gistfile1.txt

// @dart = 2.9

import 'dart:io';
import 'dart:isolate';
import 'dart:async';
import 'package:path/path.dart' as p;


void main(List<String> arguments) async {
  // var a = <int?>[];
  // print("root: can use NNBD");
  // print('root: NNBD is ${<int?>[] is! List<int>? "strong": "weak"}');

  Directory tmp = await Directory.systemTemp.createTemp("testCopy");
  var path = "${tmp.path}/other.dart";
  var sourceFile = new File(path);
  sourceFile.writeAsStringSync(r"""
    void main() {
      var a = <int?>[];
      print("child: can use NNBD");
      print('child: NNBD is ${<int?>[] is! List<int>? "strong": "weak"}');
    }
  """);

  var exitPort = new ReceivePort();
  await Isolate.spawnUri(p.toUri(p.absolute(path)), [], null,
      onExit: exitPort.sendPort);
  await exitPort.first;
  await sourceFile.delete();

}