configure.swift

import Vapor

public func configure(_ app: Application) throws {
    // register routes
    try routes(app)
}

Dependencies.swift

// swift-tools-version:5.5
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "App",
    products: [
        // ...
    ],
    dependencies: [
        // Dependencies declare other packages that this package depends on.
        // .package(url: /* package url */, from: "1.0.0"),
        .package(url: "https://github.com/vapor/vapor.git", from: "4.0.0"),
    ],
    targets: [
        // ...
    ]
)

main.swift

import App
import Vapor

var env = try Environment.detect()
try LoggingSystem.bootstrap(from: &env)
let app = Application(env)
defer { app.shutdown() }
try configure(app)
try app.run()

Package.swift

// swift-tools-version:5.5
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "App",
    products: [
        // Products define the executables and libraries a package produces, and make them visible to other packages.
        .library(
            name: "App",
            targets: ["App"]),
    ],
    dependencies: [
        // Dependencies declare other packages that this package depends on.
        // .package(url: /* package url */, from: "1.0.0"),
    ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages this package depends on.
        .target(
            name: "App",
            dependencies: []),
        .testTarget(
            name: "AppTests",
            dependencies: ["App"]),
    ]
)

routes.swift

import Vapor

func routes(_ app: Application) throws {
  app.get { req in
    return "It works!"
  }
}

Targets.swift

// swift-tools-version:5.5
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "App",
    products: [ ... ],
    dependencies: [ ... ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages this package depends on.
        .target(
            name: "App",
            dependencies: [
                .product(name: "Vapor", package: "vapor"),
            ]),
        .executableTarget(name: "Run", dependencies: ["App"]),
        .testTarget(
            name: "AppTests",
            dependencies: ["App"]),
    ]
)