# Create a side-by-side HTML word diff between two Git revisions (generated with gpt-6-luna) > Source: > Published: 2026-10-09 08:11:33+00:00 | | #!/usr/bin/env -S uv run --script | | | """Create a side-by-side HTML word diff between two Git revisions.""" | | | import argparse | | | from html import escape | | | from pathlib import Path | | | import re | | | import subprocess | | | import sys | | | MARKER = re.compile(r"(\[-.*?-\]\|\{\+.*?\+\})") | | | def parse_paths(value: str \| None) -> list[str]: | | | """Parse a comma-separated list of paths for the Git pathspec.""" | | | if value is None: | | | return [] | | | paths = [path.strip() for path in value.split(",")] | | | if any(not path for path in paths): | | | raise argparse.ArgumentTypeError("file lists must not contain empty entries") | | | return paths | | | def render_side(line: str, side: str) -> tuple[str, str]: | | | """Render one diff line for the original or new side.""" | | | rendered: list[str] = [] | | | has_deletion = has_addition = has_context = False | | | for part in MARKER.split(line): | | | if not part: | | | continue | | | if part.startswith("[-") and part.endswith("-]"): | | | has_deletion = True | | | if side == "old": | | | rendered.append(f'{escape(part[2:-2])}') | | | elif part.startswith("{+") and part.endswith("+}"): | | | has_addition = True | | | if side == "new": | | | rendered.append(f'{escape(part[2:-2])}') | | | else: | | | has_context \|= bool(part.strip()) | | | rendered.append(escape(part)) | | | cell_class = "" | | | if side == "old" and has_deletion and not has_addition and not has_context: | | | cell_class = ' class="whole-del"' | | | elif side == "new" and has_addition and not has_deletion and not has_context: | | | cell_class = ' class="whole-add"' | | | return "".join(rendered) or "​", cell_class | | | def diff_to_html(diff: str, old: str, new: str) -> str: | | | rows: list[str] = [] | | | for line in diff.splitlines(): | | | if line.startswith("diff --git "): | | | heading = escape(line[len("diff --git ") :]) | | | rows.append(f'{heading}') | | | elif line.startswith("@@ "): | | | rows.append(f'{escape(line)}') | | | elif line.startswith(("index ", "--- ", "+++ ")): | | | rows.append(f'{escape(line)}') | | | else: | | | original, original_class = render_side(line, "old") | | | updated, updated_class = render_side(line, "new") | | | rows.append( | | | f"
{original}
" | | | f"
{updated}
" | | | ) | | | return f''' | | | | | | | | | | | | | | | Diff: {escape(old)} → {escape(new)} | | | | | | | | | | | |
Original: {escape(old)}
New: {escape(new)}
| | |
| | | {chr(10).join(rows)} | | |
| | | | | | | | | ''' | | | def safe_name(revision: str) -> str: | | | """Make a revision label suitable for a default output filename.""" | | | name = re.sub(r"[^A-Za-z0-9._-]+", "-", revision).strip(".-") | | | return name or "revision" | | | def main() -> int: | | | parser = argparse.ArgumentParser( | | | description="Create a side-by-side HTML word diff between two Git revisions." | | | ) | | | parser.add_argument("oldbranch", help="original branch, tag, or commit") | | | parser.add_argument("newbranch", help="new branch, tag, or commit") | | | parser.add_argument( | | | "--only", | | | type=parse_paths, | | | metavar="FILE1,FILE2,...", | | | help="include only these comma-separated paths", | | | ) | | | parser.add_argument( | | | "--exclude", | | | type=parse_paths, | | | metavar="FILE1,FILE2,...", | | | help="exclude these comma-separated paths", | | | ) | | | parser.add_argument( | | | "-o", | | | "--output", | | | type=Path, | | | help="output HTML path (default: OLD-to-NEW.html)", | | | ) | | | args = parser.parse_args() | | | pathspecs: list[str] = [] | | | if args.only: | | | pathspecs.extend(f":(top){path}" for path in args.only) | | | if args.exclude: | | | pathspecs.extend(f":(top,exclude){path}" for path in args.exclude) | | | command = [ | | | "git", | | | "diff", | | | "--ignore-all-space", | | | "--word-diff=plain", | | | args.oldbranch, | | | args.newbranch, | | | "--", | | | *pathspecs, | | | ] | | | try: | | | result = subprocess.run(command, check=True, capture_output=True, text=True) | | | except FileNotFoundError: | | | print("deezer: git was not found; install Git and try again", file=sys.stderr) | | | return 127 | | | except subprocess.CalledProcessError as error: | | | if error.stderr: | | | print(error.stderr, end="", file=sys.stderr) | | | return error.returncode | | | output = args.output or Path( | | | f"{safe_name(args.oldbranch)}-to-{safe_name(args.newbranch)}.html" | | | ) | | | try: | | | output.write_text( | | | diff_to_html(result.stdout, args.oldbranch, args.newbranch), | | | encoding="utf-8", | | | ) | | | except OSError as error: | | | print(f"deezer: cannot write {output}: {error}", file=sys.stderr) | | | return 1 | | | print(f"Wrote {output}") | | | return 0 | | | if __name__ == "__main__": | | | raise SystemExit(main()) |