Patch Generate & Apply Skill

Generates and applies unified diff patches for code fixes.

When to Use

• You need to generate a patch file from code changes
• You need to apply a .diff/.patch file to a repository
• Automating code fixes via the diff/patch workflow

Workflow

1. Generate diff using generate_unified_diff() with a/b prefixes
2. Handle EOF using handle_no_newline_at_eof() for POSIX compliance
3. Write patch using write_patch_file() to create patch_N.diff
4. Apply patch using apply_patch() with git apply and fallbacks
5. Validate using validate_patch_applied() to confirm changes
6. Batch apply using apply_all_patches() for multiple patches

Key Functions

All functions are in scripts/patch.py:

• generate_unified_diff(original, modified, file_path) - Creates git-compatible unified diff
• handle_no_newline_at_eof(diff_lines) - Adds missing EOF newline markers
• write_patch_file(diff_content, output_dir, index) - Writes patch_N.diff
• apply_patch(patch_path, target_dir) - Applies via git apply with fallbacks
• validate_patch_applied(file_path, expected_content) - Confirms patch worked
• apply_all_patches(patch_dir, target_dir) - Applies all patches in order

Important Notes

• Use splitlines(keepends=True) to preserve trailing newlines
• Always add a/ and b/ prefixes for git apply compatibility
• Handle "No newline at end of file" marker manually
• git apply uses -p1 by default to strip a/ b/ prefixes
• Use --3way flag as fallback for context mismatches

Reference

See references/domain_reference.md for detailed domain knowledge.