nodejs/node · error · MBErr

args file "%s" not found

Error message

args file "%s" not found

What it means

In mb.py Lookup()/ConfigFromArgs(), when the resolved config string starts with '//' it is treated as a GN-style path to an args file (relative to src). mb checks self.Exists(self.ToAbsPath(config)); if that file is absent it raises MBErr('args file "%s" not found'). This is the //path/to/args.gn form of -c.

Source

Thrown at deps/v8/tools/mb/mb.py:533

    if self.Exists(gn_args_path):
      args_contents = self.ReadFile(gn_args_path)
    gn_args = []
    for l in args_contents.splitlines():
      fields = l.split(' ')
      name = fields[0]
      val = ' '.join(fields[2:])
      gn_args.append('%s=%s' % (name, val))

    return ' '.join(gn_args)

  def Lookup(self):
    vals = self.ReadIOSBotConfig()
    if not vals:
      self.ReadConfigFile()
      config = self.ConfigFromArgs()
      if config.startswith('//'):
        if not self.Exists(self.ToAbsPath(config)):
          raise MBErr('args file "%s" not found' % config)
        vals = self.DefaultVals()
        vals['args_file'] = config
      else:
        if not config in self.configs:
          raise MBErr('Config "%s" not found in %s' %
                      (config, self.args.config_file))
        vals = self.FlattenConfig(config)
    return vals

  def ReadIOSBotConfig(self):
    if not self.args.builder_group or not self.args.builder:
      return {}
    path = self.PathJoin(self.chromium_src_dir, 'ios', 'build', 'bots',
                         self.args.builder_group, self.args.builder + '.json')
    if not self.Exists(path):
      return {}

    contents = json.loads(self.ReadFile(path))

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Verify the // path resolves to a real file: `ls <src-root>/<path-without-//>`.
2. Correct the typo in the -c argument or commit/restore the missing args file.
3. Confirm you are running mb from the intended source root (chromium_src_dir / V8 root).

Example fix

// before
  mb.py gen -c //build/arg/my.gn out/Default    // typo 'arg'
// after
  mb.py gen -c //build/args/my.gn out/Default    // matches actual file

if config.startswith('//'):
    abs_path = os.path.join(src_root, config[2:].replace('/', os.sep))
    if not os.path.isfile(abs_path):
        sys.exit(f'args file not found: {abs_path}')

null

null

When it happens

Trigger: Running `mb.py gen -c //build/args/my.gn` (or lookup/analyze) where the // path does not resolve to an existing file under the source root. The ToAbsPath + Exists check fails.

Common situations: Typo in the // path; the args file was deleted or never committed; running mb from a checkout where the referenced build config lives on a different branch; wrong src root.

Related errors

• mb config file %s has problems:
• Config "%s" not found in %s
• config file not found at %s
• Failed to parse config file "%s": %s
• unrecognized platform string "%s"

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/e81044d36a7eaef1. Report an issue: GitHub.