[MDX] Support img component prop for optimized images (#8468)

Co-authored-by: Erika <3019731+Princesseuh@users.noreply.github.com>

.changeset/cyan-penguins-divide.md

@@ -0,0 +1,48 @@
+---
+'@astrojs/mdx': minor
+---
+
+Support the `img` component export for optimized images. This allows you to customize how optimized images are styled and rendered.
+
+When rendering an optimized image, Astro will pass the `ImageMetadata` object to your `img` component as the `src` prop. For unoptimized images (i.e. images using URLs or absolute paths), Astro will continue to pass the `src` as a string.
+
+This example handles both cases and applies custom styling:
+
+```astro
+---
+// src/components/MyImage.astro
+import type { ImageMetadata } from 'astro';
+import { Image } from 'astro:assets';
+
+type Props = {
+	src: string | ImageMetadata;
+	alt: string;
+};
+
+const { src, alt } = Astro.props;
+---
+
+{
+	typeof src === 'string' ? (
+		<img class="custom-styles" src={src} alt={alt} />
+	) : (
+		<Image class="custom-styles" {src} {alt} />
+	)
+}
+
+<style>
+	.custom-styles {
+		border: 1px solid red;
+	}
+</style>
+```
+
+Now, this components can be applied to the `img` component props object or file export:
+
+```md
+import MyImage from '../../components/MyImage.astro';
+
+export const components = { img: MyImage };
+
+# My MDX article
+```

packages/integrations/mdx/src/index.ts

@@ -14,6 +14,7 @@ import type { Plugin as VitePlugin } from 'vite';
 import { getRehypePlugins, getRemarkPlugins, recmaInjectImportMetaEnvPlugin } from './plugins.js';
 import type { OptimizeOptions } from './rehype-optimize-static.js';
 import { getFileInfo, ignoreStringPlugins, parseFrontmatter } from './utils.js';
+import { ASTRO_IMAGE_ELEMENT, ASTRO_IMAGE_IMPORT, USES_ASTRO_IMAGE_FLAG } from './remark-images-to-component.js';
 
 export type MdxOptions = Omit<typeof markdownConfigDefaults, 'remarkPlugins' | 'rehypePlugins'> & {
 	extendMarkdownConfig: boolean;
@@ -194,12 +195,19 @@ export default function mdx(partialMdxOptions: Partial<MdxOptions> = {}): AstroI
 									if (!moduleExports.find(({ n }) => n === 'Content')) {
 										// If have `export const components`, pass that as props to `Content` as fallback
 										const hasComponents = moduleExports.find(({ n }) => n === 'components');
+										const usesAstroImage = moduleExports.find(({n}) => n === USES_ASTRO_IMAGE_FLAG);
+
+										let componentsCode = `{ Fragment${hasComponents ? ', ...components' : ''}, ...props.components,`
+										if (usesAstroImage) {
+											componentsCode += ` ${JSON.stringify(ASTRO_IMAGE_ELEMENT)}: ${hasComponents ? 'components.img ?? ' : ''} props.components?.img ?? ${ASTRO_IMAGE_IMPORT}`;
+										}
+										componentsCode += ' }';
 
 										// Make `Content` the default export so we can wrap `MDXContent` and pass in `Fragment`
 										code = code.replace('export default MDXContent;', '');
 										code += `\nexport const Content = (props = {}) => MDXContent({
 											...props,
-											components: { Fragment${hasComponents ? ', ...components' : ''}, ...props.components },
+											components: ${componentsCode},
 										});
 										export default Content;`;
 									}

packages/integrations/mdx/src/remark-images-to-component.ts

@@ -4,6 +4,10 @@ import type { MdxJsxFlowElement, MdxjsEsm } from 'mdast-util-mdx';
 import { visit } from 'unist-util-visit';
 import { jsToTreeNode } from './utils.js';
 
+export const ASTRO_IMAGE_ELEMENT = 'astro-image';
+export const ASTRO_IMAGE_IMPORT = '__AstroImage__';
+export const USES_ASTRO_IMAGE_FLAG = '__usesAstroImage';
+
 export function remarkImageToComponent() {
 	return function (tree: any, file: MarkdownVFile) {
 		if (!file.data.imagePaths) return;
@@ -48,7 +52,7 @@ export function remarkImageToComponent() {
 
 				// Build a component that's equivalent to <Image src={importName} alt={node.alt} title={node.title} />
 				const componentElement: MdxJsxFlowElement = {
-					name: '__AstroImage__',
+					name: ASTRO_IMAGE_ELEMENT,
 					type: 'mdxJsxFlowElement',
 					attributes: [
 						{
@@ -92,7 +96,9 @@ export function remarkImageToComponent() {
 		// Add all the import statements to the top of the file for the images
 		tree.children.unshift(...importsStatements);
 
-		// Add an import statement for the Astro Image component, we rename it to avoid conflicts
-		tree.children.unshift(jsToTreeNode(`import { Image as __AstroImage__ } from "astro:assets";`));
+		tree.children.unshift(jsToTreeNode(`import { Image as ${ASTRO_IMAGE_IMPORT} } from "astro:assets";`));
+		// Export `__usesAstroImage` to pick up `astro:assets` usage in the module graph.
+		// @see the '@astrojs/mdx-postprocess' plugin
+		tree.children.push(jsToTreeNode(`export const ${USES_ASTRO_IMAGE_FLAG} = true`));
 	};
 }

packages/integrations/mdx/test/fixtures/mdx-images/src/components/Component.mdx

@@ -0,0 +1,5 @@
+Optimized image:
+![Houston](../assets/houston.webp)
+
+Public image:
+![Astro logo](/favicon.svg)

packages/integrations/mdx/test/fixtures/mdx-images/src/components/MyImage.astro

@@ -0,0 +1,25 @@
+---
+import type { ImageMetadata } from 'astro';
+import { Image } from 'astro:assets';
+
+type Props = {
+	src: string | ImageMetadata;
+	alt: string;
+};
+
+const { src, alt } = Astro.props;
+---
+
+{
+	typeof src === 'string' ? (
+		<img data-my-image src={src} alt={alt} />
+	) : (
+		<Image data-my-image {src} {alt} />
+	)
+}
+
+<style>
+	[data-my-image] {
+		border: 1px solid red;
+	}
+</style>

packages/integrations/mdx/test/fixtures/mdx-images/src/content/blog/entry.mdx

@@ -0,0 +1,5 @@
+Optimized image:
+![Houston](../../assets/houston.webp)
+
+Public image:
+![Astro logo](/favicon.svg)

packages/integrations/mdx/test/fixtures/mdx-images/src/pages/content-collection.astro

@@ -0,0 +1,19 @@
+---
+import { getEntry } from 'astro:content';
+import MyImage from 'src/components/MyImage.astro';
+
+const entry = await getEntry('blog', 'entry');
+const { Content } = await entry.render();
+---
+
+<!DOCTYPE html>
+<html lang="en">
+<head>
+	<meta charset="UTF-8">
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+	<title>Renderer</title>
+</head>
+<body>
+	<Content components={{ img: MyImage }} />
+</body>
+</html>

packages/integrations/mdx/test/fixtures/mdx-images/src/pages/esm-import.astro

@@ -0,0 +1,16 @@
+---
+import MDX from '../components/Component.mdx';
+import MyImage from 'src/components/MyImage.astro';
+---
+
+<!DOCTYPE html>
+<html lang="en">
+<head>
+	<meta charset="UTF-8">
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+	<title>Renderer</title>
+</head>
+<body>
+	<MDX components={{ img: MyImage }} />
+</body>
+</html>

packages/integrations/mdx/test/fixtures/mdx-images/src/pages/with-components.mdx

@@ -0,0 +1,9 @@
+import MyImage from '../components/MyImage.astro';
+
+export const components = { img: MyImage };
+
+Optimized image:
+![Houston](../assets/houston.webp)
+
+Public image:
+![Astro logo](/favicon.svg)

packages/integrations/mdx/test/mdx-images.test.js

@@ -2,6 +2,8 @@ import { expect } from 'chai';
 import { parseHTML } from 'linkedom';
 import { loadFixture } from '../../../astro/test/test-utils.js';
 
+const imageTestRoutes = ['with-components', 'esm-import', 'content-collection']
+
 describe('MDX Page', () => {
 	let devServer;
 	let fixture;
@@ -36,5 +38,26 @@ describe('MDX Page', () => {
 			// Image with spaces in the path
 			expect(imgs.item(3).src.startsWith('/_image')).to.be.true;
 		});
+
+		for (const route of imageTestRoutes) {
+			it(`supports img component - ${route}`, async () => {
+				const res = await fixture.fetch(`/${route}`);
+				expect(res.status).to.equal(200);
+
+				const html = await res.text();
+				const { document } = parseHTML(html);
+
+				const imgs = document.getElementsByTagName('img');
+				expect(imgs.length).to.equal(2);
+
+				const assetsImg = imgs.item(0);
+				expect(assetsImg.src.startsWith('/_image')).to.be.true;
+				expect(assetsImg.hasAttribute('data-my-image')).to.be.true;
+
+				const publicImg = imgs.item(1);
+				expect(publicImg.src).to.equal('/favicon.svg');
+				expect(publicImg.hasAttribute('data-my-image')).to.be.true;
+			});
+		}
 	});
 });