False positive on type alias with Annotated and multiple type arguments upon import

[luwqz1]

I made a type alias with Annotated, which has two arguments in the generic. Everything works correctly, but as soon as i import this type alias into another file, some strange behavior occurs. Unfortunately, I couldn't reproduce other examples, so I can't pinpoint the exact issue. Eric Traut, i hope you'll be able to figure it out, though it's possible that Pyright is working as intended. I'm always open to discussion!

File foo.py

import typing

First = typing.TypeVar("First")
Meta = typing.TypeVar("Meta")

type FooType[First, Meta] = typing.Annotated[First, Meta]
Foo: typing.TypeAlias = FooType[First, Meta]

def bar(foo: Foo[str, int]): ...  # Ok

File bar.py

from foo import Foo

def bar(foo: Foo[str, int]): ... # Error: Too many type arguments provided for "type[First@Foo]"; expected 1 but received 2

[erictraut]

I agree this is a bug. It will be addressed in the next release.

What you're doing here is pretty suspect though. Type parameters are intended to parameterize types. Here you're using a type parameter that appears only within an Annotated metadata expression, not within the base type expression. Any type argument supplied for the second type parameter will therefore be ignored by static type checkers. I guess this construct might be valid if you intend to use it with a runtime type checker or perform introspection of annotations in your own code.

[luwqz1]

I guess this construct might be valid if you intend to use it with a runtime type checker or perform introspection of annotations in your own code.

Thank you very much for such a quick answer! You are absolutely right, i plan to use the second type parameter at runtime for other libraries that may perform checks/validation.

[erictraut]

This is addressed in pyright 1.1.386