Multi-cursor removal possibility (#13431)

Release Notes:

- Added the ability to remove multi-cursors by clicking on them again.
([#13058](https://github.com/zed-industries/zed/issues/13058)).

crates/editor/src/editor.rs

@@ -2564,14 +2564,47 @@ impl Editor {
             }
         }
 
-        self.change_selections(auto_scroll.then(|| Autoscroll::newest()), cx, |s| {
-            if !add {
-                s.clear_disjoint();
-            } else if click_count > 1 {
-                s.delete(newest_selection.id)
-            }
+        let point_to_delete: Option<usize> = {
+            let selected_points: Vec<Selection<Point>> =
+                self.selections.disjoint_in_range(start..end, cx);
 
-            s.set_pending_anchor_range(start..end, mode);
+            if !add || click_count > 1 {
+                None
+            } else if selected_points.len() > 0 {
+                Some(selected_points[0].id)
+            } else {
+                let clicked_point_already_selected =
+                    self.selections.disjoint.iter().find(|selection| {
+                        selection.start.to_point(buffer) == start.to_point(buffer)
+                            || selection.end.to_point(buffer) == end.to_point(buffer)
+                    });
+
+                if let Some(selection) = clicked_point_already_selected {
+                    Some(selection.id)
+                } else {
+                    None
+                }
+            }
+        };
+
+        let selections_count = self.selections.count();
+
+        self.change_selections(auto_scroll.then(|| Autoscroll::newest()), cx, |s| {
+            if let Some(point_to_delete) = point_to_delete {
+                s.delete(point_to_delete);
+
+                if selections_count == 1 {
+                    s.set_pending_anchor_range(start..end, mode);
+                }
+            } else {
+                if !add {
+                    s.clear_disjoint();
+                } else if click_count > 1 {
+                    s.delete(newest_selection.id)
+                }
+
+                s.set_pending_anchor_range(start..end, mode);
+            }
         });
     }
 

crates/editor/src/editor_tests.rs

@@ -436,6 +436,57 @@ fn test_selection_with_mouse(cx: &mut TestAppContext) {
     );
 }
 
+#[gpui::test]
+fn test_multiple_cursor_removal(cx: &mut TestAppContext) {
+    init_test(cx, |_| {});
+
+    let editor = cx.add_window(|cx| {
+        let buffer = MultiBuffer::build_simple("aaaaaa\nbbbbbb\ncccccc\nddddddd\n", cx);
+        build_editor(buffer, cx)
+    });
+
+    _ = editor.update(cx, |view, cx| {
+        view.begin_selection(DisplayPoint::new(DisplayRow(2), 1), false, 1, cx);
+    });
+
+    _ = editor.update(cx, |view, cx| {
+        view.end_selection(cx);
+    });
+
+    _ = editor.update(cx, |view, cx| {
+        view.begin_selection(DisplayPoint::new(DisplayRow(3), 2), true, 1, cx);
+    });
+
+    _ = editor.update(cx, |view, cx| {
+        view.end_selection(cx);
+    });
+
+    assert_eq!(
+        editor
+            .update(cx, |view, cx| view.selections.display_ranges(cx))
+            .unwrap(),
+        [
+            DisplayPoint::new(DisplayRow(2), 1)..DisplayPoint::new(DisplayRow(2), 1),
+            DisplayPoint::new(DisplayRow(3), 2)..DisplayPoint::new(DisplayRow(3), 2)
+        ]
+    );
+
+    _ = editor.update(cx, |view, cx| {
+        view.begin_selection(DisplayPoint::new(DisplayRow(2), 1), true, 1, cx);
+    });
+
+    _ = editor.update(cx, |view, cx| {
+        view.end_selection(cx);
+    });
+
+    assert_eq!(
+        editor
+            .update(cx, |view, cx| view.selections.display_ranges(cx))
+            .unwrap(),
+        [DisplayPoint::new(DisplayRow(3), 2)..DisplayPoint::new(DisplayRow(3), 2)]
+    );
+}
+
 #[gpui::test]
 fn test_canceling_pending_selection(cx: &mut TestAppContext) {
     init_test(cx, |_| {});