Fix resolve base in esbuild loader

Related to mdx-js/mdx#1821.

lib/integration/esbuild.js

@@ -13,7 +13,9 @@
  * @typedef {ProcessorOptions & {allowDangerousRemoteMdx?: boolean}} Options
  */
 
+import assert from 'node:assert'
 import {promises as fs} from 'node:fs'
+import path from 'node:path'
 import process from 'node:process'
 import got from 'got'
 import {VFile} from 'vfile'
@@ -48,6 +50,7 @@ export function esbuild(options = {}) {
     const filter = extnamesToRegex(extnames)
     /* eslint-disable-next-line security/detect-non-literal-regexp */
     const filterHttp = new RegExp('^https?:\\/{2}.+' + filter.source)
+    const http = /^https?:\/{2}/
     const filterHttpOrRelative = /^(https?:\/{2}|.{1,2}\/).*/
 
     if (allowDangerousRemoteMdx) {
@@ -197,9 +200,19 @@ export function esbuild(options = {}) {
         })
       }
 
+      // Safety check: the file has a path, so there has to be a `dirname`.
+      assert(file.dirname, 'expected `dirname` to be defined')
+
       // V8 on Erbium.
       /* c8 ignore next 2 */
-      return {contents: value, errors, warnings, resolveDir: p.cwd()}
+      return {
+        contents: value,
+        errors,
+        warnings,
+        resolveDir: http.test(file.path)
+          ? p.cwd()
+          : path.resolve(file.cwd, file.dirname)
+      }
     }
   }
 }

test/esbuild.js

@@ -47,6 +47,43 @@ test('xdm (esbuild)', async (t) => {
   await fs.unlink(path.join(base, 'esbuild.mdx'))
   await fs.unlink(path.join(base, 'esbuild.js'))
 
+  // Resolve directory.
+  await fs.writeFile(
+    path.join(base, 'esbuild-resolve.mdx'),
+    'import Content from "./folder/file.mdx"\n\n<Content/>'
+  )
+  await fs.mkdir(path.join(base, 'folder'))
+  await fs.writeFile(
+    path.join(base, 'folder', 'file.mdx'),
+    'import {data} from "./file.js"\n\n{data}'
+  )
+  await fs.writeFile(
+    path.join(base, 'folder', 'file.js'),
+    'export const data = 0.1'
+  )
+  await esbuild.build({
+    bundle: true,
+    define: {'process.env.NODE_ENV': '"development"'},
+    entryPoints: [path.join(base, 'esbuild-resolve.mdx')],
+    outfile: path.join(base, 'esbuild-resolve.js'),
+    format: 'esm',
+    plugins: [esbuildXdm()]
+  })
+  /** @type {MDXContent} */
+  Content =
+    /* @ts-expect-error file is dynamically generated */
+    (await import('./context/esbuild-resolve.js')).default // type-coverage:ignore-line
+
+  t.equal(
+    renderToStaticMarkup(React.createElement(Content)),
+    '0.1',
+    'should compile'
+  )
+
+  await fs.unlink(path.join(base, 'esbuild-resolve.mdx'))
+  await fs.unlink(path.join(base, 'esbuild-resolve.js'))
+  await fs.rmdir(path.join(base, 'folder'), {recursive: true})
+
   // Markdown.
   await fs.writeFile(path.join(base, 'esbuild.md'), '\ta')