Implement new reportIncompatibleVariableOverride

[erictraut]

Pyright currently supports a diagnostic rule called reportIncompatibleMethodOverride that detects when a subclass overrides a base class method in an incompatible way.

It would be useful to have a similar rule called reportIncompatibleVariableOverride that detects when a subclass declares an instance variable that is of an incompatible type. Properties and class variables will need to be taken into consideration.

For more thoughts, refer to this issue: microsoft/pylance-release#157 (comment)

[jakebailey]

For reference, this rule would not flag the code in #157 (actually) #867 as it would be "compatible", correct?

[erictraut]

No, it would still flag the code as in error because a property is not the same as a variable. They have different semantics. However, the user could disable this rule if they don't care about those semantic differences.

[jakebailey]

Oh, this is my mistake. I meant the other override issue we had talked about previously, which is #867.

[erictraut]

Correct. reportIncompatibleMethodOverride would be specific to methods, and reportIncompatibleVariableOverride would be specific to non-method fields including instance variables and property objects.

[erictraut]

This is addressed in Pyright version 1.1.57, which I just published. It will also be included in the next version of Pylance.