Modified AppSignal deploy task to make it work with Capistrano 3.

appsignal-capistrano-3.rake

namespace :appsignal do
  # Description is required for it to show up in the tasks list.
  desc 'Notify AppSignal of this deploy!'
  task :deploy do
    # 1. Needs to be run inside an `on` block
    # 2. `appsignal_roles` setting set and supplied with default
    on roles(fetch(:appsignal_roles, :app)) do
      env = fetch(:rails_env, 'production')
      user = ENV['USER'] || ENV['USERNAME']

      appsignal_config = Appsignal::Config.new(
        ENV['PWD'],
        env,
        fetch(:appsignal_config, {}),
        self
      )

      if appsignal_config && appsignal_config.active?
        # `current_revision` method has been removed.
        # When run from `deploy` the `current_revision` setting should be
        # set (see:
        # https://github.com/capistrano/capistrano/blob/3d641ea994627a22edd01529440b12a9e565001d/lib/capistrano/tasks/git.rake#L52
        # https://github.com/capistrano/capistrano/blob/5986983915163e6681f2546bf6fad599d58cd024/lib/capistrano/dsl.rb#L32
        # ), otherwise (when run with `cap appsignal:deploy`) check again with
        # `fetch_revision`.
        marker_data = {
          revision: fetch(:current_revision) || fetch_revision,
          repository: fetch(:repo_url),
          user: user
        }

        marker = Appsignal::Marker.new(marker_data, appsignal_config, self)
        # Dry run conditional removed, now Capistrano does this on a higher level.
        marker.transmit
      end
    end
  end
end

after 'deploy', 'appsignal:deploy'