Hot Reload for Dart CLI

main.dart

import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:vm_service/vm_service_io.dart';

void main() async {
  var process = await Process.start('dart', ['run', '--enable-vm-service', 'lib/main.dart']);
  var completer = Completer<String>();
  process.stdout
    .transform(utf8.decoder)
    .transform(const LineSplitter())
    .listen((String line) {
      print(line);
      const message = 'Observatory listening on ';
      if (line.startsWith(message)) {
        completer.complete(line.split(message)[1].trim());
      }
  });
  process.stderr
    .transform(utf8.decoder)
    .transform(const LineSplitter())
    .listen(print);

  var url = Uri.parse(await completer.future);
  print('connecting to ${url.replace(scheme: 'ws').toString() + 'ws/'}');
  var service = await vmServiceConnectUri(url.replace(scheme: 'ws').toString() + 'ws/');

  stdin.echoMode = false;
  stdin.lineMode = false;
  var pending = false;
  print('Ready');
  stdin.transform(utf8.decoder).listen((String command) async {
    if (pending) {
      return;
    }
    try {
      pending = true;
      switch (command) {
        case 'h':
          print('Press r to hot reload and q to quit');
          break;
        case 'r':
        case 'R':
          var vm = await service.getVM();
          for (var isolateRef in vm.isolates!) {
            var report = await service.reloadSources(isolateRef.id!);
            print(report);
          }
          break;
        case 'q':
          await service.dispose();
          process.kill();
          exit(0);
      }
    } finally {
      pending = false;
    }
  });
}