Add back experimental attribute objc_suppress_protocol_methods (slightly renamed).

This is still an experimental attribute, but I wanted it in tree
for review.  It may still get yanked.

This attribute can only be applied to a class @interface, not
a class extension or category.  It does not change the type
system rules for Objective-C, but rather the implementation checking
for Objective-C classes that explicitly conform to a protocol.
During protocol conformance checking, clang recursively searches
up the class hierarchy for the set of methods that compose
a protocol.  This attribute will cause the compiler to not consider
the methods contributed by a super class, its categories, and those
from its ancestor classes.  Thus this attribute is used to force
subclasses to redeclare (and hopefully re-implement) methods if
they decide to explicitly conform to a protocol where some of those
methods may be provided by a super class.

This attribute intentionally leaves out properties, which are associated
with state.  This attribute only considers methods (at least right now)
that are non-property accessors.  These represent methods that "do something"
as dictated by the protocol.  This may be further refined, and this
should be considered a WIP until documentation gets written or this
gets removed.

llvm-svn: 195533

1 files changed, 18 insertions, 1 deletions

diff --git a/clang/lib/AST/DeclObjC.cpp b/clang/lib/AST/DeclObjC.cpp
index ca87bb8197f..a4857b60731 100644
--- a/clang/lib/AST/DeclObjC.cpp
+++ b/clang/lib/AST/DeclObjC.cpp
@@ -460,7 +460,8 @@ ObjCMethodDecl *ObjCInterfaceDecl::lookupMethod(Selector Sel,
                                                 bool isInstance,
                                                 bool shallowCategoryLookup,
                                                 bool followSuper,
-                                                const ObjCCategoryDecl *C) const
+                                                const ObjCCategoryDecl *C,
+                                                const ObjCProtocolDecl *P) const
 {
   // FIXME: Should make sure no callers ever do this.
   if (!hasDefinition())
@@ -473,6 +474,22 @@ ObjCMethodDecl *ObjCInterfaceDecl::lookupMethod(Selector Sel,
     LoadExternalDefinition();
 
   while (ClassDecl) {
+    // If we are looking for a method that is part of protocol conformance,
+    // check if the superclass has been marked to suppress conformance
+    // of that protocol.
+    if (P && ClassDecl->hasAttrs()) {
+      const AttrVec &V = ClassDecl->getAttrs();
+      const IdentifierInfo *PI = P->getIdentifier();
+      for (AttrVec::const_iterator I = V.begin(), E = V.end(); I != E; ++I) {
+        if (const ObjCSuppressProtocolAttr *A =
+            dyn_cast<ObjCSuppressProtocolAttr>(*I)){
+          if (A->getProtocol() == PI) {
+            return 0;
+          }
+        }
+      }
+    }
+
     if ((MethodDecl = ClassDecl->getMethod(Sel, isInstance)))
       return MethodDecl;