remove unreferenced variable from initial context (sveltejs#4941)

Author: tanhauhau

src/compiler/compile/render_dom/Renderer.ts

@@ -26,6 +26,7 @@ export default class Renderer {
 	options: CompileOptions;
 
 	context: ContextMember[] = [];
+	initial_context: ContextMember[] = [];
 	context_lookup: Map<string, ContextMember> = new Map();
 	context_overflow: boolean;
 	blocks: Array<Block | Node | Node[]> = [];
@@ -110,8 +111,12 @@ export default class Renderer {
 
 				// these determine whether variable is included in initial context
 				// array, so must have the highest priority
-				if (variable.export_name) member.priority += 8;
-				if (variable.referenced) member.priority += 16;
+				if (variable.export_name) member.priority += 16;
+				if (variable.referenced) member.priority += 32;
+			} else if (member.is_non_contextual) {
+				// determine whether variable is included in initial context
+				// array, so must have the highest priority
+				member.priority += 8;
 			}
 
 			if (!member.is_contextual) {
@@ -121,6 +126,17 @@ export default class Renderer {
 
 		this.context.sort((a, b) => (b.priority - a.priority) || ((a.index.value as number) - (b.index.value as number)));
 		this.context.forEach((member, i) => member.index.value = i);
+
+		let i = this.context.length;
+		while (i--) {
+			const member = this.context[i];
+			if (member.variable) {
+				if (member.variable.referenced || member.variable.export_name) break;
+			} else if (member.is_non_contextual) {
+				break;
+			}
+		}
+		this.initial_context = this.context.slice(0, i + 1);
 	}
 
 	add_to_context(name: string, contextual = false) {

src/compiler/compile/render_dom/index.ts

@@ -301,24 +301,13 @@ export default function dom(
 
 	const instance_javascript = component.extract_javascript(component.ast.instance);
 
-	let i = renderer.context.length;
-	while (i--) {
-		const member = renderer.context[i];
-		if (member.variable) {
-			if (member.variable.referenced || member.variable.export_name) break;
-		} else if (member.is_non_contextual) {
-			break;
-		}
-	}
-	const initial_context = renderer.context.slice(0, i + 1);
-
 	const has_definition = (
 		component.compile_options.dev ||
 		(instance_javascript && instance_javascript.length > 0) ||
 		filtered_props.length > 0 ||
 		uses_props ||
 		component.partly_hoisted.length > 0 ||
-		initial_context.length > 0 ||
+		renderer.initial_context.length > 0 ||
 		component.reactive_declarations.length > 0 ||
 		capture_state ||
 		inject_state
@@ -404,7 +393,7 @@ export default function dom(
 
 		const return_value = {
 			type: 'ArrayExpression',
-			elements: initial_context.map(member => ({
+			elements: renderer.initial_context.map(member => ({
 				type: 'Identifier',
 				name: member.name
 			}) as Expression)

test/js/samples/initial-context/expected.js

@@ -0,0 +1,59 @@
+/* generated by Svelte vX.Y.Z */
+import {
+	SvelteComponent,
+	detach,
+	element,
+	init,
+	insert,
+	listen,
+	noop,
+	safe_not_equal
+} from "svelte/internal";
+
+function create_fragment(ctx) {
+	let button;
+	let mounted;
+	let dispose;
+
+	return {
+		c() {
+			button = element("button");
+		},
+		m(target, anchor) {
+			insert(target, button, anchor);
+
+			if (!mounted) {
+				dispose = listen(button, "click", /*click_handler*/ ctx[1]);
+				mounted = true;
+			}
+		},
+		p: noop,
+		i: noop,
+		o: noop,
+		d(detaching) {
+			if (detaching) detach(button);
+			mounted = false;
+			dispose();
+		}
+	};
+}
+
+function instance($$self, $$props, $$invalidate) {
+	let foo;
+
+	function unreferenced() {
+		$$invalidate(0, foo = 1);
+	}
+
+	const click_handler = () => $$invalidate(0, foo = 2);
+	return [foo, click_handler];
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		init(this, options, instance, create_fragment, safe_not_equal, {});
+	}
+}
+
+export default Component;

test/js/samples/initial-context/input.svelte

@@ -0,0 +1,7 @@
+<script>
+  let foo;
+  function unreferenced () {
+    foo = 1;
+  }
+</script>
+<button on:click={() => foo = 2}></button>