Add error handling for error being thrown in _app getinitialProps (#6680)

* Fix handling of undefined being thrown
in getInitialProps and update integration test

* Update test

* Move test to app-document

package.json

@@ -10,7 +10,9 @@
     "testonly": "jest",
     "testall": "yarn check && yarn run testonly -- --coverage --forceExit --runInBand --reporters=default --reporters=jest-junit",
     "pretest": "yarn run lint",
-    "test-take2": "git clean -d -x -e node_modules -e packages -f && yarn testall",
+    "git-reset": "git reset --hard HEAD",
+    "git-clean": "git clean -d -x -e node_modules -e packages -f",
+    "test-take2": "yarn git-reset && yarn git-clean && yarn testall",
     "test": "yarn run testall || yarn run test-take2",
     "coveralls": "cat ./test/coverage/lcov.info | coveralls",
     "lint": "lerna run typescript && standard && standard --parser typescript-eslint-parser --plugin typescript packages/**/*.ts",

packages/next-server/server/render.tsx

@@ -235,7 +235,15 @@ export async function renderToHTML(
   const asPath: string = req.url
   const ctx = { err, req, res, pathname, query, asPath }
   const router = new ServerRouter(pathname, query, asPath)
-  const props = await loadGetInitialProps(App, { Component, router, ctx })
+  let props: any
+
+  try {
+    props = await loadGetInitialProps(App, { Component, router, ctx })
+  } catch (err) {
+    if (!dev || !err) throw err
+    ctx.err = err
+    renderOpts.err = err
+  }
 
   // the response might be finished on the getInitialProps call
   if (isResSent(res)) return null
@@ -256,8 +264,8 @@ export async function renderToHTML(
       ? renderToStaticMarkup
       : renderToString
 
-    if (err && ErrorDebug) {
-      return render(renderElementToString, <ErrorDebug error={err} />)
+    if (ctx.err && ErrorDebug) {
+      return render(renderElementToString, <ErrorDebug error={ctx.err} />)
     }
 
     if (dev && (props.router || props.Component)) {

test/integration/app-document/pages/_app.js

@@ -27,6 +27,7 @@ class Layout extends React.Component {
 
 export default class MyApp extends App {
   static async getInitialProps ({ Component, router, ctx }) {
+    // throw _app GIP err here
     let pageProps = {}
 
     if (Component.getInitialProps) {

test/integration/app-document/test/rendering.js

 /* eslint-env jest */
 
+import { join } from 'path'
 import cheerio from 'cheerio'
+import { check, File, waitFor } from 'next-test-utils'
 
 export default function ({ app }, suiteName, render, fetch) {
   async function get$ (path, query) {
@@ -102,6 +104,32 @@ export default function ({ app }, suiteName, render, fetch) {
         const $ = await get$('/shared')
         expect($('#currentstate').text() === 'UPDATED')
       })
+
+      test('It should show valid error when thrown in _app getInitialProps', async () => {
+        const errMsg = 'have an error from _app getInitialProps'
+        const _app = new File(join(__dirname, '../pages/_app.js'))
+
+        let foundErr = false
+        expect(await render('/')).toMatch('page-index')
+        _app.replace('// throw _app GIP err here', `throw new Error("${errMsg}")`)
+
+        try {
+          let tries = 0
+          while (!foundErr && tries < 5) {
+            foundErr = (await render('/')).indexOf(errMsg) > -1
+            await waitFor(1000)
+            tries++
+          }
+        } finally {
+          _app.restore()
+          // Make sure _app is restored
+          await check(
+            () => render('/'),
+            /page-index/
+          )
+          expect(foundErr).toBeTruthy()
+        }
+      })
     })
   })
 }