From e06d6ff30b5cd6351476b857e0ff087a8667cac5 Mon Sep 17 00:00:00 2001
From: Lukas Taegert-Atkinson <lukas.taegert-atkinson@tngtech.com>
Date: Thu, 18 Mar 2021 05:55:26 +0100
Subject: [PATCH] Do not count accessing members of an external namespace as
 side-effects.

---
 src/ast/variables/ExternalVariable.ts                 |  5 +++++
 .../samples/treeshake-namespace-access/_config.js     |  4 ++++
 .../treeshake-namespace-access/_expected/amd.js       |  5 +++++
 .../treeshake-namespace-access/_expected/cjs.js       |  5 +++++
 .../treeshake-namespace-access/_expected/es.js        |  3 +++
 .../treeshake-namespace-access/_expected/iife.js      |  6 ++++++
 .../treeshake-namespace-access/_expected/system.js    | 11 +++++++++++
 .../treeshake-namespace-access/_expected/umd.js       |  8 ++++++++
 test/form/samples/treeshake-namespace-access/main.js  |  4 ++++
 9 files changed, 51 insertions(+)
 create mode 100644 test/form/samples/treeshake-namespace-access/_config.js
 create mode 100644 test/form/samples/treeshake-namespace-access/_expected/amd.js
 create mode 100644 test/form/samples/treeshake-namespace-access/_expected/cjs.js
 create mode 100644 test/form/samples/treeshake-namespace-access/_expected/es.js
 create mode 100644 test/form/samples/treeshake-namespace-access/_expected/iife.js
 create mode 100644 test/form/samples/treeshake-namespace-access/_expected/system.js
 create mode 100644 test/form/samples/treeshake-namespace-access/_expected/umd.js
 create mode 100644 test/form/samples/treeshake-namespace-access/main.js

diff --git a/src/ast/variables/ExternalVariable.ts b/src/ast/variables/ExternalVariable.ts
index 9ffe9679cb0..b0f2ce6a416 100644
--- a/src/ast/variables/ExternalVariable.ts
+++ b/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;
diff --git a/test/form/samples/treeshake-namespace-access/_config.js b/test/form/samples/treeshake-namespace-access/_config.js
new file mode 100644
index 00000000000..8f398f593b2
--- /dev/null
+++ b/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' }
+};
diff --git a/test/form/samples/treeshake-namespace-access/_expected/amd.js b/test/form/samples/treeshake-namespace-access/_expected/amd.js
new file mode 100644
index 00000000000..0bae1e8d57f
--- /dev/null
+++ b/test/form/samples/treeshake-namespace-access/_expected/amd.js
@@ -0,0 +1,5 @@
+define(['external'], function (external) { 'use strict';
+
+	console.log('main');
+
+});
diff --git a/test/form/samples/treeshake-namespace-access/_expected/cjs.js b/test/form/samples/treeshake-namespace-access/_expected/cjs.js
new file mode 100644
index 00000000000..d1e28fe4f99
--- /dev/null
+++ b/test/form/samples/treeshake-namespace-access/_expected/cjs.js
@@ -0,0 +1,5 @@
+'use strict';
+
+require('external');
+
+console.log('main');
diff --git a/test/form/samples/treeshake-namespace-access/_expected/es.js b/test/form/samples/treeshake-namespace-access/_expected/es.js
new file mode 100644
index 00000000000..cedb294ffee
--- /dev/null
+++ b/test/form/samples/treeshake-namespace-access/_expected/es.js
@@ -0,0 +1,3 @@
+import 'external';
+
+console.log('main');
diff --git a/test/form/samples/treeshake-namespace-access/_expected/iife.js b/test/form/samples/treeshake-namespace-access/_expected/iife.js
new file mode 100644
index 00000000000..d283cbce8ba
--- /dev/null
+++ b/test/form/samples/treeshake-namespace-access/_expected/iife.js
@@ -0,0 +1,6 @@
+(function () {
+	'use strict';
+
+	console.log('main');
+
+}());
diff --git a/test/form/samples/treeshake-namespace-access/_expected/system.js b/test/form/samples/treeshake-namespace-access/_expected/system.js
new file mode 100644
index 00000000000..d927c51ce7d
--- /dev/null
+++ b/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');
+
+		}
+	};
+});
diff --git a/test/form/samples/treeshake-namespace-access/_expected/umd.js b/test/form/samples/treeshake-namespace-access/_expected/umd.js
new file mode 100644
index 00000000000..a0358332ac1
--- /dev/null
+++ b/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');
+
+})));
diff --git a/test/form/samples/treeshake-namespace-access/main.js b/test/form/samples/treeshake-namespace-access/main.js
new file mode 100644
index 00000000000..59de52af6c6
--- /dev/null
+++ b/test/form/samples/treeshake-namespace-access/main.js
@@ -0,0 +1,4 @@
+import * as external from 'external';
+
+const unused = external.foo;
+console.log('main');