Add new attribute 'objc_suppress_protocol' to suppress protocol conformance for a class.

The idea is to allow a class to stipulate that its methods (and those
of its parents) cannot be used for protocol conformance in a subclass.
A subclass is then explicitly required to re-implement those methods
of they are present in the class marked with this attribute.

Currently the attribute can only be applied to an @interface, and
not a category or class extension.  This is by design.  Unlike
protocol conformance, where a category can add explicit conformance
of a protocol to class, this anti-conformance really needs to be
observed uniformly by all clients of the class.  That's because
the absence of the attribute implies more permissive checking of
protocol conformance.

This unfortunately required changing method lookup in ObjCInterfaceDecl
to take an optional protocol parameter.  This should not slow down
method lookup in most cases, and is just used for protocol conformance.

llvm-svn: 195323

clang/include/clang/AST/DeclObjC.h

@@ -1142,14 +1142,17 @@ public:
   // found, we search referenced protocols and class categories.
   ObjCMethodDecl *lookupMethod(Selector Sel, bool isInstance,
                                bool shallowCategoryLookup= false,
-                               const ObjCCategoryDecl *C= 0) const;
+                               const ObjCCategoryDecl *C = 0,
+                               const ObjCProtocolDecl *P = 0) const;
   ObjCMethodDecl *lookupInstanceMethod(Selector Sel,
-                            bool shallowCategoryLookup = false) const {
-    return lookupMethod(Sel, true/*isInstance*/, shallowCategoryLookup);
+                                       bool shallowCategoryLookup = false,
+                                       ObjCProtocolDecl *P = 0) const {
+    return lookupMethod(Sel, true/*isInstance*/, shallowCategoryLookup, 0, P);
   }
   ObjCMethodDecl *lookupClassMethod(Selector Sel,
-                     bool shallowCategoryLookup = false) const {
-    return lookupMethod(Sel, false/*isInstance*/, shallowCategoryLookup);
+                                    bool shallowCategoryLookup = false,
+                                    ObjCProtocolDecl *P = 0) const {
+    return lookupMethod(Sel, false/*isInstance*/, shallowCategoryLookup, 0, P);
   }
   ObjCInterfaceDecl *lookupInheritedClass(const IdentifierInfo *ICName);
 

clang/include/clang/Basic/Attr.td

@@ -613,6 +613,12 @@ def ObjCRootClass : InheritableAttr {
   let Subjects = [ObjCInterface];
 }
 
+def ObjCSuppressProtocol : InheritableAttr {
+  let Spellings = [GNU<"objc_suppress_protocol">];
+  let Subjects = [ObjCInterface];
+  let Args = [IdentifierArgument<"Protocol", 1>];
+}
+
 def Overloadable : Attr {
   let Spellings = [GNU<"overloadable">];
 }

clang/lib/AST/DeclObjC.cpp

@@ -457,9 +457,11 @@ ObjCInterfaceDecl::lookupNestedProtocol(IdentifierInfo *Name) {
 /// When argument category "C" is specified, any implicit method found
 /// in this category is ignored.
 ObjCMethodDecl *ObjCInterfaceDecl::lookupMethod(Selector Sel, 
-                                     bool isInstance,
-                                     bool shallowCategoryLookup,
-                                     const ObjCCategoryDecl *C) const {
+                                                bool isInstance,
+                                                bool shallowCategoryLookup,
+                                                const ObjCCategoryDecl *C,
+                                                const ObjCProtocolDecl *P) const
+{
   // FIXME: Should make sure no callers ever do this.
   if (!hasDefinition())
     return 0;
@@ -470,7 +472,23 @@ ObjCMethodDecl *ObjCInterfaceDecl::lookupMethod(Selector Sel,
   if (data().ExternallyCompleted)
     LoadExternalDefinition();
 
-  while (ClassDecl != NULL) {
+  while (ClassDecl) {
+    // If we are looking for a method that is part of protocol conformance,
+    // check if the class 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;
 

clang/lib/Sema/SemaDeclAttr.cpp

@@ -2134,6 +2134,30 @@ static void handleObjCRootClassAttr(Sema &S, Decl *D,
                                Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleObjCSuppresProtocolAttr(Sema &S, Decl *D,
+                                          const AttributeList &Attr) {
+  if (!isa<ObjCInterfaceDecl>(D)) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_wrong_decl_type)
+      << Attr.getName() << ExpectedObjectiveCInterface;
+    return;
+  }
+
+  IdentifierLoc *Parm = NULL;
+  if (Attr.getNumArgs() == 1) {
+    Parm = Attr.isArgIdent(0) ? Attr.getArgAsIdent(0) : 0;
+  }
+
+  if (!Parm) {
+    S.Diag(D->getLocStart(), diag::err_objc_attr_not_id) << Attr.getName() << 1;
+    return;
+  }
+
+  D->addAttr(::new (S.Context)
+             ObjCSuppressProtocolAttr(Attr.getRange(), S.Context, Parm->Ident,
+                                      Attr.getAttributeSpellingListIndex()));
+}
+
+
 static void handleObjCRequiresPropertyDefsAttr(Sema &S, Decl *D,
                                                const AttributeList &Attr) {
   if (!isa<ObjCInterfaceDecl>(D)) {
@@ -4690,7 +4714,10 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_ObjCRootClass:
     handleObjCRootClassAttr(S, D, Attr);
     break;
-  case AttributeList::AT_ObjCRequiresPropertyDefs: 
+  case AttributeList::AT_ObjCSuppressProtocol:
+    handleObjCSuppresProtocolAttr(S, D, Attr);
+    break;
+  case AttributeList::AT_ObjCRequiresPropertyDefs:
     handleObjCRequiresPropertyDefsAttr (S, D, Attr); 
     break;
   case AttributeList::AT_Unused:      handleUnusedAttr      (S, D, Attr); break;

clang/lib/Sema/SemaDeclObjC.cpp

@@ -1664,7 +1664,8 @@ void Sema::CheckProtocolMethodDefs(SourceLocation ImpLoc,
       if (method->getImplementationControl() != ObjCMethodDecl::Optional &&
           !method->isPropertyAccessor() &&
           !InsMap.count(method->getSelector()) &&
-          (!Super || !Super->lookupInstanceMethod(method->getSelector()))) {
+          (!Super || !Super->lookupInstanceMethod(method->getSelector(),
+                                                  false, PDecl))) {
             // If a method is not implemented in the category implementation but
             // has been declared in its primary class, superclass,
             // or in one of their protocols, no need to issue the warning. 
@@ -1676,7 +1677,8 @@ void Sema::CheckProtocolMethodDefs(SourceLocation ImpLoc,
             // uses the protocol.
             if (ObjCMethodDecl *MethodInClass =
                   IDecl->lookupInstanceMethod(method->getSelector(), 
-                                              true /*shallowCategoryLookup*/))
+                                              true /*shallowCategoryLookup*/,
+                                              PDecl))
               if (C || MethodInClass->isPropertyAccessor())
                 continue;
             unsigned DIAG = diag::warn_unimplemented_protocol_method;
@@ -1695,10 +1697,13 @@ void Sema::CheckProtocolMethodDefs(SourceLocation ImpLoc,
     ObjCMethodDecl *method = *I;
     if (method->getImplementationControl() != ObjCMethodDecl::Optional &&
         !ClsMap.count(method->getSelector()) &&
-        (!Super || !Super->lookupClassMethod(method->getSelector()))) {
+        (!Super || !Super->lookupClassMethod(method->getSelector(),
+                                             /* shallowCategoryLookup */ false,
+                                             PDecl))) {
       // See above comment for instance method lookups.
       if (C && IDecl->lookupClassMethod(method->getSelector(), 
-                                        true /*shallowCategoryLookup*/))
+                                        true /*shallowCategoryLookup*/,
+                                        PDecl))
         continue;
       unsigned DIAG = diag::warn_unimplemented_protocol_method;
       if (Diags.getDiagnosticLevel(DIAG, ImpLoc) !=

clang/test/SemaObjC/protocols-suppress-conformance.m

@@ -0,0 +1,27 @@
+// RUN: %clang_cc1  -fsyntax-only -verify %s -Wno-objc-root-class
+
+@protocol FooProto
+- (void) theBestOfTimes; // expected-note {{method 'theBestOfTimes' declared here}}
+@end
+
+__attribute__((objc_suppress_protocol(FooProto)))
+@interface Bar
+- (void) theBestOfTimes;
+@end
+
+@interface Bar2 : Bar
+@end
+
+@interface Baz : Bar2 <FooProto> // expected-note {{required for direct or indirect protocol 'FooProto'}}
+@end
+
+@interface Baz2 : Bar2 <FooProto>
+- (void) theBestOfTimes;
+@end
+
+@implementation Baz // expected-warning {{method 'theBestOfTimes' in protocol not implemented}}
+@end
+
+@implementation Baz2 // no-warning
+- (void) theBestOfTimes {}
+@end