editor: Highlight all matching occurrences of text in selection (#24835)

Closes #12635

- [x] Get it working
- [x] Disable for multi cursor
- [x] Disable for vim visual line selection
- [x] Add setting to disable it
- [x] Add scrollbar marker
- [x] Handle delete state capturing selection

Preview:

https://github.com/user-attachments/assets/a76cde64-4f6c-4575-91cc-3a03a954e7a9

Release Notes:

- Added support to highlight all matching occurrences of text within the
selection in editor.

---------

Co-authored-by: Agus Zubiaga <agus@zed.dev>
Co-authored-by: Danilo <danilo@zed.dev>

crates/editor/src/editor.rs

@@ -283,6 +283,7 @@ impl InlayId {
 enum DocumentHighlightRead {}
 enum DocumentHighlightWrite {}
 enum InputComposition {}
+enum SelectedTextHighlight {}
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum Navigated {
@@ -681,6 +682,7 @@ pub struct Editor {
     next_completion_id: CompletionId,
     available_code_actions: Option<(Location, Rc<[AvailableCodeAction]>)>,
     code_actions_task: Option<Task<Result<()>>>,
+    selection_highlight_task: Option<Task<()>>,
     document_highlights_task: Option<Task<()>>,
     linked_editing_range_task: Option<Task<Option<()>>>,
     linked_edit_ranges: linked_editing_ranges::LinkedEditingRanges,
@@ -1384,6 +1386,7 @@ impl Editor {
             code_action_providers,
             available_code_actions: Default::default(),
             code_actions_task: Default::default(),
+            selection_highlight_task: Default::default(),
             document_highlights_task: Default::default(),
             linked_editing_range_task: Default::default(),
             pending_rename: Default::default(),
@@ -2165,6 +2168,7 @@ impl Editor {
             }
             self.refresh_code_actions(window, cx);
             self.refresh_document_highlights(cx);
+            self.refresh_selected_text_highlights(window, cx);
             refresh_matching_bracket_highlights(self, window, cx);
             self.update_visible_inline_completion(window, cx);
             self.edit_prediction_requires_modifier_in_leading_space = true;
@@ -4722,6 +4726,93 @@ impl Editor {
         None
     }
 
+    pub fn refresh_selected_text_highlights(
+        &mut self,
+        window: &mut Window,
+        cx: &mut Context<Editor>,
+    ) {
+        self.selection_highlight_task.take();
+        if !EditorSettings::get_global(cx).selection_highlight {
+            self.clear_background_highlights::<SelectedTextHighlight>(cx);
+            return;
+        }
+        if self.selections.count() != 1 || self.selections.line_mode {
+            self.clear_background_highlights::<SelectedTextHighlight>(cx);
+            return;
+        }
+        let selection = self.selections.newest::<Point>(cx);
+        if selection.is_empty() || selection.start.row != selection.end.row {
+            self.clear_background_highlights::<SelectedTextHighlight>(cx);
+            return;
+        }
+        let debounce = EditorSettings::get_global(cx).selection_highlight_debounce;
+        self.selection_highlight_task = Some(cx.spawn_in(window, |editor, mut cx| async move {
+            cx.background_executor()
+                .timer(Duration::from_millis(debounce))
+                .await;
+            let Some(matches_task) = editor
+                .read_with(&mut cx, |editor, cx| {
+                    let buffer = editor.buffer().read(cx).snapshot(cx);
+                    cx.background_executor().spawn(async move {
+                        let mut ranges = Vec::new();
+                        let buffer_ranges =
+                            vec![buffer.anchor_before(0)..buffer.anchor_after(buffer.len())];
+                        let query = buffer.text_for_range(selection.range()).collect::<String>();
+                        for range in buffer_ranges {
+                            for (search_buffer, search_range, excerpt_id) in
+                                buffer.range_to_buffer_ranges(range)
+                            {
+                                ranges.extend(
+                                    project::search::SearchQuery::text(
+                                        query.clone(),
+                                        false,
+                                        false,
+                                        false,
+                                        Default::default(),
+                                        Default::default(),
+                                        None,
+                                    )
+                                    .unwrap()
+                                    .search(search_buffer, Some(search_range.clone()))
+                                    .await
+                                    .into_iter()
+                                    .map(|match_range| {
+                                        let start = search_buffer
+                                            .anchor_after(search_range.start + match_range.start);
+                                        let end = search_buffer
+                                            .anchor_before(search_range.start + match_range.end);
+                                        Anchor::range_in_buffer(
+                                            excerpt_id,
+                                            search_buffer.remote_id(),
+                                            start..end,
+                                        )
+                                    }),
+                                );
+                            }
+                        }
+                        ranges
+                    })
+                })
+                .log_err()
+            else {
+                return;
+            };
+            let matches = matches_task.await;
+            editor
+                .update_in(&mut cx, |editor, _, cx| {
+                    editor.clear_background_highlights::<SelectedTextHighlight>(cx);
+                    if !matches.is_empty() {
+                        editor.highlight_background::<SelectedTextHighlight>(
+                            &matches,
+                            |theme| theme.editor_document_highlight_bracket_background,
+                            cx,
+                        )
+                    }
+                })
+                .log_err();
+        }));
+    }
+
     pub fn refresh_inline_completion(
         &mut self,
         debounce: bool,