Fix: Legacy fallback env var (#2074)

Co-authored-by: Nick Taylor <nick@iamdeveloper.com>
Co-authored-by: Lennart <lekoarts@gmail.com>

Author: 3 people

README.md

@@ -89,6 +89,10 @@ The Next.js Runtime fully supports ISR on Netlify. For more details see
 
 Note that Netlify has a minimum TTL of 60 seconds for revalidation.
 
+## Disable Static 404 on Dynamic Routes with fallback:false
+
+Currently when hitting a non-prerendered path with `fallback=false` it will default to a 404 page. You can now change this default setting by using the environemnt variable `LEGACY_FALLBACK_FALSE=true`. With the environment variable set, those non-prerendered paths will now be routed through using the ISR Handler and will allow you to add redirects for those non-prerendered paths. 
+
 ## Use with `next export`
 
 If you are using `next export` to generate a static site, you do not need most of the functionality of this Next.js

demos/default/next.config.js

@@ -67,6 +67,11 @@ module.exports = {
         destination: '/',
         permanent: true,
       },
+      {
+        source: '/getStaticProps/4/',
+        destination: '/',
+        permanent: true,
+      },
     ]
   },
   // https://nextjs.org/docs/basic-features/image-optimization#domains

packages/runtime/src/helpers/redirects.ts

@@ -1,5 +1,6 @@
 import type { NetlifyConfig } from '@netlify/build'
 import { yellowBright } from 'chalk'
+import destr from 'destr'
 import { readJSON } from 'fs-extra'
 import type { NextConfig } from 'next'
 import type { PrerenderManifest, SsgRoute } from 'next/dist/build'
@@ -194,7 +195,7 @@ const generateStaticIsrRewrites = ({
 /**
  * Generate rewrites for all dynamic routes
  */
-const generateDynamicRewrites = ({
+export const generateDynamicRewrites = ({
   dynamicRoutes,
   prerenderedDynamicRoutes,
   middleware,
@@ -238,7 +239,11 @@ const generateDynamicRewrites = ({
             withData: true,
           }),
         )
-      } else if (prerenderedDynamicRoutes[route.page].fallback === false && !is404Isr) {
+      } else if (
+        prerenderedDynamicRoutes[route.page].fallback === false &&
+        !is404Isr &&
+        !destr(process.env.LEGACY_FALLBACK_FALSE)
+      ) {
         dynamicRewrites.push(...redirectsForNext404Route({ route: route.page, buildId, basePath, i18n }))
       } else {
         dynamicRewrites.push(

test/helpers/utils.spec.ts

@@ -1,13 +1,55 @@
 import Chance from 'chance'
+import type { PrerenderManifest } from 'next/dist/build'
 import { ExperimentalConfig } from 'next/dist/server/config-shared'
 
+import { generateDynamicRewrites } from '../../packages/runtime/src/helpers/redirects'
 import {
   getCustomImageResponseHeaders,
   getRemotePatterns,
   ImagesConfig,
   redirectsForNext404Route,
 } from '../../packages/runtime/src/helpers/utils'
 
+const basePrerenderManifest: PrerenderManifest = {
+  version: 3,
+  routes: {},
+  dynamicRoutes: {},
+  notFoundRoutes: [],
+}
+
+const prerenderManifest: PrerenderManifest = {
+  ...basePrerenderManifest,
+  dynamicRoutes: {
+    '/getStaticProps/[id]': {
+      routeRegex: '^/getStaticProps/([^/]+?)(?:/)?$',
+      dataRoute: '/_next/data/build-id/getStaticProps/[id].json',
+      fallback: false,
+      dataRouteRegex: '^/_next/data/build\\-id/getStaticProps/([^/]+?)\\.json$',
+    },
+  },
+}
+
+const dynamicRoutes = [
+  {
+    page: '/getStaticProps/[id]',
+    regex: '^/getStaticProps/([^/]+?)(?:/)?$',
+    routeKeys: {
+      nextParamid: 'nextParamid',
+    },
+    namedRegex: '^/getStaticProps/(?<nextParamid>[^/]+?)(?:/)?$',
+  },
+]
+
+const route = {
+  dynamicRoutes,
+  prerenderedDynamicRoutes: prerenderManifest.dynamicRoutes,
+  basePath: '',
+  i18n: null,
+  buildId: 'test',
+  middleware: [],
+  is404Isr: false,
+}
+
 const chance = new Chance()
 
 describe('getCustomImageResponseHeaders', () => {
@@ -132,4 +174,52 @@ describe('redirectsForNext404Route', () => {
       { force: false, from: '/fr/test', status: 404, to: '/server/pages/fr/404.html' },
     ])
   })
+
+  it('returns static 404 redirects when LEGACY_FALLBACK_FALSE is not set', async () => {
+    const expected = {
+      dynamicRewrites: [
+        {
+          force: false,
+          from: '/_next/data/test/getStaticProps/:id.json',
+          status: 404,
+          to: '/server/pages/404.html',
+        },
+        {
+          force: false,
+          from: '/getStaticProps/:id',
+          status: 404,
+          to: '/server/pages/404.html',
+        },
+      ],
+      dynamicRoutesThatMatchMiddleware: [],
+    }
+
+    expect(generateDynamicRewrites(route)).toStrictEqual(expected)
+  })
+
+  it('does not return static 404 redirects when LEGACY_FALLBACK_FALSE is set', async () => {
+    process.env.LEGACY_FALLBACK_FALSE = 'true'
+
+    const expected = {
+      dynamicRewrites: [
+        {
+          force: false,
+          from: '/_next/data/test/getStaticProps/:id.json',
+          status: 200,
+          to: '/.netlify/builders/___netlify-odb-handler',
+        },
+        {
+          force: false,
+          from: '/getStaticProps/:id',
+          status: 200,
+          to: '/.netlify/builders/___netlify-odb-handler',
+        },
+      ],
+      dynamicRoutesThatMatchMiddleware: [],
+    }
+
+    expect(generateDynamicRewrites(route)).toStrictEqual(expected)
+
+    delete process.env.LEGACY_FALLBACK_FALSE
+  })
 })