feat: debug throw on too many rerenders

debug/src/debug.js

@@ -247,11 +247,31 @@ export function initDebug() {
 		if (oldBeforeDiff) oldBeforeDiff(vnode);
 	};
 
+	let renderCount = 0;
+	let currentComponent;
 	options._render = vnode => {
 		if (oldRender) {
 			oldRender(vnode);
 		}
 		hooksAllowed = true;
+
+		const nextComponent = vnode._component;
+		if (nextComponent === currentComponent) {
+			renderCount++;
+		} else {
+			renderCount = 1;
+		}
+
+		if (renderCount >= 25) {
+			throw new Error(
+				`Too many re-renders. This is limited to prevent an infinite loop ` +
+					`which may lock up your browser. The component causing this is: ${getDisplayName(
+						vnode
+					)}`
+			);
+		}
+
+		currentComponent = nextComponent;
 	};
 
 	options._hook = (comp, index, type) => {

debug/test/browser/debug.test.js

@@ -1,4 +1,5 @@
 import { createElement, render, createRef, Component, Fragment } from 'preact';
+import { useState } from 'preact/hooks';
 import {
 	setupScratch,
 	teardown,
@@ -271,6 +272,37 @@ describe('debug', () => {
 		expect(console.error).to.not.be.called;
 	});
 
+	it('throws an error if a component rerenders too many times', () => {
+		let rerenderCount = 0;
+		function TestComponent({ loop = false }) {
+			const [count, setCount] = useState(0);
+			if (loop) {
+				setCount(count + 1);
+			}
+
+			if (count > 30) {
+				expect.fail(
+					'Repeated rerenders did not cause the expected error. This test is failing.'
+				);
+			}
+
+			rerenderCount += 1;
+			return <div />;
+		}
+
+		expect(() => {
+			render(
+				<Fragment>
+					<TestComponent />
+					<TestComponent loop />
+				</Fragment>,
+				scratch
+			);
+		}).to.throw(/Too many re-renders/);
+		// 1 for first TestComponent + 24 for second TestComponent
+		expect(rerenderCount).to.equal(25);
+	});
+
 	describe('duplicate keys', () => {
 		const List = props => <ul>{props.children}</ul>;
 		const ListItem = props => <li>{props.children}</li>;