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

This reverts commit r290080 as it leads to many Clang crashes, e.g.:
http://lab.llvm.org:8011/builders/clang-cmake-aarch64-quick/builds/1814

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@290092 91177308-0d34-0410-b5e6-96231b3b80d8

9 files changed, 17 insertions, 146 deletions

diff --git a/include/clang/AST/DeclCXX.h b/include/clang/AST/DeclCXX.h
index 06ecd3c373..46434c4c7b 100644
--- a/include/clang/AST/DeclCXX.h
+++ b/include/clang/AST/DeclCXX.h
@@ -3140,77 +3140,6 @@ public:
   friend class ASTDeclWriter;
 };
 
-/// Represents a pack of using declarations that a single
-/// using-declarator pack-expanded into.
-///
-/// \code
-/// template<typename ...T> struct X : T... {
-///   using T::operator()...;
-///   using T::operator T...;
-/// };
-/// \endcode
-///
-/// In the second case above, the UsingPackDecl will have the name
-/// 'operator T' (which contains an unexpanded pack), but the individual
-/// UsingDecls and UsingShadowDecls will have more reasonable names.
-class UsingPackDecl final
-    : public NamedDecl, public Mergeable<UsingPackDecl>,
-      private llvm::TrailingObjects<UsingPackDecl, NamedDecl *> {
-  void anchor() override;
-
-  /// The UnresolvedUsingValueDecl or UnresolvedUsingTypenameDecl from
-  /// which this waas instantiated.
-  NamedDecl *InstantiatedFrom;
-
-  /// The number of using-declarations created by this pack expansion.
-  unsigned NumExpansions;
-
-  UsingPackDecl(DeclContext *DC, NamedDecl *InstantiatedFrom,
-                ArrayRef<NamedDecl *> UsingDecls)
-      : NamedDecl(UsingPack, DC,
-                  InstantiatedFrom ? InstantiatedFrom->getLocation()
-                                   : SourceLocation(),
-                  InstantiatedFrom ? InstantiatedFrom->getDeclName()
-                                   : DeclarationName()),
-        InstantiatedFrom(InstantiatedFrom), NumExpansions(UsingDecls.size()) {
-    std::uninitialized_copy(UsingDecls.begin(), UsingDecls.end(),
-                            getTrailingObjects<NamedDecl *>());
-  }
-
-public:
-  /// Get the using declaration from which this was instantiated. This will
-  /// always be an UnresolvedUsingValueDecl or an UnresolvedUsingTypenameDecl
-  /// that is a pack expansion.
-  NamedDecl *getInstantiatedFromUsingDecl() { return InstantiatedFrom; }
-
-  /// Get the set of using declarations that this pack expanded into. Note that
-  /// some of these may still be unresolved.
-  ArrayRef<NamedDecl *> expansions() const {
-    return llvm::makeArrayRef(getTrailingObjects<NamedDecl *>(), NumExpansions);
-  }
-
-  static UsingPackDecl *Create(ASTContext &C, DeclContext *DC,
-                               NamedDecl *InstantiatedFrom,
-                               ArrayRef<NamedDecl *> UsingDecls);
-
-  static UsingPackDecl *CreateDeserialized(ASTContext &C, unsigned ID,
-                                           unsigned NumExpansions);
-
-  SourceRange getSourceRange() const override LLVM_READONLY {
-    return InstantiatedFrom->getSourceRange();
-  }
-
-  UsingPackDecl *getCanonicalDecl() override { return getFirstDecl(); }
-  const UsingPackDecl *getCanonicalDecl() const { return getFirstDecl(); }
-
-  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
-  static bool classofKind(Kind K) { return K == UsingPack; }
-
-  friend class ASTDeclReader;
-  friend class ASTDeclWriter;
-  friend TrailingObjects;
-};
-
 /// \brief Represents a dependent using declaration which was not marked with
 /// \c typename.
 ///
@@ -3229,9 +3158,6 @@ class UnresolvedUsingValueDecl : public ValueDecl,
   /// \brief The source location of the 'using' keyword
   SourceLocation UsingLocation;
 
-  /// \brief If this is a pack expansion, the location of the '...'.
-  SourceLocation EllipsisLoc;
-
   /// \brief The nested-name-specifier that precedes the name.
   NestedNameSpecifierLoc QualifierLoc;
 
@@ -3242,12 +3168,11 @@ class UnresolvedUsingValueDecl : public ValueDecl,
   UnresolvedUsingValueDecl(DeclContext *DC, QualType Ty,
                            SourceLocation UsingLoc,
                            NestedNameSpecifierLoc QualifierLoc,
-                           const DeclarationNameInfo &NameInfo,
-                           SourceLocation EllipsisLoc)
+                           const DeclarationNameInfo &NameInfo)
     : ValueDecl(UnresolvedUsingValue, DC,
                 NameInfo.getLoc(), NameInfo.getName(), Ty),
-      UsingLocation(UsingLoc), EllipsisLoc(EllipsisLoc),
-      QualifierLoc(QualifierLoc), DNLoc(NameInfo.getInfo())
+      UsingLocation(UsingLoc), QualifierLoc(QualifierLoc),
+      DNLoc(NameInfo.getInfo())
   { }
 
 public:
@@ -3273,20 +3198,10 @@ public:
     return DeclarationNameInfo(getDeclName(), getLocation(), DNLoc);
   }
 
-  /// \brief Determine whether this is a pack expansion.
-  bool isPackExpansion() const {
-    return EllipsisLoc.isValid();
-  }
-
-  /// \brief Get the location of the ellipsis if this is a pack expansion.
-  SourceLocation getEllipsisLoc() const {
-    return EllipsisLoc;
-  }
-
   static UnresolvedUsingValueDecl *
     Create(ASTContext &C, DeclContext *DC, SourceLocation UsingLoc,
            NestedNameSpecifierLoc QualifierLoc,
-           const DeclarationNameInfo &NameInfo, SourceLocation EllipsisLoc);
+           const DeclarationNameInfo &NameInfo);
 
   static UnresolvedUsingValueDecl *
   CreateDeserialized(ASTContext &C, unsigned ID);
@@ -3327,9 +3242,6 @@ class UnresolvedUsingTypenameDecl
   /// \brief The source location of the 'typename' keyword
   SourceLocation TypenameLocation;
 
-  /// \brief If this is a pack expansion, the location of the '...'.
-  SourceLocation EllipsisLoc;
-
   /// \brief The nested-name-specifier that precedes the name.
   NestedNameSpecifierLoc QualifierLoc;
 
@@ -3337,12 +3249,10 @@ class UnresolvedUsingTypenameDecl
                               SourceLocation TypenameLoc,
                               NestedNameSpecifierLoc QualifierLoc,
                               SourceLocation TargetNameLoc,
-                              IdentifierInfo *TargetName,
-                              SourceLocation EllipsisLoc)
+                              IdentifierInfo *TargetName)
     : TypeDecl(UnresolvedUsingTypename, DC, TargetNameLoc, TargetName,
                UsingLoc),
-      TypenameLocation(TypenameLoc), EllipsisLoc(EllipsisLoc),
-      QualifierLoc(QualifierLoc) { }
+      TypenameLocation(TypenameLoc), QualifierLoc(QualifierLoc) { }
 
   friend class ASTDeclReader;
 
@@ -3362,25 +3272,10 @@ public:
     return QualifierLoc.getNestedNameSpecifier();
   }
 
-  DeclarationNameInfo getNameInfo() const {
-    return DeclarationNameInfo(getDeclName(), getLocation());
-  }
-
-  /// \brief Determine whether this is a pack expansion.
-  bool isPackExpansion() const {
-    return EllipsisLoc.isValid();
-  }
-
-  /// \brief Get the location of the ellipsis if this is a pack expansion.
-  SourceLocation getEllipsisLoc() const {
-    return EllipsisLoc;
-  }
-
   static UnresolvedUsingTypenameDecl *
     Create(ASTContext &C, DeclContext *DC, SourceLocation UsingLoc,
            SourceLocation TypenameLoc, NestedNameSpecifierLoc QualifierLoc,
-           SourceLocation TargetNameLoc, DeclarationName TargetName,
-           SourceLocation EllipsisLoc);
+           SourceLocation TargetNameLoc, DeclarationName TargetName);
 
   static UnresolvedUsingTypenameDecl *
   CreateDeserialized(ASTContext &C, unsigned ID);
diff --git a/include/clang/AST/RecursiveASTVisitor.h b/include/clang/AST/RecursiveASTVisitor.h
index afacfd5723..058ab1fcbe 100644
--- a/include/clang/AST/RecursiveASTVisitor.h
+++ b/include/clang/AST/RecursiveASTVisitor.h
@@ -1505,8 +1505,6 @@ DEF_TRAVERSE_DECL(UsingDecl, {
   TRY_TO(TraverseDeclarationNameInfo(D->getNameInfo()));
 })
 
-DEF_TRAVERSE_DECL(UsingPackDecl, {})
-
 DEF_TRAVERSE_DECL(UsingDirectiveDecl, {
   TRY_TO(TraverseNestedNameSpecifierLoc(D->getQualifierLoc()));
 })
diff --git a/include/clang/Basic/DeclNodes.td b/include/clang/Basic/DeclNodes.td
index 7b581d3eec..6da2c2c3d6 100644
--- a/include/clang/Basic/DeclNodes.td
+++ b/include/clang/Basic/DeclNodes.td
@@ -67,7 +67,6 @@ 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 b5f3246e53..0ebf34802b 100644
--- a/include/clang/Basic/DiagnosticParseKinds.td
+++ b/include/clang/Basic/DiagnosticParseKinds.td
@@ -740,8 +740,6 @@ 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<
@@ -751,11 +749,6 @@ 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 e98d282a21..73f7f4ddd6 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -474,8 +474,6 @@ 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">,
@@ -4157,9 +4155,6 @@ 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">;
diff --git a/include/clang/Parse/Parser.h b/include/clang/Parse/Parser.h
index 972f13daca..3d098fab84 100644
--- a/include/clang/Parse/Parser.h
+++ b/include/clang/Parse/Parser.h
@@ -2436,10 +2436,9 @@ private:
     CXXScopeSpec SS;
     SourceLocation TemplateKWLoc;
     UnqualifiedId Name;
-    SourceLocation EllipsisLoc;
 
     void clear() {
-      TypenameLoc = TemplateKWLoc = EllipsisLoc = SourceLocation();
+      TypenameLoc = TemplateKWLoc = SourceLocation();
       SS.clear();
       Name.clear();
     }
@@ -2451,6 +2450,9 @@ private:
                                        SourceLocation UsingLoc,
                                        SourceLocation &DeclEnd,
                                        AccessSpecifier AS = AS_none);
+  Decl *ParseAliasTemplate(const ParsedTemplateInfo &TemplateInfo,
+                           SourceLocation &DeclEnd, AccessSpecifier AS,
+                           ParsedAttributesWithRange &MisplacedAttrs1);
   Decl *ParseAliasDeclarationAfterDeclarator(
       const ParsedTemplateInfo &TemplateInfo, SourceLocation UsingLoc,
       UsingDeclarator &D, SourceLocation &DeclEnd, AccessSpecifier AS,
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index ebbc1e1b3e..136f848338 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -4324,15 +4324,12 @@ public:
 
   NamedDecl *BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
                                    SourceLocation UsingLoc,
-                                   bool HasTypenameKeyword,
-                                   SourceLocation TypenameLoc,
                                    CXXScopeSpec &SS,
                                    DeclarationNameInfo NameInfo,
-                                   SourceLocation EllipsisLoc,
                                    AttributeList *AttrList,
-                                   bool IsInstantiation);
-  NamedDecl *BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
-                                ArrayRef<NamedDecl *> Expansions);
+                                   bool IsInstantiation,
+                                   bool HasTypenameKeyword,
+                                   SourceLocation TypenameLoc);
 
   bool CheckInheritingConstructorUsingDecl(UsingDecl *UD);
 
@@ -4346,11 +4343,10 @@ public:
   Decl *ActOnUsingDeclaration(Scope *CurScope,
                               AccessSpecifier AS,
                               SourceLocation UsingLoc,
-                              SourceLocation TypenameLoc,
                               CXXScopeSpec &SS,
                               UnqualifiedId &Name,
-                              SourceLocation EllipsisLoc,
-                              AttributeList *AttrList);
+                              AttributeList *AttrList,
+                              SourceLocation TypenameLoc);
   Decl *ActOnAliasDeclaration(Scope *CurScope,
                               AccessSpecifier AS,
                               MultiTemplateParamsArg TemplateParams,
@@ -6355,7 +6351,7 @@ public:
   ///
   /// \param SS The nested-name-specifier that will be traversed to find
   /// unexpanded parameter packs.
-  void collectUnexpandedParameterPacks(NestedNameSpecifierLoc NNS,
+  void collectUnexpandedParameterPacks(CXXScopeSpec &SS,
                          SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// \brief Collect the set of unexpanded parameter packs within the given
diff --git a/include/clang/Sema/Template.h b/include/clang/Sema/Template.h
index 401bbbf1e5..0d12880354 100644
--- a/include/clang/Sema/Template.h
+++ b/include/clang/Sema/Template.h
@@ -515,11 +515,6 @@ namespace clang {
         VarTemplateDecl *VarTemplate,
         VarTemplatePartialSpecializationDecl *PartialSpec);
     void InstantiateEnumDefinition(EnumDecl *Enum, EnumDecl *Pattern);
-
-  private:
-    template<typename T>
-    Decl *instantiateUnresolvedUsingDecl(T *D,
-                                         bool InstantiatingPackElement = false);
   };  
 }
 
diff --git a/include/clang/Serialization/ASTBitCodes.h b/include/clang/Serialization/ASTBitCodes.h
index 4e29ad6a02..611c00d0e9 100644
--- a/include/clang/Serialization/ASTBitCodes.h
+++ b/include/clang/Serialization/ASTBitCodes.h
@@ -1103,8 +1103,6 @@ namespace clang {
       DECL_NAMESPACE_ALIAS,
       /// \brief A UsingDecl record.
       DECL_USING,
-      /// \brief A UsingPackDecl record.
-      DECL_USING_PACK,
       /// \brief A UsingShadowDecl record.
       DECL_USING_SHADOW,
       /// \brief A ConstructorUsingShadowDecl record.