CommandLine.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import SwiftShims

#if SWIFT_STDLIB_HAS_COMMANDLINE

@_silgen_name("_swift_stdlib_getUnsafeArgvArgc")
internal func _swift_stdlib_getUnsafeArgvArgc(_: UnsafeMutablePointer<Int32>)
  -> UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>

/// Command-line arguments for the current process.
@frozen // namespace
public enum CommandLine: ~BitwiseCopyable {}

extension CommandLine {
  /// The backing static variable for argument count may come either from the
  /// entry point or it may need to be computed e.g. if we're in the REPL.
  @usableFromInline
  internal static var _argc: Int32 = 0

  /// The backing static variable for arguments may come either from the
  /// entry point or it may need to be computed e.g. if we're in the REPL.
  ///
  /// Care must be taken to ensure that `_swift_stdlib_getUnsafeArgvArgc` is
  /// not invoked more times than is necessary (at most once).
  @usableFromInline
  internal static var _unsafeArgv:
    UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>
      = unsafe _swift_stdlib_getUnsafeArgvArgc(&_argc)

  /// Access to the raw argc value from C.
  public static var argc: Int32 {
    // We intentionally ignore the argc value given to us from
    // '_swift_stdlib_getUnsafeArgvArgc' because argv and argc are mutable, so
    // someone can mutate the contents of argv and never update the argc value.
    // This results in an out of sync argc which can lead to crashes on first
    // access to 'CommandLine.arguments' due to attempting to read '0 ..< argc'
    // strings.
    //
    // Note: It's still entirely possible that someone may update argv after
    // this iteration and before we actually read argv, but we have no control
    // over synchronizing access to argc and argv.
    var argc: Int32 = 0

    while let _ = unsafe _unsafeArgv[Int(argc)] {
      argc += 1
    }

    return argc
  }

  /// Access to the raw argv value from C.
  ///
  /// The value of this property is a `nil`-terminated C array. Including the
  /// trailing `nil`, there are ``argc`` `+ 1` elements in the array.
  ///
  /// - Note: Accessing the argument vector through this pointer is unsafe.
  ///   Where possible, use ``arguments`` instead.
  public static var unsafeArgv:
    UnsafeMutablePointer<UnsafeMutablePointer<Int8>?> {
    return unsafe _unsafeArgv
  }

  // This is extremely unsafe and allows for concurrent writes with no
  // synchronization to the underlying data. In a future version of Swift you
  // will not be able to write to 'CommandLine.arguments'.
  static nonisolated(unsafe) var _arguments: [String] = (0 ..< Int(argc)).map {
    unsafe String(cString: _unsafeArgv[$0]!)
  }

  /// An array that provides access to this program's command line arguments.
  ///
  /// Use `CommandLine.arguments` to access the command line arguments used
  /// when executing the current program. The name of the executed program is
  /// the first argument.
  ///
  /// The following example shows a command line executable that squares the
  /// integer given as an argument.
  ///
  ///     if CommandLine.arguments.count == 2,
  ///        let number = Int(CommandLine.arguments[1]) {
  ///         print("\(number) x \(number) is \(number * number)")
  ///     } else {
  ///         print(
  ///           """
  ///           Error: Please provide a number to square.
  ///           Usage: command <number>
  ///           """
  ///         )
  ///     }
  ///
  /// Running the program results in the following output:
  ///
  ///     $ command 5
  ///     5 x 5 is 25
  ///     $ command ZZZ
  ///     Error: Please provide a number to square.
  ///     Usage: command <number>
  public static var arguments: [String] {
    get {
      _arguments
    }

    @available(*, deprecated, message: "Do not modify CommandLine.arguments. It will become read-only in a future version of Swift.")
    @available(swift, obsoleted: 6.0)
    set {
      _arguments = newValue
    }
  }
}

#endif // SWIFT_STDLIB_HAS_COMMANDLINE