mypy

8b86349e - Fix spurious errors in inherited dataclasses in incremental mode (#7596)

Fix spurious errors in inherited dataclasses in incremental mode (#7596) The dataclasses plugin incorrectly expected json to preserve the ordering of its dictionaries, which led to spurious errors about "Attributes without a default cannot follow attributes with one". Worse, the errors are reported in the wrong file: they use the line number of the attribute but the file of the dataclass being checked! Fix the spurious error by serializing attributes in a list, since we care about the order. Reporting this error for attributes in parent classes is actually useful, since multiple inheritance can cause this error. Report the error at the class definition site causing the problem instead. (The error message here could certainly be improved, but right now I just want to fix the "wrong file" bugs, which are I think the worst kind of bugs after crashes.)