fix(runtime-core): avoid repeated hydration mismatch checks

[edison1105]

close #14855

Summary by CodeRabbit

• Bug Fixes

  • Fixed duplicate warning messages during SSR hydration mismatches. Diagnostics are now emitted only once per mismatch event, reducing console noise and improving debugging clarity.

• Tests

  • Added test coverage for hydration mismatch warning behavior to verify warnings are emitted exactly once during hydration operations with excess or missing DOM nodes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 23e0cb5a-9ca4-484e-83f6-b13503d7ba91

📥 Commits

Reviewing files that changed from the base of the PR and between 1ce598e and b50e0b2.

📒 Files selected for processing (2)

• packages/runtime-core/__tests__/hydration.spec.ts
• packages/runtime-core/src/hydration.ts

---

📝 Walkthrough

Walkthrough

This PR refactors hydration mismatch handling to emit warnings and diagnostic logs only once per mismatch event, eliminating redundant isMismatchAllowed() and logMismatchError() calls during node removal and mounting loops. Test coverage validates both the excess-node and missing-node warning paths.

Changes

Hydration mismatch warning deduplication

Layer / File(s)	Summary
Excess DOM nodes mismatch handling packages/runtime-core/src/hydration.ts, packages/runtime-core/__tests__/hydration.spec.ts	After hydrateChildren() returns, the "more child nodes" warning and logMismatchError() call move outside the node-removal loop, executing once if mismatches aren't allowed. Test spies on Element.prototype.hasAttribute to verify the warning fires exactly once and the data-allow-mismatch check occurs once.
Missing child nodes mismatch handling packages/runtime-core/src/hydration.ts, packages/runtime-core/__tests__/hydration.spec.ts	When server children run out, hasWarned is replaced with hasCheckedMismatch to gate the "fewer child nodes" warning and logMismatchError() call on the first encounter only. Test spies on Element.prototype.hasAttribute to verify the warning fires exactly once and the data-allow-mismatch check occurs once.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Suggested labels

scope:hydration, :hammer: p3-minor-bug

Suggested reviewers

• Doctor-wu
• LittleSound
• KazariEX

Poem

🐰 A curious bunny hops through hydration's flow,
Where warnings once whispered with each DOM node below—
Now one chirp per mismatch, no redundant refrain,
The tests guard this promise with spy-powered chain!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: avoiding repeated hydration mismatch checks during SSR hydration, which directly addresses the linked issue.
Linked Issues check	✅ Passed	The PR successfully addresses issue #14855 by hoisting mismatch checks outside loops so isMismatchAllowed() and logMismatchError() are called once per mismatch event rather than on every iteration.
Out of Scope Changes check	✅ Passed	All changes are focused on resolving the redundant mismatch checks in hydration.ts and adding tests to verify the fix, with no unrelated modifications.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ 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 edison/fix-hydration-mismatch-log

---

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commit: b50e0b2