Interface Builder: Typed segues on a per scene basis

[djbe]

Transfer PRs SwiftGen/SwiftGenKit#54 and SwiftGen/templates#79.
Fixes #362.

SwiftgenKit Changes

This PR improves the storyboards parser in 2 ways:

• Know which segues start from which scenes
• Know the type information for a segue destination
  The PR also refactors the Storyboards parser a bit (split up in files).

Templates Changes

Uses the improvements added in SwiftGenKit to generate extensions for non-base classes (UIKit/AppKit), so that a user can:

• Perform a segue safely with an enum of segues that start from that scene (you can no longer incorrectly start a segue from a VC that doesn't support it).
• Prepare for a segue in a type safe way:
  • Have an exhaustive list of possible cases, including one for unnamed segues.
  • Get the segue's destination in the correct type (no need to cast it).
  • Get the segue itself as the correct subclass if you're using custom segues.

---

For performing a segue, the user goes from:

perform(segue: StoryboardSegue.MyStoryboard.nextStep)

To:

perform(segue: .nextStep)

For preparing for a segue, the user goes from:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
  // autocomplete for cases won't work because of optionals
  switch segueEnum {
  case .nextStep?:
    guard let destination = segue.destination as? NextStepViewController else { return }
    // destination is casted version
  case .login?:
    guard let destination = segue.destination as? LoginViewController else { return }
    // destination is casted version
  default:
    // Handle segues that are for other scenes, or unnamed segues
  }
}

To:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
  switch TypedStoryboardSegue(segue: segue) {
  case .nextStep(let destination):
    // destination is casted version
  case .login(let destination):
    // destination is casted version
  case .unnamedSegue:
    // This case is added if you have unnamed segues (with identifier "")
  }
}

[djbe]

@AliSoftware proposed another idea, that we could add to this template (or an alternative one):

protocol MyViewControllerTypedStoryboardSegue {
  func prepareSegueForEmbed(destination: EmbedDestinationVC)
  func prepareSegueForModal(destination: ModalDestionationVC)
  …
  func prepare(for segue: NSStoryboardSegue, sender: Any?)
}
extension MyViewControllerTypedStoryboardSegue {
  func prepare(for segue: NSStoryboardSegue, sender: Any?) {
    /* generate that switch/case implementation here which calls the proper prepareSegueForXXX(destionation:) method */
  }
}

There could be issues here because of @objc dispatch and stuff, but could be interesting.

Another proposal was:

/* Generated by SwiftGen */
protocol MyViewControllerTypedStoryboardSegue {
  func prepareSegueForEmbed(destination: EmbedDestinationVC)
  func prepareSegueForModal(destination: ModalDestionationVC)
  …
  func prepare(for segue: NSStoryboardSegue)
}
extension MyViewControllerTypedStoryboardSegue {
  func prepare(for segue: NSStoryboardSegue) {
    /* generate that switch/case implementation here which calls
        the proper prepareSegueForXXX(destionation:) method */
  }
}

/* Added by the user */
extension MyViewController: MyViewControlelrTypedStoryboardSegue {
  @objc func prepare(for segue: NSStoryboardSegue, sender: Any?) {
    self.prepare(for: segue)
  }
}

I'd probably rename the function here, because users want access to the sender argument so we'd need to pass it along.

[parallaxe]

To know where the segues originate from would be a killer-feature for me to use SwiftGen. I have no opinion regarding the templates though.
Is it foreseeable that it will be merged soon? Is there something I could do to accelerate it?

[djbe]

To begin with: any and all suggestions are welcome!

You could try mock-generating the code (manually) for one of your projects (or just 1 storyboard), and see if the generated code works for you? Are all features there that you might want? Does the functionality match with your project structure?

Maybe go through your project's current segues, their names and controller types, and whatever else you need when performing segues. See if there might be an issue (or not) with the generated code.

[parallaxe]

For my understanding, the StoryboardSegue-enum that is created inside the extensions of each custom Scene-class should only contain the segues that are started from that specific scene.
If this is the case, the xpath has to be "./connections/segue"

[djbe]

The reason for the // in sceneSegueXPath is to be able to match segues started from (for example):

• container views --> embed segues
• triggered by a button or cell

sceneSegueXPath is only used to match children of a scene object:
https://github.com/SwiftGen/SwiftGen/pull/364/files#diff-aab03c1cbf39dc54bf61cfae345dfc87R43

[parallaxe]

I made a reduced-version of your storyboard-template which contains only the scene-extensions with an segue-enum containing all segues that are started from the scene. Essentially, that is all i would need for know. You can find it here https://gist.github.com/parallaxe/7815fc6a8ed98e2e66de20d65169d608
Though, to make it work as I expected it, I had to change one of the XPaths in the storyboard-parser - I added a comment to the specific line in the "File Changes"-part of the merge-request.

[domasn]

Hi all 👋

@djbe thank you for this PR! I think it would be really valuable to a lot of users. I see that you add new commits from time to time and wonder what's the state of this feature?

It there anything I can do to help? 🙂