Update swift-tools version to use Swift 6 when available.

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.5
+// swift-tools-version:6.0
 // The swift-tools-version declares the minimum version of Swift required to build this package.
 
 // Copyright 2021 Google LLC

Package@swift-5.5.swift

@@ -0,0 +1,133 @@
+// swift-tools-version:5.5
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import PackageDescription
+
+let googleSignInVersion = "9.0.0"
+
+let package = Package(
+  name: "GoogleSignIn",
+  defaultLocalization: "en",
+  platforms: [
+    .macOS(.v10_15),
+    .iOS(.v12)
+  ],
+  products: [
+    .library(
+      name: "GoogleSignIn",
+      targets: [
+        "GoogleSignIn",
+      ]
+    ),
+    .library(
+      name: "GoogleSignInSwift",
+      targets: [
+        "GoogleSignInSwift",
+      ]
+    ),
+  ],
+  dependencies: [
+    .package(
+      name: "AppAuth",
+      url: "https://github.com/openid/AppAuth-iOS.git",
+      from: "2.0.0"),
+    .package(
+      name: "AppCheck",
+      url: "https://github.com/google/app-check.git",
+      from: "11.0.0"),
+    .package(
+      name: "GTMAppAuth",
+      url: "https://github.com/google/GTMAppAuth.git",
+      from: "5.0.0"),
+    .package(
+      name: "GTMSessionFetcher",
+      url: "https://github.com/google/gtm-session-fetcher.git",
+      from: "3.3.0"),
+    .package(
+      name: "OCMock",
+      url: "https://github.com/firebase/ocmock.git",
+      .revision("7291762d3551c5c7e31c49cce40a0e391a52e889")),
+    .package(
+      name: "GoogleUtilities",
+      url: "https://github.com/google/GoogleUtilities.git",
+      from: "8.0.0"),
+  ],
+  targets: [
+    .target(
+      name: "GoogleSignIn",
+      dependencies: [
+        .product(name: "AppAuth", package: "AppAuth"),
+        .product(name: "AppAuthCore", package: "AppAuth"),
+        .product(name: "AppCheckCore", package: "AppCheck"),
+        .product(name: "GTMAppAuth", package: "GTMAppAuth"),
+        .product(name: "GTMSessionFetcherCore", package: "GTMSessionFetcher"),
+      ],
+      path: "GoogleSignIn/Sources",
+      resources: [
+        .process("Resources"),
+        .process("Strings"),
+      ],
+      publicHeadersPath: "Public",
+      cSettings: [
+        .headerSearchPath("../../"),
+        .define("GID_SDK_VERSION", to: googleSignInVersion),
+      ],
+      linkerSettings: [
+        .linkedFramework("CoreGraphics"),
+        .linkedFramework("CoreText"),
+        .linkedFramework("Foundation"),
+        .linkedFramework("LocalAuthentication"),
+        .linkedFramework("Security"),
+        .linkedFramework("AppKit", .when(platforms: [.macOS])),
+        .linkedFramework("UIKit", .when(platforms: [.iOS])),
+      ]
+    ),
+    .target(
+      name: "GoogleSignInSwift",
+      dependencies: [
+        "GoogleSignIn",
+      ],
+      path: "GoogleSignInSwift/Sources",
+      resources: [
+        .copy("Resources/PrivacyInfo.xcprivacy")
+      ]
+    ),
+    .testTarget(
+      name: "GoogleSignIn-UnitTests",
+      dependencies: [
+        "GoogleSignIn",
+        "OCMock",
+        .product(name: "AppAuth", package: "AppAuth"),
+        .product(name: "AppCheckCore", package: "AppCheck"),
+        .product(name: "GTMAppAuth", package: "GTMAppAuth"),
+        .product(name: "GTMSessionFetcherCore", package: "GTMSessionFetcher"),
+        .product(name: "GULMethodSwizzler", package: "GoogleUtilities"),
+        .product(name: "GULSwizzlerTestHelpers", package: "GoogleUtilities"),
+      ],
+      path: "GoogleSignIn/Tests/Unit",
+      cSettings: [
+        .headerSearchPath("../../../"),
+        .define("GID_SDK_VERSION", to: googleSignInVersion),
+      ]
+    ),
+    .testTarget(
+      name: "GoogleSignInSwift-UnitTests",
+      dependencies: ["GoogleSignInSwift"],
+      path: "GoogleSignInSwift/Tests/Unit"
+    )
+  ]
+)