fix(solid-query): untrack the result read in useMutationState's cache subscription

.changeset/solid-query-mutation-state-untrack.md

@@ -0,0 +1,7 @@
+---
+'@tanstack/solid-query': patch
+---
+
+fix(solid-query): stop `useMutationState` making the computation that triggers a mutation depend on its result
+
+The mutation-cache subscription read the hook's own result signal. `MutationCache` notifies synchronously, so that read happened while the computation that called `mutate` was still the active listener — registering the signal as one of its dependencies, which `setResult` then immediately invalidated. Calling `mutate` from inside an effect therefore re-ran that effect on every mutation, and an unguarded `mutate` looped. The read is now untracked.

packages/solid-query/src/__tests__/useMutationState.test.tsx

@@ -111,4 +111,36 @@ describe('useMutationState', () => {
 
     expect(variables).toEqual([[], [1], []])
   })
+
+  it('should not make the computation that triggers a mutation depend on its result', async () => {
+    const mutationKey = queryKey()
+    let effectRuns = 0
+
+    function Page() {
+      const states = useMutationState(() => ({ filters: { mutationKey } }))
+      const mutation = useMutation(() => ({
+        mutationKey,
+        mutationFn: (input: number) => sleep(150).then(() => 'data' + input),
+      }))
+
+      createEffect(() => {
+        effectRuns++
+        // Guarded so that a genuine feedback loop still terminates the test.
+        if (effectRuns === 1) {
+          mutation.mutate(1)
+        }
+      })
+
+      return <div>count: {states().length}</div>
+    }
+
+    renderWithClient(queryClient, () => <Page />)
+    await vi.advanceTimersByTimeAsync(150)
+
+    // `mutate` notifies the mutation cache synchronously, so the subscription
+    // callback runs while this effect is the active computation. Reading the
+    // result signal there used to register it as a dependency of that effect,
+    // which `setResult` then immediately invalidated.
+    expect(effectRuns).toBe(1)
+  })
 })

packages/solid-query/src/useMutationState.ts

@@ -1,4 +1,10 @@
-import { createEffect, createMemo, createSignal, onCleanup } from 'solid-js'
+import {
+  createEffect,
+  createMemo,
+  createSignal,
+  onCleanup,
+  untrack,
+} from 'solid-js'
 import { replaceEqualDeep } from '@tanstack/query-core'
 import { useQueryClientResolver } from './QueryClientProvider'
 import type {
@@ -66,11 +72,15 @@ export function useMutationState<
 
   createEffect(() => {
     const unsubscribe = mutationCache().subscribe(() => {
+      // `subscribe` invokes this synchronously, so reading `result` while the
+      // enclosing effect is still tracking would make the effect depend on the
+      // signal it sets, re-running and re-subscribing on every mutation.
+      const previousResult = untrack(result)
       const nextResult = replaceEqualDeep(
-        result(),
+        previousResult,
         getResult(mutationCache(), options()),
       )
-      if (result() !== nextResult) {
+      if (previousResult !== nextResult) {
         setResult(nextResult)
       }
     })