Correctly handle offsets in Multibyte::Chars#index and #rindex.

The offset in codepoints was being passed directly to the wrapped string's index/rindex method. Now we translate the offset into bytes first.

[#3028 state:committed]

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

activesupport/lib/active_support/multibyte/chars.rb

@@ -206,7 +206,8 @@ def include?(other)
       #   'Café périferôl'.mb_chars.index('ô') #=> 12
       #   'Café périferôl'.mb_chars.index(/\w/u) #=> 0
       def index(needle, offset=0)
-        index = @wrapped_string.index(needle, offset)
+        wrapped_offset = self.first(offset).wrapped_string.length
+        index = @wrapped_string.index(needle, wrapped_offset)
         index ? (self.class.u_unpack(@wrapped_string.slice(0...index)).size) : nil
       end
 
@@ -215,11 +216,12 @@ def index(needle, offset=0)
       # string. Returns +nil+ if _needle_ isn't found.
       #
       # Example:
-      #   'Café périferôl'.mb_chars.rindex('é') #=> 5
+      #   'Café périferôl'.mb_chars.rindex('é') #=> 6
       #   'Café périferôl'.mb_chars.rindex(/\w/u) #=> 13
       def rindex(needle, offset=nil)
         offset ||= length
-        index = @wrapped_string.rindex(needle, offset)
+        wrapped_offset = self.first(offset).wrapped_string.length
+        index = @wrapped_string.rindex(needle, wrapped_offset)
         index ? (self.class.u_unpack(@wrapped_string.slice(0...index)).size) : nil
       end
 

activesupport/test/multibyte_chars_test.rb

@@ -230,14 +230,19 @@ def test_index_should_return_character_offset
     assert_nil @chars.index('u')
     assert_equal 0, @chars.index('こに')
     assert_equal 2, @chars.index('ち')
+    assert_equal 2, @chars.index('ち', -2)
+    assert_equal nil, @chars.index('ち', -1)
     assert_equal 3, @chars.index('わ')
+    assert_equal 5, 'ééxééx'.mb_chars.index('x', 4)
   end
 
   def test_rindex_should_return_character_offset
     assert_nil @chars.rindex('u')
     assert_equal 1, @chars.rindex('に')
+    assert_equal 2, @chars.rindex('ち', -2)
+    assert_nil @chars.rindex('ち', -3)
     assert_equal 6, 'Café périferôl'.mb_chars.rindex('é')
-    assert_equal 12, 'Café périferôl'.mb_chars.rindex(/\w/u)
+    assert_equal 13, 'Café périferôl'.mb_chars.rindex(/\w/u)
   end
 
   def test_indexed_insert_should_take_character_offsets