dash-guard

1// dash-guard: refuses prose that Claude writes with an em dash, an en dash or
2// a double hyphen (which of the three: the banned setting), and tells
3// Claude which lines to rewrite. Code is left alone: fenced blocks, inline
4// code, HTML comments, and files that are not prose. Lines that already had a
5// dash before this call are not reported, so old files can still be edited.
6//
7// It is a style rule, not a safety gate, so a hook failure lets the call
8// through (no .catch).
9
10const PROSE_FILE = /\.(md|mdx|markdown|txt)$/i
11const MAX_REPORTED = 8
12
13// Exactly two hyphens used as punctuation: "a -- b", "a--b", "end--". A CLI flag such as
14// " --force" (a space or start of line before, a letter after) is not punctuation.
15const DOUBLE_HYPHEN = /(?<!-)--(?![-\w])|(?<=\w)--(?=\w)/
16
17let enabled = true
18// From the settings: which marks are refused, and which MCP tools are checked besides Write and Edit
19let banned = new Set(['em', 'en', 'double'])
20let mcpTools = null
21const LABEL = { em: 'em dashes', en: 'en dashes', double: 'double hyphens' }
22
23export function configure(options) {
24  const want = String(options?.banned ?? '').split(',').map((x) => x.trim().toLowerCase()).filter((x) => x in LABEL)
25  banned = new Set(want.length ? want : ['em', 'en', 'double'])
26  mcpTools = null
27  const pattern = String(options?.tools ?? '').trim()
28  if (pattern) {
29    try {
30      mcpTools = new RegExp(pattern)
31    } catch {
32      // An invalid pattern checks Write and Edit only
33    }
34  }
35}
36
37export function register(on, options) {
38  configure(options)
39  on('session.start', async ($, e, next) => {
40    await $.command.register({
41      name: 'dash-guard',
42      description: 'dash-guard on, off, or status for this session',
43      argumentHint: '[on|off]',
44    })
45    return next(e)
46  })
47
48  on('command.run', { command: 'dash-guard' }, async ($, e) => {
49    const arg = String(e.args ?? '').trim().toLowerCase()
50    if (arg === 'off') enabled = false
51    if (arg === 'on') enabled = true
52    return { text: 'dash-guard is ' + (enabled ? 'on' : 'off') + ' for this session' }
53  })
54
55  on('tool.call', { tool: ['Write', 'Edit'] }, async ($, e, next) => {
56    if (!enabled || !PROSE_FILE.test(String(e.file_path ?? ''))) return next(e)
57    let before = ''
58    if (e.tool === 'Edit') {
59      before = e.old_string ?? ''
60    } else {
61      try {
62        before = await $.fs.read(e.file_path)
63      } catch {
64        // A new file: nothing was there before
65      }
66    }
67    const text = e.tool === 'Edit' ? e.new_string : e.content
68    const found = findDashes(text, before)
69    return found.length ? { deny: denyText(e.file_path, found) } : next(e)
70  })
71
72  // MCP tools that write prose (a document, an email, a message), named by the tools setting
73  on('tool.call', { tool: /^mcp__/ }, async ($, e, next) => {
74    if (!enabled || !mcpTools || !mcpTools.test(e.tool)) return next(e)
75    const { tool, tool_use_id, agentId, ...args } = e
76    const found = []
77    for (const s of strings(args)) found.push(...findDashes(s, ''))
78    return found.length ? { deny: denyText(tool.replace(/^mcp__/, ''), found) } : next(e)
79  })
80}
81
82// Every string inside the arguments, however deeply nested
83function strings(v) {
84  if (typeof v === 'string') return [v]
85  if (Array.isArray(v)) return v.flatMap(strings)
86  if (v && typeof v === 'object') return Object.values(v).flatMap(strings)
87  return []
88}
89
90// Blanks out code so its dashes are not reported: fenced blocks (also indented ones inside a
91// list), inline code, HTML comments.
92// Newlines are kept, so line numbers still match the original text.
93export function stripCode(text) {
94  const blank = (m) => m.replace(/[^\n]/g, ' ')
95  return String(text)
96    .replace(/^[ \t]*(```|~~~)[^\n]*\n[\s\S]*?(^[ \t]*\1[^\n]*$|(?![\s\S]))/gm, blank)
97    .replace(/<!--[\s\S]*?-->/g, blank)
98    .replace(/`[^`\n]+`/g, blank)
99}
100
101// Lines of `text` holding an em dash, an en dash or exactly two hyphens, skipping code and
102// any line that already appears in `before`. Returns [{ line, kind, text }].
103export function findDashes(text, before) {
104  const old = new Set(String(before ?? '').split('\n').map((l) => l.trim()))
105  const raw = String(text ?? '').split('\n')
106  const clean = stripCode(text).split('\n')
107  const found = []
108  clean.forEach((l, i) => {
109    const kinds = []
110    if (banned.has('em') && l.includes('—')) kinds.push('em dash')
111    if (banned.has('en') && l.includes('–')) kinds.push('en dash')
112    if (banned.has('double') && DOUBLE_HYPHEN.test(l)) kinds.push('double hyphen')
113    if (kinds.length && !old.has(raw[i].trim())) found.push({ line: i + 1, kind: kinds.join(', '), text: raw[i].trim() })
114  })
115  return found
116}
117
118function denyText(where, found) {
119  const shown = found.slice(0, MAX_REPORTED).map((f) => '  line ' + f.line + ' (' + f.kind + '): ' + clip(f.text))
120  const more = found.length > MAX_REPORTED ? ['  and ' + (found.length - MAX_REPORTED) + ' more'] : []
121  return [
122    'dash-guard: nothing was written to ' + where + '. The user\'s style rule forbids ' + [...banned].map((k) => LABEL[k]).join(', ') + ' in prose.',
123    ...shown,
124    ...more,
125    'Rewrite those lines: split into a new sentence, or use a comma, colon or parentheses. Put CLI flags and code in backticks. Then try again.',
126  ].join('\n')
127}
128
129function clip(s) {
130  return s.length > 140 ? s.slice(0, 140) + '...' : s
131}
132