Objective-C : Implement NSObject attribute.

This attribute allows pointers to be marked as pointers to
an NSObject-compatible object.  This allows for additional
checking of assignment etc. when refering to pointers to
opaque types.

gcc/c-family/ChangeLog:

	* c-attribs.c (handle_nsobject_attribute): New.
	* c.opt: Add WNSObject-attribute.

gcc/objc/ChangeLog:

	* objc-act.c (objc_compare_types): Handle NSObject type
	attributes.
	(objc_type_valid_for_messaging): Likewise.

gcc/testsuite/ChangeLog:

	* obj-c++.dg/attributes/nsobject-01.mm: New test.
	* objc.dg/attributes/nsobject-01.m: New test.

1 files changed, 32 insertions, 7 deletions

diff --git a/gcc/objc/objc-act.c b/gcc/objc/objc-act.c
index 68d829f..8be4bea 100644
--- a/gcc/objc/objc-act.c
+++ b/gcc/objc/objc-act.c
@@ -2476,9 +2476,14 @@ objc_compare_types (tree ltyp, tree rtyp, int argno, tree callee)
   if (!POINTER_TYPE_P (ltyp) || !POINTER_TYPE_P (rtyp))
     return false;
 
+  tree ltyp_attr, rtyp_attr;
   do
     {
-      ltyp = TREE_TYPE (ltyp);  /* Remove indirections.  */
+      /* Remove indirections, but keep the type attributes from the innermost
+	 pointer type, to check for NSObject.  */
+      ltyp_attr = TYPE_ATTRIBUTES (ltyp);
+      ltyp = TREE_TYPE (ltyp);
+      rtyp_attr = TYPE_ATTRIBUTES (rtyp);
       rtyp = TREE_TYPE (rtyp);
     }
   while (POINTER_TYPE_P (ltyp) && POINTER_TYPE_P (rtyp));
@@ -2523,17 +2528,23 @@ objc_compare_types (tree ltyp, tree rtyp, int argno, tree callee)
       return true;
     }
 
+  /* We might have void * with NSObject type attr.  */
+  bool l_NSObject_p = ltyp_attr && lookup_attribute ("NSObject", ltyp_attr);
+  bool r_NSObject_p = rtyp_attr && lookup_attribute ("NSObject", rtyp_attr);
+
   /* Past this point, we are only interested in ObjC class instances,
-     or 'id' or 'Class'.  */
-  if (TREE_CODE (ltyp) != RECORD_TYPE || TREE_CODE (rtyp) != RECORD_TYPE)
+     or 'id' or 'Class' (except if the user applied the NSObject type
+     attribute).  */
+  if ((TREE_CODE (ltyp) != RECORD_TYPE && !l_NSObject_p)
+      || (TREE_CODE (rtyp) != RECORD_TYPE && !r_NSObject_p))
     return false;
 
   if (!objc_is_object_id (ltyp) && !objc_is_class_id (ltyp)
-      && !TYPE_HAS_OBJC_INFO (ltyp))
+      && !TYPE_HAS_OBJC_INFO (ltyp) && !l_NSObject_p)
     return false;
 
   if (!objc_is_object_id (rtyp) && !objc_is_class_id (rtyp)
-      && !TYPE_HAS_OBJC_INFO (rtyp))
+      && !TYPE_HAS_OBJC_INFO (rtyp) && !r_NSObject_p)
     return false;
 
   /* Past this point, we are committed to returning 'true' to the caller
@@ -2567,12 +2578,15 @@ objc_compare_types (tree ltyp, tree rtyp, int argno, tree callee)
     rcls = NULL_TREE;
 
   /* If either type is an unqualified 'id', we're done.  This is because
-     an 'id' can be assigned to or from any type with no warnings.  */
+     an 'id' can be assigned to or from any type with no warnings.  When
+     the pointer has NSObject attribute, consider that to be equivalent.  */
   if (argno != -5)
     {
       if ((!lproto && objc_is_object_id (ltyp))
 	  || (!rproto && objc_is_object_id (rtyp)))
 	return true;
+      if (l_NSObject_p || r_NSObject_p)
+	return true;
     }
   else
     {
@@ -2580,7 +2594,7 @@ objc_compare_types (tree ltyp, tree rtyp, int argno, tree callee)
 	 general type of object, hence if you try to specialize an
 	 'NSArray *' (ltyp) property with an 'id' (rtyp) one, we need
 	 to warn.  */
-      if (!lproto && objc_is_object_id (ltyp))
+      if (!lproto && (objc_is_object_id (ltyp) || l_NSObject_p))
 	return true;
     }
 
@@ -8659,11 +8673,19 @@ objc_type_valid_for_messaging (tree type, bool accept_classes)
   if (!POINTER_TYPE_P (type))
     return false;
 
+  /* We will check for an NSObject type attribute  on the pointer if other
+     tests fail.  */
+  tree type_attr = TYPE_ATTRIBUTES (type);
+
   /* Remove the pointer indirection; don't remove more than one
      otherwise we'd consider "NSObject **" a valid type for messaging,
      which it isn't.  */
   type = TREE_TYPE (type);
 
+  /* We allow void * to have an NSObject type attr.  */
+  if (VOID_TYPE_P (type) && type_attr)
+    return lookup_attribute ("NSObject", type_attr) != NULL_TREE;
+
   if (TREE_CODE (type) != RECORD_TYPE)
     return false;
 
@@ -8676,6 +8698,9 @@ objc_type_valid_for_messaging (tree type, bool accept_classes)
   if (TYPE_HAS_OBJC_INFO (type))
     return true;
 
+  if (type_attr)
+    return lookup_attribute ("NSObject", type_attr) != NULL_TREE;
+
   return false;
 }