CircleCI shallow clone issue

[dankohn]

If you're getting an Object not found - no matching loose object error like the following on CircleCI or similar continuous integration servers, it may be caused by them running a shallow clone:

bundle exec pronto run -f github -c=$(git log --pretty=format:%H | tail -1) --exit-code
/home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/pronto-0.4.3/lib/pronto/git/repository.rb:68:in `merge_base': Object not found - no matching loose object (9035627bcab7e9bd64dd47c37b7fbfd67045a106) (Rugged::OdbError)
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/pronto-0.4.3/lib/pronto/git/repository.rb:68:in `merge_base'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/pronto-0.4.3/lib/pronto/git/repository.rb:15:in `diff'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/pronto-0.4.3/lib/pronto.rb:33:in `run'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/pronto-0.4.3/lib/pronto/cli.rb:52:in `run'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/thor-0.19.1/lib/thor/command.rb:27:in `run'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/thor-0.19.1/lib/thor/invocation.rb:126:in `invoke_command'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/thor-0.19.1/lib/thor.rb:359:in `dispatch'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/thor-0.19.1/lib/thor/base.rb:440:in `start'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/gems/pronto-0.4.3/bin/pronto:6:in `<top (required)>'
    from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/bin/pronto:23:in `load'

from /home/ubuntu/cii-best-practices-badge/vendor/bundle/ruby/2.2.0/bin/pronto:23:in `<main>' bundle exec pronto run -f github -c=$(git log --pretty=format:%H | tail -1) --exit-code returned exit code 1

The solution is do an unshallow git fetch before running pronto. For example, use the following syntax for circle.yml:

test:
  pre:
    - "[[ ! -s \"$(git rev-parse --git-dir)/shallow\" ]] || git fetch --unshallow"
  post:
    - bundle exec pronto run -f github -c=$(git log --pretty=format:%H | tail -1) --exit-code