Add error messages for dynamic SSG page without getStaticPaths

packages/next/build/utils.ts

@@ -543,10 +543,19 @@ export async function isPageStatic(
       throw new Error(SERVER_PROPS_SSG_CONFLICT)
     }
 
+    const pageIsDynamic = isDynamicRoute(page)
     // A page cannot have static parameters if it is not a dynamic page.
-    if (hasStaticProps && hasStaticPaths && !isDynamicRoute(page)) {
+    if (hasStaticProps && hasStaticPaths && !pageIsDynamic) {
       throw new Error(
-        `unstable_getStaticPaths can only be used with dynamic pages. https://nextjs.org/docs#dynamic-routing`
+        `unstable_getStaticPaths can only be used with dynamic pages, not '${page}'.` +
+          `\nLearn more: https://nextjs.org/docs#dynamic-routing`
+      )
+    }
+
+    if (hasStaticProps && pageIsDynamic && !hasStaticPaths) {
+      throw new Error(
+        `unstable_getStaticPaths is required for dynamic SSG pages and is missing for '${page}'.` +
+          `\nRead more: https://err.sh/next.js/invalid-getstaticpaths-value`
       )
     }
 

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

@@ -317,6 +317,8 @@ export async function renderToHTML(
 
   const hasPageGetInitialProps = !!(Component as any).getInitialProps
 
+  const pageIsDynamic = isDynamicRoute(pathname)
+
   const isAutoExport =
     !hasPageGetInitialProps &&
     defaultAppGetInitialProps &&
@@ -326,7 +328,7 @@ export async function renderToHTML(
   if (
     process.env.NODE_ENV !== 'production' &&
     (isAutoExport || isFallback) &&
-    isDynamicRoute(pathname) &&
+    pageIsDynamic &&
     didRewrite
   ) {
     // TODO: add err.sh when rewrites go stable
@@ -361,6 +363,13 @@ export async function renderToHTML(
     )
   }
 
+  if (isSpr && pageIsDynamic && !unstable_getStaticPaths) {
+    throw new Error(
+      `unstable_getStaticPaths is required for dynamic SSG pages and is missing for '${pathname}'.` +
+        `\nRead more: https://err.sh/next.js/invalid-getstaticpaths-value`
+    )
+  }
+
   if (dev) {
     const { isValidElementType } = require('react-is')
     if (!isValidElementType(Component)) {
@@ -459,7 +468,7 @@ export async function renderToHTML(
       // invoke, where we'd have to consider server & serverless.
       const previewData = tryGetPreviewData(req, res, previewProps)
       const data = await unstable_getStaticProps!({
-        ...(isDynamicRoute(pathname)
+        ...(pageIsDynamic
           ? {
               params: query as ParsedUrlQuery,
             }

test/integration/dynamic-routing/pages/p1/p2/all-ssg/[...rest].js

@@ -6,4 +6,10 @@ export function unstable_getStaticProps({ params }) {
   return { props: { params } }
 }
 
+export function unstable_getStaticPaths() {
+  return {
+    paths: [],
+  }
+}
+
 export default All

test/integration/dynamic-routing/pages/p1/p2/nested-all-ssg/[...rest]/index.js

@@ -12,4 +12,10 @@ export function unstable_getStaticProps({ params }) {
   return { props: { params } }
 }
 
+export function unstable_getStaticPaths() {
+  return {
+    paths: [],
+  }
+}
+
 export default All

test/integration/prerender/test/index.test.js

@@ -1,7 +1,7 @@
 /* eslint-env jest */
 /* global jasmine */
 import fs from 'fs-extra'
-import { join } from 'path'
+import { join, dirname } from 'path'
 import cheerio from 'cheerio'
 import webdriver from 'next-webdriver'
 import escapeRegex from 'escape-string-regexp'
@@ -448,6 +448,33 @@ const runTests = (dev = false) => {
       }
     })
 
+    it('should error on dynamic page without getStaticPaths', async () => {
+      const curPage = join(__dirname, '../pages/temp/[slug].js')
+      await fs.mkdirp(dirname(curPage))
+      await fs.writeFile(
+        curPage,
+        `
+          export async function unstable_getStaticProps() {
+            return {
+              props: {
+                hello: 'world'
+              }
+            }
+          }
+          export default () => 'oops'
+        `
+      )
+      await waitFor(1000)
+      try {
+        const html = await renderViaHTTP(appPort, '/temp/hello')
+        expect(html).toMatch(
+          /unstable_getStaticPaths is required for dynamic SSG pages and is missing for/
+        )
+      } finally {
+        await fs.remove(curPage)
+      }
+    })
+
     it('should not re-call getStaticProps when updating query', async () => {
       const browser = await webdriver(appPort, '/something?hello=world')
       await waitFor(2000)