Add comprehensive GitHub Copilot instructions for pylint development with mandatory pre-commit (#10522)

Co-authored-by: Pierre Sassoulas <[email protected]>

Author: Copilot

.github/copilot-instructions.md

@@ -0,0 +1,253 @@
+# Pylint Development Instructions
+
+Always follow these instructions first and fallback to additional search and context
+gathering only if the information in these instructions is incomplete or found to be in
+error.
+
+## Issue Label Guidelines
+
+Before attempting to fix any issue, check the GitHub issue labels using the GitHub API:
+
+- If an issue is labeled with "Astroid", "Needs astroid update", "Needs astroid
+  constraint", or "Needs astroid Brain 🧠", **ONLY** create regression tests
+- Do **NOT** attempt to fix astroid-related issues as you cannot modify astroid from
+  this repository
+- For astroid-related issues, focus on creating comprehensive regression tests that
+  reproduce the problem
+- All other issues can be fixed normally following the standard development workflow
+
+## Development Environment Setup
+
+### Basic Installation
+
+Clone and set up pylint development environment:
+
+- `git clone https://github.com/pylint-dev/pylint` -- clone repository
+- `cd pylint` -- enter directory
+- `python3 -m venv venv` -- create virtual environment
+- `source venv/bin/activate` -- activate virtual environment (Linux/Mac)
+- `pip install -r requirements_test_min.txt` -- install test dependencies (~30 seconds)
+- `pip install -e .` -- install pylint in editable mode (~30-60 seconds)
+
+### Optional Setup Steps
+
+- `pre-commit install` -- enable pre-commit hooks for autoformatting
+- `pip install pre-commit` -- install pre-commit separately if needed
+
+### Astroid Development (if needed)
+
+If working on astroid changes:
+
+- `git clone https://github.com/pylint-dev/astroid.git` -- clone astroid
+- `pip install -e astroid/` -- install astroid in editable mode
+- `cd astroid/ && git switch my-astroid-dev-branch` -- switch to development branch
+
+## Running Tests
+
+### Core Test Commands
+
+- `pytest tests/test_functional.py -k test_functional` -- run functional tests (~60
+  seconds, NEVER CANCEL, set timeout to 120+ seconds)
+- `pytest tests/` -- run all tests (several minutes, NEVER CANCEL, set timeout to 300+
+  seconds)
+- `python3 -m pytest` -- run tests with local python
+- `pytest tests/test_check_parallel.py -v` -- quick test file (~2 seconds)
+
+### Specific Test Types
+
+- **Functional tests:**
+  `pytest "tests/test_functional.py::test_functional[missing_kwoa_py3]"` -- single
+  functional test (~1 second)
+- **Unit tests:** Located in `/tests/` directory, test specific pylint functionality
+- **Configuration tests:** In `/tests/config/functional/` for testing configuration
+  loading
+- **Primer tests:** `pytest -m primer_stdlib --primer-stdlib` -- test on stdlib for
+  crashes
+
+### Test with Coverage
+
+- `pytest tests/message/ --cov=pylint.message` -- run with coverage
+- `coverage html` -- generate HTML coverage report
+
+### Tox Usage (Optional)
+
+- `python -m tox` -- run all tox environments
+- `python -m tox -epy313` -- run Python 3.13 suite only
+- `python -m tox -epylint` -- run pylint on pylint's codebase
+- `python -m tox -eformatting` -- run formatting checks
+- `python -m tox --recreate` -- recreate environments (recommended)
+- `python -m tox -e py310 -- -k test_functional` -- run specific tests in tox
+
+## Documentation
+
+### Building Documentation
+
+- `make -C doc/ install-dependencies` -- install doc dependencies (~10 seconds)
+- `make -C doc/ html` -- build documentation (~3 minutes, NEVER CANCEL, set timeout to
+  300+ seconds)
+- `make -C doc/ clean` -- clean build files when starting from scratch
+- `tox -e docs` -- alternative way to build docs
+
+**Network dependency:** Documentation build requires internet access to fetch external
+inventories.
+
+## Validation and Quality Checks
+
+### Running Pylint on Code
+
+- `pylint --help` -- verify pylint installation works
+- `pylint --disable=all --enable=E,F pylint/` -- run pylint on itself for errors only
+  (~20 seconds)
+- `pylint --rcfile=pylintrc --fail-on=I path/to/your/changes.py` -- standard pylint run
+- `pylint --disable=all --enable=E,F,W path/to/your/changes.py` -- focus on errors and
+  warnings
+
+### Pre-commit and Formatting
+
+- `pre-commit run --all-files` -- run all formatting checks (requires network for
+  initial setup)
+- **Network dependency:** pre-commit may fail in isolated environments due to hook
+  downloads
+
+### Validation Test Scenarios
+
+Always test your changes with these validation scenarios:
+
+- `echo "def badFunction(): pass" > /tmp/test_sample.py && pylint --enable=C0103 /tmp/test_sample.py`
+  -- should find naming issues
+- `pylint --help` and `pylint --list-msgs | head -10` -- verify CLI functionality
+- `pylint --help-msg=C0103` -- should show invalid-name help
+- `pylint --rcfile=pylintrc --fail-on=I pylint/__init__.py` -- should get 10.00/10
+  rating
+
+## Writing Tests
+
+### Functional Tests
+
+Located in `/tests/functional/`, consists of `.py` test files with corresponding `.txt`
+expected output files:
+
+- Annotate lines where messages are expected:
+  `a, b, c = 1 # [unbalanced-tuple-unpacking]`
+- Multiple messages on same line:
+  `a, b, c = 1.test # [unbalanced-tuple-unpacking, no-member]`
+- Use offset syntax for special cases: `# +1: [singleton-comparison]`
+- **Run and update:**
+  `python tests/test_functional.py --update-functional-output -k "test_functional[test_name]"`
+
+### Test File Organization
+
+- **New checkers:** Create `new_checker_message.py` in `/tests/functional/n/`
+- **Extensions:** Place in `/tests/functional/ext/extension_name/`
+- **Regression tests:** Place in `/tests/r/regression/` with `regression_` prefix
+- **Configuration tests:** Place in `/tests/config/functional/`
+
+### Configuration Test Files
+
+Create `.result.json` files with configuration differences from standard config:
+
+```json
+{
+  "functional_append": {
+    "disable": [["a-message-to-be-added"]]
+  },
+  "jobs": 10
+}
+```
+
+## Codebase Structure
+
+```
+pylint/                    # Main package
+├── checkers/             # All pylint checkers (rules implementation)
+├── config/               # Configuration handling and parsing
+├── message/              # Message system and formatting
+├── reporters/            # Output formatters (text, json, etc.)
+├── testutils/            # Testing utilities and helpers
+└── extensions/           # Optional extensions and plugins
+
+tests/                     # Test suite
+├── functional/           # Functional test files (.py + .txt expected output)
+├── config/functional/    # Configuration functional tests
+├── r/regression/         # Regression tests
+├── test_*.py            # Unit tests
+└── regrtest_data/       # Test data files
+
+doc/                      # Documentation
+├── user_guide/          # User documentation
+├── development_guide/   # Developer and contributor documentation
+│   ├── contributor_guide/    # Setup, testing, contribution guidelines
+│   ├── technical_reference/  # Technical implementation details
+│   └── how_tos/             # Guides for custom checkers, plugins
+└── additional_tools/    # Tools documentation
+
+script/                   # Development utility scripts
+```
+
+### Key Files
+
+- `pyproject.toml` -- Main configuration (dependencies, build, tools)
+- `tox.ini` -- Multi-environment testing configuration
+- `.pre-commit-config.yaml` -- Code quality checks configuration
+- `pylintrc` -- Pylint's own configuration
+- `requirements_test_min.txt` -- Minimal test dependencies
+
+## Creating New Checkers
+
+### Getting Started
+
+- `python script/get_unused_message_id_category.py` -- get next available message ID
+- Study existing checkers in `pylint/checkers/` for patterns
+- Read technical reference documentation in `doc/development_guide/technical_reference/`
+- Use `astroid.extract_node` for AST manipulation
+
+### Workflow
+
+1. Create checker class in appropriate `pylint/checkers/` file
+2. Add functional tests in `tests/functional/`
+3. Search existing code for warning message to find where logic exists
+4. Test with sample code to ensure functionality works
+
+## Pull Request Guidelines
+
+### Before Submitting
+
+- Use Python 3.8+ for development (required for latest AST parser and pre-commit hooks)
+- Write comprehensive commit messages relating to tracker issues
+- Keep changes small and separate consensual from opinionated changes
+- Add news fragment: `towncrier create <IssueNumber>.<type>`
+- Always launch `pre-commit run -a` before committing
+
+### Documentation Changes
+
+- Document non-trivial changes
+- Generate docs with `tox -e docs`
+- Maintainers may label issues `skip-news` if no changelog needed
+
+### Contribution Credits
+
+- Add emails/names to `script/.contributors_aliases.json` if using multiple identities
+
+## Critical Timing Information
+
+- **NEVER CANCEL:** All operations that show "NEVER CANCEL" may take significant time
+- **Full test suite:** 60+ seconds (set timeout to 120+ seconds)
+- **Documentation build:** 180 seconds (set timeout to 300+ seconds)
+- **Functional tests:** 60 seconds (set timeout to 120+ seconds)
+- **Pylint self-check:** 20 seconds (set timeout to 60+ seconds)
+- **Individual test files:** 1-15 seconds
+- **Installation steps:** 30-60 seconds each
+
+## Environment Limitations and Workarounds
+
+- **Network connectivity required:** Documentation build and pre-commit setup require
+  internet access
+- **Tox failures:** In isolated environments, use direct pytest and pip commands instead
+  of tox
+- **Import errors in self-check:** Some import errors when running pylint on itself are
+  expected (git dependencies not installed)
+- **Build environments:** Use direct pip/pytest commands when tox environments fail to
+  build
+
+Always validate your changes by running pylint on sample code to ensure functionality
+works correctly.