The code in class_hierarchy.dart that looped over override pairs
included implementations inherited from its superclass as potential
overriders, presumably in a broken attempt to include some interface
checks into the mix.
With this problem fixed, the special case in kernel_class_builder.dart
that excluded overriders not declared in the current class (i.e.
declared in a mixin) could be removed without incurring false
positives.
These override checks performed on members from a mixin produce an
extra context message indicating the class where the two members meet,
giving rise to the override relation (similarly to interface checks).
Since the same member can now override more than one member (or even
the same member more than once), the diagnostics message duplication
check has been extended to also include the context in the comparison.
Fixes https://github.com/dart-lang/sdk/issues/34235
Fixes https://github.com/dart-lang/sdk/issues/34285
Change-Id: I990e5719ae1749fd1aad1ad478aaa6e173cb170b
Reviewed-on: https://dart-review.googlesource.com/c/76900
Reviewed-by: Daniel Hillerström <hillerstrom@google.com>
Aske Simon Christensen
bb2775b16a