[clang] [Clang] Fix the normalization of fold constraints (PR #177531)

[Younan Zhang via cfe-commits]

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@@ -2239,16 +2253,39 @@ bool SubstituteParameterMappings::substitute(NormalizedConstraint &N) {
     }
     assert(!ArgsAsWritten);
     const ConceptSpecializationExpr *CSE = CC.getConceptSpecializationExpr();
+    SmallVector<TemplateArgument> InnerArgs(CSE->getTemplateArguments());
     ConceptDecl *Concept = CSE->getNamedConcept();
+    if (RemovePacksForFoldExpr) {
+      TemplateArgumentListInfo OutArgs;
+      ArrayRef<TemplateArgumentLoc> InputArgLoc =
+          CSE->getConceptReference()->getTemplateArgsAsWritten()->arguments();
+      if (AdjustConstraints(SemaRef, /*TemplateDepth=*/0,
+                            /*RemoveNonPackExpansionPacks=*/true)
+              .TransformTemplateArguments(InputArgLoc.begin(),
+                                          InputArgLoc.end(), OutArgs))
+        return true;
+      Sema::CheckTemplateArgumentInfo CTAI;
+      // Repack the packs.
+      if (SemaRef.CheckTemplateArgumentList(
+              Concept, Concept->getTemplateParameters(), Concept->getBeginLoc(),
+              OutArgs,
+              /*DefaultArguments=*/{},
+              /*PartialTemplateArgs=*/false, CTAI))
+        return true;
+      InnerArgs = std::move(CTAI.SugaredConverted);
+      RemovePacksForFoldExpr = false;
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zyn0217 wrote:

No it doesn't seem very useful ...
I thought we were collecting template arguments at each level of concept constraints, I was wrong :(

https://github.com/llvm/llvm-project/pull/177531