fix(types): allow nonpromise return types for static functions (verce…

…l#24685)

## Bug

- [x] fixes vercel#24684
- [x] Integration tests added

Intentionally omitted changing the types for `GetServerSideProps` etc. as its imo less reasonable to leverage SSR with a sync `getServerSideProps`. Can of course change the type too if you consider that also a valid case.

packages/next/types/index.d.ts

@@ -109,13 +109,15 @@ export type GetStaticPropsResult<P> =
 export type GetStaticProps<
   P extends { [key: string]: any } = { [key: string]: any },
   Q extends ParsedUrlQuery = ParsedUrlQuery
-> = (context: GetStaticPropsContext<Q>) => Promise<GetStaticPropsResult<P>>
+> = (
+  context: GetStaticPropsContext<Q>
+) => Promise<GetStaticPropsResult<P>> | GetStaticPropsResult<P>
 
 export type InferGetStaticPropsType<T> = T extends GetStaticProps<infer P, any>
   ? P
   : T extends (
       context?: GetStaticPropsContext<any>
-    ) => Promise<GetStaticPropsResult<infer P>>
+    ) => Promise<GetStaticPropsResult<infer P>> | GetStaticPropsResult<infer P>
   ? P
   : never
 
@@ -131,7 +133,7 @@ export type GetStaticPathsResult<P extends ParsedUrlQuery = ParsedUrlQuery> = {
 
 export type GetStaticPaths<P extends ParsedUrlQuery = ParsedUrlQuery> = (
   context: GetStaticPathsContext
-) => Promise<GetStaticPathsResult<P>>
+) => Promise<GetStaticPathsResult<P>> | GetStaticPathsResult<P>
 
 export type GetServerSidePropsContext<
   Q extends ParsedUrlQuery = ParsedUrlQuery

test/integration/typescript/test/index.test.js

@@ -111,5 +111,16 @@ export default function EvilPage(): JSX.Element {
         errorPage.restore()
       }
     })
+
+    it('should compile sync getStaticPaths & getStaticProps', async () => {
+      const page = new File(join(appDir, 'pages/ssg/[slug].tsx'))
+      try {
+        page.replace(/async \(/g, '(')
+        const output = await nextBuild(appDir, [], { stdout: true })
+        expect(output.stdout).toMatch(/Compiled successfully/)
+      } finally {
+        page.restore()
+      }
+    })
   })
 })