fix(hmr): avoid hydration for hmr updating

[edison1105]

close #7706
close #8170

Summary by CodeRabbit

• Tests

  • Added a new test to verify Hot Module Replacement (HMR) reload functionality for child components wrapped in KeepAlive during SSR hydration.

• Refactor

  • Adjusted the timing of hydration avoidance for HMR updates to ensure it occurs earlier during component mounting.

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	101 kB	38.2 kB	34.4 kB
vue.global.prod.js	159 kB	58.4 kB	51.9 kB

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.5 kB	18.2 kB	16.6 kB
createApp	54.5 kB	21.2 kB	19.4 kB
createSSRApp	58.7 kB	22.9 kB	20.9 kB
defineCustomElement	59.3 kB	22.8 kB	20.8 kB
overall	68.6 kB	26.4 kB	24 kB

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commit: ee8dc27

[coderabbitai]

Walkthrough

The changes introduce a new SSR hydration test validating HMR reload behavior for child components wrapped in KeepAlive. Additionally, the hydration avoidance logic for HMR updating is repositioned in the mountComponent function to occur earlier, ensuring hydration is skipped during HMR reload regardless of async dependencies.

Changes

File(s)	Change Summary
packages/runtime-core/__tests__/hydration.spec.ts	Added a test case for HMR reload of a child component wrapped in KeepAlive during SSR hydration.
packages/runtime-core/src/renderer.ts	Moved the conditional that sets initialVNode.el = null for HMR updating to occur earlier in mountComponent.

Sequence Diagram(s)

sequenceDiagram
    participant TestRunner as Test Runner
    participant App as Parent App
    participant Child as Child Component
    participant HMR as HMR Runtime

    TestRunner->>App: Render to string (SSR)
    App->>Child: Render Child
    TestRunner->>App: Mount on root (hydrate)
    App->>Child: Hydrate Child (wrapped in KeepAlive)
    TestRunner->>HMR: Call reload with new Child definition
    HMR->>App: Trigger reload
    App->>Child: Replace with new definition
    TestRunner->>App: Wait for next tick
    App->>Child: Render with new template

Loading

Assessment against linked issues

Objective	Addressed	Explanation
Ensure HMR does not perform hydration during reload, preventing removal of SSR content (#7706, #8170)	✅
Add regression test for HMR reload of child in KeepAlive during SSR hydration (#7706, #8170)	✅

Poem

A bunny hopped through code so bright,
Ensuring HMR would work just right.
With tests for KeepAlive in tow,
SSR and reloads now smoothly flow.
Hydration bugs, we bid adieu—
The patch is in, thanks to the Vue!
🐇✨

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📥 Commits

Reviewing files that changed from the base of the PR and between 258f78b and ee8dc27.

📒 Files selected for processing (2)

• packages/runtime-core/__tests__/hydration.spec.ts (2 hunks)
• packages/runtime-core/src/renderer.ts (1 hunks)

🧰 Additional context used

🧬 Code Graph Analysis (1)

packages/runtime-core/src/renderer.ts (1)

packages/runtime-core/src/hmr.ts (1)

• isHmrUpdating (15-15)

⏰ Context from checks skipped due to timeout of 90000ms (2)

• GitHub Check: test / unit-test-windows
• GitHub Check: test / e2e-test

🔇 Additional comments (2)

packages/runtime-core/src/renderer.ts (1)

1211-1212: Well-placed optimization for HMR hydration avoidance

Moving this condition earlier in the mountComponent function ensures that hydration is skipped during HMR updates regardless of whether the component has async dependencies. This fixes the issue where components wrapped in KeepAlive weren't updating correctly when HMR updates were triggered.

The previous placement inside the async dependency check block meant this optimization only applied conditionally, leading to issues #7706 and #8170.

packages/runtime-core/__tests__/hydration.spec.ts (1)

1849-1881: Good test case that validates the bug fix

This test correctly validates the fix for HMR updates within components wrapped in KeepAlive during SSR hydration. It:

1. Creates a child component with an HMR ID
2. Registers it with the HMR runtime
3. Creates a parent app wrapping the child in KeepAlive
4. Tests both initial SSR hydration and HMR updates
5. Verifies that DOM updates correctly reflect the template changes after HMR reload

The test demonstrates that the change in mountComponent function properly addresses the issue where HMR updates weren't being reflected for components inside KeepAlive.

✨ Finishing Touches

• 📝 Generate Docstrings

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[edison1105]

/ecosystem-ci run

[vue-bot]

📝 Ran ecosystem CI: Open

suite	result	latest scheduled
pinia	✅ success	✅ success
nuxt	✅ success	✅ success
primevue	✅ success	✅ success
language-tools	✅ success	✅ success
router	✅ success	✅ success
test-utils	✅ success	✅ success
vant	✅ success	✅ success
vue-macros	✅ success	✅ success
vuetify	✅ success	✅ success
quasar	✅ success	✅ success
vueuse	✅ success	✅ success
vue-i18n	✅ success	✅ success
radix-vue	✅ success	✅ success
vitepress	✅ success	✅ success
vue-simple-compiler	✅ success	✅ success
vite-plugin-vue	✅ success	✅ success