Include `Enumerable` in `ActiveRecord::Relation`

After discussing, we've decided it makes more sense to include it. We're
already forwarding every conflicting method to `to_a`, and there's no
conflation of concerns. `Enumerable` has no mutating methods, and it
just allows us to simplify the code. No existing methods will have a
change in behavior. Un-overridden Enumerable methods will simply
delegate to `each`.

[Sean Griffin & bogdan]

activerecord/CHANGELOG.md

+*   Include the `Enumerable` module in `ActiveRecord::Relation`
+
+    *Sean Griffin & bogdan*
+
 *   Use `Enumerable#sum` in `ActiveRecord::Relation` if a block is given.
 
     *Sean Griffin*

activerecord/lib/active_record/relation.rb

@@ -15,6 +15,7 @@ class Relation
 
     VALUE_METHODS = MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS + CLAUSE_METHODS
 
+    include Enumerable
     include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches, Explain, Delegation
 
     attr_reader :table, :klass, :loaded, :predicate_builder
@@ -275,38 +276,26 @@ def empty?
 
     # Returns true if there are no records.
     def none?
-      if block_given?
-        to_a.none? { |*block_args| yield(*block_args) }
-      else
-        empty?
-      end
+      return super if block_given?
+      empty?
     end
 
     # Returns true if there are any records.
     def any?
-      if block_given?
-        to_a.any? { |*block_args| yield(*block_args) }
-      else
-        !empty?
-      end
+      return super if block_given?
+      !empty?
     end
 
     # Returns true if there is exactly one record.
     def one?
-      if block_given?
-        to_a.one? { |*block_args| yield(*block_args) }
-      else
-        limit_value ? to_a.one? : size == 1
-      end
+      return super if block_given?
+      limit_value ? to_a.one? : size == 1
     end
 
     # Returns true if there is more than one record.
     def many?
-      if block_given?
-        to_a.many? { |*block_args| yield(*block_args) }
-      else
-        limit_value ? to_a.many? : size > 1
-      end
+      return super if block_given?
+      limit_value ? to_a.many? : size > 1
     end
 
     # Scope all queries to the current scope.

activerecord/lib/active_record/relation/calculations.rb

@@ -70,12 +70,9 @@ def maximum(column_name)
     # +calculate+ for examples with options.
     #
     #   Person.sum(:age) # => 4562
-    def sum(*args, &block)
-      if block_given?
-        to_a.sum(&block)
-      else
-        calculate(:sum, *args)
-      end
+    def sum(*args)
+      return super if block_given?
+      calculate(:sum, *args)
     end
 
     # This calculates aggregate values in the given column. Methods for count, sum, average,

activerecord/lib/active_record/relation/finder_methods.rb

@@ -62,11 +62,8 @@ module FinderMethods
     #   Person.where(name: 'Spartacus', rating: 4).pluck(:field1, :field2)
     #   # returns an Array of the required fields.
     def find(*args)
-      if block_given?
-        to_a.find(*args) { |*block_args| yield(*block_args) }
-      else
-        find_with_ids(*args)
-      end
+      return super if block_given?
+      find_with_ids(*args)
     end
 
     # Finds the first record matching the specified conditions. There

activerecord/lib/active_record/relation/query_methods.rb

@@ -242,12 +242,9 @@ def references!(*table_names) # :nodoc:
     #   Model.select(:field).first.other_field
     #   # => ActiveModel::MissingAttributeError: missing attribute: other_field
     def select(*fields)
-      if block_given?
-        to_a.select { |*block_args| yield(*block_args) }
-      else
-        raise ArgumentError, 'Call this with at least one field' if fields.empty?
-        spawn._select!(*fields)
-      end
+      return super if block_given?
+      raise ArgumentError, 'Call this with at least one field' if fields.empty?
+      spawn._select!(*fields)
     end
 
     def _select!(*fields) # :nodoc: