[1.11 regression] Infinite recursion with callables and follow imports skip

[Viicos]

With pydantic_core installed, the following file:

from typing import Callable

from pydantic_core import core_schema

Recurse = Callable[[core_schema.CoreSchema, 'Walk'], core_schema.CoreSchema]
Walk = Callable[[core_schema.CoreSchema, Recurse], core_schema.CoreSchema]

Results in a segmentation fault on compiled version.

The end of the traceback using interpreted from master:

  ...
  File "/fakepath/lib/python3.12/site-packages/mypy/typetraverser.py", line 85, in visit_callable_type
    self.traverse_types(t.arg_types)
  File "/fakepath/lib/python3.12/site-packages/mypy/typetraverser.py", line 148, in traverse_types
    typ.accept(self)
  File "/fakepath/lib/python3.12/site-packages/mypy/types.py", line 410, in accept
    return visitor.visit_type_alias_type(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/messages.py", line 2754, in visit_type_alias_type
    get_proper_type(t).accept(self)
    ^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/types.py", line 3185, in get_proper_type
    typ = typ._expand_once()
          ^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/types.py", line 352, in _expand_once
    new_tp = self.alias.target.accept(InstantiateAliasVisitor(mapping))
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/types.py", line 2018, in accept
    return visitor.visit_callable_type(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/expandtype.py", line 409, in visit_callable_type
    arg_types = self.expand_types(t.arg_types)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/expandtype.py", line 515, in expand_types
    a.append(t.accept(self))
             ^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/types.py", line 410, in accept
    return visitor.visit_type_alias_type(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/expandtype.py", line 510, in visit_type_alias_type
    return t.copy_modified(args=args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/types.py", line 443, in copy_modified
    return TypeAliasType(
           ^^^^^^^^^^^^^^
  File "/fakepath/lib/python3.12/site-packages/mypy/types.py", line 318, in __init__
RecursionError: maximum recursion depth exceeded

Your Environment

• Mypy version used: 1.11.0 through 1.12.0
• Python version used: 3.12
• Mypy command: mypy t.py --config-file mypy.ini
• Operating system and version: Ubuntu

Config file (the two config values are necessary to reproduce):

[mypy]
disallow_any_unimported = True

[mypy-pydantic_core.*]
follow_imports = skip

[hauntsaninja]

Bisects to #17495

[ilevkivskyi]

Yeah, I was a bit worried this may happen, I will take this one.

[Viicos]

Thanks for the quick fix!