Provide watch/build helper to make CLI tooling easier

[kevmoo]

Per google/json_serializable.dart#80 (comment)

It's common to create two files in the tool directory (see below).

It'd be nice to have a run(List<String> args, List<BuildAction> buildActions, {...}) method in build_runner so we could create a trivial hybrid scripts. Where run does the work to switch between build or watch based on args, prints help w/ invalid args, sets the exit code, etc etc etc

#!/usr/bin/env dart --checked
import 'dart:io';
import 'package:build_runner/build_runner.dart';

Future main(List<String> args) => run(args, _buildActions, ...);

final _buildActions = ...

build and watch today...

build.dart

#!/usr/bin/env dart --checked
import 'dart:io';
import 'package:build_runner/build_runner.dart';
import 'build_actions.dart';

main() async {
  var result = await build(buildActions, deleteFilesByDefault: true);
  if (result.status == BuildStatus.failure) {
    exitCode = 1;
  }
}

and watch.dart

#!/usr/bin/env dart --checked
import 'package:build_runner/build_runner.dart';
import 'build_actions.dart';

main() {
  watch(buildActions, deleteFilesByDefault: true);
}

[jakemac53]

I think it would make sense if this was used by the automated entrypoint as well so we can unify things and expose the same basic command line args (port numbers etc).

[kevmoo]

I think it would make sense if this was used by the automated entrypoint as well so we can unify things and expose the same basic command line args (port numbers etc).

That too! We could work towards that!