dotfiles/dots/scripts/build.swift

#!/usr/bin/env swift
import Foundation

try build()

func build() throws {
  try withVersion(in: "Sources/dots/Version.swift", as: currentVersion()) {
    try foregroundShell(
      "swift", "build",
      "--disable-sandbox",
      "--configuration", "release",
      "-Xswiftc", "-cross-module-optimization"
    )
  }
}

func withVersion(in file: String, as version: String, _ closure: () throws -> ()) throws {
  let fileURL = URL(fileURLWithPath: file)
  let originalFileContents = try String(contentsOf: fileURL, encoding: .utf8)
  // set version
  try originalFileContents
    .replacingOccurrences(of: "nil", with: "\"\(version)\"")
    .write(to: fileURL, atomically: true, encoding: .utf8)
  defer {
    // undo set version
    try! originalFileContents
      .write(to: fileURL, atomically: true, encoding: .utf8)
  }
  // run closure
  try closure()
}

func currentVersion() throws -> String {
  do {
    let tag = try backgroundShell("git", "describe", "--tags", "--exact-match")
    return tag
  } catch {
    let branch = try backgroundShell("git", "symbolic-ref", "-q", "--short", "HEAD")
    let commit = try backgroundShell("git", "rev-parse", "--short", "HEAD")
    return "\(branch) (\(commit))"
  }
}

func foregroundShell(_ args: String...) throws {
  print("$", args.joined(separator: " "))
  let task = Process()
  task.launchPath = "/usr/bin/env"
  task.arguments = args
  task.launch()
  task.waitUntilExit()
  
  guard task.terminationStatus == 0 else {
    throw ShellError(terminationStatus: task.terminationStatus)
  }
}

@discardableResult
func backgroundShell(_ args: String...) throws -> String {
  let task = Process()
  task.launchPath = "/usr/bin/env"
  task.arguments = args
  // grab stdout
  let output = Pipe()
  task.standardOutput = output
  // ignore stderr
  let error = Pipe()
  task.standardError = error
  task.launch()
  task.waitUntilExit()
  
  guard task.terminationStatus == 0 else {
    throw ShellError(terminationStatus: task.terminationStatus)
  }
  
  return String(decoding: output.fileHandleForReading.readDataToEndOfFile(), as: UTF8.self)
    .trimmingCharacters(in: .whitespacesAndNewlines)
}

struct ShellError: Swift.Error {
  var terminationStatus: Int32
}