Check superclass for property persistence

A subclass can shadow a parent's property declaration, either explicitly
with a `@property` directive or implicitly by conforming to a protocol
that requires a particular property. The result is that the subclass
property record has no associated ivar (or methods), and calls to get /
set the property will fall up to the superclass's methods (backed by the
superclass's ivar).

Mantle/MTLModel.m

@@ -232,7 +232,12 @@ + (MTLPropertyStorage)storageBehaviorForPropertyWithKey:(NSString *)propertyKey
 	};
 
 	if (attributes->readonly && attributes->ivar == NULL) {
-		return MTLPropertyStorageNone;
+		if ([self isEqual:MTLModel.class]) {
+			return MTLPropertyStorageNone;
+		} else {
+			// Check superclass in case the subclass redeclares a property that falls through
+			return [self.superclass storageBehaviorForPropertyWithKey:propertyKey];
+		}
 	} else {
 		return MTLPropertyStoragePermanent;
 	}

MantleTests/MTLModelSpec.m

@@ -137,18 +137,27 @@
 
 it(@"should consider primitive properties permanent", ^{
 	expect(@([MTLStorageBehaviorModel storageBehaviorForPropertyWithKey:@"primitive"])).to(equal(@(MTLPropertyStoragePermanent)));
+	expect(@([MTLStorageBehaviorModelSubclass storageBehaviorForPropertyWithKey:@"primitive"])).to(equal(@(MTLPropertyStoragePermanent)));
 });
 
 it(@"should consider object-type assign properties permanent", ^{
 	expect(@([MTLStorageBehaviorModel storageBehaviorForPropertyWithKey:@"assignProperty"])).to(equal(@(MTLPropertyStoragePermanent)));
+	expect(@([MTLStorageBehaviorModelSubclass storageBehaviorForPropertyWithKey:@"assignProperty"])).to(equal(@(MTLPropertyStoragePermanent)));
 });
 
 it(@"should consider object-type strong properties permanent", ^{
 	expect(@([MTLStorageBehaviorModel storageBehaviorForPropertyWithKey:@"strongProperty"])).to(equal(@(MTLPropertyStoragePermanent)));
+	expect(@([MTLStorageBehaviorModelSubclass storageBehaviorForPropertyWithKey:@"strongProperty"])).to(equal(@(MTLPropertyStoragePermanent)));
 });
 
 it(@"should ignore readonly properties without backing ivar", ^{
 	expect(@([MTLStorageBehaviorModel storageBehaviorForPropertyWithKey:@"notIvarBacked"])).to(equal(@(MTLPropertyStorageNone)));
+	expect(@([MTLStorageBehaviorModelSubclass storageBehaviorForPropertyWithKey:@"notIvarBacked"])).to(equal(@(MTLPropertyStorageNone)));
+});
+
+it(@"should consider properties declared in protocol, and backed by ivar in superclass, permanent", ^{
+	expect(@([MTLStorageBehaviorModel storageBehaviorForPropertyWithKey:@"dateFromProtocol"])).to(equal(@(MTLPropertyStoragePermanent)));
+	expect(@([MTLStorageBehaviorModelSubclass storageBehaviorForPropertyWithKey:@"dateFromProtocol"])).to(equal(@(MTLPropertyStoragePermanent)));
 });
 
 describe(@"merging with model subclasses", ^{

MantleTests/MTLTestModel.h

@@ -97,6 +97,20 @@ extern const NSInteger MTLTestModelNameMissing;
 @property (readonly, nonatomic, weak) id weakProperty;
 @property (readonly, nonatomic, strong) id strongProperty;
 
+@property (readonly, nonatomic, copy) NSDate *dateFromProtocol;
+
+@end
+
+@protocol MTLDateProtocol <NSObject>
+
+@property (readonly, nonatomic, copy) NSDate *dateFromProtocol;
+
+@end
+
+@interface MTLStorageBehaviorModelSubclass : MTLStorageBehaviorModel <MTLDateProtocol>
+
+@property (readonly, nonatomic, strong) id strongProperty; // shadows superclass without providing storage
+
 @end
 
 @interface MTLBoolModel : MTLModel <MTLJSONSerializing>

MantleTests/MTLTestModel.m

@@ -355,6 +355,12 @@ - (id)notIvarBacked {
 
 @end
 
+@implementation MTLStorageBehaviorModelSubclass
+
+@dynamic strongProperty;
+
+@end
+
 @implementation MTLMultiKeypathModel
 
 #pragma mark MTLJSONSerializing