babel/babel · error · ConfigError

Negation of file paths is not supported.

Error message

Negation of file paths is not supported.

What it means

The readIgnoreConfig loader parses a .babelignore file line by line, strips comments and blank lines, then iterates the patterns. If any pattern begins with '!' (gitignore-style negation), Babel throws a ConfigError because Babel's ignore matching is unidirectional - it does not support re-including previously ignored files. This is a deliberate limitation of the pathPatternToRegex-based matcher.

Source

Thrown at packages/babel-core/src/config/files/configuration.ts:200

  delete options.$schema;

  return {
    filepath,
    dirname: path.dirname(filepath),
    options,
  };
});

const readIgnoreConfig = makeStaticFileCache((filepath, content) => {
  const ignoreDir = path.dirname(filepath);
  const ignorePatterns = content
    .split("\n")
    .map(line => line.replace(/^#.*$/, "").trim())
    .filter(Boolean);

  for (const pattern of ignorePatterns) {
    if (pattern.startsWith("!")) {
      throw new ConfigError(
        `Negation of file paths is not supported.`,
        filepath,
      );
    }
  }

  return {
    filepath,
    dirname: path.dirname(filepath),
    ignore: ignorePatterns.map(pattern =>
      pathPatternToRegex(pattern, ignoreDir),
    ),
  };
});

export function findConfigUpwards(rootDir: string): string | null {
  let dirname = rootDir;
  for (;;) {

View on GitHub (pinned to 06b6eae39d)

Solutions

1. Remove all lines starting with '!' from .babelignore; Babel ignore is additive only.
2. Restructure ignore patterns so that the file you wanted to re-include is simply not matched by any ignore pattern (use more specific exclude patterns instead).
3. If you need conditional inclusion logic, use the per-file `ignore`/`only` functions in babel.config.js instead of .babelignore.

Example fix

// before - .babelignore throws error 26
build/
!src/runtime.js

// after - no negation; narrow the ignore instead
build/
src/generated/

const fs = require('fs');
if (fs.existsSync('.babelignore')) {
  const lines = fs.readFileSync('.babelignore', 'utf8').split('\n');
  const negated = lines.filter(l => l.replace(/#.*/, '').trim().startsWith('!'));
  if (negated.length) throw new Error('.babelignore does not support negation: ' + negated.join(', '));
}

function hasNoNegation(patterns: string[]): boolean {
  return patterns.every(p => !p.trim().startsWith('!'));
}

try { babel.transformFileSync(file); }
catch (err) {
  if (/Negation of file paths is not supported/.test(err.message)) {
    console.error('Remove lines starting with ! from', err.filename);
  }
  throw err;
}

When it happens

Trigger: A .babelignore file containing a line such as `!src/keep.js` intended to un-ignore a file that an earlier pattern excluded.

Common situations: Developers familiar with .gitignore syntax who try to reuse negation patterns in .babelignore; migrating a .gitignore to .babelignore by copy-paste.

Related errors

• .babel property must be an object
• No config detected
• Config returned typeof ${typeof options}
• Expected config object but found array
• Config file contains no configuration data

AI-assisted analysis of babel/babel@06b6eae39d (2026-08-03). Data as JSON: /data/errors/87cebbc758ddc3b2.json. Report an issue: GitHub.