1.11 crash with TypeDict+(Not)Required and type: ignore

[nernst]

Crash Report

I upgraded to mypy 1.11 from 1.08, and previously accepted code started causing crashes.

Traceback

$ mypy mypy-repro.py --show-traceback
mypy-repro.py:8: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.11.0
Traceback (most recent call last):
  File "mypy/checker.py", line 591, in accept
  File "mypy/nodes.py", line 1351, in accept
  File "mypy/checker.py", line 2948, in visit_assignment_stmt
  File "mypy/messages.py", line 1768, in unimported_type_becomes_any
  File "mypy/messages.py", line 2805, in format_type
  File "mypy/messages.py", line 2822, in format_type_bare
  File "mypy/messages.py", line 2540, in format_type_inner
  File "mypy/types.py", line 3111, in get_proper_type
TypeError: mypy.types.ProperType object expected; got mypy.types.RequiredType
mypy-repro.py:8: : note: use --pdb to drop into pdb

To Reproduce

mypy-repro.py:

from typing import NotRequired, Required, TypedDict
from bson.objectid import ObjectId  # type: ignore

class Data(TypedDict, total=False):
    # NOTE: not complete
    _id: Required[ObjectId]
    appId: str

(Write what you did to reproduce the crash. Full source code is
appreciated. We also very much appreciate it if you try to narrow the
source down to a small stand-alone example.)

Your Environment

In this repro, I'm using pymongo ^3.13,<4 because I cannot currently upgrade any further due to server dependencies, so bson is untyped.

• Mypy version used: 1.11.0
• Mypy command-line flags: mpypy mypy-repro.py
• Mypy configuration options from pyproject.toml:

...
[tool.mypy]
python_version = "3.12"

# set mypy_path and explicit_package_bases, otherwise mypy gets confused about package names
# due to the use of namespace packages.
mypy_path = "src"
explicit_package_bases = true
enable_incomplete_feature = ["NewGenericSyntax"]

pretty = true
disallow_any_unimported = true
disallow_any_expr = false
disallow_any_explicit = false
disallow_any_generics = true
disallow_subclassing_any = true
disallow_untyped_calls = true
disallow_untyped_defs = true
disallow_incomplete_defs = true
disallow_untyped_decorators = true
implicit_optional = true
strict_optional = true
warn_redundant_casts = true
warn_unused_ignores = true
warn_no_return = true
warn_return_any = true
warn_unreachable = true
warn_unused_configs = true
exclude = ["(dist|docs)/.*/.*\\.py$"]

• Python version used: Python 3.12.2
• Operating system and version: Debian GNU/Linux 12 (bookworm)

[andersk]

git bisect says this was introduced by e5b3b56 (Fix daemon crash on invalid type in TypedDict, #17495).

Note that to reproduce without mypyc, you need to manually insert this assertion that would be enforced automatically by mypyc:

--- a/mypy/types.py
+++ b/mypy/types.py
@@ -3108,7 +3108,8 @@ def get_proper_type(typ: Type | None) -> ProperType | None:
     while isinstance(typ, TypeAliasType):
         typ = typ._expand_once()
     # TODO: store the name of original type alias on this type, so we can show it in errors.
-    return cast(ProperType, typ)
+    assert isinstance(typ, ProperType)
+    return typ
 
 
 @overload