[clang] [Clang][Parse] Diagnose member template declarations with multiple declarators (PR #78243)

[via cfe-commits]

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@@ -3167,6 +3167,15 @@ Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
 
     DeclaratorInfo.complete(ThisDecl);
 
+    if (TemplateInfo.Kind != ParsedTemplateInfo::NonTemplate) {
+      if (Tok.is(tok::comma)) {
+        Diag(Tok, diag::err_multiple_template_declarators)
+            << (int)TemplateInfo.Kind;
+        SkipUntil(tok::semi, StopBeforeMatch);
+      }
+      break;
+    }
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cor3ntin wrote:

I am not sure it make sense to do that in the parser.
Can we maybe to that in `FinalizeDeclaratorGroup`?
At that point we should have fully formed `Decl`s and we can check whether they are templates

https://github.com/llvm/llvm-project/pull/78243