Add Macro for Passing Down OptionGroups

Package.swift

@@ -17,6 +17,7 @@
 
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
+import CompilerPluginSupport
 import Foundation
 import PackageDescription
 
@@ -55,6 +56,7 @@ let package = Package(
         .package(url: "https://github.com/orlandos-nl/DNSClient.git", from: "2.4.1"),
         .package(url: "https://github.com/Bouke/DNS.git", from: "1.2.0"),
         .package(url: "https://github.com/apple/containerization.git", exact: Version(stringLiteral: scVersion)),
+        .package(url: "https://github.com/swiftlang/swift-syntax.git", from: "602.0.0"),
     ],
     targets: [
         .executableTarget(
@@ -259,6 +261,7 @@ let package = Package(
                 "ContainerPlugin",
                 "ContainerXPC",
                 "TerminalProgress",
+                "HelperMacros",
             ]
         ),
         .testTarget(
@@ -373,5 +376,18 @@ let package = Package(
                 .define("BUILDER_SHIM_VERSION", to: "\"\(builderShimVersion)\""),
             ]
         ),
+        .macro(
+            name: "HelperMacrosMacros",
+            dependencies: [
+                .product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
+                .product(name: "SwiftCompilerPlugin", package: "swift-syntax"),
+            ]
+        ),
+
+        // Library that exposes a macro as part of its API, which is used in client programs.
+        .target(
+            name: "HelperMacros",
+            dependencies: ["HelperMacrosMacros"]
+        ),
     ]
 )

Sources/ContainerClient/Flags.swift

@@ -17,15 +17,18 @@
 import ArgumentParser
 import ContainerizationError
 import Foundation
+import HelperMacros
 
 public struct Flags {
+    @OptionGroupPassthrough
     public struct Global: ParsableArguments {
         public init() {}
 
         @Flag(name: .long, help: "Enable debug output [environment: CONTAINER_DEBUG]")
         public var debug = false
     }
 
+    @OptionGroupPassthrough
     public struct Process: ParsableArguments {
         public init() {}
 
@@ -63,6 +66,7 @@ public struct Flags {
         public var cwd: String?
     }
 
+    @OptionGroupPassthrough
     public struct Resource: ParsableArguments {
         public init() {}
 
@@ -76,6 +80,7 @@ public struct Flags {
         public var memory: String?
     }
 
+    @OptionGroupPassthrough
     public struct Registry: ParsableArguments {
         public init() {}
 
@@ -87,6 +92,7 @@ public struct Flags {
         public var scheme: String = "auto"
     }
 
+    @OptionGroupPassthrough
     public struct Management: ParsableArguments {
         public init() {}
 
@@ -201,6 +207,7 @@ public struct Flags {
         public var virtualization: Bool = false
     }
 
+    @OptionGroupPassthrough
     public struct Progress: ParsableArguments {
         public init() {}
 

Sources/HelperMacros/HelperMacros.swift

@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+//
+//  HelperMacros.swift
+//  container
+//
+//  Created by Morris Richman on 10/3/25.
+//
+
+import Foundation
+
+/// Creates a function in OptionGroups called `passThroughCommands` to return an array of strings to be appended and passed down for Plugin support.
+@attached(member, names: named(passThroughCommands))
+public macro OptionGroupPassthrough() = #externalMacro(module: "HelperMacrosMacros", type: "OptionGroupPassthrough")

Sources/HelperMacrosMacros/HelperMacrosMacros.swift

@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+//
+//  HelperMacrosMacros.swift
+//  container
+//
+//  Created by Morris Richman on 10/3/25.
+//
+
+import SwiftCompilerPlugin
+import SwiftDiagnostics
+import SwiftSyntaxMacros
+
+@main
+struct SwiftMacrosAndMePlugin: CompilerPlugin {
+    let providingMacros: [Macro.Type] = [
+        OptionGroupPassthrough.self
+    ]
+}
+
+extension String: @retroactive Error {
+}
+
+enum MacroExpansionError: Error {
+    case unsupportedDeclaration
+
+    var localizedDescription: String {
+        switch self {
+        case .unsupportedDeclaration:
+            return "Unsupported declaration for macro expansion."
+        }
+    }
+}