[clang] [Clang] Reapply CWG2369 "Ordering between constraints and substitution" (PR #122423)

[via cfe-commits]

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@@ -1432,12 +1459,20 @@ namespace {
                                  ArrayRef<UnexpandedParameterPack> Unexpanded,
                                  bool &ShouldExpand, bool &RetainExpansion,
                                  UnsignedOrNone &NumExpansions) {
-      return getSema().CheckParameterPacksForExpansion(EllipsisLoc,
-                                                       PatternRange, Unexpanded,
-                                                       TemplateArgs,
-                                                       ShouldExpand,
-                                                       RetainExpansion,
-                                                       NumExpansions);
+      if (SemaRef.CurrentInstantiationScope &&
+          SemaRef.inConstraintSubstitution()) {
+        for (UnexpandedParameterPack ParmPack : Unexpanded) {
+          NamedDecl *VD = ParmPack.first.dyn_cast<NamedDecl *>();
+          if (!isa_and_present<ParmVarDecl>(VD))
+            continue;
+          if (maybeInstantiateFunctionParameterToScope(cast<ParmVarDecl>(VD)))
+            return true;
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cor3ntin wrote:

You can use dyn_cast

https://github.com/llvm/llvm-project/pull/122423