Add support for baseUrl as a URL

packages/mdx/lib/core.js

@@ -15,7 +15,7 @@
  * @property {SourceMapGenerator | null | undefined} [SourceMapGenerator]
  *   Add a source map (object form) as the `map` field on the resulting file
  *   (optional).
- * @property {string | null | undefined} [baseUrl]
+ * @property {URL | string | null | undefined} [baseUrl]
  *   Resolve `import`s (and `export … from`, and `import.meta.url`) from this
  *   URL (optional, example: `import.meta.url`);
  *   this option is useful when code will run in a different place, such as

packages/mdx/lib/plugin/recma-document.js

@@ -46,7 +46,8 @@ import {specifiersToDeclarations} from '../util/estree-util-specifiers-to-declar
  *   Transform.
  */
 export function recmaDocument(options) {
-  const baseUrl = options.baseUrl || undefined
+  const baseUrl_ = options.baseUrl || undefined
+  const baseUrl = typeof baseUrl_ === 'object' ? baseUrl_.href : baseUrl_
   const useDynamicImport = options.useDynamicImport || undefined
   const outputFormat = options.outputFormat || 'program'
   const pragma =

packages/mdx/readme.md

@@ -493,7 +493,7 @@ Configuration for `createProcessor` (TypeScript type).
     ```
 
     </details>
-*   `baseUrl` (`string`, optional, example: `import.meta.url`)
+*   `baseUrl` (`URL` or `string`, optional, example: `import.meta.url`)
     — resolve `import`s (and `export … from`, and `import.meta.url`) from this
     URL;
     this option is useful when code will run in a different place, such as when

packages/mdx/test/evaluate.js

@@ -360,6 +360,18 @@ test('@mdx-js/mdx: evaluate', async function (t) {
     }
   )
 
+  await t.test(
+    'should support rewriting `import.meta.url` w/ `baseUrl` as an URL',
+    async function () {
+      const mod = await evaluate(
+        'export const x = new URL("example.png", import.meta.url).href',
+        {baseUrl: new URL('https://example.com'), ...runtime}
+      )
+
+      assert.equal(mod.x, 'https://example.com/example.png')
+    }
+  )
+
   await t.test('should throw on an export all from', async function () {
     try {
       await evaluate('export * from "a"', runtime)