servo: Merge #19946 - Change Offset_to_text_point function and add unit tests (from paavininanda:Issue18613); r=jdm

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---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #18613.

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- [x] Added unit tests and web platform tests

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Source-Repo: https://github.com/servo/servo
Source-Revision: 36eb711d3b324de5437cc586bb6a8e09b2219108

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : d46bcef667987e9e24be95160713ec0c5ffe868b

servo/components/script/textinput.rs

@@ -871,13 +871,12 @@ impl<T: ClipboardProvider> TextInput<T> {
     fn offset_to_text_point(&self, abs_point: usize) -> TextPoint {
         let mut index = abs_point;
         let mut line = 0;
-
         let last_line_idx = self.lines.len() - 1;
         self.lines.iter().enumerate().fold(0, |acc, (i, val)| {
             if i != last_line_idx {
-                let line_end = max(val.len(), 1);
-                let new_acc = acc + line_end;
-                if abs_point > new_acc && index > line_end {
+                let line_end = val.len();
+                let new_acc = acc + line_end + 1;
+                if abs_point >= new_acc && index > line_end {
                     index -= line_end + 1;
                     line += 1;
                 }

servo/tests/unit/script/textinput.rs

@@ -600,6 +600,27 @@ fn test_textinput_set_selection_with_direction() {
     assert!(textinput.selection_origin.is_some());
     assert_eq!(textinput.selection_origin.unwrap().line, 0);
     assert_eq!(textinput.selection_origin.unwrap().index, 6);
+
+    textinput = text_input(Lines::Multiple, "\n\n");
+    textinput.set_selection_range(0, 1, SelectionDirection::Forward);
+    assert_eq!(textinput.edit_point.line, 1);
+    assert_eq!(textinput.edit_point.index, 0);
+    assert_eq!(textinput.selection_direction, SelectionDirection::Forward);
+
+    assert!(textinput.selection_origin.is_some());
+    assert_eq!(textinput.selection_origin.unwrap().line, 0);
+    assert_eq!(textinput.selection_origin.unwrap().index, 0);
+
+    textinput = text_input(Lines::Multiple, "\n");
+    textinput.set_selection_range(0, 1, SelectionDirection::Forward);
+    assert_eq!(textinput.edit_point.line, 1);
+    assert_eq!(textinput.edit_point.index, 0);
+    assert_eq!(textinput.selection_direction, SelectionDirection::Forward);
+
+    assert!(textinput.selection_origin.is_some());
+    assert_eq!(textinput.selection_origin.unwrap().line, 0);
+    assert_eq!(textinput.selection_origin.unwrap().index, 0);
+
 }
 
 #[test]
@@ -629,4 +650,11 @@ fn test_selection_bounds() {
     assert_eq!(TextPoint { line: 0, index: 6 }, textinput.selection_end());
     assert_eq!(3, textinput.selection_start_offset());
     assert_eq!(6, textinput.selection_end_offset());
+
+    textinput = text_input(Lines::Multiple, "\n\n");
+    textinput.set_selection_range(0, 1, SelectionDirection::Forward);
+    assert_eq!(TextPoint { line: 0, index: 0 }, textinput.selection_origin_or_edit_point());
+    assert_eq!(TextPoint { line: 0, index: 0 }, textinput.selection_start());
+    assert_eq!(TextPoint { line: 1, index: 0 }, textinput.selection_end());
+
 }