Cryptic Error with Fastlane build of MacOS project on CircleCI

Question

I am experiencing the below error when building a MacOS project using FastLane on circleCI. I am able to build the project locally using bundle exec fastlane test, so the problem would seem to be related to the CircleCI environment, but am at a loss as to how to track it down. I am able to reproduce it on the command line when I ssh into CircleCI.

Here is the error:

bundler: failed to load command: fastlane (/usr/local/bin/fastlane)
NoMethodError: [!] undefined method `each' for nil:NilClass
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/scan/lib/scan/runner.rb:172:in `copy_simulator_logs'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/scan/lib/scan/runner.rb:108:in `handle_results'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/scan/lib/scan/runner.rb:22:in `run'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/scan/lib/scan/manager.rb:23:in `work'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/actions/run_tests.rb:16:in `run'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/runner.rb:261:in `block (2 levels) in execute_action'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/actions/actions_helper.rb:50:in `execute_action'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/runner.rb:253:in `block in execute_action'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/runner.rb:227:in `chdir'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/runner.rb:227:in `execute_action'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/runner.rb:157:in `trigger_action_by_name'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/fast_file.rb:159:in `method_missing'
  Fastfile:26:in `block (2 levels) in parsing_binding'
  /Library/Ruby/Gems/2.6.0/gems/fastlane-2.149.1/fastlane/lib/fastlane/lane.rb:33:in `call'
            ----snip----

My Fastfile looks like this:

default_platform :mac

platform :mac do
  before_all do
    setup_circle_ci
  end

  desc "Runs all the tests"
  lane :test do
    scan(skip_testing: "ChronosUITests")
  end

  desc "Ad-hoc build"
  lane :adhoc do
    match(type: "adhoc")
    gym(export_method: "ad-hoc")
  end
end

and my circleci config is this:

# .circleci/config.yml
version: 2.1
jobs:
  build-and-test:
    macos:
      xcode: 11.5.0
    environment:
      FL_OUTPUT_DIR: output
      FASTLANE_LANE: test
    steps:
      - checkout
      # https://support.circleci.com/hc/en-us/articles/360044709573-Swift-Package-Manager-fails-to-clone-from-private-Git-repositories
      - run: rm ~/.ssh/id_rsa
      - run: for ip in $(dig @8.8.8.8 bitbucket.org +short); do ssh-keyscan bitbucket.org,$ip; ssh-keyscan $ip; done 2>/dev/null >> ~/.ssh/known_hosts || true
      - run: for ip in $(dig @8.8.8.8 github.com +short); do ssh-keyscan github.com,$ip; ssh-keyscan $ip; done 2>/dev/null >> ~/.ssh/known_hosts || true
      # -------
      - run: bundle install
      - run:
          name: Fastlane
          command: bundle exec fastlane $FASTLANE_LANE
      - store_artifacts:
          path: output
      - store_test_results:
          path: output/scan

  adhoc:
    macos:
      xcode: 11.5.0
    environment:
      FL_OUTPUT_DIR: output
      FASTLANE_LANE: adhoc
    steps:
      - checkout
      # https://support.circleci.com/hc/en-us/articles/360044709573-Swift-Package-Manager-fails-to-clone-from-private-Git-repositories
      - run: rm ~/.ssh/id_rsa
      - run: for ip in $(dig @8.8.8.8 bitbucket.org +short); do ssh-keyscan bitbucket.org,$ip; ssh-keyscan $ip; done 2>/dev/null >> ~/.ssh/known_hosts || true
      - run: for ip in $(dig @8.8.8.8 github.com +short); do ssh-keyscan github.com,$ip; ssh-keyscan $ip; done 2>/dev/null >> ~/.ssh/known_hosts || true
      # -----
      - run: bundle install
      - run:
          name: Fastlane
          command: bundle exec fastlane $FASTLANE_LANE
      - store_artifacts:
          path: output

workflows:
  build-test-adhoc:
    jobs:
      - build-and-test
      - adhoc:
          filters:
            branches:
              only: development
          requires:
            - build-and-test

Answer 1

I discovered a solution, or at lease a workaround. The failing step is copying simulator logs (does this even apply to a mac project?). In any case, adding the option to not include simulator logs fixed the issue.

scan(include_simulator_logs: false)