add a separate check for this special case

Source/ASDisplayNode.mm

@@ -2104,7 +2104,7 @@ - (void)_insertSubnode:(ASDisplayNode *)subnode atSubnodeIndex:(NSInteger)subnod
     ASDisplayNodeFailAssert(@"Cannot add a view-backed node as a subnode of a layer-backed node. Supernode: %@, subnode: %@", self, subnode);
     return;
   }
-  
+
   BOOL isRasterized = subtreeIsRasterized(self);
   if (isRasterized && subnode.nodeLoaded) {
     ASDisplayNodeFailAssert(@"Cannot add loaded node %@ to rasterized subtree of node %@", ASObjectDescriptionMakeTiny(subnode), ASObjectDescriptionMakeTiny(self));
@@ -2114,13 +2114,18 @@ - (void)_insertSubnode:(ASDisplayNode *)subnode atSubnodeIndex:(NSInteger)subnod
   __instanceLock__.lock();
     NSUInteger subnodesCount = _subnodes.count;
   __instanceLock__.unlock();
-
-  // If the subnodeIndex is out of bounds OR it will be once we call [subnode removeFromSupernode], exit early
-  if (subnodeIndex > subnodesCount || subnodeIndex < 0 || (subnode.supernode == self && subnodeIndex >= subnodesCount)) {
+
+  if (subnodeIndex > subnodesCount || subnodeIndex < 0) {
     ASDisplayNodeFailAssert(@"Cannot insert a subnode at index %ld. Count is %ld", (long)subnodeIndex, (long)subnodesCount);
     return;
   }
-
+
+  // Check if subnode is already a in _subnodes. If so make sure the subnodeIndex will not be out of bounds once we call [subnode removeFromSupernode]
+  if (subnode.supernode == self && subnodeIndex >= subnodesCount) {
+    ASDisplayNodeFailAssert(@"node %@ is already a subnode of %@. index %ld will be out of bounds once we call [subnode removeFromSupernode]. This can be caused by using automaticallyManagesSubnodes while also calling addSubnode explicitly.", subnode, self, subnodeIndex);
+    return;
+  }
+
   // Disable appearance methods during move between supernodes, but make sure we restore their state after we do our thing
   ASDisplayNode *oldParent = subnode.supernode;
   BOOL disableNotifications = shouldDisableNotificationsForMovingBetweenParents(oldParent, self);

Tests/ASDisplayNodeTests.mm

@@ -2789,7 +2789,7 @@ - (void)testInsertExistingSubnode
   DeclareNodeNamed(child);
 
   [parent addSubnode:child];
-  // Previously this would cause a crash. We now protect inserting an already existing subnode
+  // Previously this would cause a crash. We now protect inserting an already existing subnode out of bounds
   XCTAssertThrows([parent insertSubnode:child atIndex:1]);
   XCTAssertTrue(parent.subnodes.count == 1);
 }