perf: speed up large markdown rendering

crates/editor/src/markdown.rs

@@ -7,7 +7,7 @@
 use gpui::prelude::FluentBuilder as _;
 use gpui::{
     AnyElement, App, Context, Div, ElementId, FontStyle, FontWeight, HighlightStyle,
-    InteractiveElement as _, InteractiveText, IntoElement, ListAlignment, ListState,
+    InteractiveElement as _, InteractiveText, IntoElement, ListAlignment, ListOffset, ListState,
     ParentElement as _, Pixels, Render, SharedString, StatefulInteractiveElement as _,
     StrikethroughStyle, Styled as _, StyledText, UnderlineStyle, Window, div, list, px, relative,
 };
@@ -190,7 +190,7 @@ impl MarkdownViewState {
             source,
             blocks,
             highlight_code: true,
-            handle: ListState::new(count, ListAlignment::Top, px(400.)).measure_all(),
+            handle: ListState::new(count, ListAlignment::Top, px(400.)),
             a11y_label: None,
         }
     }
@@ -207,7 +207,11 @@ impl MarkdownViewState {
     where
         S: Into<SharedString>,
     {
-        self.source = source.into();
+        let source = source.into();
+        if self.source == source {
+            return;
+        }
+        self.source = source;
         self.reparse();
         cx.notify();
     }
@@ -233,10 +237,13 @@ impl MarkdownViewState {
         self.highlight_code
     }
 
-    /// Scrolls `block` into view.
+    /// Scrolls `block` to the top of the view.
     pub fn scroll_to_block(&self, block: usize) {
-        self.handle
-            .scroll_to_reveal_item(block.min(self.blocks.len().saturating_sub(1)));
+        let item_ix = block.min(self.blocks.len().saturating_sub(1));
+        self.handle.scroll_to(ListOffset {
+            item_ix,
+            offset_in_item: px(0.),
+        });
     }
 
     /// Overrides the accessibility label of the view.