fix(plugin-webpack): better webpack-dev-server types

packages/plugin/webpack/src/Config.ts

@@ -1,4 +1,5 @@
 import { Configuration as RawWebpackConfiguration } from 'webpack';
+import WebpackDevServer from 'webpack-dev-server';
 import { ConfigurationFactory as WebpackConfigurationFactory } from './WebpackConfig';
 
 export interface WebpackPluginEntryPoint {
@@ -151,8 +152,7 @@ export interface WebpackPluginConfig {
    * * `setupExitSignals`
    * * `headers.Content-Security-Policy` (use the `devContentSecurityPolicy` config option)
    */
-  devServer?: Record<string, unknown>;
-  // TODO: use webpack-dev-server.Configuration when @types/webpack-dev-server upgrades to v4
+  devServer?: Omit<WebpackDevServer.Configuration, 'port' | 'static' | 'setupExitSignals' | 'Content-Security-Policy'>;
 }
 
 export type WebpackConfiguration = RawWebpackConfiguration | WebpackConfigurationFactory;

packages/plugin/webpack/src/WebpackPlugin.ts

@@ -326,7 +326,7 @@ the generated files). Instead, it is ${JSON.stringify(pj.main)}`);
       const compiler = webpack(config);
       const webpackDevServer = new WebpackDevServer(this.devServerOptions(), compiler);
       await webpackDevServer.start();
-      this.servers.push(webpackDevServer.server);
+      this.servers.push(webpackDevServer.server!);
     });
 
     await asyncOra('Compiling Preload Scripts', async () => {
@@ -365,14 +365,14 @@ the generated files). Instead, it is ${JSON.stringify(pj.main)}`);
     const cspDirectives =
       this.config.devContentSecurityPolicy ?? "default-src 'self' 'unsafe-inline' data:; script-src 'self' 'unsafe-eval' 'unsafe-inline' data:";
 
-    const defaults = {
+    const defaults: Partial<WebpackDevServer.Configuration> = {
       hot: true,
       devMiddleware: {
         writeToDisk: true,
       },
       historyApiFallback: true,
     };
-    const overrides = {
+    const overrides: Partial<WebpackDevServer.Configuration> = {
       port: this.port,
       setupExitSignals: true,
       static: path.resolve(this.baseDir, 'renderer'),