[clang] [Clang] Diagnose unexpanded packs for NTTP type constraints (PR #121296)

[Younan Zhang via cfe-commits]

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@@ -857,7 +857,8 @@ class PackDeductionScope {
       if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(
               TemplateParams->getParam(Index))) {
         if (!NTTP->isExpandedParameterPack())
-          if (auto *Expansion = dyn_cast<PackExpansionType>(NTTP->getType()))
+          if (auto *Expansion = dyn_cast<PackExpansionType>(
+                  S.Context.getUnconstrainedType(NTTP->getType())))
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zyn0217 wrote:

Sigh. Looks like having run into another dark corner of C++ :/

https://github.com/llvm/llvm-project/pull/121296