Enable C++11 attribute syntax for warn_unused_result and allow it to be

applied to CXXRecordDecls, where functions with that return type will
inherit the warn_unused_result attribute.

Also includes a tiny fix (with no discernable behavior change for
existing code) to re-sync AttributeDeclKind enum and
err_attribute_wrong_decl_type with warn_attribute_wrong_decl_type since
the enum is used with both diagnostic messages to chose the correct
description.

llvm-svn: 167783

clang/include/clang/Basic/Attr.td

@@ -699,7 +699,7 @@ def VecReturn : InheritableAttr {
 }
 
 def WarnUnusedResult : InheritableAttr {
-  let Spellings = [GNU<"warn_unused_result">];
+  let Spellings = [GNU<"warn_unused_result">, CXX11<"","warn_unused_result">];
 }
 
 def Weak : InheritableAttr {

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1773,17 +1773,18 @@ def err_alias_not_supported_on_darwin : Error <
 def warn_attribute_wrong_decl_type : Warning<
   "%0 attribute only applies to %select{functions|unions|"
   "variables and functions|functions and methods|parameters|"
-  "functions, methods and blocks|functions, methods, and parameters|"
-  "classes|variables|methods|variables, functions and labels|"
-  "fields and global variables|structs|"
+  "functions, methods and blocks|functions, methods, and classes|"
+  "functions, methods, and parameters|classes|variables|methods|"
+  "variables, functions and labels|fields and global variables|structs|"
   "variables, functions and tag types|thread-local variables}1">,
   InGroup<IgnoredAttributes>;
 def err_attribute_wrong_decl_type : Error<
   "%0 attribute only applies to %select{functions|unions|"
   "variables and functions|functions and methods|parameters|"
-  "functions, methods and blocks|functions, methods, and parameters|"
-  "classes|variables|methods|variables, functions and labels|"
-  "fields and global variables|structs|thread-local variables}1">;
+  "functions, methods and blocks|functions, methods, and classes|"
+  "functions, methods, and parameters|classes|variables|methods|"
+  "variables, functions and labels|fields and global variables|structs|"
+  "variables, functions and tag types|thread-local variables}1">;
 def warn_function_attribute_wrong_type : Warning<
   "'%0' only applies to function types; type here is %1">,
   InGroup<IgnoredAttributes>;

clang/lib/Sema/SemaDecl.cpp

@@ -5691,6 +5691,14 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
   ProcessDeclAttributes(S, NewFD, D,
                         /*NonInheritable=*/false, /*Inheritable=*/true);
 
+  QualType RetType = NewFD->getResultType();
+  const CXXRecordDecl *Ret = RetType->isRecordType() ?
+      RetType->getAsCXXRecordDecl() : RetType->getPointeeCXXRecordDecl();
+  if (!NewFD->isInvalidDecl() && !NewFD->hasAttr<WarnUnusedResultAttr>() &&
+      Ret && Ret->hasAttr<WarnUnusedResultAttr>()) {
+    NewFD->addAttr(new (Context) WarnUnusedResultAttr(SourceRange(), Context));
+  }
+
   if (!getLangOpts().CPlusPlus) {
     // Perform semantic checking on the function declaration.
     bool isExplicitSpecialization=false;

clang/lib/Sema/SemaDeclAttr.cpp

@@ -37,6 +37,7 @@ enum AttributeDeclKind {
   ExpectedFunctionOrMethod,
   ExpectedParameter,
   ExpectedFunctionMethodOrBlock,
+  ExpectedFunctionMethodOrClass,
   ExpectedFunctionMethodOrParameter,
   ExpectedClass,
   ExpectedVariable,
@@ -44,6 +45,7 @@ enum AttributeDeclKind {
   ExpectedVariableFunctionOrLabel,
   ExpectedFieldOrGlobalVar,
   ExpectedStruct,
+  ExpectedVariableFunctionOrTag,
   ExpectedTLSVar
 };
 
@@ -2445,7 +2447,7 @@ static void handleWarnUnusedResult(Sema &S, Decl *D, const AttributeList &Attr)
   if (!checkAttributeNumArgs(S, Attr, 0))
     return;
 
-  if (!isFunction(D) && !isa<ObjCMethodDecl>(D)) {
+  if (!isFunction(D) && !isa<ObjCMethodDecl>(D) && !isa<CXXRecordDecl>(D)) {
     S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
       << Attr.getName() << ExpectedFunctionOrMethod;
     return;

clang/test/SemaCXX/warn-unused-result.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
 
 int f() __attribute__((warn_unused_result));
 
@@ -42,3 +42,33 @@ void bah() {
   x.foo(); // expected-warning {{ignoring return value}}
   x2->foo(); // expected-warning {{ignoring return value}}
 }
+
+namespace warn_unused_CXX11 {
+struct [[warn_unused_result]] Status {
+  bool ok() const;
+};
+Status DoSomething();
+Status& DoSomethingElse();
+Status* DoAnotherThing();
+Status** DoYetAnotherThing();
+void lazy() {
+  Status s = DoSomething();
+  if (!s.ok()) return;
+  Status &rs = DoSomethingElse();
+  if (!rs.ok()) return;
+  Status *ps = DoAnotherThing();
+  if (!ps->ok()) return;
+  Status **pps = DoYetAnotherThing();
+  if (!(*pps)->ok()) return;
+
+  (void)DoSomething();
+  (void)DoSomethingElse();
+  (void)DoAnotherThing();
+  (void)DoYetAnotherThing();
+
+  DoSomething(); // expected-warning {{ignoring return value}}
+  DoSomethingElse(); // expected-warning {{ignoring return value}}
+  DoAnotherThing(); // expected-warning {{ignoring return value}}
+  DoYetAnotherThing();
+}
+}