Enable mapping to nil in enums

Enum in Rails 5 does not map nil values - IOW nil value remains nil,
even if there is a key with nil value in the enum definition.

This commit overrides the underlying Enum methods so nil value is
still mapped. This solution is far from being ideal: it uses dynamic
definition of methods which introduces more magic/confusion
into the codebase.

It would be better to get rid of the nil value in enums.

1 files changed, 33 insertions, 0 deletions

diff --git a/app/models/concerns/enum_with_nil.rb b/app/models/concerns/enum_with_nil.rb
new file mode 100644
index 00000000000..6b37903da20
--- /dev/null
+++ b/app/models/concerns/enum_with_nil.rb
@@ -0,0 +1,33 @@
+module EnumWithNil
+  extend ActiveSupport::Concern
+
+  included do
+    def self.enum_with_nil(definitions)
+      # use original `enum` to auto-define all methods
+      enum(definitions)
+
+      # override auto-defined methods only for the
+      # key which uses nil value
+      definitions.each do |name, values|
+        next unless key_with_nil = values.key(nil)
+
+        # E.g. for enum_with_nil failure_reason: { unknown_failure: nil }
+        # this overrides auto-generated method `unknown_failure?`
+        define_method("#{key_with_nil}?") do
+          Gitlab.rails5? ? self[name].nil? : super()
+        end
+
+        # E.g. for enum_with_nil failure_reason: { unknown_failure: nil }
+        # this overrides auto-generated method `failure_reason`
+        define_method(name) do
+          orig = super()
+
+          return orig unless Gitlab.rails5?
+          return orig unless orig.nil?
+
+          self.class.public_send(name.to_s.pluralize).key(nil) # rubocop:disable GitlabSecurity/PublicSend
+        end
+      end
+    end
+  end
+end