Pass children to client components even if they do not render them (#2588)

* Pass children to client components even if they do not render them

* Handle when no children are provided

* Adds a changeset

* Use roots directly i guess

* Use an attribute to signal that the template is needed

12 files changed, 149 insertions, 11 deletions

diff --git a/.changeset/great-suns-pump.md b/.changeset/great-suns-pump.md
new file mode 100644
index 000000000..0d4a2541e
--- /dev/null
+++ b/.changeset/great-suns-pump.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix for passing children to client component when the component does not render them
diff --git a/packages/astro/src/@types/astro.ts b/packages/astro/src/@types/astro.ts
index d93563352..c2708ab1e 100644
--- a/packages/astro/src/@types/astro.ts
+++ b/packages/astro/src/@types/astro.ts
@@ -213,6 +213,7 @@ export type GetStaticPathsResultKeyed = GetStaticPathsResult & {
 };
 
 export interface HydrateOptions {
+	name: string;
 	value?: string;
 }
 
diff --git a/packages/astro/src/runtime/client/idle.ts b/packages/astro/src/runtime/client/idle.ts
index c3914cfbe..6a5bf15e1 100644
--- a/packages/astro/src/runtime/client/idle.ts
+++ b/packages/astro/src/runtime/client/idle.ts
@@ -4,10 +4,26 @@ import type { GetHydrateCallback, HydrateOptions } from '../../@types/astro';
  * Hydrate this component as soon as the main thread is free
  * (or after a short delay, if `requestIdleCallback`) isn't supported
  */
-export default async function onIdle(astroId: string, _options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
+export default async function onIdle(astroId: string, options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
 	const cb = async () => {
 		const roots = document.querySelectorAll(`astro-root[uid="${astroId}"]`);
-		const innerHTML = roots[0].querySelector(`astro-fragment`)?.innerHTML ?? null;
+		if(roots.length === 0) {
+			throw new Error(`Unable to find the root for the component ${options.name}`);
+		}
+	
+		let innerHTML: string | null = null;
+		let fragment = roots[0].querySelector(`astro-fragment`);
+		if(fragment == null && roots[0].hasAttribute('tmpl')) {
+			// If there is no child fragment, check to see if there is a template.
+			// This happens if children were passed but the client component did not render any.
+			let template = roots[0].querySelector(`template[data-astro-template]`);
+			if(template) {
+				innerHTML = template.innerHTML;
+				template.remove();
+			}
+		} else if(fragment) {
+			innerHTML = fragment.innerHTML;
+		}
 		const hydrate = await getHydrateCallback();
 
 		for (const root of roots) {
diff --git a/packages/astro/src/runtime/client/load.ts b/packages/astro/src/runtime/client/load.ts
index c3fae489e..73bb441cf 100644
--- a/packages/astro/src/runtime/client/load.ts
+++ b/packages/astro/src/runtime/client/load.ts
@@ -3,9 +3,27 @@ import type { GetHydrateCallback, HydrateOptions } from '../../@types/astro';
 /**
  * Hydrate this component immediately
  */
-export default async function onLoad(astroId: string, _options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
+export default async function onLoad(astroId: string, options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
 	const roots = document.querySelectorAll(`astro-root[uid="${astroId}"]`);
-	const innerHTML = roots[0].querySelector(`astro-fragment`)?.innerHTML ?? null;
+	if(roots.length === 0) {
+		throw new Error(`Unable to find the root for the component ${options.name}`);
+	}
+
+	let innerHTML: string | null = null;
+	let fragment = roots[0].querySelector(`astro-fragment`);
+	if(fragment == null && roots[0].hasAttribute('tmpl')) {
+		// If there is no child fragment, check to see if there is a template.
+		// This happens if children were passed but the client component did not render any.
+		let template = roots[0].querySelector(`template[data-astro-template]`);
+		if(template) {
+			innerHTML = template.innerHTML;
+			template.remove();
+		}
+	} else if(fragment) {
+		innerHTML = fragment.innerHTML;
+	}
+
+	//const innerHTML = roots[0].querySelector(`astro-fragment`)?.innerHTML ?? null;
 	const hydrate = await getHydrateCallback();
 
 	for (const root of roots) {
diff --git a/packages/astro/src/runtime/client/media.ts b/packages/astro/src/runtime/client/media.ts
index ef2f65260..f5ae240c1 100644
--- a/packages/astro/src/runtime/client/media.ts
+++ b/packages/astro/src/runtime/client/media.ts
@@ -5,7 +5,23 @@ import type { GetHydrateCallback, HydrateOptions } from '../../@types/astro';
  */
 export default async function onMedia(astroId: string, options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
 	const roots = document.querySelectorAll(`astro-root[uid="${astroId}"]`);
-	const innerHTML = roots[0].querySelector(`astro-fragment`)?.innerHTML ?? null;
+	if(roots.length === 0) {
+		throw new Error(`Unable to find the root for the component ${options.name}`);
+	}
+
+	let innerHTML: string | null = null;
+	let fragment = roots[0].querySelector(`astro-fragment`);
+	if(fragment == null && roots[0].hasAttribute('tmpl')) {
+		// If there is no child fragment, check to see if there is a template.
+		// This happens if children were passed but the client component did not render any.
+		let template = roots[0].querySelector(`template[data-astro-template]`);
+		if(template) {
+			innerHTML = template.innerHTML;
+			template.remove();
+		}
+	} else if(fragment) {
+		innerHTML = fragment.innerHTML;
+	}
 
 	const cb = async () => {
 		const hydrate = await getHydrateCallback();
diff --git a/packages/astro/src/runtime/client/only.ts b/packages/astro/src/runtime/client/only.ts
index c3fae489e..cc4efb99d 100644
--- a/packages/astro/src/runtime/client/only.ts
+++ b/packages/astro/src/runtime/client/only.ts
@@ -3,9 +3,25 @@ import type { GetHydrateCallback, HydrateOptions } from '../../@types/astro';
 /**
  * Hydrate this component immediately
  */
-export default async function onLoad(astroId: string, _options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
+export default async function onLoad(astroId: string, options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
 	const roots = document.querySelectorAll(`astro-root[uid="${astroId}"]`);
-	const innerHTML = roots[0].querySelector(`astro-fragment`)?.innerHTML ?? null;
+	if(roots.length === 0) {
+		throw new Error(`Unable to find the root for the component ${options.name}`);
+	}
+
+	let innerHTML: string | null = null;
+	let fragment = roots[0].querySelector(`astro-fragment`);
+	if(fragment == null && roots[0].hasAttribute('tmpl')) {
+		// If there is no child fragment, check to see if there is a template.
+		// This happens if children were passed but the client component did not render any.
+		let template = roots[0].querySelector(`template[data-astro-template]`);
+		if(template) {
+			innerHTML = template.innerHTML;
+			template.remove();
+		}
+	} else if(fragment) {
+		innerHTML = fragment.innerHTML;
+	}
 	const hydrate = await getHydrateCallback();
 
 	for (const root of roots) {
diff --git a/packages/astro/src/runtime/client/visible.ts b/packages/astro/src/runtime/client/visible.ts
index e06aabab4..101551ec0 100644
--- a/packages/astro/src/runtime/client/visible.ts
+++ b/packages/astro/src/runtime/client/visible.ts
@@ -5,9 +5,25 @@ import type { GetHydrateCallback, HydrateOptions } from '../../@types/astro';
  * We target the children because `astro-root` is set to `display: contents`
  * which doesn't work with IntersectionObserver
  */
-export default async function onVisible(astroId: string, _options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
+export default async function onVisible(astroId: string, options: HydrateOptions, getHydrateCallback: GetHydrateCallback) {
 	const roots = document.querySelectorAll(`astro-root[uid="${astroId}"]`);
-	const innerHTML = roots[0].querySelector(`astro-fragment`)?.innerHTML ?? null;
+	if(roots.length === 0) {
+		throw new Error(`Unable to find the root for the component ${options.name}`);
+	}
+
+	let innerHTML: string | null = null;
+	let fragment = roots[0].querySelector(`astro-fragment`);
+	if(fragment == null && roots[0].hasAttribute('tmpl')) {
+		// If there is no child fragment, check to see if there is a template.
+		// This happens if children were passed but the client component did not render any.
+		let template = roots[0].querySelector(`template[data-astro-template]`);
+		if(template) {
+			innerHTML = template.innerHTML;
+			template.remove();
+		}
+	} else if(fragment) {
+		innerHTML = fragment.innerHTML;
+	}
 
 	const cb = async () => {
 		const hydrate = await getHydrateCallback();
diff --git a/packages/astro/src/runtime/server/hydration.ts b/packages/astro/src/runtime/server/hydration.ts
index b339b934f..2ffdc9144 100644
--- a/packages/astro/src/runtime/server/hydration.ts
+++ b/packages/astro/src/runtime/server/hydration.ts
@@ -116,7 +116,7 @@ export async function generateHydrateScript(scriptOptions: HydrateScriptOptions,
 	const hydrationScript = {
 		props: { type: 'module', 'data-astro-component-hydration': true },
 		children: `import setup from '${await result.resolve(hydrationSpecifier(hydrate))}';
-setup("${astroId}", {${metadata.hydrateArgs ? `value: ${JSON.stringify(metadata.hydrateArgs)}` : ''}}, async () => {
+setup("${astroId}", {name:"${metadata.displayName}",${metadata.hydrateArgs ? `value: ${JSON.stringify(metadata.hydrateArgs)}` : ''}}, async () => {
   ${hydrationSource}
 });
 `,
diff --git a/packages/astro/src/runtime/server/index.ts b/packages/astro/src/runtime/server/index.ts
index 56a6a2a49..2253e2b99 100644
--- a/packages/astro/src/runtime/server/index.ts
+++ b/packages/astro/src/runtime/server/index.ts
@@ -274,7 +274,10 @@ If you're still stuck, please open an issue on GitHub or join us at https://astr
 	// INVESTIGATE: This will likely be a problem in streaming because the `<head>` will be gone at this point.
 	result.scripts.add(await generateHydrateScript({ renderer, result, astroId, props }, metadata as Required<AstroComponentMetadata>));
 
-	return unescapeHTML(`<astro-root uid="${astroId}">${html ?? ''}</astro-root>`);
+	// Render a template if no fragment is provided.
+	const needsAstroTemplate = children && !/<\/?astro-fragment\>/.test(html);
+	const template = needsAstroTemplate ? `<template data-astro-template>${children}</template>` : '';
+	return unescapeHTML(`<astro-root uid="${astroId}"${needsAstroTemplate ? ' tmpl' : ''}>${html ?? ''}${template}</astro-root>`);
 }
 
 /** Create the Astro.fetchContent() runtime function. */
diff --git a/packages/astro/test/astro-children.test.js b/packages/astro/test/astro-children.test.js
index 99c19387c..3df65e2e6 100644
--- a/packages/astro/test/astro-children.test.js
+++ b/packages/astro/test/astro-children.test.js
@@ -69,4 +69,24 @@ describe('Component children', () => {
 		expect($svelte.children(':first-child').text().trim()).to.equal('Hello world');
 		expect($svelte.children(':last-child').text().trim()).to.equal('Goodbye world');
 	});
+
+	it('Renders a template when children are not rendered for client components', async () => {
+		const html = await fixture.readFile('/no-render/index.html');
+		const $ = cheerio.load(html);
+
+		// test 1: If SSR only, no children are rendered.
+		expect($('#ssr-only').children()).to.have.lengthOf(0);
+
+		// test 2: If client, and no children are rendered, a template is.
+		expect($('#client').parent().children()).to.have.lengthOf(2, 'rendered the client component and a template');
+		expect($('#client').parent().find('template[data-astro-template]')).to.have.lengthOf(1, 'Found 1 template');
+
+		// test 3: If client, and children are rendered, no template is.
+		expect($('#client-render').parent().children()).to.have.lengthOf(1);
+		expect($('#client-render').parent().find('template')).to.have.lengthOf(0);
+
+		// test 4: If client and no children are provided, no template is.
+		expect($('#client-no-children').parent().children()).to.have.lengthOf(1);
+		expect($('#client-no-children').parent().find('template')).to.have.lengthOf(0);
+	});
 });
diff --git a/packages/astro/test/fixtures/astro-children/src/components/NoRender.jsx b/packages/astro/test/fixtures/astro-children/src/components/NoRender.jsx
new file mode 100644
index 000000000..f3c41eb54
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-children/src/components/NoRender.jsx
@@ -0,0 +1,5 @@
+import { h } from 'preact';
+
+export default function PreactComponent({ id, children, render = false }) {
+  return <div id={id} class="preact-no-children">{render && children}</div>;
+}
diff --git a/packages/astro/test/fixtures/astro-children/src/pages/no-render.astro b/packages/astro/test/fixtures/astro-children/src/pages/no-render.astro
new file mode 100644
index 000000000..9b2c3e867
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-children/src/pages/no-render.astro
@@ -0,0 +1,22 @@
+---
+import PreactComponent from '../components/NoRender.jsx';
+---
+<html>
+<head><title>Children</title></head>
+<body>
+  <PreactComponent id="ssr-only">
+    <h1>Hello world</h1>
+    <h1>Goodbye world</h1>
+  </PreactComponent>
+	<PreactComponent id="client" client:load>
+	  <h1>Hello world</h1>
+    <h1>Goodbye world</h1>
+	</PreactComponent>
+	<PreactComponent id="client-render" render={true} client:load>
+	  <h1>Hello world</h1>
+    <h1>Goodbye world</h1>
+	</PreactComponent>
+
+	<PreactComponent id="client-no-children" client:load></PreactComponent>
+</body>
+</html>