[SR-14764] @MainActor ignored by the compiler #57114

import SwiftUI

class Model: ObservableObject {
  @Published
  var data: Data?
}

struct TestView: View {
  @ObservedObject
  var _model = Model()

  @MainActor
  func apply(_ data: Data) {
    // runtime warning:
    // Publishing changes from background threads is not allowed; make
    // sure to publish values from the main thread (via operators like
    // receive(on:)) on model updates.

    _model.data = data

    // runtime crash
    dispatchPrecondition(condition: .onQueue(.main))
  }

  func fetchData() async throws {
    let urlString = "https://google.com"
    guard case let url? = URL(string: urlString) else {
      return
    }
    let (data, response) = try await URLSession.shared.data(from: url)
    guard
      case let httpResponse? = response as? HTTPURLResponse,
      httpResponse.statusCode == 200
    else {
      return
    }

    // note there is NO `await` here as the compiler does not ask for it at all
    apply(data)
  }

  var body: some View {
    Text("\(_model.data.map(\.count) ?? 0)")
      .task {
        do {
          try await fetchData()
        } catch {
          print(error)
        }
      }
  }
}