fix: handle undefined options in Server constructor (#5695)

* fix: handle undefined options in Server constructor and update type definitions

* fix: handle undefined options in Server constructor and add schema validation for null options

Author: bjohansebas

.changeset/constructor-options-undefined.md

@@ -0,0 +1,8 @@
+---
+"webpack-dev-server": patch
+---
+
+fix: allow `undefined` as the `Server` constructor `options` argument again
+
+Restores accepting `undefined` (defaulting it to `{}`) for the `options`
+argument, so passing a webpack config's optional `devServer` field type-checks and works as before.

lib/Server.js

@@ -325,10 +325,12 @@ const DEFAULT_ALLOWED_PROTOCOLS = /^(file|.+-extension):/i;
  */
 class Server {
   /**
-   * @param {Configuration<A, S>} options options
+   * @param {Configuration<A, S> | undefined} options options
    * @param {Compiler | MultiCompiler} compiler compiler
    */
   constructor(options, compiler) {
+    options = options === undefined ? {} : options;
+
     validate(/** @type {Schema} */ (schema), options, {
       name: "Dev Server",
       baseDataPath: "options",

test/e2e/api.test.js

@@ -71,6 +71,29 @@ describe("API", () => {
     });
   });
 
+  describe("constructor options", () => {
+    it("should default `undefined` options to `{}`", async () => {
+      const compiler = webpack(config);
+      const server = new Server(undefined, compiler);
+
+      expect(server.options).toEqual({});
+
+      try {
+        await server.start();
+      } finally {
+        await server.stop();
+      }
+    });
+
+    it("should reject `null` options via schema validation", () => {
+      const compiler = webpack(config);
+
+      expect(() => new Server(null, compiler)).toThrow(
+        /Invalid options object/,
+      );
+    });
+  });
+
   describe("latest async API", () => {
     it("should work with async API", async () => {
       const compiler = webpack(config);

types/lib/Server.d.ts

@@ -1173,10 +1173,13 @@ declare class Server<
    */
   private static isWebTarget;
   /**
-   * @param {Configuration<A, S>} options options
+   * @param {Configuration<A, S> | undefined} options options
    * @param {Compiler | MultiCompiler} compiler compiler
    */
-  constructor(options: Configuration<A, S>, compiler: Compiler | MultiCompiler);
+  constructor(
+    options: Configuration<A, S> | undefined,
+    compiler: Compiler | MultiCompiler,
+  );
   compiler: import("webpack").Compiler | import("webpack").MultiCompiler;
   /**
    * @type {ReturnType<Compiler["getInfrastructureLogger"]>}