rust-analyzer overview

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History

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Started out as an error-resilient parser

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Few years later RFC2912, transition to r-a as the official LSP implementation, was filed

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Implementation Details

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• ungrammar for concrete syntax tree definitions
• rowan for syntax trees, inspired by Roslyn, Swift's libsyntax
• lexer shared with rustc
• handwritten recursive-descent parser, different needs
  • low latency incremental reparses
  • Concrete Syntax Tree

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• salsa, similar to rustc's query system
• chalk for trait solving

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Big Milestones

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Semantic Highlighting

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Inlay Hints

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Procedural-Macro and Attribute support

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Current Shortcomings

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• no as-you-type error checking
  • need to run cargo check to get most errors and lints
• no persistent state
  • new session takes time to index dependencies
• completion slower than we would like
• proc-macro ABI is unstable

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Type System

• type inference does not always agree with rustc
• missing const generics support
• missing lifetime generics support
  • 'static all the things

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Contributor Experience

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• architecture docs and videos, style guide
• point out style guide/architecture doc entries in PR reviews
  • Reduces need to write lengthy reviews for repeating problems
• don't bother with clippy
  • defaults are subjectively questionable

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Workflow differences from rust-lang

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• builds with and targets latest stable Rust
  • No compiler internals -> easier to reuse
• low entry bar, just cargo
  • git clone -> cargo test
• merge PRs optimistically, refactor later
• it's okay for team members to self-approve PRs
• no auto assigned reviewers
  • causes some PRs to not get reviewed for a long time

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Meetings

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• weekly sync meeting
  • what has happened the past week
• every 6 weeks steering meeting
  • plan ahead for the next 6 weeks

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Showcase

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• @HKalbasi's WASM demos
  • Monaco/Playground integration
  • Mdbook hover hints for rust snippets
• cargo-modules
  • A cargo plugin for showing an overview of a crate's modules.
• evcxr
  • A Jupyter kernel and REPL
• …

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What's Next

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Better const generics support

• tracking issue r-a#8655
• lots of work yet to be done

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Librarification of rustc's exhaustiveness checking

• so we can replace our sometimes incorrect copy

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A request for Procedural (Attribute) Macro authors

• Try to recover on parse errors, don't just discard the input and emit a compile_error!
• Consider not using syn unless it is really required
• Or explore an infallible alternative to syn