graphql-core crashing on latest master

[hauntsaninja]

Bisects to #19810 cc @ilevkivskyi

  File "/Users/shantanu/dev/mypy/mypy/messages.py", line 2802, in visit_type_alias_type
    get_proper_type(t).accept(self)
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 2773, in accept
    return visitor.visit_tuple_type(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/typetraverser.py", line 97, in visit_tuple_type
    self.traverse_type_list(t.items)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/typetraverser.py", line 154, in traverse_type_list
    typ.accept(self)
    ~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 1634, in accept
    return visitor.visit_instance(self)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/messages.py", line 2798, in visit_instance
    super().visit_instance(t)
    ~~~~~~~~~~~~~~~~~~~~~~^^^
  File "/Users/shantanu/dev/mypy/mypy/typetraverser.py", line 82, in visit_instance
    self.traverse_type_tuple(t.args)
    ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/typetraverser.py", line 159, in traverse_type_tuple
    typ.accept(self)
    ~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 406, in accept
    return visitor.visit_type_alias_type(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/messages.py", line 2802, in visit_type_alias_type
    get_proper_type(t).accept(self)
    ~~~~~~~~~~~~~~~^^^
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 3577, in get_proper_type
    typ = typ._expand_once()
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 370, in _expand_once
    return self.alias.target.accept(InstantiateAliasVisitor(mapping))
           ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 3334, in accept
    return visitor.visit_union_type(self)
           ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 4315, in visit_union_type
    return TypeTranslator.visit_union_type(self, t)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
  File "/Users/shantanu/dev/mypy/mypy/type_visitor.py", line 302, in visit_union_type
    self.translate_type_list(t.items),
    ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
RecursionError: maximum recursion depth exceeded
/tmp/mypy_primer/projects/graphql-core/src/graphql/execution/incremental_publisher.py:1057: : note: use --pdb to drop into pdb

[hauntsaninja]

Okay. I fed the whole repro case in to GPT-5 codex (via codex cli) and gave it some instructions on how to make a minimal reproducible example. It worked for half an hour and produced:

from __future__ import annotations

from typing import Awaitable, NamedTuple, TypeVar, Union

T = TypeVar("T")
AwaitableOrValue = Union[Awaitable[T], T]


class DeferredGroupedFieldSetRecord:
    result: AwaitableOrValue[DeferredGroupedFieldSetResult]
    incremental_data_records: IncrementalDataRecord

class ReconcilableDeferredGroupedFieldSetResult(NamedTuple):
    incremental_data_records: IncrementalDataRecord


DeferredGroupedFieldSetResult = ReconcilableDeferredGroupedFieldSetResult


class StreamItemsRecord(NamedTuple):
    result: AwaitableOrValue[DeferredGroupedFieldSetResult]


IncrementalDataRecord = Union[DeferredGroupedFieldSetRecord, StreamItemsRecord]


def use(result: DeferredGroupedFieldSetResult | StreamItemsRecord) -> None:
    record: StreamItemsRecord = result

[hauntsaninja]

I cleaned it up a little by hand the old-fashioned way:

from __future__ import annotations

from typing import Awaitable, NamedTuple, TypeVar, Union

T = TypeVar("T")
AwaitOrValue = Union[Awaitable[T], T]

class Leaf(NamedTuple):
    data: Wrapper

class Wrapper(NamedTuple):
    result: AwaitOrValue[Leaf]

def foo(value: Leaf | Wrapper) -> None:
    wrapper: Wrapper = value

[ilevkivskyi]

Yeah, noticed it myself in #19936.