[class.compare.default] Clarify whether a defaulted comparison operator that is a `friend` can be redeclared in a class

[Sirraide]

Full name of submitter (unless configured in github; will be published with the issue): Ambrose T.

[class.compare.default]p1 states:

A definition of a comparison operator as defaulted that appears in a class shall be the first declaration of that function

Does this apply to the following friend declarations?

struct b {
  friend bool operator==(b, b);
  friend bool operator==(b, b) = default;
};

I’m mainly asking because Clang and EDG diagnose this as an error whereas GCC and MSVC accept this code. At the same time, it’s already invalid for members to be redeclared in a class, so by that logic the fact that this sentence is even there would indicate that it should (also) apply to non-members, i.e. friends (if that is the intended reading, maybe adding a note/example for this would help?).

[frederick-vs-ja]

Does this apply to the following friend declarations?

I believe the answer is clearly yes. The current standard wording looks very clear to me here.

[Endilll]

We have rigorous terminology to talk about these things, so we should clarify which scope we're talking about (immediate vs target).

At the same time, it’s already invalid for members to be redeclared in a class

I'm not following. Member functions can be redeclared with e.g. additional default arguments.

[Endilll]

The wording in question comes from P2085R0 "Consistent defaulted comparisons" by Davis.