unnecessary_async

Don't make a function 'async' if it doesn't use 'await'.

The analyzer produces this diagnostic when a function, method, or closure is marked async but doesn't contain any await expressions or await for statements. The async modifier is unnecessary in these cases and can be removed without changing the behavior of the code.

The following code produces this diagnostic because the function f is marked async but doesn't use await:

void f() async {
  print('done');
}

Remove the async modifier:

void f() {
  print('done');
}