Plugin: How to resolve to package from node_modules

[levino]

I have a written a plugin like so:

import { mergeConfig, Plugin } from 'vite'
import fs from 'fs'
import path from 'path'

function customResolverPlugin() {
  return {
    name: 'custom-resolver',
    resolveId(source) {
      if (source.startsWith('@theme/')) {
        const packageName = source.slice(7) // Remove '@theme/'
        const srcPath = path.resolve(__dirname, `src/theme/${packageName}`)

        // Check if the module exists in 'src/theme'
        if (fs.existsSync(srcPath)) {
          return srcPath
        }

        return `@docusaurus/theme-classic/lib/theme/${packageName}`
      }
    },
  } satisfies Plugin
}

Unfortunately it does not work. I get:

6:52:42 PM [vite] Pre-transform error: Failed to load url @docusaurus/theme-classic/lib/theme/Navbar (resolved id: @docusaurus/theme-classic/lib/theme/Navbar) in /Users/levinkeller/coding/levino/levinkeller.de/shipyard/base/components/Header.tsx. Does the file exist?

However stuff like

resolve: {
  alias: {
    '@theme': '@docusaurus/theme-classic/lib/theme'
  }
}

in the vite config, it works fine.

If I use

path.resolve(__dirname, `../node_modules/@docusaurus/theme-classic/lib/theme/${packageName}/index.js`)

as a return value in the plugin, vite resolves the file, but that creates issues of its own (suddenly vite is unable to transpile the .jsx content).

I want to implement some kind of import hierarchy to use the swizzling from docusaurus in my other (astro) app.

Thanks for help!