When transforming a substituted template type parameter, try to

transform the type that replaces the template type parameter. In the
vast majority of cases, there's nothing to do, because most template
type parameters are replaced with something non-dependent that doesn't
need further transformation. However, when we're dealing with the
default template arguments of template template parameters, we might
end up replacing a template parameter (of the template template
parameter) with a template parameter of the enclosing template. 
 
This addresses part of PR9016, but not within function
templates. That's a separate issue.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@127091 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 1 deletions

diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index 1a5a98a23e..94aac52e5b 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -4126,7 +4126,28 @@ template<typename Derived>
 QualType TreeTransform<Derived>::TransformSubstTemplateTypeParmType(
                                          TypeLocBuilder &TLB,
                                          SubstTemplateTypeParmTypeLoc TL) {
-  return TransformTypeSpecType(TLB, TL);
+  const SubstTemplateTypeParmType *T = TL.getTypePtr();
+  
+  // Substitute into the replacement type, which itself might involve something
+  // that needs to be transformed. This only tends to occur with default
+  // template arguments of template template parameters.
+  TemporaryBase Rebase(*this, TL.getNameLoc(), DeclarationName());
+  QualType Replacement = getDerived().TransformType(T->getReplacementType());
+  if (Replacement.isNull())
+    return QualType();
+  
+  // Always canonicalize the replacement type.
+  Replacement = SemaRef.Context.getCanonicalType(Replacement);
+  QualType Result
+    = SemaRef.Context.getSubstTemplateTypeParmType(T->getReplacedParameter(), 
+                                                   Replacement);
+  
+  // Propagate type-source information.
+  SubstTemplateTypeParmTypeLoc NewTL
+    = TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
+  NewTL.setNameLoc(TL.getNameLoc());
+  return Result;
+
 }
 
 template<typename Derived>