fixes webpack#8666

Author: sokra

lib/optimize/ConcatenatedModule.js

@@ -1096,7 +1096,7 @@ class ConcatenatedModule extends Module {
 
 		// add harmony compatibility flag (must be first because of possible circular dependencies)
 		const usedExports = this.rootModule.usedExports;
-		if (usedExports === true) {
+		if (usedExports === true || usedExports === null) {
 			result.add(
 				runtimeTemplate.defineEsModuleFlagStatement({
 					exportsArgument: this.exportsArgument

test/cases/scope-hoisting/esModule/index.js

@@ -0,0 +1,6 @@
+it("should have the __esModule flag", () => {
+	return import("./module").then(mod => {
+		expect(mod.__esModule).toBe(true);
+		expect(mod.default).toBe(84);
+	})
+})

test/cases/scope-hoisting/esModule/module.js

@@ -0,0 +1,3 @@
+import other from "./other";
+
+export default other * 2;

test/cases/scope-hoisting/esModule/other.js

@@ -0,0 +1 @@
+export default 42;

test/configCases/scope-hoisting/esModule/index.js

@@ -0,0 +1,6 @@
+it("should have the __esModule flag", () => {
+	return import("./module").then(mod => {
+		expect(mod.__esModule).toBe(true);
+		expect(mod.default).toBe(84);
+	})
+})

test/configCases/scope-hoisting/esModule/module.js

@@ -0,0 +1,3 @@
+import other from "./other";
+
+export default other * 2;

test/configCases/scope-hoisting/esModule/other.js

@@ -0,0 +1 @@
+export default 42;

test/configCases/scope-hoisting/esModule/webpack.config.js

@@ -0,0 +1,7 @@
+module.exports = {
+	mode: "development",
+	devtool: false,
+	optimization: {
+		concatenateModules: true
+	}
+};