code: func EvalDataForInstanceKey(key addrs.InstanceKey) InstanceKeyEvalData {
  	// At the moment we don't actually implement for_each, so we only
  	// ever populate CountIndex.
  	// (When we implement for_each later we may need to reorganize this some,
  	// so that we can resolve the ambiguity that an int key may either be
  	// a count.index or an each.key where for_each is over a list.)
  
  	var countIdx cty.Value
  	if intKey, ok := key.(addrs.IntKey); ok {
  		countIdx = cty.NumberIntVal(int64(intKey))
  	}
  
  	return InstanceKeyEvalData{
  		CountIndex: countIdx,
  	}
  }
docs: // EvalDataForInstanceKey constructs a suitable InstanceKeyEvalData for
  // evaluating in a context that has the given instance key.