[cxx-interop] Do not add base class members that cause lookup ambigui…

[hyp]

…ties with a derived class member of the same name

Fixes #66323

[hyp]

@swift-ci please test

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@swift-ci please test source compatibility

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@swift-ci please test

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@swift-ci please test macOS platform

[egorzhdan]

Would we still be able to import void foo in this scenario?

// C++
struct A {};
struct B : A {
  void foo(int x);
};

// Swift
extension A {
  func foo(s: String) {}
}

[hyp]

Would we still be able to import void foo in this scenario?

// C++
struct A {};
struct B : A {
  void foo(int x);
};

// Swift
extension A {
 func foo(s: String) {}
}

Good question, I will check.

[hyp]

Would we still be able to import void foo in this scenario?

// C++
struct A {};
struct B : A {
  void foo(int x);
};

// Swift
extension A {
 func foo(s: String) {}
}

Good question, I will check.

Yes, this appears to work. The reason is that methods in Swift extensions on base classes can't be duplicated over as we're only considering original C++ methods for duplication. And of course the inheritance hierarchy is not present in Swift, so B.foo where foo is foo(s: String) wouldn't have worked anyway.