Fixed index out of bounds for unicode code points

Author: Örjan Persson

diffmatchpatch/dmp.go

@@ -901,16 +901,15 @@ func (dmp *DiffMatchPatch) DiffCleanupSemanticLossless(diffs []Diff) []Diff {
 			return 6
 		}
 
-		_one := []rune(one)
-		_two := []rune(two)
-
 		// Each port of this function behaves slightly differently due to
 		// subtle differences in each language's definition of things like
 		// 'whitespace'.  Since this function's purpose is largely cosmetic,
 		// the choice has been made to use each language's native features
 		// rather than force total conformity.
-		char1 := string(_one[len(one)-1])
-		char2 := string(_two[0])
+		rune1, _ := utf8.DecodeLastRuneInString(one)
+		rune2, _ := utf8.DecodeRuneInString(two)
+		char1 := string(rune1)
+		char2 := string(rune2)
 
 		nonAlphaNumeric1 := nonAlphaNumericRegex_.MatchString(char1)
 		nonAlphaNumeric2 := nonAlphaNumericRegex_.MatchString(char2)

diffmatchpatch/dmp_test.go

@@ -437,6 +437,19 @@ func Test_diffCleanupSemanticLossless(t *testing.T) {
 		Diff{DiffEqual, "The xxx."},
 		Diff{DiffInsert, " The zzz."},
 		Diff{DiffEqual, " The yyy."}}, diffs)
+
+	// UTF-8 strings.
+	diffs = []Diff{
+		Diff{DiffEqual, "The ♕. The "},
+		Diff{DiffInsert, "♔. The "},
+		Diff{DiffEqual, "♖."}}
+
+	dmp.DiffCleanupSemanticLossless(diffs)
+
+	assertDiffEqual(t, []Diff{
+		Diff{DiffEqual, "The ♕."},
+		Diff{DiffInsert, " The ♔."},
+		Diff{DiffEqual, " The ♖."}}, diffs)
 }
 
 func Test_diffCleanupSemantic(t *testing.T) {