Explicitly set the Swift language mode on package init

[rconnell9]

Explicitly set the Swift language mode on package init

Motivation:

When a package is created using swift package init no language mode is specified and defaults to using Swift 5.

New packages should be written in Swift 6, so explicitly set the language mode to 6 on package init.

Modifications:

Include a language mode on package init

Result:

New packages created using swift package init will include the following by default: swiftLanguageModes: [.v6]

let package = Package(
    name: "tmp",
    products: [
        // Products define the executables and libraries a package produces, making them visible to other packages.
        .library(
            name: "tmp",
            targets: ["tmp"]
        ),
    ],
    targets: [
        // Targets are the basic building blocks of a package, defining a module or a test suite.
        // Targets can depend on other targets in this package and products from dependencies.
        .target(
            name: "tmp"
        ),
        .testTarget(
            name: "tmpTests",
            dependencies: ["tmp"]
        ),
    ],
    swiftLanguageModes: [.v6]
)

[rconnell9]

@swift-ci test

[rconnell9]

@swift-ci test linux