Swift `UpcomingFeature` enum

UpcomingFeature.swift

// Please feel free to add this gist to your own `Package.swift` file to enable quick type-safe Swift language feature flagging.

extension SwiftSetting {
    /// Feature Flag Strings
    ///
    /// Found at https://www.swift.org/migration/documentation/swift-6-concurrency-migration-guide/sourcecompatibility/
    /// Please update this list as new feature flags are added.
    enum UpcomingFeature: String {
        /// SE-0418: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0418-inferring-sendable-for-methods.md
        case inferringSendableFromCapture = "InferSendableFromCaptures"
        /// SE-0423: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0423-dynamic-actor-isolation.md
        case dynamicActorIsolation = "DynamicActorIsolation"
        /// SE-0434: https://github.com/swiftlang/swift-evolution/blob/main/proposals/0434-global-actor-isolated-types-usability.md
        case globalActorIsolatedTypesUsability = "GlobalActorIsolatedTypesUsability"
    }
    
    /// Enable an upcoming feature flag, using a static type.
    ///
    /// - Parameters:
    ///  - upcomingFeature: The feature flag to enable.
    ///  - condition: The condition under which the feature flag should be enabled.
    ///             If `nil`, the feature flag will always be enabled.
    /// ## Usage
    /// ```swift
    /// let package = Package(
    ///     name: "MyLibrary",
    ///     products: [
    ///         .library(
    ///             name: "MyLibrary",
    ///             targets: ["MyLibrary"]),
    ///     ],
    ///     targets: [
    ///         .target(
    ///             name: "MyLibrary",
    ///             swiftSettings: [
    ///                 .enableUpcomingFeature(.globalActorIsolatedTypesUsability)
    ///             ]
    ///         ),
    ///
    ///     ],
    ///     swiftLanguageVersions: [
    ///         .v5
    ///     ]
    /// )
    /// ```
    static func enableUpcomingFeature(_ upcomingFeature: UpcomingFeature, condition: BuildSettingCondition? = nil) -> SwiftSetting {
        enableUpcomingFeature(upcomingFeature.rawValue, condition)
    }
        
}