breaking: review async APIs by teemingc · Pull Request #16352 · sveltejs/kit

teemingc · 2026-07-14T19:47:32Z

This PR turns on the no-misused-promises rule partially and attempts to standardise functions that are usually asynchronous more often than not (and therefore don't really need to use MaybePromise)

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pkg-svelte-dev · 2026-07-14T19:47:35Z

Install the latest version of @sveltejs/kit from 72b507e:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/72b507e36c4ed6e107f8caace5690d46a818eca3

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16352

changeset-bot · 2026-07-14T19:47:36Z

🦋 Changeset detected

Latest commit: 72b507e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@sveltejs/kit	Major

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teemingc · 2026-07-14T19:48:23Z

-	resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>;
-}) => MaybePromise<Response>;
+	resolve: (event: RequestEvent, opts?: ResolveOptions) => Promise<Response>;
+}) => Promise<Response>;


More often than not you'd call await resolve(event) inside the hook anyway. If you did do return resolve(event) it'd still return a Promise

EDIT: you could end up with:

export const handle = ({ event, resolve }) => { if (...) { return new Response(...); } return resolve(event); }

And then you'd needlessly have to add async to the function, so maybe we need to reconsider this

yeah I think this does need to be MaybePromise for exactly that reason

svelte-docs-bot · 2026-07-14T19:49:02Z

Preview: https://svelte-dev-git-preview-kit-16352-svelte.vercel.app/

teemingc · 2026-07-14T20:22:26Z

 	event: RequestEvent;
-	resolve: (event: RequestEvent, opts?: ResolveOptions) => MaybePromise<Response>;
-}) => MaybePromise<Response>;
+	resolve: (event: RequestEvent, opts?: ResolveOptions) => Promise<Response>;


This is always await resolve() in apps so it makes sense to be a Promise

teemingc · 2026-07-14T20:42:04Z

 	// is running because subsequent invalidations may make earlier ones outdated,
 	// but batch multiple synchronous invalidations.
 	await (pending_invalidate ||= Promise.resolve());
-	if (!pending_invalidate) return;


eslint thinks this is evaluating a promise which will always be true

vercel

Additional Suggestion:

Three synchronous resolve mocks in sequence.spec.js return Response, which is not assignable to the Handle type's resolve param that is now typed (event, opts?) => Promise<Response>, causing tsc/pnpm check to fail.

…Response`, which is not assignable to the `Handle` type's `resolve` param that is now typed `(event, opts?) => Promise<Response>`, causing `tsc`/`pnpm check` to fail. This commit fixes the issue reported at packages/kit/src/exports/hooks/sequence.spec.js:58 ## Bug `packages/kit/src/exports/public.d.ts` (line ~965) types the `Handle` hook's `resolve` parameter as: ```ts resolve: (event: RequestEvent, opts?: ResolveOptions) => Promise<Response>; ``` `packages/kit/tsconfig.json` has `checkJs: true` and includes `src/**/*`, so `sequence.spec.js` is type-checked, and the `check` script runs `tsc`. Three `resolve` mocks in the spec return a **synchronous** `Response`: - Line 58: `resolve: () => response` - The "uses first defined preload option" test: `resolve: (_event, opts = {}) => { ...; return new Response(html); }` - The "uses first defined filterSerializedResponseHeaders option" test: same synchronous shape A function returning `Response` is **not** assignable to a parameter typed `(...) => Promise<Response>` — `Response` has no `.then`/thenable structure — so `tsc` reports an assignability error at each of these mock sites. This matches commit `dc67c02` reverting the earlier fix (`f7b69b9`) while keeping the `Promise<Response>` typing. The two `async` resolve mocks (in the `transformPageChunk` tests) are unaffected because an `async` function already returns `Promise<Response>`. ## Fix Re-apply the `f7b69b9` change: wrap the three synchronous returns in `Promise.resolve(...)`: - `resolve: () => Promise.resolve(response)` - `return Promise.resolve(new Response(html));` (preload test) - `return Promise.resolve(new Response(html));` (filterSerializedResponseHeaders test) This makes each mock return `Promise<Response>`, satisfying the `Handle` type and restoring the type-check. Note: I could not execute `tsc` here because TypeScript/deps are not installed in the environment, but the mismatch is structural and deterministic under `checkJs`. Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com> Co-authored-by: teemingc <chewteeming01@gmail.com>

teemingc · 2026-07-15T10:33:54Z

/autofix

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to version-3, this PR will be updated. ⚠️

⚠️

⚠️ `version-3` is currently in **pre mode** so this branch has prereleases rather than normal releases. If you want to exit prereleases, run `changeset pre exit` on `version-3`. ⚠️

⚠️

⚠️ # Releases ## @sveltejs/kit@3.0.0-next.9 ### Major Changes - breaking: `handle`'s `resolve` is now typed to always return a `Promise` ([#16352](#16352)) - breaking: replace the `$lib` alias with `#lib` and remove `files.lib` config. ([#16360](#16360)) - breaking: disallow cross-origin form submissions without a `Content-Type` header ([#16347](#16347)) - breaking: Server-only directories (`/server/` in the path) are now treated as server-only everywhere inside the project (except `src/routes` and the assets directory) ([#16360](#16360)) - breaking: delegate CORS handling to Vite for static directory requests during development ([#16357](#16357)) ### Minor Changes - feat: reinstate `$env/static/private`, `$env/dynamic/private`, `$env/static/public`, `$env/dynamic/public` and `$app/environment` as deprecated aliases for `$app/env/private` `$app/env/public` and `$app/env` ([#16334](#16334)) ### Patch Changes - perf: cache the default cookie header parse and avoid allocations in `cookies.get` ([#16341](#16341)) - fix: avoid client-side code being bundled by Cloudflare Wrangler ([#16364](#16364)) - fix: handle rejected streamed server data after delayed loads ([#16268](#16268)) - fix: enable CSRF protection in builds with a non-production `NODE_ENV` value ([#16313](#16313)) ## @sveltejs/package@3.0.0-next.3 ### Minor Changes - feat: transform import aliases into relative imports in files ([#16360](#16360)) ## @sveltejs/adapter-node@6.0.0-next.4 ### Patch Changes - fix: correctly bundle entrypoints on Windows ([#16367](#16367)) - Updated dependencies [[`c1ee782`](c1ee782), [`1a1b3ea`](1a1b3ea), [`6423d98`](6423d98), [`6d1f4f0`](6d1f4f0), [`5ca9906`](5ca9906), [`b148d31`](b148d31), [`5ca9906`](5ca9906), [`9f3d9bb`](9f3d9bb), [`7bfd922`](7bfd922), [`ffa0e3b`](ffa0e3b)]: - @sveltejs/kit@3.0.0-next.9 ## @sveltejs/enhanced-img@1.0.0-next.2 ### Patch Changes - chore: replace the `$lib` alias with `#lib` in docs ([#16360](#16360)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

teemingc added 2 commits July 15, 2026 03:38

turn on lint rule and address errors

878c049

more often than not you'd do await request.formData()

d7b559e

teemingc commented Jul 14, 2026

View reviewed changes

this ain't needed

6155f84

teemingc marked this pull request as ready for review July 14, 2026 19:52

teemingc added 3 commits July 15, 2026 03:57

nope

01df0e8

another nope

40fb74c

Update sequence.spec.js

f7b69b9

teemingc commented Jul 14, 2026

View reviewed changes

teemingc added 2 commits July 15, 2026 17:22

revert

dc67c02

changeset

d521f9e

vercel Bot reviewed Jul 15, 2026

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chore: autofix lint

72b507e

Rich-Harris approved these changes Jul 16, 2026

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Rich-Harris merged commit 1a1b3ea into version-3 Jul 16, 2026
6 checks passed

Rich-Harris deleted the review-async-apis branch July 16, 2026 02:28

github-actions Bot mentioned this pull request Jul 16, 2026

Version Packages (next) #16344

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breaking: review async APIs - #16352

breaking: review async APIs#16352
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