[clang] [Clang] Remove the wrong assumption when rebuilding SizeOfPackExprs for constraint normalization (PR #115120)

[Matheus Izvekov via cfe-commits]

================
@@ -1731,31 +1731,21 @@ namespace {
       return inherited::TransformLambdaBody(E, Body);
     }
 
-    ExprResult RebuildSizeOfPackExpr(SourceLocation OperatorLoc,
-                                     NamedDecl *Pack, SourceLocation PackLoc,
-                                     SourceLocation RParenLoc,
-                                     std::optional<unsigned> Length,
-                                     ArrayRef<TemplateArgument> PartialArgs) {
-      if (SemaRef.CodeSynthesisContexts.back().Kind !=
-          Sema::CodeSynthesisContext::ConstraintNormalization)
-        return inherited::RebuildSizeOfPackExpr(OperatorLoc, Pack, PackLoc,
-                                                RParenLoc, Length, PartialArgs);
-
-#ifndef NDEBUG
-      for (auto *Iter = TemplateArgs.begin(); Iter != TemplateArgs.end();
-           ++Iter)
-        for (const TemplateArgument &TA : Iter->Args)
-          assert(TA.getKind() != TemplateArgument::Pack || TA.pack_size() == 1);
-#endif
-      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(
-          SemaRef, /*NewSubstitutionIndex=*/0);
-      Decl *NewPack = TransformDecl(PackLoc, Pack);
-      if (!NewPack)
-        return ExprError();
-
-      return inherited::RebuildSizeOfPackExpr(OperatorLoc,
-                                              cast<NamedDecl>(NewPack), PackLoc,
-                                              RParenLoc, Length, PartialArgs);
+    ExprResult TransformSizeOfPackExpr(SizeOfPackExpr *E) {
+      ExprResult Transformed = inherited::TransformSizeOfPackExpr(E);
+      if (!Transformed.isUsable())
+        return Transformed;
+      auto *TransformedExpr = cast<SizeOfPackExpr>(Transformed.get());
+      if (SemaRef.CodeSynthesisContexts.back().Kind ==
+              Sema::CodeSynthesisContext::ConstraintNormalization &&
+          TransformedExpr->getPack() == E->getPack()) {
+        Decl *NewPack =
+            TransformDecl(E->getPackLoc(), TransformedExpr->getPack());
+        if (!NewPack)
+          return ExprError();
+        TransformedExpr->setPack(cast<NamedDecl>(NewPack));
----------------
mizvekov wrote:

It looks like there is some dance here that could be avoided if we moved this into the inherited transform function in TreeTransform.h instead.

https://github.com/llvm/llvm-project/pull/115120