Use correct byte indices in replace_selection

components/script/textinput.rs

@@ -107,6 +107,16 @@ fn is_printable_key(key: Key) -> bool {
     }
 }
 
+/// The length in bytes of the first n characters in a UTF-8 string.
+///
+/// If the string has fewer than n characters, returns the length of the whole string.
+fn len_of_first_n_chars(text: &str, n: usize) -> usize {
+    match text.char_indices().take(n).last() {
+        Some((index, ch)) => index + ch.len_utf8(),
+        None => 0
+    }
+}
+
 impl<T: ClipboardProvider> TextInput<T> {
     /// Instantiate a new text input control
     pub fn new(lines: Lines, initial: DOMString, clipboard_provider: T, max_length: Option<usize>) -> TextInput<T> {
@@ -213,8 +223,8 @@ impl<T: ClipboardProvider> TextInput<T> {
                 usize::MAX
             };
 
-            let last_char_to_insert = min(allowed_to_insert_count, insert.chars().count());
+            let last_char_index = len_of_first_n_chars(&*insert, allowed_to_insert_count);
-            let chars_to_insert = (&insert[0 .. last_char_to_insert]).to_owned();
+            let chars_to_insert = &insert[..last_char_index];
 
             self.clear_selection();
 
@@ -225,7 +235,7 @@ impl<T: ClipboardProvider> TextInput<T> {
                 let lines_suffix = &self.lines[end.line + 1..];
 
                 let mut insert_lines = if self.multiline {
-                    chars_to_insert.split('\n').map(|s| DOMString::from(s.to_owned())).collect()
+                    chars_to_insert.split('\n').map(|s| DOMString::from(s)).collect()
                 } else {
                     vec!(DOMString::from(chars_to_insert))
                 };

tests/unit/script/textinput.rs

@@ -206,6 +206,15 @@ fn test_textinput_replace_selection() {
     assert_eq!(textinput.get_content(), "abxyzefg");
 }
 
+#[test]
+fn test_textinput_replace_selection_multibyte_char() {
+    let mut textinput = text_input(Lines::Single, "é");
+    textinput.adjust_horizontal_by_one(Direction::Forward, Selection::Selected);
+
+    textinput.replace_selection(DOMString::from("e"));
+    assert_eq!(textinput.get_content(), "e");
+}
+
 #[test]
 fn test_textinput_current_line_length() {
     let mut textinput = text_input(Lines::Multiple, "abc\nde\nf");