From 47ad4b912fc0854a90868002b3a1cea3bbbb7634 Mon Sep 17 00:00:00 2001
From: Carlos Ballesteros Velasco <soywiz@gmail.com>
Date: Thu, 6 Jul 2023 08:23:06 +0200
Subject: [PATCH] Prevents a stackoverflow when creating a view graph cycle
 (#1771)

---
 .../kotlin/korlibs/korge/view/Container.kt    | 10 ++++++++
 .../kotlin/korlibs/korge/view/ViewTest.kt     | 25 +++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/korge/src/commonMain/kotlin/korlibs/korge/view/Container.kt b/korge/src/commonMain/kotlin/korlibs/korge/view/Container.kt
index 802ad38cbe..96c39cb096 100644
--- a/korge/src/commonMain/kotlin/korlibs/korge/view/Container.kt
+++ b/korge/src/commonMain/kotlin/korlibs/korge/view/Container.kt
@@ -3,6 +3,7 @@ package korlibs.korge.view
 import korlibs.datastructure.*
 import korlibs.datastructure.iterators.*
 import korlibs.event.*
+import korlibs.io.lang.*
 import korlibs.korge.internal.*
 import korlibs.korge.render.*
 import korlibs.korge.view.property.*
@@ -395,12 +396,21 @@ open class Container(
         stage?.views?.invalidatedView(this)
     }
 
+
+    internal fun checkValidChild(child: View) {
+        val parent = this
+        if (parent === child) invalidOp("Can't addChild to itself")
+        if (parent.hasAncestor(child)) invalidOp("Can't addChild to an ancestor")
+    }
+
     /**
      * Adds the [view] [View] as a child at a specific [index].
      *
      * Remarks: if [index] is outside bounds 0..[numChildren], it will be clamped to the nearest valid value.
      */
     fun addChildAt(view: View, index: Int) {
+        checkValidChild(view)
+
         view.parent?.invalidateZIndexChildren()
         view.removeFromParent()
         val aindex = index.clamp(0, this.numChildren)
diff --git a/korge/src/commonTest/kotlin/korlibs/korge/view/ViewTest.kt b/korge/src/commonTest/kotlin/korlibs/korge/view/ViewTest.kt
index c5c369227d..0fafac16e9 100644
--- a/korge/src/commonTest/kotlin/korlibs/korge/view/ViewTest.kt
+++ b/korge/src/commonTest/kotlin/korlibs/korge/view/ViewTest.kt
@@ -2,6 +2,7 @@ package korlibs.korge.view
 
 import assertEqualsFloat
 import korlibs.image.bitmap.*
+import korlibs.io.lang.*
 import korlibs.korge.tests.*
 import korlibs.math.geom.*
 import kotlin.test.*
@@ -280,4 +281,28 @@ class ViewTest {
             logs.joinToString("\n")
         )
     }
+
+    @Test
+    fun testViewAddToItself() {
+        val text = Text("hello")
+        assertEquals(
+            "Can't addChild to itself",
+            assertFailsWith<InvalidOperationException> { text.addChild(text) }.message
+        )
+        assertNull(text.parent)
+    }
+
+    @Test
+    fun testViewCreateCycle() {
+        val container1 = Container()
+        val container2 = Container()
+        val container3 = Container()
+        container1.addChild(container2)
+        container2.addChild(container3)
+        assertEquals(
+            "Can't addChild to an ancestor",
+            assertFailsWith<InvalidOperationException> { container3.addChild(container1) }.message
+        )
+        assertNull(container1.parent)
+    }
 }