Fatou

A language server, formatter, and linter for Julia that doesn't require running Julia itself. Fatou is written in Rust and is designed to be fast, safe, and easy to integrate into editors and tooling. It is named after the French mathematician Pierre Fatou, whose Fatou set is the complement of the Julia set.

Fatou follows the rust-analyzer design (a lossless rowan CST, salsa for incremental computation, and lsp-server for the language-server transport).

Installation

Fatou is available from several sources:

crates.io: cargo install fatou
npm: npm install -g fatou-cli (bundles a prebuilt binary)
PyPI: uv tool install fatou/pipx install fatou
Prebuilt binaries: from the releases page
VS Code/Open VSX: the Fatou extension (Marketplace, Open VSX); also works in Positron

Runs on Linux, macOS, and Windows (x86_64 and arm64).

Usage

fatou parse <file.jl>          # print the CST (stdin if no file)
fatou format <file.jl>         # format to stdout (stdin if omitted)
fatou format --check <dir>     # check formatting; non-zero exit if any differ
fatou lint --check <dir>       # lint
fatou lsp                      # run the language server on stdio

Configuration lives in fatou.toml ([format] line-width/indent-width, [lint] select/ignore).

Editor integration

The language server (fatou lsp) provides a broad set of features over stdio: completion, hover, go-to-definition, find references and document highlights, rename, document and workspace symbols, call and type hierarchy, signature help, code actions, folding and selection ranges, document links, and semantic tokens, alongside formatting (whole-document and range) and diagnostics (push and pull). The Fatou extension for VS Code/Open VSX (and Positron) (Marketplace, Open VSX) bundles the binary and starts the server automatically; see editors/code. For Neovim and other editors, see the editor setup guide.

CI integration

Run format and lint checks in GitHub Actions with fatou-action, which installs a prebuilt, checksum- and provenance-verified binary:

- uses: jolars/fatou-action@v1

Or as pre-commit hooks with fatou-pre-commit:

repos:
  - repo: https://github.com/jolars/fatou-pre-commit
    # fatou version
    rev: v0.7.0
    hooks:
      - id: fatou-lint
      - id: fatou-format

Development

cargo build
cargo test
cargo clippy --all-targets --all-features -- -D warnings
cargo fmt -- --check

Or via task: task test, task lint, task format. See CONTRIBUTING.md for details.

License

MIT—see LICENSE.

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Release history Release notifications | RSS feed

0.15.0

Aug 17, 2026

0.14.0

Aug 13, 2026

0.13.0

Aug 10, 2026

0.12.0

Aug 8, 2026

0.11.1

Aug 7, 2026

0.11.0

Aug 7, 2026

0.10.0

Aug 3, 2026

This release

0.9.0

Aug 1, 2026

0.8.0

Jul 30, 2026

0.7.0

Jul 25, 2026

0.6.0

Jul 20, 2026

0.5.0

Jul 8, 2026

0.4.0

Jul 2, 2026

0.3.0

Jul 1, 2026

fatou 0.9.0

Fatou

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