CLAUDE.md -> AGENTS.md (#23791)

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Carl Meyer
2026-03-07 10:18:03 -08:00
committed by GitHub
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# 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):
```sh
cargo nextest run
```
For faster test execution, use the `fast-test` profile which enables optimizations while retaining debug info:
```sh
cargo nextest run --cargo-profile fast-test
```
Run tests for a specific crate:
```sh
cargo nextest run -p ty_python_semantic
```
Run a single mdtest file:
```sh
cargo nextest run -p ty_python_semantic --test mdtest -- 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:
```sh
MDTEST_TEST_FILTER="<filter>" cargo nextest run -p ty_python_semantic --test mdtest -- mdtest::<path/to/mdtest_file.md>
```
Update snapshots after running tests:
```sh
cargo insta accept
```
## Running Clippy
```sh
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:
```sh
cargo run --bin ruff -- check path/to/file.py
```
Run ty:
```sh
cargo run --bin ty -- check path/to/file.py
```
## Reproducing ty ecosystem changes
If asked to reproduce changes in the ty ecosystem, use this script to clone the project to some
directory and install its dependencies into `.venv`:
```sh
uv run scripts/setup_primer_project.py <project-name> <some-temp-dir>
```
## 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.
- 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.
- Rust imports should always go at the top of the file, never locally in functions.
- Always run `uvx prek run -a` at the end of a task, after every rebase, after addressing any review comment, and before pushing any code.
- 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.
- When adding new ty checks, it's important to make error messages concise. Think about how an error message would look on a narrow terminal screen. Sometimes more detail can be provided in subdiagnostics or secondary annotations, but it's also important to make sure that the diagnostic is understandable if the user has passed `--output-format=concise`.
- **Salsa incrementality (ty):** Any method that accesses `.node()` must be `#[salsa::tracked]`, or it will break incrementality. Prefer higher-level semantic APIs over raw AST access.
- 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.
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# 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):
```sh
cargo nextest run
```
For faster test execution, use the `fast-test` profile which enables optimizations while retaining debug info:
```sh
cargo nextest run --cargo-profile fast-test
```
Run tests for a specific crate:
```sh
cargo nextest run -p ty_python_semantic
```
Run a single mdtest file:
```sh
cargo nextest run -p ty_python_semantic --test mdtest -- 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:
```sh
MDTEST_TEST_FILTER="<filter>" cargo nextest run -p ty_python_semantic --test mdtest -- mdtest::<path/to/mdtest_file.md>
```
Update snapshots after running tests:
```sh
cargo insta accept
```
## Running Clippy
```sh
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:
```sh
cargo run --bin ruff -- check path/to/file.py
```
Run ty:
```sh
cargo run --bin ty -- check path/to/file.py
```
## Reproducing ty ecosystem changes
If asked to reproduce changes in the ty ecosystem, use this script to clone the project to some
directory and install its dependencies into `.venv`:
```sh
uv run scripts/setup_primer_project.py <project-name> <some-temp-dir>
```
## 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.
- 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.
- Rust imports should always go at the top of the file, never locally in functions.
- Always run `uvx prek run -a` at the end of a task, after every rebase, after addressing any review comment, and before pushing any code.
- 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.
- When adding new ty checks, it's important to make error messages concise. Think about how an error message would look on a narrow terminal screen. Sometimes more detail can be provided in subdiagnostics or secondary annotations, but it's also important to make sure that the diagnostic is understandable if the user has passed `--output-format=concise`.
- **Salsa incrementality (ty):** Any method that accesses `.node()` must be `#[salsa::tracked]`, or it will break incrementality. Prefer higher-level semantic APIs over raw AST access.
- 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.
@AGENTS.md