[-fms-extensions] Allow multiply derived types to override ambiguously named members

[majnemer]

Bugzilla Link	17629
Version	trunk
OS	All
Blocks	#14079
CC	@DougGregor,@timurrrr

Extended Description

Consider:

struct T1 {
  virtual int Foo() = 0;
};

struct T2 {
  virtual int Foo() = 0;
};

struct T3 : public virtual T1, public virtual T2 {
  virtual int T1::Foo() { return 19; }
  virtual int T2::Foo() { return 42; }
};

MSVC allows T1::Foo and T2::Foo to be overridden.

[majnemer]

This is documented here: http://msdn.microsoft.com/en-us/library/vstudio/ksek8777.aspx

[majnemer]

Furthermore, I believe that this extension is what permits them to allow extra qualifiers on members a la:

struct S {
  void S::fun() {}
}

[majnemer]

*** Bug llvm/llvm-bugzilla-archive#26735 has been marked as a duplicate of this bug. ***

[majnemer]

mentioned in issue llvm/llvm-bugzilla-archive#26735

[Endilll]

Clang 21.0 still rejects this: https://godbolt.org/z/3dGE45PnK

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (991901f3-cc14-4404-b340-165691b62a58)

| | | | --- | --- | | Bugzilla Link | [17629](https://llvm.org/bz17629) | | Version | trunk | | OS | All | | Blocks | llvm/llvm-project#14079 | | CC | @DougGregor,@timurrrr |

Extended Description

Consider:

struct T1 {
  virtual int Foo() = 0;
};

struct T2 {
  virtual int Foo() = 0;
};

struct T3 : public virtual T1, public virtual T2 {
  virtual int T1::Foo() { return 19; }
  virtual int T2::Foo() { return 42; }
};

MSVC allows T1::Foo and T2::Foo to be overridden.