Fix crash with esbuild loader and jsx option

Closes GH-2593.
Closes GH-2594.

Author: egnor

packages/esbuild/lib/index.js

@@ -66,10 +66,8 @@ const name = '@mdx-js/esbuild'
  *   Plugin.
  */
 export function esbuild(options) {
-  const {extnames, process} = createFormatAwareProcessors({
-    ...options,
-    SourceMapGenerator
-  })
+  const settings = {...options, SourceMapGenerator};
+  const {extnames, process} = createFormatAwareProcessors(settings)
 
   return {name, setup}
 
@@ -142,6 +140,7 @@ export function esbuild(options) {
       return {
         contents: value || '',
         errors,
+        loader: settings.jsx ? 'jsx' : 'js',
         resolveDir: path.resolve(file.cwd, file.dirname),
         warnings
       }

packages/esbuild/test/index.js

@@ -570,6 +570,36 @@ test('@mdx-js/esbuild', async function (t) {
     await fs.rm(mdxUrl)
     await fs.rm(jsUrl)
   })
+
+  await t.test('should use esbuild "jsx" loader for JSX output', async () => {
+    const mdxUrl = new URL('esbuild.mdx', import.meta.url)
+    const jsUrl = new URL('esbuild.js', import.meta.url)
+    await fs.writeFile(
+      mdxUrl,
+      'export function Message() { return <>World!</> }\n\n# Hello, <Message />'
+    )
+
+    await esbuild.build({
+      entryPoints: [fileURLToPath(mdxUrl)],
+      outfile: fileURLToPath(jsUrl),
+      plugins: [esbuildMdx({jsx: true})],
+      define: {'process.env.NODE_ENV': '"development"'},
+      format: 'esm',
+      bundle: true
+    })
+
+    /** @type {MDXModule} */
+    const result = await import(jsUrl.href + '#' + Math.random())
+    const Content = result.default
+
+    assert.equal(
+      renderToStaticMarkup(React.createElement(Content)),
+      '<h1>Hello, World!</h1>'
+    )
+
+    await fs.rm(mdxUrl)
+    await fs.rm(jsUrl)
+  })
 })
 
 /**