[ObjC][Sema] Avoid warning about a call to an instance method on an

instance of a qualified Class object when that instance method comes from
a protocol that's implemented by NSObject

Instance methods from a root class like NSObject are also class methods because
the metaclass of root class derives from that root class. Therefore, we can
avoid the warning for instances of qualified Class objects that point to classes
that derive from NSObject. Note that we actually don't know if a Class instance
points to a class that derives from NSObject at compile-time, so we have to
make a reasonable assumption that the majority of instances will do so.

rdar://22812517


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@297862 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Sema/SemaExprObjC.cpp

@@ -2556,6 +2556,24 @@ ExprResult Sema::BuildInstanceMessageImplicit(Expr *Receiver,
                               /*isImplicit=*/true);
 }
 
+static bool isMethodDeclaredInRootProtocol(Sema &S, const ObjCMethodDecl *M) {
+  if (!S.NSAPIObj)
+    return false;
+  const auto *Protocol = dyn_cast<ObjCProtocolDecl>(M->getDeclContext());
+  if (!Protocol)
+    return false;
+  const IdentifierInfo *II = S.NSAPIObj->getNSClassId(NSAPI::ClassId_NSObject);
+  if (const auto *RootClass = dyn_cast_or_null<ObjCInterfaceDecl>(
+          S.LookupSingleName(S.TUScope, II, Protocol->getLocStart(),
+                             Sema::LookupOrdinaryName))) {
+    for (const ObjCProtocolDecl *P : RootClass->all_referenced_protocols()) {
+      if (P->getCanonicalDecl() == Protocol->getCanonicalDecl())
+        return true;
+    }
+  }
+  return false;
+}
+
 /// \brief Build an Objective-C instance message expression.
 ///
 /// This routine takes care of both normal instance messages and
@@ -2731,7 +2749,7 @@ ExprResult Sema::BuildInstanceMessage(Expr *Receiver,
         if (!Method) {
           Method = LookupMethodInQualifiedType(Sel, QClassTy, true);
           // warn if instance method found for a Class message.
-          if (Method) {
+          if (Method && !isMethodDeclaredInRootProtocol(*this, Method)) {
             Diag(SelLoc, diag::warn_instance_method_on_class_found)
               << Method->getSelector() << Sel;
             Diag(Method->getLocation(), diag::note_method_declared_at)

test/SemaObjC/class-message-protocol-lookup.m

@@ -32,3 +32,30 @@ int main ()
     Class<Test2Protocol> c2 = [c2 alloc]; //  ok
     return 0;
 }
+
+// rdar://22812517
+
+@protocol NSObject
+
+- (int)respondsToSelector:(SEL)aSelector;
+
+@end
+
+__attribute__((objc_root_class))
+@interface NSObject <NSObject>
+
+@end
+
+@protocol OtherProto
+
+- (void)otherInstanceMethod; // expected-note {{method 'otherInstanceMethod' declared here}}
+
+@end
+
+@protocol MyProto <NSObject, OtherProto>
+@end
+
+void allowInstanceMethodsFromRootProtocols(Class<MyProto> c) {
+  [c respondsToSelector: @selector(instanceMethod)]; // no warning
+  [c otherInstanceMethod]; //  expected-warning {{instance method 'otherInstanceMethod' found instead of class method 'otherInstanceMethod'}}
+}