为什么我不能使用SwiftPM作为依赖关系使用Swift软件包管理器？

Question

我有以下Package.swift：

// swift-tools-version:5.2
import PackageDescription

let package = Package(
    name: "my-vapor-project",
    platforms: [
       .macOS(.v10_15)
    ],
    dependencies: [
        //  A server-side Swift web framework.
        .package(url: "https://github.com/vapor/vapor.git", from: "4.0.0-rc"),
        .package(url: "https://github.com/vapor/fluent.git", from: "4.0.0-rc"),
        .package(url: "https://github.com/vapor/fluent-mysql-driver.git", from: "4.0.0-rc"),
        .package(url: "https://github.com/apple/swift-package-manager", .branch("master")),
    ],
    targets: [
        .target(name: "App", dependencies: [
            .product(name: "Fluent", package: "fluent"),
            .product(name: "FluentMySQLDriver", package: "fluent-mysql-driver"),
            .product(name: "Vapor", package: "vapor"),
            .product(name: "SwiftPM", package: "swift-package-manager")
        ]),
        .target(name: "Run", dependencies: ["App"]),
        .testTarget(name: "AppTests", dependencies: [
            .target(name: "App"),
            .product(name: "XCTVapor", package: "vapor"),
        ])
    ]
)

当我保存文件时，Xcode尝试自动解析依赖项，并得到以下错误和警告：

在“快速包管理器”中显示/Users/sluther/Projects/my-vapor-project/Package.swift:产品依赖“SwiftPM”的所有消息的

未找到

：依赖项“SwiftPM”不被任何目标使用

Answer 1

在编写本报告时，在使用SWIFTToolsVersion5.2时无法作为依赖项包括在内，该版本删除了用于定义产品依赖项的旧语法。将Swift工具版本切换到5.1解决了这个问题。

// swift-tools-version:5.1
import PackageDescription

let package = Package(
    name: "my-vapor-project",
    platforms: [
       .macOS(.v10_15)
    ],
    dependencies: [
        //  A server-side Swift web framework.
        .package(url: "https://github.com/vapor/vapor.git", from: "4.0.0-rc"),
        .package(url: "https://github.com/vapor/fluent.git", from: "4.0.0-rc"),
        .package(url: "https://github.com/vapor/fluent-mysql-driver.git", from: "4.0.0-rc"),
        .package(url: "https://github.com/apple/swift-package-manager", .branch("master")),
    ],
    targets: [
        .target(name: "App", dependencies: [
            .product(name: "Fluent", package: "fluent"),
            .product(name: "FluentMySQLDriver", package: "fluent-mysql-driver"),
            .product(name: "Vapor", package: "vapor"),
            "SwiftPM"
        ]),
        .target(name: "Run", dependencies: ["App"]),
        .testTarget(name: "AppTests", dependencies: [
            .target(name: "App"),
            .product(name: "XCTVapor", package: "vapor"),
        ])
    ]
)