Make arrays with default values use their elements' defaultValueDescription (#209)

* Make array arguments/options use their elements' defaultArgumentValue

* Add test

* Don't wrap the output in square brackets

* Change testHelpWithDefaultValues() to expect bracketless array description

Author: Wevah

Sources/ArgumentParser/Parsable Properties/Argument.swift

@@ -377,7 +377,7 @@ extension Argument {
         initial: { origin, values in
           values.set(wrappedValue, forKey: key, inputOrigin: origin)
         })
-      arg.help.defaultValue = !wrappedValue.isEmpty ? "\(wrappedValue)" : nil
+      arg.help.defaultValue = !wrappedValue.isEmpty ? wrappedValue.defaultValueDescription : nil
       return ArgumentSet(alternatives: [arg])
     })
   }

Sources/ArgumentParser/Parsable Properties/Option.swift

@@ -506,7 +506,7 @@ extension Option {
       var arg = ArgumentDefinition(kind: kind, help: help, parsingStrategy: ArgumentDefinition.ParsingStrategy(parsingStrategy), update: .appendToArray(forType: Element.self, key: key), initial: { origin, values in
         values.set(wrappedValue, forKey: key, inputOrigin: origin)
       })
-      arg.help.defaultValue = !wrappedValue.isEmpty ? "\(wrappedValue)" : nil
+      arg.help.defaultValue = !wrappedValue.isEmpty ? wrappedValue.defaultValueDescription : nil
       return ArgumentSet(alternatives: [arg])
       })
   }

Sources/ArgumentParser/Parsable Types/ExpressibleByArgument.swift

@@ -66,3 +66,9 @@ extension Float: ExpressibleByArgument {}
 extension Double: ExpressibleByArgument {}
 
 extension Bool: ExpressibleByArgument {}
+
+extension Array where Element: ExpressibleByArgument {
+  var defaultValueDescription: String {
+    return map { $0.defaultValueDescription }.joined(separator: ", ")
+  }
+}

Tests/ArgumentParserUnitTests/HelpGenerationTests.swift

@@ -174,7 +174,7 @@ extension HelpGenerationTests {
                                       Your middle name. (default: Winston)
               --age <age>             Your age. (default: 20)
               --logging <logging>     Whether logging is enabled. (default: false)
-              --lucky <numbers>       Your lucky numbers. (default: [7, 14])
+              --lucky <numbers>       Your lucky numbers. (default: 7, 14)
               --optional/--required   Vegan diet. (default: optional)
               --degree <degree>       Your degree. (default: bachelor)
               --directory <directory> Directory. (default: current directory)
@@ -401,4 +401,38 @@ extension HelpGenerationTests {
       See 'n help <subcommand>' for detailed help.
     """)
   }
+
+  enum O: String, ExpressibleByArgument {
+    case small
+    case medium
+    case large
+
+    init?(argument: String) {
+      guard let result = Self(rawValue: argument) else {
+        return nil
+      }
+      self = result
+    }
+  }
+  struct P: ParsableArguments {
+    @Option(name: [.short], help: "Help Message")
+    var o: [O] = [.small, .medium]
+
+    @Argument(help: "Help Message")
+    var remainder: [O] = [.large]
+  }
+
+  func testHelpWithDefaultValueForArray() {
+    AssertHelp(for: P.self, equals: """
+    USAGE: p [-o <o> ...] [<remainder> ...]
+
+    ARGUMENTS:
+      <remainder>             Help Message (default: large)
+
+    OPTIONS:
+      -o <o>                  Help Message (default: small, medium)
+      -h, --help              Show help information.
+
+    """)
+  }
 }