Update to show build indicator while re-fetching GS(S)P data in dev

packages/next/client/dev/dev-build-watcher.js

@@ -1,6 +1,6 @@
 import { getEventSourceWrapper } from './error-overlay/eventsource'
 
-export default function initializeBuildWatcher() {
+export default function initializeBuildWatcher(toggleCallback) {
   const shadowHost = document.createElement('div')
   shadowHost.id = '__next-build-watcher'
   // Make sure container is fixed and on a high zIndex so it shows
@@ -52,7 +52,8 @@ export default function initializeBuildWatcher() {
   })
 
   function handleMessage(event) {
-    const obj = JSON.parse(event.data)
+    const obj =
+      typeof event === 'string' ? { action: event } : JSON.parse(event.data)
 
     // eslint-disable-next-line default-case
     switch (obj.action) {
@@ -75,6 +76,8 @@ export default function initializeBuildWatcher() {
     }
   }
 
+  toggleCallback(handleMessage)
+
   function updateContainer() {
     if (isBuilding) {
       container.classList.add(`${prefix}building`)

packages/next/client/next-dev.js

@@ -33,6 +33,8 @@ initNext({ webpackHMR })
   .then(({ renderCtx, render }) => {
     initOnDemandEntries({ assetPrefix: prefix })
 
+    let buildIndicatorHandler = () => {}
+
     function devPagesManifestListener(event) {
       if (event.data.indexOf('devPagesManifest') !== -1) {
         fetch(`${prefix}/_next/static/development/_devPagesManifest.json`)
@@ -50,24 +52,34 @@ initNext({ webpackHMR })
         if (pages.includes(router.pathname)) {
           console.log('Refreshing page data due to server-side change')
 
-          router.replace(
-            router.pathname +
-              '?' +
-              String(
-                querystring.assign(
-                  querystring.urlQueryToSearchParams(router.query),
-                  new URLSearchParams(location.search)
-                )
-              ),
-            router.asPath
-          )
+          buildIndicatorHandler('building')
+
+          const clearIndicator = () => buildIndicatorHandler('built')
+
+          router
+            .replace(
+              router.pathname +
+                '?' +
+                String(
+                  querystring.assign(
+                    querystring.urlQueryToSearchParams(router.query),
+                    new URLSearchParams(location.search)
+                  )
+                ),
+              router.asPath
+            )
+            .finally(clearIndicator)
         }
       }
     }
     devPagesManifestListener.unfiltered = true
     getEventSourceWrapper({}).addMessageListener(devPagesManifestListener)
 
-    if (process.env.__NEXT_BUILD_INDICATOR) initializeBuildWatcher()
+    if (process.env.__NEXT_BUILD_INDICATOR) {
+      initializeBuildWatcher((handler) => {
+        buildIndicatorHandler = handler
+      })
+    }
     if (
       process.env.__NEXT_PRERENDER_INDICATOR &&
       // disable by default in electron

test/integration/gssp-ssr-change-reloading/pages/gsp-blog/[post].js

@@ -13,9 +13,13 @@ export default function Gsp(props) {
   )
 }
 
-export const getStaticProps = ({ params }) => {
+export const getStaticProps = async ({ params }) => {
   const count = 1
 
+  if (params.post === 'second') {
+    await new Promise((resolve) => setTimeout(resolve, 2000))
+  }
+
   return {
     props: {
       count,

test/integration/gssp-ssr-change-reloading/test/index.test.js

@@ -10,6 +10,19 @@ const appDir = join(__dirname, '..')
 let appPort
 let app
 
+const installCheckVisible = (browser) => {
+  return browser.eval(`(function() {
+    window.checkInterval = setInterval(function() {
+      let watcherDiv = document.querySelector('#__next-build-watcher')
+      watcherDiv = watcherDiv.shadowRoot || watcherDiv
+      window.showedBuilder = window.showedBuilder || (
+        watcherDiv.querySelector('div').className.indexOf('visible') > -1
+      )
+      if (window.showedBuilder) clearInterval(window.checkInterval)
+    }, 50)
+  })()`)
+}
+
 describe('GS(S)P Server-Side Change Reloading', () => {
   beforeAll(async () => {
     appPort = await findPort()
@@ -62,6 +75,33 @@ describe('GS(S)P Server-Side Change Reloading', () => {
     )
   })
 
+  it('should show indicator when re-fetching data', async () => {
+    const browser = await webdriver(appPort, '/gsp-blog/second')
+    await installCheckVisible(browser)
+    await browser.eval(() => (window.beforeChange = 'hi'))
+
+    const props = JSON.parse(await browser.elementByCss('#props').text())
+    expect(props.count).toBe(1)
+
+    const page = new File(join(appDir, 'pages/gsp-blog/[post].js'))
+    page.replace('count = 1', 'count = 2')
+
+    await check(
+      async () =>
+        JSON.parse(await browser.elementByCss('#props').text()).count + '',
+      '2'
+    )
+    expect(await browser.eval(() => window.beforeChange)).toBe('hi')
+    expect(await browser.eval(() => window.showedBuilder)).toBe(true)
+    page.restore()
+
+    await check(
+      async () =>
+        JSON.parse(await browser.elementByCss('#props').text()).count + '',
+      '1'
+    )
+  })
+
   it('should update page when getStaticPaths is changed only', async () => {
     const browser = await webdriver(appPort, '/gsp-blog/first')
     await browser.eval(() => (window.beforeChange = 'hi'))