Clear list pointers of child before adding it to a JsonValue (libgdx#…

…7044)

* Add test for removing and adding a json value

* Clear list pointers of child before adding it to a JsonValue

* Update CHANGES

CHANGES

@@ -71,6 +71,7 @@
 - API Fix: MathUtils.lerpAngle() fixed for extreme inputs
 - MathUtils trigonometry improvements
 - Various Scene2D fixes and improvements
+- Fix: JsonValue#addChild now clears leftover list pointers, preventing inconsistent or looping JSON objects.
 
 [1.11.0]
 - [BREAKING CHANGE] iOS: Increased min supported iOS version to 9.0. Update your Info.plist file if necessary.

gdx/src/com/badlogic/gdx/utils/JsonValue.java

@@ -912,11 +912,13 @@ public void addChild (JsonValue value) {
 		if (type == ValueType.object && value.name == null)
 			throw new IllegalStateException("An object child requires a name: " + value);
 		value.parent = this;
+		value.next = null;
 		size++;
 		JsonValue current = child;
-		if (current == null)
+		if (current == null) {
+			value.prev = null;
 			child = value;
-		else {
+		} else {
 			while (true) {
 				if (current.next == null) {
 					current.next = value;

gdx/test/com/badlogic/gdx/utils/JsonValueTest.java

@@ -0,0 +1,32 @@
+
+package com.badlogic.gdx.utils;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class JsonValueTest {
+
+	@Test
+	public void testAddingRemovedValue () {
+		// Prepare two JSON objects
+		JsonValue firstObject = new JsonValue(JsonValue.ValueType.object);
+		JsonValue secondObject = new JsonValue(JsonValue.ValueType.object);
+
+		firstObject.addChild("a", new JsonValue("A"));
+		secondObject.addChild("b", new JsonValue("B"));
+		secondObject.addChild("c", new JsonValue("C"));
+
+		// Remove an item from one object and add it to the other
+		JsonValue b = secondObject.remove("b");
+		firstObject.addChild(b);
+
+		// Check if both objects have the expected children
+		Assert.assertNotNull(firstObject.get("a"));
+		Assert.assertNotNull(firstObject.get("b"));
+		Assert.assertNull(firstObject.get("c"));
+
+		Assert.assertNull(secondObject.get("a"));
+		Assert.assertNull(secondObject.get("b"));
+		Assert.assertNotNull(secondObject.get("c"));
+	}
+}