Creating a command line tool using the Swift Package Manager

While developing iOS applications we often find ourselves using command-line tools in Ruby.
Now let’s create a command-line tools with the Swift Package Manager.

Creating a command-line tool

Make a new directory and initialize it using Swift Package Manager

mkdir xcode-helper && cd xcode-helper
swift package init --type executable

type

• Library. Use a library product to vend library targets. This makes a target’s public APIs available to clients that integrate the Swift package.
• Executable. Use an executable product to vend an executable target. Use this only if you want to make the executable available to clients.

Build and run an executable product

command

swift run
> swift run
[3/3] Linking xcode-helper
* Build Completed!
Hello, world!

or using Xcode

swift package generate-xcodeproj
open *.xcodeproj

Adding dependencies

apple/swift-argument-parser, type-safe argument parsing for Swift.
Add the following line to the dependencies in your Package.swift file:

vi Package.swift
.package(
    url: "https://github.com/apple/swift-argument-parser", 
    from: "0.4.0"
)

Include “ArgumentParser” as a dependency for your executable target:

.product(name: "ArgumentParser", package: "swift-argument-parser"),

Package.swift Example:

// swift-tools-version:5.3
// The swift-tools-version declares the minimum version of Swift required to build this package.
import PackageDescription
let package = Package(
  name: "xcode-helper",
  dependencies: [
    .package(
      url: "https://github.com/apple/swift-argument-parser",
      from: "0.4.0"
    )
  ],
  targets: [
    .target(
      name: "xcode-helper",
      dependencies: [
        .product(name: "ArgumentParser", package: "swift-argument-parser"),
      ]),
    .testTarget(
      name: "xcode-helperTests",
      dependencies: ["xcode-helper"]),
  ]
)

Installing dependencies

swift package update

Creating the main execution command

The “main.swift” file can contain top-level code, and the order-dependent rules apply as well.
Sources/<target_name>/main.swift

vi Sources/xcode-helper/main.swift
import Foundation
import ArgumentParser
struct Constant {
  struct App {
    static let version = "0.0.1"
  }
}
@discardableResult
func shell(_ command: String) -> String {
  let task = Process()
  let pipe = Pipe()
  
  task.standardOutput = pipe
  task.standardError = pipe
  task.arguments = ["-c", command]
  task.launchPath = "/bin/zsh"
  task.launch()
  
  let data = pipe.fileHandleForReading.readDataToEndOfFile()
  let output = String(data: data, encoding: .utf8)!
  
  return output
}
struct Print {
  enum Color: String {
    case reset = "\u{001B}[0;0m"
    case black = "\u{001B}[0;30m"
    case red = "\u{001B}[0;31m"
    case green = "\u{001B}[0;32m"
    case yellow = "\u{001B}[0;33m"
    case blue = "\u{001B}[0;34m"
    case magenta = "\u{001B}[0;35m"
    case cyan = "\u{001B}[0;36m"
    case white = "\u{001B}[0;37m"
  }
  
  static func h3(_ items: Any..., separator: String = " ", terminator: String = "\n") {
    // https://stackoverflow.com/questions/39026752/swift-extending-functionality-of-print-function
    let output = items.map { "\($0)" }.joined(separator: separator)
    print("\(Color.green.rawValue)\(output)\(Color.reset.rawValue)")
  }
  
  static func h6(_ verbose: Bool, _ items: Any..., separator: String = " ", terminator: String = "\n") {
    if verbose {
      let output = items.map { "\($0)" }.joined(separator: separator)
      print("\(output)")
    }
  }
}
extension XcodeHelper {
  enum CacheFolder: String, ExpressibleByArgument, CaseIterable {
    case all
    case archives
    case simulators
    case deviceSupport
    case derivedData
    case previews
    case coreSimulatorCaches
  }
}
fileprivate extension XcodeHelper.CacheFolder {
  var paths: [String] {
    switch self {
    case .archives:
      return ["~/Library/Developer/Xcode/Archives"]
    case .simulators:
      return ["~/Library/Developer/CoreSimulator/Devices"]
    case .deviceSupport:
      return ["~/Library/Developer/Xcode"]
    case .derivedData:
      return ["~/Library/Developer/Xcode/DerivedData"]
    case .previews:
      return ["~/Library/Developer/Xcode/UserData/Previews/Simulator Devices"]
    case .coreSimulatorCaches:
      return ["~/Library/Developer/CoreSimulator/Caches/dyld"]
    case .all:
      var paths: [String] = []
      for caseValue in Self.allCases {
        if caseValue != self {
          paths.append(contentsOf: caseValue.paths)
        }
      }
      return paths
    }
  }
  
  static var suggestion: String {
    let suggestion = Self.allCases.map { caseValue in
      return caseValue.rawValue
    }.joined(separator: " | ")
    return "[ \(suggestion) ]"
  }
}
struct XcodeHelper: ParsableCommand {
  public static let configuration = CommandConfiguration(
    abstract: "Xcode helper",
    version: "xcode-helper version \(Constant.App.version)",
    subcommands: [
      Cache.self
    ]
  )
}
extension XcodeHelper {
  struct Cache: ParsableCommand {
    public static let configuration = CommandConfiguration(
      abstract: "Xcode cache helper",
      subcommands: [
        List.self
      ]
    )
  }
}
extension XcodeHelper.Cache {
  struct List: ParsableCommand {
    public static let configuration = CommandConfiguration(
      abstract: "Show Xcode cache files"
    )
    
    @Option(name: .shortAndLong, help: "The cache folder")
    private var cacheFolder: XcodeHelper.CacheFolder = .all
    
    @Flag(name: .shortAndLong, help: "Show extra logging for debugging purposes.")
    private var verbose: Bool = false
    
    func run() throws {
      Print.h3("list cache files:")
      Print.h3("------------------------")
      
      if cacheFolder == .all {
        var allCases = XcodeHelper.CacheFolder.allCases
        allCases.remove(at: allCases.firstIndex(of: .all)!)
        handleList(allCases)
      } else {
        handleList([cacheFolder])
      }
    }
    
    private func handleList(_ folders: [XcodeHelper.CacheFolder]) {
      for folder in folders {
        Print.h3(folder.rawValue)
        for path in folder.paths {
          let cmd = "du -hs \(path)"
          Print.h6(verbose, cmd)
          let output =  shell(cmd)
          print(output)
        }
      }
    }
  }
}
XcodeHelper.main()

Build and run an executable product

Get all targets

python3 -c "\
import sys, json, subprocess;\
package_data = subprocess.Popen('swift package dump-package', shell=True, stdout=subprocess.PIPE).stdout.read().decode('utf-8');\
targets = json.loads(package_data)['targets'];\
target_names = list(map(lambda x: x['name'], targets));\
print(target_names)\
"

Start using command-line, swift run <target>, example:

swift run xcode-helper

Start using subcommand, swift run <target>, example:

swift run xcode-helper cache list

Writing Unit testing

Tests/<target_name>Tests/<target_name>Tests.swift, add a standard test for the library module function.

vi Tests/xcode-helperTests/xcode_helperTests.swift
import XCTest
import class Foundation.Bundle
extension XCTest {
  public var debugURL: URL {
    let bundleURL = Bundle(for: type(of: self)).bundleURL
    return bundleURL.lastPathComponent.hasSuffix("xctest")
      ? bundleURL.deletingLastPathComponent()
      : bundleURL
  }
  
  public func AssertExecuteCommand(
    command: String,
    expected: String? = nil,
    exitCode: Int32 = EXIT_SUCCESS,
    file: StaticString = #file, line: UInt = #line) {
    let splitCommand = command.split(separator: " ")
    let arguments = splitCommand.dropFirst().map(String.init)
    
    let commandName = String(splitCommand.first!)
    let commandURL = debugURL.appendingPathComponent(commandName)
    guard (try? commandURL.checkResourceIsReachable()) ?? false else {
      XCTFail("No executable at '\(commandURL.standardizedFileURL.path)'.",
              file: (file), line: line)
      return
    }
    
    let process = Process()
    if #available(macOS 10.13, *) {
      process.executableURL = commandURL
    } else {
      process.launchPath = commandURL.path
    }
    process.arguments = arguments
    
    let output = Pipe()
    process.standardOutput = output
    let error = Pipe()
    process.standardError = error
    
    if #available(macOS 10.13, *) {
      guard (try? process.run()) != nil else {
        XCTFail("Couldn't run command process.", file: (file), line: line)
        return
      }
    } else {
      process.launch()
    }
    process.waitUntilExit()
    
    let outputData = output.fileHandleForReading.readDataToEndOfFile()
    let outputActual = String(data: outputData, encoding: .utf8)!.trimmingCharacters(in: .whitespacesAndNewlines)
    
    let errorData = error.fileHandleForReading.readDataToEndOfFile()
    let errorActual = String(data: errorData, encoding: .utf8)!.trimmingCharacters(in: .whitespacesAndNewlines)
    
    if let expected = expected {
      XCTAssertEqual(expected, errorActual + outputActual)
    }
    
    XCTAssertEqual(process.terminationStatus, exitCode, file: (file), line: line)
  }
}
final class xcode_helperTests: XCTestCase {
  func test_Xcode_Helper_Versions() throws {
    AssertExecuteCommand(command: "xcode-helper --version",
                         expected: "xcode-helper version 0.0.1")
  }
  
  func test_Xcode_Helper_Help() throws {
    let helpText = """
        OVERVIEW: Xcode helper
        
        USAGE: xcode-helper <subcommand>
        
        OPTIONS:
          --version               Show the version.
          -h, --help              Show help information.
        
        SUBCOMMANDS:
          cache                   Xcode cache helper
        
          See 'xcode-helper help <subcommand>' for detailed help.
        """
    
    AssertExecuteCommand(command: "xcode-helper", expected: helpText)
    AssertExecuteCommand(command: "xcode-helper -h", expected: helpText)
    AssertExecuteCommand(command: "xcode-helper --help", expected: helpText)
  }
}

To run the unit tests, use swift test.

swift test
> swift test
Test Suite 'All tests' started at 2021-07-17 14:01:47.357
Test Suite 'xcode-helperPackageTests.xctest' started at 2021-07-17 14:01:47.358
Test Suite 'xcode_helperTests' started at 2021-07-17 14:01:47.358
Test Case '-[xcode_helperTests.xcode_helperTests test_Xcode_Helper_Help]' started.
Test Case '-[xcode_helperTests.xcode_helperTests test_Xcode_Helper_Help]' passed (0.202 seconds).
Test Case '-[xcode_helperTests.xcode_helperTests test_Xcode_Helper_Versions]' started.
Test Case '-[xcode_helperTests.xcode_helperTests test_Xcode_Helper_Versions]' passed (0.074 seconds).
Test Suite 'xcode_helperTests' passed at 2021-07-17 14:01:47.634.
	 Executed 2 tests, with 0 failures (0 unexpected) in 0.276 (0.276) seconds
Test Suite 'xcode-helperPackageTests.xctest' passed at 2021-07-17 14:01:47.634.
	 Executed 2 tests, with 0 failures (0 unexpected) in 0.276 (0.276) seconds
Test Suite 'All tests' passed at 2021-07-17 14:01:47.634.
	 Executed 2 tests, with 0 failures (0 unexpected) in 0.276 (0.277) seconds

Tests can also be invoked with Command-U, from the Test Inspector (Command-5), or from the sub-menu under the play button in the top bar.

Installing your command line tool

Build the tool using the release configuration, and then move the compiled binary to /usr/local/bin.

swift build -c release
cp -f .build/release/xcode-helper /usr/local/bin/xcode-helper
xcode-helper --version
> xcode-helper --version
xcode-helper version 0.0.1

Demo

This is a demo that shows how you can create a command-line tools with the Swift Package Manager.

• https://github.com/QiuZhiFei/xcode-helper

References

• https://github.com/apple/swift-package-manager/blob/main/Documentation/Usage.md
• https://www.avanderlee.com/swift/command-line-tool-package-manager/
• https://www.swiftbysundell.com/articles/building-a-command-line-tool-using-the-swift-package-manager/
• https://docs.swift.org/package-manager/PackageDescription/PackageDescription.html
• https://developer.apple.com/swift/blog/?id=7
• swift-argument-parser Documentation
• https://github.com/apple/swift-package-manager/blob/4fd4df4275627ebc91a0f288c38658738cd9fa0f/Sources/Commands/SwiftPackageTool.swift