replace x = x in template

src/compile/nodes/shared/Expression.ts

@@ -10,6 +10,7 @@ import Wrapper from '../../render-dom/wrappers/shared/Wrapper';
 import sanitize from '../../../utils/sanitize';
 import TemplateScope from './TemplateScope';
 import getObject from '../../../utils/getObject';
+import { nodes_match } from '../../../utils/nodes_match';
 
 const binaryOperators: Record<string, number> = {
 	'**': 15,
@@ -253,11 +254,21 @@ export default class Expression {
 							? [getObject(node.left).name]
 							: extractNames(node.left);
 
-						names.forEach(name => {
-							if (!scope.declarations.has(name)) {
-								pending_assignments.add(name);
-							}
-						});
+						if (node.operator === '=' && nodes_match(node.left, node.right)) {
+							const dirty = names.filter(name => {
+								return !scope.declarations.has(name);
+							});
+
+							if (dirty.length) component.has_reactive_assignments = true;
+
+							code.overwrite(node.start, node.end, dirty.map(n => `$$make_dirty('${n}')`).join('; '));
+						} else {
+							names.forEach(name => {
+								if (!scope.declarations.has(name)) {
+									pending_assignments.add(name);
+								}
+							});
+						}
 					} else if (node.type === 'UpdateExpression') {
 						const { name } = getObject(node.argument);
 

test/js/samples/instrumentation-template-x-equals-x/expected.js

@@ -0,0 +1,67 @@
+/* generated by Svelte vX.Y.Z */
+import { SvelteComponent as SvelteComponent_1, addListener, append, createElement, createText, detachNode, init, insert, run, safe_not_equal, setData } from "svelte/internal.js";
+
+function create_fragment(component, ctx) {
+	var button, text1, p, text2, text3_value = ctx.things.length, text3, current, dispose;
+
+	return {
+		c() {
+			button = createElement("button");
+			button.textContent = "foo";
+			text1 = createText("\n\n");
+			p = createElement("p");
+			text2 = createText("number of things: ");
+			text3 = createText(text3_value);
+			dispose = addListener(button, "click", ctx.click_handler);
+		},
+
+		m(target, anchor) {
+			insert(target, button, anchor);
+			insert(target, text1, anchor);
+			insert(target, p, anchor);
+			append(p, text2);
+			append(p, text3);
+			current = true;
+		},
+
+		p(changed, ctx) {
+			if ((changed.things) && text3_value !== (text3_value = ctx.things.length)) {
+				setData(text3, text3_value);
+			}
+		},
+
+		i(target, anchor) {
+			if (current) return;
+			this.m(target, anchor);
+		},
+
+		o: run,
+
+		d(detach) {
+			if (detach) {
+				detachNode(button);
+				detachNode(text1);
+				detachNode(p);
+			}
+
+			dispose();
+		}
+	};
+}
+
+function define($$self, $$props, $$make_dirty) {
+	let things = [];
+
+	function click_handler() { things.push(1); $$make_dirty('things') }
+
+	$$self.$$.get = () => ({ things, click_handler });
+}
+
+class SvelteComponent extends SvelteComponent_1 {
+	constructor(options) {
+		super();
+		init(this, options, define, create_fragment, safe_not_equal);
+	}
+}
+
+export default SvelteComponent;

test/js/samples/instrumentation-template-x-equals-x/input.html

@@ -0,0 +1,7 @@
+<script>
+	let things = [];
+</script>
+
+<button on:click="{() => { things.push(1); things = things }}">foo</button>
+
+<p>number of things: {things.length}</p>