Draw insertion point even for empty input fields

This allows text layout to generate an empty text fragment if the fragment
contains the insertion point for a text input box.

components/layout/display_list_builder.rs

@@ -1014,13 +1014,9 @@ impl FragmentDisplayListBuilding for Fragment {
         // display list items.
         let mut clip = (*clip).clone();
         self.adjust_clip_for_style(&mut clip, &stacking_relative_border_box);
-        if !clip.might_intersect_rect(&stacking_relative_border_box) {
+        let empty_rect = !clip.might_intersect_rect(&stacking_relative_border_box);
-            return;
-        }
 
-        debug!("Fragment::build_display_list: intersected. Adding display item...");
+        if self.is_primary_fragment() && !empty_rect {
-
-        if self.is_primary_fragment() {
             // Add shadows, background, borders, and outlines, if applicable.
             if let Some(ref inline_context) = self.inline_context {
                 for node in inline_context.nodes.iter().rev() {
@@ -1080,14 +1076,23 @@ impl FragmentDisplayListBuilding for Fragment {
                                                                   &stacking_relative_border_box,
                                                                   &clip);
             }
+        }
 
-            // Paint the selection point if necessary.
+        if self.is_primary_fragment() {
+            // Paint the selection point if necessary.  Even an empty text fragment may have an
+            // insertion point, so we do this even if `empty_rect` is true.
             self.build_display_items_for_selection_if_necessary(state,
                                                                 &stacking_relative_border_box,
                                                                 display_list_section,
                                                                 &clip);
         }
 
+        if empty_rect {
+            return;
+        }
+
+        debug!("Fragment::build_display_list: intersected. Adding display item...");
+
         // Create special per-fragment-type display items.
         self.build_fragment_type_specific_display_items(state,
                                                         &stacking_relative_border_box,

components/layout/fragment.rs

@@ -1709,6 +1709,9 @@ impl Fragment {
                 if other_info.requires_line_break_afterward_if_wrapping_on_newlines() {
                     this_info.flags.insert(REQUIRES_LINE_BREAK_AFTERWARD_IF_WRAPPING_ON_NEWLINES);
                 }
+                if other_info.insertion_point.is_some() {
+                    this_info.insertion_point = other_info.insertion_point;
+                }
                 self.border_padding.inline_end = next_fragment.border_padding.inline_end;
             }
             _ => panic!("Can only merge two scanned-text fragments!"),

components/layout/text.rs

@@ -239,6 +239,7 @@ impl TextRunScanner {
                         mapping.flush(&mut mappings,
                                          &mut run_info,
                                          &**text,
+                                         insertion_point,
                                          compression,
                                          text_transform,
                                          &mut last_whitespace,
@@ -268,6 +269,7 @@ impl TextRunScanner {
                 mapping.flush(&mut mappings,
                               &mut run_info,
                               &**text,
+                              insertion_point,
                               compression,
                               text_transform,
                               &mut last_whitespace,
@@ -336,6 +338,7 @@ impl TextRunScanner {
                 let scanned_run = runs[mapping.text_run_index].clone();
 
                 let requires_line_break_afterward_if_wrapping_on_newlines =
+                    !mapping.byte_range.is_empty() &&
                     scanned_run.run.text.char_at_reverse(mapping.byte_range.end()) == '\n';
                 if requires_line_break_afterward_if_wrapping_on_newlines {
                     mapping.char_range.extend_by(CharIndex(-1));
@@ -575,12 +578,13 @@ impl RunMapping {
              mappings: &mut Vec<RunMapping>,
              run_info: &mut RunInfo,
              text: &str,
+             insertion_point: Option<CharIndex>,
              compression: CompressionMode,
              text_transform: text_transform::T,
              last_whitespace: &mut bool,
              start_position: &mut usize,
              end_position: usize) {
-        if *start_position == end_position {
+        if *start_position == end_position && insertion_point.is_none() {
             return;
         }
         let old_byte_length = run_info.text.len();
@@ -601,9 +605,9 @@ impl RunMapping {
         run_info.character_length = run_info.character_length + character_count;
         *start_position = end_position;
 
-        // Don't flush empty mappings.
+        // Don't flush mappings that contain no characters and no insertion_point.
-        if character_count == 0 {
+        if character_count == 0 && !self.contains_insertion_point(insertion_point) {
-            return
+            return;
         }
 
         let new_byte_length = run_info.text.len();

tests/wpt/mozilla/tests/css/focus_selector_ref.html

@@ -11,5 +11,8 @@
   <body>
     <input id="a">
     <input id="b">
+    <script>
+      document.getElementById("a").focus();
+    </script>
   </body>
 </html>