feat: useStorage generic support (#1279)

docs/content/1.guide/4.storage.md

@@ -70,6 +70,22 @@ await useStorage().setItem('redis:foo', { hello: 'world' })
 await useStorage().getItem('redis:foo')
 ```
 
+Usage with [generics](https://unstorage.unjs.io/usage#type-inference):
+
+```ts
+await useStorage().getItem<string>('foo')
+// => string
+await useStorage<string>().getItem('foo')
+// => string
+
+await useStorage<string>().setItem('foo', 123) // ts error
+
+type Foo = { data: number }
+
+await useStorage().getItem<Foo>('foo')
+// => Foo
+```
+
 You can find the list of drivers on [unstorage documentation](https://unstorage.unjs.io/).
 
 In development, Nitro adds the `cache` mountpoint using the [FS driver](https://unstorage.unjs.io/drivers/fs) writting to `.nitro/cache` or `.nuxt/cache` if using [Nuxt](https://nuxt.com).

src/runtime/storage.ts

@@ -1,7 +1,9 @@
-import type { Storage } from "unstorage";
+import type { Storage, StorageValue } from "unstorage";
 import { prefixStorage } from "unstorage";
 import { storage } from "#internal/nitro/virtual/storage";
 
-export function useStorage(base = ""): Storage {
-  return base ? prefixStorage(storage, base) : storage;
+export function useStorage<T extends StorageValue = StorageValue>(
+  base = ""
+): Storage<T> {
+  return base ? prefixStorage<T>(storage, base) : storage;
 }