Do not count accessing members of an external namespace as side-effects.

src/ast/variables/ExternalVariable.ts

@@ -1,5 +1,6 @@
 import ExternalModule from '../../ExternalModule';
 import Identifier from '../nodes/Identifier';
+import { ObjectPath } from '../utils/PathTracker';
 import Variable from './Variable';
 
 export default class ExternalVariable extends Variable {
@@ -21,6 +22,10 @@ export default class ExternalVariable extends Variable {
 		}
 	}
 
+	hasEffectsWhenAccessedAtPath(path: ObjectPath) {
+		return path.length > (this.isNamespace ? 1 : 0);
+	}
+
 	include() {
 		if (!this.included) {
 			this.included = true;

test/form/samples/treeshake-namespace-access/_config.js

@@ -0,0 +1,4 @@
+module.exports = {
+	description: 'does not count namespace property access as side-effect',
+	options: { external: 'external' }
+};

test/form/samples/treeshake-namespace-access/_expected/amd.js

@@ -0,0 +1,5 @@
+define(['external'], function (external) { 'use strict';
+
+	console.log('main');
+
+});

test/form/samples/treeshake-namespace-access/_expected/cjs.js

@@ -0,0 +1,5 @@
+'use strict';
+
+require('external');
+
+console.log('main');

test/form/samples/treeshake-namespace-access/_expected/es.js

@@ -0,0 +1,3 @@
+import 'external';
+
+console.log('main');

test/form/samples/treeshake-namespace-access/_expected/iife.js

@@ -0,0 +1,6 @@
+(function () {
+	'use strict';
+
+	console.log('main');
+
+}());

test/form/samples/treeshake-namespace-access/_expected/system.js

@@ -0,0 +1,11 @@
+System.register(['external'], function () {
+	'use strict';
+	return {
+		setters: [function () {}],
+		execute: function () {
+
+			console.log('main');
+
+		}
+	};
+});

test/form/samples/treeshake-namespace-access/_expected/umd.js

@@ -0,0 +1,8 @@
+(function (factory) {
+	typeof define === 'function' && define.amd ? define(['external'], factory) :
+	factory();
+}((function () { 'use strict';
+
+	console.log('main');
+
+})));

test/form/samples/treeshake-namespace-access/main.js

@@ -0,0 +1,4 @@
+import * as external from 'external';
+
+const unused = external.foo;
+console.log('main');