Frontmatter injection for MD and MDX (#4176)

* feat: inject vfile data as exports

* feat: add vfile to renderMarkdown output

* feat: add safe astroExports parser to utils

* refactor: expose vite-plugin-utils on astro package

* feat: handle astroExports in mdx

* deps: vfile

* chore: lockfile

* test: astroExports in mdx

* refactor: merge plugin exports into forntmatter

* refactor: astroExports -> astro.frontmatter

* refactor: md astroExports -> astro.frontmatter

* feat: astro.frontmatter vite-plugin-markdown

* chore: remove unused import

* fix: inline safelyGetAstroData in MDX integration

* chore: check that frontmatter export is valid export name

* chore: error log naming

* test: mdx remark frontmatter injection

* fix: inconsistent shiki mod resolution

* fix: add new frontmatter and heading props

* test: remark vdata

* fix: spread astro.data.frontmatter

* test deps: mdast-util-to-string, reading-time

* fix: astro-md test package name

* test: md frontmatter injection

* fix: layouts

* deps: remove vite-plugin-utils export

* fix: package lock

* chore: remove dup import

* chore: changeset

* chore: add comment on safelyGetAstroData source

* deps: move mdast-util-to-string + reading-time to test fixture

* chore: move remark plugins to test fixture

* fix: override plugin frontmatter with user frontmatter

* test: md injected frontmatter overrides

* test: frontmatter injection overrides mdx

3 files changed, 18 insertions, 5 deletions

diff --git a/packages/markdown/remark/src/index.ts b/packages/markdown/remark/src/index.ts
index 4dfd7240f..0bb827c30 100644
--- a/packages/markdown/remark/src/index.ts
+++ b/packages/markdown/remark/src/index.ts
@@ -13,6 +13,7 @@ import remarkPrism from './remark-prism.js';
 import scopedStyles from './remark-scoped-styles.js';
 import remarkShiki from './remark-shiki.js';
 import remarkUnwrap from './remark-unwrap.js';
+import { remarkInitializeAstroData } from './remark-initialize-astro-data.js';
 
 import rehypeRaw from 'rehype-raw';
 import rehypeStringify from 'rehype-stringify';
@@ -45,6 +46,7 @@ export async function renderMarkdown(
 
 	let parser = unified()
 		.use(markdown)
+		.use(remarkInitializeAstroData)
 		.use(isAstroFlavoredMd ? [remarkMdxish, remarkMarkAndUnravel, remarkUnwrap, remarkEscape] : []);
 
 	if (remarkPlugins.length === 0 && rehypePlugins.length === 0) {
@@ -99,10 +101,9 @@ export async function renderMarkdown(
 		)
 		.use(rehypeStringify, { allowDangerousHtml: true });
 
-	let result: string;
+	let vfile: VFile;
 	try {
-		const vfile = await parser.process(input);
-		result = vfile.toString();
+		vfile = await parser.process(input);
 	} catch (err) {
 		// Ensure that the error message contains the input filename
 		// to make it easier for the user to fix the issue
@@ -113,8 +114,9 @@ export async function renderMarkdown(
 	}
 
 	return {
-		metadata: { headings, source: content, html: result.toString() },
-		code: result.toString(),
+		metadata: { headings, source: content, html: String(vfile.value) },
+		code: String(vfile.value),
+		vfile,
 	};
 }
 
diff --git a/packages/markdown/remark/src/remark-initialize-astro-data.ts b/packages/markdown/remark/src/remark-initialize-astro-data.ts
new file mode 100644
index 000000000..37af8aeaf
--- /dev/null
+++ b/packages/markdown/remark/src/remark-initialize-astro-data.ts
@@ -0,0 +1,9 @@
+import type { VFile } from 'vfile';
+
+export function remarkInitializeAstroData() {
+	return function (tree: any, vfile: VFile) {
+		if (!vfile.data.astro) {
+			vfile.data.astro = { frontmatter: {} };
+		}
+	};
+}
diff --git a/packages/markdown/remark/src/types.ts b/packages/markdown/remark/src/types.ts
index 9d09ef294..3569e8d04 100644
--- a/packages/markdown/remark/src/types.ts
+++ b/packages/markdown/remark/src/types.ts
@@ -2,6 +2,7 @@ import type * as hast from 'hast';
 import type * as mdast from 'mdast';
 import type { ILanguageRegistration, IThemeRegistration, Theme } from 'shiki';
 import type * as unified from 'unified';
+import type { VFile } from 'vfile';
 
 export type { Node } from 'unist';
 
@@ -58,5 +59,6 @@ export interface MarkdownMetadata {
 
 export interface MarkdownRenderingResult {
 	metadata: MarkdownMetadata;
+	vfile: VFile;
 	code: string;
 }