Fix AS::HWIA#select and #reject on Ruby 2.1.1+

In Ruby 2.1.1 and later select and reject return a new instance of
Hash rather than the subclass so we need to override them to return
an instance of the correct class.

activesupport/lib/active_support/hash_with_indifferent_access.rb

@@ -153,6 +153,20 @@ def stringify_keys; dup end
     def symbolize_keys; to_hash.symbolize_keys end
     def to_options!; self end
 
+    if RUBY_VERSION > '2.1.0'
+      # On Ruby 2.1.1 and later the behavior of .select and reject changed to
+      # return a new Hash instance so we need to override them to return an
+      # instance of the correct class.
+
+      def select(*args, &block)
+        dup.tap { |hash| hash.select!(*args, &block) }
+      end
+
+      def reject(*args, &block)
+        dup.tap { |hash| hash.reject!(*args, &block) }
+      end
+    end
+
     # Convert to a Hash with String keys.
     def to_hash
       Hash.new(default).merge!(self)

activesupport/test/core_ext/hash_ext_test.rb

@@ -259,6 +259,36 @@ def test_indifferent_deleting
     assert_equal hash.delete('a'), nil
   end
 
+  def test_indifferent_select
+    hash = ActiveSupport::HashWithIndifferentAccess.new(@strings).select { |k, v| v == 1 }
+
+    assert_equal({ "a" => 1 }, hash)
+    assert_instance_of ActiveSupport::HashWithIndifferentAccess, hash
+  end
+
+  def test_indifferent_select_bang
+    indifferent_strings = ActiveSupport::HashWithIndifferentAccess.new(@strings)
+    indifferent_strings.select! { |k, v| v == 1 }
+
+    assert_equal({ "a" => 1 }, indifferent_strings)
+    assert_instance_of ActiveSupport::HashWithIndifferentAccess, indifferent_strings
+  end
+
+  def test_indifferent_reject
+    hash = ActiveSupport::HashWithIndifferentAccess.new(@strings).reject { |k, v| v != 1 }
+
+    assert_equal({ "a" => 1 }, hash)
+    assert_instance_of ActiveSupport::HashWithIndifferentAccess, hash
+  end
+
+  def test_indifferent_reject_bang
+    indifferent_strings = ActiveSupport::HashWithIndifferentAccess.new(@strings)
+    indifferent_strings.reject! { |k, v| v != 1 }
+
+    assert_equal({ "a" => 1 }, indifferent_strings)
+    assert_instance_of ActiveSupport::HashWithIndifferentAccess, indifferent_strings
+  end
+
   def test_indifferent_to_hash
     # Should convert to a Hash with String keys.
     assert_equal @strings, @mixed.with_indifferent_access.to_hash