What causes "pattern (?x) not supported" in neoclide/coc.nvim?

Remove (?x) and collapse the pattern to a single line.

pattern (?x) not supported

Error message

pattern (?x) not supported

What it means

Python's (?x) verbose/extended-mode inline flag is unsupported in the JS regex conversion for snippet transforms. The converter throws at parse time to avoid compiling a pattern whose whitespace/comment semantics would differ in JavaScript.

Source

Thrown at src/snippets/util.ts:78

const conditionRe = /\(\?\(\w+\).+\|/
const commentRe = /\(\?#.*?\)/
const namedCaptureRe = /\(\?P<\w+>.*?\)/
const namedReferenceRe = /\(\?P=(\w+)\)/
const regex = new RegExp(`${commentRe.source}|${stringStartRe.source}|${namedCaptureRe.source}|${namedReferenceRe.source}`, 'g')

/**
 * Convert python regex to javascript regex,
 * throw error when unsupported pattern found
 */
export function convertRegex(str: string): string {
  if (str.indexOf('\\z') !== -1) {
    throw new Error('pattern \\z not supported')
  }
  if (str.indexOf('(?s)') !== -1) {
    throw new Error('pattern (?s) not supported')
  }
  if (str.indexOf('(?x)') !== -1) {
    throw new Error('pattern (?x) not supported')
  }
  if (str.indexOf('\n') !== -1) {
    throw new Error('pattern \\n not supported')
  }
  if (conditionRe.test(str)) {
    throw new Error('pattern (?id/name)yes-pattern|no-pattern not supported')
  }
  return str.replace(regex, (match, p1) => {
    if (match.startsWith('(?#')) return ''
    if (match.startsWith('(?P<')) return '(?' + match.slice(3)
    if (match.startsWith('(?P=')) return `\\k<${p1}>`
    // if (match == '\\A') return '^'
    return '^'
  })
}

/**
 * Action code from context or option

View on GitHub (pinned to 50e974d969)

Solutions

Remove (?x) and collapse the pattern to a single line.
Strip insignificant whitespace and comments from the pattern manually.
Simplify the transform regex.
Test the snippet after edit via snippetManager to confirm parsing succeeds.

Example fix

// before
'${1/(?x) foo \\d+ /x/}'
// after
'${1/ foo \\d+ /x/}'

Defensive patterns

Strategy: validation

Validate before calling

function regexIsPortable(pattern: string): boolean {
  return !pattern.includes('(?x)')
}

Type guard

null

Try / catch

try {
  let js = convertRegex(pattern)
} catch (e) {
  if (String(e.message).includes('(?x)')) pattern = collapseVerboseRegex(pattern) // strip whitespace/comments
}

Prevention

Flatten verbose regexes to a single line before porting.
Remove comments/whitespace from patterns.
Prefer simple transforms in snippets.
Validate snippets with the parser before distribution.

When it happens

Trigger: A snippet transform regex containing (?x) or free-spacing formatting (whitespace/comments in the pattern).

Common situations: Snippets copied from Python-based snippet engines (UltiSnips) that use verbose regexes.

Related errors

AI-assisted analysis of neoclide/coc.nvim@50e974d969 (2026-08-31). Data as JSON: /api/errors/8ae52b4621af21d1. Report an issue: GitHub.