Fix and test for disabling stateful re-rendering during string rendering. Fixes preactjs/preact#524

Author: developit

src/index.js

@@ -84,6 +84,8 @@ export default function renderToString(vnode, context, opts, inner, isSvgMode) {
 			else {
 				// class-based components
 				let c = new nodeName(props, context);
+				// turn off stateful re-rendering:
+				c._disable = c.__x = true;
 				c.props = props;
 				c.context = context;
 				if (c.componentWillMount) c.componentWillMount();

test/render.js

@@ -1,7 +1,7 @@
 import { render, shallowRender } from '../src';
 import { h, Component } from 'preact';
 import chai, { expect } from 'chai';
-import { spy, match } from 'sinon';
+import { spy, stub, match } from 'sinon';
 import sinonChai from 'sinon-chai';
 chai.use(sinonChai);
 
@@ -467,4 +467,43 @@ describe('render', () => {
 			expect(renderXml(<div foo={false} bar={0} />)).to.equal(`<div bar="0" />`);
 		});
 	});
+	
+	describe('state locking', () => {
+		it('should set _disable and __x to true', () => {
+			let inst;
+			class Foo extends Component {
+				constructor(props, context) {
+					super(props, context);
+					inst = this;
+				}
+				render() {
+					return <div />;
+				}
+			}
+			
+			expect(render(<Foo />)).to.equal('<div></div>');
+			
+			expect(inst).to.have.property('_disable', true);
+			expect(inst).to.have.property('__x', true);
+		});
+
+		it('should prevent re-rendering', () => {
+			const Bar = stub().returns(<div />);
+
+			let count = 0;
+
+			class Foo extends Component {
+				componentWillMount() {
+					this.forceUpdate();
+				}
+				render() {
+					return <Bar count={++count} />;
+				}
+			}
+			
+			expect(render(<Foo />)).to.equal('<div></div>');
+			
+			expect(Bar).to.have.been.calledOnce.and.calledWithMatch({ count: 1 });
+		});
+	});
 });