fix: Fix ConcurrentModificationException occurring when calling GroupingBlockIndex#removeAll

Author: phinner

src/main/kotlin/com/xpdustry/nohorny/geometry/GroupingBlockIndex.kt

@@ -81,10 +81,7 @@ public interface GroupingBlockIndex<T : Any> {
 @Suppress("UnstableApiUsage")
 internal class GroupingBlockIndexImpl<T : Any>(private val group: GroupingFunction<T>) : GroupingBlockIndex<T> {
     private val index = IntMap<IndexBlock<T>>()
-    internal val graph =
-        GraphBuilder.undirected()
-            .nodeOrder(ElementOrder.unordered<Int>())
-            .build<Int>()
+    internal var graph = createGraph()
 
     override fun select(
         x: Int,
@@ -156,7 +153,7 @@ internal class GroupingBlockIndexImpl<T : Any>(private val group: GroupingFuncti
 
     override fun removeAll() {
         index.clear()
-        graph.nodes().forEach { graph.removeNode(it) }
+        graph = createGraph()
     }
 
     override fun neighbors(
@@ -231,4 +228,10 @@ internal class GroupingBlockIndexImpl<T : Any>(private val group: GroupingFuncti
         }
         return result.values().toSet()
     }
+
+    private fun createGraph() =
+        GraphBuilder
+            .undirected()
+            .nodeOrder(ElementOrder.unordered<Int>())
+            .build<Int>()
 }

src/test/kotlin/com/xpdustry/nohorny/geometry/GroupingBlockIndexImplTest.kt

@@ -202,5 +202,24 @@ class GroupingBlockIndexImplTest {
         Assertions.assertEquals(4, index.groups().size)
     }
 
+    @Test
+    fun `test remove all`() {
+        val index = createIndex()
+        repeat(5) { x ->
+            index.insert(x, 0, 1, Unit)
+        }
+
+        Assertions.assertEquals(1, index.groups().size)
+        Assertions.assertEquals(5, index.groups().toList()[0].blocks.size)
+        Assertions.assertEquals(5, index.graph.nodes().size)
+        Assertions.assertEquals(4, index.graph.edges().size)
+
+        index.removeAll()
+
+        Assertions.assertEquals(0, index.groups().size)
+        Assertions.assertEquals(0, index.graph.nodes().size)
+        Assertions.assertEquals(0, index.graph.edges().size)
+    }
+
     private fun createIndex() = GroupingBlockIndex.create<Unit>() as GroupingBlockIndexImpl<Unit>
 }