Refactor how a few ActiveRecord enums are definedrefactor-enums-for-ee

In a few models we define ActiveRecord enums that are redefined in EE
using the following pattern:

    enum :some_enum, {
      ...
    }.merge(EE_ENUM_VALUES)

This particular approach is problematic to deal with, because it
requires that we `prepend` and EE module _before_ defining the enum.
This typically translates to the `prepend` being the first line in the
model in EE, but this can easily lead to merge conflicts when developers
add more `include` and/or `prepend` lines.

As part of https://gitlab.com/gitlab-org/gitlab-ee/issues/8244 and
https://gitlab.com/gitlab-org/gitlab-ee/issues/8241 we are moving
`prepend` to the last line in a file, reducing the chances of running
into merge conflicts. This poses a bit of a problem with the pattern
above, because this pattern does not allow us to move the `prepend`
further down a file.

To resolve this problem, we simply move the Hash value of the enum to a
separate class method. This method is defined in a separate module where
necessary, allowing us to use it like so:

    enum :failure_reasons, ::SomeModelEnums.failure_reasons

The method in turn is defined in a very straightforward manner:

    module SomeModelEnums
      def self.failure_reasons
        {
          ...
        }
      end
    end

This makes it easy for EE to add values without requiring the `prepend`
to be placed before the `enum` is defined.

For more information, see the following issues and merge requests:

* https://gitlab.com/gitlab-org/gitlab-ee/issues/8244
* https://gitlab.com/gitlab-org/gitlab-ee/issues/8241
* https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8424

1 files changed, 16 insertions, 0 deletions

diff --git a/app/models/user_callout_enums.rb b/app/models/user_callout_enums.rb
new file mode 100644
index 00000000000..b9373ae6166
--- /dev/null
+++ b/app/models/user_callout_enums.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module UserCalloutEnums
+  # Returns the `Hash` to use for the `feature_name` enum in the `UserCallout`
+  # model.
+  #
+  # This method is separate from the `UserCallout` model so that it can be
+  # extended by EE.
+  def self.feature_names
+    {
+      gke_cluster_integration: 1,
+      gcp_signup_offer: 2,
+      cluster_security_warning: 3
+    }
+  end
+end