Fix instance where renderToStringAsync returns a promise of a promise (#378)

* Fix issue where rendered is a promise

I want to test this in my project to see if this change fixes it.

All being well, I'll then add a test here and submit it for review

* Different syntax, but more success

I'm unclear why the previous didn't seem to work for me

* Attempt to write a test for the case based on my app

So far no luck actually reproducing the issue.

I will take a different tact and remove code from my app until the issue
goes away, to figure out what causes the behaviour.

* Add test that tests behaviour

* Further simplify test case

* Further simplify test case

* Create the test I want

* Revert unrelated change

* Add changeset

* Add missing imports

* Reproduce without useClient

But I still need the provider

* Avoid using urql

* Better description

* Update test/compat/async.test.jsx

---------

Co-authored-by: Jovi De Croock <[email protected]>

Author: ccouzens

.changeset/famous-experts-decide.md

@@ -0,0 +1,5 @@
+---
+'preact-render-to-string': patch
+---
+
+Fix issue where preactRenderToString returns a promise of a promise

src/index.js

@@ -109,7 +109,7 @@ export async function renderToStringAsync(vnode, context) {
 	parent[CHILDREN] = [vnode];
 
 	try {
-		const rendered = _renderToString(
+		const rendered = await _renderToString(
 			vnode,
 			context || EMPTY_OBJ,
 			false,

test/compat/async.test.jsx

@@ -1,6 +1,6 @@
 import { renderToStringAsync } from '../../src/index.js';
-import { h } from 'preact';
-import { Suspense, useId } from 'preact/compat';
+import { h, Fragment } from 'preact';
+import { Suspense, useId, lazy, createContext } from 'preact/compat';
 import { expect } from 'chai';
 import { createSuspender } from '../utils.jsx';
 
@@ -26,10 +26,14 @@ describe('Async renderToString', () => {
 	});
 
 	it('should render JSX with nested suspended components', async () => {
-		const { Suspender: SuspenderOne, suspended: suspendedOne } =
-			createSuspender();
-		const { Suspender: SuspenderTwo, suspended: suspendedTwo } =
-			createSuspender();
+		const {
+			Suspender: SuspenderOne,
+			suspended: suspendedOne
+		} = createSuspender();
+		const {
+			Suspender: SuspenderTwo,
+			suspended: suspendedTwo
+		} = createSuspender();
 
 		const promise = renderToStringAsync(
 			<ul>
@@ -56,10 +60,14 @@ describe('Async renderToString', () => {
 	});
 
 	it('should render JSX with nested suspense boundaries', async () => {
-		const { Suspender: SuspenderOne, suspended: suspendedOne } =
-			createSuspender();
-		const { Suspender: SuspenderTwo, suspended: suspendedTwo } =
-			createSuspender();
+		const {
+			Suspender: SuspenderOne,
+			suspended: suspendedOne
+		} = createSuspender();
+		const {
+			Suspender: SuspenderTwo,
+			suspended: suspendedTwo
+		} = createSuspender();
 
 		const promise = renderToStringAsync(
 			<ul>
@@ -88,12 +96,18 @@ describe('Async renderToString', () => {
 	});
 
 	it('should render JSX with multiple suspended direct children within a single suspense boundary', async () => {
-		const { Suspender: SuspenderOne, suspended: suspendedOne } =
-			createSuspender();
-		const { Suspender: SuspenderTwo, suspended: suspendedTwo } =
-			createSuspender();
-		const { Suspender: SuspenderThree, suspended: suspendedThree } =
-			createSuspender();
+		const {
+			Suspender: SuspenderOne,
+			suspended: suspendedOne
+		} = createSuspender();
+		const {
+			Suspender: SuspenderTwo,
+			suspended: suspendedTwo
+		} = createSuspender();
+		const {
+			Suspender: SuspenderThree,
+			suspended: suspendedThree
+		} = createSuspender();
 
 		const promise = renderToStringAsync(
 			<ul>
@@ -175,4 +189,41 @@ describe('Async renderToString', () => {
 		const rendered = await promise;
 		expect(rendered).to.equal('<p>ok</p>');
 	});
+
+	it('should work with an in-render suspension', async () => {
+		const Context = createContext();
+
+		let c = 0;
+
+		const Fetcher = ({ children }) => {
+			c++;
+			if (c === 1) {
+				throw Promise.resolve();
+			}
+			return <Fragment>{children}</Fragment>;
+		};
+
+		const LazyComponent = lazy(
+			async () =>
+				function ImportedComponent() {
+					return <div>2</div>;
+				}
+		);
+
+		const LoadableComponent = ({}) => (
+			<Suspense fallback={'...loading'}>
+				<LazyComponent />
+			</Suspense>
+		);
+
+		const rendered = await renderToStringAsync(
+			<Context.Provider>
+				<Fetcher>
+					<LoadableComponent />
+				</Fetcher>
+			</Context.Provider>
+		);
+
+		expect(rendered).to.equal(`<div>2</div>`);
+	});
 });