lib: fix ESM default export handling for .mjs files in Module Federation

y-okt · y-okt · commit b0929e012389 · 2025-12-16T07:19:50.000+09:00
When .mjs files import a default export from a shared/remote module in
Module Federation, they receive the ESM namespace object instead of the
actual default export value.
The solution of this approach is to override the getExportsType() method
in ConsumeSharedModule and RemoteModule to always return "dynamic".
diff --git a/lib/container/RemoteModule.js b/lib/container/RemoteModule.js
@@ -25,6 +25,8 @@ const RemoteToExternalDependency = require("./RemoteToExternalDependency");
 /** @typedef {import("../Module").NeedBuildCallback} NeedBuildCallback */
 /** @typedef {import("../Module").NeedBuildContext} NeedBuildContext */
 /** @typedef {import("../Module").SourceTypes} SourceTypes */
+/** @typedef {import("../ModuleGraph")} ModuleGraph */
+/** @typedef {import("../Module").ExportsType} ExportsType */
 /** @typedef {import("../RequestShortener")} RequestShortener */
 /** @typedef {import("../ResolverFactory").ResolverWithOptions} ResolverWithOptions */
 /** @typedef {import("../serialization/ObjectMiddleware").ObjectDeserializerContext} ObjectDeserializerContext */
@@ -128,6 +130,15 @@ class RemoteModule extends Module {
 		return REMOTE_AND_SHARE_INIT_TYPES;
 	}
 
+	/**
+	 * @param {ModuleGraph} moduleGraph the module graph
+	 * @param {boolean | undefined} strict the importing module is strict
+	 * @returns {ExportsType} export type
+	 */
+	getExportsType(moduleGraph, strict) {
+		return "dynamic";
+	}
+
 	/**
 	 * @returns {NameForCondition | null} absolute path which should be used for condition matching (usually the resource path)
 	 */
diff --git a/lib/sharing/ConsumeSharedModule.js b/lib/sharing/ConsumeSharedModule.js
@@ -28,6 +28,8 @@ const ConsumeSharedFallbackDependency = require("./ConsumeSharedFallbackDependen
 /** @typedef {import("../Module").NeedBuildCallback} NeedBuildCallback */
 /** @typedef {import("../Module").NeedBuildContext} NeedBuildContext */
 /** @typedef {import("../Module").SourceTypes} SourceTypes */
+/** @typedef {import("../ModuleGraph")} ModuleGraph */
+/** @typedef {import("../Module").ExportsType} ExportsType */
 /** @typedef {import("../RequestShortener")} RequestShortener */
 /** @typedef {import("../ResolverFactory").ResolverWithOptions} ResolverWithOptions */
 /** @typedef {import("../serialization/ObjectMiddleware").ObjectDeserializerContext} ObjectDeserializerContext */
@@ -153,6 +155,15 @@ class ConsumeSharedModule extends Module {
 		return CONSUME_SHARED_TYPES;
 	}
 
+	/**
+	 * @param {ModuleGraph} moduleGraph the module graph
+	 * @param {boolean | undefined} strict the importing module is strict
+	 * @returns {ExportsType} export type
+	 */
+	getExportsType(moduleGraph, strict) {
+		return "dynamic";
+	}
+
 	/**
 	 * @param {string=} type the source type for which the size should be estimated
 	 * @returns {number} the estimated size of the module (must be non-zero)
diff --git a/test/ConsumeSharedModule.unittest.js b/test/ConsumeSharedModule.unittest.js
@@ -0,0 +1,41 @@
+"use strict";
+
+const ConsumeSharedModule = require("../lib/sharing/ConsumeSharedModule");
+
+describe("ConsumeSharedModule", () => {
+	let module;
+	const context = "/some/context";
+	const options = {
+		shareKey: "my-package",
+		shareScope: "default",
+		import: false,
+		importResolved: undefined,
+		requiredVersion: undefined,
+		strictVersion: false,
+		singleton: false,
+		eager: false
+	};
+
+	beforeEach(() => {
+		module = new ConsumeSharedModule(context, options);
+		module.buildMeta = {};
+		module.buildInfo = {};
+	});
+
+	describe("#getExportsType", () => {
+		it('returns "dynamic" regardless of strict parameter', () => {
+			const mockModuleGraph = {};
+
+			expect(module.getExportsType(mockModuleGraph, false)).toBe("dynamic");
+
+			expect(module.getExportsType(mockModuleGraph, true)).toBe("dynamic");
+		});
+
+		it('returns "dynamic" to enable runtime __esModule check', () => {
+			const mockModuleGraph = {};
+			const exportsType = module.getExportsType(mockModuleGraph, true);
+
+			expect(exportsType).toBe("dynamic");
+		});
+	});
+});
diff --git a/test/RemoteModule.unittest.js b/test/RemoteModule.unittest.js
@@ -0,0 +1,39 @@
+"use strict";
+
+const RemoteModule = require("../lib/container/RemoteModule");
+
+describe("RemoteModule", () => {
+	let module;
+	const request = "my-remote/module";
+	const externalRequests = ["remote1@https://example.com/remote1.js"];
+	const internalRequest = "./module";
+	const shareScope = "default";
+
+	beforeEach(() => {
+		module = new RemoteModule(
+			request,
+			externalRequests,
+			internalRequest,
+			shareScope
+		);
+		module.buildMeta = {};
+		module.buildInfo = { strict: true };
+	});
+
+	describe("#getExportsType", () => {
+		it('returns "dynamic" regardless of strict parameter', () => {
+			const mockModuleGraph = {};
+
+			expect(module.getExportsType(mockModuleGraph, false)).toBe("dynamic");
+
+			expect(module.getExportsType(mockModuleGraph, true)).toBe("dynamic");
+		});
+
+		it('returns "dynamic" to enable runtime __esModule check', () => {
+			const mockModuleGraph = {};
+			const exportsType = module.getExportsType(mockModuleGraph, true);
+
+			expect(exportsType).toBe("dynamic");
+		});
+	});
+});
diff --git a/test/configCases/sharing/consume-module-mjs-default-export/index.js b/test/configCases/sharing/consume-module-mjs-default-export/index.js
@@ -0,0 +1,10 @@
+it("should correctly handle default imports in .mjs files from shared modules", async () => {
+	await __webpack_init_sharing__("default");
+
+	const { testDefaultImport } = await import("./pure-esm-consumer.mjs");
+	const result = testDefaultImport();
+
+	expect(result.defaultType).toBe("function");
+	expect(result.defaultValue).toBe("shared default export");
+	expect(result.namedExportValue).toBe("shared named export");
+});
diff --git a/test/configCases/sharing/consume-module-mjs-default-export/node_modules/shared-esm-pkg/index.js b/test/configCases/sharing/consume-module-mjs-default-export/node_modules/shared-esm-pkg/index.js
diff --git a/test/configCases/sharing/consume-module-mjs-default-export/node_modules/shared-esm-pkg/package.json b/test/configCases/sharing/consume-module-mjs-default-export/node_modules/shared-esm-pkg/package.json
diff --git a/test/configCases/sharing/consume-module-mjs-default-export/pure-esm-consumer.mjs b/test/configCases/sharing/consume-module-mjs-default-export/pure-esm-consumer.mjs
@@ -0,0 +1,10 @@
+import something from "shared-esm-pkg";
+import { namedExport } from "shared-esm-pkg";
+
+export function testDefaultImport() {
+	return {
+		defaultType: typeof something,
+		defaultValue: typeof something === "function" ? something() : something,
+		namedExportValue: namedExport
+	};
+}
diff --git a/test/configCases/sharing/consume-module-mjs-default-export/webpack.config.js b/test/configCases/sharing/consume-module-mjs-default-export/webpack.config.js
@@ -0,0 +1,25 @@
+"use strict";
+
+const { ConsumeSharedPlugin, ProvideSharedPlugin } =
+	require("../../../../").sharing;
+
+/** @type {import("../../../../").Configuration} */
+module.exports = {
+	mode: "development",
+	plugins: [
+		new ProvideSharedPlugin({
+			provides: {
+				"shared-esm-pkg": {
+					version: "1.0.0"
+				}
+			}
+		}),
+		new ConsumeSharedPlugin({
+			consumes: {
+				"shared-esm-pkg": {
+					requiredVersion: "^1.0.0"
+				}
+			}
+		})
+	]
+};
