Updating documentation on FeatureFlag.accessible? (#15492)

* Updating documentation on FeatureFlag.accessible?

Related to clarifying behavior for #15475

* Update app/services/feature_flag.rb

Co-authored-by: Julianna Tetreault <32834804+juliannatetreault@users.noreply.github.com>

Co-authored-by: Julianna Tetreault <32834804+juliannatetreault@users.noreply.github.com>

app/services/feature_flag.rb

@@ -1,9 +1,31 @@
+# This module provides mechanisms for toggling on and off features.
+#
+# @note A wrapper around the Flipper gem
 module FeatureFlag
   class << self
     delegate :add, :disable, :enable, :enabled?, :exist?, :remove, to: Flipper
 
+    # Unless the given :feature_flag_name is _explicitly_ disabled,
+    # this method returns true.
+    #
+    # @param feature_flag_name [Symbol]
+    # @param args [Array] passed to FeatureFlag.enabled?
+    #
+    # @return [TrueClass] go ahead and use this feature
+    # @return [FalseClass] don't use this feature
+    #
+    # @note This is an optimistic test, namely if the given
+    #       :feature_flag_name does not exist (e.g., has never been
+    #       enabled, disabled, or has been removed), the feature is
+    #       accessible.
+    #
+    # @see https://github.com/forem/forem/pull/8149
+    #      for further discussion.
     def accessible?(feature_flag_name, *args)
-      feature_flag_name.blank? || !exist?(feature_flag_name) || enabled?(feature_flag_name, *args)
+      return true if feature_flag_name.blank?
+      return true unless exist?(feature_flag_name)
+
+      enabled?(feature_flag_name, *args)
     end
   end
 end