fix: Properly typecheck webpack-dev-server and fix several undefined issues (#16503)

Author: agg23

npm/webpack-dev-server/src/aut-runner.ts

@@ -1,6 +1,6 @@
 /* eslint-env browser */
 
-export function init (importPromises, parent: Window = (window.opener || window.parent)) {
+export function init (importPromises: Array<() => Promise<void>>, parent: Window = (window.opener || window.parent)) {
   const Cypress = window.Cypress = parent.Cypress
 
   if (!Cypress) {

npm/webpack-dev-server/src/makeWebpackConfig.ts

@@ -3,7 +3,7 @@ import * as path from 'path'
 import * as webpack from 'webpack'
 import { merge } from 'webpack-merge'
 import makeDefaultWebpackConfig from './webpack.config'
-import CypressCTOptionsPlugin, { CypressCTOptionsPluginOptions } from './plugin'
+import CypressCTOptionsPlugin, { CypressCTOptionsPluginOptionsWithEmitter } from './plugin'
 
 const debug = debugFn('cypress:webpack-dev-server:makeWebpackConfig')
 
@@ -17,7 +17,7 @@ export interface UserWebpackDevServerOptions {
   disableLazyCompilation?: boolean
 }
 
-interface MakeWebpackConfigOptions extends CypressCTOptionsPluginOptions, UserWebpackDevServerOptions {
+interface MakeWebpackConfigOptions extends CypressCTOptionsPluginOptionsWithEmitter, UserWebpackDevServerOptions {
   devServerPublicPathRoute: string
   isOpenMode: boolean
   template?: string

npm/webpack-dev-server/src/measureWebpackPerformance.ts

@@ -1,11 +1,13 @@
 /* eslint-disable no-console */
-import * as webpack from 'webpack'
+import type { Configuration } from 'webpack'
 import path from 'path'
 import fs from 'fs'
 import chalk from 'chalk'
+
+// @ts-ignore
 import SpeedMeasurePlugin from 'speed-measure-webpack-plugin'
 
-export function measureWebpackPerformance (webpackConfig: webpack.Configuration): webpack.Configuration {
+export function measureWebpackPerformance (webpackConfig: Configuration): Configuration {
   if (!process.env.WEBPACK_PERF_MEASURE) {
     throw new Error('Performance monitoring is possible only with WEBPACK_PERF_MEASURE env variable set')
   }

npm/webpack-dev-server/src/plugin.ts

@@ -4,6 +4,8 @@ import _ from 'lodash'
 import semver from 'semver'
 import fs, { PathLike } from 'fs'
 import path from 'path'
+// eslint-disable-next-line no-duplicate-imports
+import type { Compilation } from 'webpack'
 
 type UtimesSync = (path: PathLike, atime: string | number | Date, mtime: string | number | Date) => void
 
@@ -14,10 +16,23 @@ export interface CypressCTOptionsPluginOptions {
   devServerEvents?: EventEmitter
 }
 
+export type CypressCTOptionsPluginOptionsWithEmitter = CypressCTOptionsPluginOptions & {
+  devServerEvents: EventEmitter
+}
+
 export interface CypressCTWebpackContext {
   _cypress: CypressCTOptionsPluginOptions
 }
 
+export type Webpack45Compilation = Compilation & {
+  // TODO: Drop these additional Webpack 4 types
+  inputFileSystem: {
+    fileSystem: {
+      utimesSync: UtimesSync
+    }
+  }
+}
+
 export default class CypressCTOptionsPlugin {
   private files: Cypress.Cypress['spec'][] = []
   private supportFile: string
@@ -26,7 +41,7 @@ export default class CypressCTOptionsPlugin {
   private readonly projectRoot: string
   private readonly devServerEvents: EventEmitter
 
-  constructor (options: CypressCTOptionsPluginOptions) {
+  constructor (options: CypressCTOptionsPluginOptionsWithEmitter) {
     this.files = options.files
     this.supportFile = options.supportFile
     this.projectRoot = options.projectRoot
@@ -49,7 +64,7 @@ export default class CypressCTOptionsPlugin {
 
         if (stats.hasErrors()) {
           this.errorEmitted = true
-          this.devServerEvents.emit('dev-server:compile:error', stats.toJson().errors[0])
+          this.devServerEvents.emit('dev-server:compile:error', stats.toJson().errors?.[0])
         } else if (this.errorEmitted) {
           // compilation succeed but assets haven't emitted to the output yet
           this.devServerEvents.emit('dev-server:compile:error', null)
@@ -72,7 +87,7 @@ export default class CypressCTOptionsPlugin {
    * @param compilation webpack 4 `compilation.Compilation`, webpack 5
    *   `Compilation`
    */
-  private plugin = (compilation) => {
+  private plugin = (compilation: Webpack45Compilation) => {
     this.devServerEvents.on('dev-server:specs:changed', (specs) => {
       if (_.isEqual(specs, this.files)) return
 
@@ -86,10 +101,9 @@ export default class CypressCTOptionsPlugin {
     // Webpack 5
     /* istanbul ignore next */
     if ('NormalModule' in webpack) {
-      // @ts-ignore
       webpack.NormalModule.getCompilationHooks(compilation).loader.tap(
         'CypressCTOptionsPlugin',
-        this.pluginFunc,
+        (context) => this.pluginFunc(context as CypressCTWebpackContext),
       )
 
       return
@@ -98,12 +112,12 @@ export default class CypressCTOptionsPlugin {
     // Webpack 4
     compilation.hooks.normalModuleLoader.tap(
       'CypressCTOptionsPlugin',
-      this.pluginFunc,
+      (context) => this.pluginFunc(context as CypressCTWebpackContext),
     )
   };
 
   apply (compiler: Compiler): void {
     this.setupCustomHMR(compiler)
-    compiler.hooks.compilation.tap('CypressCTOptionsPlugin', this.plugin)
+    compiler.hooks.compilation.tap('CypressCTOptionsPlugin', (compilation) => this.plugin(compilation as Webpack45Compilation))
   }
 }

npm/webpack-dev-server/src/startServer.ts

@@ -50,7 +50,7 @@ export async function start ({ webpackConfig: userWebpackConfig, template, optio
 
   debug('starting webpack dev server')
   let webpackDevServerConfig: WebpackDevServer.Configuration = {
-    ...userWebpackConfig.devServer,
+    ...userWebpackConfig?.devServer,
     hot: false,
   }
 
@@ -63,7 +63,7 @@ export async function start ({ webpackConfig: userWebpackConfig, template, optio
     }
   } else if (webpackDevServerPkg.version.match(/4\./)) {
     webpackDevServerConfig = {
-      ...userWebpackConfig.devServer,
+      ...userWebpackConfig?.devServer,
       devMiddleware: {
         publicPath: devServerPublicPathRoute,
       },

npm/webpack-dev-server/tsconfig.json

@@ -24,7 +24,7 @@
     // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
 
     /* Strict Type-Checking Options */
-    "strict": false /* Enable all strict type-checking options. */,
+    "strict": true /* Enable all strict type-checking options. */,
     // "noImplicitAny": true,
 
     /* Module Resolution Options */

yarn.lock

@@ -7819,9 +7819,9 @@
     source-map "^0.6.0"
 
 "@types/webpack@^4.4.31", "@types/webpack@^4.41.21", "@types/webpack@^4.41.26", "@types/webpack@^4.41.8":
-  version "4.41.27"
-  resolved "https://registry.yarnpkg.com/@types/webpack/-/webpack-4.41.27.tgz#f47da488c8037e7f1b2dbf2714fbbacb61ec0ffc"
-  integrity sha512-wK/oi5gcHi72VMTbOaQ70VcDxSQ1uX8S2tukBK9ARuGXrYM/+u4ou73roc7trXDNmCxCoerE8zruQqX/wuHszA==
+  version "4.41.28"
+  resolved "https://registry.yarnpkg.com/@types/webpack/-/webpack-4.41.28.tgz#0069a2159b7ad4d83d0b5801942c17d54133897b"
+  integrity sha512-Nn84RAiJjKRfPFFCVR8LC4ueTtTdfWAMZ03THIzZWRJB+rX24BD3LqPSFnbMscWauEsT4segAsylPDIaZyZyLQ==
   dependencies:
     "@types/anymatch" "*"
     "@types/node" "*"