fix(compiler-core): ignore whitespace when matching adjacent v-if #12321

edison1105 · 2024-11-04T12:58:39Z

Summary by CodeRabbit

Bug Fixes
- Improved detection of adjacent v-if directives for named slots with v-else by ignoring whitespace-only nodes, ensuring more accurate slot transformation.
Tests
- Added a new test case for named slots using v-if and v-else directives to verify correct behavior.

github-actions · 2024-11-04T12:59:41Z

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	101 kB	38.3 kB	34.5 kB
vue.global.prod.js	159 kB (+12 B)	58.5 kB (+8 B)	52.1 kB (+40 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.6 kB	18.2 kB	16.6 kB
createApp	54.5 kB	21.2 kB	19.4 kB
createSSRApp	58.8 kB	23 kB	20.9 kB
defineCustomElement	59.5 kB	22.8 kB	20.8 kB
overall	68.6 kB	26.4 kB	24.1 kB

pkg-pr-new · 2024-11-04T12:59:52Z

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commit: bbaa005

vidal7 · 2025-01-23T19:24:37Z

Hello. Do you think this PR can be merged soon? I have the issue that this PR is fixing when migrating large Vue 2 repo to Vue 3. I want to preserve the behavior of whitespace config of Vue 2 on Vue 3

vidal7 · 2025-05-12T18:37:50Z

No news? It is still preventing us migrating our large repo to Vue 3 without having visual regressions.

vidal7 · 2025-05-23T18:45:21Z

@edison1105, is this something preventing you for submiting this PR to reviewers? I would very like this PR being merged.

coderabbitai · 2025-06-04T09:14:13Z

Walkthrough

A new test was added to verify correct handling of named slots with v-if and v-else directives when whitespace is preserved. The slot transformation logic was updated to ensure the compiler skips over whitespace-only nodes (in addition to comments) when searching for an adjacent v-if before an v-else slot.

Changes

File(s)	Change Summary
`packages/compiler-core/__tests__/transforms/vSlot.spec.ts`	Added test for named slots with `v-if` and `v-else` using `whitespace: 'preserve'`.
`packages/compiler-core/src/transforms/vSlot.ts`	Refined loop to skip whitespace-only nodes (and comments) when searching for adjacent `v-if`.

Sequence Diagram(s)

sequenceDiagram
    participant Parser
    participant Transformer
    participant SlotNode

    Parser->>Transformer: Parse template with v-if/v-else slots (whitespace: 'preserve')
    Transformer->>SlotNode: Iterate backwards to find adjacent v-if for v-else slot
    Note right of Transformer: Skips comments and whitespace-only nodes
    Transformer->>SlotNode: Associates v-else slot with correct v-if slot

Assessment against linked issues

Objective	Addressed	Explanation
Fix compiler error when using v-slot with v-if/v-else(-if) and whitespace: "preserve" (#9173)	✅

Assessment against linked issues: Out-of-scope changes

No out-of-scope changes found.

Poem

In the garden of slots, where whitespace grew,
The v-if and v-else now know what to do.
Skipping blank leaves and commenty dew,
The compiler hops on, its logic anew.
🐇✨ No errors in sight, just templates that flow—
The rabbit approves, with a satisfied glow!

📜 Recent review details

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Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between e53a4ff and 5cc3a7a.

⛔ Files ignored due to path filters (1)

packages/compiler-core/__tests__/transforms/__snapshots__/vSlot.spec.ts.snap is excluded by !**/*.snap

📒 Files selected for processing (2)

packages/compiler-core/__tests__/transforms/vSlot.spec.ts (1 hunks)
packages/compiler-core/src/transforms/vSlot.ts (1 hunks)

⏰ Context from checks skipped due to timeout of 90000ms (3)

GitHub Check: Redirect rules
GitHub Check: Header rules
GitHub Check: Pages changed

🔇 Additional comments (2)

packages/compiler-core/src/transforms/vSlot.ts (1)

225-225: LGTM! Correctly implements whitespace-aware adjacent v-if detection.

This change properly extends the logic to skip over whitespace-only nodes (in addition to comments) when searching for adjacent v-if directives before v-else(-if) slots. The modification ensures that the compiler preserves Vue 2's whitespace handling behavior during migration to Vue 3, which addresses the core issue described in the PR.

The use of isNonWhitespaceContent(prev) is appropriate as it correctly identifies nodes that contain meaningful content versus whitespace-only text nodes.

packages/compiler-core/__tests__/transforms/vSlot.spec.ts (1)

992-1004: Excellent test coverage for the whitespace-aware v-if detection.

This test case effectively validates the core functionality addressed by this PR:

Comprehensive scenario: Tests named slots with v-if + v-else directives separated by whitespace

Critical options: Uses whitespace: 'preserve' which is essential for reproducing the Vue 2 migration issue

Proper validation: Snapshot testing ensures consistent code generation behavior

The test directly covers the edge case where whitespace between conditional slot templates could break adjacent directive detection, which was the root cause of the migration blocker described in the PR comments.

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vidal7 · 2025-06-05T11:44:54Z

Very much appreciated @edison1105. Thanks!

fix(compiler-core): handle named slot + v-if with preserve whitespace

aeaf100

edison1105 added ready to merge The PR is ready to be merged. scope: compiler 🍰 p2-nice-to-have Priority 2: this is not breaking anything but nice to have it addressed. labels Nov 4, 2024

edison1105 added 🔨 p3-minor-bug Priority 3: this fixes a bug, but is an edge case that only affects very specific usage. and removed 🍰 p2-nice-to-have Priority 2: this is not breaking anything but nice to have it addressed. labels Feb 18, 2025

vidal7 mentioned this pull request May 12, 2025

vue-template-compiler: whitespace "preserve" option causes compiler error when using v-slot with v-if/v-else-if/v-else #9173

Closed

edison1105 changed the title ~~fix(compiler-core): handle named slot + v-if with preserve whitespace~~ fix(compiler-core): ignore whitespace when matching adjacent v-if Jun 4, 2025

Merge branch 'main' into edison/fix/9173

5cc3a7a

Merge branch 'main' into edison/fix/9173

bbaa005

edison1105 merged commit 10ebcef into main Jun 5, 2025
16 checks passed

edison1105 deleted the edison/fix/9173 branch June 5, 2025 01:44

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