mark module variables as mutated or reassigned (sveltejs#4469)

Author: tanhauhau

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* In `vars` array, correctly indicate whether `module` variables are `mutated` or `reassigned` ([#3215](https://github.com/sveltejs/svelte/issues/3215))
 * Exclude global variables from `$capture_state` ([#4463](https://github.com/sveltejs/svelte/issues/4463))
 
 ## 3.19.1

src/compiler/compile/Component.ts

@@ -780,7 +780,7 @@ export default class Component {
 
 		const component = this;
 		const { content } = script;
-		const { instance_scope, instance_scope_map: map } = this;
+		const { instance_scope, module_scope, instance_scope_map: map } = this;
 
 		let scope = instance_scope;
 
@@ -797,7 +797,12 @@ export default class Component {
 					const deep = assignee.type === 'MemberExpression';
 
 					names.forEach(name => {
-						if (scope.find_owner(name) === instance_scope) {
+						const scope_owner = scope.find_owner(name);
+						if (
+							scope_owner !== null
+								? scope_owner === instance_scope
+								: module_scope && module_scope.has(name)
+						) {
 							const variable = component.var_lookup.get(name);
 							variable[deep ? 'mutated' : 'reassigned'] = true;
 						}

test/vars/samples/modules-vars/_config.js

@@ -0,0 +1,72 @@
+export default {
+	test(assert, vars) {
+		assert.deepEqual(vars, [
+			{
+				name: "a",
+				export_name: null,
+				injected: false,
+				module: true,
+				mutated: false,
+				reassigned: true,
+				referenced: false,
+				referenced_from_script: false,
+				writable: true
+			},
+			{
+				name: "b",
+				export_name: null,
+				injected: false,
+				module: true,
+				mutated: true,
+				reassigned: false,
+				referenced: false,
+				referenced_from_script: false,
+				writable: true
+			},
+			{
+				name: "c",
+				export_name: null,
+				injected: false,
+				module: true,
+				mutated: false,
+				reassigned: false,
+				referenced: false,
+				referenced_from_script: false,
+				writable: true
+			},
+			{
+				name: "d",
+				export_name: null,
+				injected: false,
+				module: true,
+				mutated: false,
+				reassigned: false,
+				referenced: false,
+				referenced_from_script: false,
+				writable: true
+			},
+			{
+				name: "c",
+				export_name: null,
+				injected: false,
+				module: false,
+				mutated: false,
+				reassigned: true,
+				referenced: false,
+				referenced_from_script: true,
+				writable: true
+			},
+			{
+				name: "foo",
+				export_name: null,
+				injected: false,
+				module: false,
+				mutated: false,
+				reassigned: false,
+				referenced: false,
+				referenced_from_script: false,
+				writable: false
+			}
+		]);
+	}
+};

test/vars/samples/modules-vars/input.svelte

@@ -0,0 +1,18 @@
+<script context='module'>
+	let a = {};
+	let b = {};
+	let c = {};
+	let d = {};
+</script>
+<script>
+	let c = {};
+
+	a = 1;
+	b.x = 1;
+
+	function foo() {
+		let d = {};
+		c = 1;
+		d.x = 1;
+	}
+</script>