fix(types): prevent shallowReactive marker from leaking into value unions

[edison1105]

close #14490

Summary by CodeRabbit

• Bug Fixes
  • Corrected type behavior for shallow reactive objects to properly handle marker propagation in type unions.

[coderabbitai]

📝 Walkthrough

Walkthrough

Fixes a TypeScript typing issue where the ShallowReactive marker was leaking into union types, causing incorrect type errors. The marker type is changed from an optional boolean to a required never property, with corresponding unwrapping logic updates to correctly handle the new signature.

Changes

Cohort / File(s)	Summary
ShallowReactive Type Signature packages/reactivity/src/reactive.ts	Changed ShallowReactive marker from optional boolean ([ShallowReactiveMarker]?: true) to required never ([ShallowReactiveMarker]: never) to prevent marker leakage into value unions.
Type Unwrapping Logic packages/reactivity/src/ref.ts	Updated UnwrapRefSimple type branching to match the new required marker property, adjusting when shallow reactive objects short-circuit unwrapping versus proceeding through general object unwrapping paths.
Test Coverage packages-private/dts-test/reactivity.test-d.ts	Added test case verifying that the ShallowReactive marker does not leak into value unions, confirming correct type narrowing for properties in shallow reactive objects.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• vuejs/core#12420: Modifies the same ref/unwrapping type-level logic for shallowReactive in packages/reactivity (ref.ts/reactive.ts).

Suggested labels

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

Poem

🐰 A marker once hid in the union's dark fold,
Making types misbehave, oh what a scold!
But clever word "never" set things right,
Now shallowReactive glows pure and bright! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Linked Issues check	✅ Passed	The pull request addresses the core issue #14490 by changing ShallowReactiveMarker from optional true to required never, preventing the marker from leaking into v-for type inference for shallowReactive objects.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the shallowReactive typing issue: marker type definition, UnwrapRefSimple logic, and a test case validating the fix.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title 'prevent shallowReactive marker from leaking into value unions' directly and clearly summarizes the main change across the PR: modifying the ShallowReactive marker from optional to required to prevent it from appearing in union types during iteration.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch edison/fix/14490

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[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	104 kB	39.3 kB	35.4 kB
vue.global.prod.js	162 kB	59.3 kB	52.8 kB

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	47.8 kB	18.6 kB	17.1 kB
createApp	56 kB	21.7 kB	19.8 kB
createSSRApp	60.2 kB	23.4 kB	21.4 kB
defineCustomElement	61.6 kB	23.4 kB	21.4 kB
overall	70.4 kB	27 kB	24.6 kB

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commit: 7c14ef3

[edison1105]

/ecosystem-ci run

[vue-bot]

📝 Ran ecosystem CI: Open

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

[edison1105]

/ecosystem-ci run vuetify

[vue-bot]

📝 Ran ecosystem CI: Open

suite	result	latest scheduled
vuetify	❌ failure	✅ success