ruff

Imported from YYC-Cube/YYC3-Knowledge-Base (YYC3-F/ruff/AGENTS.md). Install upstream with npx skills add YYC-Cube/YYC3-Knowledge-Base --skill ruff. Copyright stays with the author.

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).

Code reviews

When reviewing a branch or pull request, be deliberately nitpicky. Report not only bugs and regressions, but also architectural and maintenance risks, weak test coverage, unclear code, unnecessary complexity, and meaningful style or consistency issues. Order findings by severity, cite files and lines, and distinguish blockers from non-blocking improvements. Number each review point for easy reference in subsequent review discussion.

Running Tests

Run all tests (setting CARGO_PROFILE_DEV_OPT_LEVEL=1 CARGO_PROFILE_DEV_DEBUG="line-tables-only" to enable optimizations while retaining some debug info, and setting INSTA_FORCE_PASS=1 INSTA_UPDATE=always MDTEST_UPDATE_SNAPSHOTS=1 to ensure all snapshots are updated):

CARGO_PROFILE_DEV_OPT_LEVEL=1 INSTA_FORCE_PASS=1 INSTA_UPDATE=always CARGO_PROFILE_DEV_DEBUG="line-tables-only" MDTEST_UPDATE_SNAPSHOTS=1 cargo test

Run tests for a specific crate:

CARGO_PROFILE_DEV_OPT_LEVEL=1 INSTA_FORCE_PASS=1 INSTA_UPDATE=always CARGO_PROFILE_DEV_DEBUG="line-tables-only" MDTEST_UPDATE_SNAPSHOTS=1 cargo test -p ty_python_semantic

Run a single mdtest file. The path to the mdtest file should be relative to the crates/ty_python_semantic/resources/mdtest folder:

CARGO_PROFILE_DEV_OPT_LEVEL=1 INSTA_FORCE_PASS=1 INSTA_UPDATE=always CARGO_PROFILE_DEV_DEBUG="line-tables-only" MDTEST_UPDATE_SNAPSHOTS=1 cargo test -p ty_python_semantic --test mdtest -- <path/to/mdtest_file.md>

To run a specific mdtest within a file, use a substring of the Markdown header text as MDTEST_TEST_FILTER. Only use this if it's necessary to isolate a single test case:

MDTEST_TEST_FILTER="<filter>" CARGO_PROFILE_DEV_OPT_LEVEL=1 INSTA_FORCE_PASS=1 INSTA_UPDATE=always CARGO_PROFILE_DEV_DEBUG="line-tables-only" MDTEST_UPDATE_SNAPSHOTS=1 cargo test -p ty_python_semantic --test mdtest -- <path/to/mdtest_file.md>

After running the tests, always review the contents of any snapshots that have been added or updated.

When running tests with INSTA_FORCE_PASS=1, check for .pending-snap files if any affected tests use inline snapshots.

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

When working on ty, first read .agents/skills/working-on-ty/SKILL.md, then also read and follow any more specific ty skills it points to.

Development Guidelines

• All changes must be tested. If you're not testing your changes, you're not done.
• Look to see if your tests could go in an existing file before adding a new file for your tests.
• 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.
• Prefer narrow visibility by default because this workspace is generally its own consumer. However, do not add workarounds solely to avoid pub: make an item public when another workspace crate needs it and that produces the cleaner implementation.
• Rust imports should always go at the top of the file, never locally in functions.
• Run uvx prek at the end of a task if you changed files in the repo. This includes changes such as rebases or addressing review comments. Use uvx prek run --files <path1> <path2> and pass every file you changed. This keeps the hook run independent of staged state and avoids sweeping unrelated changes. Use uvx prek run -a when a full-repository hook sweep is specifically needed.
• 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.
• Try hard to avoid patterns that require panic!, unreachable!, or .unwrap(). Instead, try to encode those constraints in the type system. Don't be afraid to write code that's more verbose or requires largeish refactors if it enables you to avoid these unsafe calls.
• Prefer let chains (if let combined with &&) over nested if let statements to reduce indentation and improve readability. At the end of a task, always check your work to see if you missed opportunities to use let chains.
• If you have to suppress a Clippy lint, prefer to use #[expect()] over [allow()], where possible. But if a lint is complaining about unused/dead code, it's usually best to just delete the unused code.
• Use comments purposefully. Don't use comments to narrate code, but do use them to explain invariants and why something unusual was done a particular way.
• Run cargo dev generate-all after changing configuration options, CLI arguments, lint rules, or environment variable definitions, as these changes require regeneration of schemas, docs, and CLI references.
• Don't prefix tests with test_.
• Don't separate struct definitions from their impl blocks unless the impl is deliberately placed in a separate file, as for large structs.
• Avoid running uv run for any scripts from the repository root unless you use --no-project, --script or similar. Using uv run from the Ruff repo root without these flags will build Ruff from source, which is very slow and usually unnecessary.