keep/restore comments in export default

lib/dependencies/HarmonyExportDependencyParserPlugin.js

@@ -54,10 +54,25 @@ module.exports = class HarmonyExportDependencyParserPlugin {
 		parser.hooks.exportExpression.tap(
 			"HarmonyExportDependencyParserPlugin",
 			(statement, expr) => {
+				const comments = parser.getComments([
+					statement.range[0],
+					expr.range[0]
+				]);
 				const dep = new HarmonyExportExpressionDependency(
 					parser.state.module,
 					expr.range,
-					statement.range
+					statement.range,
+					comments
+						.map(c => {
+							switch (c.type) {
+								case "Block":
+									return `/*${c.value}*/`;
+								case "Line":
+									return `//${c.value}\n`;
+							}
+							return "";
+						})
+						.join("")
 				);
 				dep.loc = Object.create(statement.loc);
 				dep.loc.index = -1;

lib/dependencies/HarmonyExportExpressionDependency.js

@@ -6,11 +6,12 @@
 const NullDependency = require("./NullDependency");
 
 class HarmonyExportExpressionDependency extends NullDependency {
-	constructor(originModule, range, rangeStatement) {
+	constructor(originModule, range, rangeStatement, prefix) {
 		super();
 		this.originModule = originModule;
 		this.range = range;
 		this.rangeStatement = rangeStatement;
+		this.prefix = prefix;
 	}
 
 	get type() {
@@ -31,7 +32,11 @@ HarmonyExportExpressionDependency.Template = class HarmonyExportDependencyTempla
 		const content = this.getContent(dep.originModule, used);
 
 		if (dep.range) {
-			source.replace(dep.rangeStatement[0], dep.range[0] - 1, content + "(");
+			source.replace(
+				dep.rangeStatement[0],
+				dep.range[0] - 1,
+				content + "(" + dep.prefix
+			);
 			source.replace(dep.range[1], dep.rangeStatement[1] - 1, ");");
 			return;
 		}

test/configCases/code-generation/harmony-pure-default/index.js

@@ -0,0 +1,11 @@
+import { value as v1 } from "./module1";
+import { value as v2 } from "./module2";
+import { value as v3 } from "./module3";
+import { value as v4 } from "./module4";
+
+it("should not execute exports when annotated with pure comment", () => {
+	expect(v1).toBe(42);
+	expect(v2).toBe(42);
+	expect(v3).toBe(42);
+	expect(v4).toBe(42);
+});

test/configCases/code-generation/harmony-pure-default/module1.js

@@ -0,0 +1,9 @@
+let value = 42;
+
+const inc = () => {
+	value++;
+};
+
+export default /*#__PURE__*/inc();
+
+export { value };

test/configCases/code-generation/harmony-pure-default/module2.js

@@ -0,0 +1,9 @@
+let value = 42;
+
+const inc = () => {
+	value++;
+};
+
+export default (/*#__PURE__*/inc());
+
+export { value };

test/configCases/code-generation/harmony-pure-default/module3.js

@@ -0,0 +1,9 @@
+let value = 42;
+
+const inc = () => {
+	value++;
+};
+
+export default /*#__PURE__*/(inc());
+
+export { value };

test/configCases/code-generation/harmony-pure-default/module4.js

@@ -0,0 +1,15 @@
+let value = 42;
+
+const inc = () => {
+	value++;
+};
+
+export
+// hello
+default
+// world
+/*#__PURE__*/
+inc()
+;
+
+export { value };

test/configCases/code-generation/harmony-pure-default/webpack.config.js

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