Key-Value Observing: Add support for observing through a proxy

Source/NSKVOInternal.h

@@ -123,6 +123,7 @@ _NSKVOEnsureKeyWillNotify(id object, NSString *key);
  */
 @interface
 NSObject (NSKeyValueObservingPrivate)
+- (Class)_underlyingClass;
 - (void)_notifyObserversOfChangeForKey:(NSString *)key
                               oldValue:(id)oldValue
                               newValue:(id)newValue;

Source/NSKVOSupport.m

@@ -333,7 +333,11 @@ - (bool) isEmpty
   // Aggregate all keys whose values will affect us.
   if (dependents)
     {
-      Class cls = [object class];
+      // Make sure to retrieve the underlying class of the observee.
+      // This is just [object class] for an NSObject derived class.
+      // When observing an object through a proxy, we instead use KVC
+      // to optain the underlying class.
+      Class cls = [object _underlyingClass];
       NSSet *valueInfluencingKeys = [cls keyPathsForValuesAffectingValueForKey: key];
       if (valueInfluencingKeys.count > 0)
         {
@@ -1123,6 +1127,11 @@ - (void)didChangeValueForKey: (NSString *)key
 @implementation
 NSObject (NSKeyValueObservingPrivate)
 
+- (Class)_underlyingClass
+{
+  return [self class];
+}
+
 - (void)_notifyObserversOfChangeForKey: (NSString *)key
                               oldValue: (id)oldValue
                               newValue: (id)newValue
@@ -1254,3 +1263,19 @@ - (void)removeObserver: (id)observer forKeyPath:(NSString *)keyPath
 @end
 
 #pragma endregion
+
+#pragma region KVO forwarding - NSProxy category
+
+@implementation
+NSProxy (NSKeyValueObserving)
+
+- (Class)_underlyingClass
+{
+  // Retrieve the underlying class via KVC
+  // Note that we assume that the class is KVC-compliant, when KVO is used
+  return [(NSObject *)self valueForKey: @"class"];
+}
+
+@end
+
+#pragma endregion

Source/NSKVOSwizzling.m

@@ -666,6 +666,8 @@ static void funcName(id self, SEL _cmd, type val)                            \
 _NSKVOEnsureKeyWillNotify(id object, NSString *key)
 {
   char *rawKey;
+  Class cls;
+  Class underlyingCls;
 
   // Since we cannot replace the isa of tagged pointer objects, we can't swizzle
   // them.
@@ -674,8 +676,17 @@ static void funcName(id self, SEL _cmd, type val)                            \
       return;
     }
 
+  cls = [object class];
+  underlyingCls = [object _underlyingClass];
+  // If cls differs from underlyingCls, object is actually a proxy.
+  // Retrieve the underlying object with KVC.
+  if (cls != underlyingCls)
+  {
+    object = [object valueForKey: @"self"];
+  }
+
   // A class is allowed to decline automatic swizzling for any/all of its keys.
-  if (![[object class] automaticallyNotifiesObserversForKey: key])
+  if (![underlyingCls automaticallyNotifiesObserversForKey: key])
     {
       return;
     }

Tests/base/NSKVOSupport/proxy.m

@@ -96,9 +96,41 @@ - (void) dealloc
 
 @end
 
+@interface Wrapper : NSObject
+{
+    TProxy *_proxy;
+}
+
+- (instancetype) initWithProxy: (TProxy *) proxy; 
+
+- (TProxy *) proxy;
+
+@end
+
+@implementation Wrapper
+
+- (instancetype) initWithProxy: (TProxy *) proxy
+{
+    self = [super init];
+    if (self)
+    {
+        _proxy = proxy;
+    }
+
+    return self;
+}
+
+- (TProxy *) proxy
+{
+    return _proxy;
+}
+
+@end
+
 @interface Observer: NSObject
 {
     int count;
+    NSArray *keys;
 }
 
 - (void)runTest;
@@ -107,10 +139,13 @@ - (void)runTest;
 
 @implementation Observer
 
-- (void)runTest
+- (void)simpleKeypathTest
 {
 	Observee *obj = [[Observee alloc] init];
 	TProxy *proxy = [[TProxy alloc] initWithProxiedObject:obj];
+
+    keys = [NSArray arrayWithObjects: @"derivedName", @"name", nil];
+    count = 0;
 
 	[(Observee *)proxy addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew context:NULL];
 	[(Observee *)proxy addObserver:self forKeyPath:@"derivedName" options:NSKeyValueObservingOptionNew context:NULL];
@@ -128,21 +163,50 @@ - (void)runTest
     [obj release];
 }
 
+- (void)nestedKeypathTest
+{
+	Observee *obj = [[Observee alloc] init];
+	TProxy *proxy = [[TProxy alloc] initWithProxiedObject:obj];
+    Wrapper *w = [[Wrapper alloc] initWithProxy: proxy];
+
+    keys = [NSArray arrayWithObjects: @"proxy.derivedName", @"proxy.name", nil];
+    count = 0;
+
+	[w addObserver:self forKeyPath:@"proxy.name" options:NSKeyValueObservingOptionNew context:NULL];
+	[w addObserver:self forKeyPath:@"proxy.derivedName" options:NSKeyValueObservingOptionNew context:NULL];
+
+	[((Observee *)proxy) setName: @"MOO"];
+    PASS(count == 2, "Got two change notifications");
+
+	[obj setName: @"BAH"];
+    PASS(count == 4, "Got two change notifications");
+
+	[w removeObserver:self forKeyPath:@"proxy.name" context:NULL];
+	[w removeObserver:self forKeyPath:@"proxy.derivedName" context:NULL];
+
+    [w release];
+    [proxy release];
+    [obj release];
+
+    count = 0;
+
+}
+
 - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
 {
     count += 1;
     switch (count) {
         case 1:
-            PASS_EQUAL(keyPath, @"derivedName", "change notification for dependent key 'derivedName' is emitted first");
+            PASS_EQUAL(keyPath, [keys objectAtIndex: 0], "change notification for dependent key 'derivedName' is emitted first");
             break;
         case 2:
-            PASS_EQUAL(keyPath, @"name", "'name' change notification for proxy is second");
+            PASS_EQUAL(keyPath, [keys objectAtIndex: 1], "'name' change notification for proxy is second");
             break;
         case 3:
-            PASS_EQUAL(keyPath, @"derivedName", "'derivedName' change notification for object is third");
+            PASS_EQUAL(keyPath, [keys objectAtIndex: 0], "'derivedName' change notification for object is third");
             break;
         case 4:
-            PASS_EQUAL(keyPath, @"name", "'name' change notification for object is fourth");
+            PASS_EQUAL(keyPath, [keys objectAtIndex: 1], "'name' change notification for object is fourth");
             break;
         default:
             PASS(0, "unexpected -[Observer observeValueForKeyPath:ofObject:change:context:] callback");
@@ -154,15 +218,15 @@ - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(N
 int
 main(int argc, char *argv[])
 {
-    NSAutoreleasePool *arp = [NSAutoreleasePool new];
+    START_SET("KVO Proxy Tests")
     Observer *obs = [Observer new];
 
     testHopeful = YES;
-    [obs runTest];
+    [obs simpleKeypathTest];
+    [obs nestedKeypathTest];
     testHopeful = NO;
 
     [obs release];
-
-    DESTROY(arp);
+    END_SET("KVO Proxy Tests")
     return 0;
 }