docs: add AI Coding Guide for cpp-linter-hooks (#172)

Author: shenxianpeng

.github/copilot-instructions.md

@@ -0,0 +1,113 @@
+# cpp-linter-hooks AI Coding Guide
+
+## Project Overview
+Pre-commit hooks wrapper that auto-installs and runs clang-format and clang-tidy from Python wheels. Supports Python 3.9-3.14 across Windows, Linux, and macOS.
+
+## Architecture
+
+### Entry Points & Flow
+- **Entry scripts**: `clang-format-hook` and `clang-tidy-hook` (defined in `pyproject.toml`)
+- **Hook definitions**: `.pre-commit-hooks.yaml` configures both hooks with `types_or: [c++, c]`
+- **Execution pattern**: Parse args → resolve/install tool version → subprocess.run → return (exit_code, output)
+
+### Core Modules
+- **`clang_format.py`**: Wraps clang-format with `-i` (in-place), supports `--verbose` and `--dry-run` modes
+  - Returns `-1` for dry-run to distinguish from actual failures
+- **`clang_tidy.py`**: Wraps clang-tidy, forces exit code 1 if "warning:" or "error:" in output
+- **`util.py`**: Version resolution and pip-based tool installation
+  - `_resolve_version()`: Supports partial matches (e.g., "20" → "20.1.7")
+  - `DEFAULT_CLANG_FORMAT_VERSION` and `DEFAULT_CLANG_TIDY_VERSION` read from `pyproject.toml`
+- **`versions.py`**: Auto-generated by `scripts/update_versions.py` (runs weekly via GitHub Actions)
+
+### Version Management Pattern
+```python
+# Users can specify partial versions
+--version=21      # Resolves to latest 21.x.x
+--version=21.1    # Resolves to latest 21.1.x
+--version=21.1.8  # Exact version
+```
+
+## Development Workflows
+
+### Local Testing
+```bash
+# Test hooks locally without installing
+pre-commit try-repo ./.. clang-format --verbose --all-files
+pre-commit try-repo ./.. clang-tidy --verbose --all-files
+
+# Run test suite
+uv run pytest -vv                    # All tests
+uv run coverage run -m pytest        # With coverage
+uv run pytest -m benchmark           # Performance tests only
+```
+
+### Adding/Modifying Features
+1. **Update hook logic** in `cpp_linter_hooks/{clang_format,clang_tidy}.py`
+2. **Add tests** in `tests/test_*.py` with `@pytest.mark.benchmark` for performance tracking
+3. **Test with sample files** in `testing/` directory (use `good.c` as expected output)
+4. **Update README.md** if user-facing behavior changes
+
+### Dependency Management
+- **Uses `uv`** for all dev operations (not pip directly)
+- **Pin versions**: Default tool versions in `pyproject.toml` dependencies section
+- **Update versions**: Run `python scripts/update_versions.py` (auto-runs weekly on Monday 2 AM UTC)
+
+## Project-Specific Conventions
+
+### Return Value Pattern
+All hook functions return `Tuple[int, str]`:
+- `(0, "")` → Success
+- `(1, output)` → Failure (print output)
+- `(-1, output)` → Dry-run mode (clang-format only, convert to success in main)
+
+### Testing Conventions
+- Use `tmp_path` fixture to avoid modifying repo files
+- Parametrize version tests: `@pytest.mark.parametrize` with versions 16-21
+- Mark performance-sensitive tests with `@pytest.mark.benchmark`
+- Compare formatted output against `testing/good.c` for correctness
+
+### Argument Handling
+```python
+# Standard pattern in both hooks
+parser = ArgumentParser()
+parser.add_argument("--version", default=DEFAULT_VERSION)
+hook_args, other_args = parser.parse_known_args(args)
+# ... install tool if needed ...
+command = ["tool-name"] + other_args  # Pass through unknown args
+```
+
+## Critical Files
+
+- **`pyproject.toml`**: Defines entry points, dependencies, default versions
+- **`versions.py`**: Auto-updated; DO NOT edit manually (see comment)
+- **`.pre-commit-hooks.yaml`**: Hook metadata for pre-commit framework
+- **`testing/run.sh`**: Integration test script used in CI
+
+## Integration Points
+
+### PyPI Dependencies
+- Fetches available versions from `https://pypi.org/pypi/{package}/json`
+- Filters out pre-release versions using regex pattern `(alpha|beta|rc|dev|a\d+|b\d+)`
+- Installs via `subprocess.run([sys.executable, "-m", "pip", "install", f"{tool}=={version}"])`
+
+### Pre-commit Framework
+- Hooks run in parallel (`require_serial: false`) for performance
+- File type filtering via `types_or: [c++, c]`
+- Users configure via `.pre-commit-config.yaml` with `args:` list
+
+## Common Tasks
+
+**Add support for a new argument:**
+1. Add to ArgumentParser in hook module
+2. Pass to subprocess command or handle in Python
+3. Add test case in `tests/test_*.py`
+
+**Update default tool versions:**
+1. Edit `dependencies` in `pyproject.toml`
+2. Run tests to ensure compatibility
+3. Update version in README examples
+
+**Debug hook failures:**
+- Add `--verbose` to clang-format args for detailed output
+- Check `testing/run.sh` for integration test patterns
+- Use `pre-commit run --verbose` for detailed pre-commit logs