AS::Concern is not really needed for AR::Explain

activerecord/lib/active_record/base.rb

@@ -699,7 +699,7 @@ module ActiveRecord #:nodoc:
     include Associations
     include IdentityMap
     include ActiveModel::SecurePassword
-    include Explain
+    extend Explain
 
     # AutosaveAssociation needs to be included before Transactions, because we want
     # #save_with_autosave_associations to be wrapped inside a transaction.

activerecord/lib/active_record/explain.rb

@@ -1,17 +1,16 @@
-require 'active_support/concern'
+require 'active_support/core_ext/class/attribute'
 
 module ActiveRecord
   module Explain
-    extend ActiveSupport::Concern
-
-    included do
+    def self.extended(base)
+      base.class_eval do
         # If a query takes longer than these many seconds we log its query plan
         # automatically. nil disables this feature.
         class_attribute :auto_explain_threshold_in_seconds, :instance_writer => false
         self.auto_explain_threshold_in_seconds = nil
       end
+    end
 
-    module ClassMethods
     # If auto explain is enabled, this method triggers EXPLAIN logging for the
     # queries triggered by the block if it takes more than the threshold as a
     # whole. That is, the threshold is not checked against each individual
@@ -82,4 +81,3 @@ module ActiveRecord
     end
   end
 end
-end

activerecord/lib/active_record/relation.rb

@@ -9,7 +9,7 @@ module ActiveRecord
     MULTI_VALUE_METHODS = [:select, :group, :order, :joins, :where, :having, :bind]
     SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :from, :reorder, :reverse_order, :uniq]
 
-    include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches, Explain::ClassMethods, Delegation
+    include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches, Explain, Delegation
 
     attr_reader :table, :klass, :loaded
     attr_accessor :extensions, :default_scoped