Do scroll restoration in userland

app/hooks/use-scroll-restoration.ts

@@ -0,0 +1,30 @@
+import { useEffect } from 'react'
+import { useLocation, useNavigation } from 'react-router-dom'
+
+function getScrollPosition(key: string) {
+  const pos = window.sessionStorage.getItem(key)
+  return pos && /^[0-9]+$/.test(pos) ? parseInt(pos, 10) : 0
+}
+
+function setScrollPosition(key: string, pos: number) {
+  window.sessionStorage.setItem(key, pos.toString())
+}
+
+/**
+ * Given a ref to a scrolling container element, keep track of its scroll
+ * position before navigation and restore it on return (e.g., back/forward nav).
+ * Note that `location.key` is used in the cache key, not `location.pathname`,
+ * so the same path navigated to at different points in the history stack will
+ * not share the same scroll position.
+ */
+export function useScrollRestoration(container: React.RefObject<HTMLElement>) {
+  const key = `scroll-position-${useLocation().key}`
+  const { state } = useNavigation()
+  useEffect(() => {
+    if (state === 'loading') {
+      setScrollPosition(key, container.current?.scrollTop ?? 0)
+    } else if (state === 'idle') {
+      container.current?.scrollTo(0, getScrollPosition(key))
+    }
+  }, [key, state, container])
+}

app/layouts/helpers.tsx

@@ -1,20 +1,21 @@
 import { useRef } from 'react'
-import { Outlet, ScrollRestoration } from 'react-router-dom'
+import { Outlet } from 'react-router-dom'
 
 import { apiQueryClient } from '@oxide/api'
 import { Pagination } from '@oxide/pagination'
 import { SkipLinkTarget } from '@oxide/ui'
 import { classed } from '@oxide/util'
 
 import { PageActionsTarget } from 'app/components/PageActions'
+import { useScrollRestoration } from 'app/hooks/use-scroll-restoration'
 
 export const PageContainer = classed.div`grid h-screen grid-cols-[14.25rem,1fr] grid-rows-[60px,1fr]`
 
 export function ContentPane() {
   const ref = useRef<HTMLDivElement>(null)
+  useScrollRestoration(ref)
   return (
-    <div ref={ref} className="flex flex-col overflow-auto">
-      <ScrollRestoration elementRef={ref} />
+    <div ref={ref} className="flex flex-col overflow-auto" data-testid="scroll-container">
       <div className="flex flex-grow flex-col pb-8">
         <SkipLinkTarget />
         <main className="[&>*]:gutter">

app/test/e2e/scroll-restore.e2e.ts

@@ -0,0 +1,65 @@
+import { type Page, expect, test } from './utils'
+
+async function expectScrollTop(page: Page, expected: number) {
+  const container = await page.getByTestId('scroll-container')
+  const getScrollTop = () => container.evaluate((el: HTMLElement) => el.scrollTop)
+  await expect.poll(getScrollTop).toBe(expected)
+}
+
+async function scrollTo(page: Page, to: number) {
+  const container = await page.getByTestId('scroll-container')
+  await container.evaluate((el: HTMLElement, to) => el.scrollTo(0, to), to)
+}
+
+test('scroll restore', async ({ page }) => {
+  // open small window to make scrolling easier
+  await page.setViewportSize({ width: 800, height: 500 })
+
+  // nav to disks and scroll it
+  await page.goto('/projects/mock-project/disks')
+  await expectScrollTop(page, 0)
+  await scrollTo(page, 143)
+
+  // nav to snapshots
+  await page.getByRole('link', { name: 'Snapshots' }).click()
+  await expectScrollTop(page, 0)
+
+  // go back to disks, scroll is restored, scroll it some more
+  await page.goBack()
+  await expect(page).toHaveURL('/projects/mock-project/disks')
+  await expectScrollTop(page, 143)
+  await scrollTo(page, 190)
+
+  // go forward to snapshots, now scroll it
+  await page.goForward()
+  await expect(page).toHaveURL('/projects/mock-project/snapshots')
+  await expectScrollTop(page, 0)
+  await scrollTo(page, 30)
+
+  // new nav to disks
+  await page.getByRole('link', { name: 'Disks' }).click()
+  await expectScrollTop(page, 0)
+
+  // this is too flaky so forget it for now
+
+  // random reload in there because we use sessionStorage. note we are
+  // deliberately on the disks page here because there's a quirk in playwright
+  // that seems to reset to the disks page on reload
+  // await page.reload()
+
+  // back to snapshots, scroll is restored
+  await page.goBack()
+  await expect(page).toHaveURL('/projects/mock-project/snapshots')
+  await expectScrollTop(page, 30)
+
+  // back again to disks, newer scroll value is restored
+  await page.goBack()
+  await expect(page).toHaveURL('/projects/mock-project/disks')
+  await expectScrollTop(page, 190)
+
+  // forward again to newest disks history entry, scroll remains 0
+  await page.goForward()
+  await page.goForward()
+  await expect(page).toHaveURL('/projects/mock-project/disks')
+  await expectScrollTop(page, 0)
+})