From ed346835d324fc88b07bdb8450f93c21008b660a Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Thu, 18 Jul 2019 19:34:57 -0500
Subject: [PATCH] Fix /_error not rendering 404 in development

---
 packages/next-server/lib/constants.ts              |  2 +-
 packages/next-server/server/next-server.ts         | 14 ++++++++++----
 .../client-navigation/test/index.test.js           |  9 +++++++++
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/packages/next-server/lib/constants.ts b/packages/next-server/lib/constants.ts
index 2a2834aba5da8..82c5376f4ad6f 100644
--- a/packages/next-server/lib/constants.ts
+++ b/packages/next-server/lib/constants.ts
@@ -10,7 +10,7 @@ export const SERVER_DIRECTORY = 'server'
 export const SERVERLESS_DIRECTORY = 'serverless'
 export const CONFIG_FILE = 'next.config.js'
 export const BUILD_ID_FILE = 'BUILD_ID'
-export const BLOCKED_PAGES = ['/_document', '/_app']
+export const BLOCKED_PAGES = ['/_document', '/_app', '/_error']
 export const CLIENT_PUBLIC_FILES_PATH = 'public'
 export const CLIENT_STATIC_FILES_PATH = 'static'
 export const CLIENT_STATIC_FILES_RUNTIME = 'runtime'
diff --git a/packages/next-server/server/next-server.ts b/packages/next-server/server/next-server.ts
index 683bd8e0f413c..26cfbd8a065db 100644
--- a/packages/next-server/server/next-server.ts
+++ b/packages/next-server/server/next-server.ts
@@ -14,6 +14,7 @@ import {
   PHASE_PRODUCTION_SERVER,
   SERVER_DIRECTORY,
   SERVERLESS_DIRECTORY,
+  BLOCKED_PAGES,
 } from '../lib/constants'
 import {
   getRouteMatcher,
@@ -240,6 +241,15 @@ export default class Server {
       },
     ]
 
+    BLOCKED_PAGES.map(page => {
+      routes.unshift({
+        match: route(page),
+        fn: async (req, res, params, parsedUrl) => {
+          return this.render404(req, res, parsedUrl)
+        },
+      })
+    })
+
     if (
       this.nextConfig.experimental.publicDirectory &&
       fs.existsSync(this.publicDir)
@@ -414,10 +424,6 @@ export default class Server {
       return this.handleRequest(req, res, parsedUrl)
     }
 
-    if (isBlockedPage(pathname)) {
-      return this.render404(req, res, parsedUrl)
-    }
-
     const html = await this.renderToHTML(req, res, pathname, query, {
       dataOnly:
         (this.renderOpts.ampBindInitData && Boolean(query.dataOnly)) ||
diff --git a/test/integration/client-navigation/test/index.test.js b/test/integration/client-navigation/test/index.test.js
index 469739e649460..ae64a560307bc 100644
--- a/test/integration/client-navigation/test/index.test.js
+++ b/test/integration/client-navigation/test/index.test.js
@@ -1038,6 +1038,15 @@ describe('Client Navigation', () => {
     await browser.close()
   })
 
+  it('should render 404 for reserved pages', async () => {
+    const reservedPages = ['/_app', '/_document', '/_error']
+
+    for (const page of reservedPages) {
+      const html = await renderViaHTTP(context.appPort, page)
+      expect(html).toMatch(/This page could not be found/)
+    }
+  })
+
   renderingSuite(
     (p, q) => renderViaHTTP(context.appPort, p, q),
     (p, q) => fetchViaHTTP(context.appPort, p, q)