async-rust-lsp

A standalone LSP server that provides real-time diagnostics for async Rust antipatterns — focusing on patterns that clippy and rust-analyzer miss.

Problem

Existing Rust tooling has a blind spot for tokio-specific async antipatterns:

clippy only checks std::sync::Mutex across .await, not tokio::sync::Mutex
rust-analyzer has no plugin system for custom diagnostics
Runtime tools (tokio-console) only help during execution, not during editing

This LSP fills the gap with real-time editor feedback for async lock patterns, blocking operations in async contexts, and other tokio-specific footguns.

Goals

Diagnostics

tokio-mutex-across-await: Warn when tokio::sync::Mutex/RwLock guards are held across .await points
blocking-in-async: Detect std::thread::sleep, std::fs::*, and other blocking calls inside async functions
nested-lock-ordering: Flag potential deadlocks from inconsistent lock acquisition order
unbounded-channel-in-loop: Warn about unbounded channel sends in hot loops

LSP Features

textDocument/publishDiagnostics — real-time warnings as you type
textDocument/codeAction — quick fixes (scope the guard, clone Arc, use spawn_blocking)
Incremental parsing via tree-sitter-rust for fast feedback

Integration

Works with any LSP-compatible editor (VS Code, Zed, Neovim, Helix)
Claude Code consumes LSP diagnostics automatically — diagnostics appear in agent context
Configurable via .async-rust-lsp.toml per project

Architecture (aspirational)

┌─────────────┐    LSP/stdio    ┌──────────────────┐
│   Editor    │ ◄─────────────► │  async-rust-lsp  │
│ (or Claude) │                 │                  │
└─────────────┘                 │  tree-sitter-rust│
                                │  + custom rules  │
                                └──────────────────┘

Built with:

tower-lsp — async LSP framework
tree-sitter-rust — incremental Rust parser
Custom rule engine for async pattern matching

Origin

Born from a real deadlock in the nteract desktop daemon. See nteract/desktop#1614. The gap in static analysis for tokio async patterns is well-known but no one has filled it with an LSP yet.

License

MIT

async-rust-lsp 0.1.0