Fix head injection in body with slots.render() and head buffering (#6216)

* Fix head injection in body with slots.render() and head buffering

* Adding a changeset

* An MDX test too

.changeset/eight-cameras-itch.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix head injection in body with slots.render() and head buffering

packages/astro/src/runtime/server/render/common.ts

@@ -72,13 +72,22 @@ export function stringifyChunk(result: SSRResult, chunk: string | SlotString | R
 					}
 
 					// If the current scope is with Astro.slots.render()
-					case ScopeFlags.Slot: {
+					case ScopeFlags.Slot:
+					case ScopeFlags.Slot | ScopeFlags.HeadBuffer: {
 						if (hasScopeFlag(result, ScopeFlags.RenderSlot)) {
 							return '';
 						}
 						break;
 					}
 
+					// Nested element inside of JSX during head buffering phase
+					case ScopeFlags.HeadBuffer: {
+            if(hasScopeFlag(result, ScopeFlags.JSX | ScopeFlags.HeadBuffer)) {
+              return "";
+            }
+						break;
+          }
+
 					// Astro.slots.render() should never render head content.
 					case ScopeFlags.RenderSlot | ScopeFlags.Astro:
 					case ScopeFlags.RenderSlot | ScopeFlags.Astro | ScopeFlags.JSX:

packages/astro/test/fixtures/head-injection/src/components/UsesSlotRender.astro

@@ -0,0 +1,7 @@
+---
+import SlotRenderComponent from "./SlotRenderComponent.astro";
+---
+
+<SlotRenderComponent>
+    <p slot="slot-name">Paragraph.</p>
+</SlotRenderComponent>

packages/astro/test/fixtures/head-injection/src/pages/with-render-slot-in-head-buffer.astro

@@ -0,0 +1,7 @@
+---
+import Layout from "../components/Layout.astro";
+import UsesSlotRender from "../components/UsesSlotRender.astro"
+---
+<Layout>
+	<UsesSlotRender />
+</Layout>

packages/astro/test/head-injection.test.js

@@ -50,6 +50,14 @@ describe('Head injection', () => {
 				expect($('head link[rel=stylesheet]')).to.have.a.lengthOf(2);
 				expect($('body link[rel=stylesheet]')).to.have.a.lengthOf(0);
 			});
+
+			it('Using slots in Astro.slots.render() inside head buffering', async () => {
+				const html = await fixture.readFile('/with-render-slot-in-head-buffer/index.html');
+				const $ = cheerio.load(html);
+
+				expect($('head link[rel=stylesheet]')).to.have.a.lengthOf(2);
+				expect($('body link[rel=stylesheet]')).to.have.a.lengthOf(0);
+			});
 		});
 	});
 });

packages/integrations/mdx/test/css-head-mdx.test.js

@@ -69,5 +69,17 @@ describe('Head injection w/ MDX', () => {
 			const bodyLinks = $('body link[rel=stylesheet]');
 			expect(bodyLinks).to.have.a.lengthOf(0);
 		});
+
+		it('JSX component rendering Astro children within head buffering phase', async () => {
+			const html = await fixture.readFile('/posts/using-component/index.html');
+			// Using cheerio here because linkedom doesn't support head tag injection
+			const $ = cheerio.load(html);
+
+			const headLinks = $('head link[rel=stylesheet]');
+			expect(headLinks).to.have.a.lengthOf(1);
+
+			const bodyLinks = $('body link[rel=stylesheet]');
+			expect(bodyLinks).to.have.a.lengthOf(0);
+		});
 	});
 });

packages/integrations/mdx/test/fixtures/css-head-mdx/src/components/BaseHead.astro

@@ -0,0 +1,11 @@
+---
+const { title } = Astro.props;
+---
+<meta charset="UTF-8" />
+<meta name="viewport" content="width=device-width" />
+<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+<meta name="generator" content={Astro.generator} />
+<title>{title}</title>
+<style is:global>
+	@import "../styles/global.css";
+</style>

packages/integrations/mdx/test/fixtures/css-head-mdx/src/components/GenericComponent.astro

@@ -0,0 +1 @@
+<span>just a generic component</span>

packages/integrations/mdx/test/fixtures/css-head-mdx/src/components/MDXWrapper.astro

@@ -0,0 +1,9 @@
+---
+import Component from "./GenericComponent.astro";
+---
+
+<div>
+	<slot name="title" />
+	<slot name="intro" class="inline" />
+  <Component />
+</div>

packages/integrations/mdx/test/fixtures/css-head-mdx/src/content/posts/using-component.mdx

@@ -0,0 +1,13 @@
+---
+title: testing
+---
+import MDXWrapper from "../../components/MDXWrapper.astro";
+
+<MDXWrapper>
+  <h1 slot="title">
+    testing
+  </h1>
+  <div slot="intro">
+    Intro
+  </div>
+</MDXWrapper>

packages/integrations/mdx/test/fixtures/css-head-mdx/src/layouts/ContentLayout.astro

@@ -1,4 +1,5 @@
 ---
+import BaseHead from "../components/BaseHead.astro";
 export interface Props {
 	title: string;
 }
@@ -9,14 +10,7 @@ const { title } = Astro.props;
 <!DOCTYPE html>
 <html lang="en">
 	<head>
-		<meta charset="UTF-8" />
-		<meta name="viewport" content="width=device-width" />
-		<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
-		<meta name="generator" content={Astro.generator} />
-		<title>{title}</title>
-		<style is:global>
-			@import "../styles/global.css";
-		</style>
+		<BaseHead title={title} />
 	</head>
 	<body>
 		<slot />