Make `@safe(exceptions=(TypeError, ValueError))` variant

[sobolevn]

This decorator will help to catch only expected errors, not all.

[sobolevn]

This also applies to impure_safe and future_safe

[thepabloaguilar]

Hey @sobolevn, I'm working on this issue but I got a problem with typesafety tests :(

Here's the implementation:

@overload
def safe(
    arg: Callable[..., _ValueType],
) -> Callable[..., ResultE[_ValueType]]:
    """Decorator to convert exception-throwing for any kind of Exception."""


@overload
def safe(
    arg: Tuple[Type[Exception], ...],
) -> Callable[
    [Callable[..., _ValueType]],
    Callable[..., ResultE[_ValueType]],
]:
    """Decorator to convert exception-throwing just for a set of Exceptions."""


def safe(  # noqa: WPS234
    arg: Union[
        Tuple[Type[Exception], ...],
        Callable[..., _ValueType],
    ],
) -> Union[
    Callable[
        [Callable[..., _ValueType]],
        Callable[..., ResultE[_ValueType]],
    ],
    Callable[..., ResultE[_ValueType]],
]:
    ...

pytest output:

__________________________________________________________________________________________________________ safe_decorator_no_params __________________________________________________________________________________________________________
returns/typesafety/test_result/test_safe.yml:10: 
E   pytest_mypy_plugins.utils.TypecheckAssertionError: Invalid output: 
E   Expected:
E     main:7: note: Revealed type is 'def () -> returns.result.Result[builtins.int, builtins.Exception]' (diff)
E   Actual:
E     main:7: note: Revealed type is 'def (*Any, **Any) -> returns.result.Result[builtins.int, builtins.Exception]' (diff)

It should work by the fact we have the overload signature correctly!

Do you have any idea of why it's not working?

[sobolevn]

I think that the reason is https://github.com/dry-python/returns/blob/master/returns/contrib/mypy/_features/decorators.py#L26-L27

Try to catch FunctionalLike and Overloaded types there.

[thepabloaguilar]

Just a question, should it work if we don't use our plugin??

[sobolevn]

It would work partially (except argument types). Because we don't have ParamSpec support yet.

[thepabloaguilar]

@sobolevn You were right, the problem is in that statement!

I'll try to fix it!

[thepabloaguilar]

It's not treating tuples correctly 😢

@safe(args=(ValueError, EOFError))
def test() -> int:
    return 1

E   Expected:
E     main:7: note: Revealed type is 'def () -> returns.result.Result[builtins.int, builtins.Exception]' (diff)
E   Actual:
E     main:3: error: No overload variant of "safe" matches argument type "Tuple[Type[ValueError], Type[EOFError]]" (diff)
E     main:3: note:     def [_ValueType] safe(arg: Callable[..., _ValueType]) -> Callable[..., Result[_ValueType, Exception]] (diff)
E     main:3: note:     def safe(arg: Tuple[Type[Exception], ...]) -> Callable[[Callable[..., _ValueType]], Callable[..., Result[_ValueType, Exception]]] (diff)
E     main:3: note: Possible overload variants:     (diff)
E     main:7: note: Revealed type is 'Any'          (diff)

[thepabloaguilar]

And that error isn't our fault (I guess), 'cause it is not executing our decorator plugin function!

[thepabloaguilar]

Oh, my fault! I've used wrong parameter name args instead of arg

[thepabloaguilar]

Ok, now I think I have the same feelings you have about mypy!! 😠

The problem is when decorator has parameters, like we trying to do here, see the example below:

def decorator_argument(arg: int) -> Callable[[Callable[..., int]], Callable[..., int]]:
    def decorator(function: Callable[..., int]) -> Callable[..., int]:
        @wraps(function)
        def decorated(*args, **kwargs):
            pass
        return decorated
    return decorator

Test case:

@decorator_argument(42)
def test() -> int:
    return 1

reveal_type(test)  # N: Revealed type is 'def () -> builtins.int'

Output:

E   pytest_mypy_plugins.utils.TypecheckAssertionError: Invalid output: 
E   Expected:
E     main:8: note: Revealed type is 'def () -> builtins.int' (diff)
E   Actual:
E     main:8: note: Revealed type is 'def (*Any, **Any) -> builtins.int' (diff)

[sobolevn]

The problem is when decorator has parameters

Yeah, that's a known problem. We had solved it already in the previous versions.

Take a look at our definitions: https://github.com/dry-python/returns/blob/0.14.0/returns/_generated/pointfree/map.pyi#L22
And mypy plugin for it: https://github.com/dry-python/returns/blob/0.14.0/returns/contrib/mypy/returns_plugin.py#L46 and https://github.com/dry-python/returns/blob/0.14.0/returns/contrib/mypy/_features/pointfree.py

I hope, it helps.

[thepabloaguilar]

I'm thinking, it is worth it now? I'm saying this because I can implement this and maintain the backward compatibility. The guys who use safe without passing the exceptions won't be affected.

In about 4 months we'll have ParamSpec