Add support to Prism for the Astro language

package.json

@@ -14,6 +14,7 @@
     "write-heading-ids": "docusaurus write-heading-ids"
   },
   "dependencies": {
+    "@astrojs/prism": "1.0.1",
     "@docusaurus/core": "2.0.1",
     "@docusaurus/preset-classic": "2.0.1",
     "@mdx-js/react": "^1.6.22",

src/theme/prism-include-languages.js

@@ -0,0 +1,25 @@
+import siteConfig from '@generated/docusaurus.config';
+
+export default function prismIncludeLanguages(PrismObject) {
+  const {
+    themeConfig: {prism},
+  } = siteConfig;
+  const {additionalLanguages} = prism;
+  // Prism components work on the Prism instance on the window, while prism-
+  // react-renderer uses its own Prism instance. We temporarily mount the
+  // instance onto window, import components to enhance it, then remove it to
+  // avoid polluting global namespace.
+  // You can mutate PrismObject: registering plugins, deleting languages... As
+  // long as you don't re-assign it
+  globalThis.Prism = PrismObject;
+  additionalLanguages.forEach((lang) => {
+    // eslint-disable-next-line global-require, import/no-dynamic-require
+    require(`prismjs/components/prism-${lang}`);
+  });
+
+  // TODO: This is a hack. This can be done properly if Astro agree to the
+  //       package exposing this entrypoint.
+  require('../../node_modules/@astrojs/prism/dist/plugin.js').addAstro(PrismObject);
+
+  delete globalThis.Prism;
+}