Implement support for [[nodiscard]] in C++1z that is based off existing support for warn_unused_result, and treat it as an extension pre-C++1z. This also means extending the existing warn_unused_result attribute so that it can be placed on an enum as well as a class.

llvm-svn: 262872

4 files changed, 25 insertions, 12 deletions

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 041b530bf07..abaec2d7e10 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -2935,16 +2935,22 @@ SourceRange FunctionDecl::getReturnTypeSourceRange() const {
   return RTRange;
 }
 
-bool FunctionDecl::hasUnusedResultAttr() const {
+const Attr *FunctionDecl::getUnusedResultAttr() const {
   QualType RetType = getReturnType();
   if (RetType->isRecordType()) {
     const CXXRecordDecl *Ret = RetType->getAsCXXRecordDecl();
     const auto *MD = dyn_cast<CXXMethodDecl>(this);
-    if (Ret && Ret->hasAttr<WarnUnusedResultAttr>() &&
-        !(MD && MD->getCorrespondingMethodInClass(Ret, true)))
-      return true;
+    if (Ret && !(MD && MD->getCorrespondingMethodInClass(Ret, true))) {
+      if (const auto *R = Ret->getAttr<WarnUnusedResultAttr>())
+        return R;
+    }
+  } else if (const auto *ET = RetType->getAs<EnumType>()) {
+    if (const EnumDecl *ED = ET->getDecl()) {
+      if (const auto *R = ED->getAttr<WarnUnusedResultAttr>())
+        return R;
+    }
   }
-  return hasAttr<WarnUnusedResultAttr>();
+  return getAttr<WarnUnusedResultAttr>();
 }
 
 /// \brief For an inline function definition in C, or for a gnu_inline function
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 798284b3d39..15aded52b45 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -3635,7 +3635,8 @@ static bool IsBuiltInOrStandardCXX11Attribute(IdentifierInfo *AttrName,
   case AttributeList::AT_FallThrough:
   case AttributeList::AT_CXX11NoReturn:
     return true;
-
+  case AttributeList::AT_WarnUnusedResult:
+    return !ScopeName && AttrName->getName().equals("nodiscard");
   default:
     return false;
   }
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index bb02e0b59c4..ce78ab00926 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -2463,6 +2463,12 @@ static void handleWarnUnusedResult(Sema &S, Decl *D, const AttributeList &Attr)
       return;
     }
   
+  // If this is spelled as the standard C++1z attribute, but not in C++1z, warn
+  // about using it as an extension.
+  if (!S.getLangOpts().CPlusPlus1z && Attr.isCXX11Attribute() &&
+      !Attr.getScopeName())
+    S.Diag(Attr.getLoc(), diag::ext_nodiscard_attr_is_a_cxx1z_extension);
+
   D->addAttr(::new (S.Context) 
              WarnUnusedResultAttr(Attr.getRange(), S.Context,
                                   Attr.getAttributeSpellingListIndex()));
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index c58bf464004..b73b4f08841 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -249,10 +249,10 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
     // is written in a macro body, only warn if it has the warn_unused_result
     // attribute.
     if (const Decl *FD = CE->getCalleeDecl()) {
-      const FunctionDecl *Func = dyn_cast<FunctionDecl>(FD);
-      if (Func ? Func->hasUnusedResultAttr()
-               : FD->hasAttr<WarnUnusedResultAttr>()) {
-        Diag(Loc, diag::warn_unused_result) << R1 << R2;
+      if (const Attr *A = isa<FunctionDecl>(FD)
+                              ? cast<FunctionDecl>(FD)->getUnusedResultAttr()
+                              : FD->getAttr<WarnUnusedResultAttr>()) {
+        Diag(Loc, diag::warn_unused_result) << A << R1 << R2;
         return;
       }
       if (ShouldSuppress)
@@ -276,8 +276,8 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
     }
     const ObjCMethodDecl *MD = ME->getMethodDecl();
     if (MD) {
-      if (MD->hasAttr<WarnUnusedResultAttr>()) {
-        Diag(Loc, diag::warn_unused_result) << R1 << R2;
+      if (const auto *A = MD->getAttr<WarnUnusedResultAttr>()) {
+        Diag(Loc, diag::warn_unused_result) << A << R1 << R2;
         return;
       }
     }