Light/dark theming for shikiji's codeblocks (#8903)

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

8 files changed, 62 insertions, 8 deletions

diff --git a/.changeset/tender-suits-glow.md b/.changeset/tender-suits-glow.md
new file mode 100644
index 000000000..a01662ce6
--- /dev/null
+++ b/.changeset/tender-suits-glow.md
@@ -0,0 +1,6 @@
+---
+'@astrojs/markdown-remark': minor
+'astro': minor
+---
+
+Adds experimental support for multiple shiki themes with the new `markdown.shikiConfig.experimentalThemes` option.
diff --git a/packages/astro/components/Code.astro b/packages/astro/components/Code.astro
index 0a4fff6b9..b1d21fd9e 100644
--- a/packages/astro/components/Code.astro
+++ b/packages/astro/components/Code.astro
@@ -33,6 +33,11 @@ interface Props {
 	 */
 	theme?: BuiltinTheme | ThemeRegistration | ThemeRegistrationRaw;
 	/**
+	 * Multiple themes to style with -- alternative to "theme" option.
+	 * Supports all themes found above; see https://github.com/antfu/shikiji#lightdark-dual-themes for more information.
+	 */
+	experimentalThemes?: Record<string, BuiltinTheme | ThemeRegistration | ThemeRegistrationRaw>;
+	/**
 	 * Enable word wrapping.
 	 *  - true: enabled.
 	 *  - false: disabled.
@@ -53,6 +58,7 @@ const {
 	code,
 	lang = 'plaintext',
 	theme = 'github-dark',
+	experimentalThemes = {},
 	wrap = false,
 	inline = false,
 } = Astro.props;
@@ -88,12 +94,15 @@ if (typeof lang === 'object') {
 
 const highlighter = await getCachedHighlighter({
 	langs: [lang],
-	themes: [theme],
+	themes: Object.values(experimentalThemes).length ? Object.values(experimentalThemes) : [theme],
 });
 
+const themeOptions = Object.values(experimentalThemes).length
+	? { themes: experimentalThemes }
+	: { theme };
 const html = highlighter.codeToHtml(code, {
 	lang: typeof lang === 'string' ? lang : lang.name,
-	theme,
+	...themeOptions,
 	transforms: {
 		pre(node) {
 			// Swap to `code` tag if inline
@@ -123,6 +132,10 @@ const html = highlighter.codeToHtml(code, {
 			}
 		},
 		root(node) {
+			if (Object.values(experimentalThemes).length) {
+				return;
+			}
+
 			// theme.id for shiki -> shikiji compat
 			const themeName = typeof theme === 'string' ? theme : theme.name;
 			if (themeName === 'css-variables') {
diff --git a/packages/astro/src/core/config/schema.ts b/packages/astro/src/core/config/schema.ts
index 5a5964a12..ea656b9bf 100644
--- a/packages/astro/src/core/config/schema.ts
+++ b/packages/astro/src/core/config/schema.ts
@@ -292,7 +292,14 @@ export const AstroConfigSchema = z.object({
 					theme: z
 						.enum(Object.keys(bundledThemes) as [BuiltinTheme, ...BuiltinTheme[]])
 						.or(z.custom<ShikiTheme>())
-						.default(ASTRO_CONFIG_DEFAULTS.markdown.shikiConfig.theme as BuiltinTheme),
+						.default(ASTRO_CONFIG_DEFAULTS.markdown.shikiConfig.theme!),
+					experimentalThemes: z
+						.record(
+							z
+								.enum(Object.keys(bundledThemes) as [BuiltinTheme, ...BuiltinTheme[]])
+								.or(z.custom<ShikiTheme>())
+						)
+						.default(ASTRO_CONFIG_DEFAULTS.markdown.shikiConfig.experimentalThemes!),
 					wrap: z.boolean().or(z.null()).default(ASTRO_CONFIG_DEFAULTS.markdown.shikiConfig.wrap!),
 				})
 				.default({}),
diff --git a/packages/astro/src/vite-plugin-markdown/index.ts b/packages/astro/src/vite-plugin-markdown/index.ts
index 3c8a1af46..fdfe3db37 100644
--- a/packages/astro/src/vite-plugin-markdown/index.ts
+++ b/packages/astro/src/vite-plugin-markdown/index.ts
@@ -81,6 +81,7 @@ export default function markdown({ settings, logger }: AstroPluginOptions): Plug
 
 				const renderResult = await processor
 					.render(raw.content, {
+						// @ts-expect-error passing internal prop
 						fileURL,
 						frontmatter: raw.data,
 					})
diff --git a/packages/markdown/remark/src/index.ts b/packages/markdown/remark/src/index.ts
index 89c9ca8bd..61f97072b 100644
--- a/packages/markdown/remark/src/index.ts
+++ b/packages/markdown/remark/src/index.ts
@@ -39,6 +39,7 @@ export const markdownConfigDefaults: Omit<Required<AstroMarkdownOptions>, 'draft
 	shikiConfig: {
 		langs: [],
 		theme: 'github-dark',
+		experimentalThemes: {},
 		wrap: false,
 	},
 	remarkPlugins: [],
diff --git a/packages/markdown/remark/src/remark-shiki.ts b/packages/markdown/remark/src/remark-shiki.ts
index bf3dd0b78..4eaae5ff2 100644
--- a/packages/markdown/remark/src/remark-shiki.ts
+++ b/packages/markdown/remark/src/remark-shiki.ts
@@ -30,9 +30,15 @@ const highlighterCacheAsync = new Map<string, Promise<Highlighter>>();
 export function remarkShiki({
 	langs = [],
 	theme = 'github-dark',
+	experimentalThemes = {},
 	wrap = false,
 }: ShikiConfig = {}): ReturnType<RemarkPlugin> {
+	const themes = experimentalThemes;
+
 	const cacheId =
+		Object.values(themes)
+			.map((t) => (typeof t === 'string' ? t : t.name ?? ''))
+			.join(',') +
 		(typeof theme === 'string' ? theme : theme.name ?? '') +
 		langs.map((l) => l.name ?? (l as any).id).join(',');
 
@@ -40,7 +46,7 @@ export function remarkShiki({
 	if (!highlighterAsync) {
 		highlighterAsync = getHighlighter({
 			langs: langs.length ? langs : Object.keys(bundledLanguages),
-			themes: [theme],
+			themes: Object.values(themes).length ? Object.values(themes) : [theme],
 		});
 		highlighterCacheAsync.set(cacheId, highlighterAsync);
 	}
@@ -64,7 +70,8 @@ export function remarkShiki({
 				lang = 'plaintext';
 			}
 
-			let html = highlighter.codeToHtml(node.value, { lang, theme });
+			let themeOptions = Object.values(themes).length ? { themes } : { theme };
+			let html = highlighter.codeToHtml(node.value, { ...themeOptions, lang });
 
 			// Q: Couldn't these regexes match on a user's inputted code blocks?
 			// A: Nope! All rendered HTML is properly escaped.
diff --git a/packages/markdown/remark/src/types.ts b/packages/markdown/remark/src/types.ts
index 4abcf578d..7038e2425 100644
--- a/packages/markdown/remark/src/types.ts
+++ b/packages/markdown/remark/src/types.ts
@@ -42,6 +42,7 @@ export type RemarkRehype = Omit<RemarkRehypeOptions, 'handlers' | 'unknownHandle
 export interface ShikiConfig {
 	langs?: LanguageRegistration[];
 	theme?: BuiltinTheme | ThemeRegistration | ThemeRegistrationRaw;
+	experimentalThemes?: Record<string, BuiltinTheme | ThemeRegistration | ThemeRegistrationRaw>;
 	wrap?: boolean | null;
 }
 
diff --git a/packages/markdown/remark/test/shiki.js b/packages/markdown/remark/test/shiki.js
index cc5c6b771..c7ace6187 100644
--- a/packages/markdown/remark/test/shiki.js
+++ b/packages/markdown/remark/test/shiki.js
@@ -1,12 +1,30 @@
 import { createMarkdownProcessor } from '../dist/index.js';
 import chai from 'chai';
 
-describe('shiki syntax highlighting', async () => {
-	const processor = await createMarkdownProcessor();
-
+describe('shiki syntax highlighting', () => {
 	it('does not add is:raw to the output', async () => {
+		const processor = await createMarkdownProcessor();
 		const { code } = await processor.render('```\ntest\n```');
 
 		chai.expect(code).not.to.contain('is:raw');
 	});
+
+	it('supports light/dark themes', async () => {
+		const processor = await createMarkdownProcessor({
+			shikiConfig: {
+				experimentalThemes: {
+					light: 'github-light',
+					dark: 'github-dark',
+				},
+			},
+		});
+		const { code } = await processor.render('```\ntest\n```');
+
+		// light theme is there:
+		chai.expect(code).to.contain('background-color:');
+		chai.expect(code).to.contain('github-light');
+		// dark theme is there:
+		chai.expect(code).to.contain('--shiki-dark-bg:');
+		chai.expect(code).to.contain('github-dark');
+	});
 });