2 files changed, 15 insertions, 7 deletions
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index b0351d69ad..c83e70a72b 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -2892,10 +2892,17 @@ QualType ASTContext::getPackExpansionType(QualType Pattern,
 
   QualType Canon;
   if (!Pattern.isCanonical()) {
-    Canon = getPackExpansionType(getCanonicalType(Pattern), NumExpansions);
-
-    // Find the insert position again.
-    PackExpansionTypes.FindNodeOrInsertPos(ID, InsertPos);
+    Canon = getCanonicalType(Pattern);
+    // The canonical type might not contain an unexpanded parameter pack, if it
+    // contains an alias template specialization which ignores one of its
+    // parameters.
+    if (Canon->containsUnexpandedParameterPack()) {
+      Canon = getPackExpansionType(getCanonicalType(Pattern), NumExpansions);
+
+      // Find the insert position again, in case we inserted an element into
+      // PackExpansionTypes and invalidated our insert position.
+      PackExpansionTypes.FindNodeOrInsertPos(ID, InsertPos);
+    }
   }
 
   T = new (*this) PackExpansionType(Pattern, Canon, NumExpansions);
diff --git a/lib/AST/Type.cpp b/lib/AST/Type.cpp
index 4fef11f2a8..eacf505442 100644
--- a/lib/AST/Type.cpp
+++ b/lib/AST/Type.cpp
@@ -1862,8 +1862,7 @@ TemplateSpecializationType(TemplateName T,
          Canon.isNull()? T.isDependent() 
                        : Canon->isInstantiationDependentType(),
          false,
-         Canon.isNull()? T.containsUnexpandedParameterPack()
-                       : Canon->containsUnexpandedParameterPack()),
+         T.containsUnexpandedParameterPack()),
     Template(T), NumArgs(NumArgs), TypeAlias(!AliasedType.isNull()) {
   assert(!T.getAsDependentTemplateName() && 
          "Use DependentTemplateSpecializationType for dependent template-name");
@@ -1888,6 +1887,8 @@ TemplateSpecializationType(TemplateName T,
     // arguments is. Given:
     //   template<typename T> using U = int;
     // U<T> is always non-dependent, irrespective of the type T.
+    // However, U<Ts> contains an unexpanded parameter pack, even though
+    // its expansion (and thus its desugared type) doesn't.
     if (Canon.isNull() && Args[Arg].isDependent())
       setDependent();
     else if (Args[Arg].isInstantiationDependent())
@@ -1896,7 +1897,7 @@ TemplateSpecializationType(TemplateName T,
     if (Args[Arg].getKind() == TemplateArgument::Type &&
         Args[Arg].getAsType()->isVariablyModifiedType())
       setVariablyModified();
-    if (Canon.isNull() && Args[Arg].containsUnexpandedParameterPack())
+    if (Args[Arg].containsUnexpandedParameterPack())
       setContainsUnexpandedParameterPack();
 
     new (&TemplateArgs[Arg]) TemplateArgument(Args[Arg]);