Fix cycle detection

See emberjs/ember.js#17220

Author: hjdivad

addon/copy.js

@@ -15,29 +15,44 @@ function _copy(obj, deep, seen, copies) {
     return copies[loc];
   }
 
+  if (deep) {
+    seen.push(obj);
+  }
+
   // IMPORTANT: this specific test will detect a native array only. Any other
   // object will need to implement Copyable.
   if (Array.isArray(obj)) {
     ret = obj.slice();
 
     if (deep) {
+      copies.push(ret);
       loc = ret.length;
 
       while (--loc >= 0) {
         ret[loc] = _copy(ret[loc], deep, seen, copies);
       }
     }
   } else if (Copyable.detect(obj)) {
-      ret = obj.copy(deep, seen, copies);
+    ret = obj.copy(deep, seen, copies);
+    if (deep) {
+      copies.push(ret);
+    }
   } else if (obj instanceof Date) {
     ret = new Date(obj.getTime());
+    if (deep) {
+      copies.push(ret);
+    }
   } else {
     assert(
       'Cannot clone an EmberObject that does not implement Copyable',
-      !(obj instanceof EmberObject)
+      !(obj instanceof EmberObject) || Copyable.detect(obj)
     );
-  
+
     ret = {};
+    if (deep) {
+      copies.push(ret);
+    }
+
     let key;
     for (key in obj) {
       // support Null prototype
@@ -54,10 +69,6 @@ function _copy(obj, deep, seen, copies) {
       ret[key] = deep ? _copy(obj[key], deep, seen, copies) : obj[key];
     }
   }
-  if (deep) {
-    seen.push(obj);
-    copies.push(ret);
-  }
 
   return ret;
 }

tests/unit/copy-test.js

@@ -28,4 +28,18 @@ module('Unit | Utility | copy', function(/*hooks*/) {
     assert.deepEqual(array, arrayCopy, 'array content cloned successfully in new array');
   });
 
+
+  test('copy cycle detection', function(assert) {
+    let obj = {
+      foo: {
+        bar: 'bar',
+      },
+    };
+    obj.foo.foo = obj.foo;
+    let cycleCopy = copy(obj, true);
+
+    assert.equal(cycleCopy.foo.bar, 'bar');
+    assert.notEqual(cycleCopy.foo.foo, obj.foo.foo);
+    assert.strictEqual(cycleCopy.foo.foo, cycleCopy.foo.foo);
+  });
 });