Revert "Remove unicode character encoding from ActiveSupport::JSON.encode"

This reverts commit 815a9431ab61376a7e8e1bdff21f87bc557992f8.

Conflicts:
	activesupport/test/json/encoding_test.rb

Reason: This was causing a regression where the resulting string is always
returning UTF-8. Also it changes the behavior of this method on a stable release.

Fixes #9498.

1 files changed, 7 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/json/encoding.rb b/activesupport/lib/active_support/json/encoding.rb
index a50e6524c6..bd2f909ca9 100644
--- a/activesupport/lib/active_support/json/encoding.rb
+++ b/activesupport/lib/active_support/json/encoding.rb
@@ -122,7 +122,13 @@ module ActiveSupport
           if string.respond_to?(:force_encoding)
             string = string.encode(::Encoding::UTF_8, :undef => :replace).force_encoding(::Encoding::BINARY)
           end
-          json = string.gsub(escape_regex) { |s| ESCAPED_CHARS[s] }
+          json = string.
+            gsub(escape_regex) { |s| ESCAPED_CHARS[s] }.
+            gsub(/([\xC0-\xDF][\x80-\xBF]|
+                   [\xE0-\xEF][\x80-\xBF]{2}|
+                   [\xF0-\xF7][\x80-\xBF]{3})+/nx) { |s|
+            s.unpack("U*").pack("n*").unpack("H*")[0].gsub(/.{4}/n, '\\\\u\&')
+          }
           json = %("#{json}")
           json.force_encoding(::Encoding::UTF_8) if json.respond_to?(:force_encoding)
           json