Hi,

I tried it myself and it doesn't seems like an error due to RF. It looks like you're using TypeForm from typing_extensions incorrectly.

According to the error message, TypeForm[object] is not valid syntax. The TypeForm class is likely not designed to be used with type parameters like [object].

I fixed it with this approach:

from robot.api.deco import keyword
from typing import TypeVar

T = TypeVar('T', bound=object)

@keyword
def foo(a: T):
    print(a)

Robotframework file is the same. With this approach i get no errors.

i think you're getting TypeForm mixed up with TypeVar, they're two completely different concepts. TypeVar is for declaring generics (aka type variables), whereas TypeForm is a way to type a type annotation itself. it's useful for functions that cast or do runtime type checking:

from typing_extensions import TypeForm

def validate_type(value: object, t: TypeForm[object]):
    ... # do some runtime type check

validate_type(1, int | str)

see https://peps.python.org/pep-0747/ for more info

I can reproduce the problem. It's due to our type hint inspecting code considering that nothing that's not an instance of type can have parameters. That's a false assumption and TypeForm isn't the only such special form. Another example is Annotated[int, 'xxx'], but it doesn't cause problems for us, because get_type_hints by default strips the wrapping Annotation and returns just the actual type.

Luckily this problem doesn't cause the whole execution to crash, but not being able to use a keyword with such a type hint is obviously annoying as well. This certainly needs to be fixed and luckily the fix seem to be rather simple. There will be no conversion for TypeForm, though, unless we explicitly add it. Do you think it would make sense? If yes, please submit a separate issue about that.

sounds good, like i said a converter isn't really necessary because a string is already a valid TypeForm, which is mentioned here:

A string literal expression containing a valid type expression should likewise be assignable to TypeForm:

v5: TypeForm[set[str]] = "set[str]"  # OK

so that should make it trivial to support it in robotframework. though i guess it could be enhanced further to validate that the string is actually a valid type, but i'm happy to just have the fix for the crash, because i don't use .robot files much anymore since i made my pytest plugin so i don't really need converters since all of our new tests are written in python.

Converting string "set[str]" to actual set[str] and validating that it matches TypeForm[set[str]] wouldn't be trivial, but it wouldn't be that complicated either. Anyway, that requires a separate issue.

TypeForm is apparently supported natively by Python 3.14, so this issues is also related to the general Python 3.14 support (#5352).