build: Add package traits for conditional module compilation

.gitignore

@@ -100,4 +100,7 @@ fastlane/test_output
 iOSInjectionProject/
 
 # Tuist
-**/Derived/*
+**/Derived/*
+
+# mcp
+.mcp_data/

Package.swift

@@ -2,6 +2,25 @@
 
 import PackageDescription
 
+let moduleDefines: [(trait: String, define: String)] = [
+    ("ecdh", "ENABLE_MODULE_ECDH"),
+    ("ellswift", "ENABLE_MODULE_ELLSWIFT"),
+    ("musig", "ENABLE_MODULE_MUSIG"),
+    ("recovery", "ENABLE_MODULE_RECOVERY"),
+    ("schnorrsig", "ENABLE_MODULE_SCHNORRSIG")
+]
+
+let zkpModuleDefines: [(trait: String, define: String)] = [
+    ("bppp", "ENABLE_MODULE_BPPP"),
+    ("ecdsaAdaptor", "ENABLE_MODULE_ECDSA_ADAPTOR"),
+    ("ecdsaS2C", "ENABLE_MODULE_ECDSA_S2C"),
+    ("generator", "ENABLE_MODULE_GENERATOR"),
+    ("rangeproof", "ENABLE_MODULE_RANGEPROOF"),
+    ("schnorrsigHalfagg", "ENABLE_MODULE_SCHNORRSIG_HALFAGG"),
+    ("surjectionproof", "ENABLE_MODULE_SURJECTIONPROOF"),
+    ("whitelist", "ENABLE_MODULE_WHITELIST")
+]
+
 let package = Package(
     name: "swift-secp256k1",
     products: [
@@ -11,6 +30,26 @@ let package = Package(
         .library(name: "P256K", targets: ["P256K"]),
         .library(name: "ZKP", targets: ["ZKP"])
     ],
+    traits: [
+        .default(enabledTraits: ["ecdh", "musig", "recovery", "schnorrsig"]),
+        .trait(name: "ecdh"),
+        .trait(name: "ellswift"),
+        .trait(name: "recovery"),
+        .trait(name: "schnorrsig"),
+        .trait(name: "musig", enabledTraits: ["schnorrsig"]),
+        .trait(name: "bppp"),
+        .trait(name: "ecdsaAdaptor"),
+        .trait(name: "ecdsaS2C"),
+        .trait(name: "generator"),
+        .trait(name: "rangeproof"),
+        .trait(name: "schnorrsigHalfagg"),
+        .trait(name: "surjectionproof"),
+        .trait(name: "whitelist"),
+        .trait(name: "zkp", enabledTraits: [
+            "bppp", "ecdsaAdaptor", "ecdsaS2C", "ellswift", "generator",
+            "rangeproof", "schnorrsigHalfagg", "surjectionproof", "whitelist"
+        ])
+    ],
     dependencies: [
         // Dependencies used for package development
         .package(url: "https://github.com/csjones/lefthook-plugin.git", exact: "2.1.2"),
@@ -32,48 +71,75 @@ let package = Package(
         .target(
             name: "P256K",
             dependencies: ["libsecp256k1"],
+            swiftSettings: PackageDescription.SwiftSetting.moduleSettings,
             plugins: ["SharedSourcesPlugin"]
         ),
         .target(
             name: "ZKP",
             dependencies: ["libsecp256k1_zkp"],
+            swiftSettings: PackageDescription.SwiftSetting.moduleSettings
+                + PackageDescription.SwiftSetting.zkpModuleSettings,
             plugins: ["SharedSourcesPlugin"]
         ),
         .target(
             name: "libsecp256k1",
             cSettings: PackageDescription.CSetting.baseSettings
+                + PackageDescription.CSetting.moduleSettings
         ),
         .target(
             name: "libsecp256k1_zkp",
-            cSettings: PackageDescription.CSetting.baseSettings + [
-                .define("ENABLE_MODULE_BPPP"),
-                .define("ENABLE_MODULE_ECDSA_ADAPTOR"),
-                .define("ENABLE_MODULE_ECDSA_S2C"),
-                .define("ENABLE_MODULE_GENERATOR"),
-                .define("ENABLE_MODULE_RANGEPROOF"),
-                .define("ENABLE_MODULE_SCHNORRSIG_HALFAGG"),
-                .define("ENABLE_MODULE_SURJECTIONPROOF"),
-                .define("ENABLE_MODULE_WHITELIST")
-            ]
+            cSettings: PackageDescription.CSetting.baseSettings
+                + PackageDescription.CSetting.moduleSettings
+                + PackageDescription.CSetting.zkpModuleSettings
+        ),
+        .testTarget(
+            name: "libsecp256k1zkpTests",
+            dependencies: ["ZKP", "libsecp256k1_zkp"],
+            swiftSettings: PackageDescription.SwiftSetting.moduleSettings
+                + PackageDescription.SwiftSetting.zkpModuleSettings
         ),
-        .testTarget(name: "libsecp256k1zkpTests", dependencies: ["ZKP", "libsecp256k1_zkp"]),
-        .testTarget(name: "ZKPTests", dependencies: ["ZKP"])
+        .testTarget(
+            name: "ZKPTests",
+            dependencies: ["ZKP"],
+            swiftSettings: PackageDescription.SwiftSetting.moduleSettings
+                + PackageDescription.SwiftSetting.zkpModuleSettings
+        )
     ],
     swiftLanguageModes: [.v6],
     cLanguageStandard: .c89
 )
 
 extension PackageDescription.CSetting {
+    /// Basic config values that are universal and require no dependencies.
     static let baseSettings: [Self] = [
-        // Basic config values that are universal and require no dependencies.
         .define("ECMULT_GEN_PREC_BITS", to: "4"),
         .define("ECMULT_WINDOW_SIZE", to: "15"),
-        // Enabling additional secp256k1 modules.
-        .define("ENABLE_MODULE_ECDH"),
-        .define("ENABLE_MODULE_ELLSWIFT"),
-        .define("ENABLE_MODULE_EXTRAKEYS"),
-        .define("ENABLE_MODULE_MUSIG"),
-        .define("ENABLE_MODULE_RECOVERY"),
-        .define("ENABLE_MODULE_SCHNORRSIG")
+        .define("ENABLE_MODULE_EXTRAKEYS")
     ]
+
+    /// Trait-conditional settings for secp256k1 modules.
+    static let moduleSettings: [Self] = moduleDefines.map {
+        .define($0.define, .when(traits: [$0.trait]))
+    }
+
+    /// Trait-conditional settings for ZKP-only modules.
+    static let zkpModuleSettings: [Self] = zkpModuleDefines.map {
+        .define($0.define, .when(traits: [$0.trait]))
+    }
+}
+
+extension PackageDescription.SwiftSetting {
+    /// Trait-conditional settings for secp256k1 modules.
+    ///
+    /// - Note: Xcode does not resolve `.when(traits:)` conditions for Swift settings,
+    ///   so Swift source files use `#if Xcode || ENABLE_MODULE_*` guards as a workaround.
+    ///   Xcode automatically defines `Xcode` in all Swift compilations.
+    static let moduleSettings: [Self] = moduleDefines.map {
+        .define($0.define, .when(traits: [$0.trait]))
+    }
+
+    /// Trait-conditional settings for ZKP-only modules.
+    static let zkpModuleSettings: [Self] = zkpModuleDefines.map {
+        .define($0.define, .when(traits: [$0.trait]))
+    }
 }

Projects/Project.swift

@@ -16,7 +16,7 @@ let project = Project(
     settings: .settings(
         configurations: [
             .debug(name: "Debug", xcconfig: "Resources/Project/Debug.xcconfig"),
-            .debug(name: "Release", xcconfig: "Resources/Project/Release.xcconfig")
+            .release(name: "Release", xcconfig: "Resources/Project/Release.xcconfig")
         ]
     ),
     targets: [
@@ -33,6 +33,7 @@ let project = Project(
             ],
             settings: .settings(
                 base: [
+                    "SWIFT_ACTIVE_COMPILATION_CONDITIONS": "$(inherited) Xcode",
                     "BUILD_LIBRARY_FOR_DISTRIBUTION": "YES",
                     "MACOSX_DEPLOYMENT_TARGET": "13.0"
                 ],
@@ -67,7 +68,10 @@ let project = Project(
             bundleId: "dev.21.BindingsTests",
             deploymentTargets: deploymentTargets,
             sources: ["Sources/BindingsTests/**"],
-            dependencies: [.package(product: "libsecp256k1")],
+            dependencies: [
+                .target(name: "P256K"),
+                .package(product: "libsecp256k1")
+            ],
             settings: .settings(
                 configurations: [
                     .debug(name: "Debug", xcconfig: "Resources/BindingsTests/Debug.xcconfig"),

README.md

@@ -58,6 +58,35 @@ Use [SPI Playgrounds app](https://swiftpackageindex.com/try-in-a-playground):
 arena 21-DOT-DEV/swift-secp256k1
 ```
 
+## Package Traits
+
+This package uses [SE-0450 Package Traits](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0450-swiftpm-package-traits.md) (Swift 6.1+) to enable fine-grained module selection. By default, the following traits are enabled: `ecdh`, `musig`, `recovery`, and `schnorrsig`.
+
+To use only specific modules, specify traits in your dependency:
+
+```swift
+.package(
+    url: "https://github.com/21-DOT-DEV/swift-secp256k1",
+    from: "0.21.1",
+    traits: ["schnorrsig"]
+),
+```
+
+To enable all ZKP modules, use the `zkp` bundle trait:
+
+```swift
+.package(
+    url: "https://github.com/21-DOT-DEV/swift-secp256k1",
+    from: "0.21.1",
+    traits: ["zkp"]
+),
+```
+
+Available traits: `ecdh`, `ellswift`, `musig`, `recovery`, `schnorrsig`, `bppp`, `ecdsaAdaptor`, `ecdsaS2C`, `generator`, `rangeproof`, `schnorrsigHalfagg`, `surjectionproof`, `whitelist`, `zkp`.
+
+> [!NOTE]
+> Xcode does not currently resolve SwiftPM package trait conditions for Swift settings. As a workaround, all optional modules are compiled when building in Xcode. Package traits are fully supported when building with `swift build` from the command line.
+
 ## Swift Versions
 
 | swift-secp256k1       | Minimum Swift Version | Minimum Xcode Version |