fix(hydration): handle empty content in Transition appear edge case #13396

edison1105 · 2025-05-28T00:13:59Z

Summary by CodeRabbit

Bug Fixes
- Improved node replacement logic to prevent errors when no new node is provided, ensuring smoother updates and reducing potential issues during hydration.
Tests
- Added a test to verify correct handling of transitions with empty content during hydration, preventing mismatch warnings.

coderabbitai · 2025-05-28T00:14:05Z

"""

Walkthrough

The replaceNode function in the hydration logic was updated to check if the new node exists before attempting to replace the old node. If the new node is absent, the old node is simply removed, preventing errors from invalid node replacements during server-side rendering hydration. Additionally, a new test verifies that the <Transition appear> component correctly handles empty content during hydration without errors.

Changes

File(s)	Change Summary
packages/runtime-core/src/hydration.ts	Updated `replaceNode` to check for a valid new node before replacing, else remove the old node.
packages/runtime-core/tests/hydration.spec.ts	Added test for `<Transition appear>` with empty content to ensure no hydration errors occur.

Sequence Diagram(s)

sequenceDiagram
    participant ParentNode
    participant OldNode
    participant NewNode

    alt NewNode exists
        ParentNode->>ParentNode: replaceChild(NewNode, OldNode)
    else NewNode is null/undefined
        ParentNode->>ParentNode: removeChild(OldNode)
    end

Assessment against linked issues

Objective	Addressed	Explanation
Prevent SSR hydration error when replacing node with empty/invalid content (#13394)	✅

Suggested labels

ready to merge, :hammer: p3-minor-bug

Poem

A hop, a skip, a gentle patch,
No more errors when nodes don’t match!
If new is missing, old hops away,
Hydration’s smooth, hooray, hooray!
With careful checks and tidy code,
This bunny’s proud of what’s bestowed. 🐇✨
"""

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Reviewing files that changed from the base of the PR and between a890378 and bd7d569.

📒 Files selected for processing (1)

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

🔇 Additional comments (1)

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

1680-1697: LGTM! Well-written test case for the empty content edge case.

This test properly covers the specific edge case mentioned in issue #13394 where a Transition with appear: true has empty content. The test:

Correctly sets up the scenario with empty template and null default slot

Uses appropriate assertions to verify the DOM state and vnode element reference

Importantly checks that no hydration mismatch warnings are emitted

Follows the existing test patterns and fits well within the transition test suite

The test complements the related fix in the replaceNode function and ensures that empty content during Transition appear is handled correctly during hydration.

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pkg-pr-new · 2025-05-28T00:15:31Z

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commit: bd7d569

github-actions · 2025-05-28T00:15:35Z

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	101 kB (+9 B)	38.3 kB (+7 B)	34.5 kB (+19 B)
vue.global.prod.js	159 kB (+9 B)	58.5 kB (+8 B)	52.1 kB (+50 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.6 kB	18.2 kB	16.7 kB
createApp	54.5 kB	21.2 kB	19.4 kB
createSSRApp	58.8 kB (+9 B)	23 kB (+6 B)	21 kB (+5 B)
defineCustomElement	59.5 kB	22.8 kB	20.8 kB
overall	68.6 kB	26.4 kB	24 kB

fix(hydration): handle empty content in Transition appear edge case

a890378

test: add test

bd7d569

edison1105 added scope: transition 🔨 p3-minor-bug Priority 3: this fixes a bug, but is an edge case that only affects very specific usage. scope:hydration ready to merge The PR is ready to be merged. labels May 28, 2025

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