Fix overly aggressive function hoisting (#3125)

src/compiler/compile/Component.ts

@@ -790,6 +790,20 @@ export default class Component {
 					scope = map.get(node);
 				}
 
+				if (node.type === 'VariableDeclarator' && node.init !== null && node.init.type === 'Identifier') {
+					const variable = component.var_lookup.get(node.init.name);
+					variable.aliased = true;
+				}
+
+				if (node.type === 'CallExpression') {
+					node.arguments.forEach(arg => {
+						if (arg.type === 'Identifier' && scope.find_owner(arg.name) === instance_scope) {
+							const variable = component.var_lookup.get(arg.name);
+							variable.aliased = true;
+						}
+					});
+				}
+
 				if (node.type === 'AssignmentExpression' || node.type === 'UpdateExpression') {
 					const assignee = node.type === 'AssignmentExpression' ? node.left : node.argument;
 					const names = extract_names(assignee);
@@ -1077,7 +1091,7 @@ export default class Component {
 						} else if (owner === instance_scope) {
 							const variable = var_lookup.get(name);
 
-							if (variable.reassigned || variable.mutated) hoistable = false;
+							if (variable.reassigned || variable.mutated || variable.aliased) hoistable = false;
 
 							if (name === fn_declaration.id.name) return;
 

src/compiler/interfaces.ts

@@ -161,6 +161,7 @@ export interface Var {
 	hoistable?: boolean;
 	subscribable?: boolean;
 	is_reactive_dependency?: boolean;
+	aliased?: boolean;
 }
 
 export interface CssResult { 

test/js/samples/aliased-function/expected.js

@@ -0,0 +1,21 @@
+/* generated by Svelte vX.Y.Z */
+import { SvelteComponent, init, safe_not_equal } from "svelte/internal";
+
+function instance($$self) {
+	function foo() {
+
+	}
+
+	const foo_alias = foo;
+	foo_alias.nasty_but_legal();
+	return [];
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		init(this, options, instance, null, safe_not_equal, {});
+	}
+}
+
+export default Component;

test/js/samples/aliased-function/input.svelte

@@ -0,0 +1,5 @@
+<script>
+	function foo() {}
+	const foo_alias = foo;
+	foo_alias.nasty_but_legal();
+</script>

test/js/samples/hoisted-function/expected.js

@@ -0,0 +1,50 @@
+/* generated by Svelte vX.Y.Z */
+import {
+	SvelteComponent,
+	detach,
+	element,
+	init,
+	insert,
+	noop,
+	safe_not_equal
+} from "svelte/internal";
+
+import { bar } from "./utils.js";
+
+function create_fragment(ctx) {
+	let p;
+
+	return {
+		c() {
+			p = element("p");
+			p.textContent = `You'll be pleased to know the answer is ${/*foo*/ ctx[0]()}.`;
+		},
+		m(target, anchor) {
+			insert(target, p, anchor);
+		},
+		p: noop,
+		i: noop,
+		o: noop,
+		d(detaching) {
+			if (detaching) detach(p);
+		}
+	};
+}
+
+function instance($$self) {
+	function foo() {
+		return 42;
+	}
+
+	bar(foo);
+	return [foo];
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		init(this, options, instance, create_fragment, safe_not_equal, {});
+	}
+}
+
+export default Component;

test/js/samples/hoisted-function/input.svelte

@@ -0,0 +1,11 @@
+<script>
+	import { bar } from './utils.js';
+
+	function foo() {
+		return 42;
+	}
+
+	bar(foo);
+</script>
+
+<p>You'll be pleased to know the answer is {foo()}.</p>

test/js/samples/hoisted-function/utils.js

@@ -0,0 +1,3 @@
+export function bar(fn) {
+	console.log(`I'm safe but you'd never know, ${fn}!`);
+}