fix: handle undefined configuration export

packages/webpack-cli/lib/webpack-cli.js

@@ -67,10 +67,18 @@ class WebpackCLI {
     }
 
     // For babel/typescript
-    if (result.default) {
+    if (result && result.default) {
       result = result.default;
     }
 
+    // Treat undefined configuration for zero-config
+    if (!result) {
+      this.logger.info(
+        "Configuration file provided didn't export any configuration, using defaults to build.",
+      );
+      result = {};
+    }
+
     return result;
   }
 

test/build/config/undefined/src/index.js

@@ -0,0 +1 @@
+console.log("Percy Weasley")

test/build/config/undefined/undefined.test.js

@@ -0,0 +1,16 @@
+"use strict";
+const { resolve } = require("path");
+const { run } = require("../../../utils/test-utils");
+
+describe("config flag with undefined export config file", () => {
+  it("should throw error with no configuration or index file", async () => {
+    const { exitCode, stderr, stdout } = await run(__dirname, [
+      "-c",
+      resolve(__dirname, "webpack.config.js"),
+    ]);
+
+    expect(exitCode).toBe(0);
+    expect(stderr).toBeFalsy();
+    expect(stdout).toBeTruthy();
+  });
+});

test/build/config/undefined/webpack.config.js

@@ -0,0 +1 @@
+module.exports = undefined;