Unreviewed patch [was : PATCH: Protocol Warning]

[Devang Patel]

On Tuesday, August 20, 2002, at 09:45  AM, Jason Merrill wrote:

> This seems harmless to me, but I'm curious as to how a type with a
> different TYPE_CONTEXT can have the same TYPE_MAIN_VARIANT.

In Objective-C, a type can be qualified for a protocol. This permits the
compiler to test for a type based on conformance to a protocol.

Objective-C front end uses macro TYPE_PROTOCOL_LIST to keep list
of qualified protocols.

Here is relevant code snippet ...

objc-act.h:106:#define TYPE_PROTOCOL_LIST(TYPE) ((TYPE)->type.context)

objc-act.h:279 #define IS_PROTOCOL_QUALIFIED_ID(TYPE) \
objc-act.h:280   (IS_ID (TYPE) && TYPE_PROTOCOL_LIST (TYPE))

And from objc-act.c

     830   /* This clause creates a new pointer type that is qualified 
with
     831      the protocol specification...this info is used later to do 
more
     832      elaborate type checking.  */
     833
     834   if (protocols)
     835     {
     836       tree t, m = TYPE_MAIN_VARIANT (type);
     837
     838       t = copy_node (type);
     839       TYPE_BINFO (t) = make_tree_vec (2);
     840
     841       /* Add this type to the chain of variants of TYPE.  */
     842       TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (m);
     843       TYPE_NEXT_VARIANT (m) = t;
     844
     845       /* Look up protocols...and install in lang specific list 
*/
     846       TYPE_PROTOCOL_LIST (t) = lookup_and_install_protocols 
(protocols);
     847
     848       /* This forces a new pointer type to be created later
     849          (in build_pointer_type)...so that the new template
     850          we just created will actually be used...what a hack!  
*/
     851       if (TYPE_POINTER_TO (t))
     852         TYPE_POINTER_TO (t) = NULL_TREE;
     853
     854       type = t;
     855     }


-Devang