3 files changed, 39 insertions, 10 deletions
diff --git a/lib/Sema/SemaTemplateDeduction.cpp b/lib/Sema/SemaTemplateDeduction.cpp
index 4a667cdf57..99b6daceed 100644
--- a/lib/Sema/SemaTemplateDeduction.cpp
+++ b/lib/Sema/SemaTemplateDeduction.cpp
@@ -2926,6 +2926,10 @@ MarkUsedTemplateParameters(Sema &SemaRef,
                            bool OnlyDeduced,
                            unsigned Depth,
                            llvm::SmallVectorImpl<bool> &Used) {
+  // We can deduce from a pack expansion.
+  if (const PackExpansionExpr *Expansion = dyn_cast<PackExpansionExpr>(E))
+    E = Expansion->getPattern();
+      
   // FIXME: if !OnlyDeduced, we have to walk the whole subexpression to 
   // find other occurrences of template parameters.
   const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E);
diff --git a/lib/Sema/SemaTemplateVariadic.cpp b/lib/Sema/SemaTemplateVariadic.cpp
index 3dac8a0408..030a0423f7 100644
--- a/lib/Sema/SemaTemplateVariadic.cpp
+++ b/lib/Sema/SemaTemplateVariadic.cpp
@@ -79,9 +79,6 @@ namespace {
     
     // FIXME: Record occurrences of template template parameter packs.
 
-    // FIXME: Once we have pack expansions in the AST, block their
-    // traversal.
-
     //------------------------------------------------------------------------
     // Pruning the search for unexpanded parameter packs.
     //------------------------------------------------------------------------
@@ -299,14 +296,17 @@ Sema::ActOnPackExpansion(const ParsedTemplateArgument &Arg,
                                   Arg.getLocation());
   }
 
-  case ParsedTemplateArgument::NonType:
-    Diag(EllipsisLoc, diag::err_pack_expansion_unsupported)
-      << 0;
-    return ParsedTemplateArgument();
-
+  case ParsedTemplateArgument::NonType: {
+    ExprResult Result = ActOnPackExpansion(Arg.getAsExpr(), EllipsisLoc);
+    if (Result.isInvalid())
+      return ParsedTemplateArgument();
+    
+    return ParsedTemplateArgument(Arg.getKind(), Result.get(), 
+                                  Arg.getLocation());
+  }
+    
   case ParsedTemplateArgument::Template:
-    Diag(EllipsisLoc, diag::err_pack_expansion_unsupported)
-      << 1;
+    Diag(EllipsisLoc, diag::err_pack_expansion_unsupported);
     return ParsedTemplateArgument();
   }
   llvm_unreachable("Unhandled template argument kind?");
@@ -352,6 +352,24 @@ TypeSourceInfo *Sema::CheckPackExpansion(TypeSourceInfo *Pattern,
   return TSResult;
 }
 
+ExprResult Sema::ActOnPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc) {
+  if (!Pattern)
+    return ExprError();
+  
+  // C++0x [temp.variadic]p5:
+  //   The pattern of a pack expansion shall name one or more
+  //   parameter packs that are not expanded by a nested pack
+  //   expansion.
+  if (!Pattern->containsUnexpandedParameterPack()) {
+    Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
+    << Pattern->getSourceRange();
+    return ExprError();
+  }
+  
+  // Create the pack expansion expression and source-location information.
+  return Owned(new (Context) PackExpansionExpr(Context.DependentTy, Pattern,
+                                               EllipsisLoc));
+}
 
 bool Sema::CheckParameterPacksForExpansion(SourceLocation EllipsisLoc,
                                            SourceRange PatternRange,
diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index de13084fbc..992b849904 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -6439,6 +6439,13 @@ TreeTransform<Derived>::TransformCXXNoexceptExpr(CXXNoexceptExpr *E) {
 
 template<typename Derived>
 ExprResult
+TreeTransform<Derived>::TransformPackExpansionExpr(PackExpansionExpr *E) {
+  llvm_unreachable("pack expansion expression in unhandled context");
+  return ExprError();
+}
+  
+template<typename Derived>
+ExprResult
 TreeTransform<Derived>::TransformObjCStringLiteral(ObjCStringLiteral *E) {
   return SemaRef.Owned(E);
 }