Regression when loading types for python 3.9

[last-partizan]

Describe the bug
After updating to pyright@1.1.364 i encounter following error, but only for python 3.9.

Code or Screenshots

pip install pytest-cases typing-extensions

from typing_extensions import reveal_type
from pytest_cases import fixture

reveal_type(fixture)


@fixture()
def f1_call(): ...


@fixture
def f2_plain(): ...

Note incorrect types for fixture.

pytest-cases are using decopatch.function_decorator, it has types defined in .pyi file, but they're ignored.

> npx pyright@1.1.364 --pythonversion 3.9 pytest-cases.py

/home/serg/src/pyright-examples/pytest-cases.py
  /home/serg/src/pyright-examples/pytest-cases.py:4:13 - information: Type of "fixture" is "(scope: str = "function", autouse: bool = False, name: str = None, unpack_into: Iterable[str] = None, hook: ((...) -> Unknown) -> ((...) -> Unknown) = None, fixture_func: _Symbol | Unknown = DECORATED, **kwargs: Unknown) -> Generator[None, Any, Unknown]"
  /home/serg/src/pyright-examples/pytest-cases.py:7:2 - error: Object of type "Generator[None, Any, Unknown]" is not callable
    Attribute "__call__" is unknown (reportCallIssue)
  /home/serg/src/pyright-examples/pytest-cases.py:11:2 - error: Argument of type "() -> None" cannot be assigned to parameter "scope" of type "str" in function "fixture"
    "function" is incompatible with "str" (reportArgumentType)
2 errors, 0 warnings, 1 information

Larger version of python is not affected and produce correct result:

> npx pyright@1.1.364 --pythonversion 3.10 pytest-cases.py

/home/serg/src/pyright-examples/pytest-cases.py
  /home/serg/src/pyright-examples/pytest-cases.py:4:13 - information: Type of "fixture" is "_Decorator[(scope: str = "function", autouse: bool = False, name: str = None, unpack_into: Iterable[str] = None, hook: ((...) -> Unknown) -> ((...) -> Unknown) = None, fixture_func: _Symbol | Unknown = DECORATED, **kwargs: Unknown)]"
0 errors, 0 warnings, 1 information

[erictraut]

This is caused by a bug in the decopatch stubs. They're using a try/except block in the import of ParamSpec. Stub files are not executed, and they're not allowed to use dynamic code like try/except blocks.

try:
    from typing import ParamSpec
except ImportError:
    from typing_extensions import ParamSpec

should be replaced by

from typing_extensions import ParamSpec

An older bug in pyright happened to mask the effects of the bug in the stubs, which explains why this apparently worked for you prior to pyright 1.1.364.

The correct fix here is to address the bug in the stubs. I recommend that you file a bug report with the maintainers of the decopatch stubs.

[last-partizan]

Thanks!