@fet.web/parcel-namer-simple-structure/index.js

Plugin tries to retain the existing folder structure of your source files.

const { Namer } = require("@parcel/plugin");
const path = require('path')

module.exports = new Namer({
  async name({ bundle, bundleGraph, logger, options }) {
    const bundleGroup = bundleGraph.getBundleGroupsContainingBundle(bundle)[0]
    const bundleGroupBundles = bundleGraph.getBundlesInBundleGroup(bundleGroup, {
      includeInline: true,
    });
    const mainBundle = bundleGroupBundles.find(b => b.getEntryAssets().some(a => a.id === bundleGroup.entryAssetId))
    const isEntry = bundleGraph.isEntryBundleGroup(bundleGroup)
    let name = getFileName(bundle, bundleGraph)
    if (!(isEntry && bundle.id === mainBundle.id)) {
      name += "." + bundle.hashReference
    }
    return name + "." + bundle.type
  },
});

function getFileName(bundle, bundleGraph) {
  let root = bundleGraph.getEntryRoot(bundle.target)
  let filePath = bundle.getMainEntry().filePath
  filePath = filePath.replace(root, '')
  filePathObj = path.parse(filePath)
  filePath = path.join(filePathObj.dir, filePathObj.name)
  return filePath
}