[Clang][P1061] Move rebuild of resolved packs into TreeTransform

Author: ricejasonf

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -2490,7 +2490,9 @@ TemplateInstantiator::TransformDeclRefExpr(DeclRefExpr *E) {
       return TransformFunctionParmPackRefExpr(E, PD);
 
   if (BindingDecl *BD = dyn_cast<BindingDecl>(D); BD && BD->isParameterPack()) {
-    BD = cast<BindingDecl>(TransformDecl(BD->getLocation(), BD));
+    BD = cast_or_null<BindingDecl>(TransformDecl(BD->getLocation(), BD));
+    if (!BD)
+      return ExprError();
     if (auto *RP =
             dyn_cast_if_present<ResolvedUnexpandedPackExpr>(BD->getBinding())) {
       return TransformResolvedUnexpandedPackExpr(RP);
@@ -2671,18 +2673,7 @@ ExprResult TemplateInstantiator::TransformResolvedUnexpandedPackExpr(
         E->getExpansion(getSema().ArgumentPackSubstitutionIndex));
   }
 
-  if (!AlwaysRebuild())
-    return E;
-
-  SmallVector<Expr *, 12> NewExprs;
-  if (TransformExprs(E->getExprs().begin(), E->getNumExprs(),
-                     /*IsCall=*/false, NewExprs))
-    return ExprError();
-
-  // NOTE: The type is just a superficial PackExpansionType
-  //       that needs no substitution.
-  return ResolvedUnexpandedPackExpr::Create(SemaRef.Context, E->getBeginLoc(),
-                                            E->getType(), NewExprs);
+  return inherited::TransformResolvedUnexpandedPackExpr(E);
 }
 
 QualType TemplateInstantiator::TransformSubstTemplateTypeParmPackType(

clang/lib/Sema/TreeTransform.h

@@ -3676,6 +3676,13 @@ class TreeTransform {
                                            FullySubstituted);
   }
 
+  ExprResult RebuildResolvedUnexpandedPackExpr(SourceLocation BeginLoc,
+                                               QualType T,
+                                               ArrayRef<Expr *> Exprs) {
+    return ResolvedUnexpandedPackExpr::Create(SemaRef.Context, BeginLoc, T,
+                                              Exprs);
+  }
+
   /// Build a new expression representing a call to a source location
   ///  builtin.
   ///
@@ -15994,8 +16001,19 @@ TreeTransform<Derived>::TransformFunctionParmPackExpr(FunctionParmPackExpr *E) {
 template <typename Derived>
 ExprResult TreeTransform<Derived>::TransformResolvedUnexpandedPackExpr(
     ResolvedUnexpandedPackExpr *E) {
-  // Default behavior is to do nothing with this transformation.
-  return E;
+  bool ArgumentChanged = false;
+  SmallVector<Expr *, 12> NewExprs;
+  if (TransformExprs(E->getExprs().begin(), E->getNumExprs(),
+                     /*IsCall=*/false, NewExprs, &ArgumentChanged))
+    return ExprError();
+
+  if (!AlwaysRebuild() && !ArgumentChanged)
+    return E;
+
+  // NOTE: The type is just a superficial PackExpansionType
+  //       that needs no substitution.
+  return RebuildResolvedUnexpandedPackExpr(E->getBeginLoc(), E->getType(),
+                                           NewExprs);
 }
 
 template<typename Derived>