I'm seeing this error, "Unnamed argument #2 must precede argument 'destination'" on the NavigationLink instantiation. I've checked the documentation and indeed there isn't one where destination is the starting parameter. I did try adding a first parameter of a title, and that ends up showing a different error. Have I missed something in my ContentView code or does anyone else see something else that's going on? Thank you for your help.

struct ContentView: View {
    @Environment(\.managedObjectContext) var moc
    @FetchRequest(entity: Book.entity(), sortDescriptors: [
        NSSortDescriptor(keyPath: \Book.title, ascending: true),
        NSSortDescriptor(keyPath: \Book.author, ascending: true)
    ]) var books: FetchedResults<Book>

    @State private var showingAddScreen = false

    var body: some View {
        NavigationView {
            List {
                ForEach(books, id: \.self) { book in
                    NavigationLink(destination: DetailView(book: book)) {
                        EmojiRatingView(rating: book.rating)
                            .font(.largeTitle)

                        VStack(alignment: .leading) {
                            Text(bool.title ?? "Unknown title")
                                .font(.headline)
                            Text(book.author ?? "Unknown author")
                                .foregroundColor(.secondary)
                        }
                    }
                }
                .onDelete(perform: deleteBooks)
            }
            .navigationBarTitle("Bookworm")
            .navigationBarItems(leading: EditButton(), trailing:
                                    Button(action: {
                                        self.showingAddScreen.toggle()
                                    }) {
                                        Image(systemName: "plus")
                                    }
            )
            .sheet(isPresented: $showingAddScreen) {
                AddBookView().environment(\.managedObjectContext, self.moc)
            }
        }
    }

    func deleteBooks(at offsets: IndexSet) {
        for offset in offsets {
            let book = books[offset]
            moc.delete(book)
        }

        try? moc.save()
    }
}

Got it. It's working now. Thank you.