Becca Royal-Gordon 94ec99c7f0 Avoid invalidating @_objcImplementation ...

In #69257, we modified `ObjCReason` to carry a pointer to the @implementation attribute for the `MemberOfObjCImplementationExtension` kind. This made it mark the @implementation attribute as invalid, suppressing diagnostics from the ObjCImplementationChecker.

However, invalidating the attribute *also* causes it to be skipped by serialization. That isn’t a problem if the diagnostics are errors, since we’ll never emit the serialized module, but #74135 softened these diagnostics to warnings for early adopters.

The upshot was that if Swift emitted one of these warnings when it compiled a library, clients of that library would see the objcImpl extension as a normal extension instead. This would cause various kinds of mischief: ambiguous name lookups because implementations weren’t being excluded, overrides failing because an implementation was `public` instead of `open`, asserts and crashes in SILGen and IRGen because stored properties were found in seemingly normal extensions, etc.

Fix this by setting a separate bit on ObjCImplementationAttr, rather than the invalid bit, and modifying the implementation checker to manually suppress many diagnostics when that bit is set.

Fixes rdar://134730183.

2024-09-05 17:55:12 -07:00

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