Add source maps to node loader

Closes GH-2458.

Reviewed-by: Titus Wormer <[email protected]>

Author: remcohaszing

packages/node-loader/lib/index.js

@@ -21,6 +21,7 @@
 import fs from 'node:fs/promises'
 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 {development as defaultDevelopment} from '#condition'
 
@@ -36,7 +37,8 @@ export function createLoader(options) {
   const options_ = options || {}
   const {extnames, process} = createFormatAwareProcessors({
     development: defaultDevelopment,
-    ...options_
+    ...options_,
+    SourceMapGenerator
   })
   const regex = extnamesToRegex(extnames)
 
@@ -62,7 +64,15 @@ export function createLoader(options) {
       const value = await fs.readFile(url)
       const file = await process(new VFile({value, path: url}))
 
-      return {format: 'module', shortCircuit: true, source: String(file)}
+      return {
+        format: 'module',
+        shortCircuit: true,
+        source:
+          String(file) +
+          '\n//# sourceMappingURL=data:application/json;base64,' +
+          Buffer.from(JSON.stringify(file.map)).toString('base64') +
+          '\n'
+      }
     }
 
     return nextLoad(href, context)

packages/node-loader/package.json

@@ -44,12 +44,13 @@
   ],
   "dependencies": {
     "@mdx-js/mdx": "^3.0.0",
+    "source-map": "^0.7.0",
     "vfile": "^6.0.0"
   },
   "devDependencies": {},
   "scripts": {
     "test": "npm run test-coverage",
-    "test-api": "node --conditions development --loader=@mdx-js/node-loader test/index.js",
+    "test-api": "node --conditions development --enable-source-maps --loader=@mdx-js/node-loader test/index.js",
     "test-coverage": "c8 --100 --reporter lcov npm run test-api"
   },
   "xo": {

packages/node-loader/test/index.js

@@ -52,4 +52,48 @@ test('@mdx-js/node-loader', async function (t) {
 
     await fs.rm(mdxUrl)
   })
+
+  await t.test('supports source maps work', async function () {
+    const mdxUrl = new URL('crash.mdx', import.meta.url)
+
+    await fs.writeFile(
+      mdxUrl,
+      '<Throw />\nexport function Throw() { throw new Error("Boom") }\n'
+    )
+
+    /** @type {MDXModule} */
+    let result
+
+    try {
+      result = await import(mdxUrl.href)
+    } catch (error) {
+      const exception = /** @type {NodeJS.ErrnoException} */ (error)
+
+      if (exception.code === 'ERR_UNKNOWN_FILE_EXTENSION') {
+        await fs.rm(mdxUrl)
+
+        throw new Error(
+          'Please run Node with `--loader=@mdx-js/node-loader` to test the ESM loader'
+        )
+      }
+
+      throw error
+    }
+
+    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)
+  })
 })