fix(svelte-query): useMutationState array never shrank when mutations stopped matching filter

[okxint]

Summary

Object.assign copies enumerable own properties but never sets Array.length. When nextResult was shorter than result (fewer mutations matched the filter), trailing stale entries were never removed — the array only ever grew.

Fix: replace Object.assign(result, nextResult) with result.splice(0, result.length, ...nextResult).

splice keeps the reactive $state array reference intact (required by Svelte 5 runes) while correctly adjusting length, adding, and removing elements in one operation.

Fixes #11152

Changes

• packages/svelte-query/src/useMutationState.svelte.ts — one-line fix
• packages/svelte-query/tests/useMutationState/useMutationState.svelte.test.ts — regression test: two pending mutations both settle, assert the filtered result shrinks to []
• .changeset/fix-svelte-use-mutation-state-shrink.md — patch changeset

Test plan

pnpm --filter @tanstack/svelte-query test

The new test (should remove mutations that no longer match the filter) would have failed before this fix.

Summary by CodeRabbit

• Bug Fixes

  • Fixed mutation state results so entries are removed when mutations no longer match the active filter.
  • Ensured filtered mutation lists accurately reflect the current mutation status.

• Tests

  • Added coverage confirming that pending mutation results shrink correctly after mutations settle.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between d346e85 and be3610e.

📒 Files selected for processing (3)

• .changeset/fix-svelte-use-mutation-state-shrink.md
• packages/svelte-query/src/useMutationState.svelte.ts
• packages/svelte-query/tests/useMutationState/useMutationState.svelte.test.ts

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📝 Walkthrough

Walkthrough

useMutationState now updates its reactive array with splice, so entries that no longer match the filter are removed. A regression test verifies the array changes from two pending mutations to an empty array after both mutations settle.

Changes

Mutation state filtering

Layer / File(s)	Summary
In-place filtered result update and regression coverage packages/svelte-query/src/useMutationState.svelte.ts, packages/svelte-query/tests/useMutationState/useMutationState.svelte.test.ts, .changeset/fix-svelte-use-mutation-state-shrink.md	The reactive result array now replaces its contents with the current filtered results. The test verifies that settled mutations are removed, and the changeset records the patch release.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: sukvvon

Merge Risk: ⚪ Minimal · up to be361

The mutation-state result now removes settled mutations while retaining the reactive array reference, with regression coverage for the reported failure. No actionable merge risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main fix: preventing the useMutationState result array from retaining stale entries.
Description check	✅ Passed	The description clearly explains the defect, fix, affected files, regression test, test command, and changeset. It omits the template's Checklist and Release Impact headings, but the core required inf…
Linked Issues check	✅ Passed	For #11152, the cache subscription now uses result.splice(0, result.length, ...nextResult). This preserves the existing array reference and replaces all contents, including removal of stale trailing…
Out of Scope Changes check	✅ Passed	The changed source line directly fixes the stale-array behavior in #11152. The added test covers the reported regression. The changeset documents the package fix. No unrelated product behavior or unre…

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (1 skipped: 1 unsupported.)

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create a new PR

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