GranularChunks conformance check

packages/next/build/webpack-config.ts

@@ -49,6 +49,7 @@ import WebpackConformancePlugin, {
   DuplicatePolyfillsConformanceCheck,
   MinificationConformanceCheck,
   ReactSyncScriptsConformanceCheck,
+  GranularChunksConformanceCheck,
 } from './webpack/plugins/webpack-conformance-plugin'
 import { WellKnownErrorsPlugin } from './webpack/plugins/wellknown-errors-plugin'
 import { codeFrameColumns } from '@babel/code-frame'
@@ -490,6 +491,9 @@ export default async function getBaseWebpackConfig(
             ?.BlockedAPIToBePolyfilled || []
         ),
       },
+      GranularChunksConformanceCheck: {
+        enabled: true,
+      },
     },
     config.conformance
   )
@@ -1019,6 +1023,12 @@ export default async function getBaseWebpackConfig(
                   conformanceConfig.DuplicatePolyfillsConformanceCheck
                     .BlockedAPIToBePolyfilled,
               }),
+            !isServer &&
+              config.experimental.granularChunks &&
+              conformanceConfig.GranularChunksConformanceCheck.enabled &&
+              new GranularChunksConformanceCheck(
+                splitChunksConfigs.prodGranular
+              ),
           ].filter(Boolean),
         }),
       new WellKnownErrorsPlugin(),

packages/next/build/webpack/plugins/webpack-conformance-plugin/checks/granular-chunks-conformance.ts

@@ -0,0 +1,104 @@
+import chalk from 'chalk'
+import {
+  IWebpackConformanceTest,
+  IConformanceTestResult,
+  IConformanceTestStatus,
+} from '../TestInterface'
+import {
+  CONFORMANCE_ERROR_PREFIX,
+  CONFORMANCE_WARNING_PREFIX,
+} from '../constants'
+import { deepEqual } from '../utils/utils'
+
+export interface GranularChunksConformanceCheck
+  extends IWebpackConformanceTest {
+  granularChunksConfig: any
+}
+
+function getWarningMessage(modifiedProp: string) {
+  return (
+    `${CONFORMANCE_WARNING_PREFIX}: The splitChunks config as part of the granularChunks flag has ` +
+    `been carefully crafted to optimize build size and build times. Modifying - ${chalk.bold(
+      modifiedProp
+    )} could result in slower builds and increased code duplication`
+  )
+}
+
+function getErrorMessage(message: string) {
+  return (
+    `${CONFORMANCE_ERROR_PREFIX}: The splitChunks config as part of the granularChunks flag has ` +
+    `been carefully crafted to optimize build size and build times. Please avoid changes to ${chalk.bold(
+      message
+    )}`
+  )
+}
+
+export class GranularChunksConformanceCheck {
+  constructor(granularChunksConfig: any) {
+    this.granularChunksConfig = granularChunksConfig
+  }
+
+  public buildStared(options: any): IConformanceTestResult {
+    const userSplitChunks = options.optimization.splitChunks
+    const warnings = []
+    const errors = []
+
+    if (
+      userSplitChunks.maxInitialRequests !==
+      this.granularChunksConfig.maxInitialRequests
+    ) {
+      warnings.push('splitChunks.maxInitialRequests')
+    }
+
+    if (userSplitChunks.minSize !== this.granularChunksConfig.minSize) {
+      warnings.push('splitChunks.minSize')
+    }
+
+    const userCacheGroup = userSplitChunks.cacheGroups
+    const originalCacheGroup = this.granularChunksConfig.cacheGroups
+
+    if (userCacheGroup.vendors !== false) {
+      errors.push('splitChunks.cacheGroups.vendors')
+    }
+
+    if (!deepEqual(userCacheGroup.framework, originalCacheGroup.framework)) {
+      errors.push('splitChunks.cacheGroups.framework')
+    }
+
+    if (!deepEqual(userCacheGroup.lib, originalCacheGroup.lib)) {
+      errors.push('splitChunks.cacheGroups.lib')
+    }
+
+    if (!deepEqual(userCacheGroup.commons, originalCacheGroup.commons)) {
+      errors.push('splitChunks.cacheGroups.commons')
+    }
+
+    if (!deepEqual(userCacheGroup.shared, originalCacheGroup.shared)) {
+      errors.push('splitChunks.cacheGroups.shared')
+    }
+
+    if (!warnings.length && !errors.length) {
+      return {
+        result: IConformanceTestStatus.SUCCESS,
+      }
+    }
+
+    const failedResult: IConformanceTestResult = {
+      result: IConformanceTestStatus.FAILED,
+    }
+
+    if (warnings.length) {
+      failedResult.warnings = warnings.map((warning) => ({
+        message: getWarningMessage(warning),
+      }))
+    }
+
+    if (errors.length) {
+      failedResult.warnings = errors.map((error) => ({
+        message: getErrorMessage(error),
+      }))
+    }
+
+    return failedResult
+  }
+}

packages/next/build/webpack/plugins/webpack-conformance-plugin/index.ts

@@ -13,6 +13,7 @@ import { visit } from 'next/dist/compiled/recast'
 export { MinificationConformanceCheck } from './checks/minification-conformance-check'
 export { ReactSyncScriptsConformanceCheck } from './checks/react-sync-scripts-conformance-check'
 export { DuplicatePolyfillsConformanceCheck } from './checks/duplicate-polyfills-conformance-check'
+export { GranularChunksConformanceCheck } from './checks/granular-chunks-conformance'
 
 export interface IWebpackConformancePluginOptions {
   tests: IWebpackConformanceTest[]

packages/next/build/webpack/plugins/webpack-conformance-plugin/utils/utils.ts

@@ -0,0 +1,10 @@
+const assert = require('assert').strict
+
+export function deepEqual(a: any, b: any) {
+  try {
+    assert.deepStrictEqual(a, b)
+    return true
+  } catch (_) {
+    return false
+  }
+}

test/integration/conformance/next.config.js

@@ -2,4 +2,16 @@ module.exports = {
   experimental: {
     conformance: true,
   },
+  webpack(cfg, { dev, isServer }) {
+    if (!dev && !isServer) {
+      cfg.optimization.splitChunks.cacheGroups.vendors = {
+        chunks: 'initial',
+        name: 'vendor',
+        test: 'vendor',
+        enforce: true,
+      }
+    }
+
+    return cfg
+  },
 }

test/integration/conformance/test/index.test.js

@@ -1,7 +1,8 @@
 /* eslint-env jest */
 
-import { join } from 'path'
+import chalk from 'chalk'
 import { nextBuild } from 'next-test-utils'
+import { join } from 'path'
 
 const appDir = join(__dirname, '../')
 jest.setTimeout(1000 * 60 * 2)
@@ -28,4 +29,14 @@ describe('Conformance system', () => {
       '[BUILD CONFORMANCE WARNING]: Found polyfill.io loading polyfill for fetch.'
     )
   })
+
+  it('Should warn about changes to granularChunks config', async () => {
+    const { stderr } = build
+    expect(stderr).toContain(
+      '[BUILD CONFORMANCE ERROR]: The splitChunks config as part of the granularChunks flag has ' +
+        `been carefully crafted to optimize build size and build times. Please avoid changes to ${chalk.bold(
+          'splitChunks.cacheGroups.vendors'
+        )}`
+    )
+  })
 })