feat(markdown): add support for TOML frontmatter in Markdown files.

.changeset/lazy-pandas-love.md

@@ -0,0 +1,24 @@
+---
+'@astrojs/markdown-remark': minor
+---
+
+Adds support for TOML frontmatter in `.md` and `.mdx` files
+
+Astro 5.2 automatically identifies the format of your Markdown and MDX frontmatter based on the delimiter used.  With `+++` as a delimiter (instead of the `---` YAML code fence), your frontmatter will automatically be recognized and parsed as [TOML](https://toml.io). 
+
+This is useful for adding existing content files with TOML frontmatter to your project from another framework such as Hugo.
+
+TOML frontmatter can also be used with [content collections](https://docs.astro.build/guides/content-collections/), and files with different frontmatter languages can live together in the same project.
+
+No configuration is required to use TOML frontmatter in your content files. Your delimiter will indicate your chosen frontmatter language:
+
+```md
++++
+date = 2025-01-30
+title = 'Use TOML frontmatter in Astro!'
+[author]
+name = 'Colin Bate'
++++
+
+# Support for TOML frontmatter is here!
+```

packages/markdown/remark/package.json

@@ -46,6 +46,7 @@
     "remark-rehype": "^11.1.1",
     "remark-smartypants": "^3.0.2",
     "shiki": "^1.29.1",
+    "smol-toml": "^1.3.1",
     "unified": "^11.0.5",
     "unist-util-remove-position": "^5.0.0",
     "unist-util-visit": "^5.0.0",

packages/markdown/remark/src/frontmatter.ts

@@ -1,4 +1,5 @@
 import yaml from 'js-yaml';
+import * as toml from 'smol-toml';
 
 export function isFrontmatterValid(frontmatter: Record<string, any>) {
 	try {
@@ -10,15 +11,19 @@ export function isFrontmatterValid(frontmatter: Record<string, any>) {
 	return typeof frontmatter === 'object' && frontmatter !== null;
 }
 
-// Capture frontmatter wrapped with `---`, including any characters and new lines within it.
-// Only capture if `---` exists near the top of the file, including:
+// Capture frontmatter wrapped with `---` or `+++`, including any characters and new lines within it.
+// Only capture if `---` or `+++` exists near the top of the file, including:
 // 1. Start of file (including if has BOM encoding)
-// 2. Start of file with any whitespace (but `---` must still start on a new line)
-const frontmatterRE = /(?:^\uFEFF?|^\s*\n)---([\s\S]*?\n)---/;
+// 2. Start of file with any whitespace (but `---` or `+++` must still start on a new line)
+const frontmatterRE = /(?:^\uFEFF?|^\s*\n)(?:---|\+\+\+)([\s\S]*?\n)(?:---|\+\+\+)/;
+const frontmatterTypeRE = /(?:^\uFEFF?|^\s*\n)(---|\+\+\+)/;
 export function extractFrontmatter(code: string): string | undefined {
 	return frontmatterRE.exec(code)?.[1];
 }
 
+function getFrontmatterParser(code: string): [string, (str: string) => unknown] {
+	return frontmatterTypeRE.exec(code)?.[1] === '+++' ? ['+++', toml.parse] : ['---', yaml.load];
+}
 export interface ParseFrontmatterOptions {
 	/**
 	 * How the frontmatter should be handled in the returned `content` string.
@@ -47,8 +52,8 @@ export function parseFrontmatter(
 	if (rawFrontmatter == null) {
 		return { frontmatter: {}, rawFrontmatter: '', content: code };
 	}
-
-	const parsed = yaml.load(rawFrontmatter);
+	const [delims, parser] = getFrontmatterParser(code);
+	const parsed = parser(rawFrontmatter);
 	const frontmatter = (parsed && typeof parsed === 'object' ? parsed : {}) as Record<string, any>;
 
 	let content: string;
@@ -57,16 +62,16 @@ export function parseFrontmatter(
 			content = code;
 			break;
 		case 'remove':
-			content = code.replace(`---${rawFrontmatter}---`, '');
+			content = code.replace(`${delims}${rawFrontmatter}${delims}`, '');
 			break;
 		case 'empty-with-spaces':
 			content = code.replace(
-				`---${rawFrontmatter}---`,
+				`${delims}${rawFrontmatter}${delims}`,
 				`   ${rawFrontmatter.replace(/[^\r\n]/g, ' ')}   `,
 			);
 			break;
 		case 'empty-with-lines':
-			content = code.replace(`---${rawFrontmatter}---`, rawFrontmatter.replace(/[^\r\n]/g, ''));
+			content = code.replace(`${delims}${rawFrontmatter}${delims}`, rawFrontmatter.replace(/[^\r\n]/g, ''));
 			break;
 	}
 

packages/markdown/remark/test/frontmatter.test.js

@@ -5,7 +5,7 @@ import { extractFrontmatter, parseFrontmatter } from '../dist/index.js';
 const bom = '\uFEFF';
 
 describe('extractFrontmatter', () => {
-	it('works', () => {
+	it('handles YAML', () => {
 		const yaml = `\nfoo: bar\n`;
 		assert.equal(extractFrontmatter(`---${yaml}---`), yaml);
 		assert.equal(extractFrontmatter(`${bom}---${yaml}---`), yaml);
@@ -19,10 +19,25 @@ describe('extractFrontmatter', () => {
 		assert.equal(extractFrontmatter(`---${yaml} ---`), undefined);
 		assert.equal(extractFrontmatter(`text\n---${yaml}---\n\ncontent`), undefined);
 	});
+
+	it('handles TOML', () => {
+		const toml = `\nfoo = "bar"\n`;
+		assert.equal(extractFrontmatter(`+++${toml}+++`), toml);
+		assert.equal(extractFrontmatter(`${bom}+++${toml}+++`), toml);
+		assert.equal(extractFrontmatter(`\n+++${toml}+++`), toml);
+		assert.equal(extractFrontmatter(`\n  \n+++${toml}+++`), toml);
+		assert.equal(extractFrontmatter(`+++${toml}+++\ncontent`), toml);
+		assert.equal(extractFrontmatter(`${bom}+++${toml}+++\ncontent`), toml);
+		assert.equal(extractFrontmatter(`\n\n+++${toml}+++\n\ncontent`), toml);
+		assert.equal(extractFrontmatter(`\n  \n+++${toml}+++\n\ncontent`), toml);
+		assert.equal(extractFrontmatter(` +++${toml}+++`), undefined);
+		assert.equal(extractFrontmatter(`+++${toml} +++`), undefined);
+		assert.equal(extractFrontmatter(`text\n+++${toml}+++\n\ncontent`), undefined);
+	});
 });
 
 describe('parseFrontmatter', () => {
-	it('works', () => {
+	it('works for YAML', () => {
 		const yaml = `\nfoo: bar\n`;
 		assert.deepEqual(parseFrontmatter(`---${yaml}---`), {
 			frontmatter: { foo: 'bar' },
@@ -81,7 +96,66 @@ describe('parseFrontmatter', () => {
 		});
 	});
 
-	it('frontmatter style', () => {
+	it('works for TOML', () => {
+		const toml = `\nfoo = "bar"\n`;
+		assert.deepEqual(parseFrontmatter(`+++${toml}+++`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: '',
+		});
+		assert.deepEqual(parseFrontmatter(`${bom}+++${toml}+++`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: bom,
+		});
+		assert.deepEqual(parseFrontmatter(`\n+++${toml}+++`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: '\n',
+		});
+		assert.deepEqual(parseFrontmatter(`\n  \n+++${toml}+++`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: '\n  \n',
+		});
+		assert.deepEqual(parseFrontmatter(`+++${toml}+++\ncontent`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: '\ncontent',
+		});
+		assert.deepEqual(parseFrontmatter(`${bom}+++${toml}+++\ncontent`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: `${bom}\ncontent`,
+		});
+		assert.deepEqual(parseFrontmatter(`\n\n+++${toml}+++\n\ncontent`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: '\n\n\n\ncontent',
+		});
+		assert.deepEqual(parseFrontmatter(`\n  \n+++${toml}+++\n\ncontent`), {
+			frontmatter: { foo: 'bar' },
+			rawFrontmatter: toml,
+			content: '\n  \n\n\ncontent',
+		});
+		assert.deepEqual(parseFrontmatter(` +++${toml}+++`), {
+			frontmatter: {},
+			rawFrontmatter: '',
+			content: ` +++${toml}+++`,
+		});
+		assert.deepEqual(parseFrontmatter(`+++${toml} +++`), {
+			frontmatter: {},
+			rawFrontmatter: '',
+			content: `+++${toml} +++`,
+		});
+		assert.deepEqual(parseFrontmatter(`text\n+++${toml}+++\n\ncontent`), {
+			frontmatter: {},
+			rawFrontmatter: '',
+			content: `text\n+++${toml}+++\n\ncontent`,
+		});
+	});
+
+	it('frontmatter style for YAML', () => {
 		const yaml = `\nfoo: bar\n`;
 		const parse1 = (style) => parseFrontmatter(`---${yaml}---`, { frontmatter: style }).content;
 		assert.deepEqual(parse1('preserve'), `---${yaml}---`);
@@ -96,4 +170,20 @@ describe('parseFrontmatter', () => {
 		assert.deepEqual(parse2('empty-with-spaces'), `\n  \n   \n        \n   \n\ncontent`);
 		assert.deepEqual(parse2('empty-with-lines'), `\n  \n\n\n\n\ncontent`);
 	});
+
+	it('frontmatter style for TOML', () => {
+		const toml = `\nfoo = "bar"\n`;
+		const parse1 = (style) => parseFrontmatter(`+++${toml}+++`, { frontmatter: style }).content;
+		assert.deepEqual(parse1('preserve'), `+++${toml}+++`);
+		assert.deepEqual(parse1('remove'), '');
+		assert.deepEqual(parse1('empty-with-spaces'), `   \n           \n   `);
+		assert.deepEqual(parse1('empty-with-lines'), `\n\n`);
+
+		const parse2 = (style) =>
+			parseFrontmatter(`\n  \n+++${toml}+++\n\ncontent`, { frontmatter: style }).content;
+		assert.deepEqual(parse2('preserve'), `\n  \n+++${toml}+++\n\ncontent`);
+		assert.deepEqual(parse2('remove'), '\n  \n\n\ncontent');
+		assert.deepEqual(parse2('empty-with-spaces'), `\n  \n   \n           \n   \n\ncontent`);
+		assert.deepEqual(parse2('empty-with-lines'), `\n  \n\n\n\n\ncontent`);
+	});
 });