MVVMLint

A linter tool for data flow of MVVM architecture using SwiftSyntax.

Target architectures

Enum approach

public protocol ViewModelType {
    associatedtype Inputs
    associatedtype Outputs

    func apply(_ inputs: Inputs)
    var outputsObservable: Observable<Outputs> { get } // Observable is custom type
}

class FooViewModel: ViewModelType {
    enum Inputs {
        case viewDidLoad
        case buttonTapped(Data)
        case unusedInput // this case is defined in view model, but never used in view controller
    }

    enum Outputs {
        case reloadData
        case showError(Error)
        case unusedOutput
    }
}

class FooViewController {
    var viewModel: FooViewModel
    func viewDidLoad() {
        viewModel.apply(.viewDidLoad)
    }
    func buttonTapped() {
        viewModel.apply(.buttonTapped(data))
    }
    func bindViewModel() {
        viewModel.outputsObservable.subscribe { output in
            switch output {
            case .reloadData: break
            case .showError(let error): break
            case .set(let number): break
            }
        }
    }
}

Protocol approach

protocol FooViewModelInputs {
    func viewDidLoad()
    func buttonTapped(data: Data)
    func unusedInput() // this function is defined in view model, but never used in view controller
}
protocol FooViewModelOutputs {
    var reloadData: (() -> Void)? { get set }
    var showError: (() -> Error)? { get set }
    var unusedOutput: (() -> Void)? { get set }

    var title: String? { get }
}
protocol FooViewModelType {
    var inputs: FooViewModelInputs { get }
    var outputs: FooViewModelOutputs { get }
}
class FooViewModel: FooViewModelInputs, FooViewModelOutputs, FooViewModelType {...}

class FooViewController: FooViewModelType {
    var viewModel: FooViewModel
    func viewDidLoad() {
        view.apply(viewModel.outputs.title)

        viewModel.inputs.viewDidLoad()
    }
    func buttonTapped() {
        viewModel.inputs.buttonTapped(data)
    }
    func bindViewModel() {
        viewModel.outputs.reloadData = { _ in }
        viewModel.outputs.showError = { _ in Error() }
    }
}

Requirements

Swift 5.0+
Xcode 11.0+

How to use

Installation

Run below command

$ make install
$ mvvmlint help

Available Commands

help

Display general or command-specific help

run --paths <path,path...>

Display unused identifiers

Examples

$ mvvmlint run --paths "~/dev/"
input: viewDidLoad not called at: ~/dev/xxx.swift
output: showHUD not called at: ~/dev/zzz.swift
output: dismissHUD not called at: ~/dev/zzz.swift

TODOs

• Same identifier, but different label
• Same identifier and same type
• Combine usage

Acknowledgements

• swift-ast-explorer-playground