XCode preview crashes when using resources accessed in another Swift Package

** For everyone searching for a workaround, there is one! It's on the workaround branch. It's mainly the 6599c31 commit, but check the branch, as I might improve it later.**

Context

• I have a package shared by multiple projects (MySubLibrary in this example). It contains localized strings (see MySubLibrary/Resources/Strings). Localization works, as the tests, when run in French language, all pass.

  public struct MySubLibrary {
  
    public static var helloWorld: String {
      return NSLocalizedString("HELLO_WORLD", bundle: .module, comment: "Hello world sentence")
    }
  
  }
  

• I have another package which contains SwiftUI Views (MyLibrary in this example), and which depends on the shared package. It also contains resources (see MyLibrary/Resources), such as images.

  Text(MySubLibrary.helloWorld)
  

Bug

When I use a localized string from the shared package, preview crashes.

The underlying error is:

Fatal error: unable to find bundle named MySubLibrary_MySubLibrary: file MySubLibrary/resource_bundle_accessor.swift, line 27

Crash example

I recreated a very small package showing the bug, detailed below.

Working

Code:

static var previews: some View {
    // This works
    MyView(text: "This works")
    
    // This doesn't work
    //MyView(text: MySubLibrary.helloWorld)
}

Result:

Not working

Code:

static var previews: some View {
    // This works
    //MyView(text: "This works")
    
    // This doesn't work
    MyView(text: MySubLibrary.helloWorld)
}

Result:

Diagnostics:

CrashError: XCPreviewAgent crashed

XCPreviewAgent crashed. Check ~/Library/Logs/DiagnosticReports for crash logs from your application.

==================================

|  RemoteHumanReadableError: Failed to update preview.
|  
|  The preview process appears to have crashed.
|  
|  Error encountered when sending 'previewInstances' message to agent.
|  
|  ==================================
|  
|  |  RemoteHumanReadableError: The operation couldnt be completed. (BSServiceConnectionErrorDomain error 3.)
|  |  
|  |  BSServiceConnectionErrorDomain (3):
|  |  ==BSErrorCodeDescription: OperationFailed

Crash report:

The generated crash report can be found in the assets folder as XCPreviewAgent_2021-02-04-203128_Remis-MacBook-Pro.crash.

Diagnostics report:

The full diagnostics report can be found in the assets folder as previews-diagnostics-20210204-203222.

Environment

• swift --version

  Apple Swift version 5.3.2 (swiftlang-1200.0.45 clang-1200.0.32.28)
  Target: x86_64-apple-darwin20.1.0
  

• XCode version

  Version 12.4 (12D4e)
  

• Simulator

  iPhone 11 / iOS 14.4 (18D46)