unnecessary_to_list_in_spreads

Unnecessary use of 'toList' in a spread.

The analyzer produces this diagnostic when toList is used to convert an Iterable to a List just before a spread operator is applied to the list. The spread operator can be applied to any Iterable, so the conversion isn't necessary.

The following code produces this diagnostic because toList is invoked on the result of map, which is an Iterable that the spread operator could be applied to directly:

List<String> toLowercase(List<String> strings) {
  return [
    ...strings.map((String s) => s.toLowerCase()).toList(),
  ];
}

Remove the invocation of toList:

List<String> toLowercase(List<String> strings) {
  return [
    ...strings.map((String s) => s.toLowerCase()),
  ];
}