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TypeAlias does not work when attribute-accessed from the typing_extensions package #12179
Description
Bug Report
TypeAlias does not trigger errors in mypy if accessed from the typing_extensions package (rather than being imported directly).
To Reproduce
import typing as tp
import typing_extensions as tpx
from typing_extensions import TypeAlias
ASDF: TypeAlias = tp.Literal["A", "S", "D", "F"]
JKL: tpx.TypeAlias = tp.Literal["J", "K", "L"]
Int: tpx.TypeAlias = int
Str: TypeAlias = strExpected Behavior
Everything below should throw errors in mypy:
G: ASDF = "G" # error: Incompatible types in assignment (expression has type "Literal['G']", variable has type "Union[Literal['A'], Literal['S'], Literal['D'], Literal['F']]")
H: JKL = "H" # error: Incompatible types in assignment (expression has type "Literal['H']", variable has type "Union[Literal['J'], Literal['K'], Literal['L']]")
n: Int = "9" # error: Incompatible types in assignment (expression has type "str", variable has type "int")
s: Str = 9 # error: Incompatible types in assignment (expression has type "int", variable has type "str")Actual Behavior
The aliases JKL and Int, typed using tpx.TypeAlias, do not trigger errors with mypy:
G: ASDF = "G" # error: Incompatible types in assignment (expression has type "Literal['G']", variable has type "Union[Literal['A'], Literal['S'], Literal['D'], Literal['F']]")
H: JKL = "H" # Expected error here; got none
n: Int = "9" # Expected error here; got none
s: Str = 9 # error: Incompatible types in assignment (expression has type "int", variable has type "str")Your Environment
- Mypy version used:
0.931 - Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files):[mypy] plugins = numpy.typing.mypy_plugin ignore_missing_imports = True - Python version used:
3.8.12 - Operating system and version: Elementary OS 6.1 Jólnir (Based on Ubuntu 20.04 LTS)
Activity
hauntsaninja commentedon Feb 15, 2022
Yikes, this is pretty bad. Thanks for the report. I think the issue isn't about typing_extensions vs typing (which tests cover), but rather the import alias. That is,
tp.TypeAliasfails as well. Looks easy to fix, though!Fix use of TypeAlias from aliased imports
Fix use of TypeAlias from aliased imports (#12180)