Fix Experimental Modern Mode with CSS

packages/next/build/webpack/plugins/build-manifest-plugin.ts

@@ -33,7 +33,9 @@ const generateClientManifest = (
     // Filter out dependencies in the _app entry, because those will have already
     // been loaded by the client prior to a navigation event
     const filteredDeps = dependencies.filter(
-      dep => !appDependencies.has(dep) && /\.module\.js$/.test(dep) === isModern
+      dep =>
+        !appDependencies.has(dep) &&
+        (!dep.endsWith('.js') || dep.endsWith('.module.js') === isModern)
     )
 
     // The manifest can omit the page if it has no requirements

test/integration/css-client-nav/test/index.test.js

@@ -171,3 +171,159 @@ describe('CSS Module client-side navigation in Production', () => {
     }
   })
 })
+
+describe('CSS Module client-side navigation in Production (Modern)', () => {
+  const appDir = join(fixturesDir, 'multi-module-modern')
+
+  beforeAll(async () => {
+    await remove(join(appDir, '.next'))
+  })
+
+  let appPort
+  let app
+  beforeAll(async () => {
+    await nextBuild(appDir)
+    appPort = await findPort()
+    app = await nextStart(appDir, appPort)
+  })
+  afterAll(async () => {
+    await killApp(app)
+  })
+
+  it('should be able to client-side navigate from red to blue', async () => {
+    let browser
+    try {
+      browser = await webdriver(appPort, '/red')
+
+      await browser.eval(`window.__did_not_ssr = 'make sure this is set'`)
+
+      const redColor = await browser.eval(
+        `window.getComputedStyle(document.querySelector('#verify-red')).color`
+      )
+      expect(redColor).toMatchInlineSnapshot(`"rgb(255, 0, 0)"`)
+
+      await browser.elementByCss('#link-blue').click()
+
+      await browser.waitForElementByCss('#verify-blue')
+
+      const blueColor = await browser.eval(
+        `window.getComputedStyle(document.querySelector('#verify-blue')).color`
+      )
+      expect(blueColor).toMatchInlineSnapshot(`"rgb(0, 0, 255)"`)
+
+      expect(await browser.eval(`window.__did_not_ssr`)).toMatchInlineSnapshot(
+        `"make sure this is set"`
+      )
+    } finally {
+      if (browser) {
+        await browser.close()
+      }
+    }
+  })
+
+  it('should be able to client-side navigate from blue to red', async () => {
+    const content = await renderViaHTTP(appPort, '/blue')
+    const $ = cheerio.load(content)
+
+    // Ensure only `/blue` page's CSS is preloaded
+    const serverCssPreloads = $('link[rel="preload"][as="style"]')
+    expect(serverCssPreloads.length).toBe(1)
+
+    const serverCssPrefetches = $('link[rel="prefetch"][as="style"]')
+    expect(serverCssPrefetches.length).toBe(0)
+
+    let browser
+    try {
+      browser = await webdriver(appPort, '/blue')
+      await browser.eval(`window.__did_not_ssr = 'make sure this is set'`)
+
+      const redColor = await browser.eval(
+        `window.getComputedStyle(document.querySelector('#verify-blue')).color`
+      )
+      expect(redColor).toMatchInlineSnapshot(`"rgb(0, 0, 255)"`)
+
+      // Check that Red was preloaded
+      const result = await browser.eval(
+        `[].slice.call(document.querySelectorAll('link[rel="prefetch"][as="style"]')).map(e=>({href:e.href})).sort()`
+      )
+      expect(result.length).toBe(1)
+
+      // Check that CSS was not loaded as script
+      const cssPreloads = await browser.eval(
+        `[].slice.call(document.querySelectorAll('link[rel=preload][href*=".css"]')).map(e=>e.as)`
+      )
+      expect(cssPreloads.every(e => e === 'style')).toBe(true)
+      const cssPreloads2 = await browser.eval(
+        `[].slice.call(document.querySelectorAll('link[rel=prefetch][href*=".css"]')).map(e=>e.as)`
+      )
+      expect(cssPreloads2.every(e => e === 'style')).toBe(true)
+
+      await browser.elementByCss('#link-red').click()
+
+      await browser.waitForElementByCss('#verify-red')
+
+      const blueColor = await browser.eval(
+        `window.getComputedStyle(document.querySelector('#verify-red')).color`
+      )
+      expect(blueColor).toMatchInlineSnapshot(`"rgb(255, 0, 0)"`)
+
+      expect(await browser.eval(`window.__did_not_ssr`)).toMatchInlineSnapshot(
+        `"make sure this is set"`
+      )
+    } finally {
+      if (browser) {
+        await browser.close()
+      }
+    }
+  })
+
+  it('should be able to client-side navigate from none to red', async () => {
+    let browser
+    try {
+      browser = await webdriver(appPort, '/none')
+
+      await browser.eval(`window.__did_not_ssr = 'make sure this is set'`)
+
+      await browser.elementByCss('#link-red').click()
+      await browser.waitForElementByCss('#verify-red')
+
+      const blueColor = await browser.eval(
+        `window.getComputedStyle(document.querySelector('#verify-red')).color`
+      )
+      expect(blueColor).toMatchInlineSnapshot(`"rgb(255, 0, 0)"`)
+
+      expect(await browser.eval(`window.__did_not_ssr`)).toMatchInlineSnapshot(
+        `"make sure this is set"`
+      )
+    } finally {
+      if (browser) {
+        await browser.close()
+      }
+    }
+  })
+
+  it('should be able to client-side navigate from none to blue', async () => {
+    let browser
+    try {
+      browser = await webdriver(appPort, '/none')
+
+      await browser.eval(`window.__did_not_ssr = 'make sure this is set'`)
+
+      await browser.elementByCss('#link-blue').click()
+      await browser.waitForElementByCss('#verify-blue')
+
+      const blueColor = await browser.eval(
+        `window.getComputedStyle(document.querySelector('#verify-blue')).color`
+      )
+      expect(blueColor).toMatchInlineSnapshot(`"rgb(0, 0, 255)"`)
+
+      expect(await browser.eval(`window.__did_not_ssr`)).toMatchInlineSnapshot(
+        `"make sure this is set"`
+      )
+    } finally {
+      if (browser) {
+        await browser.close()
+      }
+    }
+  })
+})

test/integration/css-fixtures/multi-module-modern/next.config.js

@@ -0,0 +1,9 @@
+const parent = require('../next.config')
+
+module.exports = {
+  ...parent,
+  experimental: {
+    ...parent.experimental,
+    modern: true,
+  },
+}

test/integration/css-fixtures/multi-module-modern/pages/blue.js

@@ -0,0 +1,20 @@
+import Link from 'next/link'
+import { blueText } from './blue.module.css'
+
+export default function Blue() {
+  return (
+    <>
+      <div id="verify-blue" className={blueText}>
+        This text should be blue.
+      </div>
+      <br />
+      <Link href="/red" prefetch>
+        <a id="link-red">Red</a>
+      </Link>
+      <br />
+      <Link href="/none" prefetch={false}>
+        <a id="link-none">None</a>
+      </Link>
+    </>
+  )
+}

test/integration/css-fixtures/multi-module-modern/pages/blue.module.css

@@ -0,0 +1,3 @@
+.blueText {
+  color: blue;
+}

test/integration/css-fixtures/multi-module-modern/pages/none.js

@@ -0,0 +1,19 @@
+import Link from 'next/link'
+
+export default function None() {
+  return (
+    <>
+      <div id="verify-black" style={{ color: 'black' }}>
+        This text should be black.
+      </div>
+      <br />
+      <Link href="/red" prefetch={false}>
+        <a id="link-red">Red</a>
+      </Link>
+      <br />
+      <Link href="/blue" prefetch={false}>
+        <a id="link-blue">Blue</a>
+      </Link>
+    </>
+  )
+}

test/integration/css-fixtures/multi-module-modern/pages/red.js

@@ -0,0 +1,20 @@
+import Link from 'next/link'
+import { redText } from './red.module.css'
+
+export default function Red() {
+  return (
+    <>
+      <div id="verify-red" className={redText}>
+        This text should be red.
+      </div>
+      <br />
+      <Link href="/blue" prefetch={false}>
+        <a id="link-blue">Blue</a>
+      </Link>
+      <br />
+      <Link href="/none" prefetch={false}>
+        <a id="link-none">None</a>
+      </Link>
+    </>
+  )
+}

test/integration/css-fixtures/multi-module-modern/pages/red.module.css

@@ -0,0 +1,3 @@
+.redText {
+  color: red;
+}

test/integration/css-fixtures/multi-module/next.config.js

@@ -0,0 +1,9 @@
+const parent = require('../next.config')
+
+module.exports = {
+  ...parent,
+  experimental: {
+    ...parent.experimental,
+    modern: false,
+  },
+}