Highlight issue when a lazy boundary returns a fragment

compat/test/browser/suspense-hydration.test.js

@@ -139,6 +139,36 @@ describe('suspense hydration', () => {
 		});
 	});
 
+	it('Should hydrate a fragment with multiple children correctly', () => {
+		scratch.innerHTML = '<div>Hello</div><div>World!</div>';
+		clearLog();
+
+		const [Lazy, resolve] = createLazy();
+		hydrate(
+			<Suspense>
+				<Lazy />
+			</Suspense>,
+			scratch
+		);
+		rerender(); // Flush rerender queue to mimic what preact will really do
+		expect(scratch.innerHTML).to.equal('<div>Hello</div><div>World!</div>');
+		expect(getLog()).to.deep.equal([]);
+		clearLog();
+
+		return resolve(() => (
+			<>
+				<div>Hello</div>
+				<div>World!</div>
+			</>
+		)).then(() => {
+			rerender();
+			expect(scratch.innerHTML).to.equal('<div>Hello</div><div>World!</div>');
+			expect(getLog()).to.deep.equal([]);
+
+			clearLog();
+		});
+	});
+
 	it('should allow siblings to update around suspense boundary', () => {
 		scratch.innerHTML = '<div>Count: 0</div><div>Hello</div>';
 		clearLog();

src/diff/index.js

@@ -53,7 +53,7 @@ export function diff(
 	if (oldVNode._flags & MODE_SUSPENDED) {
 		isHydrating = !!(oldVNode._flags & MODE_HYDRATE);
 		oldDom = newVNode._dom = oldVNode._dom;
-		excessDomChildren = [oldDom];
+		excessDomChildren = oldVNode._excess;
 	}
 
 	if ((tmp = options._diff)) tmp(newVNode);
@@ -277,6 +277,7 @@ export function diff(
 				newVNode._flags |= isHydrating
 					? MODE_HYDRATE | MODE_SUSPENDED
 					: MODE_HYDRATE;
+				newVNode._excess = [...excessDomChildren];
 				excessDomChildren[excessDomChildren.indexOf(oldDom)] = null;
 				// ^ could possibly be simplified to:
 				// excessDomChildren.length = 0;