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Gemfile guidelines

When adding a new entry to Gemfile or upgrading an existing dependency pay attention to the following rules.

No gems fetched from Git repositories

We do not allow gems that are fetched from Git repositories. All gems have to be available in the RubyGems index. We want to minimize external build dependencies and build times.

License compliance

Refer to licensing guidelines for ensuring license compliance.

GitLab-created gems

Sometimes we create libraries within our codebase that we want to extract, either because we want to use them in other applications ourselves, or because we think it would benefit the wider community. Extracting code to a gem also means that we can be sure that the gem does not contain any hidden dependencies on our application code.

In general, we want to think carefully before doing this as there are also disadvantages:

  1. Gems - even those maintained by GitLab - do not necessarily go through the same code review process as the main Rails application.
  2. Extracting the code into a separate project means that we need a minimum of two merge requests to change functionality: one in the gem to make the functional change, and one in the Rails app to bump the version.
  3. Our needs for our own usage of the gem may not align with the wider community's needs. In general, if we are not using the latest version of our own gem, that might be a warning sign.

In the case where we do want to extract some library code we've written to a gem, go through these steps:

  1. Start with the code in the Rails application. Here it's fine to have the code in lib/ and loaded automatically. We can skip this step if the step below makes more sense initially.
  2. Before extracting to its own project, move the gem to vendor/gems and load it in the Gemfile using the path option. This gives us a gem that can be published to RubyGems.org, with its own test suite and isolated set of dependencies, that is still in our main code tree and goes through the standard code review process.
  3. Once the gem is stable - we have been using it in production for a while with few, if any, changes - extract to its own project under the gitlab-org namespace. 1. When creating the project, follow the instructions for new projects. 1. Follow the instructions for setting up a CI/CD configuration. 1. Follow the instructions for publishing a project.

    • See issue #325463 for an example.

    • In some cases we may want to move a gem to its own namespace. Some examples might be that it will naturally have more than one project (say, something that has plugins as separate libraries), or that we expect non-GitLab-team-members to be maintainers on this project as well as GitLab team members.

      The latter situation (maintainers from outside GitLab) could also apply if someone who currently works at GitLab wants to maintain the gem beyond their time working at GitLab.

When publishing a gem to RubyGems.org, also note the section on gem owners in the handbook.

Upgrade Rails

When upgrading the Rails gem and its dependencies, you also should update the following:

You should also update npm packages that follow the current version of Rails:

  • @rails/ujs
  • @rails/actioncable

Upgrading dependencies because of vulnerabilities

When upgrading dependencies because of a vulnerability, we should pin the minimal version of the gem in which the vulnerability was fixed in our Gemfile to avoid accidentally downgrading.

For example, consider that the gem license_finder has thor as its dependency. thor was found vulnerable until its version 1.1.1, which includes the vulnerability fix.

In the Gemfile, make sure to pin thor to 1.1.1. The direct dependency license_finder should already have the version specified.

gem 'license_finder', '~> 6.0'
# Dependency of license_finder with fix for vulnerability
# _link to initial security issue that will become public in time_
gem 'thor', '>= 1.1.1'

Here we're using the operator >= (greater than or equal to) rather than ~> (pessimistic operator) making it possible to upgrade license_finder or any other gem to a version that depends on thor 1.2.

Similarly, if license_finder had a vulnerability fixed in 6.0.1, we should add:

gem 'license_finder', '~> 6.0', '>= 6.0.1'

This way, other dependencies rather than license_finder can still depend on a newer version of thor, such as 6.0.2, but would not be able to depend on the vulnerable version 6.0.0.

A downgrade like that could happen if we introduced a new dependency that also relied on thor but had its version pinned to a vulnerable one. These changes are easy to miss in the Gemfile.lock. Pinning the version would result in a conflict that would need to be solved.

To avoid upgrading indirect dependencies, we can use bundle update --conservative.

When submitting a merge request including a dependency update, include a link to the Gem diff between the 2 versions in the merge request description. You can find this link on rubygems.org under Review Changes. When you click it, RubyGems generates a comparison between the versions on diffend.io. For example, this is the gem diff for thor 1.0.0 vs 1.0.1. Use the links directly generated from RubyGems, since the links from GitLab or other code-hosting platforms might not reflect the code that's actually published.