Fix: use set:html when markdown mode is md (#4008)

* refactor: add legacy.jsxInMarkdown flag to config

* fix: use `set:html` when `markdown.mode` is 'md'

* Revert "refactor: add legacy.jsxInMarkdown flag to config"

This reverts commit 5572e8d.

* fix: move `remarkUnwrap, remarkEscape` to MDX only

* fix: only apply scary HTML passthroughs on MDX

* fix: move all JSX-specific rehype plugins under `isMDX`

* fix: "allowDangerousHtml" for md (required for Shiki)

* fix: apply `set:html` for non-layouts too

* test: JSX expressions, components, syntax highlighting

* chore: changeset

* fix: ignore "setup" and "components" in plain MD mode

* refactor: create new fixture to avoid weird caching error

* fix: dup package name

* chore: update lock

* fix: apply rehypeCollectHeaders to md

.changeset/moody-crabs-occur.md

@@ -0,0 +1,6 @@
+---
+'astro': patch
+'@astrojs/markdown-remark': patch
+---
+
+Avoid parsing JSX, components, and Astro islands when using "plain" md mode. This brings `markdown.mode: 'md'` in-line with our docs description.

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

@@ -137,6 +137,7 @@ export default function markdown({ config }: AstroPluginOptions): Plugin {
 				const filename = normalizeFilename(id);
 				const source = await fs.promises.readFile(filename, 'utf8');
 				const renderOpts = config.markdown;
+				const isMDX = renderOpts.mode === 'mdx';
 
 				const fileUrl = new URL(`file://${filename}`);
 				const isPage = fileUrl.pathname.startsWith(resolvePages(config).pathname);
@@ -148,7 +149,7 @@ export default function markdown({ config }: AstroPluginOptions): Plugin {
 				// Turn HTML comments into JS comments while preventing nested `*/` sequences
 				// from ending the JS comment by injecting a zero-width space
 				// Inside code blocks, this is removed during renderMarkdown by the remark-escape plugin.
-				if (renderOpts.mode === 'mdx') {
+				if (isMDX) {
 					markdownContent = markdownContent.replace(
 						/<\s*!--([^-->]*)(.*?)-->/gs,
 						(whole) => `{/*${whole.replace(/\*\//g, '*\u200b/')}*/}`
@@ -167,19 +168,30 @@ export default function markdown({ config }: AstroPluginOptions): Plugin {
 				const prelude = `---
 import Slugger from 'github-slugger';
 ${layout ? `import Layout from '${layout}';` : ''}
-${components ? `import * from '${components}';` : ''}
+${isMDX && components ? `import * from '${components}';` : ''}
 ${hasInjectedScript ? `import '${PAGE_SSR_SCRIPT_ID}';` : ''}
-${setup}
+${isMDX ? setup : ''}
 
 const slugger = new Slugger();
 function $$slug(value) {
 	return slugger.slug(value);
 }
 
-const $$content = ${JSON.stringify(content)}
+const $$content = ${JSON.stringify(isMDX
+	? content
+	// Avoid stripping "setup" and "components"
+	// in plain MD mode
+	: { ...content, setup, components })}
 ---`;
 				const imports = `${layout ? `import Layout from '${layout}';` : ''}
-${setup}`.trim();
+${isMDX ? setup : ''}`.trim();
+
+				// Wrap with set:html fragment to skip
+				// JSX expressions and components in "plain" md mode
+				if (!isMDX) {
+					astroResult = `<Fragment set:html={${JSON.stringify(astroResult)}} />`
+				}
+
 				// If the user imported "Layout", wrap the content in a Layout
 				if (/\bLayout\b/.test(imports)) {
 					astroResult = `${prelude}\n<Layout content={$$content}>\n\n${astroResult}\n\n</Layout>`;

packages/astro/test/astro-markdown-md-mode.test.js

@@ -0,0 +1,52 @@
+import { expect } from 'chai';
+import * as cheerio from 'cheerio';
+import { loadFixture } from './test-utils.js';
+
+describe('Astro Markdown - plain MD mode', () => {
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: './fixtures/astro-markdown-md-mode/',
+		});
+		await fixture.build();
+	});
+
+	it('Leaves JSX expressions unprocessed', async () => {
+		const html = await fixture.readFile('/jsx-expressions/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('h2').html()).to.equal('{frontmatter.title}');
+	});
+
+	it('Leaves JSX components un-transformed', async () => {
+		const html = await fixture.readFile('/components/index.html');
+
+		expect(html).to.include('<counter client:load="" count="{0}">');
+	});
+
+	describe('syntax highlighting', async () => {
+		it('handles Shiki', async () => {
+			const html = await fixture.readFile('/code-in-md/index.html');
+			const $ = cheerio.load(html);
+
+			expect($('pre.astro-code').length).to.not.equal(0);
+		});
+
+		it('handles Prism', async () => {
+			fixture = await loadFixture({
+				root: './fixtures/astro-markdown-md-mode/',
+				markdown: {
+					syntaxHighlight: 'prism',
+					mode: 'md',
+				},
+			});
+			await fixture.build();
+
+			const html = await fixture.readFile('/code-in-md/index.html');
+			const $ = cheerio.load(html);
+
+			expect($('pre.language-html').length).to.not.equal(0);
+		});
+	});
+});

packages/astro/test/fixtures/astro-markdown-md-mode/astro.config.mjs

@@ -0,0 +1,11 @@
+import { defineConfig } from 'astro/config';
+import svelte from "@astrojs/svelte";
+
+// https://astro.build/config
+export default defineConfig({
+	markdown: {
+		mode: 'md',
+	},
+  integrations: [svelte()],
+  site: 'https://astro.build/',
+});

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

@@ -0,0 +1,9 @@
+{
+  "name": "@test/astro-markdown-md-mode",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "@astrojs/svelte": "workspace:*",
+    "astro": "workspace:*"
+  }
+}

packages/astro/test/fixtures/astro-markdown-md-mode/src/components/Counter.svelte

@@ -0,0 +1,5 @@
+<script>
+	export let count = 0;
+</script>
+
+<button onClick={() => count += 1}>{count}</button>

packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/code-in-md.md

@@ -0,0 +1,7 @@
+# Fenced code blocks
+
+```html
+<body>
+	<div>This should also work without any problems.</div>
+</body>
+```

packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/components.md

@@ -0,0 +1,5 @@
+---
+setup: import Counter from '../components/Counter.svelte'
+---
+
+<Counter client:load count={0}></Counter>

packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/jsx-expressions.md

@@ -0,0 +1,13 @@
+---
+title: Blog Post with JSX expressions
+paragraph: JSX at the start of the line!
+list: ['test-1', 'test-2', 'test-3']
+---
+
+## {frontmatter.title}
+
+{frontmatter.paragraph}
+
+<ul>
+  {frontmatter.list.map(item => <li id={item}>{item}</li>)}
+</ul>

packages/markdown/remark/src/index.ts

@@ -46,8 +46,7 @@ export async function renderMarkdown(
 
 	let parser = unified()
 		.use(markdown)
-		.use(isMDX ? [remarkMdxish, remarkMarkAndUnravel] : [])
-		.use([remarkUnwrap, remarkEscape]);
+		.use(isMDX ? [remarkMdxish, remarkMarkAndUnravel, remarkUnwrap, remarkEscape] : [])
 
 	if (remarkPlugins.length === 0 && rehypePlugins.length === 0) {
 		remarkPlugins = [...DEFAULT_REMARK_PLUGINS];
@@ -76,13 +75,13 @@ export async function renderMarkdown(
 			markdownToHtml as any,
 			{
 				allowDangerousHtml: true,
-				passThrough: [
+				passThrough: isMDX ? [
 					'raw',
 					'mdxFlowExpression',
 					'mdxJsxFlowElement',
 					'mdxJsxTextElement',
 					'mdxTextExpression',
-				],
+				] : [],
 			},
 		],
 	]);
@@ -92,10 +91,13 @@ export async function renderMarkdown(
 	});
 
 	parser
-		.use(isMDX ? [rehypeJsx, rehypeExpressions] : [rehypeRaw])
-		.use(rehypeEscape)
-		.use(rehypeIslands)
-		.use([rehypeCollectHeaders])
+		.use(isMDX ? [
+			rehypeJsx,
+			rehypeExpressions,
+			rehypeEscape,
+			rehypeIslands,
+			rehypeCollectHeaders,
+		] : [rehypeCollectHeaders, rehypeRaw])
 		.use(rehypeStringify, { allowDangerousHtml: true });
 
 	let result: string;