Merge pull request #21 from lorentey/standard-fds

Add symbolic names for standard file descriptors

Author: milseman

Sources/System/FileDescriptor.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift System open source project
 
- Copyright (c) 2020 Apple Inc. and the Swift System project authors
+ Copyright (c) 2020 - 2021 Apple Inc. and the Swift System project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -25,6 +25,21 @@ public struct FileDescriptor: RawRepresentable, Hashable, Codable {
   public init(rawValue: CInt) { self.rawValue = rawValue }
 }
 
+// Standard file descriptors
+extension FileDescriptor {
+  /// The standard input file descriptor, with a numeric value of 0.
+  @_alwaysEmitIntoClient
+  public static var standardInput: FileDescriptor { .init(rawValue: 0) }
+
+  /// The standard output file descriptor, with a numeric value of 1.
+  @_alwaysEmitIntoClient
+  public static var standardOutput: FileDescriptor { .init(rawValue: 1) }
+
+  /// The standard error file descriptor, with a numeric value of 2.
+  @_alwaysEmitIntoClient
+  public static var standardError: FileDescriptor { .init(rawValue: 2) }
+}
+
 // @available(macOS 10.16, iOS 14.0, watchOS 7.0, tvOS 14.0, *)
 extension FileDescriptor {
   /// The desired read and write access for a newly opened file.

Tests/SystemTests/FileTypesTest.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift System open source project
 
- Copyright (c) 2020 Apple Inc. and the Swift System project authors
+ Copyright (c) 2020 - 2021 Apple Inc. and the Swift System project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -12,6 +12,12 @@ import SystemPackage
 
 // @available(macOS 10.16, iOS 14.0, watchOS 7.0, tvOS 14.0, *)
 final class FileDescriptorTest: XCTestCase {
+  func testStandardDescriptors() {
+    XCTAssertEqual(FileDescriptor.standardInput.rawValue, 0)
+    XCTAssertEqual(FileDescriptor.standardOutput.rawValue, 1)
+    XCTAssertEqual(FileDescriptor.standardError.rawValue, 2)
+  }
+
   // Test the constants match the C header values. For various reasons,
   func testConstants() {
     XCTAssertEqual(O_RDONLY, FileDescriptor.AccessMode.readOnly.rawValue)