chore: Throw a clear error when the LocationProvider is missing

src/router.js

@@ -118,6 +118,9 @@ export function Router(props) {
 	const [c, update] = useReducer(c => c + 1, 0);
 
 	const { url, query, wasPush, path } = useLocation();
+	if (!url) {
+		throw new Error(`preact-iso's <Router> must be used within a <LocationProvider>, see: https://github.com/preactjs/preact-iso#locationprovider`);
+	}
 	const { rest = path, params = {} } = useContext(RouteContext);
 
 	const isLoading = useRef(false);

test/router.test.js

@@ -42,6 +42,22 @@ describe('Router', () => {
 	});
 
 
+	it('should throw a clear error if the LocationProvider is missing', () => {
+		const Home = () => <h1>Home</h1>;
+
+		try {
+			render(
+				<Router>
+					<Home path="/" test="2" />
+				</Router>,
+				scratch
+			);
+			expect.fail('should have thrown');
+		} catch (e) {
+			expect(e.message).to.include('must be used within a <LocationProvider>');
+		}
+	});
+
 	it('should strip trailing slashes from path', async () => {
 		render(
 			<LocationProvider url="/a/">
@@ -953,7 +969,7 @@ describe('Router', () => {
 		);
 
 		shadowlink.click();
-		
+
 		await sleep(1);
 
 		expect(loc).to.deep.include({ url: '/shadow' });