Show traits package subcommand

Sources/Commands/CMakeLists.txt

@@ -31,6 +31,7 @@ add_library(Commands
   PackageCommands/Resolve.swift
   PackageCommands/ShowDependencies.swift
   PackageCommands/ShowExecutables.swift
+  PackageCommands/ShowTraits.swift
   PackageCommands/SwiftPackageCommand.swift
   PackageCommands/ToolsVersionCommand.swift
   PackageCommands/Update.swift

Sources/Commands/PackageCommands/ShowTraits.swift

@@ -0,0 +1,87 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import ArgumentParser
+import Basics
+import CoreCommands
+import Foundation
+import PackageModel
+import PackageGraph
+import Workspace
+
+struct ShowTraits: AsyncSwiftCommand {
+    static let configuration = CommandConfiguration(
+        abstract: "List the available traits for a package.")
+
+    @OptionGroup(visibility: .hidden)
+    var globalOptions: GlobalOptions
+
+    @Option(help: "Show traits for any package id in the transitive dependencies.")
+    var packageId: String?
+
+    @Option(help: "Set the output format.")
+    var format: ShowTraitsMode = .text
+
+    func run(_ swiftCommandState: SwiftCommandState) async throws {
+        let packageGraph = try await swiftCommandState.loadPackageGraph()
+
+        let traits = if let packageId {
+            packageGraph.packages.filter({ $0.identity.description == packageId }).flatMap( { $0.manifest.traits } ).sorted(by: {$0.name < $1.name} )
+        } else {
+            packageGraph.rootPackages.flatMap( { $0.manifest.traits } ).sorted(by: {$0.name < $1.name} )
+        }
+
+        switch self.format {
+        case .text:
+            let defaultTraits = traits.filter( { $0.isDefault } ).flatMap( { $0.enabledTraits })
+
+            for trait in traits {
+                guard !trait.isDefault else {
+                    continue
+                }
+
+                print("\(trait.name)\(trait.description ?? "" != "" ? " - " + trait.description! : "")\(defaultTraits.contains(trait.name) ? " (default)" : "")")
+            }
+
+        case .json:
+            let encoder = JSONEncoder()
+            encoder.outputFormatting = .sortedKeys
+
+            let data = try encoder.encode(traits)
+            if let output = String(data: data, encoding: .utf8) {
+                print(output)
+            }
+        }
+    }
+
+    enum ShowTraitsMode: String, RawRepresentable, CustomStringConvertible, ExpressibleByArgument, CaseIterable {
+        case text, json
+
+        public init?(rawValue: String) {
+            switch rawValue.lowercased() {
+            case "text":
+                self = .text
+            case "json":
+                self = .json
+            default:
+                return nil
+            }
+        }
+
+        public var description: String {
+            switch self {
+            case .text: return "text"
+            case .json: return "json"
+            }
+        }
+    }
+}

Sources/Commands/PackageCommands/SwiftPackageCommand.swift

@@ -66,6 +66,7 @@ public struct SwiftPackageCommand: AsyncParsableCommand {
 
             ShowDependencies.self,
             ShowExecutables.self,
+            ShowTraits.self,
             ToolsVersionCommand.self,
             ComputeChecksum.self,
             ArchiveSource.self,