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#!/usr/bin/env bun
/**
* Fails on the three comment patterns that are never documentation:
*
* - `banner`: a separator comment — `// ====`, `// --- Section ---`, `// ─── Title ───`,
* `/* ------ v2 ------ *\/`. The repo convention is "no separators": structure lives in the
* code (modules, functions, TSDoc), and a banner only restates the next declaration's name.
* - `commented-out-code`: a run of `//` lines whose text parses as TypeScript. Git is the
* history; dead code left in a comment rots, misleads readers and agents into thinking it
* is a live option, and survives every refactor of the code around it.
* - `eslint-directive`: an `eslint-disable` / `eslint-enable` comment. The repo lints with Biome
* and nothing runs ESLint, so the directive suppresses nothing; it only misleads a reader into
* thinking a rule is enforced and deliberately waived here. Biome's form is `// biome-ignore`.
*
* Banners and commented-out code are detected conservatively so a hit is almost always real.
* Comments are read from the Babel token stream, so `//` inside strings and template literals is
* never inspected. A commented-out run only counts when it parses with no recovery errors, contains code
* punctuation, and is not a lone label (`firstRow: bold`), literal, or `a = b` gloss; prose
* lines inside a comment group split it into separate runs. Change-history phrasing
* ("previously", "no longer", "used to") was measured and left out: most hits describe live
* runtime state or a regression a test guards, so it cannot be enforced without false alarms.
*
* A legitimate exception (a code sample that must stay a line comment) takes
* `// comment-hygiene-allow: <reason>` anywhere in the same comment group.
*
* The tree was swept clean when each rule landed (236 banners, 9 commented-out blocks, 89
* ESLint directives), so there is no baseline: every hit fails.
*
* Run: `bun run check:comment-hygiene`
*/
import { execFileSync } from 'node:child_process'
import { readFileSync } from 'node:fs'
import path from 'node:path'
import { fileURLToPath } from 'node:url'
import { parse } from '@babel/parser'
import { getErrorMessage } from '@sim/utils/errors'
const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..')
const ALLOW = 'comment-hygiene-allow:'
/** Vendored or generated sources whose comments are not ours to edit. */
const EXCLUDED = [/\.d\.ts$/, /(^|\/)bundles\//, /(^|\/)node_modules\//]
export type Rule = 'banner' | 'commented-out-code' | 'eslint-directive'
export interface Violation {
rule: Rule
line: number
text: string
}
/** Comment text that opens with a run of separator characters. */
const BANNER = /^(?:={3,}|-{3,}|─{3,}|━{3,}|\*{3,}|~{3,})/
/** Comment text that is an ESLint suppression directive. */
const ESLINT_DIRECTIVE = /^eslint-(?:disable|enable)\b/
/** At least one token that ordinary prose does not contain. */
const CODE_PUNCTUATION = /[;{}]|=>|\b(?:const|let|return|await|import|export)\s|\w\.\w+\(/
/** Single-line runs must start like a statement or end like a call to count as code. */
const SINGLE_LINE_CODE = /^(?:export|import|const|let|var|return|await|if|for|function)\b|\);?$/
/**
* A line that reads as prose: a capitalized word followed by more words, without a trailing
* code delimiter. These split a comment group, so a prose heading above commented-out code
* does not stop the code from parsing.
*/
const PROSE_LINE = /^[A-Z][\w'-]*(?:\s+[\w'(),./&:—-]+)+\s*$/
const CODE_TAIL = /[;{}]\s*$|[,([]$/
/** Expression kinds that a one-off gloss like `Total = 22` or a bare word would parse as. */
const TRIVIAL_EXPRESSIONS = new Set([
'TemplateLiteral',
'StringLiteral',
'Identifier',
'NumericLiteral',
'BinaryExpression',
'AssignmentExpression',
])
function parsesAsCode(text: string, jsx: boolean): boolean {
const plugins = jsx ? (['typescript', 'jsx'] as const) : (['typescript'] as const)
for (const candidate of [text, `[${text}]`, `({${text}})`]) {
let program
try {
program = parse(candidate, {
sourceType: 'module',
plugins: [...plugins],
allowReturnOutsideFunction: true,
allowAwaitOutsideFunction: true,
}).program
} catch {
continue
}
if (candidate !== text) return true
const trivial = program.body.every(
(node) =>
node.type === 'LabeledStatement' ||
node.type === 'EmptyStatement' ||
(node.type === 'ExpressionStatement' && TRIVIAL_EXPRESSIONS.has(node.expression.type))
)
return !trivial
}
return false
}
interface LineComment {
line: number
value: string
ownLine: boolean
}
/** Splits a group of adjacent own-line `//` comments into runs of non-prose lines. */
function codeRuns(group: LineComment[]): LineComment[][] {
const runs: LineComment[][] = []
let current: LineComment[] | null = null
for (const comment of group) {
const text = comment.value.trim()
const prose = text.startsWith('//') || (PROSE_LINE.test(text) && !CODE_TAIL.test(text))
if (!text || prose) {
current = null
continue
}
if (!current) {
current = []
runs.push(current)
}
current.push(comment)
}
return runs
}
/** Longest run a span search considers; the search is quadratic in run length. */
const MAX_RUN_LINES = 80
function isCode(span: LineComment[], jsx: boolean): boolean {
const text = span
.map((comment) => comment.value.replace(/^ /, ''))
.join('\n')
.trim()
if (!CODE_PUNCTUATION.test(text)) return false
if (span.length === 1 && !SINGLE_LINE_CODE.test(text)) return false
return parsesAsCode(text, jsx)
}
/**
* The first contiguous span of a run that parses as code. A run can hold two unrelated
* snippets back to back (an object, then a type), which only parse separately, so every start
* line is tried against every end line, longest first.
*/
function firstCodeSpan(run: LineComment[], jsx: boolean): LineComment | undefined {
const lines = run.slice(0, MAX_RUN_LINES)
for (let start = 0; start < lines.length; start++) {
for (let end = lines.length; end > start; end--) {
if (isCode(lines.slice(start, end), jsx)) return lines[start]
}
}
return undefined
}
/**
* A superset of every hit: a separator or ESLint directive right after a comment opener, or a
* `//` line holding a {@link CODE_PUNCTUATION} token. Files without one skip the parse, which
* dominates the run.
*/
const MAY_VIOLATE =
/\/[/*][*\s]*(?:={3}|-{3}|─{3}|━{3}|\*{3}|~{3}|eslint-(?:disable|enable))|\/\/[^\n]*(?:[;{}]|=>|\b(?:const|let|return|await|import|export)\b|\w\.\w+\()/
/** Every comment-hygiene hit in one source file. */
export function findViolations(file: string, source: string): Violation[] {
if (!MAY_VIOLATE.test(source)) return []
const jsx = /\.[jt]sx$/.test(file)
let comments
try {
comments =
parse(source, {
sourceType: 'module',
plugins: ['typescript', ...(jsx ? (['jsx'] as const) : []), 'decorators'],
errorRecovery: true,
}).comments ?? []
} catch (error) {
throw new Error(`Cannot parse ${file} to check its comments: ${getErrorMessage(error)}`)
}
const lines = source.split('\n')
const violations: Violation[] = []
const groups: LineComment[][] = []
let previous: LineComment | undefined
for (const comment of comments) {
const line = comment.loc?.start.line ?? 0
const directive = comment.value.replace(/^\*+/, '').trim()
if (ESLINT_DIRECTIVE.test(directive)) {
violations.push({ rule: 'eslint-directive', line, text: directive })
previous = undefined
continue
}
if (comment.type === 'CommentBlock') {
const singleLine = comment.loc?.start.line === comment.loc?.end.line
const text = comment.value.replace(/^\*+/, '').trim()
if (singleLine && BANNER.test(text)) violations.push({ rule: 'banner', line, text })
previous = undefined
continue
}
const text = comment.value.trim()
if (BANNER.test(text)) {
violations.push({ rule: 'banner', line, text })
previous = undefined
continue
}
const ownLine = /^\s*$/.test(lines[line - 1]?.slice(0, comment.loc?.start.column ?? 0) ?? '')
const entry = { line, value: comment.value, ownLine }
if (ownLine && previous?.ownLine && previous.line === line - 1) {
groups[groups.length - 1].push(entry)
} else if (ownLine) {
groups.push([entry])
}
previous = entry
}
for (const group of groups) {
if (group.some((comment) => comment.value.includes(ALLOW))) continue
for (const run of codeRuns(group)) {
const hit = firstCodeSpan(run, jsx)
if (hit)
violations.push({ rule: 'commented-out-code', line: hit.line, text: hit.value.trim() })
}
}
return violations.sort((a, b) => a.line - b.line)
}
function sourceFiles(): string[] {
return execFileSync(
'git',
[
'ls-files',
'--cached',
'--others',
'--exclude-standard',
'*.ts',
'*.tsx',
'*.mts',
'*.cts',
'*.mjs',
'*.cjs',
],
{
cwd: ROOT,
encoding: 'utf8',
// The listing is already ~1 MB, the default execFileSync ceiling.
maxBuffer: 64 * 1024 * 1024,
}
)
.split('\n')
.filter((file) => file && !EXCLUDED.some((pattern) => pattern.test(file)))
}
const FIX: Record<Rule, string> = {
banner:
'delete the separator; if the title says something the code does not, keep it as a plain ' +
'`// ...` line or move it into TSDoc on the declaration below',
'commented-out-code':
'delete the commented-out code — git keeps the history. If it is a deliberate code sample, ' +
'put it in a TSDoc `@example` or add `// comment-hygiene-allow: <reason>` to the group',
'eslint-directive':
'delete it — nothing runs ESLint. Keep any reason it carried as a plain `// ...` why; ' +
'to waive a Biome rule, use `// biome-ignore <rule>: <reason>`',
}
function main(): void {
const hits: string[] = []
for (const file of sourceFiles()) {
let source: string
try {
source = readFileSync(path.join(ROOT, file), 'utf8')
} catch {
continue
}
for (const { rule, line, text } of findViolations(file, source)) {
hits.push(`✗ ${rule}: ${file}:${line} // ${text}\n fix: ${FIX[rule]}`)
}
}
if (hits.length === 0) {
console.log('✓ comment hygiene (no banners, commented-out code, or ESLint directives)')
return
}
console.error(hits.join('\n'))
console.error(
`\n${hits.length} comment-hygiene violation(s). Comments are TSDoc or a terse inline why — ` +
'see "Comments" in CLAUDE.md.'
)
process.exit(1)
}
if (import.meta.main) main()