fix(types): correct withDefaults return type for boolean prop with undefined default value (#8602)

packages/dts-test/setupHelpers.test-d.ts

@@ -134,6 +134,26 @@ describe('defineProps w/ generic type declaration + withDefaults', <T extends nu
   expectType<boolean>(res.bool)
 })
 
+describe('withDefaults w/ boolean type', () => {
+  const res1 = withDefaults(
+    defineProps<{
+      bool?: boolean
+    }>(),
+    { bool: false }
+  )
+  expectType<boolean>(res1.bool)
+
+  const res2 = withDefaults(
+    defineProps<{
+      bool?: boolean
+    }>(),
+    {
+      bool: undefined
+    }
+  )
+  expectType<boolean | undefined>(res2.bool)
+})
+
 describe('defineProps w/ runtime declaration', () => {
   // runtime declaration
   const props = defineProps({

packages/runtime-core/src/apiSetupHelpers.ts

@@ -303,7 +303,13 @@ type PropsWithDefaults<
       ? T[K]
       : NotUndefined<T[K]>
     : never
-} & { readonly [K in BKeys]-?: boolean }
+} & {
+  readonly [K in BKeys]-?: K extends keyof Defaults
+    ? Defaults[K] extends undefined
+      ? boolean | undefined
+      : boolean
+    : boolean
+}
 
 /**
  * Vue `<script setup>` compiler macro for providing props default values when