Reduce number of snapshots and notifies during editor scrolling (#34228)

We not do not create new snapshots anymore when autoscrolling
horizontally and also do not notify any longer should the new scroll
position match the old one.

Release Notes:

- N/A

---------

Co-authored-by: Michael Sloan <mgsloan@gmail.com>

crates/editor/src/scroll.rs

@@ -27,6 +27,8 @@ use workspace::{ItemId, WorkspaceId};
 pub const SCROLL_EVENT_SEPARATION: Duration = Duration::from_millis(28);
 const SCROLLBAR_SHOW_INTERVAL: Duration = Duration::from_secs(1);
 
+pub struct WasScrolled(pub(crate) bool);
+
 #[derive(Default)]
 pub struct ScrollbarAutoHide(pub bool);
 
@@ -215,7 +217,7 @@ impl ScrollManager {
         workspace_id: Option<WorkspaceId>,
         window: &mut Window,
         cx: &mut Context<Editor>,
-    ) {
+    ) -> WasScrolled {
         let scroll_top = scroll_position.y.max(0.);
         let scroll_top = match EditorSettings::get_global(cx).scroll_beyond_last_line {
             ScrollBeyondLastLine::OnePage => scroll_top,
@@ -264,7 +266,7 @@ impl ScrollManager {
             workspace_id,
             window,
             cx,
-        );
+        )
     }
 
     fn set_anchor(
@@ -276,7 +278,7 @@ impl ScrollManager {
         workspace_id: Option<WorkspaceId>,
         window: &mut Window,
         cx: &mut Context<Editor>,
-    ) {
+    ) -> WasScrolled {
         let adjusted_anchor = if self.forbid_vertical_scroll {
             ScrollAnchor {
                 offset: gpui::Point::new(anchor.offset.x, self.anchor.offset.y),
@@ -286,10 +288,14 @@ impl ScrollManager {
             anchor
         };
 
+        self.autoscroll_request.take();
+        if self.anchor == adjusted_anchor {
+            return WasScrolled(false);
+        }
+
         self.anchor = adjusted_anchor;
         cx.emit(EditorEvent::ScrollPositionChanged { local, autoscroll });
         self.show_scrollbars(window, cx);
-        self.autoscroll_request.take();
         if let Some(workspace_id) = workspace_id {
             let item_id = cx.entity().entity_id().as_u64() as ItemId;
 
@@ -311,6 +317,8 @@ impl ScrollManager {
                 .detach()
         }
         cx.notify();
+
+        WasScrolled(true)
     }
 
     pub fn show_scrollbars(&mut self, window: &mut Window, cx: &mut Context<Editor>) {
@@ -521,13 +529,13 @@ impl Editor {
         scroll_position: gpui::Point<f32>,
         window: &mut Window,
         cx: &mut Context<Self>,
-    ) {
+    ) -> WasScrolled {
         let mut position = scroll_position;
         if self.scroll_manager.forbid_vertical_scroll {
             let current_position = self.scroll_position(cx);
             position.y = current_position.y;
         }
-        self.set_scroll_position_internal(position, true, false, window, cx);
+        self.set_scroll_position_internal(position, true, false, window, cx)
     }
 
     /// Scrolls so that `row` is at the top of the editor view.
@@ -559,7 +567,7 @@ impl Editor {
         autoscroll: bool,
         window: &mut Window,
         cx: &mut Context<Self>,
-    ) {
+    ) -> WasScrolled {
         let map = self.display_map.update(cx, |map, cx| map.snapshot(cx));
         self.set_scroll_position_taking_display_map(
             scroll_position,
@@ -568,7 +576,7 @@ impl Editor {
             map,
             window,
             cx,
-        );
+        )
     }
 
     fn set_scroll_position_taking_display_map(
@@ -579,7 +587,7 @@ impl Editor {
         display_map: DisplaySnapshot,
         window: &mut Window,
         cx: &mut Context<Self>,
-    ) {
+    ) -> WasScrolled {
         hide_hover(self, cx);
         let workspace_id = self.workspace.as_ref().and_then(|workspace| workspace.1);
 
@@ -593,7 +601,7 @@ impl Editor {
             scroll_position
         };
 
-        self.scroll_manager.set_scroll_position(
+        let editor_was_scrolled = self.scroll_manager.set_scroll_position(
             adjusted_position,
             &display_map,
             local,
@@ -605,6 +613,7 @@ impl Editor {
 
         self.refresh_inlay_hints(InlayHintRefreshReason::NewLinesShown, cx);
         self.refresh_colors(false, None, window, cx);
+        editor_was_scrolled
     }
 
     pub fn scroll_position(&self, cx: &mut Context<Self>) -> gpui::Point<f32> {