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

.changeset/cool-crabs-trade.md

@@ -0,0 +1,7 @@
+---
+'astro': minor
+'@astrojs/mdx': minor
+'@astrojs/markdown-remark': patch
+---
+
+Support frontmatter injection for MD and MDX using remark and rehype plugins

packages/astro/src/@types/astro.ts

@@ -1110,3 +1110,5 @@ export interface SSRResult {
 	response: ResponseInit;
 	_metadata: SSRMetadata;
 }
+
+export type MarkdownAstroData = { frontmatter: object };

packages/astro/src/vite-plugin-markdown/index.ts

@@ -7,7 +7,7 @@ import { collectErrorMetadata } from '../core/errors.js';
 import type { LogOptions } from '../core/logger/core.js';
 import { warn } from '../core/logger/core.js';
 import type { PluginMetadata } from '../vite-plugin-astro/types.js';
-import { getFileInfo } from '../vite-plugin-utils/index.js';
+import { getFileInfo, safelyGetAstroData } from '../vite-plugin-utils/index.js';
 
 interface AstroPluginOptions {
 	config: AstroConfig;
@@ -44,7 +44,14 @@ export default function markdown({ config, logging }: AstroPluginOptions): Plugi
 
 				const html = renderResult.code;
 				const { headings } = renderResult.metadata;
-				const frontmatter = { ...raw.data, url: fileUrl, file: fileId } as any;
+				const { frontmatter: injectedFrontmatter } = safelyGetAstroData(renderResult.vfile.data);
+				const frontmatter = {
+					...injectedFrontmatter,
+					...raw.data,
+					url: fileUrl,
+					file: fileId,
+				} as any;
+
 				const { layout } = frontmatter;
 
 				if (frontmatter.setup) {
@@ -94,6 +101,7 @@ export default function markdown({ config, logging }: AstroPluginOptions): Plugi
 				}
 				export default Content;
 				`);
+
 				return {
 					code,
 					meta: {

packages/astro/src/vite-plugin-utils/index.ts

@@ -1,4 +1,5 @@
-import type { AstroConfig } from '../@types/astro';
+import { Data } from 'vfile';
+import type { AstroConfig, MarkdownAstroData } from '../@types/astro';
 import { appendForwardSlash } from '../core/path.js';
 
 export function getFileInfo(id: string, config: AstroConfig) {
@@ -15,3 +16,30 @@ export function getFileInfo(id: string, config: AstroConfig) {
 	}
 	return { fileId, fileUrl };
 }
+
+function isValidAstroData(obj: unknown): obj is MarkdownAstroData {
+	if (typeof obj === 'object' && obj !== null && obj.hasOwnProperty('frontmatter')) {
+		const { frontmatter } = obj as any;
+		try {
+			// ensure frontmatter is JSON-serializable
+			JSON.stringify(frontmatter);
+		} catch {
+			return false;
+		}
+		return typeof frontmatter === 'object' && frontmatter !== null;
+	}
+	return false;
+}
+
+export function safelyGetAstroData(vfileData: Data): MarkdownAstroData {
+	const { astro } = vfileData;
+
+	if (!astro) return { frontmatter: {} };
+	if (!isValidAstroData(astro)) {
+		throw Error(
+			`[Markdown] A remark or rehype plugin tried to add invalid frontmatter. Ensure "astro.frontmatter" is a JSON object!`
+		);
+	}
+
+	return astro;
+}

packages/astro/test/astro-markdown-frontmatter-injection.test.js

@@ -0,0 +1,40 @@
+import { expect } from 'chai';
+import { loadFixture } from './test-utils.js';
+
+const FIXTURE_ROOT = './fixtures/astro-markdown-frontmatter-injection/';
+
+describe('Astro Markdown - frontmatter injection', () => {
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: FIXTURE_ROOT,
+		});
+		await fixture.build();
+	});
+
+	it('remark supports custom vfile data - get title', async () => {
+		const frontmatterByPage = JSON.parse(await fixture.readFile('/glob.json'));
+		const titles = frontmatterByPage.map((frontmatter = {}) => frontmatter.title);
+		expect(titles).to.contain('Page 1');
+		expect(titles).to.contain('Page 2');
+	});
+
+	it('rehype supports custom vfile data - reading time', async () => {
+		const frontmatterByPage = JSON.parse(await fixture.readFile('/glob.json'));
+		const readingTimes = frontmatterByPage.map((frontmatter = {}) => frontmatter.injectedReadingTime);
+		expect(readingTimes.length).to.be.greaterThan(0);
+		for (let readingTime of readingTimes) {
+			expect(readingTime).to.not.be.null;
+			expect(readingTime.text).match(/^\d+ min read/);
+		}
+	});
+
+	it('overrides injected frontmatter with user frontmatter', async () => {
+		const frontmatterByPage = JSON.parse(await fixture.readFile('/glob.json'));
+		const readingTimes = frontmatterByPage.map((frontmatter = {}) => frontmatter.injectedReadingTime?.text);
+		const titles = frontmatterByPage.map((frontmatter = {}) => frontmatter.title);
+		expect(titles).to.contain('Overridden title');
+		expect(readingTimes).to.contain('1000 min read');
+	});
+});

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/astro.config.mjs

@@ -0,0 +1,11 @@
+import { defineConfig } from 'astro/config';
+import { rehypeReadingTime, remarkTitle } from './src/markdown-plugins.mjs'
+
+// https://astro.build/config
+export default defineConfig({
+  site: 'https://astro.build/',
+	markdown: {
+		remarkPlugins: [remarkTitle],
+		rehypePlugins: [rehypeReadingTime],
+	}
+});

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "@test/astro-markdown-frontmatter-injection",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*",
+    "mdast-util-to-string": "^3.1.0",
+    "reading-time": "^1.5.0",
+    "unist-util-visit": "^4.1.0"
+  }
+}

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/markdown-plugins.mjs

@@ -0,0 +1,20 @@
+import getReadingTime from 'reading-time';
+import { toString } from 'mdast-util-to-string';
+import { visit } from 'unist-util-visit';
+
+export function rehypeReadingTime() {
+	return function (tree, { data }) {
+		const readingTime = getReadingTime(toString(tree));
+		data.astro.frontmatter.injectedReadingTime = readingTime;
+	};
+}
+
+export function remarkTitle() {
+	return function (tree, { data }) {
+		visit(tree, ['heading'], (node) => {
+			if (node.depth === 1) {
+				data.astro.frontmatter.title = toString(node.children);
+			}
+		});
+	};
+}

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/pages/glob.json.js

@@ -0,0 +1,6 @@
+export async function get() {
+	const docs = await import.meta.glob('./*.md', { eager: true });
+	return {
+		body: JSON.stringify(Object.values(docs).map(doc => doc.frontmatter)),
+	}
+}

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/pages/page-1.md

@@ -0,0 +1,3 @@
+# Page 1
+
+Look at that!

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/pages/page-2.md

@@ -0,0 +1,19 @@
+# Page 2
+
+## Table of contents
+
+## Section 1
+
+Some text!
+
+### Subsection 1
+
+Some subsection test!
+
+### Subsection 2
+
+Oh cool, more text!
+
+## Section 2
+
+More content

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/pages/with-overrides.md

@@ -0,0 +1,7 @@
+---
+title: 'Overridden title'
+injectedReadingTime: 
+  text: '1000 min read'
+---
+
+# Working!

packages/astro/test/fixtures/astro-markdown/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "@test/astro-markdown-md-mode",
+  "name": "@test/astro-markdown",
   "version": "0.0.0",
   "private": true,
   "dependencies": {

packages/integrations/mdx/package.json

@@ -43,7 +43,8 @@
     "remark-shiki-twoslash": "^3.1.0",
     "remark-smartypants": "^2.0.0",
     "shiki": "^0.10.1",
-    "unist-util-visit": "^4.1.0"
+    "unist-util-visit": "^4.1.0",
+    "vfile": "^5.3.2"
   },
   "devDependencies": {
     "@types/chai": "^4.3.1",

packages/integrations/mdx/src/astro-data-utils.ts

@@ -0,0 +1,82 @@
+import { name as isValidIdentifierName } from 'estree-util-is-identifier-name';
+import type { VFile } from 'vfile';
+import type { MdxjsEsm } from 'mdast-util-mdx';
+import type { MarkdownAstroData } from 'astro';
+import type { Data } from 'vfile';
+import { jsToTreeNode } from './utils.js';
+
+export function remarkInitializeAstroData() {
+	return function (tree: any, vfile: VFile) {
+		if (!vfile.data.astro) {
+			vfile.data.astro = { frontmatter: {} };
+		}
+	};
+}
+
+export function rehypeApplyFrontmatterExport(
+	pageFrontmatter: Record<string, any>,
+	exportName = 'frontmatter'
+) {
+	return function (tree: any, vfile: VFile) {
+		if (!isValidIdentifierName(exportName)) {
+			throw new Error(
+				`[MDX] ${JSON.stringify(
+					exportName
+				)} is not a valid frontmatter export name! Make sure "frontmatterOptions.name" could be used as a JS export (i.e. "export const frontmatterName = ...")`
+			);
+		}
+		const { frontmatter: injectedFrontmatter } = safelyGetAstroData(vfile.data);
+		const frontmatter = { ...injectedFrontmatter, ...pageFrontmatter };
+		let exportNodes: MdxjsEsm[] = [];
+		if (!exportName) {
+			exportNodes = Object.entries(frontmatter).map(([k, v]) => {
+				if (!isValidIdentifierName(k)) {
+					throw new Error(
+						`[MDX] A remark or rehype plugin tried to inject ${JSON.stringify(
+							k
+						)} as a top-level export, which is not a valid export name.`
+					);
+				}
+				return jsToTreeNode(`export const ${k} = ${JSON.stringify(v)};`);
+			});
+		} else {
+			exportNodes = [jsToTreeNode(`export const ${exportName} = ${JSON.stringify(frontmatter)};`)];
+		}
+		tree.children = exportNodes.concat(tree.children);
+	};
+}
+
+/**
+ * Copied from markdown utils
+ * @see "vite-plugin-utils"
+ */
+function isValidAstroData(obj: unknown): obj is MarkdownAstroData {
+	if (typeof obj === 'object' && obj !== null && obj.hasOwnProperty('frontmatter')) {
+		const { frontmatter } = obj as any;
+		try {
+			// ensure frontmatter is JSON-serializable
+			JSON.stringify(frontmatter);
+		} catch {
+			return false;
+		}
+		return typeof frontmatter === 'object' && frontmatter !== null;
+	}
+	return false;
+}
+
+/**
+ * Copied from markdown utils
+ * @see "vite-plugin-utils"
+ */
+export function safelyGetAstroData(vfileData: Data): MarkdownAstroData {
+	const { astro } = vfileData;
+
+	if (!astro) return { frontmatter: {} };
+	if (!isValidAstroData(astro)) {
+		throw Error(
+			`[MDX] A remark or rehype plugin tried to add invalid frontmatter. Ensure "astro.frontmatter" is a JSON object!`
+		);
+	}
+
+	return astro;
+}

packages/integrations/mdx/src/index.ts

@@ -1,19 +1,18 @@
 import { compile as mdxCompile, nodeTypes } from '@mdx-js/mdx';
 import mdxPlugin, { Options as MdxRollupPluginOptions } from '@mdx-js/rollup';
-import type { AstroIntegration } from 'astro';
+import type { AstroIntegration, AstroConfig } from 'astro';
+import { remarkInitializeAstroData, rehypeApplyFrontmatterExport } from './astro-data-utils.js';
 import { parse as parseESM } from 'es-module-lexer';
 import rehypeRaw from 'rehype-raw';
-import remarkFrontmatter from 'remark-frontmatter';
 import remarkGfm from 'remark-gfm';
 import type { RemarkMdxFrontmatterOptions } from 'remark-mdx-frontmatter';
-import remarkMdxFrontmatter from 'remark-mdx-frontmatter';
 import remarkShikiTwoslash from 'remark-shiki-twoslash';
 import remarkSmartypants from 'remark-smartypants';
 import { VFile } from 'vfile';
 import type { Plugin as VitePlugin } from 'vite';
 import rehypeCollectHeadings from './rehype-collect-headings.js';
 import remarkPrism from './remark-prism.js';
-import { getFileInfo, getFrontmatter } from './utils.js';
+import { getFileInfo, parseFrontmatter } from './utils.js';
 
 type WithExtends<T> = T | { extends: T };
 
@@ -37,44 +36,52 @@ function handleExtends<T>(config: WithExtends<T[] | undefined>, defaults: T[] =
 	return [...defaults, ...(config?.extends ?? [])];
 }
 
+function getRemarkPlugins(
+	mdxOptions: MdxOptions,
+	config: AstroConfig
+): MdxRollupPluginOptions['remarkPlugins'] {
+	let remarkPlugins = [
+		// Initialize vfile.data.astroExports before all plugins are run
+		remarkInitializeAstroData,
+		...handleExtends(mdxOptions.remarkPlugins, DEFAULT_REMARK_PLUGINS),
+	];
+	if (config.markdown.syntaxHighlight === 'shiki') {
+		// Default export still requires ".default" chaining for some reason
+		// Workarounds tried:
+		// - "import * as remarkShikiTwoslash"
+		// - "import { default as remarkShikiTwoslash }"
+		const shikiTwoslash = (remarkShikiTwoslash as any).default ?? remarkShikiTwoslash;
+		remarkPlugins.push([shikiTwoslash, config.markdown.shikiConfig]);
+	}
+	if (config.markdown.syntaxHighlight === 'prism') {
+		remarkPlugins.push(remarkPrism);
+	}
+	return remarkPlugins;
+}
+
+function getRehypePlugins(
+	mdxOptions: MdxOptions,
+	config: AstroConfig
+): MdxRollupPluginOptions['rehypePlugins'] {
+	let rehypePlugins = handleExtends(mdxOptions.rehypePlugins, DEFAULT_REHYPE_PLUGINS);
+
+	if (config.markdown.syntaxHighlight === 'shiki' || config.markdown.syntaxHighlight === 'prism') {
+		rehypePlugins.push([rehypeRaw, { passThrough: nodeTypes }]);
+	}
+
+	return rehypePlugins;
+}
+
 export default function mdx(mdxOptions: MdxOptions = {}): AstroIntegration {
 	return {
 		name: '@astrojs/mdx',
 		hooks: {
 			'astro:config:setup': ({ updateConfig, config, addPageExtension, command }: any) => {
 				addPageExtension('.mdx');
-				let remarkPlugins = handleExtends(mdxOptions.remarkPlugins, DEFAULT_REMARK_PLUGINS);
-				let rehypePlugins = handleExtends(mdxOptions.rehypePlugins, DEFAULT_REHYPE_PLUGINS);
-
-				if (config.markdown.syntaxHighlight === 'shiki') {
-					remarkPlugins.push([
-						// Default export still requires ".default" chaining for some reason
-						// Workarounds tried:
-						// - "import * as remarkShikiTwoslash"
-						// - "import { default as remarkShikiTwoslash }"
-						(remarkShikiTwoslash as any).default ?? remarkShikiTwoslash,
-						config.markdown.shikiConfig,
-					]);
-					rehypePlugins.push([rehypeRaw, { passThrough: nodeTypes }]);
-				}
-
-				if (config.markdown.syntaxHighlight === 'prism') {
-					remarkPlugins.push(remarkPrism);
-					rehypePlugins.push([rehypeRaw, { passThrough: nodeTypes }]);
-				}
-
-				remarkPlugins.push(remarkFrontmatter);
-				remarkPlugins.push([
-					remarkMdxFrontmatter,
-					{
-						name: 'frontmatter',
-						...mdxOptions.frontmatterOptions,
-					},
-				]);
 
 				const mdxPluginOpts: MdxRollupPluginOptions = {
-					remarkPlugins,
-					rehypePlugins,
+					remarkPlugins: getRemarkPlugins(mdxOptions, config),
+					rehypePlugins: getRehypePlugins(mdxOptions, config),
 					jsx: true,
 					jsxImportSource: 'astro',
 					// Note: disable `.md` support
@@ -93,24 +100,27 @@ export default function mdx(mdxOptions: MdxOptions = {}): AstroIntegration {
 								async transform(code, id) {
 									if (!id.endsWith('mdx')) return;
 
-									// If user overrides our default YAML parser,
-									// do not attempt to parse the `layout` via gray-matter
-									if (!mdxOptions.frontmatterOptions?.parsers) {
-										const frontmatter = getFrontmatter(code, id);
-										if (frontmatter.layout) {
-											const { layout, ...content } = frontmatter;
-											code += `\n\nexport default async function({ children }) {\nconst Layout = (await import(${JSON.stringify(
-												frontmatter.layout
-											)})).default;\nconst frontmatter=${JSON.stringify(
-												content
-											)};\nreturn <Layout frontmatter={frontmatter} content={frontmatter} headings={getHeadings()}>{children}</Layout> }`;
-										}
+									let { data: frontmatter, content: pageContent } = parseFrontmatter(code, id);
+									if (frontmatter.layout) {
+										const { layout, ...contentProp } = frontmatter;
+										pageContent += `\n\nexport default async function({ children }) {\nconst Layout = (await import(${JSON.stringify(
+											frontmatter.layout
+										)})).default;\nconst frontmatter=${JSON.stringify(
+											contentProp
+										)};\nreturn <Layout frontmatter={frontmatter} content={frontmatter} headings={getHeadings()}>{children}</Layout> }`;
 									}
 
-									const compiled = await mdxCompile(
-										new VFile({ value: code, path: id }),
-										mdxPluginOpts
-									);
+									const compiled = await mdxCompile(new VFile({ value: pageContent, path: id }), {
+										...mdxPluginOpts,
+										rehypePlugins: [
+											...(mdxPluginOpts.rehypePlugins ?? []),
+											() =>
+												rehypeApplyFrontmatterExport(
+													frontmatter,
+													mdxOptions.frontmatterOptions?.name
+												),
+										],
+									});
 
 									return {
 										code: String(compiled.value),

packages/integrations/mdx/src/utils.ts

@@ -47,9 +47,9 @@ export function getFileInfo(id: string, config: AstroConfig): FileInfo {
  * Match YAML exception handling from Astro core errors
  * @see 'astro/src/core/errors.ts'
  */
-export function getFrontmatter(code: string, id: string) {
+export function parseFrontmatter(code: string, id: string) {
 	try {
-		return matter(code).data;
+		return matter(code);
 	} catch (e: any) {
 		if (e.name === 'YAMLException') {
 			const err: SSRError = e;

packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection/astro.config.mjs

@@ -0,0 +1,12 @@
+import { defineConfig } from 'astro/config';
+import mdx from '@astrojs/mdx';
+import { rehypeReadingTime, remarkTitle } from './src/markdown-plugins.mjs';
+
+// https://astro.build/config
+export default defineConfig({
+  site: 'https://astro.build/',
+	integrations: [mdx({
+		remarkPlugins: [remarkTitle],
+		rehypePlugins: [rehypeReadingTime],
+	})],
+});

packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "@test/mdx-frontmatter-injection",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*",
+    "@astrojs/mdx": "workspace:*",
+    "mdast-util-to-string": "^3.1.0",
+    "reading-time": "^1.5.0",
+    "unist-util-visit": "^4.1.0"
+  }
+}

packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection/src/markdown-plugins.mjs

@@ -0,0 +1,20 @@
+import getReadingTime from 'reading-time';
+import { toString } from 'mdast-util-to-string';
+import { visit } from 'unist-util-visit';
+
+export function rehypeReadingTime() {
+	return function (tree, { data }) {
+		const readingTime = getReadingTime(toString(tree));
+		data.astro.frontmatter.injectedReadingTime = readingTime;
+	};
+}
+
+export function remarkTitle() {
+	return function (tree, { data }) {
+		visit(tree, ['heading'], (node) => {
+			if (node.depth === 1) {
+				data.astro.frontmatter.title = toString(node.children);
+			}
+		});
+	};
+}

packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection/src/pages/glob.json.js

@@ -0,0 +1,6 @@
+export async function get() {
+	const docs = await import.meta.glob('./*.mdx', { eager: true });
+	return {
+		body: JSON.stringify(Object.values(docs).map(doc => doc.frontmatter)),
+	}
+}

packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection/src/pages/page-1.mdx

@@ -0,0 +1,3 @@
+# Page 1
+
+Look at that!

packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection/src/pages/page-2.mdx

@@ -0,0 +1,19 @@
+# Page 2
+
+## Table of contents
+
+## Section 1
+
+Some text!
+
+### Subsection 1
+
+Some subsection test!
+
+### Subsection 2
+
+Oh cool, more text!
+
+## Section 2
+
+More content

packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection/src/pages/with-overrides.mdx

@@ -0,0 +1,7 @@
+---
+title: 'Overridden title'
+injectedReadingTime: 
+  text: '1000 min read'
+---
+
+# Working!

packages/integrations/mdx/test/fixtures/mdx-rehype-plugins/src/pages/reading-time.json.js

@@ -1,7 +1,7 @@
-import { readingTime } from './space-ipsum.mdx';
+import * as exps from './space-ipsum.mdx';
 
 export function get() {
 	return {
-		body: JSON.stringify(readingTime),
+		body: JSON.stringify(exps),
 	}
 }

packages/integrations/mdx/test/fixtures/mdx-remark-plugins/src/pages/headings-glob.json.js

@@ -0,0 +1,6 @@
+export async function get() {
+	const docs = await import.meta.glob('./*.mdx', { eager: true });
+	return {
+		body: JSON.stringify(Object.values(docs).map(doc => doc.frontmatter)),
+	}
+}

packages/integrations/mdx/test/mdx-frontmatter-injection.test.js

@@ -0,0 +1,40 @@
+import { expect } from 'chai';
+import { loadFixture } from '../../../astro/test/test-utils.js';
+
+const FIXTURE_ROOT = new URL('./fixtures/mdx-frontmatter-injection/', import.meta.url);
+
+describe('MDX frontmatter injection', () => {
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: FIXTURE_ROOT,
+		});
+		await fixture.build();
+	});
+
+	it('remark supports custom vfile data - get title', async () => {
+		const frontmatterByPage = JSON.parse(await fixture.readFile('/glob.json'));
+		const titles = frontmatterByPage.map((frontmatter = {}) => frontmatter.title);
+		expect(titles).to.contain('Page 1');
+		expect(titles).to.contain('Page 2');
+	});
+
+	it('rehype supports custom vfile data - reading time', async () => {
+		const frontmatterByPage = JSON.parse(await fixture.readFile('/glob.json'));
+		const readingTimes = frontmatterByPage.map((frontmatter = {}) => frontmatter.injectedReadingTime);
+		expect(readingTimes.length).to.be.greaterThan(0);
+		for (let readingTime of readingTimes) {
+			expect(readingTime).to.not.be.null;
+			expect(readingTime.text).match(/^\d+ min read/);
+		}
+	});
+
+	it('overrides injected frontmatter with user frontmatter', async () => {
+		const frontmatterByPage = JSON.parse(await fixture.readFile('/glob.json'));
+		const readingTimes = frontmatterByPage.map((frontmatter = {}) => frontmatter.injectedReadingTime?.text);
+		const titles = frontmatterByPage.map((frontmatter = {}) => frontmatter.title);
+		expect(titles).to.contain('Overridden title');
+		expect(readingTimes).to.contain('1000 min read');
+	});
+});

packages/integrations/mdx/test/mdx-rehype-plugins.test.js

@@ -1,15 +1,15 @@
 import mdx from '@astrojs/mdx';
-import { jsToTreeNode } from '../dist/utils.js';
 
-import { expect } from 'chai';
-import { parseHTML } from 'linkedom';
 import getReadingTime from 'reading-time';
 import { toString } from 'mdast-util-to-string';
+import { expect } from 'chai';
+import { parseHTML } from 'linkedom';
+import { jsToTreeNode } from '../dist/utils.js';
 
 import { loadFixture } from '../../../astro/test/test-utils.js';
 
-export function rehypeReadingTime() {
-	return function (tree) {
+function rehypeReadingTime() {
+	return function (tree, { data }) {
 		const readingTime = getReadingTime(toString(tree));
 		tree.children.unshift(
 			jsToTreeNode(`export const readingTime = ${JSON.stringify(readingTime)}`)
@@ -46,7 +46,7 @@ describe('MDX rehype plugins', () => {
 		});
 
 		it('supports custom rehype plugins - reading time', async () => {
-			const readingTime = JSON.parse(await fixture.readFile('/reading-time.json'));
+			const { readingTime } = JSON.parse(await fixture.readFile('/reading-time.json'));
 
 			expect(readingTime).to.not.be.null;
 			expect(readingTime.text).to.match(/^\d+ min read/);

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,
 	};
 }
 

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: {} };
+		}
+	};
+}

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;
 }

pnpm-lock.yaml

@@ -1231,6 +1231,18 @@ importers:
     dependencies:
       astro: link:../../..
 
+  packages/astro/test/fixtures/astro-markdown-frontmatter-injection:
+    specifiers:
+      astro: workspace:*
+      mdast-util-to-string: ^3.1.0
+      reading-time: ^1.5.0
+      unist-util-visit: ^4.1.0
+    dependencies:
+      astro: link:../../..
+      mdast-util-to-string: 3.1.0
+      reading-time: 1.5.0
+      unist-util-visit: 4.1.0
+
   packages/astro/test/fixtures/astro-markdown-plugins:
     specifiers:
       '@astrojs/preact': workspace:*
@@ -2183,6 +2195,7 @@ importers:
       remark-toc: ^8.0.1
       shiki: ^0.10.1
       unist-util-visit: ^4.1.0
+      vfile: ^5.3.2
     dependencies:
       '@astrojs/prism': link:../../astro-prism
       '@mdx-js/mdx': 2.1.2
@@ -2199,6 +2212,7 @@ importers:
       remark-smartypants: 2.0.0
       shiki: 0.10.1
       unist-util-visit: 4.1.0
+      vfile: 5.3.4
     devDependencies:
       '@types/chai': 4.3.1
       '@types/mocha': 9.1.1
@@ -2212,6 +2226,20 @@ importers:
       reading-time: 1.5.0
       remark-toc: 8.0.1
 
+  packages/integrations/mdx/test/fixtures/mdx-frontmatter-injection:
+    specifiers:
+      '@astrojs/mdx': workspace:*
+      astro: workspace:*
+      mdast-util-to-string: ^3.1.0
+      reading-time: ^1.5.0
+      unist-util-visit: ^4.1.0
+    dependencies:
+      '@astrojs/mdx': link:../../..
+      astro: link:../../../../../astro
+      mdast-util-to-string: 3.1.0
+      reading-time: 1.5.0
+      unist-util-visit: 4.1.0
+
   packages/integrations/mdx/test/fixtures/mdx-page:
     specifiers:
       '@astrojs/mdx': workspace:*
@@ -14710,7 +14738,6 @@ packages:
 
   /reading-time/1.5.0:
     resolution: {integrity: sha512-onYyVhBNr4CmAxFsKS7bz+uTLRakypIe4R+5A824vBSkQy/hB3fZepoVEf8OVAxzLvK+H/jm9TzpI3ETSm64Kg==}
-    dev: true
 
   /recast/0.20.5:
     resolution: {integrity: sha512-E5qICoPoNL4yU0H0NoBDntNB0Q5oMSNh9usFctYniLBluTthi3RsQVBXIJNbApOlvSwW/RGxIuokPcAc59J5fQ==}