W0103: A stateful component in a loop has no key

A stateful component (one embedding ui.Live) made in a loop, with no key on it or on the item holding it, is told apart from the others by its order: an item inserted before it hands it another item's instance, state and all. Reported by vukavet.

Wrong

for _, it := range Items {
  <Counter label={it.Name}/>
}

Right

for _, it := range Items {
  <Counter key={it.ID} label={it.Name}/>
}