Incorrect diagnostic wording for out-of-line enum declarations

[Endilll]

Consider the following (https://godbolt.org/z/cj1hMqbof):

struct A {
  enum E : int;
};

namespace N {
enum A::E : int { e1 };
}

Clang rejects this with error: cannot define or redeclare 'E' here because namespace 'N' does not enclose namespace 'A', but A is a struct and not a namespace.

Edit: more importantly, it seems that this code is well-formed per https://eel.is/c++draft/enum#dcl.enum-4:

If an enum-head-name contains a nested-name-specifier, the enclosing enum-specifier or opaque-enum-declaration D shall not inhabit a class scope and shall correspond to one or more declarations nominable in the class, class template, or namespace to which the nested-name-specifier refers ([basic.scope.scope]).
All those declarations shall have the same target scope; the target scope of D is that scope.

[llvmbot]

@llvm/issue-subscribers-c-1

Author: Vlad Serebrennikov (Endilll)

Consider the following (https://godbolt.org/z/cj1hMqbof): ```cpp struct A { enum E : int; };

namespace N {
enum A::E : int { e1 };
}

Clang rejects this with `error: cannot define or redeclare 'E' here because namespace 'N' does not enclose namespace 'A'`, but `A` is a struct and not a namespace.
</details>

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Vlad Serebrennikov (Endilll)

Consider the following (https://godbolt.org/z/cj1hMqbof): ```cpp struct A { enum E : int; };

namespace N {
enum A::E : int { e1 };
}

Clang rejects this with `error: cannot define or redeclare 'E' here because namespace 'N' does not enclose namespace 'A'`, but `A` is a struct and not a namespace.

Edit: more importantly, it seems that this code is well-formed per https://eel.is/c++draft/enum#dcl.enum-4:
> If an [enum-head-name](https://eel.is/c++draft/enum#nt:enum-head-name) contains a [nested-name-specifier](https://eel.is/c++draft/expr.prim.id.qual#nt:nested-name-specifier), the enclosing [enum-specifier](https://eel.is/c++draft/enum#nt:enum-specifier) or [opaque-enum-declaration](https://eel.is/c++draft/enum#nt:opaque-enum-declaration) D shall not inhabit a class scope and shall correspond to one or more declarations nominable in the class, class template, or namespace to which the [nested-name-specifier](https://eel.is/c++draft/expr.prim.id.qual#nt:nested-name-specifier) refers ([[basic.scope.scope]](https://eel.is/c++draft/basic.scope.scope))[.](https://eel.is/c++draft/enum#dcl.enum-4.sentence-1)
All those declarations shall have the same target scope; the target scope of D is that scope[.](https://eel.is/c++draft/enum#dcl.enum-4.sentence-2)
</details>

[zygoloid]

Clang rejects this with error: cannot define or redeclare 'E' here because namespace 'N' does not enclose namespace 'A', but A is a struct and not a namespace.

Perhaps removing the word "namespace" would help?

Edit: more importantly, it seems that this code is well-formed per https://eel.is/c++draft/enum#dcl.enum-4:

That paragraph only contains restrictions, so can't make code well-formed. It looks to me like this example violates [expr.prim.id.qual]/2:

A declaration that uses a declarative nested-name-specifier shall be a friend declaration or inhabit a scope that contains the entity being redeclared or specialized.

The scope of namespace N does not contain A::E.

[Endilll]

It looks to me like this example violates [expr.prim.id.qual]/2:

Oh, I missed that wording. I agree that the example is ill-formed.