[issue44926] typing.get_type_hints() raises for type aliases with forward references

[Maximilian Hils]

Maximilian Hils <python-bugs at maximilianhils.com> added the comment:

Thank you Ken and Guido for the super quick feedback!

> It's not fine if it were to look in the wrong namespace

That's a really good point. Here's another terrible example:


foo.py:
```
import typing

FooData: typing.TypeAlias = "Data"

class Data:
    pass

```

bar.py:
```
import typing
import foo

BarData: typing.TypeAlias = "Data"

def func1(x: foo.FooData, y: BarData):
    pass

class Data:
    pass

print(typing.get_type_hints(func1))  # incorrectly uses bar.Data twice.

```


I don't see how we could distinguish FooData from BarData without static analysis. Changing get_type_hints to not pick the unrelated class with the same name would essentially mean not using func.__globals__, which breaks almost all ForwardRef evaluation. This doesn't seem viable.

Potential alternatives:

1. Accept the current state: get_type_hints does not work well with type aliases that use forward references.
2. Fix it at least for cases where a ForwardRef is constructed immediately (typing.List["Foo"], but not "Foo" or list["Foo"]), similar to how it's been done for #41249. I have made a very basic proof-of-concept at https://github.com/mhils/cpython/commit/4adbcf088d2857166b579f7dd2954ff9981fc7db, but it's a mess (see commit comments).
3. Deprecate/discourage use of forward references in type aliases and/or change the syntax for [forward references in] type aliases so that their origin can be tracked.

In summary, it seems like there are no really good solutions here. I'm fine if this ends up as a pragmatic wontfix, maybe with a comment added somewhere in the docs or in PEP 613.

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<https://bugs.python.org/issue44926>
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