Weird behavior when wrongly combining Annotated with List

[The-Compiler]

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Example Code

from typing_extensions import Annotated
from typing import List, get_type_hints

import typer


def test(arg: List[Annotated[str, typer.Argument(help="test")]]):  # wrong!
    print("test")


if __name__ == "__main__":
    print(get_type_hints(test))
    typer.run(test)

Description

On Python 3.8, this results in:

AssertionError: List types with complex sub-types are not currently supported

from here:

typer/typer/main.py

Lines 834 to 836 in 4c6098f

	assert not getattr(
	main_type, "__origin__", None
	), "List types with complex sub-types are not currently supported"

On newer Python versions, this works, but the typer.Argument silently gets dropped. See --help:

*    arg      ARG...  [default: None] [required]

as opposed to using Annotated[List[str], typer.Argument(help="test")] correctly:

*    arg      ARG...  test [default: None] [required]  

---

The fact that Python 3.9+ fails silently is due to typing.get_type_hints() by default stripping metadata there. Thus, when it's called here:

typer/typer/utils.py

Line 110 in 4c6098f

type_hints = get_type_hints(func)

the Annotated part gets dropped here:

typer/typer/utils.py

Lines 164 to 166 in 4c6098f

	elif param.name in type_hints:
	# Resolve forward references.
	annotation = type_hints[param.name]

Operating System

Linux

Operating System Details

No response

Typer Version

0.9.0

Python Version

3.8.18, 3.9.18, 3.11.6

Additional Context

No response

[lachaib]

Actually, I would say the usage is wrong here.
It makes no sense to annotate the item type of the list with the typer.Argument description.

Your code would work just fine if you had done the reverse:

def test(arg: Annotated[List[str], typer.Argument(help="test")]):  #  <- yay!
    print("test")

[The-Compiler]

I agree, hence the # wrong! comment in the code. But it silently being ignored can be a very confused outcome to spot and/or debug.