support :unless_exist for FileCache

activesupport/CHANGELOG.md

+*   Support :unless_exist in FileStore
+
+    *Michael Grosser*
+
 *   Ensure that autoloaded constants in all-caps nestings are marked as
     autoloaded.
 

activesupport/lib/active_support/cache/file_store.rb

@@ -96,6 +96,7 @@ def read_entry(key, options)
 
         def write_entry(key, entry, options)
           file_name = key_file_path(key)
+          return false if options[:unless_exist] && File.exist?(file_name)
           ensure_cache_path(File.dirname(file_name))
           File.atomic_write(file_name, cache_path) {|f| Marshal.dump(entry, f)}
           true

activesupport/test/caching_test.rb

@@ -709,6 +709,13 @@ def test_log_exception_when_cache_read_fails
     @cache.send(:read_entry, "winston", {})
     assert @buffer.string.present?
   end
+
+  def test_write_with_unless_exist
+    assert_equal true, @cache.write(1, "aaaaaaaaaa")
+    assert_equal false, @cache.write(1, "aaaaaaaaaa", unless_exist: true)
+    @cache.write(1, nil)
+    assert_equal false, @cache.write(1, "aaaaaaaaaa", unless_exist: true)
+  end
 end
 
 class MemoryStoreTest < ActiveSupport::TestCase