Change ArgumentVisibility into a struct (#413)

- Changes ArgumentVisibility from an enum to a struct. This will allow
  ArgumentParser to add cases in the future without breaking clients
  that could have been exhaustively switching across all cases. It also
  allows us to implement protocol conformances on the internal type and
  avoid exposing them on the public type.

Author: rauhul

Sources/ArgumentParser/Completions/BashCompletionsGenerator.swift

@@ -180,7 +180,7 @@ struct BashCompletionsGenerator {
 extension ArgumentDefinition {
   /// Returns the different completion names for this argument.
   fileprivate func bashCompletionWords() -> [String] {
-    return help.visibility == .default
+    return help.visibility.base == .default
       ? names.map { $0.synopsisString }
       : []
   }

Sources/ArgumentParser/Completions/FishCompletionsGenerator.swift

@@ -100,7 +100,7 @@ extension Name {
 
 extension ArgumentDefinition {
   fileprivate func argumentSegments(_ commandChain: [String]) -> [([String], String)] {
-    guard help.visibility == .default else { return [] }
+    guard help.visibility.base == .default else { return [] }
 
     var results = [([String], String)]()
     var formattedFlags = [String]()

Sources/ArgumentParser/Completions/ZshCompletionsGenerator.swift

@@ -134,7 +134,7 @@ extension ArgumentDefinition {
   }
 
   func zshCompletionString(_ commands: [ParsableCommand.Type]) -> String? {
-    guard help.visibility == .default else { return nil }
+    guard help.visibility.base == .default else { return nil }
 
     var inputs: String
     switch update {

Sources/ArgumentParser/Parsable Properties/ArgumentHelp.swift

@@ -33,7 +33,7 @@ public struct ArgumentHelp {
   @available(*, deprecated, message: "Use visibility level instead.")
   public var shouldDisplay: Bool {
     get {
-      return visibility == .default
+      return visibility.base == .default
     }
     set {
       visibility = newValue ? .default : .hidden

Sources/ArgumentParser/Parsable Properties/ArgumentVisibility.swift

@@ -10,25 +10,35 @@
 //===----------------------------------------------------------------------===//
 
 /// Visibility level of an argument's help.
-public enum ArgumentVisibility {
-    /// Show help for this argument whenever appropriate.
+public struct ArgumentVisibility {
+  /// Internal implementation of `ArgumentVisibility` to allow for easier API
+  /// evolution.
+  internal enum Representation {
     case `default`
-
-    /// Only show help for this argument in the extended help screen.
     case hidden
-
-    /// Never show help for this argument.
     case `private`
+  }
+
+  internal var base: Representation
+
+  /// Show help for this argument whenever appropriate.
+  public static let `default` = Self(base: .default)
+
+  /// Only show help for this argument in the extended help screen.
+  public static let hidden = Self(base: .hidden)
+
+  /// Never show help for this argument.
+  public static let `private` = Self(base: .private)
 }
 
-extension ArgumentVisibility {
+extension ArgumentVisibility.Representation {
   /// A raw Integer value that represents each visibility level.
   ///
   /// `_comparableLevel` can be used to test if a Visibility case is more or
   /// less visible than another, without committing this behavior to API.
   /// A lower `_comparableLevel` indicates that the case is less visible (more
   /// secret).
-  private var _comparableLevel: Int {
+  internal var _comparableLevel: Int {
     switch self {
     case .default:
       return 2
@@ -38,9 +48,11 @@ extension ArgumentVisibility {
       return 0
     }
   }
+}
 
+extension ArgumentVisibility {
   /// - Returns: true if `self` is at least as visible as the supplied argument.
-  func isAtLeastAsVisible(as other: Self) -> Bool {
-    self._comparableLevel >= other._comparableLevel
+  internal func isAtLeastAsVisible(as other: Self) -> Bool {
+    self.base._comparableLevel >= other.base._comparableLevel
   }
 }

Sources/ArgumentParser/Parsable Types/ParsableArguments.swift

@@ -286,7 +286,7 @@ extension ArgumentSet {
 
         if let parsed = child.value as? ArgumentSetProvider {
           guard parsed._visibility.isAtLeastAsVisible(as: visibility)
-          else { return nil }
+            else { return nil }
 
           // Property wrappers have underscore-prefixed names
           codingKey = String(codingKey.first == "_"

Sources/ArgumentParser/Usage/DumpHelpGenerator.swift

@@ -125,7 +125,7 @@ fileprivate extension ArgumentInfoV0 {
     guard let kind = ArgumentInfoV0.KindV0(argument: argument) else { return nil }
     self.init(
       kind: kind,
-      shouldDisplay: argument.help.visibility == .default,
+      shouldDisplay: argument.help.visibility.base == .default,
       isOptional: argument.help.options.contains(.isOptional),
       isRepeating: argument.help.options.contains(.isRepeating),
       names: argument.names.map(ArgumentInfoV0.NameInfoV0.init),

Sources/ArgumentParser/Usage/HelpGenerator.swift

@@ -140,7 +140,7 @@ internal struct HelpGenerator {
     /// more elements at a time.
     var args = commandStack.argumentsForHelp(visibility: visibility)[...]
     while let arg = args.popFirst() {
-      guard arg.help.visibility == .default else { continue }
+      guard arg.help.visibility.base == .default else { continue }
 
       let synopsis: String
       let description: String
@@ -154,7 +154,7 @@ internal struct HelpGenerator {
 
         synopsis = groupedArgs
           .lazy
-          .filter { $0.help.visibility == .default }
+          .filter { $0.help.visibility.base == .default }
           .map { $0.synopsisForHelp }
           .joined(separator: "/")
 
@@ -172,7 +172,7 @@ internal struct HelpGenerator {
           .filter { !$0.isEmpty }
           .joined(separator: " ")
       } else {
-        synopsis = arg.help.visibility == .default
+        synopsis = arg.help.visibility.base == .default
           ? arg.synopsisForHelp
           : ""
 
@@ -275,10 +275,10 @@ fileprivate extension NameSpecification {
     self
       .makeNames(InputKey(rawValue: "help"))
       .compactMap { name in
-        guard visibility != .default else { return name }
+        guard visibility.base != .default else { return name }
         switch name {
         case .long(let helpName):
-          return .long("\(helpName)-\(visibility)")
+          return .long("\(helpName)-\(visibility.base)")
         case .longWithSingleDash(let helpName):
           return .longWithSingleDash("\(helpName)-\(visibility)")
         case .short:

Sources/ArgumentParser/Usage/UsageGenerator.swift

@@ -40,7 +40,7 @@ extension UsageGenerator {
   var synopsis: String {
     // Filter out options that should not be displayed.
     var options = definition
-      .filter { $0.help.visibility == .default }
+      .filter { $0.help.visibility.base == .default }
     switch options.count {
     case 0:
       return toolName
@@ -346,7 +346,7 @@ extension ErrorMessageGenerator {
   func noValueMessage(key: InputKey) -> String? {
     let args = arguments(for: key)
     let possibilities: [String] = args.compactMap {
-      $0.help.visibility == .default
+      $0.help.visibility.base == .default
         ? $0.nonOptional.synopsis
         : nil
     }

Sources/ArgumentParserTestHelpers/TestHelpers.swift

@@ -122,7 +122,7 @@ public func AssertHelp<T: ParsableArguments>(
   let flag: String
   let includeHidden: Bool
 
-  switch visibility {
+  switch visibility.base {
   case .default:
     flag = "--help"
     includeHidden = false
@@ -158,7 +158,7 @@ public func AssertHelp<T: ParsableCommand, U: ParsableCommand>(
 ) {
   let includeHidden: Bool
 
-  switch visibility {
+  switch visibility.base {
   case .default:
     includeHidden = false
   case .hidden: