Preserve code element node meta for rehype syntax highlighters (#5335)

.changeset/heavy-kangaroos-sin.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/mdx': patch
+---
+
+Preserve code element node `data.meta` in `properties.metastring` for rehype syntax highlighters, like `rehype-pretty-code``

packages/integrations/mdx/package.json

@@ -39,6 +39,7 @@
     "github-slugger": "^1.4.0",
     "gray-matter": "^4.0.3",
     "kleur": "^4.1.4",
+    "rehype-pretty-code": "^0.4.0",
     "rehype-raw": "^6.1.1",
     "remark-frontmatter": "^4.0.1",
     "remark-gfm": "^3.0.1",

packages/integrations/mdx/src/plugins.ts

@@ -11,6 +11,7 @@ import remarkSmartypants from 'remark-smartypants';
 import type { Data, VFile } from 'vfile';
 import { MdxOptions } from './index.js';
 import rehypeCollectHeadings from './rehype-collect-headings.js';
+import rehypeMetaString from './rehype-meta-string.js';
 import remarkPrism from './remark-prism.js';
 import remarkShiki from './remark-shiki.js';
 import { jsToTreeNode } from './utils.js';
@@ -150,6 +151,8 @@ export function getRehypePlugins(
 	let rehypePlugins: PluggableList = [
 		// getHeadings() is guaranteed by TS, so we can't allow user to override
 		rehypeCollectHeadings,
+		// ensure `data.meta` is preserved in `properties.metastring` for rehype syntax highlighters
+		rehypeMetaString,
 		// rehypeRaw allows custom syntax highlighters to work without added config
 		[rehypeRaw, { passThrough: nodeTypes }] as any,
 	];

packages/integrations/mdx/src/rehype-meta-string.ts

@@ -0,0 +1,17 @@
+import { visit } from 'unist-util-visit';
+
+/**
+ * Moves `data.meta` to `properties.metastring` for the `code` element node
+ * as `rehype-raw` strips `data` from all nodes, which may contain useful information.
+ * e.g. ```js {1:3} => metastring: "{1:3}"
+ */
+export default function rehypeMetaString() {
+	return function (tree: any) {
+		visit(tree, (node) => {
+			if (node.type === 'element' && node.tagName === 'code' && node.data?.meta) {
+				node.properties ??= {};
+				node.properties.metastring = node.data.meta;
+			}
+		});
+	};
+}

packages/integrations/mdx/test/fixtures/mdx-syntax-hightlighting/src/pages/index.mdx

@@ -1,6 +1,6 @@
 # Syntax highlighting
 
-```astro
+```astro {2}
 ---
 const handlesAstroSyntax = true
 ---

packages/integrations/mdx/test/mdx-syntax-highlighting.test.js

@@ -4,6 +4,7 @@ import { expect } from 'chai';
 import { parseHTML } from 'linkedom';
 import { loadFixture } from '../../../astro/test/test-utils.js';
 import shikiTwoslash from 'remark-shiki-twoslash';
+import rehypePrettyCode from 'rehype-pretty-code';
 
 const FIXTURE_ROOT = new URL('./fixtures/mdx-syntax-hightlighting/', import.meta.url);
 
@@ -88,4 +89,31 @@ describe('MDX syntax highlighting', () => {
 		const twoslashCodeBlock = document.querySelector('pre.shiki');
 		expect(twoslashCodeBlock).to.not.be.null;
 	});
+
+	it('supports custom highlighter - rehype-pretty-code', async () => {
+		const fixture = await loadFixture({
+			root: FIXTURE_ROOT,
+			markdown: {
+				syntaxHighlight: false,
+			},
+			integrations: [
+				mdx({
+					rehypePlugins: [
+						[
+							rehypePrettyCode,
+							{
+								onVisitHighlightedLine(node) {
+									node.properties.style = 'background-color:#000000';
+								},
+							},
+						],
+					],
+				}),
+			],
+		});
+		await fixture.build();
+
+		const html = await fixture.readFile('/index.html');
+		expect(html).to.include('style="background-color:#000000"')
+	});
 });