Ensure Array#to_sentence does not modify given hash

Also simplify I18n logic for Array#to_sentence, doing only one lookup
for all keys and using merge!, instead of one lookup for each option key.

2 files changed, 11 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/array_ext_test.rb b/activesupport/test/core_ext/array_ext_test.rb
index 58835c0ac5..9dfa2cbf11 100644
--- a/activesupport/test/core_ext/array_ext_test.rb
+++ b/activesupport/test/core_ext/array_ext_test.rb
@@ -90,6 +90,12 @@ class ArrayExtToSentenceTests < ActiveSupport::TestCase
   def test_one_non_string_element
     assert_equal '1', [1].to_sentence
   end
+
+  def test_does_not_modify_given_hash
+    options = { words_connector: ' ' }
+    assert_equal "one two, and three", ['one', 'two', 'three'].to_sentence(options)
+    assert_equal({ words_connector: ' ' }, options)
+  end
 end
 
 class ArrayExtToSTests < ActiveSupport::TestCase
diff --git a/activesupport/test/i18n_test.rb b/activesupport/test/i18n_test.rb
index 4f2027f4eb..ddbba444cf 100644
--- a/activesupport/test/i18n_test.rb
+++ b/activesupport/test/i18n_test.rb
@@ -97,4 +97,9 @@ class I18nTest < ActiveSupport::TestCase
     I18n.backend.store_translations 'en', :support => { :array => { :two_words_connector => default_two_words_connector } }
     I18n.backend.store_translations 'en', :support => { :array => { :last_word_connector => default_last_word_connector } }
   end
+
+  def test_to_sentence_with_empty_i18n_store
+    I18n.backend.store_translations 'empty', {}
+    assert_equal 'a, b, and c', %w[a b c].to_sentence(locale: 'empty')
+  end
 end