HierarchyList.swift

// https://gist.github.com/zntfdr/9d94cac84235f04f021cb6c7e8c1a1c5

// Original article here: https://www.fivestars.blog/code/swiftui-hierarchy-list.html

import SwiftUI

struct FileItem: Identifiable {
    var name: String
    var children: [FileItem]?

    let id = UUID()

    static let spmData: [FileItem] = [
        FileItem(name: ".gitignore"),
        FileItem(name: "Package.swift"),
        FileItem(name: "README.md"),
        FileItem(name: "Sources", children: [
            FileItem(name: "fivestars", children: [
                FileItem(name: "main.swift")
            ]),
        ]),
        FileItem(name: "Tests", children: [
            FileItem(name: "fivestarsTests", children: [
                FileItem(name: "fivestarsTests.swift"),
                FileItem(name: "XCTestManifests.swift"),
            ]),
            FileItem(name: "LinuxMain.swift")
        ])
    ]
}

// Compiler bug crash the compiler as of Xcode Version 13.0 beta 4 (13A5201i)
// see https://bugs.swift.org/browse/SR-15033
//    public init(@Binding data: Data, children: KeyPath<Binding<Data.Element>, Binding<Data?>>, rowContent: @escaping (Binding<Data.Element>) -> RowContent) {
//
//        recursiveView = RecursiveView(data: $data, children: children, rowContent: rowContent)
// }

public struct HierarchyList<Data, RowContent>: View where Data: MutableCollection, Data: RandomAccessCollection, Data.Index: Hashable, Data.Element: Identifiable, RowContent: View {
    private let recursiveView: RecursiveView<Data, RowContent>

    /// Make an editable HierarchyList
    ///
    /// - Parameters:
    ///   - data: A Binding to collection of data item
    ///   - children: the KeyPath to the optional children array
    ///   - rowContent: A closure View to display the row, its parameter is a binding to recursive data item
    public init(_ data: Binding<Data>, children: KeyPath<Binding<Data.Element>, Binding<Data?>>, rowContent: @escaping (Binding<Data.Element>) -> RowContent) {
        recursiveView = RecursiveView(data: data, children: children, rowContent: rowContent)
    }

    public var body: some View {
        List {
            recursiveView
        }
    }
}


// 🤢😕 👇👇
// this version uses ForEach w/ SE-0293 @Binding closure parameter.
// this version is preferred but doesn't compile as of Xcode Version 13.0 beta 4 (13A5201i)
// Compiles in Xcode Version 13.0 beta 5 (13A5212g) (beta 5)
private struct RecursiveView<Data, RowContent>: View where Data: MutableCollection, Data: RandomAccessCollection, Data.Index: Hashable, Data.Element: Identifiable, RowContent: View {
    @Binding var data: Data
    let children: KeyPath<Binding<Data.Element>, Binding<Data?>>
    let rowContent: (Binding<Data.Element>) -> RowContent

    var body: some View {
        // https://forums.swift.org/t/xcode-abort-trap-6-and-non-sensical-compile-error-maybe-related-to-se-0293/50907/2
        // Use SE-0293 @Binding property wrapper closure parameter:
        // this compiler bug is fixed: https://github.com/apple/swift/pull/38480
        ForEach($data) { $item in       // 🐞🐞 compile error: Cannot convert value of type 'Binding<Data>.Element' (aka 'Binding<Data.Element>') to expected argument type 'Binding<Data.Element>'
            if let unwrappedBindingToChildren = Binding($item[keyPath: children]) {
                DisclosureGroup(content: {
                    RecursiveView(data: unwrappedBindingToChildren, children: children, rowContent: rowContent)
                }, label: {
                    rowContent($item)
                })
            } else {
                rowContent($item)
            }
        }
    }
}


// the above do not compile, so use ForEach(.indices, ...) instead for now
//private struct RecursiveView<Data, RowContent>: View where Data: MutableCollection, Data: RandomAccessCollection, Data.Index: Hashable, Data.Element: Identifiable, RowContent: View {
//    @Binding var data: Data
//    let children: KeyPath<Binding<Data.Element>, Binding<Data?>>
//    let rowContent: (Binding<Data.Element>) -> RowContent
//
//    var body: some View {
//        ForEach(data.indices, id: \.self) { index in
//            if let unwrappedBindingToChildren = Binding($data[index][keyPath: children]) {
//                DisclosureGroup(content: {
//                    RecursiveView(data: unwrappedBindingToChildren, children: children, rowContent: rowContent)
//                }, label: {
//                    rowContent($data[index])
//                })
//            } else {
//                rowContent($data[index])
//            }
//        }
//    }
//}


struct HierarchyListDemo: View {
    @State private var data = FileItem.spmData

    var body: some View {
        // rowContent closure receive a binding to data item, enabling mutate on the item
        HierarchyList($data, children: \.children, rowContent: { $item in TextField("Edit", text: $item.name) })
    }
}


struct HierarchyList_Previews: PreviewProvider {
    static var previews: some View {
        HierarchyListDemo()
    }
}