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).

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 (also works in Positron)

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

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).

The language server (fatou lsp) provides formatting and parse diagnostics over stdio. The Fatou extension for VS Code/Open VSX (and Positron) bundles the binary and starts the server automatically; see editors/code. For Neovim and other editors, see the editor setup guide.

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

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

Or via task: task test, task lint, task format.

MIT—see LICENSE.