[clang] [clang-tools-extra] [clang] Implement CWG2398 provisional TTP matching to class templates (PR #94981)

[via cfe-commits]

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@@ -645,6 +645,9 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
      // It is sufficient to check value of getAsTemplateDecl.
      break;
 
+   case TemplateName::DeducedTemplate:
+     // FIXME: We can't reach here.
+     llvm_unreachable("unimplemented");
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cor3ntin wrote:

is it unreachable or just unimplemented?
If deduced arguments are only used during partial ordering they should never need to be compared for structural equivalence... maybe. I am not actually sure, but the fix me and the strings should agree with each other!

https://github.com/llvm/llvm-project/pull/94981