in model/src/main/java/jetbrains/jetpad/model/transform/Transformers.java [444:468]
protected void add(ItemT item, CollectionT from, ObservableList<ItemT> to) {
Iterator<ItemT> fromItr = from.iterator();
int index = 0;
boolean foundItem = false;
for (ItemT curTo : to) {
while (fromItr.hasNext()) {
ItemT curFrom = fromItr.next();
if (curFrom == curTo) {
break;
}
if (curFrom == item) {
foundItem = true;
break;
}
}
if (foundItem) {
break;
}
index++;
}
if (!fromItr.hasNext() && !foundItem) {
throw new IllegalStateException("item " + item + " has not been found in " + from);
}
to.add(index, item);
}