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Suspense mode resumes with the previous observable's value on React 19

Aberta
  • Algo errado?
#793 0 comentários 0 reações 0 responsáveis Ver no GitHub

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Avaliação

Dificuldade
4/5
Tempo estimado
3-5 dias
Facilidade para iniciantes
48/100
Tipo de issue
Bug
Clareza
Razoavelmente clara
Status de atividade
Pouca atividade
Stack de tecnologia
react, typescript
Domínio
frontend

Direção de pesquisa

Execute npx vitest run useObservable e comece por test/useObservable.test.tsx, especialmente emits the new observable's value if the observable is swapped out. Rastreie o SuspenseSubject nomeado, o cache preloadedObservables e o caminho use-sync-external-store. A tarefa estará concluída quando o teste voltar a ser um it simples e passar no React 19, mantendo o comportamento do React 18.

Escrita pelo modelo de indexação a partir do texto da issue.

Descrição

v5

useObservable in suspense mode suspends correctly when the observable and observableId are swapped, then resumes rendering the previous observable's value.

Found by the first test run ever executed against React 19 (#789); nothing had run against 19 before, only type-checks.

Reproduction

test/useObservable.test.tsx, emits the new observable's value if the observable is swapped out. The test renders a component under React.Suspense, emits Jeff on the first observable, swaps both the observable and the observableId, rerenders, then emits James on the second.

  • React 18.2.0: the fallback shows, then the component resumes with James. Passes.
  • React 19.2.8: the fallback shows (that assertion passes), then the component resumes with Jeff. Fails.

Deterministic: 3 runs each way, same @testing-library/react 16.3.2, only the React runtime swapped via npm install --no-save react@19 react-dom@19. No emulators involved, so npx vitest run useObservable reproduces it.

What is known and not known

  • The suspend half works. Only the resume is wrong, so this is not the known throw-vs-use() question: the 08-07 spike found the use() swap is a behavioural no-op on 19 and that React 19 emits no warning for the current throw form. Nothing here contradicts that.
  • The cause is not diagnosed. The plumbing involved (SuspenseSubject, the preloadedObservables cache keyed by observableId, and the use-sync-external-store shim delegating to React's own useSyncExternalStore on 19) overlaps what #790 covers, but no connection has been established and it should not be assumed.

Current state

#789's CI PR skips this test on React 19 only, so the new test job can land green. The skip is a ? it.skip : it ternary rather than it.skipIf, because these globals are typed by @types/jest and skipIf fails tsc while working at runtime.

Restore it to a plain it when this is fixed.

Linguagem predominante
TypeScript
Estrelas
3.6k
Forks
403
Merge médio
5d 1h
PRs com merge (30d)
10

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