How can a gem (unintentionally) change the migrations path?

Rails
1

I wrote a Gem (https://github.com/absolutedevops/civo) which is a simple
Rails Engine containing a few API accessing models.

However, when I include it in a Rails project, any generators create
their files under the Gem’s source code not the project’s. I can’t see
anything I’m doing in the Gem that would cause this. It’s repeatable
(it’s happening in two projects at my company and I can reproduce it
with a minimal set of steps below).

Can anyone tell me how I’ve managed this? I’ve been a Rails user for
many years but haven’t ever come across this before, nor has a skim
through the Rails code given me any indication of how I’d change the
migrations path if I wanted to!

Thanks,

Andy

Reproducible steps:

$ rails -v
Rails 4.2.6
$ rails new civo-test
[…]
Bundle complete! 12 Gemfile dependencies, 55 gems now installed.
Use bundle show [gemname] to see where a bundled gem is installed.
run bundle exec spring binstub --all

  • bin/rake: spring inserted
  • bin/rails: spring inserted
    $ cd civo-test
    $ echo ‘gem “civo”’ >> Gemfile
    $ bundle
    […]
    Bundle complete! 13 Gemfile dependencies, 66 gems now installed.
    Use bundle show [gemname] to see where a bundled gem is installed.
    $ rails g migration a_new_migration_here
    Running via Spring preloader in process 75091
    invoke active_record
    create db/migrate/20160411093346_a_new_migration_here.rb
    $ ls -l db/migrate/20160411093346_a_new_migration_here.rb
    ls: db/migrate/20160411093346_a_new_migration_here.rb: No such file or
    directory
    $ rails g migration a_new_migration_here
    Running via Spring preloader in process 75193
    invoke active_record
    identical db/migrate/20160411093346_a_new_migration_here.rb
    $ ls -l
    /Users/andy/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/civo-0.3.21/db/migrate/
    total 8
    -rw-r–r-- 1 andy staff 73 11 Apr 10:33
    20160411093346_a_new_migration_here.rb