type: extends useConfig cache interface (vercel#1938)

src/types.ts

@@ -17,8 +17,8 @@ export type Fetcher<
   : never
 
 // Configuration types that are only used internally, not exposed to the user.
-export interface InternalConfiguration {
-  cache: Cache
+export interface InternalConfiguration<T extends Cache = Cache> {
+  cache: T
   mutate: ScopedMutator
 }
 
@@ -77,7 +77,8 @@ export interface PublicConfiguration<
   isVisible: () => boolean
 }
 
-export type FullConfiguration = InternalConfiguration & PublicConfiguration
+export type FullConfiguration<T extends Cache = Cache> =
+  InternalConfiguration<T> & PublicConfiguration
 
 export type ProviderConfiguration = {
   initFocus: (callback: () => void) => (() => void) | void

src/utils/use-swr-config.ts

@@ -2,8 +2,10 @@ import { useContext } from 'react'
 import { defaultConfig } from './config'
 import { SWRConfigContext } from './config-context'
 import { mergeObjects } from './helper'
-import { FullConfiguration } from '../types'
+import { FullConfiguration, Cache } from '../types'
 
-export const useSWRConfig = (): FullConfiguration => {
+export const useSWRConfig = <
+  T extends Cache = Map<string, any>
+>(): FullConfiguration<T> => {
   return mergeObjects(defaultConfig, useContext(SWRConfigContext))
 }

test/type/config.ts

@@ -0,0 +1,12 @@
+import { useSWRConfig, Cache } from 'swr'
+import { expectType } from './utils'
+
+interface CustomCache<Data = any> extends Cache<Data> {
+  reset(): void
+}
+
+export function useTestCache() {
+  expectType<Map<string, any>>(useSWRConfig().cache)
+  expectType<Map<string, number>>(useSWRConfig<Map<string, number>>().cache)
+  expectType<CustomCache>(useSWRConfig<CustomCache>().cache)
+}