fix(svelte-query): `state_unsafe_mutation` error with `useIs...` #9493

hmnd · 2025-07-24T22:39:53Z

🎯 Changes

Fixes the bug reported by @frederikhors here.

I thoroughly dug into this issue until I found calls to Observer and MutataionOBserver were wrapped in a $derived(...) in order to make them reactive to the passed in client. This was resulting in unsafe mutation errors, and there was already an $effect.pre(...) used for updating options when they changed, so aside from the client reactivity, the $derived wasn't necessary.

To support reactivity for queryClient, the observer is now a $state and is reassigned whenever the client changes.

The useIsFetching and useIsMutating tests were previously passing because they used a QueryClient local to the component, rather than one from context. I've updated the tests to use a provider instead, in order to properly repro this issue.

✅ Checklist

I have followed the steps in the Contributing guide.
I have tested this code locally with pnpm test:pr.

🚀 Release Impact

This change affects published code, and I have generated a changeset.
This change is docs/CI/dev-only (no release).

nx-cloud · 2025-07-25T02:40:33Z

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☁️ Nx Cloud last updated this comment at 2025-09-27 12:32:45 UTC

pkg-pr-new · 2025-07-25T02:43:26Z

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commit: 62798d6

lachlancollins

Hi @hmnd , I don't seem to have permission to sync this with the changes in the svelte-5-adapter. Could you fix the merge conflicts?

changeset-bot · 2025-09-27T05:41:02Z

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coderabbitai · 2025-09-27T05:41:04Z

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hmnd · 2025-09-27T05:49:24Z

@lachlancollins should be fixed now :)

lachlancollins

Not sure if it worked, it's still showing all the conflicts

hmnd · 2025-09-27T06:04:34Z

Not sure if it worked, it's still showing all the conflicts

Oh sorry, git fetch only pulled from my fork, not upstream 🤦

One sec

…afe_mutation fixes useIsFetching and useIsMutating in svelte 5 adapter

pnpm-lock.yaml

packages/svelte-query/vite.config.ts

…est non colocated query

hmnd · 2025-09-27T07:26:49Z

packages/svelte-query/src/createMutation.svelte.ts


-  onDestroy(() => {
-    unsubscribe()
+  let result = $derived(observer.getCurrentResult())


@lachlancollins do you think we need to keep the Svelte peer dep pinned to as low as 5.7.0, or could we bump that to at least 5.25.0 so that assigning to $derived like this is supported? This was part of eslint --fix, but if we need to stay on the lower version, I'll have to revert this back to a manually managed $state.

I'm happy to bump the peer dependency version!

@hmnd I've updated this on the target branch.

It seems like this change(?) might have caused tests to start failing. It's difficult to know though, as the force pushes have erased the history.

Nevermind, I found the diff in a branch I cloned earlier. Tests are all passing again, so I think I'll merge this! Thanks heaps for your time @hmnd !

Thank you for getting this merged @lachlancollins! Sorry about the force pushes 😅

Replace derived state with direct state and add watchChanges for result updates.

* WIP: Svelte 5 adapter (#6981) * feat(svelte-query): Improve svelte runes API (#8852) * feat: Draft proposal * chore: Improve reactive containers * ci: apply automated fixes * oops * fix: Update API, add a bunch of tests * merge main * fix: use const * more tests * feat: More tests, back to thunks, fixed svelte-query-persist-client * feat: More tests and examples! * lockfile * fixes * Fix current CI errors * More small fixes/tweaks * Remove test.only * ci: apply automated fixes * Fix pnpm-lock, fix import order * update main docs * feat: More tests * ci: apply automated fixes * add back old tests * Cleanup * Fix persist client * Fix useMutationState --------- Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com> Co-authored-by: Lachlan Collins <[email protected]> * Use sleep from query-test-utils * Simplify test reset logic * Fix some merge conflicts * More fixes * A few more fixes * Fix useMutationState * Add changeset * Add migration docs * Replace Set with SvelteSet * Update minimum svelte version * Bump svelte-eslint-parser * Unwrap createQuery test * fix(svelte-query): `state_unsafe_mutation` error with `useIs...` (#9493) * fix(svelte-query): don't wrap observers in derived to avoid state_unsafe_mutation fixes useIsFetching and useIsMutating in svelte 5 adapter * test(svelte-query): wrap (useIs...) tests in QueryClientProvider to test non colocated query * fix(svelte-query): update observers when passed in query client changes * fix(svelte-query): simplify creatMutation sub/unsub * Refactor result handling in createMutation.svelte.ts Replace derived state with direct state and add watchChanges for result updates. --------- Co-authored-by: Lachlan Collins <[email protected]> * chore(svelte-query): fix eslint config (#9699) * chore(svelte-query): fix eslint config * Use @typescript-eslint/parser directly * ci: apply automated fixes * Fix sherif * Update docs and changeset * Update keywords --------- Co-authored-by: Zhiheng Zhang <[email protected]> Co-authored-by: Elliott Johnson <[email protected]> Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com> Co-authored-by: David <[email protected]>

github-actions bot added the package: svelte-query label Jul 24, 2025

hmnd force-pushed the fix/svelte-query-isfetching branch from dd04604 to e22d61e Compare July 24, 2025 22:46

lachlancollins self-requested a review July 25, 2025 02:40

lachlancollins self-assigned this Sep 22, 2025

lachlancollins requested changes Sep 26, 2025

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hmnd force-pushed the fix/svelte-query-isfetching branch from 4f57fd5 to ab7e6b4 Compare September 27, 2025 05:40

hmnd force-pushed the fix/svelte-query-isfetching branch from ab7e6b4 to 4f57fd5 Compare September 27, 2025 05:47

lachlancollins requested changes Sep 27, 2025

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fix(svelte-query): don't wrap observers in derived to avoid state_uns…

4da7817

…afe_mutation fixes useIsFetching and useIsMutating in svelte 5 adapter

hmnd force-pushed the fix/svelte-query-isfetching branch from 4f57fd5 to f8f22f7 Compare September 27, 2025 06:15

hmnd requested a review from lachlancollins September 27, 2025 06:25

lachlancollins requested changes Sep 27, 2025

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hmnd force-pushed the fix/svelte-query-isfetching branch 3 times, most recently from a9c586a to 83143f0 Compare September 27, 2025 06:42

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hmnd added 3 commits September 27, 2025 00:15

test(svelte-query): wrap (useIs...) tests in QueryClientProvider to t…

de3a48e

…est non colocated query

fix(svelte-query): update observers when passed in query client changes

f919a0f

fix(svelte-query): simplify creatMutation sub/unsub

ac2afcf

hmnd force-pushed the fix/svelte-query-isfetching branch from 83143f0 to ac2afcf Compare September 27, 2025 07:15

hmnd commented Sep 27, 2025

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lachlancollins added 2 commits September 27, 2025 17:55

Merge branch 'svelte-5-adapter' into fix/svelte-query-isfetching

000016c

Refactor result handling in createMutation.svelte.ts

62798d6

Replace derived state with direct state and add watchChanges for result updates.

lachlancollins approved these changes Sep 27, 2025

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lachlancollins merged commit 968d6a8 into TanStack:svelte-5-adapter Sep 27, 2025
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fix(svelte-query): state_unsafe_mutation error with useIs... #9493

fix(svelte-query): state_unsafe_mutation error with useIs... #9493

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fix(svelte-query): `state_unsafe_mutation` error with `useIs...` #9493

fix(svelte-query): `state_unsafe_mutation` error with `useIs...` #9493

hmnd commented Jul 24, 2025 •

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