Add async command example

Author: natecook1000

Examples/count-lines/CountLines.swift

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------*- swift -*-===//
+//
+// This source file is part of the Swift Argument Parser open source project
+//
+// Copyright (c) 2020 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
+//
+//===----------------------------------------------------------------------===//
+
+import ArgumentParser
+import Foundation
+
+struct CountLines: AsyncParsableCommand {
+    @Argument(
+        help: "A file to count lines in. If omitted, counts the lines of stdin.",
+        completion: .file(), transform: URL.init(fileURLWithPath:))
+    var inputFile: URL?
+    
+    @Option(help: "Only count lines with this prefix.")
+    var prefix: String?
+    
+    @Flag(help: "Include extra information in the output.")
+    var verbose = false
+}
+
+extension CountLines {
+    var fileHandle: FileHandle {
+        get throws {
+            guard let inputFile = inputFile else {
+                return .standardInput
+            }
+            return try FileHandle(forReadingFrom: inputFile)
+        }
+    }
+    
+    func printCount(_ count: Int) {
+        guard verbose else {
+            print(count)
+            return
+        }
+        
+        if let filename = inputFile?.lastPathComponent {
+            print("Lines in '\(filename)'", terminator: "")
+        } else {
+            print("Lines from stdin", terminator: "")
+        }
+        
+        if let prefix = prefix {
+            print(", prefixed by '\(prefix)'", terminator: "")
+        }
+        
+        print(": \(count)")
+    }
+    
+    mutating func run() async throws {
+        let countAllLines = prefix == nil
+        
+        let lineCount = try await fileHandle.bytes.lines.reduce(0) { count, line in
+            if countAllLines || line.starts(with: prefix!) {
+                return count + 1
+            } else {
+                return count
+            }
+        }
+        
+        printCount(lineCount)
+    }
+}
+
+#if swift(>=5.6)
+    @main extension CountLines {}
+#else
+    @main struct AsyncMain: AsyncMainProtocol {
+        typealias Command = CountLines
+    }
+#endif

Package.swift

@@ -47,6 +47,10 @@ let package = Package(
             name: "repeat",
             dependencies: ["ArgumentParser"],
             path: "Examples/repeat"),
+        .executableTarget(
+            name: "count-lines",
+            dependencies: ["ArgumentParser"],
+            path: "Examples/count-lines"),
 
         .executableTarget(
             name: "changelog-authors",
@@ -67,6 +71,7 @@ let package = Package(
             exclude: ["CMakeLists.txt"]),
         .testTarget(
             name: "ArgumentParserExampleTests",
-            dependencies: ["ArgumentParserTestHelpers"]),
+            dependencies: ["ArgumentParserTestHelpers"],
+            resources: [.copy("CountLinesTest.txt")]),
     ]
 )

Tests/ArgumentParserExampleTests/CountLinesExampleTests.swift

@@ -0,0 +1,41 @@
+//===----------------------------------------------------------*- swift -*-===//
+//
+// This source file is part of the Swift Argument Parser open source project
+//
+// Copyright (c) 2020 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
+//
+//===----------------------------------------------------------------------===//
+
+#if os(macOS)
+
+import XCTest
+import ArgumentParserTestHelpers
+
+final class CountLinesExampleTests: XCTestCase {
+  func testCountLines() throws {
+    let testFile = try XCTUnwrap(Bundle.module.url(forResource: "CountLinesTest", withExtension: "txt"))
+    try AssertExecuteCommand(command: "count-lines \(testFile.path)", expected: "20")
+    try AssertExecuteCommand(command: "count-lines \(testFile.path) --prefix al", expected: "4")
+  }
+  
+  func testCountLinesHelp() throws {
+    let helpText = """
+        USAGE: count-lines <input-file> [--prefix <prefix>] [--verbose]
+
+        ARGUMENTS:
+          <input-file>            A file to count lines in. If omitted, counts the
+                                  lines of stdin.
+
+        OPTIONS:
+          --prefix <prefix>       Only count lines with this prefix.
+          --verbose               Include extra information in the output.
+          -h, --help              Show help information.
+        """
+    try AssertExecuteCommand(command: "count-lines -h", expected: helpText)
+  }
+}
+
+#endif

Tests/ArgumentParserExampleTests/CountLinesTest.txt

@@ -0,0 +1,20 @@
+absinthe
+actuary
+adenoid
+affidavit
+affluent
+agnostic
+agoraphobia
+albatross
+algebra
+alkaline
+allocution
+ampule
+antimony
+argument
+artesian
+askance
+asterisk
+astonishment
+asynchronous
+axiomatic

Tests/ArgumentParserExampleTests/RepeatExampleTests.swift

@@ -10,7 +10,6 @@
 //===----------------------------------------------------------------------===//
 
 import XCTest
-import ArgumentParser
 import ArgumentParserTestHelpers
 
 final class RepeatExampleTests: XCTestCase {

Tests/ArgumentParserExampleTests/RollDiceExampleTests.swift

@@ -10,7 +10,6 @@
 //===----------------------------------------------------------------------===//
 
 import XCTest
-import ArgumentParser
 import ArgumentParserTestHelpers
 
 final class RollDiceExampleTests: XCTestCase {

Tests/ArgumentParserUnitTests/HelpGenerationTests.swift

@@ -595,7 +595,6 @@ extension HelpGenerationTests {
   }
 
   func testIssue278() {
-    print(ParserBug.helpMessage(for: ParserBug.Sub.self))
     AssertHelp(for: ParserBug.Sub.self, root: ParserBug.self, equals: """
       USAGE: parserBug sub [--example] [<argument>]