README.md

What?

This gist demonstrates a bug in SwiftUI.List animated updates when quickly applying changes. Run the gist and then tap "Move" and "Back" in quick succession. The list will be put into strange states where section titles show in rows and row titles show in section headers.

ListAnimations.swift

import SwiftUI

struct ListAnimationsView: View {
    struct Item: Identifiable {
        var name: String
        var id: String { name }
        
        static var currentID = 0
        static func new() -> Item {
            currentID += 1
            return .init(name: "Row \(currentID)")
        }
    }
    
    struct Section: Identifiable {
        var name: String
        var items: [Item]
        
        var id: String {
            name
        }
    }
    
    @State var sections: [Section] = [
        Section(name: "Section 1", items: [.new(), .new()]),
        Section(name: "Section 2", items: [.new(), .new()]),
    ]
    
    var body: some View {
        NavigationView {
            VStack {
                HStack {
                    Button(action: {
                        sections[0].items.append(Item.new())
                    }, label: {
                        Text("Add S1")
                    })
                    Button(action: {
                        guard !sections[0].items.isEmpty else { return }
                        sections[1].items.append(sections[0].items.removeLast())
                    }, label: {
                        Text("Move")
                    })
                    Button(action: {
                        guard !sections[1].items.isEmpty else { return }
                        sections[0].items.append(sections[1].items.removeLast())
                    }, label: {
                        Text("Back")
                    })
                }
                List {
                    ForEach(sections, id: \.id) { section in
                        SwiftUI.Section(header: Text(section.name)) {
                            ForEach(section.items, id: \.id) { item in
                                Text(item.name)
                            }
                            .onDelete(perform: { indexSet in
                                delete(sectionID: section.id, indexSet: indexSet)
                            })
                        }
                        .id(section.id)
                    }
                }
                .listStyle(GroupedListStyle())
                .animation(.default)
            }
        }
        .navigationBarItems(trailing: trailingNavItems)
    }
    
    var trailingNavItems: some View {
        HStack {
            Button(action: {}, label: {
                Image(systemName: "note.text")
            })
            Spacer(minLength: 20)
            Button(action: {}, label: {
                Image(systemName: "folder.fill")
            })
        }
    }
    
    func delete(sectionID: String, indexSet: IndexSet) {
        guard
            let sectionIndex = sections.firstIndex(where: { $0.id == sectionID })
        else {
            return
        }
        sections[sectionIndex].items.remove(atOffsets: indexSet)
    }
}

struct ListAnimationsView_Previews: PreviewProvider {
    static var previews: some View {
        ListAnimationsView()
    }
}