fix(svelte-db): disabled useLiveQuery no longer crashes by kevin-dp · Pull Request #1637 · TanStack/db

kevin-dp · 2026-07-02T07:38:20Z

Follow-up #1 of 3 to the conformance suite (#1636), fixing a knownGap that suite surfaced.

Base: stacked on test/live-query-conformance-suite (#1636) — it depends on the conformance drivers to clear the gap. Re-target to main once #1636 lands.

The bug

A disabled useLiveQuery — the query callback returning null/undefined, which every other adapter treats as "disabled" — crashed in svelte-db:

TypeError: Cannot read properties of undefined (reading '_getQuery')
  ❯ getQueryIR .../query/builder/index.ts
  ❯ createLiveQueryCollection .../query/live-query-collection.ts

Root cause

svelte-db added toValue() unwrapping to support the reactive () => collection input form. But toValue calls any function, so it also calls the query callback. When that callback returns null/undefined (disabled), the unwrapped value became null, which fell through to createLiveQueryCollection({ ...null, startSync: true }) → crash in getQueryIR. The existing disabled short-circuit sat behind a typeof === 'function' check that null never reaches.

It went unnoticed because svelte-db had no disabled-query tests — exactly the gap the conformance suite flagged.

Fix

Treat a null/undefined unwrapped value as a disabled query (return the disabled state), matching React/Vue/Solid/Angular. One guard in the non-function branch.

Verification

Clears the disabled-explicit and disabled-transition knownGaps in the svelte-db conformance driver — both now pass as normal tests. Full svelte-db suite green (54), svelte-check clean. Patch changeset included.

🤖 Generated with Claude Code

Summary by CodeRabbit

Bug Fixes
- Fixed useLiveQuery so queries that resolve to null or undefined are treated as disabled instead of causing runtime errors.
- Improved consistency with other adapters by returning a disabled state in these cases.
Tests
- Updated conformance coverage to reflect that disabled-query scenarios now pass.

coderabbitai · 2026-07-02T07:38:28Z

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Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: afb065d9-2c90-400d-9c45-e2e8649c180c

📥 Commits

Reviewing files that changed from the base of the PR and between 3ec3e7a and 36ef0b0.

📒 Files selected for processing (3)

.changeset/svelte-disabled-query-fix.md
packages/svelte-db/src/useLiveQuery.svelte.ts
packages/svelte-db/tests/conformance.svelte.test.ts

📝 Walkthrough

Walkthrough

Adds a guard in Svelte's useLiveQuery to return null when the resolved query parameter is null/undefined, treating it as a disabled query instead of passing it to createLiveQueryCollection. Updates conformance test knownGaps to remove now-passing disabled-query cases, and adds a changeset.

Changes

Disabled Query Handling Fix

Layer / File(s)	Summary
Guard against null/undefined query params `packages/svelte-db/src/useLiveQuery.svelte.ts`	Returns `null` early in the reactive `collection` computation when the unwrapped parameter is `undefined`/`null`, avoiding passing invalid values to `createLiveQueryCollection`.
Conformance test update and changeset `packages/svelte-db/tests/conformance.svelte.test.ts`, `.changeset/svelte-disabled-query-fix.md`	Removes `disabled-explicit`/`disabled-transition` from `knownGaps` in the Svelte driver test config and adds a changeset documenting the patch fix.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

TanStack/db#1641: Both PRs modify the Svelte useLiveQuery.svelte.ts hook's argument handling logic.

Suggested reviewers: samwillis

✨ Finishing Touches

📝 Generate docstrings

Create stacked PR
Commit on current branch

🧪 Generate unit tests (beta)

Create PR with unit tests
Commit unit tests in branch fix/svelte-disabled-query

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pkg-pr-new · 2026-07-02T07:41:14Z

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commit: 36ef0b0

github-actions · 2026-07-02T07:41:49Z

Size Change: 0 B

Total Size: 125 kB

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Filename	Size
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github-actions · 2026-07-02T07:42:23Z

Size Change: 0 B

Total Size: 4.26 kB

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`packages/react-db/dist/esm/index.js`	249 B
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A disabled query (callback returning null/undefined) crashed: the reactive-getter unwrapping (`toValue`) called the callback, and the resulting null was spread into createLiveQueryCollection → throw in getQueryIR. Now a null/undefined unwrapped value is treated as a disabled query, matching React/Vue/Solid/Angular. Clears the svelte-db conformance knownGaps (disabled-explicit, disabled-transition); both now pass as normal tests. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

kevin-dp force-pushed the fix/svelte-disabled-query branch 2 times, most recently from ac88882 to f0afcae Compare July 7, 2026 10:01

Base automatically changed from test/live-query-conformance-suite to main July 7, 2026 10:20

kevin-dp force-pushed the fix/svelte-disabled-query branch from f0afcae to 36ef0b0 Compare July 7, 2026 10:24

KyleAMathews approved these changes Jul 7, 2026

View reviewed changes

kevin-dp marked this pull request as ready for review July 9, 2026 07:32

kevin-dp merged commit b2f305a into main Jul 9, 2026
10 of 11 checks passed

kevin-dp deleted the fix/svelte-disabled-query branch July 9, 2026 07:33

github-actions Bot mentioned this pull request Jul 9, 2026

ci: Version Packages #1661

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fix(svelte-db): disabled useLiveQuery no longer crashes#1637

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