Add ability for app to run without application.yml file

[patcon]

Currently, app can't run on Heroku unless application.yml is committed,
whereas the preferred method of working is by setting envvars in .env.

[patcon]

Related to #903

[monfresh]

Good point. We upload application.yml to our servers via Chef, but we shouldn't assume that everyone will do this. We should come up with a more generic solution that uses the ENV keys. This should work:

class FigaroYamlValidator
  ENV_KEYS = ENV.keys.delete_if { |key| key.include?('_FIGARO') }

  def validate(keys = ENV_KEYS)
    bad_keys = []
    check_for_bad_values(keys, bad_keys)
    return unless bad_keys.any?
    raise warning(bad_keys).tr("\\\n", ' ')
  end

  private

  def check_for_bad_values(keys, bad_keys)
    keys.each { |key| bad_keys << key if %w(yes no).include?(ENV[key]) }
  end

  def warning(bad_keys)
    <<~HEREDOC
      You have invalid values for #{bad_keys.uniq.to_sentence} in
      config/application.yml. Please change them to 'true' or 'false'
    HEREDOC
  end
end

We should also probably rename the class to something like ConfigValidator.

[monfresh]

@patcon What do you think about my solution? If you like it, wanna update your PR to incorporate it?

[patcon]

Slightly different so that spec works cleanly. Lemme know if you'd like a different approach!

[monfresh]

LGTM. Could you please address the Code Climate issue? Not sure if you can see what it is. It's complaining about the comma at the end of the hash on line 15 of the spec.

[monfresh]

Looks great, thanks!

[monfresh]

👍