fix(compiler-sfc): properly analyze patch flag of vFor + (ref or vnodeHook or dir)

[edison1105]

close #9239 close #12569

I’m not sure if this change is correct. Here is my understanding: When an element uses ref, vnodeHook, or custom directives, the patchFlag should be NEED_PATCH. However, when they are used together with v-for, the patchFlag gets lost. related commit https://github.com/vuejs/core/commit/1c9a4810fcdd2b6c1c6c3be077aebbecbfcbcf1e

playground playground with this PR

The following problems will be fixed

• vFor + ref / with this PR
• vFor + ref(function) / with this PR
• vFor + vnode hook / with this PR
• vFor + custom directive / with this PR
  • #12569

The last two are from https://github.com/vuejs/core/pull/9240#discussion_r1348179952 created by skirtles-code

Summary by CodeRabbit

• Bug Fixes
  • Improved detection of elements requiring the NEED_PATCH flag when using v-for with static or setup-bound ref, custom directives, or vnode hooks.
• Tests
  • Added new test cases to ensure correct patch flag assignment for elements with v-for combined with various features.

[github-actions[bot]]

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 (+7 B)	58.4 kB (+3 B)	52 kB (+80 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	58.7 kB	23 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: 4780e7c

[edison1105]

/ecosystem-ci run

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[coderabbitai[bot]]

Walkthrough

The changes update the patch flag analysis in the element transform logic to ensure that ref props inside v-for are not skipped when determining if the NEED_PATCH flag is required. New tests are added to verify that elements with v-for and certain features correctly receive the NEED_PATCH flag.

Changes

File(s)	Change Summary
packages/compiler-core/src/transforms/transformElement.ts	Refined patch flag analysis: ref props are no longer skipped as constant, ensuring correct patch flag logic. Removed a redundant condition involving shouldUseBlock.
packages/compiler-core/tests/transforms/transformElement.spec.ts	Added four new test cases to verify NEED_PATCH flag for elements with v-for and static/bound ref, custom directives, or vnode hooks.

Sequence Diagram(s)

sequenceDiagram
    participant Template
    participant Compiler
    participant PatchFlagAnalyzer

    Template->>Compiler: Template with v-for and ref/custom directive
    Compiler->>PatchFlagAnalyzer: Analyze element props and directives
    PatchFlagAnalyzer-->>Compiler: Detects 'ref' in v-for, sets NEED_PATCH flag
    Compiler-->>Template: Generates code with correct patch flags

Assessment against linked issues

Objective	Addressed	Explanation
Ensure that ref attributes inside v-for elements trigger correct patching and do not accumulate refs incorrectly (#9239)	✅
Ensure that custom directive unmounted hooks are triggered on v-for elements by setting proper patch flags (#12569)	✅

Suggested labels

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

Poem

A patch for the patch flag, oh what a delight!
Now refs in v-for will behave just right.
Directives and hooks, all get their due,
No more ref arrays endlessly grew!
🐇 With each test that passes, we hop with glee—
The code is now bug-free, as it should be!

---

📜 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 1f98a9c493d01c21befa90107f0593bc92a58932 and 4780e7c64dc9befa7208bdff98bfc1524530b3c8.

⛔ Files ignored due to path filters (2)

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

📒 Files selected for processing (2)

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

🔇 Additional comments (5)

packages/compiler-core/__tests__/transforms/transformElement.spec.ts (4)

1031-1036: Good addition of test case for vFor + static ref.

This test case validates that elements with v-for directive and a static ref attribute correctly receive the NEED_PATCH flag, which is essential for proper rendering.

---

1038-1043: Good addition of test case for vFor + custom directives.

This test ensures that when an element uses both v-for and a custom directive, the correct NEED_PATCH flag is applied, which was missing in the previous implementation.

---

1045-1055: Good addition of test case for vFor + vnode hooks.

This test properly verifies that elements with both v-for and vnode hooks (like @vue:updated) correctly receive the NEED_PATCH flag. The test uses baseCompile with appropriate options, which is the right approach for testing hooks.

---

1057-1069: Good addition of test case for vFor + setup function ref.

This comprehensive test verifies that elements with v-for and a dynamic :ref bound to a setup function (constant) correctly receive the NEED_PATCH flag. The test properly simulates a real-world scenario with binding metadata configuration.

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

459-465: Fix ensures proper patch flag analysis for refs in v-for context.

The changes here correctly fix the issue by preventing the compiler from skipping ref props during patch flag analysis, even when they have constant values. This ensures that elements with both v-for and refs (especially those bound to setup functions) correctly receive the NEED_PATCH flag.

The updated comment clearly explains the logic: props are skipped only if they are cached handlers or have constant values, with a specific exclusion for :ref="setRefFn" which is a setup-const that still needs to trigger patching.

✨ Finishing Touches

• [ ] 📝 Generate Docstrings

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