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, 11 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index b8ec59ee1d6..60f5bc196e0 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/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.