nodejs/node · error · ValueError

Unsupported type when printing to GN.

Error message

Unsupported type when printing to GN.

What it means

ValueError raised by GenerateTokens for any value type it does not support: only dicts, lists, strings, ints, and bools are handled; the else branch (which the comment notes also excludes float) raises this. It is the catch-all for values the GN printer cannot serialize.

Source

Thrown at tools/gypi_to_gn.py:160

      yield ']'

    elif isinstance(v, dict):
      if level > 0:
        yield '{'
      for key in sorted(v):
        if not isinstance(key, str):
          raise ValueError('Dictionary key is not a string.')
        if not key or key[0].isdigit() or not key.replace('_', '').isalnum():
          raise ValueError('Dictionary key is not a valid GN identifier.')
        yield key  # No quotations.
        yield '='
        for tok in GenerateTokens(v[key], level + 1):
          yield tok
      if level > 0:
        yield '}'

    else:  # Not supporting float: Add only when needed.
      raise ValueError('Unsupported type when printing to GN.')

  can_start = lambda tok: tok and tok not in ',}]='
  can_end = lambda tok: tok and tok not in ',{[='

  # Adds whitespaces, trying to keep everything (except dicts) in 1 line.
  def PlainGlue(gen):
    prev_tok = None
    for i, tok in enumerate(gen):
      if i > 0:
        if can_end(prev_tok) and can_start(tok):
          yield '\n'  # New dict item.
        elif prev_tok == '[' and tok == ']':
          yield '  '  # Special case for [].
        elif tok != ',':
          yield ' '
      yield tok
      prev_tok = tok

View on GitHub (pinned to 1b2de5e052)

Solutions

1. Convert unsupported values to supported types before generation: floats to strings or ints, None to an empty string or omit, tuples to lists.
2. Extend the handling chain (str, int, bool, list, dict) explicitly for the new type if floats are genuinely needed (the comment invites this).
3. Validate the data structure recursively and reject/transform unsupported types up front.

Example fix

# before
data = {'threshold': 0.5}  # float -> raises

# after
data = {'threshold': '0.5'}  # string is supported

ALLOWED = (dict, list, str, int, bool)
def is_supported_value(obj) -> bool:
    if isinstance(obj, (str, int, bool)):
        return True
    if isinstance(obj, dict):
        return all(is_supported_value(v) for v in obj.values())
    if isinstance(obj, list):
        return all(is_supported_value(i) for i in obj)
    return False

def is_gn_primitive(v) -> bool:
    return isinstance(v, (str, int, bool, list, dict))

try:
    list(GenerateTokens(data))
except ValueError as e:
    if 'Unsupported type' in str(e):
        pass  # convert floats/None/tuples to supported types, retry

When it happens

Trigger: Passing a structure containing a float, None, tuple, set, custom object, or any non-primitive to GenerateTokens.

Common situations: GYP data containing floating-point values (e.g. version numbers as floats), None values from optional fields, or tuples introduced by preprocessing.

Related errors

• Dictionary key is not a string.
• --depfile requires --stamp and vice versa
• --depfile requires --stamp and vice versa
• Dictionary key is not a valid GN identifier.
• Invalid config specified via --build: %s

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/b1504ba487e15756. Report an issue: GitHub.