Unable to type check multiple destinations

[peramaic]

Hi,
I started to convert an app to the prerelease/1.0 branch using stack-based and tree-based navigation. Some features use multiple destinations, e.g. one alert and four fullScreenCover. Unfortunately Xcode gives me the 'The compiler is unable to type-check this expression in reasonable time' error on the view's body. I can get rid of the error by commenting a few fullScreenCover modifiers, but Xcode gives no hint on the underlying problem. I'm using Xcode 14.3.1 and the latest TCA prerelease/1.0 commit/b2815ca

The problem seems to be not related to my app because I modified PointFree's Standups example slightly (added dummy destinations, added a menu to the toolbar...) and the error showed up:

import ComposableArchitecture
import SwiftUI

struct StandupsList: Reducer {
  struct State: Equatable {
    @PresentationState var destination: Destination.State?
    var standups: IdentifiedArrayOf<Standup> = []

    init(
      destination: Destination.State? = nil
    ) {
      self.destination = destination

      do {
        @Dependency(\.dataManager.load) var load
        self.standups = try JSONDecoder().decode(IdentifiedArray.self, from: load(.standups))
      } catch is DecodingError {
        self.destination = .alert(.dataFailedToLoad)
      } catch {}
    }
  }

  enum Action: Equatable {
    case addStandupButtonTapped
    case confirmAddStandupButtonTapped
    case destination(PresentationAction<Destination.Action>)
    case dismissAddStandupButtonTapped
    case oneStandupButtonTapped
    case twoStandupButtonTapped
    case threeStandupButtonTapped
    case fourStandupButtonTapped
    case fiveStandupButtonTapped
  }

  struct Destination: Reducer {
    enum State: Equatable {
      case add(StandupForm.State)
      case one(StandupForm.State)
      case two(StandupForm.State)
      case three(StandupForm.State)
      case four(StandupForm.State)
      case five(StandupForm.State)
      case alert(AlertState<Action.Alert>)
    }

    enum Action: Equatable {
      case add(StandupForm.Action)
      case one(StandupForm.Action)
      case two(StandupForm.Action)
      case three(StandupForm.Action)
      case four(StandupForm.Action)
      case five(StandupForm.Action)
      case alert(Alert)

      enum Alert {
        case confirmLoadMockData
      }
    }

    var body: some Reducer<State, Action> {
      Scope(state: /State.add, action: /Action.add) {
        StandupForm()
      }
    }
  }

  @Dependency(\.continuousClock) var clock
  @Dependency(\.dataManager.load) var load
  @Dependency(\.uuid) var uuid

  var body: some ReducerOf<Self> {
    Reduce<State, Action> { state, action in
      switch action {
        case .addStandupButtonTapped:
          state.destination = .add(StandupForm.State(standup: Standup(id: Standup.ID(self.uuid()))))
          return .none

        case .oneStandupButtonTapped:
          state.destination = .one(StandupForm.State(standup: Standup(id: Standup.ID(self.uuid()))))
          return .none

        case .twoStandupButtonTapped:
          state.destination = .two(StandupForm.State(standup: Standup(id: Standup.ID(self.uuid()))))
          return .none

        case .threeStandupButtonTapped:
          state.destination = .three(StandupForm.State(standup: Standup(id: Standup.ID(self.uuid()))))
          return .none

        case .fourStandupButtonTapped:
          state.destination = .four(StandupForm.State(standup: Standup(id: Standup.ID(self.uuid()))))
          return .none

        case .fiveStandupButtonTapped:
          state.destination = .five(StandupForm.State(standup: Standup(id: Standup.ID(self.uuid()))))
          return .none

        case .confirmAddStandupButtonTapped:
          guard case let .some(.add(editState)) = state.destination
          else { return .none }
          var standup = editState.standup
          standup.attendees.removeAll { attendee in
            attendee.name.allSatisfy(\.isWhitespace)
          }
          if standup.attendees.isEmpty {
            standup.attendees.append(
              editState.standup.attendees.first
                ?? Attendee(id: Attendee.ID(self.uuid()))
            )
          }
          state.standups.append(standup)
          state.destination = nil
          return .none

        case .destination(.presented(.alert(.confirmLoadMockData))):
          state.standups = [
            .mock,
            .designMock,
            .engineeringMock,
          ]
          return .none

        case .destination:
          return .none

        case .dismissAddStandupButtonTapped:
          state.destination = nil
          return .none
      }
    }
    .ifLet(\.$destination, action: /Action.destination) {
      Destination()
    }
  }
}

struct StandupsListView: View {
  let store: StoreOf<StandupsList>

  var body: some View {
    WithViewStore(self.store, observe: \.standups) { viewStore in
      List {
        ForEach(viewStore.state) { standup in
          NavigationLink(
            state: AppFeature.Path.State.detail(StandupDetail.State(standup: standup))
          ) {
            CardView(standup: standup)
          }
          .listRowBackground(standup.theme.mainColor)
        }
      }
      .toolbar {
        ToolbarItem {
          Menu {
            Button {
              viewStore.send(.addStandupButtonTapped)
            } label: {
              Image(systemName: "plus")
            }
            Button {
              viewStore.send(.oneStandupButtonTapped)
            } label: {
              Image(systemName: "1.square")
            }
            Button {
              viewStore.send(.twoStandupButtonTapped)
            } label: {
              Image(systemName: "2.square")
            }
            Button {
              viewStore.send(.threeStandupButtonTapped)
            } label: {
              Image(systemName: "3.square")
            }
            Button {
              viewStore.send(.fourStandupButtonTapped)
            } label: {
              Image(systemName: "4.square")
            }
            Button {
              viewStore.send(.fiveStandupButtonTapped)
            } label: {
              Image(systemName: "5.square")
            }
          } label: {
            Image(systemName: "line.horizontal.3")
          }
        }
      }
      .navigationTitle("Daily Standups")
      .alert(
        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
        state: /StandupsList.Destination.State.alert,
        action: StandupsList.Destination.Action.alert
      )
      .sheet(
        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
        state: /StandupsList.Destination.State.add,
        action: StandupsList.Destination.Action.add
      ) { store in
        NavigationStack {
          StandupFormView(store: store)
            .navigationTitle("New standup")
            .toolbar {
              ToolbarItem(placement: .cancellationAction) {
                Button("Dismiss") {
                  viewStore.send(.dismissAddStandupButtonTapped)
                }
              }
              ToolbarItem(placement: .confirmationAction) {
                Button("Add") {
                  viewStore.send(.confirmAddStandupButtonTapped)
                }
              }
            }
        }
      }
      .sheet(
        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
        state: /StandupsList.Destination.State.one,
        action: StandupsList.Destination.Action.one
      ) { _ in
        Text("1")
      }
//      .sheet(
//        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
//        state: /StandupsList.Destination.State.two,
//        action: StandupsList.Destination.Action.two
//      ) { _ in
//        Text("2")
//      }
//      .sheet(
//        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
//        state: /StandupsList.Destination.State.three,
//        action: StandupsList.Destination.Action.three
//      ) { _ in
//        Text("3")
//      }
//      .sheet(
//        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
//        state: /StandupsList.Destination.State.four,
//        action: StandupsList.Destination.Action.four
//      ) { _ in
//        Text("4")
//      }
//      .sheet(
//        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
//        state: /StandupsList.Destination.State.five,
//        action: StandupsList.Destination.Action.five
//      ) { _ in
//        Text("5")
//      }
    }
  }
}

Has anybody noticed this problem? Any help would be appreciated.

[Alex293]

Sometimes correct code can take too much time to compile. You can add type annotations to help the compiler, because this happens in a view builder and you want to avoir explicit types you can have the same result by splitting you view into smaller ones.
For example, you could split out the toolbar like :

private var toolbar: ToolBarItem {
ToolbarItem {
          Menu {
            Button {
              viewStore.send(.addStandupButtonTapped)
            } label: {
              Image(systemName: "plus")
            }
            Button {
              viewStore.send(.oneStandupButtonTapped)
            } label: {
              Image(systemName: "1.square")
            }
           [...]
          } label: {
            Image(systemName: "line.horizontal.3")
          }
        }
}

or

.sheet(
        store: self.store.scope(state: \.$destination, action: StandupsList.Action.destination),
        state: /StandupsList.Destination.State.add,
        action: StandupsList.Destination.Action.add,
       destination: StandupsList.Destination.View.init
)

Using private computed properties is convenient as you get access to the view properties including the store and environment easily.

Now, you will often see that you get this warning on invalid code and after splitting the compiler will be able to find the issue before it times out and show it to you.

[peramaic]

Thank you @Alex293,
the code above will compile with some of the view modifiers commented-out as shown, but unfortunately Xcode shows no other error, so I'm assuming that the code is correct.
Separating the toolbar didn't change things either.

Also assuming that my additions to PointFree's example code are not the reason for compiler problems I'll create an issue from this discussion.

[Alex293]

Then it’s simply that the compiler is taking too much time. You should split some of your view into smaller one. The toolbar was juste an example. I would factor out all child views into their one struct to ease the compiler.

[Alex293]

One other thing if you are using a swift package for you code check the you are using the latest tools version at the top. I’m unsure if the latest 5.8 improvements to the results builders are gated behind this or not but it may help.