fix: error message for missing default export in configuration (#3685)

Author: alexander-akait

packages/webpack-cli/src/webpack-cli.ts

@@ -1772,6 +1772,11 @@ class WebpackCLI implements IWebpackCLI {
         process.exit(2);
       }
 
+      if (!options) {
+        this.logger.error(`Failed to load '${configPath}' config. Unable to find default export.`);
+        process.exit(2);
+      }
+
       if (Array.isArray(options)) {
         // reassign the value to assert type
         const optionsArray: ConfigOptions[] = options;

test/build/config/named-export/mjs.test.js

@@ -0,0 +1,16 @@
+const { run } = require("../../../utils/test-utils");
+
+describe("webpack cli", () => {
+  it("should support mjs config format", async () => {
+    const { exitCode, stderr } = await run(__dirname, ["-c", "webpack.config.mjs"], {
+      env: { WEBPACK_CLI_FORCE_LOAD_ESM_CONFIG: true },
+    });
+
+    if (/Error: Not supported/.test(stderr)) {
+      expect(exitCode).toBe(2);
+    } else {
+      expect(exitCode).toBe(2);
+      expect(stderr).toMatch(/Unable to find default export./);
+    }
+  });
+});

test/build/config/named-export/webpack.config.mjs

@@ -0,0 +1 @@
+export let config = {};