useSyncExternalStore loops during hydration when getServerSnapshot differs from getSnapshot (flushPending exceeded 50 iterations)

Chiusa
  • Qualcosa non va?
#79 0 commenti 1 reazione 0 assegnatari Vedi su GitHub

I maintainer di solito rispondono entro 1 giorno

Nessuno ha ancora preso questa issue.

Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
48/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
react, typescript, vite
Ambito
frontend, testing

Direzione di ricerca

Start with packages/redact/src/dom/dispatcher.ts around the cited lines 331–348 and trace how hydration state affects useSyncExternalStore snapshots and scheduled updates. Compare the reproduction's Redact and React runs, then inspect nearby hydration tests or add a focused regression case. Done means hydration settles without the iteration error and reaches the client snapshot, matching React's two renders.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

🤖 Issue drafted with Claude Code. Reproduced and verified before posting.

Version: @tanstack/redact 0.2.1 (also 0.2.0). Baseline: react/react-dom 19.3.1.

Hydrating a component whose getServerSnapshot differs from getSnapshot never settles: Redact re-renders it 50 times, then hydrateRoot throws flushPending exceeded 50 iterations — suspected infinite update loop. (a bare Error in production). React renders it twice.

This is the "still hydrating?" idiom used by Headless UI 2.x (useServerHandoffComplete, behind Popover, Dialog, Transition…), so any page with a Headless UI component hits it.

Reproduction

npm i @tanstack/[email protected] react@19 react-dom@19 jsdom, then node repro.mjs redact / node repro.mjs react:

// repro.mjs
import { JSDOM } from "jsdom"
const { window } = new JSDOM("<!doctype html><div id=root></div>")
Object.assign(globalThis, { window, document: window.document, HTMLElement: window.HTMLElement, Node: window.Node })

const redact = process.argv[2] === "redact"
const R = await import(redact ? "@tanstack/redact" : "react")
const { renderToString } = await import(redact ? "@tanstack/redact/server" : "react-dom/server")
const { hydrateRoot } = await import(redact ? "@tanstack/redact/dom-client" : "react-dom/client")

let renders = 0
function App() {
  const isServer = R.useSyncExternalStore(() => () => {}, () => false, () => true)
  renders++
  return R.createElement("p", null, isServer ? "server" : "client")
}

const root = document.getElementById("root")
root.innerHTML = renderToString(R.createElement(App))
renders = 0
try {
  hydrateRoot(root, R.createElement(App))
} catch (error) {
  console.log("hydrateRoot threw:", error.message || "Error")
}
setTimeout(() => console.log({ renders, text: root.textContent }), 100)
Renders hydrateRoot throws Final text
React 19.3.1 2 no client
Redact 0.2.1 52 yes client

Same result in Chromium with a Vite build (redact() plugin, Redact on server and client).

Likely cause

In dispatcher.ts#L331-L348, the render reads getServerSnapshot() while root.h is set. The effect's check() compares it with getSnapshot(), finds a difference and calls scheduleUpdate. That update is flushed while the root is still marked as hydrating, so it reads the server snapshot again, and check() runs again (the inline subscribe changes every render). Logging inside the loop shows rendered=true client=false hydrating=true at every iteration.

React switches to getSnapshot() once the hydration render has committed, so its second render reads the client value and stops.

Impact

On a TanStack Start storefront using a Headless UI Popover, this adds ~150 ms of main-thread work per page load (4× CPU throttling) and reports an uncaught error, though the page ends up interactive.

Lingua principale
TypeScript
Stelle
537
Fork
22
Merge medio
10h 27m
PR unite (30g)
40

Preparare l'ambiente

Questo progetto non fornisce container di sviluppo, Dockerfile né guida per i contributori, quindi l'ambiente è a tuo carico: parti dal suo README e consulta la nostra guida al primo contributo per i passaggi generali.

Come iniziare

  1. Leggi tutta la issue e poi la guida ai contributi del progetto.
  2. Commenta sulla issue per dire che te ne occupi tu — evita che due persone facciano lo stesso lavoro.
  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

Altre issue di TanStack/redact

Tutte le issue di TanStack/redact

Issue simili

Altre issue su TypeScript

Ricevi le nuove issue nella tua casella

Un breve riepilogo di issue GitHub adatte ai principianti.