Better error location for incompatible override due to argument incompatibility

[JukkaL]

An incompatible override gets reported on the first line of a method header, even though it would be better to point it at the line with an argument that is incompatible, when possible. Example:

class A:
    def f(self, x: int, y: str, z: float) -> None: pass

class B(A):
    def f(  # Argument 3 incompatible with supertype "A" <-- reported here
            self,
            x: int,
            y: str,
            z: bool,  # <-- would be better to report it here
    ) -> None:
        pass

This would improve usability, especially for methods with many arguments on many lines. This would also make it cleaner to ignore these errors, as the location of the # type: ignore comment would document which argument is incompatible (if there is one argument per line, which is a common convention).

[dhalenok]

@JukkaL I'd like to help with this issue but not quite sure about where to start, any suggestions?

[JukkaL]

@DenisOH Look for calls to argument_incompatible_with_supertype in mypy/checker.py to find the relevant code.

[Arshaan-256]

@DenisOH Can I work on this?

[emmatyping]

@Arshaan-256 it looks like Denis has already made a PR for this!

[Arshaan-256]

Oh! I am so sorry. I thought that the PR didn't work since the issue was still open. Sorry!

[dhalenok]

@Arshaan-256 I'm still waiting on that PR to be reviewed. However, if it's not good or needs improvement, feel free to take over the issue.