FuncParamType should use ValueError for self.fail(message)

[toppk]

FuncParamType currently just calls self.fail(value,...) if it self.func(value) raise a ValueError. This is missing the point of the self.fail which is to give better feedback.
Using typer so something like

@dataclass
class MyClass:
    myvalue: str
     @staticmethod
      def from_str(cls, input:Any) -> 'MyClass':
              if input != 'works':
                  raise ValueError(f'input was  {input=}, should be works')
              return cls(input)
@app.command('test', help='get snapshot')
async def test(
    mydata: Annotated[
        MyClass, typer.Argument(parser=MyClass.from_str)
    ],
) -> None:

should give str(error) not str(input)

fix would be

class FuncParamType(ParamType):
    def __init__(self, func: t.Callable[[t.Any], t.Any]) -> None:
        self.name: str = func.__name__
        self.func = func

    def to_info_dict(self) -> dict[str, t.Any]:
        info_dict = super().to_info_dict()
        info_dict["func"] = self.func
        return info_dict

    def convert(
        self, value: t.Any, param: Parameter | None, ctx: Context | None
    ) -> t.Any:
        try:
            return self.func(value)
        except ValueError as e:
            self.fail(str(e), param, ctx)

happy to submit a PR if this makes sense. Rather not have to create a customclass when FuncParamType is so close. Not sure what else FuncParamType there there for, as there isn't really any documentation of why it exists, but typer uses it.

[toppk]

in case any else finds this, enjoy my monkey patch:

def patch_click_func_param() -> None:
    """Patch click.FuncParamType to forward ValueError text to Click."""
    from click.types import FuncParamType  # noqa: PLC0415

    if getattr(FuncParamType, '_rt_original_convert', None) is not None:
        return

    def _patched_convert(
        self: FuncParamType,
        value: Any,
        param: 'Parameter | None',
        ctx: 'Context | None',
    ) -> Any:
        try:
            return self.func(value)
        except ValueError as exc:
            self.fail(str(exc), param, ctx)

    FuncParamType._rt_original_convert = FuncParamType.convert  # noqa: SLF001 # pyright: ignore[reportAttributeAccessIssue]
    FuncParamType.convert = _patched_convert


patch_click_func_param()