fix: hoist reactive imports to the module (#12845)

* fix: hoist reactive imports to the module

* fix

* Update .changeset/eleven-teachers-drive.md

* beef up test

* unused

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>
Co-authored-by: Rich Harris <hello@rich-harris.dev>

.changeset/eleven-teachers-drive.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: treat module-level imports as non-reactive in legacy mode

packages/svelte/src/compiler/phases/3-transform/client/transform-client.js

@@ -197,7 +197,7 @@ export function client_component(analysis, options) {
 		)
 	);
 
-	instance.body.unshift(...state.legacy_reactive_imports);
+	module.body.unshift(...state.legacy_reactive_imports);
 
 	/** @type {ESTree.Statement[]} */
 	const store_setup = [];

packages/svelte/src/compiler/phases/3-transform/client/visitors/Program.js

@@ -1,4 +1,4 @@
-/** @import { Expression, MemberExpression, Program } from 'estree' */
+/** @import { Expression, ImportDeclaration, MemberExpression, Program } from 'estree' */
 /** @import { ComponentContext } from '../types' */
 import { build_getter, is_prop_source } from '../utils.js';
 import * as b from '../../../../utils/builders.js';
@@ -16,16 +16,26 @@ export function Program(_, context) {
 
 		for (const [name, binding] of context.state.scope.declarations) {
 			if (binding.declaration_kind === 'import' && binding.mutated) {
-				const id = b.id('$$_import_' + name);
+				// the declaration itself is hoisted to the module scope, so we need
+				// to resort to cruder measures to differentiate instance/module imports
+				const { start, end } = context.state.analysis.instance.ast;
+				const node = /** @type {ImportDeclaration} */ (binding.initial);
+				const is_instance_import =
+					/** @type {number} */ (node.start) > /** @type {number} */ (start) &&
+					/** @type {number} */ (node.end) < /** @type {number} */ (end);
 
-				context.state.transform[name] = {
-					read: (_) => b.call(id),
-					mutate: (_, mutation) => b.call(id, mutation)
-				};
+				if (is_instance_import) {
+					const id = b.id('$$_import_' + name);
+
+					context.state.transform[name] = {
+						read: (_) => b.call(id),
+						mutate: (_, mutation) => b.call(id, mutation)
+					};
 
-				context.state.legacy_reactive_imports.push(
-					b.var(id, b.call('$.reactive_import', b.thunk(b.id(name))))
-				);
+					context.state.legacy_reactive_imports.push(
+						b.var(id, b.call('$.reactive_import', b.thunk(b.id(name))))
+					);
+				}
 			}
 		}
 	}

packages/svelte/tests/runtime-legacy/samples/reactive-import-statement-module/_config.js

@@ -0,0 +1,17 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+import state from './state.js';
+
+export default test({
+	html: '<button>0</button>',
+
+	before_test() {
+		state.count = 0;
+	},
+
+	test({ assert, target }) {
+		const button = target.querySelector('button');
+		flushSync(() => button?.click());
+		assert.htmlEqual(target.innerHTML, '<button>0</button>');
+	}
+});

packages/svelte/tests/runtime-legacy/samples/reactive-import-statement-module/main.svelte

@@ -0,0 +1,9 @@
+<script context="module">
+	import state from './state.js';
+
+	function update() {
+		state.count += 1;
+	}
+</script>
+
+<button on:click={update}>{state.count}</button>

packages/svelte/tests/runtime-legacy/samples/reactive-import-statement-module/state.js

@@ -0,0 +1,3 @@
+export default {
+	count: 0
+};