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Allow function arguments as base classes#14135

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ilevkivskyi merged 4 commits intopython:masterfrom
ilevkivskyi:allow-arg-bases
Nov 21, 2022
Merged

Allow function arguments as base classes#14135
ilevkivskyi merged 4 commits intopython:masterfrom
ilevkivskyi:allow-arg-bases

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@ilevkivskyi ilevkivskyi commented Nov 18, 2022 •
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Fixes #5865

Looks quite easy and safe, unless I am missing something. Most changes in the diff are just moving stuff around.

Previously we only applied argument types before type checking, but it looks like we can totally do this in semantic analyzer. I also enable variable annotated as type (or equivalently Type[Any]), this use case was mentioned in the comments.

This PR also accidentally fixes two additional bugs, one related to type variables with values vs walrus operator, another one for type variables with values vs self types. I include test cases for those as well.

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ilevkivskyi commented Nov 18, 2022

The homeassistant errors are caused by exposing an existing bug in walrus. On master this test

[case testNarrowOnSelfInGeneric]
# flags: --strict-optional
from typing import Generic, TypeVar, Optional

T = TypeVar("T", int, str)

class C(Generic[T]):
    x: Optional[T]
    def meth(self) -> Optional[T]:
        if (y := self.x) is not None:
            return reveal_type(y)
        return None

reveals type Any. But with this PR it becomes optional, so it is still wrong. I will first try to figure out what is going on.

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ilevkivskyi commented Nov 18, 2022

OK, I have a fix for the walrus bug, since it is an obvious bug, I am going to just add it to this PR.

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ilevkivskyi commented Nov 19, 2022

Looking again at mypy_primer it looks like this PR accidental fixes another bug related to type vars with values, this type for self types. I am going to include a regression for that one as well.

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github-actions bot commented Nov 19, 2022

Diff from mypy_primer, showing the effect of this PR on open source code:

artigraph (https://github.com/artigraph/artigraph)
+ tests/arti/producers/test_producer.py:679: error: Unused "type: ignore" comment
+ tests/arti/producers/test_producer.py:680: error: Unused "type: ignore" comment

Tanjun (https://github.com/FasterSpeeding/Tanjun)
- tanjun/dependencies/reloaders.py:566: error: Cannot determine type of "real_path"  [has-type]
- tanjun/dependencies/reloaders.py:567: error: Cannot determine type of "time"  [has-type]
- tanjun/dependencies/reloaders.py:578: error: Cannot determine type of "info"  [has-type]
- tanjun/dependencies/reloaders.py:579: error: Cannot determine type of "time"  [has-type]
- tanjun/dependencies/reloaders.py:599: error: Cannot determine type of "path"  [has-type]
- tanjun/dependencies/reloaders.py:600: error: Cannot determine type of "tracked_value"  [has-type]
- tanjun/dependencies/reloaders.py:609: error: Cannot determine type of "path"  [has-type]
- tanjun/dependencies/reloaders.py:609: error: Cannot determine type of "path_info"  [has-type]
- tanjun/commands/menu.py:580: error: Incompatible return value type (got "MenuCommand[_MenuCommandCallbackSigT, _MenuTypeT]", expected "Self")  [return-value]

mypy (https://github.com/python/mypy)
+ mypy/stubtest.py:357: error: Unused "type: ignore[valid-type]" comment

cloud-init (https://github.com/canonical/cloud-init)
+ cloudinit/templater.py:44: error: Unused "type: ignore" comment

JukkaL
JukkaL approved these changes Nov 21, 2022
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Nice -- fixing three bugs for the price of one!

I can't see why setting the argument types in the semantic analyzer would be a problem.

Left a comment that is mostly unrelated to this PR, feel free to ignore it if you are not sure.

@ilevkivskyi ilevkivskyi merged commit 3c5f368 into python:master Nov 21, 2022
@ilevkivskyi ilevkivskyi deleted the allow-arg-bases branch November 21, 2022 18:42
@tmke8 tmke8 mentioned this pull request Nov 25, 2022
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@hauntsaninja hauntsaninja mentioned this pull request Jan 12, 2023
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@hauntsaninja hauntsaninja mentioned this pull request Jun 1, 2023
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@JukkaL JukkaL JukkaL approved these changes

@JelleZijlstra JelleZijlstra Awaiting requested review from JelleZijlstra

@hauntsaninja hauntsaninja Awaiting requested review from hauntsaninja

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Function argument rejected as a base class

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