[Sema] Semantic analysis for empty-declaration and attribute-declaration.

Introduce a new AST Decl node "EmptyDecl" to model empty-declaration. Have attributes from attribute-declaration appertain
to the EmptyDecl node by creating the AST representations of these attributes and attach them to the EmptyDecl node so these
attributes can be sema checked just as attributes attached to "normal" declarations.

llvm-svn: 175900

clang/include/clang/AST/Decl.h

@@ -3297,7 +3297,21 @@ public:
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Import; }
 };
-  
+
+/// \brief Represents an empty-declaration.
+class EmptyDecl : public Decl {
+  virtual void anchor();
+  EmptyDecl(DeclContext *DC, SourceLocation L)
+    : Decl(Empty, DC, L) { }
+
+public:
+  static EmptyDecl *Create(ASTContext &C, DeclContext *DC,
+                           SourceLocation L);
+  static EmptyDecl *CreateDeserialized(ASTContext &C, unsigned ID);
+
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) { return K == Empty; }
+};
 
 /// Insertion operator for diagnostics.  This allows sending NamedDecl's
 /// into a diagnostic with <<.

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -1257,6 +1257,8 @@ DEF_TRAVERSE_DECL(BlockDecl, {
     return true;
   })
 
+DEF_TRAVERSE_DECL(EmptyDecl, { })
+
 DEF_TRAVERSE_DECL(FileScopeAsmDecl, {
     TRY_TO(TraverseStmt(D->getAsmString()));
   })

clang/include/clang/Basic/DeclNodes.td

@@ -74,4 +74,5 @@ def StaticAssert : Decl;
 def Block : Decl, DeclContext;
 def ClassScopeFunctionSpecialization : Decl;
 def Import : Decl;
+def Empty : Decl;
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1916,8 +1916,6 @@ def warn_attribute_not_on_decl : Warning<
   "%0 attribute ignored when parsing type">, InGroup<IgnoredAttributes>;
 def err_base_specifier_attribute : Error<
   "%0 attribute cannot be applied to a base specifier">;
-def err_attribute_declaration : Error<
-  "%0 attribute cannot be used in an attribute declaration">;
 
 // Availability attribute
 def warn_availability_unknown_platform : Warning<

clang/include/clang/Sema/Sema.h

@@ -1447,8 +1447,10 @@ public:
                               SourceLocation AsmLoc,
                               SourceLocation RParenLoc);
 
-  /// \brief Handle a C++11 attribute-declaration.
-  void ActOnAttributeDeclaration(AttributeList *AttrList);
+  /// \brief Handle a C++11 empty-declaration and attribute-declaration.
+  Decl *ActOnEmptyDeclaration(Scope *S,
+                              AttributeList *AttrList,
+                              SourceLocation SemiLoc);
 
   /// \brief The parser has processed a module import declaration.
   ///

clang/include/clang/Serialization/ASTBitCodes.h

@@ -1031,7 +1031,9 @@ namespace clang {
       /// function specialization. (Microsoft extension).
       DECL_CLASS_SCOPE_FUNCTION_SPECIALIZATION,
       /// \brief An ImportDecl recording a module import.
-      DECL_IMPORT
+      DECL_IMPORT,
+      /// \brief An EmptyDecl record.
+      DECL_EMPTY
     };
 
     /// \brief Record codes for each kind of statement or expression.

clang/lib/AST/Decl.cpp

@@ -3343,6 +3343,17 @@ FileScopeAsmDecl *FileScopeAsmDecl::CreateDeserialized(ASTContext &C,
   return new (Mem) FileScopeAsmDecl(0, 0, SourceLocation(), SourceLocation());
 }
 
+void EmptyDecl::anchor() {}
+
+EmptyDecl *EmptyDecl::Create(ASTContext &C, DeclContext *DC, SourceLocation L) {
+  return new (C) EmptyDecl(DC, L);
+}
+
+EmptyDecl *EmptyDecl::CreateDeserialized(ASTContext &C, unsigned ID) {
+  void *Mem = AllocateDeserializedDecl(C, ID, sizeof(EmptyDecl));
+  return new (Mem) EmptyDecl(0, SourceLocation());
+}
+
 //===----------------------------------------------------------------------===//
 // ImportDecl Implementation
 //===----------------------------------------------------------------------===//

clang/lib/AST/DeclBase.cpp

@@ -558,6 +558,7 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case ObjCCategory:
     case ObjCCategoryImpl:
     case Import:
+    case Empty:
       // Never looked up by name.
       return 0;
   }

clang/lib/AST/DeclPrinter.cpp

@@ -51,6 +51,7 @@ namespace {
     void VisitEnumDecl(EnumDecl *D);
     void VisitRecordDecl(RecordDecl *D);
     void VisitEnumConstantDecl(EnumConstantDecl *D);
+    void VisitEmptyDecl(EmptyDecl *D);
     void VisitFunctionDecl(FunctionDecl *D);
     void VisitFriendDecl(FriendDecl *D);
     void VisitFieldDecl(FieldDecl *D);
@@ -723,6 +724,11 @@ void DeclPrinter::VisitNamespaceAliasDecl(NamespaceAliasDecl *D) {
   Out << *D->getAliasedNamespace();
 }
 
+void DeclPrinter::VisitEmptyDecl(EmptyDecl *D) {
+  prettyPrintAttributes(D);
+  Out << ";\n";
+}
+
 void DeclPrinter::VisitCXXRecordDecl(CXXRecordDecl *D) {
   if (!Policy.SuppressSpecifiers && D->isModulePrivate())
     Out << "__module_private__ ";

clang/lib/CodeGen/CGDecl.cpp

@@ -83,6 +83,7 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
   case Decl::StaticAssert: // static_assert(X, ""); [C++0x]
   case Decl::Label:        // __label__ x;
   case Decl::Import:
+  case Decl::Empty:
     // None of these decls require codegen support.
     return;
 

clang/lib/CodeGen/CodeGenModule.cpp

@@ -2742,6 +2742,7 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
   case Decl::TypeAliasTemplate:
   case Decl::NamespaceAlias:
   case Decl::Block:
+  case Decl::Empty:
     break;
   case Decl::CXXConstructor:
     // Skip function templates

clang/lib/Parse/Parser.cpp

@@ -626,15 +626,11 @@ Parser::ParseExternalDeclaration(ParsedAttributesWithRange &attrs,
     return DeclGroupPtrTy();
   case tok::semi:
     // Either a C++11 empty-declaration or attribute-declaration.
-    if (attrs.Range.isValid()) {
-      // FIXME: Add an AST representation for this.
-      Actions.ActOnAttributeDeclaration(attrs.getList());
-      return DeclGroupPtrTy();
-    }
-
+    SingleDecl = Actions.ActOnEmptyDeclaration(getCurScope(),
+                                               attrs.getList(),
+                                               Tok.getLocation());
     ConsumeExtraSemi(OutsideFunction);
-    // TODO: Invoke action for top-level semicolon.
-    return DeclGroupPtrTy();
+    break;
   case tok::r_brace:
     Diag(Tok, diag::err_extraneous_closing_brace);
     ConsumeBrace();

clang/lib/Sema/SemaDeclCXX.cpp

@@ -10085,23 +10085,17 @@ Decl *Sema::ActOnFinishLinkageSpecification(Scope *S,
   return LinkageSpec;
 }
 
-/// \brief Perform semantic checks on a C++11 attribute-declaration.
-void Sema::ActOnAttributeDeclaration(AttributeList *AttrList) {
-  // FIXME: Build an AST node for an attribute declaration and return it.
-  
-  // Since we do not support any attributes which can be used in an attribute
-  // declaration, just diagnose standard and unknown attributes appropriately.
-  for (/**/; AttrList; AttrList = AttrList->getNext()) {
-    if (AttrList->getKind() == AttributeList::IgnoredAttribute ||
-        AttrList->isInvalid())
-      continue;
+Decl *Sema::ActOnEmptyDeclaration(Scope *S,
+                                  AttributeList *AttrList,
+                                  SourceLocation SemiLoc) {
+  Decl *ED = EmptyDecl::Create(Context, CurContext, SemiLoc);
+  // Attribute declarations appertain to empty declaration so we handle
+  // them here.
+  if (AttrList)
+    ProcessDeclAttributeList(S, ED, AttrList);
 
-    Diag(AttrList->getLoc(),
-         AttrList->getKind() == AttributeList::UnknownAttribute
-           ? diag::warn_unknown_attribute_ignored
-           : diag::err_attribute_declaration)
-      << AttrList->getName();
-  }
+  CurContext->addDecl(ED);
+  return ED;
 }
 
 /// \brief Perform semantic analysis for the variable declaration that

clang/lib/Serialization/ASTCommon.cpp

@@ -168,6 +168,7 @@ bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::TypeAliasTemplate:
   case Decl::ObjCProtocol:
   case Decl::ObjCInterface:
+  case Decl::Empty:
     return true;
 
   // Never redeclarable.

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -265,6 +265,7 @@ namespace clang {
     void VisitFriendTemplateDecl(FriendTemplateDecl *D);
     void VisitStaticAssertDecl(StaticAssertDecl *D);
     void VisitBlockDecl(BlockDecl *BD);
+    void VisitEmptyDecl(EmptyDecl *D);
 
     std::pair<uint64_t, uint64_t> VisitDeclContext(DeclContext *DC);
     
@@ -1526,6 +1527,10 @@ void ASTDeclReader::VisitStaticAssertDecl(StaticAssertDecl *D) {
   D->RParenLoc = ReadSourceLocation(Record, Idx);
 }
 
+void ASTDeclReader::VisitEmptyDecl(EmptyDecl *D) {
+  VisitDecl(D);
+}
+
 std::pair<uint64_t, uint64_t>
 ASTDeclReader::VisitDeclContext(DeclContext *DC) {
   uint64_t LexicalOffset = Record[Idx++];
@@ -2129,6 +2134,9 @@ Decl *ASTReader::ReadDeclRecord(DeclID ID) {
     // locations.
     D = ImportDecl::CreateDeserialized(Context, ID, Record.back());
     break;
+  case DECL_EMPTY:
+    D = EmptyDecl::CreateDeserialized(Context, ID);
+    break;
   }
 
   assert(D && "Unknown declaration reading AST file");

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -102,6 +102,7 @@ namespace clang {
     void VisitFriendTemplateDecl(FriendTemplateDecl *D);
     void VisitStaticAssertDecl(StaticAssertDecl *D);
     void VisitBlockDecl(BlockDecl *D);
+    void VisitEmptyDecl(EmptyDecl *D);
 
     void VisitDeclContext(DeclContext *DC, uint64_t LexicalOffset,
                           uint64_t VisibleOffset);
@@ -780,6 +781,11 @@ void ASTDeclWriter::VisitFileScopeAsmDecl(FileScopeAsmDecl *D) {
   Code = serialization::DECL_FILE_SCOPE_ASM;
 }
 
+void ASTDeclWriter::VisitEmptyDecl(EmptyDecl *D) {
+  VisitDecl(D);
+  Code = serialization::DECL_EMPTY;
+}
+
 void ASTDeclWriter::VisitBlockDecl(BlockDecl *D) {
   VisitDecl(D);
   Writer.AddStmt(D->getBody());

clang/test/Parser/cxx0x-attributes.cpp

@@ -279,4 +279,5 @@ int v4[2][[gnu::unused]]; // expected-warning {{attribute 'unused' ignored}}
 int v5()[[gnu::unused]]; // expected-warning {{attribute 'unused' ignored}}
 
 [[attribute_declaration]]; // expected-warning {{unknown attribute 'attribute_declaration' ignored}}
-[[noreturn]]; // expected-error {{'noreturn' attribute cannot be used in an attribute declaration}}
+[[noreturn]]; // expected-error {{'noreturn' attribute only applies to functions and methods}}
+[[carries_dependency]]; // expected-error {{'carries_dependency' attribute only applies to functions, methods, and parameters}}

clang/test/SemaCXX/cxx11-ast-print.cpp

@@ -38,3 +38,5 @@ const char *p8 = 4.9_quux;
 const char *p9 = 0x42e3F_fritz;
 // CHECK: const char *p10 = 3.300e+15_fritz;
 const char *p10 = 3.300e+15_fritz;
+// CHECK: ;
+;

clang/tools/libclang/RecursiveASTVisitor.h

@@ -1199,6 +1199,8 @@ DEF_TRAVERSE_DECL(BlockDecl, {
     return true;
   })
 
+DEF_TRAVERSE_DECL(EmptyDecl, { })
+
 DEF_TRAVERSE_DECL(FileScopeAsmDecl, {
     TRY_TO(TraverseStmt(D->getAsmString()));
   })