fix(persist): fix async migrate on persist middleware

src/middleware/persist.ts

@@ -258,13 +258,14 @@ const persistImpl: PersistImpl = (config, baseOptions) => (set, get, api) => {
             deserializedStorageValue.version !== options.version
           ) {
             if (options.migrate) {
-              return [
-                true,
-                options.migrate(
-                  deserializedStorageValue.state,
-                  deserializedStorageValue.version,
-                ),
-              ] as const
+              const migration = options.migrate(
+                deserializedStorageValue.state,
+                deserializedStorageValue.version,
+              )
+              if (migration instanceof Promise) {
+                return migration.then((result) => [true, result] as const)
+              }
+              return [true, migration] as const
             }
             console.error(
               `State loaded from storage couldn't be migrated since no migrate function was provided`,

tests/persistAsync.test.tsx

@@ -193,10 +193,10 @@ describe('persist middleware with async configuration', () => {
     })
   })
 
-  it('can migrate persisted state', async () => {
+  it('can async migrate persisted state', async () => {
     const setItemSpy = vi.fn()
     const onRehydrateStorageSpy = vi.fn()
-    const migrateSpy = vi.fn(() => ({ count: 99 }))
+    const migrateSpy = vi.fn(() => Promise.resolve({ count: 99 }))
 
     const storage = {
       getItem: async () =>

tests/persistSync.test.tsx

@@ -131,7 +131,7 @@ describe('persist middleware with sync configuration', () => {
     expect(onRehydrateStorageSpy2).toBeCalledWith({ count: 42 }, undefined)
   })
 
-  it('can migrate persisted state', () => {
+  it('can non-async migrate persisted state', () => {
     const setItemSpy = vi.fn()
     const onRehydrateStorageSpy = vi.fn()
     const migrateSpy = vi.fn(() => ({ count: 99 }))