Fix handling of visibility with nested OptionGroups.

The visibility of OptionGroups is ignored if they are nested inside another
OptionGroup. Instead of trying to filter groups when creating an ArgumentSet,
use the OptionGroup's visibility to modify the arguments within the group.

Author: bob-wilson

Sources/ArgumentParser/Parsable Properties/ArgumentVisibility.swift

@@ -57,4 +57,28 @@ extension ArgumentVisibility {
   internal func isAtLeastAsVisible(as other: Self) -> Bool {
     self.base._comparableLevel >= other.base._comparableLevel
   }
+
+  /// Reduce the visibility to a specified level if it is more restricted than the current value.
+  internal mutating func reduce(to: ArgumentVisibility) {
+    switch to.base {
+    case .default:
+      break  // No effect
+    case .hidden:
+      if case .default = self.base {
+        self.base = .hidden
+      }
+    case .private:
+      self.base = .private
+    }
+  }
+}
+
+extension ArgumentDefinition {
+  internal func reducingHelpVisibility(to visibility: ArgumentVisibility)
+    -> Self
+  {
+    var result = self
+    result.help.visibility.reduce(to: visibility)
+    return result
+  }
 }

Sources/ArgumentParser/Parsable Properties/OptionGroup.swift

@@ -88,6 +88,9 @@ public struct OptionGroup<Value: ParsableArguments>: Decodable, ParsedWrapper {
             $0.help.parentTitle = title
           }
         }
+        args.content = args.content.map { arg in
+          arg.reducingHelpVisibility(to: visibility)
+        }
         return args
       })
     self._visibility = visibility

Sources/ArgumentParser/Parsable Types/ParsableArguments.swift

@@ -316,9 +316,6 @@ extension ArgumentSet {
         guard let codingKey = child.label else { return nil }
 
         if let parsed = child.value as? ArgumentSetProvider {
-          guard parsed._visibility.isAtLeastAsVisible(as: visibility)
-          else { return nil }
-
           let key = InputKey(name: codingKey, parent: parent)
           return parsed.argumentSet(for: key)
         } else {

Tests/ArgumentParserUnitTests/HelpGenerationTests+GroupName.swift

@@ -233,6 +233,43 @@ extension HelpGenerationTests {
         """)
   }
 
+  fileprivate struct NestedGroups: ParsableArguments {
+    @OptionGroup(visibility: .hidden)
+    var flagsAndOptions: FlagsAndOptions
+
+    @OptionGroup(visibility: .private)
+    var argsAndFlags: ArgsAndFlags
+  }
+
+  fileprivate struct NestedHiddenGroups: ParsableCommand {
+    @OptionGroup()
+    var nested: NestedGroups
+  }
+
+  func testNestedHiddenGroups() {
+    AssertHelp(
+      .default, for: NestedHiddenGroups.self,
+      equals: """
+        USAGE: nested-hidden-groups
+
+        OPTIONS:
+          -h, --help              Show help information.
+
+        """)
+
+    AssertHelp(
+      .hidden, for: NestedHiddenGroups.self,
+      equals: """
+        USAGE: nested-hidden-groups [--experimental] --prefix <prefix>
+
+        OPTIONS:
+          --experimental          example
+          --prefix <prefix>       example
+          -h, --help              Show help information.
+
+        """)
+  }
+
   fileprivate struct ParentWithGroups: ParsableCommand {
     static var configuration: CommandConfiguration {
       .init(subcommands: [ChildWithGroups.self])