Fix bloat in main bundle from amp

packages/next/export/worker.ts

@@ -19,7 +19,7 @@ import '../server/node-polyfill-fetch'
 import { requireFontManifest } from '../server/require'
 import { normalizeLocalePath } from '../shared/lib/i18n/normalize-locale-path'
 import { trace } from '../trace'
-import { isInAmpMode } from '../shared/lib/amp'
+import { isInAmpMode } from '../shared/lib/amp-mode'
 import { setHttpAgentOptions } from '../server/config'
 import RenderResult from '../server/render-result'
 import isError from '../lib/is-error'

packages/next/server/render.tsx

@@ -43,7 +43,7 @@ import {
   STATIC_STATUS_PAGES,
 } from '../shared/lib/constants'
 import { isSerializableProps } from '../lib/is-serializable-props'
-import { isInAmpMode } from '../shared/lib/amp'
+import { isInAmpMode } from '../shared/lib/amp-mode'
 import { AmpStateContext } from '../shared/lib/amp-context'
 import { defaultHead } from '../shared/lib/head'
 import { HeadManagerContext } from '../shared/lib/head-manager-context'

packages/next/shared/lib/amp-mode.ts

@@ -0,0 +1,7 @@
+export function isInAmpMode({
+  ampFirst = false,
+  hybrid = false,
+  hasQuery = false,
+} = {}): boolean {
+  return ampFirst || (hybrid && hasQuery)
+}

packages/next/shared/lib/amp.ts

@@ -1,13 +1,6 @@
 import React from 'react'
 import { AmpStateContext } from './amp-context'
-
-export function isInAmpMode({
-  ampFirst = false,
-  hybrid = false,
-  hasQuery = false,
-} = {}): boolean {
-  return ampFirst || (hybrid && hasQuery)
-}
+import { isInAmpMode } from './amp-mode'
 
 export function useAmp(): boolean {
   // Don't assign the context value to a variable to save bytes

packages/next/shared/lib/head.tsx

@@ -2,7 +2,7 @@ import React, { useContext } from 'react'
 import Effect from './side-effect'
 import { AmpStateContext } from './amp-context'
 import { HeadManagerContext } from './head-manager-context'
-import { isInAmpMode } from './amp'
+import { isInAmpMode } from './amp-mode'
 import { warnOnce } from './utils'
 
 type WithInAmpMode = {

test/integration/production/test/index.test.js

@@ -313,6 +313,23 @@ describe('Production Usage', () => {
     expect(content).not.toContain('.currentScript')
   })
 
+  it('should not contain useAmp in main chunk', async () => {
+    const globResult = await glob('main-*.js', {
+      cwd: join(appDir, '.next/static/chunks'),
+    })
+
+    if (!globResult || globResult.length !== 1) {
+      throw new Error('could not find main js chunk')
+    }
+
+    const content = await fs.readFile(
+      join(appDir, '.next/static/chunks', globResult[0]),
+      'utf8'
+    )
+
+    expect(content).not.toContain('useAmp')
+  })
+
   describe('With basic usage', () => {
     it('should render the page', async () => {
       const html = await renderViaHTTP(appPort, '/')