Return sized enumerator from Enumerable#index_by

activerecord/CHANGELOG.md

-<<<<<<< HEAD
-*   `find_in_batches`, `find_each` now
+*   `find_in_batches`, `find_each`, `Result#each` and `Enumerable#index_by` now
     return an `Enumerator` that can calculate its size.
-=======
-*   `find_in_batches`, `find_each`, `Result#each` now returns an `Enumerator`
-    that can calculate its size.
->>>>>>> 5863938... Return sized enumerator from Result#each
 
     See also #13938.
 

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -35,7 +35,7 @@ def index_by
     if block_given?
       Hash[map { |elem| [yield(elem), elem] }]
     else
-      to_enum(:index_by) { size }
+      to_enum(:index_by) { size if respond_to?(:size) }
     end
   end
 

activesupport/test/core_ext/enumerable_test.rb

@@ -73,6 +73,10 @@ def test_index_by
     assert_equal({ 5 => Payment.new(5), 15 => Payment.new(15), 10 => Payment.new(10) },
                  payments.index_by { |p| p.price })
     assert_equal Enumerator, payments.index_by.class
+    if Enumerator.method_defined? :size
+      assert_equal nil, payments.index_by.size
+      assert_equal 42, (1..42).index_by.size
+    end
     assert_equal({ 5 => Payment.new(5), 15 => Payment.new(15), 10 => Payment.new(10) },
                  payments.index_by.each { |p| p.price })
   end