Implement support for [[maybe_unused]] in C++1z that is based off existing support for unused, and treat it as an extension pre-C++1z. This also means extending the existing unused attribute so that it can be placed on an enum and enumerator, in addition to the other subjects.

llvm-svn: 263025

3 files changed, 33 insertions, 6 deletions

diff --git a/clang/lib/Sema/SemaAttr.cpp b/clang/lib/Sema/SemaAttr.cpp
index 4b7aa2b07e5..7f523c465af 100644
--- a/clang/lib/Sema/SemaAttr.cpp
+++ b/clang/lib/Sema/SemaAttr.cpp
@@ -459,7 +459,8 @@ void Sema::ActOnPragmaUnused(const Token &IdTok, Scope *curScope,
   if (VD->isUsed())
     Diag(PragmaLoc, diag::warn_used_but_marked_unused) << Name;
 
-  VD->addAttr(UnusedAttr::CreateImplicit(Context, IdTok.getLocation()));
+  VD->addAttr(UnusedAttr::CreateImplicit(Context, UnusedAttr::GNU_unused,
+                                         IdTok.getLocation()));
 }
 
 void Sema::AddCFAuditedAttribute(Decl *D) {
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index f8cec752041..0cae52a299f 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1807,6 +1807,28 @@ static void handleUsedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
                       Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleUnusedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
+  bool IsCXX1zAttr = Attr.isCXX11Attribute() && !Attr.getScopeName();
+
+  if (IsCXX1zAttr && isa<VarDecl>(D)) {
+    // The C++1z spelling of this attribute cannot be applied to a static data
+    // member per [dcl.attr.unused]p2.
+    if (cast<VarDecl>(D)->isStaticDataMember()) {
+      S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+          << Attr.getName() << ExpectedForMaybeUnused;
+      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 && IsCXX1zAttr)
+    S.Diag(Attr.getLoc(), diag::ext_cxx1z_attr) << Attr.getName();
+
+  D->addAttr(::new (S.Context) UnusedAttr(
+      Attr.getRange(), S.Context, Attr.getAttributeSpellingListIndex()));
+}
+
 static void handleConstructorAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   uint32_t priority = ConstructorAttr::DefaultPriority;
   if (Attr.getNumArgs() &&
@@ -5545,7 +5567,7 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
     handleSimpleAttribute<ObjCRequiresPropertyDefsAttr>(S, D, Attr);
     break;
   case AttributeList::AT_Unused:
-    handleSimpleAttribute<UnusedAttr>(S, D, Attr);
+    handleUnusedAttr(S, D, Attr);
     break;
   case AttributeList::AT_ReturnsTwice:
     handleSimpleAttribute<ReturnsTwiceAttr>(S, D, Attr);
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 4b8817529e3..54dcced5ba9 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -76,10 +76,14 @@ bool Sema::CanUseDecl(NamedDecl *D) {
 
 static void DiagnoseUnusedOfDecl(Sema &S, NamedDecl *D, SourceLocation Loc) {
   // Warn if this is used but marked unused.
-  if (D->hasAttr<UnusedAttr>()) {
-    const Decl *DC = cast_or_null<Decl>(S.getCurObjCLexicalContext());
-    if (DC && !DC->hasAttr<UnusedAttr>())
-      S.Diag(Loc, diag::warn_used_but_marked_unused) << D->getDeclName();
+  if (const auto *A = D->getAttr<UnusedAttr>()) {
+    // [[maybe_unused]] should not diagnose uses, but __attribute__((unused))
+    // should diagnose them.
+    if (A->getSemanticSpelling() != UnusedAttr::CXX11_maybe_unused) {
+      const Decl *DC = cast_or_null<Decl>(S.getCurObjCLexicalContext());
+      if (DC && !DC->hasAttr<UnusedAttr>())
+        S.Diag(Loc, diag::warn_used_but_marked_unused) << D->getDeclName();
+    }
   }
 }