feat(trace): fix scrollbar offset bug rendering indicator in the wrong position (#67803)

Workaround the scrollbar width causing the indicator to be rendered in
the wrong position. We now force the scrollbar whenever we know the
content will scroll and disable it when it doesnt. This adds a bit of
layout thrashing, though we optimize it to only be done when the bit is
actually flipped as opposed to on each resize event

Author: JonasBa

static/app/views/performance/newTraceDetails/virtualizedViewManager.tsx

@@ -378,6 +378,15 @@ export class VirtualizedViewManager {
     this.previousDividerClientVec = [event.clientX, event.clientY];
   }
 
+  private scrollbar_width: number = 0;
+  onScrollbarWidthChange(width: number) {
+    if (width === this.scrollbar_width) {
+      return;
+    }
+    this.scrollbar_width = width;
+    this.draw();
+  }
+
   registerList(list: VirtualizedList | null) {
     this.list = list;
   }
@@ -1226,7 +1235,9 @@ export class VirtualizedViewManager {
 
     if (this.divider) {
       this.divider.style.transform = `translateX(${
-        list_width * this.container_physical_space.width - DIVIDER_WIDTH / 2 - 1
+        list_width * (this.container_physical_space.width - this.scrollbar_width) -
+        DIVIDER_WIDTH / 2 -
+        1
       }px)`;
     }
     if (this.indicator_container) {
@@ -1614,12 +1625,30 @@ export class VirtualizedList {
   }
 }
 
+function maybeToggleScrollbar(
+  container: HTMLElement,
+  containerHeight: number,
+  scrollHeight: number,
+  manager: VirtualizedViewManager
+) {
+  if (scrollHeight > containerHeight) {
+    container.style.overflowY = 'scroll';
+    container.style.scrollbarGutter = 'stable';
+    manager.onScrollbarWidthChange(container.offsetWidth - container.clientWidth);
+  } else {
+    container.style.overflowY = 'auto';
+    container.style.scrollbarGutter = 'auto';
+    manager.onScrollbarWidthChange(0);
+  }
+}
+
 interface UseVirtualizedListProps {
   container: HTMLElement | null;
   items: ReadonlyArray<TraceTreeNode<TraceTree.NodeValue>>;
   manager: VirtualizedViewManager;
   render: (item: VirtualizedRow) => React.ReactNode;
 }
+
 interface UseVirtualizedListResult {
   list: VirtualizedList;
   rendered: React.ReactNode[];
@@ -1697,6 +1726,13 @@ export const useVirtualizedList = (
         list.current.scrollHeight = scrollHeightRef.current;
       }
 
+      maybeToggleScrollbar(
+        elements[0].target as HTMLElement,
+        scrollHeightRef.current,
+        itemsRef.current.length * 24,
+        managerRef.current
+      );
+
       const recomputedItems = findRenderedItems({
         scrollTop: scrollTopRef.current,
         items: itemsRef.current,
@@ -1738,6 +1774,13 @@ export const useVirtualizedList = (
     scrollContainerRef.current!.style.willChange = 'transform';
     scrollContainerRef.current!.style.height = `${props.items.length * 24}px`;
 
+    maybeToggleScrollbar(
+      props.container,
+      scrollHeightRef.current,
+      props.items.length * 24,
+      props.manager
+    );
+
     const onScroll = event => {
       if (!list.current) {
         return;
@@ -1805,7 +1848,7 @@ export const useVirtualizedList = (
     return () => {
       props.container?.removeEventListener('scroll', onScroll);
     };
-  }, [props.container, props.items, props.items.length]);
+  }, [props.container, props.items, props.items.length, props.manager]);
 
   useLayoutEffect(() => {
     if (!list.current || !styleCache.current || !renderCache.current) {