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Fine-grained: Inconsistent behavior for nested NewType #4615
Description
The output of the second increment of this fine-grained incremental mode test case doesn't generate an error, even though nothing relevant has changed:
[case testRefreshNestedNewType]
import a
[file a.py]
from typing import Union, NewType
import b
def f(self) -> None:
X = NewType('X', A)
A = str
[file b.py]
y = 0
[file b.py.2]
y = ''
[out]
Here's the output:
a.py:5: error: Argument 2 to NewType(...) must be subclassable (got A?)
==
The expected output would be identical for both runs.
The output from the first and second runs also does not match for this slightly different test case:
[case testRefreshNestedNewType]
import a
[file a.py]
from typing import Union, NewType
import b
def f(self) -> None:
X = NewType('X', A)
A = Union[int, str]
[file b.py]
y = 0
[file b.py.2]
y = ''
[out]
Here's the output (again expected to be identical):
a.py:5: error: Argument 2 to NewType(...) must be subclassable (got A?)
==
a.py:5: error: Argument 2 to NewType(...) must be subclassable (got "Union[int, str]")
It looks like forward references within NewType declarations behave inconsistently.
Activity
ilevkivskyi commentedon Feb 21, 2018
I think that at least the second one (with union) should be fixed by my alias PR #4525. My guess is that things that should be stripped are not stripped (like
.analyzed).ilevkivskyi commentedon Feb 21, 2018
Also there is in fact no big difference between two examples from point of view of forward refs vs
NewType, in the first case the analyzed forward ref isstrwhich is a valid base class, therefore no error is shown.ilevkivskyi commentedon Mar 16, 2018
It looks like
strip_targetis not called ona.py, while it should. Therefore, the type aliases are not stripped, and appear in analyzed form on the second run. I am not yet sure how to fix this.ilevkivskyi commentedon Mar 20, 2018
After a discussion with @JukkaL it looks like the right solution for now would be to support forward references in
NewTypes. We anyway allow them in many places where they should be prohibited, so this is consistent.