[clang] [Clang][Sema] Mark partial specializations invalid when not more specialized than primary (PR #181561)

[Oliver Hunt via cfe-commits]

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@@ -4229,6 +4229,9 @@ static void checkMoreSpecializedThanPrimary(Sema &S, PartialSpecDecl *Partial) {
          diag::ext_partial_spec_not_more_specialized_than_primary)
       << isa<VarTemplateDecl>(Template);
 
+  // An invalid partial specialization should not be deduced.
+  Partial->setInvalidDecl();
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ojhunt wrote:

Why is this being marked as invalid?

https://github.com/llvm/llvm-project/pull/181561