[clang] [Clang][Sema] Diagnose friend declarations with enum elaborated-type-specifier in all language modes (PR #80171)

[Vlad Serebrennikov via cfe-commits]

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@@ -1637,10 +1637,8 @@ def err_inline_namespace_std : Error<
 def err_unexpected_friend : Error<
   "friends can only be classes or functions">;
 def ext_enum_friend : ExtWarn<
-  "befriending enumeration type %0 is a C++11 extension">, InGroup<CXX11>;
-def warn_cxx98_compat_enum_friend : Warning<
-  "befriending enumeration type %0 is incompatible with C++98">,
-  InGroup<CXX98Compat>, DefaultIgnore;
+  "elaborated enumeration type cannot be a friend">,
----------------
Endilll wrote:

> This isn't quite correct either because enum can follow the friend keyword 😛, e.g.

Ugh, you are right. I think it even defeats your initial suggestions, which read `A friend declaration cannot use an elaborated type specifier starting with enum`, because it can when befriending a function, as you just showed. I guess no way around standardese then: `Elaborated type specifier cannot be used to befriend an enumeration. Consider omitting 'enum' keyword`. I'd like the wording to be accurate on terminology, yet actionable for users who are not well-versed in standardese.

https://github.com/llvm/llvm-project/pull/80171