Quick assist for converting a switch statement in which each case just assigns to a variable

[srawlins]

It'd be great to offer to convert this to a Dart 3.0 switch expression.

For example:

String f(Color color) {
  String result;
  switch (color) {
    case Color.blue:
      result = 'blue';
      break;
    case Color.red:
      throw 'Unsupported';
  }
  return result;
}

could be converted to:

String f(Color color) {
  String result;
  result = switch (color) {
    case Color.blue => 'blue',
    case Color.red => throw 'Unsupported'
  }
  return result;
}

CC @bwilkerson @pq @mit-mit @stereotype441

[pq]

I think this is complete as part of #50417?

[pq]

(And improved w/ #51826.)

[srawlins]

When writing these multi-token assists, there is an opportunity to eat comments. 🙁 For example:

var name = '';
/* one */
switch (color) {
  /* two */ case /* three */ Color.blue /* four */: /* five */
    name /* six */ = /* seven */ 'blue' / *eight */; / * nine */
    break; /* ten */
}

It can be excruciating to try to account for all of those, and not lose them. Many of those will be exceedingly rare, but I think /* one */, /* two */, /* five */, /* nine */, and /* ten */ should be considered. Can either work to preserve them, or not offer the assist if they are detected. If there is a tracking issue or a PR, I can comment there.

For example, in our code search I see examples like:

case foo: // Comment here.
  result = 'foo';
case bar:
  // Comment here.
  result = 'bar'; // Comment here.

(here and here and here)

[srawlins]

Perfect, thanks. I see comments in the tests.