fix(types): handle union types in generic parameter (#2794)

Fix #2785

Author: jh-leong

packages/pinia/src/storeToRefs.ts

@@ -68,9 +68,11 @@ type _ToStateRefs<SS> =
  * Extracts the return type for `storeToRefs`.
  * Will convert any `getters` into `ComputedRef`.
  */
-export type StoreToRefs<SS extends StoreGeneric> = _ToStateRefs<SS> &
-  ToRefs<PiniaCustomStateProperties<StoreState<SS>>> &
-  _ToComputedRefs<StoreGetters<SS>>
+export type StoreToRefs<SS extends StoreGeneric> = SS extends unknown
+  ? _ToStateRefs<SS> &
+      ToRefs<PiniaCustomStateProperties<StoreState<SS>>> &
+      _ToComputedRefs<StoreGetters<SS>>
+  : never
 
 /**
  * Creates an object of references with all the state, getters, and plugin-added

packages/pinia/test-dts/store.test-d.ts

@@ -5,7 +5,7 @@ import {
   expectType,
   storeToRefs,
 } from './'
-import { computed, ref, UnwrapRef, watch } from 'vue'
+import { computed, Ref, ref, UnwrapRef, watch, WritableComputedRef } from 'vue'
 
 const useStore = defineStore({
   id: 'name',
@@ -328,3 +328,12 @@ expectType<number>(refs.bananasAmount.value)
 refs.bananasAmount.value = 0
 // @ts-expect-error: this one is readonly
 refs.total.value = 0
+
+const refStore = defineStore('ref-bananas', () => {
+  const bananas = ref(['banana1', 'banana2'])
+  return { bananas }
+})()
+declare const conditionalStore: typeof refStore | typeof writableComputedStore
+expectType<Ref<string[]> | WritableComputedRef<'banana'[]>>(
+  storeToRefs(conditionalStore).bananas
+)