1 files changed, 11 insertions, 6 deletions
diff --git a/lib/Sema/SemaInit.cpp b/lib/Sema/SemaInit.cpp
index c34107d54c..afa681453d 100644
--- a/lib/Sema/SemaInit.cpp
+++ b/lib/Sema/SemaInit.cpp
@@ -3515,18 +3515,23 @@ static void TryConstructorInitialization(Sema &S,
   //   If a program calls for the default initialization of an object
   //   of a const-qualified type T, T shall be a class type with a
   //   user-provided default constructor.
+  // C++ core issue 253 proposal:
+  //   If the implicit default constructor initializes all subobjects, no
+  //   initializer should be required.
+  // The 253 proposal is for example needed to process libstdc++ headers in 5.x.
+  CXXConstructorDecl *CtorDecl = cast<CXXConstructorDecl>(Best->Function);
   if (Kind.getKind() == InitializationKind::IK_Default &&
-      Entity.getType().isConstQualified() &&
-      !cast<CXXConstructorDecl>(Best->Function)->isUserProvided()) {
-    if (!maybeRecoverWithZeroInitialization(S, Sequence, Entity))
-      Sequence.SetFailed(InitializationSequence::FK_DefaultInitOfConst);
-    return;
+      Entity.getType().isConstQualified()) {
+    if (!CtorDecl->getParent()->allowConstDefaultInit()) {
+      if (!maybeRecoverWithZeroInitialization(S, Sequence, Entity))
+        Sequence.SetFailed(InitializationSequence::FK_DefaultInitOfConst);
+      return;
+    }
   }
 
   // C++11 [over.match.list]p1:
   //   In copy-list-initialization, if an explicit constructor is chosen, the
   //   initializer is ill-formed.
-  CXXConstructorDecl *CtorDecl = cast<CXXConstructorDecl>(Best->Function);
   if (IsListInit && !Kind.AllowExplicit() && CtorDecl->isExplicit()) {
     Sequence.SetFailed(InitializationSequence::FK_ExplicitConstructor);
     return;