nodejs/node · error · MBErr

Failed to parse config file "%s": %s

Error message

Failed to parse config file "%s": %s

What it means

ReadConfigFile() parses mb_config.pyl with ast.literal_eval. If the file is not a valid Python literal (syntax error), the SyntaxError is caught and re-raised as MBErr('Failed to parse config file "%s": %s') chaining the original via `from e`. The message includes the file path and the underlying parse error detail.

Source

Thrown at deps/v8/tools/mb/mb.py:565

                         self.args.builder_group, self.args.builder + '.json')
    if not self.Exists(path):
      return {}

    contents = json.loads(self.ReadFile(path))
    gn_args = ' '.join(contents.get('gn_args', []))

    vals = self.DefaultVals()
    vals['gn_args'] = gn_args
    return vals

  def ReadConfigFile(self):
    if not self.Exists(self.args.config_file):
      raise MBErr('config file not found at %s' % self.args.config_file)

    try:
      contents = ast.literal_eval(self.ReadFile(self.args.config_file))
    except SyntaxError as e:
      raise MBErr('Failed to parse config file "%s": %s' %
                 (self.args.config_file, e)) from e

    self.configs = contents['configs']
    self.luci_tryservers = contents.get('luci_tryservers', {})
    self.builder_groups = contents['builder_groups']
    self.mixins = contents['mixins']

  def ReadIsolateMap(self):
    if not self.args.isolate_map_files:
      self.args.isolate_map_files = [self.default_isolate_map]

    for f in self.args.isolate_map_files:
      if not self.Exists(f):
        raise MBErr('isolate map file not found at %s' % f)
    isolate_maps = {}
    for isolate_map in self.args.isolate_map_files:
      try:
        isolate_map = ast.literal_eval(self.ReadFile(isolate_map))

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Open mb_config.pyl and run `python3 -c "import ast; ast.literal_eval(open('infra/mb/mb_config.pyl').read())"` to get the exact line/column of the syntax error, then fix it.
2. Re-resolve any merge-conflict markers (<<<<<<, =======, >>>>>>) left in the file.
3. Validate with `mb.py validate -f <file>` after the fix.

Example fix

// before
  'configs': {
    'x64.release': {'mixins': ['x64', 'release']}   // missing trailing comma before next entry
  }
// after
  'configs': {
    'x64.release': {'mixins': ['x64', 'release']},
  }

import ast
try:
    ast.literal_eval(open(mb_config_path).read())
except SyntaxError as e:
    sys.exit(f'mb_config.pyl parse error at line {e.lineno}: {e.msg}')

null

try:
    ast.literal_eval(text)
except SyntaxError as e:
    raise MBErr(f'Failed to parse config file "{path}": {e}') from e

When it happens

Trigger: mb_config.pyl contains a Python syntax error: unbalanced brackets, a stray comma, an invalid token, a dangling quote, or trailing junk. ast.literal_eval raises SyntaxError, caught and converted to MBErr.

Common situations: Hand-editing mb_config.pyl and leaving a syntax error; a botched merge conflict resolution; copy-paste that broke quoting; a tab/space inconsistency in a Python literal.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to parse isolate map file "%s": %s
• mb config file %s has problems:
• args file "%s" not found
• Config "%s" not found in %s
• config file not found at %s

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/5a09f7e5ae18a4a1. Report an issue: GitHub.