Improve type for GSP return type (#18285)

packages/next/next-server/server/render.tsx

@@ -636,7 +636,7 @@ export async function renderToHTML(
         throw new Error(invalidKeysMsg('getStaticProps', invalidKeys))
       }
 
-      if (data.unstable_notFound) {
+      if ('unstable_notFound' in data && data.unstable_notFound) {
         if (pathname === '/404') {
           throw new Error(
             `The /404 page can not return unstable_notFound in "getStaticProps", please remove it to continue!`
@@ -649,6 +649,7 @@ export async function renderToHTML(
       }
 
       if (
+        'unstable_redirect' in data &&
         data.unstable_redirect &&
         typeof data.unstable_redirect === 'object'
       ) {
@@ -662,7 +663,7 @@ export async function renderToHTML(
         }
 
         if (isDataReq) {
-          data.props = {
+          ;(data as any).props = {
             __N_REDIRECT: data.unstable_redirect.destination,
           }
         } else {
@@ -673,7 +674,7 @@ export async function renderToHTML(
 
       if (
         (dev || isBuildTimeSSG) &&
-        !isSerializableProps(pathname, 'getStaticProps', data.props)
+        !isSerializableProps(pathname, 'getStaticProps', (data as any).props)
       ) {
         // this fn should throw an error instead of ever returning `false`
         throw new Error(
@@ -681,7 +682,7 @@ export async function renderToHTML(
         )
       }
 
-      if (typeof data.revalidate === 'number') {
+      if ('revalidate' in data && typeof data.revalidate === 'number') {
         if (!Number.isInteger(data.revalidate)) {
           throw new Error(
             `A page's revalidate option must be seconds expressed as a natural number. Mixed numbers, such as '${data.revalidate}', cannot be used.` +
@@ -702,20 +703,25 @@ export async function renderToHTML(
               `\nTo only run getStaticProps at build-time and not revalidate at runtime, you can set \`revalidate\` to \`false\`!`
           )
         }
-      } else if (data.revalidate === true) {
+      } else if ('revalidate' in data && data.revalidate === true) {
         // When enabled, revalidate after 1 second. This value is optimal for
         // the most up-to-date page possible, but without a 1-to-1
         // request-refresh ratio.
         data.revalidate = 1
       } else {
         // By default, we never revalidate.
-        data.revalidate = false
+        ;(data as any).revalidate = false
       }
 
-      props.pageProps = Object.assign({}, props.pageProps, data.props)
+      props.pageProps = Object.assign(
+        {},
+        props.pageProps,
+        'props' in data ? data.props : undefined
+      )
       // pass up revalidate and props for export
       // TODO: change this to a different passing mechanism
-      ;(renderOpts as any).revalidate = data.revalidate
+      ;(renderOpts as any).revalidate =
+        'revalidate' in data ? data.revalidate : undefined
       ;(renderOpts as any).pageData = props
     }
 

packages/next/types/index.d.ts

@@ -85,12 +85,10 @@ export type GetStaticPropsContext<Q extends ParsedUrlQuery = ParsedUrlQuery> = {
   locales?: string[]
 }
 
-export type GetStaticPropsResult<P> = {
-  props?: P
-  revalidate?: number | boolean
-  unstable_redirect?: Redirect
-  unstable_notFound?: true
-}
+export type GetStaticPropsResult<P> =
+  | { props: P; revalidate?: number | boolean }
+  | { unstable_redirect: Redirect; revalidate?: number | boolean }
+  | { unstable_notFound: true }
 
 export type GetStaticProps<
   P extends { [key: string]: any } = { [key: string]: any },
@@ -133,15 +131,9 @@ export type GetServerSidePropsContext<
 }
 
 export type GetServerSidePropsResult<P> =
-  | {
-      props: P
-    }
-  | {
-      unstable_redirect: Redirect
-    }
-  | {
-      unstable_notFound: true
-    }
+  | { props: P }
+  | { unstable_redirect: Redirect }
+  | { unstable_notFound: true }
 
 export type GetServerSideProps<
   P extends { [key: string]: any } = { [key: string]: any },