agent-skills/hooks/comment-lint.py

#!/usr/bin/env python3
"""PostToolUse nudge for code comments: Write / Edit / MultiEdit.

Lints ONLY the newly-added text against the "Code comments" contract in
~/.claude/writing.md, so legacy files are not re-flagged on every touch.

Exit 0 = silent. Exit 2 = stderr goes back to Claude as feedback; the edit is
already applied, so this is a revise-it nudge, not a block.
Fails open on anything it cannot parse.
"""
import json
import os
import re
import sys

MAX_COMMENT_RUN = 3  # contract budget; past this you are teaching, not warning

CODE_EXT = {
    ".ts", ".tsx", ".js", ".jsx", ".mjs", ".cjs", ".py", ".rs", ".go", ".sol",
    ".sh", ".bash", ".zsh", ".c", ".h", ".cc", ".cpp", ".hpp", ".java", ".kt",
    ".rb", ".lua", ".zig", ".nix", ".swift", ".php", ".cs", ".scala", ".ex",
}

COMMENT_RE = re.compile(r"^\s*(//+|#+|/\*+|\*+/?|--|;;?)\s?(.*)$")
# Only match syntax the language actually has. In a hash-comment language a `//` or `*` line is
# almost always a string literal holding code for another language, and linting it flags text the
# script is deleting rather than text it is adding.
HASH_ONLY_EXT = {".py", ".sh", ".bash", ".zsh", ".rb", ".ex", ".nix"}
HASH_RE = re.compile(r"^\s*(#+)\s?(.*)$")

# Design rationale, alternatives, history: capped at 1-2 lines, belongs in docs.
DOC_IN_SOURCE = [
    (r"rejected alternative", "rejected alternatives belong in docs/ or an ADR"),
    (r"alternatives?\s+(considered|rejected|from)", "alternatives belong in docs/ or an ADR"),
    (r"\bit used to\b", "history belongs in the commit message"),
    (r"\bused to (say|be|read|return|live|call)\b", "history belongs in the commit message"),
    (r"\b(this|it|that) was\b.{0,50}\buntil\b", "history belongs in the commit message"),
    (r"\bpreviously[, ]+(this|it|we|the)\b", "history belongs in the commit message"),
    (r"\b(originally|historically)\b", "history belongs in the commit message"),
    (r"\bthe reason (we|this module|this file|it is here|this exists)\b",
     "rationale belongs in docs/ or an ADR"),
    (r"\bwe (chose|picked|went with|settled on)\b", "rationale belongs in docs/ or an ADR"),
    (r"\bwhy (it|this) (exists|is here|lives here)\b", "rationale belongs in docs/ or an ADR"),
    (r"\brather than (standing apart|widening)\b", "rationale belongs in docs/ or an ADR"),
]

# A line that points at the doc is the fix the rule asks for, not a violation of it.
CITES_DOC = re.compile(r"docs?/|\.md\b|\bADR[- ]?\d|\bsee `", re.I)

# Deliberately narrow. `genuinely` was tried here and removed: "genuinely liquidatable",
# "a genuinely DIVERGED node" and "genuinely 1:1" all mean actually-not-apparently, so flagging it
# only rewrites correct prose.
SUPERLATIVE = [
    r"\bsingle most\b",
    r"\bmost consequential\b",
    r"\bthe (whole|entire) point\b",
    r"\bworth (money|noting)\b",
]


def fail_open(msg=""):
    if msg and os.environ.get("COMMENT_LINT_DEBUG"):
        print(f"comment-lint: {msg}", file=sys.stderr)
    sys.exit(0)


def added_text(tool_input):
    """Text this edit introduced, or None if there is nothing to lint."""
    if "content" in tool_input:
        return tool_input["content"]
    if "new_string" in tool_input:
        return tool_input["new_string"]
    edits = tool_input.get("edits")
    if isinstance(edits, list):
        parts = [e.get("new_string", "") for e in edits if isinstance(e, dict)]
        return "\n".join(parts) if parts else None
    return None


def comment_lines(text, ext=""):
    """[(index, body)] for lines that are wholly a comment."""
    pattern = HASH_RE if ext in HASH_ONLY_EXT else COMMENT_RE
    out = []
    for i, line in enumerate(text.splitlines()):
        m = pattern.match(line)
        if m and line.strip() not in ("*/", "/*"):
            out.append((i, m.group(2)))
    return out


def longest_run(indices):
    best = run = 0
    prev = None
    for i in indices:
        run = run + 1 if prev is not None and i == prev + 1 else 1
        best = max(best, run)
        prev = i
    return best


def lint(text, ext=""):
    """(problems, notes). Problems demand a revise; notes are advisory only."""
    lines = comment_lines(text, ext)
    if not lines:
        return [], []

    problems = []
    notes = []
    run = longest_run([i for i, _ in lines])
    if run > MAX_COMMENT_RUN:
        notes.append(
            f"{run}-line comment block just written. Fine IF it explains code a reader "
            "would otherwise misread (subtle math, ordering, encoding, a line that looks "
            "wrong). Not fine if it argues for a design — that is a doc."
        )

    blob = "\n".join(body for _, body in lines)
    lowered = blob.lower()

    prose = "\n".join(body for _, body in lines if not CITES_DOC.search(body))
    seen = set()
    for pattern, advice in DOC_IN_SOURCE:
        m = re.search(pattern, prose.lower())
        if m and advice not in seen:
            seen.add(advice)
            problems.append(f'"{m.group(0)}" in a comment — {advice}. Cite the path instead.')

    hits = [m.group(0) for p in SUPERLATIVE for m in [re.search(p, lowered)] if m]
    if hits:
        problems.append(f"Superlatives in comments: {', '.join(sorted(set(hits)))}. Cut them.")

    if "**" in blob:
        problems.append("Bold inside a comment. No emphasis in comments.")

    return problems, notes


def main():
    try:
        payload = json.load(sys.stdin)
    except (json.JSONDecodeError, ValueError):
        fail_open("unparseable payload")

    if payload.get("tool_name") not in ("Write", "Edit", "MultiEdit"):
        fail_open()

    tool_input = payload.get("tool_input", {})
    path = tool_input.get("file_path", "")
    if os.path.splitext(path)[1] not in CODE_EXT:
        fail_open(f"not a code file: {path}")

    text = added_text(tool_input)
    if not text:
        fail_open("no added text")

    problems, notes = lint(text, os.path.splitext(path)[1])
    name = os.path.basename(path)

    if problems:
        lines = [f"Comment contract (~/.claude/writing.md) — {name}:", ""]
        lines += [f"  - {p}" for p in problems + notes]
        lines += ["", "Trim what you just wrote, or say why it stays."]
        print("\n".join(lines), file=sys.stderr)
        sys.exit(2)

    if notes:
        # Advisory only: a long comment can be correct, so this reaches context
        # without forcing a revise cycle.
        print(json.dumps({
            "suppressOutput": True,
            "hookSpecificOutput": {
                "hookEventName": "PostToolUse",
                "additionalContext": f"Comment check ({name}): " + " ".join(notes),
            },
        }))
    sys.exit(0)


if __name__ == "__main__":
    main()