Exporting Package.swift for Swift Package Manager from existing Xcode project - swift

Question

I'm working with Xcode 11.3 on macOS Catalina 10.15.6.
I have an existing Xcode project which builds an app for iOS. I am interested in reusing some of the classes in an interactive session with the swift command line interpreter. The classes I want to work with are Core Data classes which are autogenerated from an Xcode data model and also some classes I've written which work with the Core Data classes. The app has UI screens and makes use of UIKit but I'm not trying to use any of those classes; I'm hoping that I can either compile those classes and then not refer to them, or somehow tell Swift Package Manager to ignore those classes altogether.
What I think I would like to do is to export a Package.swift for the existing Xcode project, such that swift build at the command line would be able to compile all of the project classes, or, failing that, at least the non-UI classes, and then swift run --repl would be able to load the classes via import.
I see a menu item in Xcode to create a new Swift package, but not to export an existing project. Is there a way to export an existing project?

Answer 1

There are no a menu command or utility to convert application to a static library, dynamic framework or swift package since they are different types of projects with different settings etc.
If you want to export a part of your project as a swift package you should make next steps manually:
1. Create Package.swift file in the root of your project
import PackageDescription
let package = Package(
name: “MyLib”,
products: [
.library(name: "MyLib", targets: ["MyLib"])
],
targets: [
.target(name: "MyLib"),
],
...
)
2. Make folder with subfolder ./Sources/MyLib under the projects’s root.
By default swift package structure requires to put all your sources files under Sources/LibraryName folder but you can change it below.
NOTE: you can simplify first two steps by using swift package init and it creates Package.swift, Sources and Test folders etc.
3. Include source files
a) Move the needed files to share from their current locations to MyLib folder.
For instance:
./Classes/MyEntity.swift -> ./Sources/MyLib/MyEntity.swift
Also you have to update locations of the moved files in your Xcode project to leave it compilable.
b) Use path, sources and exclude to point needed source files to your package from their current locations:
.target(name: "MyLib", path: "Classes"),
NOTE: Don't forget to make your classes public to access to them after import your package:
public class MyEntity {
...
}
After all you will have two working projects - old XCode's one and new Swift package.
4. REPL
Now you can use command line interpreter with your swift package:
swift run --repl
import MyLib
let entity = MyEntity()
...