a fix.
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* [fun](https://github.com/rust-analyzer/rust-analyzer/issues?q=is%3Aopen+is%3Aissue+label%3Afun)
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is for cool, but probably hard stuff.
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# CI
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We use GitHub Actions for CI. Most of the things, including formatting, are checked by
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`cargo test` so, if `cargo test` passes locally, that's a good sign that CI will
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be green as well. The only exception is that some long-running tests are skipped locally by default.
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Use `env RUN_SLOW_TESTS=1 cargo test` to run the full suite.
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We use bors-ng to enforce the [not rocket science](https://graydon2.dreamwidth.org/1597.html) rule.
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You can run `cargo xtask install-pre-commit-hook` to install git-hook to run rustfmt on commit.
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# Code organization
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All Rust code lives in the `crates` top-level directory, and is organized as a
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single Cargo workspace. The `editors` top-level directory contains code for
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integrating with editors. Currently, it contains the plugin for VS Code (in
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TypeScript). The `docs` top-level directory contains both developer and user
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documentation.
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We have some automation infra in Rust in the `xtask` package. It contains
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stuff like formatting checking, code generation and powers `cargo xtask install`.
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The latter syntax is achieved with the help of cargo aliases (see `.cargo`
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directory).
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# Launching rust-analyzer
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Debugging the language server can be tricky: LSP is rather chatty, so driving it
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from the command line is not really feasible, driving it via VS Code requires
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interacting with two processes.
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For this reason, the best way to see how rust-analyzer works is to find a
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relevant test and execute it (VS Code includes an action for running a single
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test).
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However, launching a VS Code instance with a locally built language server is
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possible. There's **"Run Extension (Debug Build)"** launch configuration for this.
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In general, I use one of the following workflows for fixing bugs and
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implementing features.
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If the problem concerns only internal parts of rust-analyzer (i.e. I don't need
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to touch the `rust-analyzer` crate or TypeScript code), there is a unit-test for it.
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So, I use **Rust Analyzer: Run** action in VS Code to run this single test, and
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then just do printf-driven development/debugging. As a sanity check after I'm
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done, I use `cargo xtask install --server` and **Reload Window** action in VS
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Code to sanity check that the thing works as I expect.
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If the problem concerns only the VS Code extension, I use **Run Installed Extension**
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launch configuration from `launch.json`. Notably, this uses the usual
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`rust-analyzer` binary from `PATH`. For this, it is important to have the following
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in your `settings.json` file:
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```json
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{
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"rust-analyzer.serverPath": "rust-analyzer"
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}
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```
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After I am done with the fix, I use `cargo
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xtask install --client-code` to try the new extension for real.
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If I need to fix something in the `rust-analyzer` crate, I feel sad because it's
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on the boundary between the two processes, and working there is slow. I usually
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just `cargo xtask install --server` and poke changes from my live environment.
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Note that this uses `--release`, which is usually faster overall, because
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loading stdlib into debug version of rust-analyzer takes a lot of time. To speed
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things up, sometimes I open a temporary hello-world project which has
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`"rust-analyzer.withSysroot": false` in `.code/settings.json`. This flag causes
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rust-analyzer to skip loading the sysroot, which greatly reduces the amount of
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things rust-analyzer needs to do, and makes printf's more useful. Note that you
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should only use the `eprint!` family of macros for debugging: stdout is used for LSP
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communication, and `print!` would break it.
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If I need to fix something simultaneously in the server and in the client, I
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feel even more sad. I don't have a specific workflow for this case.
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Additionally, I use `cargo run --release -p rust-analyzer -- analysis-stats
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path/to/some/rust/crate` to run a batch analysis. This is primarily useful for
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performance optimizations, or for bug minimization.
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# Code Style & Review Process
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Our approach to "clean code" is two-fold:
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* We generally don't block PRs on style changes.
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* At the same time, all code in rust-analyzer is constantly refactored.
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It is explicitly OK for a reviewer to flag only some nits in the PR, and then send a follow-up cleanup PR for things which are easier to explain by example, cc-ing the original author.
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Sending small cleanup PRs (like renaming a single local variable) is encouraged.
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## Scale of Changes
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Everyone knows that it's better to send small & focused pull requests.
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The problem is, sometimes you *have* to, eg, rewrite the whole compiler, and that just doesn't fit into a set of isolated PRs.
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The main things to keep an eye on are the boundaries between various components.
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There are three kinds of changes:
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1. Internals of a single component are changed.
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Specifically, you don't change any `pub` items.
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A good example here would be an addition of a new assist.
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2. API of a component is expanded.
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Specifically, you add a new `pub` function which wasn't there before.
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A good example here would be expansion of assist API, for example, to implement lazy assists or assists groups.
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3. A new dependency between components is introduced.
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Specifically, you add a `pub use` reexport from another crate or you add a new line to the `[dependencies]` section of `Cargo.toml`.
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A good example here would be adding reference search capability to the assists crates.
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For the first group, the change is generally merged as long as:
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* it works for the happy case,
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* it has tests,
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* it doesn't panic for the unhappy case.
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For the second group, the change would be subjected to quite a bit of scrutiny and iteration.
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The new API needs to be right (or at least easy to change later).
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The actual implementation doesn't matter that much.
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It's very important to minimize the amount of changed lines of code for changes of the second kind.
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Often, you start doing a change of the first kind, only to realise that you need to elevate to a change of the second kind.
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In this case, we'll probably ask you to split API changes into a separate PR.
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Changes of the third group should be pretty rare, so we don't specify any specific process for them.
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That said, adding an innocent-looking `pub use` is a very simple way to break encapsulation, keep an eye on it!
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Note: if you enjoyed this abstract hand-waving about boundaries, you might appreciate
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https://www.tedinski.com/2018/02/06/system-boundaries.html
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## Minimal Tests
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Most tests in rust-analyzer start with a snippet of Rust code.
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This snippets should be minimal -- if you copy-paste a snippet of real code into the tests, make sure to remove everything which could be removed.
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There are many benefits to this:
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* less to read or to scroll past
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* easier to understand what exactly is tested
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* less stuff printed during printf-debugging
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* less time to run test
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It also makes sense to format snippets more compactly (for example, by placing enum defitions like `enum E { Foo, Bar }` on a single line),
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as long as they are still readable.
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## Order of Imports
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We separate import groups with blank lines
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```rust
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mod x;
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mod y;
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use std::{ ... }
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use crate_foo::{ ... }
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use crate_bar::{ ... }
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use crate::{}
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use super::{} // but prefer `use crate::`
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```
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## Import Style
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Items from `hir` and `ast` should be used qualified:
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```rust
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// Good
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use ra_syntax::ast;
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fn frobnicate(func: hir::Function, strukt: ast::StructDef) {}
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// Not as good
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use hir::Function;
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use ra_syntax::ast::StructDef;
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fn frobnicate(func: Function, strukt: StructDef) {}
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```
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Avoid local `use MyEnum::*` imports.
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Prefer `use crate::foo::bar` to `use super::bar`.
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## Order of Items
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Optimize for the reader who sees the file for the first time, and wants to get the general idea about what's going on.
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People read things from top to bottom, so place most important things first.
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Specifically, if all items except one are private, always put the non-private item on top.
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Put `struct`s and `enum`s first, functions and impls last.
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Do
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```rust
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// Good
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struct Foo {
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bars: Vec<Bar>
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}
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struct Bar;
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```
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rather than
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```rust
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// Not as good
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struct Bar;
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struct Foo {
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bars: Vec<Bar>
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}
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```
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## Variable Naming
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We generally use boring and long names for local variables ([yay code completion](https://github.com/rust-analyzer/rust-analyzer/pull/4162#discussion_r417130973)).
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The default name is a lowercased name of the type: `global_state: GlobalState`.
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Avoid ad-hoc acronyms and contractions, but use the ones that exist consistently (`db`, `ctx`, `acc`).
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The default name for "result of the function" local variable is `res`.
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## Collection types
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We prefer `rustc_hash::FxHashMap` and `rustc_hash::FxHashSet` instead of the ones in `std::collections`.
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They use a hasher that's slightly faster and using them consistently will reduce code size by some small amount.
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## Preconditions
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Function preconditions should generally be expressed in types and provided by the caller (rather than checked by callee):
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```rust
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// Good
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fn frbonicate(walrus: Walrus) {
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...
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}
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// Not as good
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fn frobnicate(walrus: Option<Walrus>) {
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let walrus = match walrus {
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Some(it) => it,
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None => return,
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};
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...
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}
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```
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## Premature Pessimization
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While we don't specifically optimize code yet, avoid writing code which is slower than it needs to be.
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Don't allocate a `Vec` where an iterator would do, don't allocate strings needlessly.
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```rust
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// Good
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use itertools::Itertools;
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let (first_word, second_word) = match text.split_ascii_whitespace().collect_tuple() {
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Some(it) => it,
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None => return,
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}
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// Not as good
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let words = text.split_ascii_whitespace().collect::<Vec<_>>();
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if words.len() != 2 {
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return
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}
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```
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## Documentation
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For `.md` and `.adoc` files, prefer a sentence-per-line format, don't wrap lines.
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If the line is too long, you want to split the sentence in two :-)
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## Commit Style
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We don't have specific rules around git history hygiene.
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Maintaining clean git history is encouraged, but not enforced.
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We use rebase workflow, it's OK to rewrite history during PR review process.
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Avoid @mentioning people in commit messages and pull request descriptions (they are added to commit message by bors), as such messages create a lot of duplicate notification traffic during rebases.
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# Architecture Invariants
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This section tries to document high-level design constraints, which are not
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always obvious from the low-level code.
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## Incomplete syntax trees
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Syntax trees are by design incomplete and do not enforce well-formedness.
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If an AST method returns an `Option`, it *can* be `None` at runtime, even if this is forbidden by the grammar.
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## LSP independence
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rust-analyzer is independent from LSP.
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It provides features for a hypothetical perfect Rust-specific IDE client.
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Internal representations are lowered to LSP in the `rust-analyzer` crate (the only crate which is allowed to use LSP types).
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## IDE/Compiler split
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There's a semi-hard split between "compiler" and "IDE", at the `ra_hir` crate.
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Compiler derives new facts about source code.
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It explicitly acknowledges that not all info is available (i.e. you can't look at types during name resolution).
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IDE assumes that all information is available at all times.
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IDE should use only types from `ra_hir`, and should not depend on the underling compiler types.
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`ra_hir` is a facade.
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## IDE API
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The main IDE crate (`ra_ide`) uses "Plain Old Data" for the API.
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Rather than talking in definitions and references, it talks in Strings and textual offsets.
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In general, API is centered around UI concerns -- the result of the call is what the user sees in the editor, and not what the compiler sees underneath.
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The results are 100% Rust specific though.
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## Parser Tests
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Tests for the parser (`ra_parser`) live in the `ra_syntax` crate (see `test_data` directory).
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There are two kinds of tests:
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* Manually written test cases in `parser/ok` and `parser/err`
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* "Inline" tests in `parser/inline` (these are generated) from comments in `ra_parser` crate.
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The purpose of inline tests is not to achieve full coverage by test cases, but to explain to the reader of the code what each particular `if` and `match` is responsible for.
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If you are tempted to add a large inline test, it might be a good idea to leave only the simplest example in place, and move the test to a manual `parser/ok` test.
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To update test data, run with `UPDATE_EXPECT` variable:
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```bash
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env UPDATE_EXPECT=1 cargo qt
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```
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After adding a new inline test you need to run `cargo xtest codegen` and also update the test data as described above.
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# Logging
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Logging is done by both rust-analyzer and VS Code, so it might be tricky to
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figure out where logs go.
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Inside rust-analyzer, we use the standard `log` crate for logging, and
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`env_logger` for logging frontend. By default, log goes to stderr, but the
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stderr itself is processed by VS Code.
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To see stderr in the running VS Code instance, go to the "Output" tab of the
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panel and select `rust-analyzer`. This shows `eprintln!` as well. Note that
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`stdout` is used for the actual protocol, so `println!` will break things.
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To log all communication between the server and the client, there are two choices:
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* you can log on the server side, by running something like
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```
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env RA_LOG=gen_lsp_server=trace code .
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```
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* you can log on the client side, by enabling `"rust-analyzer.trace.server":
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"verbose"` workspace setting. These logs are shown in a separate tab in the
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output and could be used with LSP inspector. Kudos to
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[@DJMcNab](https://github.com/DJMcNab) for setting this awesome infra up!
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There are also two VS Code commands which might be of interest:
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* `Rust Analyzer: Status` shows some memory-usage statistics. To take full
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advantage of it, you need to compile rust-analyzer with jemalloc support:
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```
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$ cargo install --path crates/rust-analyzer --force --features jemalloc
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```
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There's an alias for this: `cargo xtask install --server --jemalloc`.
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* `Rust Analyzer: Syntax Tree` shows syntax tree of the current file/selection.
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You can hover over syntax nodes in the opened text file to see the appropriate
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rust code that it refers to and the rust editor will also highlight the proper
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text range.
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If you trigger Go to Definition in the inspected Rust source file,
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the syntax tree read-only editor should scroll to and select the
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appropriate syntax node token.
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# Profiling
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We have a built-in hierarchical profiler, you can enable it by using `RA_PROFILE` env-var:
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```
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RA_PROFILE=* // dump everything
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RA_PROFILE=foo|bar|baz // enabled only selected entries
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RA_PROFILE=*@3>10 // dump everything, up to depth 3, if it takes more than 10 ms
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```
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In particular, I have `export RA_PROFILE='*>10'` in my shell profile.
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To measure time for from-scratch analysis, use something like this:
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```
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$ cargo run --release -p rust-analyzer -- analysis-stats ../chalk/
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```
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For measuring time of incremental analysis, use either of these:
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```
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$ cargo run --release -p rust-analyzer -- analysis-bench ../chalk/ --highlight ../chalk/chalk-engine/src/logic.rs
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$ cargo run --release -p rust-analyzer -- analysis-bench ../chalk/ --complete ../chalk/chalk-engine/src/logic.rs:94:0
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```
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