Regression in SwiftUI in Xcode 14

[mackoj]

Hi,

Since WWDC and Xcode 14 I can't compile my project anymore. So I did open a feedback(FB10115879).

My project compile in Xcode 13.4.1 and in Xcode 14b1 it doesn't, I have "The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions" error in a few different SwiftUI files that used to compile in Xcode 13.4.1.

[mackoj]

Apple did respond this morning I think this could help.

Engineering has provided the following information regarding this issue:

We suggest that you refactor views that have WithViewStore call into a separate method:

Current project:

public var body: some View {
WithViewStore(self.store) { viewStore in
{INNER BODY}
}
}
`

New dedicated body function which accepts ViewStore and moves {INNER BODY} into it:

public var body: some View {
WithViewStore(self.store) { viewStore in
body(viewStore: viewStore)
}
}

func body(viewStore: ViewStore<{STATE}, {ACTION}>) -> some View {
{INNER BODY}
}

Also, please know that the performance problem is related to how result builders work and the fact that WithViewStore is overloaded and has a result builder parameter which forces body of the associated closure to be type-checked multiple times even though some of the overloads might not be applicable. The previous compiler version had an issue where "complex" closures would be allowed to type-check indefinitely which is now fixed and triggers the error in all these cases.

[tgrapperon]

This is not meant to be used in production, but it shows that there is maybe some more work to do on WithViewStore then.

[tgrapperon]

My bet is that WithViewStore's Content is not locked to be a View, so it opens too much possibilities for the content below. Without abusing your patience, does this works in place of a WithViewStore? That is, replacing WithViewStore by WithViewViewStore.

public struct WithViewViewStore<State, Action, Content: View>: View {
  let content: WithViewStore<State, Action, Content>
  public init(
    store: Store<State, Action>,
    removeDuplicates isDuplicate: @escaping (State, State) -> Bool,
    file: StaticString = #fileID,
    line: UInt = #line,
    content: @escaping (ViewStore<State, Action>) -> Content
  ) {
    self.content = WithViewStore(store: store, removeDuplicates: isDuplicate, content: content)
  }
  
  public init(
    store: Store<State, Action>,
    file: StaticString = #fileID,
    line: UInt = #line,
    content: @escaping (ViewStore<State, Action>) -> Content
  ) where State: Equatable {
    self = WithViewViewStore(store: store, removeDuplicates: ==, content: content)
  }
  
  public var body: some View {
    self.content
  }
}

[tgrapperon]

Ah, I've seen that you'll likely find a solution with @mbrandonw and @stephencelis. It will be much more effective than trying things like this. Please let me know the outcome!

[mackoj]

The WithViewViewStore approach works too.

[tgrapperon]

Nice! Because it uses a standard WithViewStore under the hood. It's maybe possible to write an extension of WithViewStore to help with this and that we could trigger using some syntax like

WithViewStore(store).asView { … }

We would be able to simply add an .asView to help the compiler in complex situations. A proper solution is desirable though, and I'm currently experimenting with some @ObservedStore property wrapper. I'll report shortly in the form of a discussion.

[mbrandonw]

Hey @mackoj, that's a bummer! Is there any chance you could share the project (either publicly or privately with just me and Stephen) so that we could poke around a bit? We would hate if we created compiler problems with some of our latest releases.

[mackoj]

What mail should I use to send it privately ?

[mbrandonw]

I'll send you an email 😃

[mbrandonw]

Also, I should mention, that another workaround besides moving the body of WithViewStore to a computed property is to use @ObservedObject for your view store:

struct SomeView: View {
  let store: Store<...>
  @ObservedObject var viewStore: ViewStore<...>

  init(store: ...) { 
    self.store = store 
    self.viewStore = ViewStore(store)
  }

  var body: some View {
    // use self.viewStore directly
  }
}

Of course, ideally we fix this compiler issues, but it is just an alternative for now.

[mackoj]

Ok thanks I did try this and it compiled too.

[mackoj]

FWIW this bug remains in the last Xcode Beta 4

[stephencelis]

Thanks for the update! We'll try to take a look at the WithViewStore overload situation to see if we can make things work better soon.