feat: prefer the local @mdx-js/mdx

..and cache any resolved imports.

src/index.ts

@@ -1,7 +1,7 @@
+import { requireMdx } from './resolveImport'
 import { remarkMdxImport } from './remarkMdxImport'
 import { stopService, transform } from './transform'
 import { MdxOptions, MdxPlugin, RemarkPlugin } from './types'
-import mdx from '@mdx-js/mdx'
 import fs from 'fs'
 
 export { MdxOptions, MdxPlugin }
@@ -55,7 +55,7 @@ function createPlugin(
                   getMdxOptions?.(filePath).remarkPlugins
                 )
                 remarkPlugins.push(mdxImportPlugin)
-                return mdx.createMdxAstCompiler({
+                return requireMdx(root).createMdxAstCompiler({
                   remarkPlugins: remarkPlugins as any[]
                 })
               }

src/resolveImport.ts

@@ -0,0 +1,40 @@
+import findDependency from 'find-dependency'
+
+const importCache: {
+  [cacheKey: string]: string | undefined
+} = {}
+
+type MdxModule = typeof import('@mdx-js/mdx')
+
+export function requireMdx(cwd: string): MdxModule {
+  return require(resolveImport('@mdx-js/mdx', cwd) || '@mdx-js/mdx')
+}
+
+/**
+ * Search the node_modules of `cwd` and its ancestors until a package is found.
+ * Skip global `node_modules` and `vite/node_modules` (since `vite` might be
+ * a local clone).
+ */
+export function resolveImport(
+  name: string,
+  cwd: string,
+  throwOnMissing?: boolean
+) {
+  const cacheKey = cwd + '\0' + name
+  if (!importCache[cacheKey]) {
+    const resolved = findDependency(name, { cwd, skipGlobal: true })
+    if (throwOnMissing && !resolved) {
+      throw new Error(`[vite-plugin-mdx] "{name}" must be installed`)
+    }
+    importCache[cacheKey] = resolved
+  }
+  return importCache[cacheKey]
+}
+
+/**
+ * Throw an error if the given `name` cannot be found from `cwd`.
+ * Otherwise, return the `name`.
+ */
+export function assertImportExists(name: string, cwd: string) {
+  return resolveImport(name, cwd, true) && name
+}

src/transform.ts

@@ -1,18 +1,16 @@
 import { startService, Service } from 'esbuild'
-import mdx from '@mdx-js/mdx'
-import findDependency from 'find-dependency'
 import { MdxOptions } from './types'
+import { assertImportExists, requireMdx, resolveImport } from './resolveImport'
 
 export { transform }
 export { stopService }
 
-const pluginName = 'vite-plugin-mdx'
-
 async function transform(
   code_mdx: string,
   mdxOptions?: MdxOptions,
   root = __dirname
 ) {
+  const mdx = requireMdx(root)
   const code_jsx = await mdx(code_mdx, mdxOptions as any)
   const code_es2019 = await jsxToES2019(code_jsx)
   const code_final = injectImports(code_es2019, root)
@@ -49,45 +47,25 @@ async function jsxToES2019(code_jsx: string) {
 }
 
 function injectImports(code_es2019: string, root: string) {
-  if (findPackage('preact', root)) {
+  if (resolveImport('preact', root)) {
     return [
       `import { h } from 'preact'`,
-      `import { mdx } from '${getMdxImportPath('@mdx-js/preact', root)}'`,
+      `import { mdx } from '${assertImportExists('@mdx-js/preact', root)}'`,
       '',
       code_es2019
     ].join('\n')
   }
 
-  if (findPackage('react', root)) {
+  if (resolveImport('react', root)) {
     return [
       `import React from 'react'`,
-      `import { mdx } from '${getMdxImportPath('@mdx-js/react', root)}'`,
+      `import { mdx } from '${assertImportExists('@mdx-js/react', root)}'`,
       '',
       code_es2019
     ].join('\n')
   }
 
-  throw new Error(
-    `[Wrong Usage][${pluginName}] You need to \`npm install react\` or \`npm install preact\`.`
-  )
-}
-
-function getMdxImportPath(mdxPackageName: string, root: string): string {
-  const mdxPackageRoot = findPackage(mdxPackageName, root)
-  if (mdxPackageRoot) {
-    return mdxPackageName
-  }
-  throw new Error(
-    `[Wrong Usage][${pluginName}] You need to \`npm install ${mdxPackageName}\`.`
-  )
-}
-
-/**
- * Search the node_modules of `cwd` and its ancestors until a package is found.
- * Skip global node_modules and vite/node_modules (local clone might be used).
- */
-function findPackage(name: string, cwd: string) {
-  return findDependency(name, { cwd, skipGlobal: true })
+  throw new Error(`[vite-plugin-mdx] "react" or "preact" must be installed`)
 }
 
 let _service: Promise<Service> | undefined