fix: don't update dataUpdateCount when setting initial data

[0xdiid]

🎯 Changes

This introduces a check when updating dataUpdateCount so that it isn't updated when setting initial data. This in turn fixes the isFetchedAfterMount bug discussed in #9656

fixes #9656

✅ 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).

Summary by CodeRabbit

• Bug Fixes

  • Corrected isFetchedAfterMount when using initial data at mount, preventing it from being incorrectly marked as fetched.
  • Prevented initial data from incrementing update counters; subsequent refetches now update data and counters as expected.

• Tests

  • Added tests to verify correct behavior with initial data and observer-initiated refetches.

• Chores

  • Added a patch changeset entry reflecting this bug fix for the package.

[changeset-bot]

🦋 Changeset detected

Latest commit: ad5d0ba

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

This PR includes changesets to release 4 packages

Name	Type
@tanstack/react-query	Patch
@tanstack/react-query-devtools	Patch
@tanstack/react-query-next-experimental	Patch
@tanstack/react-query-persist-client	Patch

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[coderabbitai]

Walkthrough

This PR adjusts Query’s success-state handling to avoid incrementing dataUpdateCount when initialData is set manually at mount. It adds a targeted test verifying isFetchedAfterMount and dataUpdateCount behavior with initialData and subsequent refetch, and includes a changeset marking a patch for @tanstack/react-query.

Changes

Cohort / File(s)	Summary
Core logic update packages/query-core/src/query.ts	Modify Success action: when action.manual is true and previous state.data is undefined (initial manual data), do not increment dataUpdateCount; otherwise increment as before. Preserve dataUpdatedAt; guard #revertState by action.manual.
Tests packages/query-core/src/__tests__/query.test.tsx	Add test ensuring initialData via observer does not increment dataUpdateCount and isFetchedAfterMount remains false until an observer-triggered refetch updates both.
Changeset .changeset/yummy-rooms-read.md	Add patch changeset for @tanstack/react-query describing the bugfix to isFetchedAfterMount with initialData.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  actor UI as Component
  participant Obs as QueryObserver
  participant QC as QueryClient
  participant Q as Query

  UI->>Obs: Mount with initialData
  Obs->>QC: Subscribe to query key
  QC->>Q: Create/attach observer
  Note right of Q: Apply initialData as manual<br/>(no dataUpdateCount increment,<br/>isFetchedAfterMount=false)

  UI->>Obs: Trigger refetch
  Obs->>Q: fetch()
  Q->>Q: Resolve to fetched data
  Note right of Q: Update data, increment dataUpdateCount,<br/>isFetchedAfterMount=true
  Q-->>Obs: Notify result
  Obs-->>UI: Render with fetched data

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• fix(query-core): update initialData when an observer mounts while a Query without data exists #9620 — Adjusts Query initialData/manual handling in query.ts to treat observer-applied initialData as manual without incrementing update counters.

Poem

A hop, a skip, a patch so neat,
My carrots count each data beat. 🥕
First nibble’s manual—no drums sound,
But fetch-time thumps now shake the ground.
Flags flip, counts tick, all set aright—
I nose-twitch, merge, and bound to night.

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title Check	✅ Passed	The title succinctly and accurately reflects the main change in the PR—preventing dataUpdateCount updates when setting initial data—and clearly indicates the nature of the fix.
Description Check	✅ Passed	The description adheres to the repository template by providing detailed 'Changes', completed 'Checklist', and 'Release Impact' sections with a summary of the implementation, issue reference, testing confirmation, and changeset inclusion.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between f4a0cd5 and ad5d0ba.

📒 Files selected for processing (3)

• .changeset/yummy-rooms-read.md (1 hunks)
• packages/query-core/src/__tests__/query.test.tsx (1 hunks)
• packages/query-core/src/query.ts (1 hunks)

🔇 Additional comments (3)

packages/query-core/src/query.ts (1)

639-641: LGTM! Correctly prevents dataUpdateCount increment for initial data.

The conditional logic appropriately identifies when initial data is being set manually at mount (action.manual && state.data === undefined) and preserves the dataUpdateCount in that case. This fix ensures that isFetchedAfterMount remains false until an actual fetch occurs, addressing the bug referenced in issue #9656.

The logic correctly handles subsequent scenarios:

• Manual data updates after initial data → increments (data no longer undefined)
• Normal fetches → increments (action.manual is false)

.changeset/yummy-rooms-read.md (1)

1-5: LGTM! Changeset appropriately documents the fix.

The changeset correctly identifies this as a patch-level change and clearly describes the behavioral fix for isFetchedAfterMount when initialData is applied at mount.

packages/query-core/src/__tests__/query.test.tsx (1)

1308-1349: LGTM! Comprehensive test validates the fix.

The test thoroughly validates the expected behavior:

1. ✓ Confirms dataUpdateCount remains 0 when initialData is set on a prefetched query
2. ✓ Verifies isFetchedAfterMount is false with only initial data
3. ✓ Confirms dataUpdateCount increments to 1 after an actual refetch
4. ✓ Verifies isFetchedAfterMount becomes true after the fetch

This directly addresses the bug scenario and provides good regression coverage.

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