ruff/CLAUDE.md

Ruff Repository

This repository contains both Ruff (a Python linter and formatter) and ty (a Python type checker). The crates follow a naming convention: ruff_* for Ruff-specific code and ty_* for ty-specific code. ty reuses several Ruff crates, including the Python parser (ruff_python_parser) and AST definitions (ruff_python_ast).

Running Tests

Run all tests (using nextest for faster execution):

cargo nextest run

For faster test execution, use the fast-test profile which enables optimizations while retaining debug info:

cargo nextest run --cargo-profile fast-test

Run tests for a specific crate:

cargo nextest run -p ty_python_semantic

Run a specific mdtest (use a substring of the test name):

MDTEST_TEST_FILTER="<filter>" cargo nextest run -p ty_python_semantic mdtest

Update snapshots after running tests:

cargo insta accept

Running Clippy

cargo clippy --workspace --all-targets --all-features -- -D warnings

Running Debug Builds

Use debug builds (not --release) when developing, as release builds lack debug assertions and have slower compile times.

Run Ruff:

cargo run --bin ruff -- check path/to/file.py

Run ty:

cargo run --bin ty -- check path/to/file.py

Pull Requests

When working on ty, PR titles should start with [ty] and be tagged with the ty GitHub label.

Development Guidelines

• All changes must be tested. If you're not testing your changes, you're not done.
• Get your tests to pass. If you didn't run the tests, your code does not work.
• Follow existing code style. Check neighboring files for patterns.
• Always run uvx prek run -a at the end of a task.
• Avoid writing significant amounts of new code. This is often a sign that we're missing an existing method or mechanism that could help solve the problem. Look for existing utilities first.
• Avoid falling back to patterns that require panic!, unreachable!, or .unwrap(). Instead, try to encode those constraints in the type system.
• Prefer let chains (if let combined with &&) over nested if let statements to reduce indentation and improve readability.
• If you have to suppress a Clippy lint, prefer to use #[expect()] over [allow()], where possible.