Properly display help message of array of enum items option

Sources/ArgumentParser/Parsable Properties/ArgumentDiscussion.swift

@@ -77,9 +77,29 @@
 ///    -h, --help           Show help information
 /// ```
 ///
-/// In any case where the argument type is not `EnumerableOptionValue`, the
-/// default implementation will use the `.staticText` case and will print a
-/// block of discussion text.
+/// Arrays of enumerable types are also supported and will display the same
+/// enumerated format:
+///
+/// ```swift
+/// @Option var colors: [Color] = [.red, .blue]
+/// ```
+///
+/// The printed usage would look like the following:
+///
+/// ```
+/// USAGE: example [--colors <colors> ...]
+///
+/// OPTIONS:
+///    --colors <colors>        (default: red, blue)
+///          red           - A red color.
+///          blue          - A blue color.
+///          yellow        - A yellow color.
+///    -h, --help           Show help information
+/// ```
+///
+/// In any case where the argument type is not `EnumerableOptionValue` or an
+/// array of `EnumerableOptionValue`, the default implementation will use the
+/// `.staticText` case and will print a block of discussion text.
 enum ArgumentDiscussion {
   case staticText(String)
   case enumerated(preamble: String? = nil, any ExpressibleByArgument.Type)

Sources/ArgumentParser/Parsable Properties/Option.swift

@@ -721,6 +721,11 @@ extension Option {
   /// var chars: [Character] = []
   /// ```
   ///
+  /// If the element type conforms to `ExpressibleByArgument` and has enumerable
+  /// value descriptions (via `defaultValueDescription`), the help output will
+  /// display each possible value with its description, similar to single
+  /// enumerable options.
+  ///
   /// - Parameters:
   ///   - wrappedValue: A default value to use for this property, provided
   ///     implicitly by the compiler during property wrapper initialization.
@@ -745,7 +750,13 @@ extension Option {
           container: Array<T>.self,
           key: key,
           kind: .name(key: key, specification: name),
-          help: help,
+          help: .init(
+            help?.abstract ?? "",
+            discussion: help?.discussion,
+            valueName: help?.valueName,
+            visibility: help?.visibility ?? .default,
+            argumentType: T.self
+          ),
           parsingStrategy: parsingStrategy.base,
           initial: wrappedValue,
           completion: completion)
@@ -765,6 +776,11 @@ extension Option {
   /// var chars: [Character]
   /// ```
   ///
+  /// If the element type conforms to `ExpressibleByArgument` and has enumerable
+  /// value descriptions (via `defaultValueDescription`), the help output will
+  /// display each possible value with its description, similar to single
+  /// enumerable options.
+  ///
   /// - Parameters:
   ///   - name: A specification for what names are allowed for this option.
   ///   - parsingStrategy: The behavior to use when parsing the elements for
@@ -784,7 +800,13 @@ extension Option {
           container: Array<T>.self,
           key: key,
           kind: .name(key: key, specification: name),
-          help: help,
+          help: .init(
+            help?.abstract ?? "",
+            discussion: help?.discussion,
+            valueName: help?.valueName,
+            visibility: help?.visibility ?? .default,
+            argumentType: T.self
+          ),
           parsingStrategy: parsingStrategy.base,
           initial: nil,
           completion: completion)

Sources/ArgumentParser/Parsing/ArgumentDefinition.swift

@@ -447,7 +447,12 @@ where Element: ExpressibleByArgument {
     guard !initial.isEmpty else { return nil }
     return initial
       .lazy
-      .map { $0.defaultValueDescription }
+      .map { element in
+        if let element = element as? (any CaseIterable & RawRepresentable) {
+          return String(describing: element.rawValue)
+        }
+        return element.defaultValueDescription
+      }
       .joined(separator: ", ")
   }
 }

Tests/ArgumentParserUnitTests/HelpGenerationTests.swift

@@ -1095,6 +1095,80 @@ extension HelpGenerationTests {
         """)
   }
 
+  struct CustomOptionAsListWithSingleDefaultValue: ParsableCommand {
+    @Option(
+      help: "An option with enumerable values.")
+    var opt: [OptionValues] = [.red]
+  }
+
+  func testEnumerableOptionAsListWithSingleDefault() {
+    AssertHelp(
+      .default,
+      for: CustomOptionAsListWithSingleDefaultValue.self,
+      columns: 100,
+      equals: """
+        USAGE: custom-option-as-list-with-single-default-value [--opt <opt> ...]
+
+        OPTIONS:
+          --opt <opt>             An option with enumerable values. (default: red)
+                blue              - The color of the sky.
+                red               - The color of a rose.
+                yellow            - The color of the sun.
+          -h, --help              Show help information.
+
+        """)
+  }
+
+  struct CustomOptionAsListWithMultipleDefaultValue: ParsableCommand {
+    @Option(
+      help: "An option with multiple enumerable values.")
+    var opt: [OptionValues] = [.red, .blue]
+  }
+
+  func testEnumerableOptionAsListWithMultipleDefault() {
+    AssertHelp(
+      .default,
+      for: CustomOptionAsListWithMultipleDefaultValue.self,
+      columns: 100,
+      equals: """
+        USAGE: custom-option-as-list-with-multiple-default-value [--opt <opt> ...]
+
+        OPTIONS:
+          --opt <opt>             An option with multiple enumerable values. (default: red, blue)
+                blue              - The color of the sky.
+                red               - The color of a rose.
+                yellow            - The color of the sun.
+          -h, --help              Show help information.
+
+        """)
+
+  }
+
+  struct CustomOptionAsListWithEmptyArrayAsDefault: ParsableCommand {
+    @Option(
+      help: "An option with default value set to empty array.")
+    var opt: [OptionValues] = []
+  }
+
+  func testEnumerableOptionAsListWithEmptyArrayAsDefault() {
+    AssertHelp(
+      .default,
+      for: CustomOptionAsListWithEmptyArrayAsDefault.self,
+      columns: 100,
+      equals: """
+        USAGE: custom-option-as-list-with-empty-array-as-default [--opt <opt> ...]
+
+        OPTIONS:
+          --opt <opt>             An option with default value set to empty array.
+                blue              - The color of the sky.
+                red               - The color of a rose.
+                yellow            - The color of the sun.
+          -h, --help              Show help information.
+
+        """)
+
+  }
+
   struct CustomOptionWithDefault: ParsableCommand {
     @Option(help: "An option with enumerable values and a custom default.")
     var opt: OptionValues = .red