more reliable way of checking the build was successful

[mcfiredrill]

There are still cases where ember-cli-rails reports the build as unsuccessful even though there were merely warnings not actual errors.

e.g.:

Warning: ignoring input sourcemap for vendor/ember/ember.debug.js because ENOENT: no such file or directory, open '/Users/tony/src/ember_rails_test/frontend/tmp/source_map_concat-input_base_path-SS0N4DR8.tmp/vendor/ember/ember.debug.map'

Lines that start with Warning are not accounted for and rejected in build_errors:
https://github.com/thoughtbot/ember-cli-rails/blob/master/lib/ember_cli/build_monitor.rb#L42

I was wondering if there is a reason this approach was taken, and if its possible to rely on something like the exit code status of ember cli building the project instead? Is the exit code status not reliable either?

Which operating system and version is the project developed on?
mac os sierra 10.12.4

Which version of ruby is the project developed on?
ruby 2.4.1

Which version of npm is the project developed on?
npm 5.3.0, but using yarn 0.27.5

Which version of ember-cli is the project developed on?
2.14.2

What is the rails version?
5.1.3

What is the ember-cli-rails version (from Gemfile)?
0.9.0

What is the ember-cli-rails-addon version (from package.json)?
0.8.0

Is your application server multi-threaded
(such as puma and unicorn) or is it multi-process (such as thin and webrick)?
using puma

What are the contents of config/initializers/ember.rb?

EmberCli.configure do |c|
  c.app :frontend
end