My ideal Swift Macro version of a Solid.js-like renderer for UIKit via Swift

solid-for-uikit-v2.swift

import SwiftSignal
import FineGrainedViews

// Macro usage:
final class CounterViewController: UIViewController {
    private let count = Signal(0)

    override func viewDidLoad() {
        super.viewDidLoad()

        self.view = #FineGrainedUIView {
            UIStackView(axis: .vertical) {
                UIButton(String(count.value)) {
                    count.value += 1
                }
                .tintColor(count.value % 2 ? .systemRed : nil)
            }
        }
    }
}

// Generated extensions using a Swift package plugin transforms
// the official UIKit API into its declarative counterpart
// as non-working extensions with the goal API.
// These APIs never actually get called in compiled code.
extension UIStackView {
    init(axis: NSLayoutConstraint.Axis, @FineGrainedUIViewBuilder builder: () -> [UIView]) {
        fatalError()
    }
}

extension UIButton {
    init(_ title: String, _ action: () -> Void) {
        fatalError()
    }

    func tintColor(_ color: UIColor) -> Self {
        fatalError()
    }
}

// The macro generates:
final class CounterViewController: UIViewController {
    private let count = Signal(0)

    override func viewDidLoad() {
        super.viewDidLoad()

        self.view = {
            let button = UIButton(
                primaryAction: UIAction { [unowned self] _ in
                    self.count.value += 1
                }
            )

            let stackView = UIStackView(arrangedSubviews: [button])
            stackView.axis = .vertical

            effect {
                button.setTitle(String(count.value))
                button.tintColor = count.value % 2 ? .systemRed : nil
            }

            return stackView
        }()
    }
}

solid-for-uikit.swift

// Macro usage:
@Component
class MyComponent {
    let count = Signal(0)

    var view: UIView {
        UIStackView(axis: .vertical) {
            UIButton(String(count.get())) {
                count.update { $0 + 1 }
            }
            .tintColor(count.get() % 2 ? .systemRed : nil)
        }
    }
}

// Generated extensions using a Swift package plugin transforms
// the official UIKit API into its declarative counterpart
// as non-working extensions with the goal API.
// These APIs never actually get called in compiled code.
extension UIStackView {
    init(axis: NSLayoutConstraint.Axis, @ComponentBuilder builder: () -> [UIView]) {
        fatalError()
    }
}

extension UIButton {
    init(_ title: String, _ action: () -> Void) {
        fatalError()
    }

    func tintColor(_ color: UIColor) -> Self {
        fatalError()
    }
}

// The macro generates:
class MyComponent {
    let ref: EffectRef?
    let count = Signal(0)

    var view: UIView {
        let button = UIButton(
            primaryAction: UIAction { [unowned self] _ in
                self.count.update { $0 + 1 }
            }
        )

        let stackView = UIStackView(arrangedSubviews: [button])
        stackView.axis = .vertical

        ref = effect {
            button.setTitle(String(count.get()))
            button.tintColor = count.get() % 2 ? .systemRed : nil
        }

        return stackView
    }

    deinit() {
        ref?.destroy()
    }
}