Fix rare scenario where an unmounted suspended tree would resolve

compat/src/suspense.js

@@ -147,7 +147,7 @@ Suspense.prototype._childDidSuspend = function (promise, suspendingVNode) {
 		if (!--c._pendingSuspensionCount) {
 			// If the suspension was during hydration we don't need to restore the
 			// suspended children into the _children array
-			if (c.state._suspended) {
+			if (c.state._suspended && c.state._suspended._component) {
 				const suspendedVNode = c.state._suspended;
 				c._vnode._children[0] = removeOriginal(
 					suspendedVNode,
@@ -181,6 +181,7 @@ Suspense.prototype._childDidSuspend = function (promise, suspendingVNode) {
 
 Suspense.prototype.componentWillUnmount = function () {
 	this._suspenders = [];
+	this.state._suspended = this._detachOnNextRender = null;
 };
 
 /**
@@ -236,6 +237,7 @@ Suspense.prototype.render = function (props, state) {
  * @returns {((unsuspend: () => void) => void)?}
  */
 export function suspended(vnode) {
+	if (!vnode._parent) return null;
 	/** @type {import('./internal').Component} */
 	let component = vnode._parent._component;
 	return component && component._suspended && component._suspended(vnode);

compat/test/browser/suspense.test.js

@@ -415,6 +415,49 @@ describe('suspense', () => {
 		});
 	});
 
+	it('should not crash when suspended child updates after unmount', () => {
+		/** @type {Component | null} */
+		let childInstance = null;
+		const neverResolvingPromise = new Promise(() => {});
+
+		class ThrowingChild extends Component {
+			constructor(props) {
+				super(props);
+				this.state = { suspend: false, value: 0 };
+				childInstance = this;
+			}
+
+			render(props, state) {
+				if (state.suspend) {
+					throw neverResolvingPromise;
+				}
+
+				return <div>value:{state.value}</div>;
+			}
+		}
+
+		render(
+			<Suspense fallback={<div>Suspended...</div>}>
+				<ThrowingChild />
+			</Suspense>,
+			scratch
+		);
+
+		expect(childInstance).to.not.equal(null);
+		expect(scratch.innerHTML).to.equal('<div>value:0</div>');
+
+		act(() => childInstance.setState({ suspend: true }));
+		rerender();
+		expect(scratch.innerHTML).to.equal('<div>Suspended...</div>');
+
+		render(null, scratch);
+
+		childInstance.setState({ value: 1 });
+		rerender();
+
+		expect(scratch.innerHTML).to.equal('');
+	});
+
 	it('should properly call lifecycle methods of an initially suspending component', () => {
 		/** @type {() => Promise<void>} */
 		let resolve;

src/component.js

@@ -126,7 +126,7 @@ function renderComponent(component) {
 		commitQueue = [],
 		refQueue = [];
 
-	if (component._parentDom) {
+	if (component._parentDom && oldVNode._parent) {
 		const newVNode = assign({}, oldVNode);
 		newVNode._original = oldVNode._original + 1;
 		if (options.vnode) options.vnode(newVNode);