[c++1z] P0195R2: Support pack-expansion of using-declarations.

This change introduces UsingPackDecl as a marker for the set of UsingDecls
produced by pack expansion of a single (unresolved) using declaration. This is
not strictly necessary (we just need to be able to map from the original using
declaration to its expansions somehow), but it's useful to maintain the
invariant that each declaration reference instantiates to refer to one
declaration.

This is a re-commit of r290080 (reverted in r290092) with a fix for a
use-after-lifetime bug.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@290203 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 13 insertions, 0 deletions

diff --git a/include/clang/Basic/DeclNodes.td b/include/clang/Basic/DeclNodes.td
index 6da2c2c3d6..7b581d3eec 100644
--- a/include/clang/Basic/DeclNodes.td
+++ b/include/clang/Basic/DeclNodes.td
@@ -67,6 +67,7 @@ def Named : Decl<1>;
     def TemplateTemplateParm : DDecl<Template>;
     def BuiltinTemplate : DDecl<Template>;
   def Using : DDecl<Named>;
+  def UsingPack : DDecl<Named>;
   def UsingShadow : DDecl<Named>;
     def ConstructorUsingShadow : DDecl<UsingShadow>;
   def ObjCMethod : DDecl<Named>, DeclContext;
diff --git a/include/clang/Basic/DiagnosticParseKinds.td b/include/clang/Basic/DiagnosticParseKinds.td
index 31e55b4aff..0943feae95 100644
--- a/include/clang/Basic/DiagnosticParseKinds.td
+++ b/include/clang/Basic/DiagnosticParseKinds.td
@@ -740,6 +740,8 @@ def err_alias_declaration_not_identifier : Error<
   "name defined in alias declaration must be an identifier">;
 def err_alias_declaration_specialization : Error<
   "%select{partial specialization|explicit specialization|explicit instantiation}0 of alias templates is not permitted">;
+def err_alias_declaration_pack_expansion : Error<
+  "alias declaration cannot be a pack expansion">;
 
 // C++1z using-declaration pack expansions
 def ext_multi_using_declaration : ExtWarn<
@@ -749,6 +751,11 @@ def warn_cxx1z_compat_multi_using_declaration : Warning<
   "use of multiple declarators in a single using declaration is "
   "incompatible with C++ standards before C++1z">,
   InGroup<CXXPre1zCompat>, DefaultIgnore;
+def ext_using_declaration_pack : ExtWarn<
+  "pack expansion of using declaration is a C++1z extension">, InGroup<CXX1z>;
+def warn_cxx1z_compat_using_declaration_pack : Warning<
+  "pack expansion using declaration is incompatible with C++ standards "
+  "before C++1z">, InGroup<CXXPre1zCompat>, DefaultIgnore;
 
 // C++11 override control
 def ext_override_control_keyword : ExtWarn<
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 69322f0f75..f32364e9af 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -474,6 +474,8 @@ def err_using_decl_conflict : Error<
 def err_using_decl_conflict_reverse : Error<
   "declaration conflicts with target of using declaration already in scope">;
 def note_using_decl : Note<"%select{|previous }0using declaration">;
+def err_using_decl_redeclaration_expansion : Error<
+  "using declaration pack expansion at block scope produces multiple values">;
 
 def warn_access_decl_deprecated : Warning<
   "access declarations are deprecated; use using declarations instead">,
@@ -4155,6 +4157,9 @@ def err_variable_instantiates_to_function : Error<
 def err_nested_name_spec_non_tag : Error<
   "type %0 cannot be used prior to '::' because it has no members">;
 
+def err_using_pack_expansion_empty : Error<
+  "%select{|member}0 using declaration %1 instantiates to an empty pack">;
+
 // C++ Explicit Instantiation
 def err_explicit_instantiation_duplicate : Error<
     "duplicate explicit instantiation of %0">;