Rust Analyzer

Rust Analyzer is an experimental modular compiler frontend for the Rust language, which aims to lay a foundation for excellent IDE support.

It doesn't implement much of compiler functionality yet, but the white-space preserving Rust parser works, and there are significant chunks of overall architecture (indexing, on-demand & lazy computation, snapshotable world view) in place. Some basic IDE functionality is provided via a language server.

Quick Start

$ cargo test
$ cargo parse < crates/libsyntax2/src/lib.rs

Trying It Out

This installs experimental VS Code plugin

$ cargo install-code

It's better to remove existing Rust plugins to avoid interference. Warning: plugin is not intended for general use, has a lot of rough edges and missing features (notably, no code completion). That said, while originally libsyntax2 was developed in IntelliJ, @matklad now uses this plugin (and thus, libsytax2) to develop libsyntax2, and it doesn't hurt too much :-)

Features:

• syntax highlighting (LSP does not have API for it, so impl is hacky and sometimes fall-backs to the horrible built-in highlighting)

• commands (ctrl+shift+p or keybindings)

  • Show Rust Syntax Tree (use it to verify that plugin works)
  • Rust Extend Selection (works with multiple cursors)
  • Rust Matching Brace (knows the difference between < and <)
  • Rust Parent Module
  • Rust Join Lines (deals with trailing commas)

• Go to symbol in file

• Go to symbol in workspace

  • #Foo searches for Foo type in the current workspace
  • #foo# searches for foo function in the current workspace
  • #Foo* searches for Foo type among dependencies, excluding stdlib
  • Sorry for a weired UI, neither LSP, not VSCode have any sane API for filtering! :)

• code actions:

  • Flip , in comma separated lists
  • Add #[derive] to struct/enum
  • Add impl block to struct/enum
  • Run tests at caret

• Go to definition ("correct" for mod foo; decls, index-based for functions).

Current Status and Plans

Rust analyzer aims to fill the same niche as the official Rust Language Server, but better. It was created because @matklad is not satisfied with RLS original starting point and current direction. More details can be found in this thread. The core issue is that RLS works in the "wait until user stops typing, run the build process, save the results of the analysis" mode, which arguably is the wrong foundation for IDE (see the thread for details).

Rust Analyzer is a hobby project at the moment, there's exactly zero guarantees that it becomes production-ready one day.

The near/mid term plan is to work independently of the main rustc compiler and implement at least simplistic versions of name resolution, macro expansion and type inference. The purpose is two fold:

• to quickly bootstrap usable and useful language server: solution that covers 80% of Rust code will be useful for IDEs, and will be vastly simpler than 100% solution.

• to understand how the consumer-side of compiler API should look like (especially it's on-demand aspects). If you have get_expression_type function, you can write a ton of purely-IDE features on top of it, even if the function is only partially correct. Plugin in the precise function afterwards should just make IDE features more reliable.

The long term plan is to merge with the mainline rustc compiler, probably around the HIR boundary? That is, use rust analyzer for parsing, macro expansion and related bits of name resolution, but leave the rest (including type inference and trait selection) to the existing rustc.

Code Walk-Through

crates/libsyntax2

• yellow, red/green syntax tree, heavily inspired by this
• grammar, the actual parser
• parser_api/parser_impl bridges the tree-agnostic parser from grammar with yellow trees
• grammar.ron RON description of the grammar, which is used to generate syntax_kinds and ast modules.
• algo: generic tree algorithms, including walk for O(1) stack space tree traversal (this is cool) and visit for type-driven visiting the nodes (this is double plus cool, if you understand how Visitor works, you understand libsyntax2).

crates/libeditor

Most of IDE features leave here, unlike libanalysis, libeditor is single-file and is basically a bunch of pure functions.

crates/libanalysis

A stateful library for analyzing many Rust files as they change. WorldState is a mutable entity (clojure's atom) which holds current state, incorporates changes and handles out Worlds --- immutable consistent snapshots of WorldState, which actually power analysis.

crates/server

An LSP implementation which uses libanalysis for managing state and libeditor for actually doing useful stuff.

crates/cli

A CLI interface to libsyntax

crate/tools

Code-gen tasks, used to develop libsyntax2:

• cargo gen-kinds -- generate ast and syntax_kinds
• cargo gen-tests -- collect inline tests from grammar
• cargo install-code -- build and install VS Code extension and server

code

VS Code plugin

Performance

Non-incremental, but seems pretty fast:

$ cargo build --release --package cli
$ wc -l ~/projects/rust/src/libsyntax/parse/parser.rs
7546 /home/matklad/projects/rust/src/libsyntax/parse/parser.rs
$ ./target/release/cli parse < ~/projects/rust/src/libsyntax/parse/parser.rs --no-dump  > /dev/null
parsing: 21.067065ms

Getting in touch

@matklad can be found at Rust discord, in #ides-and-editors.

License

libsyntax2 is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE and LICENSE-MIT for details.