[Formatting issue] trailing_commas=preserve not working for some enums with a constructor declaration

[androidseb]

When setting trailing_commas to preserve, I would expect the formatter to preserve trailing commas in my code. This is not the case when creating an enum with a constructor as shown below.

What input code did you provide to the formatter?

enum RawPhotoType {
  jpeg('image/jpeg'), png('image/png'),
  ;

  final String mimeType;
  const RawPhotoType(this.mimeType);
}

What output did the formatter produce?

enum RawPhotoType {
  jpeg('image/jpeg'),
  png('image/png');

  final String mimeType;
  const RawPhotoType(this.mimeType);
}

What output did you expect or want the formatter to produce?

enum RawPhotoType {
  jpeg('image/jpeg'),
  png('image/png'),
  ;

  final String mimeType;
  const RawPhotoType(this.mimeType);
}

[jellynoone]

Pull request #1703 intends to fix this.