Add source maps to esbuild plugin

packages/esbuild/lib/index.js

@@ -43,6 +43,7 @@ import fs from 'node:fs/promises'
 import path from 'node:path'
 import {createFormatAwareProcessors} from '@mdx-js/mdx/internal-create-format-aware-processors'
 import {extnamesToRegex} from '@mdx-js/mdx/internal-extnames-to-regex'
+import {SourceMapGenerator} from 'source-map'
 import {VFile} from 'vfile'
 import {VFileMessage} from 'vfile-message'
 
@@ -65,7 +66,10 @@ const name = '@mdx-js/esbuild'
  *   Plugin.
  */
 export function esbuild(options) {
-  const {extnames, process} = createFormatAwareProcessors(options || {})
+  const {extnames, process} = createFormatAwareProcessors({
+    ...options,
+    SourceMapGenerator
+  })
 
   return {name, setup}
 
@@ -96,7 +100,7 @@ export function esbuild(options) {
       /** @type {State} */
       const state = {doc: document, name, path: data.path}
       let file = new VFile({path: data.path, value: document})
-      /** @type {Value | undefined} */
+      /** @type {string | undefined} */
       let value
       /** @type {Array<VFileMessage>} */
       let messages = []
@@ -107,7 +111,11 @@ export function esbuild(options) {
 
       try {
         file = await process(file)
-        value = file.value
+        value =
+          String(file.value) +
+          '\n//# sourceMappingURL=data:application/json;base64,' +
+          Buffer.from(JSON.stringify(file.map)).toString('base64') +
+          '\n'
         messages = file.messages
       } catch (error_) {
         const cause = /** @type {VFileMessage | Error} */ (error_)

packages/esbuild/package.json

@@ -40,6 +40,7 @@
   "dependencies": {
     "@mdx-js/mdx": "^3.0.0",
     "@types/unist": "^3.0.0",
+    "source-map": "^0.7.0",
     "vfile": "^6.0.0",
     "vfile-message": "^4.0.0"
   },
@@ -48,7 +49,7 @@
   },
   "scripts": {
     "test": "npm run test-coverage",
-    "test-api": "node --conditions development test/index.js",
+    "test-api": "node --conditions development --enable-source-maps test/index.js",
     "test-coverage": "c8 --100 --reporter lcov npm run test-api"
   },
   "xo": {

packages/esbuild/test/index.js

@@ -539,6 +539,44 @@ test('@mdx-js/esbuild', async function (t) {
       await fs.rm(jsUrl)
     }
   )
+
+  await t.test('should support source maps', async () => {
+    const mdxUrl = new URL('crash.mdx', import.meta.url)
+    const jsUrl = new URL('crash.js', import.meta.url)
+    await fs.writeFile(
+      mdxUrl,
+      '<Throw />\nexport function Throw() { throw new Error("Boom") }\n'
+    )
+
+    await esbuild.build({
+      entryPoints: [fileURLToPath(mdxUrl)],
+      outfile: fileURLToPath(jsUrl),
+      plugins: [esbuildMdx()],
+      define: {'process.env.NODE_ENV': '"development"'},
+      format: 'esm',
+      sourcemap: true,
+      bundle: true
+    })
+
+    /** @type {MDXModule} */
+    const result = await import(jsUrl.href)
+    const Content = result.default
+
+    assert.throws(
+      () => renderToStaticMarkup(React.createElement(Content)),
+      (error) => {
+        assert(error instanceof Error)
+        assert.equal(error.message, 'Boom')
+        // Source maps are off.
+        // The column should be 26, not 8.
+        assert(error.stack?.includes('crash.mdx:2:8)'))
+        return true
+      }
+    )
+
+    await fs.rm(mdxUrl)
+    await fs.rm(jsUrl)
+  })
 })
 
 /**