[MDX] Support remark and rehype plugins, with defaults (#3977)

* feaet: allow remark and rehype plugin config

* deps: add remark-gfm, remark-smartypants

* feat: add gfm and smartypants by default

* test: add GFM and remark plugin tests

* feat: preserve default plugins with "extends"

* docs: add remarkPlugins

* docs: add rehypePlugins

* chore: changeset

* fix: remove skip from mdx tests

* chore: dup hyperlink flavor text

* chore: authGen -> autoGen

* nit: markdown -> Markdown

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

* nit: markdown -> Markdown 1

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

* nit: markdown -> Markdown 2

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

* nit: markdown -> Markdown 3

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

* nit: markdown -> Markdown 4

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

Co-authored-by: Nate Moore <natemoo-re@users.noreply.github.com>

1 files changed, 22 insertions, 2 deletions

diff --git a/packages/integrations/mdx/src/index.ts b/packages/integrations/mdx/src/index.ts
index 140e86632..af63c4ad2 100644
--- a/packages/integrations/mdx/src/index.ts
+++ b/packages/integrations/mdx/src/index.ts
@@ -1,9 +1,26 @@
-import mdxPlugin from '@mdx-js/rollup';
+import mdxPlugin, { Options as MdxRollupPluginOptions } from '@mdx-js/rollup';
 import type { AstroIntegration } from 'astro';
 import { parse as parseESM } from 'es-module-lexer';
+import remarkGfm from 'remark-gfm';
+import remarkSmartypants from 'remark-smartypants';
 import { getFileInfo } from './utils.js';
 
-export default function mdx(): AstroIntegration {
+type WithExtends<T> = T | { extends: T };
+
+type MdxOptions = {
+	remarkPlugins?: WithExtends<MdxRollupPluginOptions['remarkPlugins']>;
+	rehypePlugins?: WithExtends<MdxRollupPluginOptions['rehypePlugins']>;
+}
+
+const DEFAULT_REMARK_PLUGINS = [remarkGfm, remarkSmartypants];
+
+function handleExtends<T>(config: WithExtends<T[] | undefined>, defaults: T[] = []): T[] | undefined {
+	if (Array.isArray(config)) return config;
+
+	return [...defaults, ...(config?.extends ?? [])];
+}
+
+export default function mdx(mdxOptions: MdxOptions = {}): AstroIntegration {
 	return {
 		name: '@astrojs/mdx',
 		hooks: {
@@ -15,6 +32,9 @@ export default function mdx(): AstroIntegration {
 							{
 								enforce: 'pre',
 								...mdxPlugin({
+									remarkPlugins: handleExtends(mdxOptions.remarkPlugins, DEFAULT_REMARK_PLUGINS),
+									rehypePlugins: handleExtends(mdxOptions.rehypePlugins),
+									// place these after so the user can't override
 									jsx: true,
 									jsxImportSource: 'astro',
 									// Note: disable `.md` support