feat: add diff view component

crates/core/src/scroll_area.rs

@@ -1,3 +1,4 @@
+use std::sync::Arc;
 use std::time::Duration;
 use std::time::Instant;
 
@@ -54,9 +55,9 @@ struct AutohideState {
 }
 
 impl Autohide {
-    pub(crate) fn new(window: &mut Window, cx: &mut App) -> Self {
+    pub(crate) fn new(key: ElementId, window: &mut Window, cx: &mut App) -> Self {
         let view = window.current_view();
-        let state = window.use_keyed_state("scrollbar-autohide", cx, |_, _| AutohideState {
+        let state = window.use_keyed_state(key, cx, |_, _| AutohideState {
             last_activity: None,
             hide_task: None,
         });
@@ -195,6 +196,11 @@ impl ScrollArea {
     }
 }
 
+/// Names keyed state under the scrollbar's own id.
+pub fn scrollbar_state_key(name: &'static str, id: &ElementId) -> ElementId {
+    ElementId::NamedChild(Arc::new(id.clone()), SharedString::from(name))
+}
+
 /// Pure thumb geometry for an overlay scrollbar.
 pub(crate) fn thumb_geometry(
     viewport: Pixels,
@@ -247,11 +253,12 @@ impl RenderOnce for ScrollArea {
                 ScrollbarVisibility::Always => false,
                 ScrollbarVisibility::Autohide => true,
             };
+            let id = self.id.clone();
             wrapper.extend(std::iter::once(
                 canvas(|_, _, _| {}, {
                     let handle = handle.clone();
                     move |_, _, window, cx| {
-                        paint_scrollbar(&handle, autohide, window, cx);
+                        paint_scrollbar(&handle, &id, autohide, window, cx);
                     }
                 })
                 .absolute()
@@ -265,7 +272,13 @@ impl RenderOnce for ScrollArea {
 }
 
 /// Paints the overlay scrollbar thumb.
-fn paint_scrollbar(handle: &ScrollHandle, autohide: bool, window: &mut Window, cx: &mut App) {
+fn paint_scrollbar(
+    handle: &ScrollHandle,
+    key: &ElementId,
+    autohide: bool,
+    window: &mut Window,
+    cx: &mut App,
+) {
     let theme = cx.theme();
     let view = window.current_view();
 
@@ -281,8 +294,9 @@ fn paint_scrollbar(handle: &ScrollHandle, autohide: bool, window: &mut Window, c
         return;
     }
 
-    let autohide_state = autohide.then(|| Autohide::new(window, cx));
-    let drag = window.use_keyed_state("scrollbar-thumb-drag", cx, |_, _| {
+    let autohide_state =
+        autohide.then(|| Autohide::new(scrollbar_state_key("autohide", key), window, cx));
+    let drag = window.use_keyed_state(scrollbar_state_key("thumb-drag", key), cx, |_, _| {
         Option::<(Pixels, Pixels)>::None
     });
     let dragging = drag.read(cx).is_some();