Add comprehensive GitHub Copilot instructions for cpp-linter-hooks development

.github/copilot-instructions.md

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+# cpp-linter-hooks
+
+`cpp-linter-hooks` is a Python package that provides pre-commit hooks for C/C++ code formatting and linting using `clang-format` and `clang-tidy`. The hooks automatically install specific versions of these tools as Python wheel packages and format/lint C/C++ code.
+
+Always reference these instructions first and fallback to search or bash commands only when you encounter unexpected information that does not match the info here.
+
+## Working Effectively
+
+### Bootstrap and Setup
+- **Install dependencies**: 
+  - `python -m pip install --upgrade pip` -- takes ~5 seconds
+  - `pip install .[dev]` -- takes ~10 seconds to install development dependencies
+  - `pip install .[tools]` -- installs clang-format==21.1.0 and clang-tidy==21.1.0, takes ~2 seconds (may fail due to network timeouts in sandboxed environments)
+  - **Alternative for clang tools**: `pip install clang-format==21.1.0 clang-tidy==21.1.0` -- more reliable installation method
+
+### Build and Test Process  
+- **NEVER CANCEL builds or test commands**: The test suite takes 5.5 minutes. Set timeout to 10+ minutes.
+- **Run tests**: `coverage run --source=tests,cpp_linter_hooks -m pytest -vv` -- takes 5.5 minutes. NEVER CANCEL.
+- **Coverage report**: `coverage report` -- shows test coverage (typically 94%+)
+- **Python linting**: 
+  - `pip install ruff` (if not already installed)
+  - `ruff check .` -- takes <1 second, must pass
+  - `ruff format --check .` -- takes <1 second, checks code formatting
+
+### Testing the Hooks Manually
+- **Test clang-format hook directly**: 
+  - `clang-format-hook --version 21 --verbose /path/to/test.c` -- formats C/C++ files
+  - Requires `--version` parameter to avoid version checking issues
+- **Test clang-tidy hook directly**: 
+  - `clang-tidy-hook --version 21 /path/to/test.c` -- analyzes C/C++ files
+  - May show compilation database warnings (normal for standalone files)
+
+### Pre-commit Environment Issues
+- **Known Issue**: Pre-commit environment setup may fail with network timeouts in sandboxed environments when downloading clang tools
+- **Workaround**: Test hooks directly using the manual commands above
+- **CI Environment**: The GitHub Actions CI works correctly with longer timeouts
+
+## Validation
+
+### Required Validation Steps
+- **ALWAYS run the full test suite** after making changes: `coverage run --source=tests,cpp_linter_hooks -m pytest -vv` (5.5 minutes)
+- **ALWAYS run Python linting** before committing: `ruff check .` and `ruff format --check .`
+- **ALWAYS test both hooks manually** with sample C++ files using the direct hook commands
+- **Test end-to-end scenarios**: Create a malformed C++ file, run clang-format hook, verify it gets formatted correctly
+
+### Manual Testing Scenario
+```bash
+# Create test file with poor formatting
+echo '#include <stdio.h>
+int main() {for (;;) break; printf("Hello world!\n");return 0;}' > /tmp/test.c
+
+# Test clang-format (should reformat the file)
+clang-format-hook --version 21 --verbose /tmp/test.c
+
+# Verify file was formatted (should show properly indented code)
+cat /tmp/test.c
+
+# Test clang-tidy (should run without errors)
+clang-tidy-hook --version 21 /tmp/test.c
+```
+
+## Project Structure
+
+### Key Directories and Files
+```
+.
+├── cpp_linter_hooks/          # Main package source code
+│   ├── __init__.py
+│   ├── clang_format.py        # clang-format hook implementation  
+│   ├── clang_tidy.py         # clang-tidy hook implementation
+│   └── util.py               # Shared utilities for tool installation
+├── tests/                    # Unit tests (73 tests total)
+│   ├── test_clang_format.py
+│   ├── test_clang_tidy.py  
+│   └── test_util.py
+├── testing/                  # Integration testing and examples
+│   ├── run.sh               # Integration test script
+│   ├── main.c               # Test C file (poorly formatted)
+│   ├── good.c               # Well-formatted test file
+│   ├── .clang-format        # Example clang-format config
+│   ├── .clang-tidy          # Example clang-tidy config
+│   └── pre-commit-config*.yaml # Example pre-commit configurations
+├── .github/workflows/        # CI/CD pipelines
+│   ├── test.yml             # Main test workflow  
+│   ├── pre-commit.yml       # Pre-commit validation
+│   └── publish.yml          # Package publishing
+├── pyproject.toml           # Package configuration and dependencies
+├── .pre-commit-hooks.yaml   # Hook definitions for pre-commit
+└── .pre-commit-config.yaml  # Repository's own pre-commit config
+```
+
+### Entry Points
+- `clang-format-hook` → `cpp_linter_hooks.clang_format:main`
+- `clang-tidy-hook` → `cpp_linter_hooks.clang_tidy:main`
+
+## Common Commands Reference
+
+### Repository Root Contents
+```bash
+ls -la
+# .github/         - GitHub workflows and configurations
+# cpp_linter_hooks/ - Main Python package source
+# docs/            - Documentation (migration notes)
+# testing/         - Integration tests and examples  
+# tests/           - Unit tests
+# pyproject.toml   - Package configuration
+# .pre-commit-hooks.yaml - Hook definitions
+# README.md        - Main documentation
+```
+
+### Package Configuration (pyproject.toml)
+- **Python support**: 3.9-3.14
+- **Main dependencies**: setuptools>=45.0.0, tomli (Python <3.11)
+- **Dev dependencies**: coverage, pre-commit, pytest, pytest-codspeed
+- **Optional clang tools**: clang-format==21.1.0, clang-tidy==21.1.0
+
+### Common Workflow Times
+- **Dependency installation**: ~10-15 seconds
+- **Test suite execution**: 5.5 minutes (NEVER CANCEL - use 10+ minute timeouts)
+- **Python linting**: <1 second
+- **Hook execution**: <1 second per file
+- **Coverage reporting**: <1 second
+
+## Troubleshooting
+
+### Version Checking Issues
+- **Problem**: Hook fails with version checking TypeError
+- **Solution**: Always specify `--version 21` parameter when testing hooks directly
+
+### Network Timeout Issues  
+- **Problem**: Pre-commit environment setup fails with pip timeout errors
+- **Cause**: Downloading large clang tool packages in sandboxed environments
+- **Workaround**: Test functionality using direct hook commands instead of pre-commit
+
+### Test Environment Setup
+- **Always install dev dependencies first**: `pip install .[dev]`
+- **Separately install clang tools**: `pip install clang-format==21.1.0 clang-tidy==21.1.0`
+- **Verify installation**: Check that `clang-format-hook --help` and `clang-tidy-hook --help` work
+
+## CI/CD Pipeline Notes
+
+- **GitHub Actions**: Uses Python 3.9-3.14 matrix testing
+- **Test timeout**: Set to allow 5.5+ minutes for full test suite
+- **Pre-commit CI**: May encounter timeout issues in certain environments
+- **Publishing**: Automated via GitHub Actions on releases