Add an attribute to forbid temporary instances of a type. This allows class

authors to write 

  class __attribute__((forbid_temporaries)) Name { ... };

when they want to force users to name all variables of the type. This protects
people from doing things like creating a scoped_lock that only lives for a
single statement instead of an entire scope.

The warning produced by this attribute can be disabled by
-Wno-forbid-temporaries.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124217 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 20 insertions, 0 deletions

diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 474c7cb82f..21d0f46528 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -885,6 +885,24 @@ static void HandleVecReturnAttr(Decl *d, const AttributeList &Attr,
   d->addAttr(::new (S.Context) VecReturnAttr(Attr.getLoc(), S.Context));
 }
 
+static void HandleForbidTemporariesAttr(Decl *d, const AttributeList &Attr,
+                                        Sema &S) {
+  assert(Attr.isInvalid() == false);
+
+  if (Attr.getNumArgs() != 0) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 0;
+    return;
+  }
+
+  if (!isa<TypeDecl>(d)) {
+    S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+      << Attr.getName() << 9 /*class*/;
+    return;
+  }
+
+  d->addAttr(::new (S.Context) ForbidTemporariesAttr(Attr.getLoc(), S.Context));
+}
+
 static void HandleDependencyAttr(Decl *d, const AttributeList &Attr, Sema &S) {
   if (!isFunctionOrMethod(d) && !isa<ParmVarDecl>(d)) {
     S.Diag(Attr.getLoc(), diag::err_attribute_wrong_decl_type)
@@ -2674,6 +2692,8 @@ static void ProcessInheritableDeclAttr(Scope *scope, Decl *D,
   case AttributeList::AT_ext_vector_type:
     HandleExtVectorTypeAttr(scope, D, Attr, S);
     break;
+  case AttributeList::AT_forbid_temporaries:
+    HandleForbidTemporariesAttr(D, Attr, S); break;
   case AttributeList::AT_format:      HandleFormatAttr      (D, Attr, S); break;
   case AttributeList::AT_format_arg:  HandleFormatArgAttr   (D, Attr, S); break;
   case AttributeList::AT_global:      HandleGlobalAttr      (D, Attr, S); break;