A single class allows multiple categories to be defined for it. But if
two of such categories have the same name, we emit a warning. It's not a
hard error but a good indication of a potential mistake.
With modules, we can end up with the same category in different modules.
Diagnosing such a situation has little value as the categories in
different modules are equivalent and don't reflect the usage of the same
name for different purposes. When we deserialize a duplicate category,
compare it to an existing one and warn only when the new one is
different.
rdar://104582081
Differential Revision: https://reviews.llvm.org/D144149
Instead of emitting a redefinition error, check that definitions are
equivalent and allow such scenario.
A few non-obvious implementation details:
* to avoid multiple definitions in the redeclaration chain we just drop
the new definition after checking for equivalence;
* for checking definition equivalence use ODR hash instead of
ASTStructuralEquivalence because it avoids excessive recursive
deserialization. Though after detecting a mismatch we do deserialize
multiple entities to provide a better error message.
rdar://82908223
Differential Revision: https://reviews.llvm.org/D124286
When two modules contain interfaces with the same name, check the
definitions are equivalent and diagnose if they are not.
Differential Revision: https://reviews.llvm.org/D140073
