mark reassigned/mutated values as non-hoistable - fixes #2731

src/compiler/compile/Component.ts

@@ -1069,9 +1069,12 @@ export default class Component {
 						} else if (name[0] === '$' && !owner) {
 							hoistable = false;
 						} else if (owner === instance_scope) {
+							const variable = var_lookup.get(name);
+
+							if (variable.reassigned || variable.mutated) hoistable = false;
+
 							if (name === fn_declaration.id.name) return;
 
-							const variable = var_lookup.get(name);
 							if (variable.hoistable) return;
 
 							if (top_level_function_declarations.has(name)) {

test/runtime/samples/reactive-value-function/_config.js

@@ -0,0 +1,9 @@
+export default {
+	html: `1-2`,
+
+	async test({ assert, component, target }) {
+		await component.update();
+
+		assert.htmlEqual(target.innerHTML, `3-4`);
+	}
+};

test/runtime/samples/reactive-value-function/main.svelte

@@ -0,0 +1,14 @@
+<script>
+	let foo = () => 1;
+
+	function bar() {
+		return 2;
+	}
+
+	export function update() {
+		foo = () => 3;
+		bar = () => 4;
+	}
+</script>
+
+{foo()}-{bar()}