ParamSpec seems to match only the first overload in this use case

[Glinte]

playground

from collections.abc import Callable
from typing import Any, overload


def signature_from[**P, T](_original: Callable[P, T]) -> Callable[[Callable[P, T]], Callable[P, T]]:
    """Copies the signature of a function to another function."""

    def decorator(func: Callable[P, T]) -> Callable[P, T]:
        return func

    return decorator


@overload
def f(x: int) -> int: ...
@overload
def f(x: str) -> str: ...
@overload
def f(x: Any) -> Any: ...
def f(x: Any) -> Any:
    return x

# Expected
y1 = f(1)    # int
y2 = f("1")  # str
y3 = f(1.0)  # Any

@signature_from(f)
def g(*args, **kwargs) -> Any:
    if (len(args) + len(kwargs)) != 1:
        raise ValueError
    
    x = args[0] if len(args) == 1 else kwargs["x"]
    return f(x)

# y5, y6 unexpected
y4 = g(1)    # int
y5 = g("1")
#      ^^^
#Argument of type "Literal['1']" cannot be assigned to parameter "x" of type "int"
#  "Literal['1']" is not assignable to "int"  (reportArgumentType)
y6 = g(1.0)
#      ^^^
#Argument of type "float" cannot be assigned to parameter "x" of type "int"
#  "float" is not assignable to "int"  (reportArgumentType)

[Glinte]

This works though

from collections.abc import Callable
from typing import Any, overload


def signature_from[F: Callable](_original: F) -> Callable[[F], F]:
    """Copies the signature of a function to another function."""

    def decorator(func: F) -> F:
        return func

    return decorator


@overload
def f(x: int) -> int: ...
@overload
def f(x: str) -> str: ...
@overload
def f(x: Any) -> Any: ...
def f(x: Any) -> Any:
    return x

# Expected
y1 = f(1)    # int
y2 = f("1")  # str
y3 = f(1.0)  # Any

@signature_from(f)
def g(*args, **kwargs) -> Any:
    if (len(args) + len(kwargs)) != 1:
        raise ValueError
    
    x = args[0] if len(args) == 1 else kwargs["x"]
    return f(x)

y4 = g(1)    # int
y5 = g("1")  # str
y6 = g(1.0)  # Any