Fix missing active constant error

When we refer to a constant from initializers which is supposed to be
loaded by `ActiveSupport::Dependencies`, it's possible to get an error
in the development environment if Rails tries to load/reload a missing
constant under the namespace of that constant.

The reason is since the constant is loaded in initializers, it stays in
the memory and conflicts with the one reloaded by Rails.

This commit fixes only the `Gitlab::Metrics::Subscribers::ActiveRecord`
case which has been used in lograge configuration.

config/initializers/lograge.rb

 # Only use Lograge for Rails
 unless Gitlab::Runtime.sidekiq?
-  filename = File.join(Rails.root, 'log', "#{Rails.env}_json.log")
+  Rails.application.reloader.to_prepare do
+    filename = File.join(Rails.root, 'log', "#{Rails.env}_json.log")
+    db_counter = Gitlab::Metrics::Subscribers::ActiveRecord
 
-  Rails.application.configure do
-    config.lograge.enabled = true
-    # Store the lograge JSON files in a separate file
-    config.lograge.keep_original_rails_log = Gitlab::Utils.to_boolean(ENV.fetch('UNSTRUCTURED_RAILS_LOG', 'true'))
-    # Don't use the Logstash formatter since this requires logstash-event, an
-    # unmaintained gem that monkey patches `Time`
-    config.lograge.formatter = Lograge::Formatters::Json.new
-    config.lograge.logger = ActiveSupport::Logger.new(filename)
-    config.lograge.before_format = lambda do |data, payload|
-      data.delete(:error)
-      data[:db_duration_s] = Gitlab::Utils.ms_to_round_sec(data.delete(:db)) if data[:db]
-      data[:view_duration_s] = Gitlab::Utils.ms_to_round_sec(data.delete(:view)) if data[:view]
-      data[:duration_s] = Gitlab::Utils.ms_to_round_sec(data.delete(:duration)) if data[:duration]
-      data.merge!(::Gitlab::Metrics::Subscribers::ActiveRecord.db_counter_payload)
+    Rails.application.configure do
+      config.lograge.enabled = true
+      # Store the lograge JSON files in a separate file
+      config.lograge.keep_original_rails_log = Gitlab::Utils.to_boolean(ENV.fetch('UNSTRUCTURED_RAILS_LOG', 'true'))
+      # Don't use the Logstash formatter since this requires logstash-event, an
+      # unmaintained gem that monkey patches `Time`
+      config.lograge.formatter = Lograge::Formatters::Json.new
+      config.lograge.logger = ActiveSupport::Logger.new(filename)
+      config.lograge.before_format = lambda do |data, payload|
+        data.delete(:error)
+        data[:db_duration_s] = Gitlab::Utils.ms_to_round_sec(data.delete(:db)) if data[:db]
+        data[:view_duration_s] = Gitlab::Utils.ms_to_round_sec(data.delete(:view)) if data[:view]
+        data[:duration_s] = Gitlab::Utils.ms_to_round_sec(data.delete(:duration)) if data[:duration]
+        data.merge!(db_counter.db_counter_payload)
 
-      # Remove empty hashes to prevent type mismatches
-      # These are set to empty hashes in Lograge's ActionCable subscriber
-      # https://github.com/roidrage/lograge/blob/v0.11.2/lib/lograge/log_subscribers/action_cable.rb#L14-L16
-      %i(method path format).each do |key|
-        data[key] = nil if data[key] == {}
-      end
+        # Remove empty hashes to prevent type mismatches
+        # These are set to empty hashes in Lograge's ActionCable subscriber
+        # https://github.com/roidrage/lograge/blob/v0.11.2/lib/lograge/log_subscribers/action_cable.rb#L14-L16
+        %i(method path format).each do |key|
+          data[key] = nil if data[key] == {}
+        end
 
-      data
-    end
+        data
+      end
 
-    # This isn't a user-reachable controller; we use it to check for a
-    # valid CSRF token in the API
-    config.lograge.ignore_actions = ['Gitlab::RequestForgeryProtection::Controller#index']
+      # This isn't a user-reachable controller; we use it to check for a
+      # valid CSRF token in the API
+      config.lograge.ignore_actions = ['Gitlab::RequestForgeryProtection::Controller#index']
 
-    # Add request parameters to log output
-    config.lograge.custom_options = Gitlab::Lograge::CustomOptions
+      # Add request parameters to log output
+      config.lograge.custom_options = Gitlab::Lograge::CustomOptions
+    end
   end
 end