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

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -4166,9 +4166,17 @@ MarkUsedTemplateParameters(ASTContext &Ctx,
   if (const PackExpansionExpr *Expansion = dyn_cast<PackExpansionExpr>(E))
     E = Expansion->getPattern();
 
-  // Skip through any implicit casts we added while type-checking.
-  while (const ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E))
-    E = ICE->getSubExpr();
+  // Skip through any implicit casts we added while type-checking, and any
+  // substitutions performed by template alias expansion.
+  while (1) {
+    if (const ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E))
+      E = ICE->getSubExpr();
+    else if (const SubstNonTypeTemplateParmExpr *Subst =
+               dyn_cast<SubstNonTypeTemplateParmExpr>(E))
+      E = Subst->getReplacement();
+    else
+      break;
+  }
 
   // FIXME: if !OnlyDeduced, we have to walk the whole subexpression to
   // find other occurrences of template parameters.

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) {

clang/test/SemaTemplate/alias-templates.cpp

@@ -109,3 +109,22 @@ namespace PR13243 {
   template<typename A, int I> void f(X<A>, Ci<I>) {}
   template void f(X<int>, C<0>);
 }
+
+namespace PR13136 {
+  template <typename T, T... Numbers>
+  struct NumberTuple { };
+
+  template <unsigned int... Numbers>
+  using MyNumberTuple = NumberTuple<unsigned int, Numbers...>;
+
+  template <typename U, unsigned int... Numbers>
+  void foo(U&&, MyNumberTuple<Numbers...>);
+
+  template <typename U, unsigned int... Numbers>
+  void bar(U&&, NumberTuple<unsigned int, Numbers...>);
+
+  int main() {
+    foo(1, NumberTuple<unsigned int, 0, 1>());
+    bar(1, NumberTuple<unsigned int, 0, 1>());
+  }
+}