Workaround for previewing SwiftPM resources

BundleCurrent.swift

// Workaround for Bundle resource when running on Xcode previews
// https://forums.swift.org/t/xcode-previews-swiftpm-resources-xcpreviewagent-crashed/51680/10
// https://developer.apple.com/forums/thread/664295?answerId=673644022#673644022
// https://gist.github.com/ctreffs/ad9d23e08d586cf75e4d1c3bb1b1061f

import class Foundation.Bundle
import class Foundation.ProcessInfo

private class BundleFinder {}

extension Foundation.Bundle {
  /// Returns the resource bundle associated with the current Swift module.
  static var current: Bundle = {
    let bundleName = "MyLibrary_Styleguide"

    var candidates = [
      // Bundle should be present here when the package is linked into an App.
      Bundle.main.resourceURL,

      // Bundle should be present here when the package is linked into a framework.
      Bundle(for: BundleFinder.self).resourceURL,

      // For command-line tools.
      Bundle.main.bundleURL,
    ]

    // FIX FOR PREVIEWS
    if ProcessInfo.processInfo.environment["XCODE_RUNNING_FOR_PREVIEWS"] == "1" {
      candidates.append(contentsOf: [
        // Bundle should be present here when running previews from a different package
        Bundle(for: BundleFinder.self).resourceURL?.deletingLastPathComponent().deletingLastPathComponent().deletingLastPathComponent(),
        Bundle(for: BundleFinder.self).resourceURL?.deletingLastPathComponent().deletingLastPathComponent()
      ])
    }

    for candidate in candidates {
      let bundlePath = candidate?.appendingPathComponent(bundleName + ".bundle")
      if let bundle = bundlePath.flatMap(Bundle.init(url:)) {
        return bundle
      }
    }
    fatalError("unable to find bundle named \(bundleName)")
  }()
}