[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.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@290080 91177308-0d34-0410-b5e6-96231b3b80d8

Author: zygoloid

Diff for: include/clang/AST/DeclCXX.h

@@ -3140,6 +3140,77 @@ class UsingDecl : public NamedDecl, public Mergeable<UsingDecl> {
   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.
 ///
@@ -3158,6 +3229,9 @@ 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;
 
@@ -3168,11 +3242,12 @@ class UnresolvedUsingValueDecl : public ValueDecl,
   UnresolvedUsingValueDecl(DeclContext *DC, QualType Ty,
                            SourceLocation UsingLoc,
                            NestedNameSpecifierLoc QualifierLoc,
-                           const DeclarationNameInfo &NameInfo)
+                           const DeclarationNameInfo &NameInfo,
+                           SourceLocation EllipsisLoc)
     : ValueDecl(UnresolvedUsingValue, DC,
                 NameInfo.getLoc(), NameInfo.getName(), Ty),
-      UsingLocation(UsingLoc), QualifierLoc(QualifierLoc),
-      DNLoc(NameInfo.getInfo())
+      UsingLocation(UsingLoc), EllipsisLoc(EllipsisLoc),
+      QualifierLoc(QualifierLoc), DNLoc(NameInfo.getInfo())
   { }
 
 public:
@@ -3198,10 +3273,20 @@ class UnresolvedUsingValueDecl : public ValueDecl,
     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);
+           const DeclarationNameInfo &NameInfo, SourceLocation EllipsisLoc);
 
   static UnresolvedUsingValueDecl *
   CreateDeserialized(ASTContext &C, unsigned ID);
@@ -3242,17 +3327,22 @@ 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;
 
   UnresolvedUsingTypenameDecl(DeclContext *DC, SourceLocation UsingLoc,
                               SourceLocation TypenameLoc,
                               NestedNameSpecifierLoc QualifierLoc,
                               SourceLocation TargetNameLoc,
-                              IdentifierInfo *TargetName)
+                              IdentifierInfo *TargetName,
+                              SourceLocation EllipsisLoc)
     : TypeDecl(UnresolvedUsingTypename, DC, TargetNameLoc, TargetName,
                UsingLoc),
-      TypenameLocation(TypenameLoc), QualifierLoc(QualifierLoc) { }
+      TypenameLocation(TypenameLoc), EllipsisLoc(EllipsisLoc),
+      QualifierLoc(QualifierLoc) { }
 
   friend class ASTDeclReader;
 
@@ -3272,10 +3362,25 @@ class UnresolvedUsingTypenameDecl
     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 TargetNameLoc, DeclarationName TargetName,
+           SourceLocation EllipsisLoc);
 
   static UnresolvedUsingTypenameDecl *
   CreateDeserialized(ASTContext &C, unsigned ID);

Diff for: include/clang/AST/RecursiveASTVisitor.h

@@ -1505,6 +1505,8 @@ DEF_TRAVERSE_DECL(UsingDecl, {
   TRY_TO(TraverseDeclarationNameInfo(D->getNameInfo()));
 })
 
+DEF_TRAVERSE_DECL(UsingPackDecl, {})
+
 DEF_TRAVERSE_DECL(UsingDirectiveDecl, {
   TRY_TO(TraverseNestedNameSpecifierLoc(D->getQualifierLoc()));
 })

Diff for: 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 for: 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 for: 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">;

Diff for: include/clang/Parse/Parser.h

@@ -2436,9 +2436,10 @@ class Parser : public CodeCompletionHandler {
     CXXScopeSpec SS;
     SourceLocation TemplateKWLoc;
     UnqualifiedId Name;
+    SourceLocation EllipsisLoc;
 
     void clear() {
-      TypenameLoc = TemplateKWLoc = SourceLocation();
+      TypenameLoc = TemplateKWLoc = EllipsisLoc = SourceLocation();
       SS.clear();
       Name.clear();
     }
@@ -2450,9 +2451,6 @@ class Parser : public CodeCompletionHandler {
                                        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 for: include/clang/Sema/Sema.h

@@ -4324,12 +4324,15 @@ class Sema {
 
   NamedDecl *BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
                                    SourceLocation UsingLoc,
+                                   bool HasTypenameKeyword,
+                                   SourceLocation TypenameLoc,
                                    CXXScopeSpec &SS,
                                    DeclarationNameInfo NameInfo,
+                                   SourceLocation EllipsisLoc,
                                    AttributeList *AttrList,
-                                   bool IsInstantiation,
-                                   bool HasTypenameKeyword,
-                                   SourceLocation TypenameLoc);
+                                   bool IsInstantiation);
+  NamedDecl *BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
+                                ArrayRef<NamedDecl *> Expansions);
 
   bool CheckInheritingConstructorUsingDecl(UsingDecl *UD);
 
@@ -4343,10 +4346,11 @@ class Sema {
   Decl *ActOnUsingDeclaration(Scope *CurScope,
                               AccessSpecifier AS,
                               SourceLocation UsingLoc,
+                              SourceLocation TypenameLoc,
                               CXXScopeSpec &SS,
                               UnqualifiedId &Name,
-                              AttributeList *AttrList,
-                              SourceLocation TypenameLoc);
+                              SourceLocation EllipsisLoc,
+                              AttributeList *AttrList);
   Decl *ActOnAliasDeclaration(Scope *CurScope,
                               AccessSpecifier AS,
                               MultiTemplateParamsArg TemplateParams,
@@ -6351,7 +6355,7 @@ class Sema {
   ///
   /// \param SS The nested-name-specifier that will be traversed to find
   /// unexpanded parameter packs.
-  void collectUnexpandedParameterPacks(CXXScopeSpec &SS,
+  void collectUnexpandedParameterPacks(NestedNameSpecifierLoc NNS,
                          SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// \brief Collect the set of unexpanded parameter packs within the given

Diff for: include/clang/Sema/Template.h

@@ -515,6 +515,11 @@ namespace clang {
         VarTemplateDecl *VarTemplate,
         VarTemplatePartialSpecializationDecl *PartialSpec);
     void InstantiateEnumDefinition(EnumDecl *Enum, EnumDecl *Pattern);
+
+  private:
+    template<typename T>
+    Decl *instantiateUnresolvedUsingDecl(T *D,
+                                         bool InstantiatingPackElement = false);
   };  
 }
 

Diff for: include/clang/Serialization/ASTBitCodes.h

@@ -1103,6 +1103,8 @@ 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.

Diff for: lib/AST/DeclBase.cpp

@@ -651,18 +651,21 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case Typedef:
     case TypeAlias:
     case TypeAliasTemplate:
-    case UnresolvedUsingTypename:
     case TemplateTypeParm:
     case ObjCTypeParam:
       return IDNS_Ordinary | IDNS_Type;
 
+    case UnresolvedUsingTypename:
+      return IDNS_Ordinary | IDNS_Type | IDNS_Using;
+
     case UsingShadow:
       return 0; // we'll actually overwrite this later
 
     case UnresolvedUsingValue:
       return IDNS_Ordinary | IDNS_Using;
 
     case Using:
+    case UsingPack:
       return IDNS_Using;
 
     case ObjCProtocol: