Don't represent editor's scroll top anchor as an option

Use Anchor::min as the special value representing a scroll top of zero

crates/editor/src/editor.rs

@@ -438,7 +438,7 @@ pub struct Editor {
     select_larger_syntax_node_stack: Vec<Box<[Selection<usize>]>>,
     active_diagnostics: Option<ActiveDiagnosticGroup>,
     scroll_position: Vector2F,
-    scroll_top_anchor: Option<Anchor>,
+    scroll_top_anchor: Anchor,
     autoscroll_request: Option<Autoscroll>,
     soft_wrap_mode_override: Option<settings::SoftWrap>,
     get_field_editor_theme: Option<GetFieldEditorTheme>,
@@ -473,7 +473,7 @@ pub struct EditorSnapshot {
     pub placeholder_text: Option<Arc<str>>,
     is_focused: bool,
     scroll_position: Vector2F,
-    scroll_top_anchor: Option<Anchor>,
+    scroll_top_anchor: Anchor,
 }
 
 #[derive(Clone)]
@@ -915,7 +915,7 @@ impl Editor {
             get_field_editor_theme,
             project,
             scroll_position: Vector2F::zero(),
-            scroll_top_anchor: None,
+            scroll_top_anchor: Anchor::min(),
             autoscroll_request: None,
             focused: false,
             show_local_cursors: false,
@@ -1020,7 +1020,7 @@ impl Editor {
         let map = self.display_map.update(cx, |map, cx| map.snapshot(cx));
 
         if scroll_position.y() == 0. {
-            self.scroll_top_anchor = None;
+            self.scroll_top_anchor = Anchor::min();
             self.scroll_position = scroll_position;
         } else {
             let scroll_top_buffer_offset =
@@ -1032,19 +1032,14 @@ impl Editor {
                 scroll_position.x(),
                 scroll_position.y() - anchor.to_display_point(&map).row() as f32,
             );
-            self.scroll_top_anchor = Some(anchor);
+            self.scroll_top_anchor = anchor;
         }
 
         cx.emit(Event::ScrollPositionChanged { local: true });
         cx.notify();
     }
 
-    fn set_scroll_top_anchor(
-        &mut self,
-        anchor: Option<Anchor>,
-        local: bool,
-        cx: &mut ViewContext<Self>,
-    ) {
+    fn set_scroll_top_anchor(&mut self, anchor: Anchor, local: bool, cx: &mut ViewContext<Self>) {
         self.scroll_position = Vector2F::zero();
         self.scroll_top_anchor = anchor;
         cx.emit(Event::ScrollPositionChanged { local });
@@ -5636,10 +5631,10 @@ impl Deref for EditorSnapshot {
 fn compute_scroll_position(
     snapshot: &DisplaySnapshot,
     mut scroll_position: Vector2F,
-    scroll_top_anchor: &Option<Anchor>,
+    scroll_top_anchor: &Anchor,
 ) -> Vector2F {
-    if let Some(anchor) = scroll_top_anchor {
-        let scroll_top = anchor.to_display_point(snapshot).row() as f32;
+    if *scroll_top_anchor != Anchor::min() {
+        let scroll_top = scroll_top_anchor.to_display_point(snapshot).row() as f32;
         scroll_position.set_y(scroll_top + scroll_position.y());
     } else {
         scroll_position.set_y(0.);

crates/editor/src/items.rs

@@ -70,17 +70,15 @@ impl FollowableItem for Editor {
 
                 if let Some(anchor) = state.scroll_top {
                     editor.set_scroll_top_anchor(
-                        Some(Anchor {
+                        Anchor {
                             buffer_id: Some(state.buffer_id as usize),
                             excerpt_id: excerpt_id.clone(),
                             text_anchor: language::proto::deserialize_anchor(anchor)
                                 .ok_or_else(|| anyhow!("invalid scroll top"))?,
-                        }),
+                        },
                         false,
                         cx,
                     );
-                } else {
-                    editor.set_scroll_top_anchor(None, false, cx);
                 }
 
                 Ok::<_, anyhow::Error>(())
@@ -113,10 +111,9 @@ impl FollowableItem for Editor {
         let buffer_id = self.buffer.read(cx).as_singleton()?.read(cx).remote_id();
         Some(proto::view::Variant::Editor(proto::view::Editor {
             buffer_id,
-            scroll_top: self
-                .scroll_top_anchor
-                .as_ref()
-                .map(|anchor| language::proto::serialize_anchor(&anchor.text_anchor)),
+            scroll_top: Some(language::proto::serialize_anchor(
+                &self.scroll_top_anchor.text_anchor,
+            )),
             selections: self.selections.iter().map(serialize_selection).collect(),
         }))
     }
@@ -129,10 +126,9 @@ impl FollowableItem for Editor {
         match event {
             Event::ScrollPositionChanged { .. } | Event::SelectionsChanged { .. } => {
                 Some(update_view::Variant::Editor(update_view::Editor {
-                    scroll_top: self
-                        .scroll_top_anchor
-                        .as_ref()
-                        .map(|anchor| language::proto::serialize_anchor(&anchor.text_anchor)),
+                    scroll_top: Some(language::proto::serialize_anchor(
+                        &self.scroll_top_anchor.text_anchor,
+                    )),
                     selections: self.selections.iter().map(serialize_selection).collect(),
                 }))
             }
@@ -155,17 +151,15 @@ impl FollowableItem for Editor {
 
                 if let Some(anchor) = message.scroll_top {
                     self.set_scroll_top_anchor(
-                        Some(Anchor {
+                        Anchor {
                             buffer_id: Some(buffer_id),
                             excerpt_id: excerpt_id.clone(),
                             text_anchor: language::proto::deserialize_anchor(anchor)
                                 .ok_or_else(|| anyhow!("invalid scroll top"))?,
-                        }),
+                        },
                         false,
                         cx,
                     );
-                } else {
-                    self.set_scroll_top_anchor(None, false, cx);
                 }
 
                 let selections = message