Return enumerator from each_pair and each_value

This matches Hash's behaviour for those methods.

actionpack/CHANGELOG.md

+*   Calling `each_pair` or `each_value` on an `ActionController::Parameters`
+    without passing a block now returns an enumerator.
+
+    *Eugene Kenny*
+
 *   `fixture_file_upload` now uses path relative to `file_fixture_path`
 
     Previously the path had to be relative to `fixture_path`.

actionpack/lib/action_controller/metal/strong_parameters.rb

@@ -360,6 +360,7 @@ def to_unsafe_h
     # Convert all hashes in values into parameters, then yield each pair in
     # the same way as <tt>Hash#each_pair</tt>.
     def each_pair(&block)
+      return to_enum(__callee__) unless block_given?
       @parameters.each_pair do |key, value|
         yield [key, convert_hashes_to_parameters(key, value)]
       end
@@ -369,6 +370,7 @@ def each_pair(&block)
     # Convert all hashes in values into parameters, then yield each value in
     # the same way as <tt>Hash#each_value</tt>.
     def each_value(&block)
+      return to_enum(:each_value) unless block_given?
       @parameters.each_pair do |key, value|
         yield convert_hashes_to_parameters(key, value)
       end

actionpack/test/controller/parameters/accessors_test.rb

@@ -58,6 +58,11 @@ class ParametersAccessorsTest < ActiveSupport::TestCase
     end
   end
 
+  test "each without a block returns an enumerator" do
+    assert_kind_of Enumerator, @params.each
+    assert_equal @params, @params.each.to_h
+  end
+
   test "each_pair carries permitted status" do
     @params.permit!
     @params.each_pair { |key, value| assert(value.permitted?) if key == "person" }
@@ -75,6 +80,11 @@ class ParametersAccessorsTest < ActiveSupport::TestCase
     end
   end
 
+  test "each_pair without a block returns an enumerator" do
+    assert_kind_of Enumerator, @params.each_pair
+    assert_equal @params, @params.each_pair.to_h
+  end
+
   test "each_value carries permitted status" do
     @params.permit!
     @params.each_value do |value|
@@ -88,6 +98,11 @@ class ParametersAccessorsTest < ActiveSupport::TestCase
     end
   end
 
+  test "each_value without a block returns an enumerator" do
+    assert_kind_of Enumerator, @params.each_value
+    assert_equal @params.values, @params.each_value.to_a
+  end
+
   test "each_key converts to hash for permitted" do
     @params.permit!
     @params.each_key { |key| assert_kind_of(String, key) if key == "person" }
@@ -97,6 +112,11 @@ class ParametersAccessorsTest < ActiveSupport::TestCase
     @params.each_key { |key| assert_kind_of(String, key) if key == "person" }
   end
 
+  test "each_key without a block returns an enumerator" do
+    assert_kind_of Enumerator, @params.each_key
+    assert_equal @params.keys, @params.each_key.to_a
+  end
+
   test "empty? returns true when params contains no key/value pairs" do
     params = ActionController::Parameters.new
     assert_empty params