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

Author: tuzixiangs

packages-private/dts-test/issue-13935.test-d.ts

@@ -0,0 +1,21 @@
+import { defineEmits } from 'vue'
+import { describe } from './utils'
+
+describe('defineEmits w/ type declaration (Issue #13935)', () => {
+  const emit = defineEmits<{
+    open: [payload: number]
+    close: [payload: string]
+  }>()
+
+  // Correct usages
+  emit('open', 123)
+  emit('close', 'abc')
+
+  // Incorrect usages (should fail type check)
+  // @ts-expect-error
+  emit('open', 'string')
+  // @ts-expect-error
+  emit('close', 123)
+  // @ts-expect-error
+  emit('unknown', 123)
+})

packages/runtime-core/src/apiSetupHelpers.ts

@@ -2,7 +2,6 @@ import {
   type IfAny,
   type LooseRequired,
   type Prettify,
-  type UnionToIntersection,
   extend,
   isArray,
   isFunction,
@@ -151,13 +150,10 @@ export function defineEmits() {
 
 export type ComponentTypeEmits = ((...args: any[]) => any) | Record<string, any>
 
-type RecordToUnion<T extends Record<string, any>> = T[keyof T]
-
-type ShortEmits<T extends Record<string, any>> = UnionToIntersection<
-  RecordToUnion<{
-    [K in keyof T]: (evt: K, ...args: T[K]) => void
-  }>
->
+type ShortEmits<T extends Record<string, any>> = <K extends keyof T>(
+  evt: K,
+  ...args: T[K]
+) => void
 
 /**
  * Vue `<script setup>` compiler macro for declaring a component's exposed