Add Codable property support via a new attributeCodableTypeName user …

…info key, as described in #375.

mogenerator.m

@@ -586,6 +586,13 @@ - (NSString*)objectAttributeClassName {
         if (!result) {
             result = gSwift ? @"AnyObject" : @"NSObject";
         }
+    } else if (gSwift && [self attributeType] == NSBinaryDataAttributeType) {
+        NSString *codableName = [self userInfo][@"attributeCodableTypeName"];
+        if (!codableName) {
+            result = @"Data";
+        } else {
+            result = codableName;
+        }
     } else {
         // Forcibly generate the correct class name in case we are
         // running on macOS < 10.13
@@ -638,6 +645,10 @@ - (BOOL)usesCustomObjectAttributeType {
     return (attributeValueClassName != nil);
 }
 
+- (BOOL)usesCustomCodableAttributeType {
+    return [self userInfo][@"attributeCodableTypeName"] != NULL;
+}
+
 - (NSString*)objectAttributeType {
     NSString *result = [self objectAttributeClassName];
     if ([result isEqualToString:@"Class"]) {

templates/machine.swift.motemplate

@@ -128,6 +128,29 @@ public extension <$managedObjectClassName$> {
 			setPrimitiveValue(value.rawValue, forKey: key)
 		}
 	}
+<$elseif Attribute.usesCustomCodableAttributeType$>
+		// Attribute <$Attribute.name$> with Codable type <$Attribute.objectAttributeType$>
+		public<$if Attribute.isReadonly$> private(set)<$endif$> var <$Attribute.name$>: <$Attribute.objectAttributeType$>? {
+			get {
+				let key = <$managedObjectClassName$>.Attributes.<$Attribute.name$>
+				willAccessValue(forKey: key)
+				defer { didAccessValue(forKey: key) }
+
+				guard let primitiveValue = primitiveValue(forKey: key) as? Data else {
+					return nil
+				}
+
+				return try? JSONDecoder().decode(<$Attribute.objectAttributeType$>.self, from: primitiveValue)
+			}
+			set {
+				let key = <$managedObjectClassName$>.Attributes.<$Attribute.name$>
+				willChangeValue(forKey: key)
+				defer { didChangeValue(forKey: key) }
+
+				let primitiveValue = try? JSONEncoder().encode(newValue)
+				setPrimitiveValue(primitiveValue, forKey: key)
+			}
+		}
 <$else$> <$comment usesRawValueEnumType = false $>
     @NSManaged public<$if Attribute.isReadonly$> private(set)<$endif$> var <$Attribute.name$>: <$Attribute.objectAttributeType$><$if Attribute.isOptional$>?<$endif$>
 <$endif$> <$comment usesRawValueEnumType $>