fix(types): enable proper type narrowing for defineEmits (#13935)

[tuzixiangs]

close #13935

This PR fixes the type narrowing issue with defineEmits when using type-based declaration.

Summary by CodeRabbit

• Refactor

  • Improved type inference and streamlined internal type definitions for event emission handling in defineEmits.

• Tests

  • Added comprehensive type-checking test coverage for defineEmits with type declarations to ensure correct payload types and event names are enforced.

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[coderabbitai]

Walkthrough

The ShortEmits type in the runtime-core package is refactored from a complex intersection-based construction to a straightforward generic function signature. This change enables proper TypeScript type narrowing when using defineEmits with event declarations, allowing the compiler to correctly infer payload types for specific event keys. Type-checking tests are added to validate the narrowing behavior.

Changes

Cohort / File(s)	Summary
Type definition refactoring packages/runtime-core/src/apiSetupHelpers.ts	Replaced complex ShortEmits type using UnionToIntersection<RecordToUnion<...>> with a simple generic function signature <K extends keyof T>(evt: K, ...args: T[K]) => void. Removed helper types RecordToUnion and import of UnionToIntersection from shared utilities.
Type-checking tests packages-private/dts-test/setupHelpers.test-d.ts	Added new test block validating defineEmits type narrowing for Issue #13935, including correct emit calls with specific payload types and @ts-expect-error cases for incorrect usages.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

• Focused change affecting one core type definition with clear before/after semantics
• Type system changes require careful verification that the new signature properly enables narrowing
• Added tests provide direct validation of expected behavior
• Areas needing attention: Verify that the new type signature correctly narrows in real-world TypeScript scenarios; confirm backward compatibility with existing defineEmits usage

Poem

🐰 A simpler path for types to trace,
No intersection loops—just function's grace,
When "open" calls, the args align,
No more ambiguous—the types now shine! ✨

Pre-merge checks and finishing touches

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: fixing type narrowing for defineEmits to properly resolve event-specific argument types.
Linked Issues check	✅ Passed	The PR directly addresses issue #13935 by replacing the complex UnionToIntersection-based ShortEmits type with a straightforward generic function signature that enables proper type narrowing for event names and their corresponding argument types.
Out of Scope Changes check	✅ Passed	All changes are scoped to the defineEmits type system; the main file modifies ShortEmits type definition and the test file adds type-checking tests validating the fix.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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📜 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 ebc4f0f and ba68414.

📒 Files selected for processing (1)

• packages-private/dts-test/setupHelpers.test-d.ts (1 hunks)

🧰 Additional context used

🧬 Code graph analysis (1)

packages-private/dts-test/setupHelpers.test-d.ts (1)

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

• defineEmits (144-149)

🔇 Additional comments (1)

packages-private/dts-test/setupHelpers.test-d.ts (1)

636-653: Test structure is appropriate for validating type narrowing behavior.

The test correctly uses @ts-expect-error guards to validate that defineEmits with mapped event signatures properly enforces type checking for both correct payload types (emit('open', 123), emit('close', 'abc')) and rejects invalid cases (wrong payload types and unknown events). The test follows the established pattern in the file and adequately validates the fix for issue #13935.

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[spaansba]

Would it be possible to still have 'open' / 'close' instead of evt: keyof __VLS_Emit

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	103 kB	39 kB	35.1 kB
vue.global.prod.js	161 kB	58.9 kB	52.6 kB

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	47 kB	18.3 kB	16.8 kB
createApp	55.1 kB	21.4 kB	19.6 kB
createSSRApp	59.4 kB	23.2 kB	21.1 kB
defineCustomElement	60.7 kB	23.1 kB	21.1 kB
overall	69.4 kB	26.6 kB	24.3 kB