From 8b9d53037879cd7ca7bee4d20b4e6f08e984a7df Mon Sep 17 00:00:00 2001
From: Bjorn Lu <bjornlu.dev@gmail.com>
Date: Tue, 7 Jan 2025 23:05:01 +0800
Subject: [PATCH] Process empty markdown body for remark/rehype plugins
 (#12920)

---
 .changeset/pink-years-warn.md                          |  5 +++++
 .../src/vite-plugin-markdown/content-entry-type.ts     |  8 ++------
 packages/astro/test/astro-markdown-plugins.test.js     | 10 ++++++++++
 .../content-layer-remark-plugins/astro.config.mjs      |  8 ++++++++
 .../src/content/docs/empty-content.md                  |  3 +++
 .../src/pages/[...slug].astro                          |  3 ++-
 6 files changed, 30 insertions(+), 7 deletions(-)
 create mode 100644 .changeset/pink-years-warn.md
 create mode 100644 packages/astro/test/fixtures/content-layer-remark-plugins/src/content/docs/empty-content.md

diff --git a/.changeset/pink-years-warn.md b/.changeset/pink-years-warn.md
new file mode 100644
index 000000000000..aa2c6ccd920e
--- /dev/null
+++ b/.changeset/pink-years-warn.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Processes markdown with empty body as remark and rehype plugins may add additional content or frontmatter
diff --git a/packages/astro/src/vite-plugin-markdown/content-entry-type.ts b/packages/astro/src/vite-plugin-markdown/content-entry-type.ts
index 3ca85a35655c..6f248853f51e 100644
--- a/packages/astro/src/vite-plugin-markdown/content-entry-type.ts
+++ b/packages/astro/src/vite-plugin-markdown/content-entry-type.ts
@@ -20,12 +20,8 @@ export const markdownContentEntryType: ContentEntryType = {
 	async getRenderFunction(config) {
 		const processor = await createMarkdownProcessor(config.markdown);
 		return async function renderToString(entry) {
-			if (!entry.body) {
-				return {
-					html: '',
-				};
-			}
-			const result = await processor.render(entry.body, {
+			// Process markdown even if it's empty as remark/rehype plugins may add content or frontmatter dynamically
+			const result = await processor.render(entry.body ?? '', {
 				frontmatter: entry.data,
 				// @ts-expect-error Internal API
 				fileURL: entry.filePath ? pathToFileURL(entry.filePath) : undefined,
diff --git a/packages/astro/test/astro-markdown-plugins.test.js b/packages/astro/test/astro-markdown-plugins.test.js
index 3429c2ed7b70..78db0e6dcbf6 100644
--- a/packages/astro/test/astro-markdown-plugins.test.js
+++ b/packages/astro/test/astro-markdown-plugins.test.js
@@ -135,6 +135,16 @@ describe('Astro Markdown plugins', () => {
 			const $ = cheerio.load(html);
 			assert.equal($('p').text(), 'Not transformed');
 		});
+
+		it('processes empty markdown content with remark plugins', async () => {
+			const html = await fixture.readFile('/empty-content/index.html');
+			const $ = cheerio.load(html);
+			assert.equal($('h1').text(), 'Test Empty Markdown');
+			assert.equal(
+				$('#frontmatter-custom-property').text(),
+				'Generated property via remark plugin!',
+			);
+		});
 	});
 });
 
diff --git a/packages/astro/test/fixtures/content-layer-remark-plugins/astro.config.mjs b/packages/astro/test/fixtures/content-layer-remark-plugins/astro.config.mjs
index 950fdd73ba26..22efd09740ef 100644
--- a/packages/astro/test/fixtures/content-layer-remark-plugins/astro.config.mjs
+++ b/packages/astro/test/fixtures/content-layer-remark-plugins/astro.config.mjs
@@ -15,6 +15,14 @@ export default defineConfig({
 					});
         };
       },
+      function addFrontmatter() {
+        return function (tree, file) {
+          if (file.data.astro?.frontmatter) {
+          file.data.astro.frontmatter.customProperty =
+            'Generated property via remark plugin!';
+          }
+        };
+      }
     ],
   },
 });
diff --git a/packages/astro/test/fixtures/content-layer-remark-plugins/src/content/docs/empty-content.md b/packages/astro/test/fixtures/content-layer-remark-plugins/src/content/docs/empty-content.md
new file mode 100644
index 000000000000..840d7d64ac72
--- /dev/null
+++ b/packages/astro/test/fixtures/content-layer-remark-plugins/src/content/docs/empty-content.md
@@ -0,0 +1,3 @@
+---
+title: Test Empty Markdown
+---
diff --git a/packages/astro/test/fixtures/content-layer-remark-plugins/src/pages/[...slug].astro b/packages/astro/test/fixtures/content-layer-remark-plugins/src/pages/[...slug].astro
index 757765a4c7ea..b25523258acc 100644
--- a/packages/astro/test/fixtures/content-layer-remark-plugins/src/pages/[...slug].astro
+++ b/packages/astro/test/fixtures/content-layer-remark-plugins/src/pages/[...slug].astro
@@ -10,7 +10,7 @@ export async function getStaticPaths() {
 }
 
 const { doc } = Astro.props;
-const { Content } = await render(doc);
+const { Content, remarkPluginFrontmatter } = await render(doc);
 ---
 
 <!DOCTYPE html>
@@ -22,6 +22,7 @@ const { Content } = await render(doc);
 </head>
 <body>
 	<h1>{doc.data.title}</h1>
+  <div id="frontmatter-custom-property">{remarkPluginFrontmatter?.customProperty}</div>
 	<Content />
 </body>
 </html>