mozlint

## Overview Firefox's linting infrastructure (mozlint) provides a unified way to run various linters across the codebase. It integrates multiple linters including ESLint, Stylelint, ruff, clippy, clang-format, and many others. ## Workflow - Run `./mach lint` without arguments to lint all modified files in your working directory - Run `./mach lint --fix` to automatically fix issues where possible - Run `./mach lint <path>` to lint specific files or directories - Run `./mach lint --list` to see all available linters - Run `./mach lint --linter <name>` to run a specific linter (e.g., `./mach lint --linter eslint`) - Use `./mach lint --outgoing` to lint only outgoing changes (useful before pushing) - Use `./mach lint --rev <rev>` to lint changes in a specific revision - Use `./mach lint --warnings` to also show warnings, not just errors ### Python linters Python-based linters are the right choice when the linter primarily calls external programs (e.g., eslint, ruff, clang-format) or needs complex Python library integrations. They use types like `external`, `string`, `regex`, `structured_log`, or `global`, with a `payload` of the form `module:function`. ### mozcheck (Rust linter binary) Rust-based checks in `mozcheck` are preferred over new Python linters whenever feasible. `tools/lint/mozcheck/` is a Rust crate hosting fast, in-process checks (currently `file-perm`, `file-whitespace`, `license`, `rejected-words`, `test-manifest-toml`, `trojan-source`). The Python shim at `tools/lint/mozcheck/__init__.py` finds or builds the binary and invokes it in batch mode. Wire a YAML to it with `type: external`, `payload: mozcheck:lint`, `check: <subcommand>`, and `support-files: ['tools/lint/mozcheck/**']`. Extra YAML keys are forwarded as the check's `config`. To add a check: add `src/<name>.rs`, register it in `src/main.rs` and `src/batch.rs`, create the YAML, and add tests under `tools/lint/test/`. Prefer this over a new Python linter for self-contained file checks. ## Adding New Linters See `docs/code-quality/lint/create.rst` for the full guide on creating a new linter. - Linter configurations are in `tools/lint/` directory - Each linter has a YAML configuration file (e.g., `tools/lint/eslint.yml`, `tools/lint/ruff.yml`). Adding the YAML file is what registers the linter with mozlint. - Python-based linters are typically in `tools/lint/python/` - To add a new linter: 1. Create a YAML configuration in `tools/lint/` 2. If it's a custom linter, implement the Python module in `tools/lint/python/` (or add a check to `tools/lint/mozcheck/` for fast file checks) 3. Add tests in `tools/lint/test/` - To run the full mozlint test suite (slow): `./mach python-test --subsuite mozlint --run-slow` - To run a single mozlint test: `./mach python-test --subsuite mozlint <test_name>` ## Common Linters - **eslint**: JavaScript and JSX linting - **stylelint**: CSS and related files linting - **ruff**: Python linting and formatting - **clippy**: Rust linting - **clang-format**: C/C++ code formatting - **prettier**: JavaScript/JSON/YAML formatting - **shellcheck**: Shell script linting - **yamllint**: YAML file linting - **rstcheck**: reStructuredText linting - **license**: License header checking ## Configuration Files - ESLint: `eslint.config.mjs` - Stylelint: `.stylelintrc.js`, `.stylelintignore` - Ruff: `pyproject.toml` - Prettier: `.prettierrc.js`, `.prettierignore` - List of third party code: `tools/rewriting/ThirdPartyPaths.txt` ## Tips - Use `./mach lint --verbose` for more detailed output when debugging linter issues - Check `docs/code-quality/lint/` for documentation on specific linters - Some linters may require additional setup (e.g., node modules for ESLint) - Run `./mach bootstrap` if linters are missing dependencies - To exclude files from linting, use the appropriate ignore file or add exclusions in the linter's YAML config