commit-style

1import type { Register } from 'claude-code'
2import { RULES, extractMessage, findProblems } from './message'
3
4export const register: Register = on => {
5  on('attribution.text', { kind: 'commit' }, () => ({ text: '' }))
6
7  on('prompt.compose', async ($, e, next) => {
8    const { sections } = await next(e)
9    return {
10      sections: [
11        ...sections,
12        { id: `${$.plugin.name}:rules`, text: RULES, scope: 'session' },
13      ],
14    }
15  })
16
17  on('tool.call', { tool: 'Bash' }, ($, e, next) => {
18    const message = extractMessage(e.command)
19    const problems = message === null ? [] : findProblems(message)
20    return problems.length > 0
21      ? {
22          deny: `${$.plugin.name}: fix the commit message:\n- ${problems.join('\n- ')}`,
23        }
24      : next(e)
25  }).catch(($, e, next) => next(e))
26}
27

1const SUBJECT_MAX = 50
2const BODY_MAX = 72
3
4const CONVENTIONAL =
5  /^(feat|fix|docs|style|refactor|perf|tests?|build|ci|chore|revert)(\([^)]*\))?!?:/i
6const TRAILER = /^co-authored-by:/im
7const GIT_COMMIT = /\bgit\b(\s+-\S+(\s+[^-\s]\S*)?)*\s+commit\b/
8const HEREDOC = /<<-?\s*(['"]?)(\w+)\1[^\n]*\n([\s\S]*?)\n\s*\2\b/
9const MESSAGE_FLAG =
10  /(?:^|\s)(?:-m|--message)(?:=|\s+)("((?:[^"\\]|\\.)*)"|'([^']*)')/g
11
12export const RULES = `\
13When writing a git commit message:
14- The subject is "scope: summary in imperative mood", e.g. \
15"cfg/tmux: give panes an explicit foreground". Use a scope when the \
16repository's history uses them; never a conventional commits type such as \
17"feat:", "fix:" or "chore(x):".
18- The subject is at most ${SUBJECT_MAX} characters, with no trailing period.
19- If a body is needed, leave a blank line after the subject, then write the \
20body in third person ("Moves the search box so it no longer..."), wrapped \
21at ${BODY_MAX} characters.
22- Never add a Co-Authored-By trailer or any other attribution lines.`
23
24const unescapeDouble = (text: string): string =>
25  text.replace(/\\([\\"$`])/g, '$1')
26
27/** The message a `git commit` command passes inline, or null if none. */
28export const extractMessage = (command: string): string | null => {
29  if (!GIT_COMMIT.test(command)) {
30    return null
31  }
32  const heredoc = HEREDOC.exec(command)
33  if (heredoc) {
34    return heredoc[3]
35  }
36  const parts = [...command.matchAll(MESSAGE_FLAG)].map(m =>
37    m[2] !== undefined ? unescapeDouble(m[2]) : m[3],
38  )
39  return parts.length > 0 ? parts.join('\n\n') : null
40}
41
42/** Why the message breaks the house style, one line per problem. */
43export const findProblems = (message: string): string[] => {
44  const lines = message.trim().split('\n')
45  const subject = lines[0].trim()
46  const problems: string[] = []
47
48  if (TRAILER.test(message)) {
49    problems.push('remove the Co-Authored-By trailer')
50  }
51  if (CONVENTIONAL.test(subject)) {
52    problems.push(
53      'do not use conventional commits; write "scope: imperative summary"',
54    )
55  }
56  if (subject.length > SUBJECT_MAX) {
57    problems.push(
58      `shorten the subject to ${SUBJECT_MAX} characters (it has ${subject.length})`,
59    )
60  }
61  if (lines.length > 1 && lines[1].trim() !== '') {
62    problems.push('leave a blank line between the subject and the body')
63  }
64  const longLines = lines
65    .slice(1)
66    .filter(line => line.length > BODY_MAX && /\s/.test(line.trim()))
67  if (longLines.length > 0) {
68    problems.push(
69      `wrap the body at ${BODY_MAX} characters (${longLines.length} line(s) are longer)`,
70    )
71  }
72  return problems
73}
74