[clang] [Clang][Sema] Ensure that the selected candidate for a member function explicit specialization is more constrained than all others (PR #101721)

[Krystian Stasiowski via cfe-commits]

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@@ -7964,8 +7964,9 @@ NamedDecl *Sema::ActOnVariableDeclarator(
     D.setRedeclaration(CheckVariableDeclaration(NewVD, Previous));
   } else {
     // If this is an explicit specialization of a static data member, check it.
-    if (IsMemberSpecialization && !IsVariableTemplateSpecialization &&
-        !NewVD->isInvalidDecl() && CheckMemberSpecialization(NewVD, Previous))
+    if (IsMemberSpecialization && !IsVariableTemplate &&
+        !IsVariableTemplateSpecialization && !NewVD->isInvalidDecl() &&
+        CheckMemberSpecialization(NewVD, Previous))
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sdkrystian wrote:

> Hm, do we not want to do these checks for an explicit specialization of a member template? Or do we also do those checks somewhere else?

`CheckMemberSpecialization` only handles explicit specializations of non-template members specialized for an implicit instantiation of a class template. 

Explicit specializations of _member templates_ specialized for an implicit instantiation of a class template are handled on the same codepath as normal templates, and we set the correct "instantiated from" template there.

https://github.com/llvm/llvm-project/pull/101721