[PR #979] [MERGED] fix: unstable_io() returns hanging promise during prerendering #1000

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opened 2026-05-06 13:11:29 +02:00 by BreizhHardware · 0 comments

BreizhHardware commented

2026-05-06 13:11:29 +02:00

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📋 Pull Request Information

Original PR: https://github.com/cloudflare/vinext/pull/979
Author: @Divkix
Created: 4/30/2026
Status: ✅ Merged
Merged: 5/1/2026
Merged by: @james-elicx

Base: main ← Head: fix/972-unstable-io-prerender-hang

📝 Commits (7)

ea50693 fix: unstable_io() returns hanging promise during prerendering (#972)
f415e57 fix: add knip entries for prerender-work-unit and work-unit types (#972)
035a54f fix(prerender): address PR review feedback for unstable_io work unit store
7963603 fix(app-rsc-entry): place route option in correct location
0617b21 fix: address prerender hanging promise review feedback
01b5c18 fix: resolve merge conflicts with main for prerender work unit
feab64b fix: resolve merge conflicts with main for test files

📊 Changes

9 files changed (+1239 additions, -2941 deletions)

View changed files

📝 knip.ts (+6 -0)
📝 packages/vinext/src/entries/app-rsc-entry.ts (+98 -399)
➕ packages/vinext/src/server/prerender-work-unit-setup.ts (+34 -0)
📝 packages/vinext/src/shims/cache.ts (+48 -5)
➕ packages/vinext/src/shims/internal/make-hanging-promise.ts (+64 -0)
📝 packages/vinext/src/shims/internal/work-unit-async-storage.ts (+46 -4)
📝 tests/__snapshots__/entry-templates.test.ts.snap (+504 -2388)
📝 tests/app-router.test.ts (+317 -145)
📝 tests/shims.test.ts (+122 -0)

📄 Description

Fixes #972

Summary

unstable_io() now branches on work unit store type, matching Next.js implementation in packages/next/src/server/request/io.ts
During prerendering (prerender/prerender-client/prerender-runtime), returns a hanging promise that suspends React past the IO boundary
During requests, cache scopes, and other contexts, resolves immediately (existing behavior)
When no work unit store is present, falls back to resolved promise (client/standalone)

What changed

New: make-hanging-promise.ts — promise that never resolves, rejects when AbortSignal fires (ported from Next.js dynamic-rendering-utils.ts)
Modified: work-unit-async-storage.ts — typed WorkUnitStore discriminated union with store types
Modified: cache.ts — unstable_io() checks work unit store type and delegates to makeHangingPromise during prerendering
New: prerender-work-unit-setup.ts — helper that sets up prerender store in workUnitAsyncStorage when VINEXT_PRERENDER=1
Modified: app-rsc-entry.ts — wraps request handler in prerender work unit scope
Updated: entry template snapshots to reflect generated code changes

Test plan

Added 5 new tests in tests/shims.test.ts covering: hanging promise during prerender, resolved promise with request/cache stores, rejection on abort, rejection on pre-aborted signal
All 835 existing shim tests pass
Entry template snapshot tests updated

_{🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.}

## 📋 Pull Request Information **Original PR:** https://github.com/cloudflare/vinext/pull/979 **Author:** [@Divkix](https://github.com/Divkix) **Created:** 4/30/2026 **Status:** ✅ Merged **Merged:** 5/1/2026 **Merged by:** [@james-elicx](https://github.com/james-elicx) **Base:** `main` ← **Head:** `fix/972-unstable-io-prerender-hang` --- ### 📝 Commits (7) - [`ea50693`](https://github.com/cloudflare/vinext/commit/ea5069383ba205488222a718980f62217e10f7eb) fix: unstable_io() returns hanging promise during prerendering (#972) - [`f415e57`](https://github.com/cloudflare/vinext/commit/f415e57feb32f3d7bd828a85ab2d6738a8999456) fix: add knip entries for prerender-work-unit and work-unit types (#972) - [`035a54f`](https://github.com/cloudflare/vinext/commit/035a54fedf7946f08e24fd308ad9a3e788c2da5e) fix(prerender): address PR review feedback for unstable_io work unit store - [`7963603`](https://github.com/cloudflare/vinext/commit/79636031f889fc0a6ae23cfd326e2353b04837b6) fix(app-rsc-entry): place route option in correct location - [`0617b21`](https://github.com/cloudflare/vinext/commit/0617b21c1f923acf3bc666f67aaaddd2283f7abb) fix: address prerender hanging promise review feedback - [`01b5c18`](https://github.com/cloudflare/vinext/commit/01b5c183cb981c7aa2af09a44972e061b52aa176) fix: resolve merge conflicts with main for prerender work unit - [`feab64b`](https://github.com/cloudflare/vinext/commit/feab64b29a4dcba3205151c3764142f89be7a083) fix: resolve merge conflicts with main for test files ### 📊 Changes **9 files changed** (+1239 additions, -2941 deletions) <details> <summary>View changed files</summary> 📝 `knip.ts` (+6 -0) 📝 `packages/vinext/src/entries/app-rsc-entry.ts` (+98 -399) ➕ `packages/vinext/src/server/prerender-work-unit-setup.ts` (+34 -0) 📝 `packages/vinext/src/shims/cache.ts` (+48 -5) ➕ `packages/vinext/src/shims/internal/make-hanging-promise.ts` (+64 -0) 📝 `packages/vinext/src/shims/internal/work-unit-async-storage.ts` (+46 -4) 📝 `tests/__snapshots__/entry-templates.test.ts.snap` (+504 -2388) 📝 `tests/app-router.test.ts` (+317 -145) 📝 `tests/shims.test.ts` (+122 -0) </details> ### 📄 Description Fixes #972 ## Summary - unstable_io() now branches on work unit store type, matching Next.js implementation in packages/next/src/server/request/io.ts - During prerendering (prerender/prerender-client/prerender-runtime), returns a hanging promise that suspends React past the IO boundary - During requests, cache scopes, and other contexts, resolves immediately (existing behavior) - When no work unit store is present, falls back to resolved promise (client/standalone) ## What changed - **New**: make-hanging-promise.ts — promise that never resolves, rejects when AbortSignal fires (ported from Next.js dynamic-rendering-utils.ts) - **Modified**: work-unit-async-storage.ts — typed WorkUnitStore discriminated union with store types - **Modified**: cache.ts — unstable_io() checks work unit store type and delegates to makeHangingPromise during prerendering - **New**: prerender-work-unit-setup.ts — helper that sets up prerender store in workUnitAsyncStorage when VINEXT_PRERENDER=1 - **Modified**: app-rsc-entry.ts — wraps request handler in prerender work unit scope - **Updated**: entry template snapshots to reflect generated code changes ## Test plan - Added 5 new tests in tests/shims.test.ts covering: hanging promise during prerender, resolved promise with request/cache stores, rejection on abort, rejection on pre-aborted signal - All 835 existing shim tests pass - Entry template snapshot tests updated --- <sub>🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.</sub>