PR13136:

 * When substituting a reference to a non-type template parameter pack where the
   corresponding argument is a pack expansion, transform into an expression
   which contains an unexpanded parameter pack rather than into an expression
   which contains a pack expansion. This causes the SubstNonTypeTemplateParmExpr
   to be inside the PackExpansionExpr, rather than outside, so the expression
   still looks like a pack expansion and can be deduced.

 * Teach MarkUsedTemplateParameters that we can deduce a reference to a template
   parameter if it's wrapped in a SubstNonTypeTemplateParmExpr (such nodes are
   added during alias template substitution).

llvm-svn: 159922

1 files changed, 10 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 7416d123017..239a0d73ebc 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -851,7 +851,7 @@ namespace {
   private:
     ExprResult transformNonTypeTemplateParmRef(NonTypeTemplateParmDecl *parm,
                                                SourceLocation loc,
-                                               const TemplateArgument &arg);
+                                               TemplateArgument arg);
   };
 }
 
@@ -1140,10 +1140,18 @@ TemplateInstantiator::TransformTemplateParmRefExpr(DeclRefExpr *E,
 ExprResult TemplateInstantiator::transformNonTypeTemplateParmRef(
                                                  NonTypeTemplateParmDecl *parm,
                                                  SourceLocation loc,
-                                                 const TemplateArgument &arg) {
+                                                 TemplateArgument arg) {
   ExprResult result;
   QualType type;
 
+  // If the argument is a pack expansion, the parameter must actually be a
+  // parameter pack, and we should substitute the pattern itself, producing
+  // an expression which contains an unexpanded parameter pack.
+  if (arg.isPackExpansion()) {
+    assert(parm->isParameterPack() && "pack expansion for non-pack");
+    arg = arg.getPackExpansionPattern();
+  }
+
   // The template argument itself might be an expression, in which
   // case we just return that expression.
   if (arg.getKind() == TemplateArgument::Expression) {