Add semantic analysis for the creation of and an AST representation

for template template argument pack expansions. This allows fun such
as: 

  template<template<class> class ...> struct apply_impl { /*...*/ };
  template<template<class> class ...Metafunctions> struct apply {
    typedef typename apply_impl<Metafunctions...>::type type;
  };

However, neither template argument deduction nor template
instantiation is implemented for template template argument packs, so
this functionality isn't useful yet.

I'll probably replace the encoding of template template
argument pack expansions in TemplateArgument so that it's harder to
accidentally forget about the expansion. However, this is a step in
the right general direction.

llvm-svn: 122890

1 files changed, 26 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaTemplateVariadic.cpp b/clang/lib/Sema/SemaTemplateVariadic.cpp
index acb73144d92..fb88bd114b4 100644
--- a/clang/lib/Sema/SemaTemplateVariadic.cpp
+++ b/clang/lib/Sema/SemaTemplateVariadic.cpp
@@ -130,6 +130,22 @@ namespace {
 
       return true; 
     }
+
+    /// \brief Suppress traversal of template argument pack expansions.
+    bool TraverseTemplateArgument(const TemplateArgument &Arg) {
+      if (Arg.isPackExpansion())
+        return true;
+
+      return inherited::TraverseTemplateArgument(Arg);
+    }
+
+    /// \brief Suppress traversal of template argument pack expansions.
+    bool TraverseTemplateArgumentLoc(const TemplateArgumentLoc &ArgLoc) {
+      if (ArgLoc.getArgument().isPackExpansion())
+        return true;
+      
+      return inherited::TraverseTemplateArgumentLoc(ArgLoc);
+    }
   };
 }
 
@@ -335,8 +351,16 @@ Sema::ActOnPackExpansion(const ParsedTemplateArgument &Arg,
   }
     
   case ParsedTemplateArgument::Template:
-    Diag(EllipsisLoc, diag::err_pack_expansion_unsupported);
-    return ParsedTemplateArgument();
+    if (!Arg.getAsTemplate().get().containsUnexpandedParameterPack()) {
+      SourceRange R(Arg.getLocation());
+      if (Arg.getScopeSpec().isValid())
+        R.setBegin(Arg.getScopeSpec().getBeginLoc());
+      Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
+        << R;
+      return ParsedTemplateArgument();
+    }
+      
+    return Arg.getTemplatePackExpansion(EllipsisLoc);
   }
   llvm_unreachable("Unhandled template argument kind?");
   return ParsedTemplateArgument();