Update -swift-version to default to 6 for swift-tools-version 6

Fixtures/Miscellaneous/Plugins/DependentPlugins/Package.swift

@@ -10,15 +10,15 @@ let package = Package(
     targets: [
         .executableTarget(name: "MyExecutable"),
         .executableTarget(name: "MyExecutable2"),
-        
+
         .plugin(
             name: "MyPlugin",
             capability: .buildTool(),
             dependencies: [
                 "MyExecutable"
             ]
         ),
-        
+
         .plugin(
             name: "MyPlugin2",
             capability: .buildTool(),
@@ -34,5 +34,6 @@ let package = Package(
                 "MyPlugin2",
             ]
         ),
-    ]
+    ],
+    swiftLanguageVersions: [.v5]
 )

Fixtures/Miscellaneous/Plugins/MyBuildToolPluginDependencies/Sources/MySourceGenBuildTool/main.swift

@@ -13,6 +13,6 @@ let variableName = URL(fileURLWithPath: inputFile).deletingPathExtension().lastP
 
 let inputData = FileManager.default.contents(atPath: inputFile) ?? Data()
 let dataAsHex = inputData.map { String(format: "%02hhx", $0) }.joined()
-let outputString = "public var \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
+let outputString = "public let \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
 let outputData = outputString.data(using: .utf8)
 FileManager.default.createFile(atPath: outputFile, contents: outputData)

Fixtures/Miscellaneous/Plugins/MySourceGenPlugin/Sources/MySourceGenBuildTool/main.swift

@@ -13,6 +13,6 @@ let variableName = URL(fileURLWithPath: inputFile).deletingPathExtension().lastP
 
 let inputData = FileManager.default.contents(atPath: inputFile) ?? Data()
 let dataAsHex = inputData.map { String(format: "%02hhx", $0) }.joined()
-let outputString = "public var \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
+let outputString = "public let \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
 let outputData = outputString.data(using: .utf8)
 FileManager.default.createFile(atPath: outputFile, contents: outputData)

Fixtures/Miscellaneous/Plugins/MySourceGenPluginUsingURLBasedAPI/Sources/MySourceGenBuildTool/main.swift

@@ -13,6 +13,6 @@ let variableName = URL(fileURLWithPath: inputFile).deletingPathExtension().lastP
 
 let inputData = FileManager.default.contents(atPath: inputFile) ?? Data()
 let dataAsHex = inputData.map { String(format: "%02hhx", $0) }.joined()
-let outputString = "public var \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
+let outputString = "public let \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
 let outputData = outputString.data(using: .utf8)
 FileManager.default.createFile(atPath: outputFile, contents: outputData)

Fixtures/Miscellaneous/Plugins/PluginWithInternalExecutable/Sources/PluginExecutable/main.swift

@@ -12,6 +12,6 @@ let variableName = URL(fileURLWithPath: inputFile).deletingPathExtension().lastP
 
 let inputData = FileManager.default.contents(atPath: inputFile) ?? Data()
 let dataAsHex = inputData.map { String(format: "%02hhx", $0) }.joined()
-let outputString = "public var \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
+let outputString = "public let \(variableName) = \(dataAsHex.quotedForSourceCode)\n"
 let outputData = outputString.data(using: .utf8)
 FileManager.default.createFile(atPath: outputFile, contents: outputData)

IntegrationTests/Tests/IntegrationTests/BasicTests.swift

@@ -19,6 +19,7 @@ final class BasicTests: XCTestCase {
 
     func testExamplePackageDealer() throws {
         try XCTSkipIf(isSelfHosted, "These packages don't use the latest runtime library, which doesn't work with self-hosted builds.")
+        try skipUnlessAtLeastSwift6()
 
         try withTemporaryDirectory { tempDir in
             let packagePath = tempDir.appending(component: "dealer")
@@ -93,9 +94,7 @@ final class BasicTests: XCTestCase {
     }
 
     func testSwiftPackageInitExec() throws {
-        #if swift(<5.5)
-        try XCTSkipIf(true, "skipping because host compiler doesn't support '-entry-point-function-name'")
-        #endif
+        try skipUnlessAtLeastSwift6()
 
         try withTemporaryDirectory { tempDir in
             // Create a new package with an executable target.
@@ -122,9 +121,7 @@ final class BasicTests: XCTestCase {
     }
 
     func testSwiftPackageInitExecTests() throws {
-        #if swift(<5.5)
-        try XCTSkipIf(true, "skipping because host compiler doesn't support '-entry-point-function-name'")
-        #endif
+        try skipUnlessAtLeastSwift6()
 
         try XCTSkip("FIXME: swift-test invocations are timing out in Xcode and self-hosted CI")
 
@@ -149,6 +146,8 @@ final class BasicTests: XCTestCase {
     }
 
     func testSwiftPackageInitLib() throws {
+        try skipUnlessAtLeastSwift6()
+
         try withTemporaryDirectory { tempDir in
             // Create a new package with an executable target.
             let packagePath = tempDir.appending(component: "Project")
@@ -167,6 +166,8 @@ final class BasicTests: XCTestCase {
     }
 
     func testSwiftPackageLibsTests() throws {
+        try skipUnlessAtLeastSwift6()
+
         try XCTSkip("FIXME: swift-test invocations are timing out in Xcode and self-hosted CI")
 
         try withTemporaryDirectory { tempDir in
@@ -225,9 +226,7 @@ final class BasicTests: XCTestCase {
     }
 
     func testSwiftRun() throws {
-        #if swift(<5.5)
-        try XCTSkipIf(true, "skipping because host compiler doesn't support '-entry-point-function-name'")
-        #endif
+        try skipUnlessAtLeastSwift6()
 
         try withTemporaryDirectory { tempDir in
             let packagePath = tempDir.appending(component: "secho")
@@ -256,6 +255,8 @@ final class BasicTests: XCTestCase {
     }
 
     func testSwiftTest() throws {
+        try skipUnlessAtLeastSwift6()
+
         try XCTSkip("FIXME: swift-test invocations are timing out in Xcode and self-hosted CI")
 
         try withTemporaryDirectory { tempDir in
@@ -377,3 +378,9 @@ private extension Character {
         }
     }
 }
+
+private func skipUnlessAtLeastSwift6() throws {
+    #if compiler(<6.0)
+    try XCTSkipIf(true, "Skipping because test requires at least Swift 6.0")
+    #endif
+}

IntegrationTests/Tests/IntegrationTests/SwiftPMTests.swift

@@ -53,6 +53,9 @@ final class SwiftPMTests: XCTestCase {
         #if !os(macOS)
         try XCTSkip("Test requires macOS")
         #endif
+        #if swift(<6.0)
+        try XCTSkipIf(true, "Skipping because test requires at least Swift 6.0")
+        #endif
 
         try withTemporaryDirectory { tmpDir in
             let packagePath = tmpDir.appending(component: "foo")

Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift

@@ -405,6 +405,11 @@ package final class SwiftTargetBuildDescription {
             """
             import Foundation
 
+            #if compiler(>=6.0)
+            extension Foundation.Bundle: @unchecked @retroactive Sendable {}
+            #else
+            extension Foundation.Bundle: @unchecked Sendable {}
+            #endif
             extension Foundation.Bundle {
                 static let module: Bundle = {
                     let mainPath = \(mainPathSubstitution)

Sources/CoreCommands/SwiftCommandState.swift

@@ -881,23 +881,6 @@ package final class SwiftCommandState {
             }
 
             var extraManifestFlags = self.options.build.manifestFlags
-            // Disable the implicit concurrency import if the compiler in use supports it to avoid warnings if we are building against an older SDK that does not contain a Concurrency module.
-            if DriverSupport.checkSupportedFrontendFlags(
-                flags: ["disable-implicit-concurrency-module-import"],
-                toolchain: try self.toolsBuildParameters.toolchain,
-                fileSystem: self.fileSystem
-            ) {
-                extraManifestFlags += ["-Xfrontend", "-disable-implicit-concurrency-module-import"]
-            }
-            // Disable the implicit string processing import if the compiler in use supports it to avoid warnings if we are building against an older SDK that does not contain a StringProcessing module.
-            if DriverSupport.checkSupportedFrontendFlags(
-                flags: ["disable-implicit-string-processing-module-import"],
-                toolchain: try self.toolsBuildParameters.toolchain,
-                fileSystem: self.fileSystem
-            ) {
-                extraManifestFlags += ["-Xfrontend", "-disable-implicit-string-processing-module-import"]
-            }
-
             if self.logLevel <= .info {
                 extraManifestFlags.append("-v")
             }

Sources/PackageModel/ToolsVersion.swift

@@ -182,10 +182,11 @@ public struct ToolsVersion: Equatable, Hashable, Codable, Sendable {
 
             // Otherwise, use 4.2
             return .v4_2
-
-        default:
-            // Anything above 4 major version uses version 5.
+        case 5:
             return .v5
+        default:
+            // Anything above 5 major version uses version 6.
+            return .v6
         }
     }
 }

Sources/SPMTestSupport/XCTSkipHelpers.swift

@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Basics
+import PackageModel
+import XCTest
+
+import class TSCBasic.Process
+import struct TSCBasic.StringError
+
+extension Toolchain {
+    package func skipUnlessAtLeastSwift6(
+        file: StaticString = #file,
+        line: UInt = #line
+    ) async throws {
+        #if compiler(<6.0)
+        try XCTSkipIf(true, "Skipping because test requires at least Swift 6.0")
+        #endif
+    }
+}

Tests/BuildTests/BuildPlanTests.swift

@@ -6368,4 +6368,51 @@ final class BuildPlanTests: XCTestCase {
             ]
         )
     }
+
+    func testDefaultVersions() throws {
+        let fs = InMemoryFileSystem(emptyFiles:
+            "/Pkg/Sources/foo/foo.swift"
+        )
+
+        let expectedVersions = [
+          ToolsVersion.v4: "4",
+          ToolsVersion.v4_2: "4.2",
+          ToolsVersion.v5: "5",
+          ToolsVersion.v6_0: "6",
+          ToolsVersion.vNext: "6"
+        ]
+        for (toolsVersion, expectedVersionString) in expectedVersions {
+            let observability = ObservabilitySystem.makeForTesting()
+            let graph = try loadModulesGraph(
+              fileSystem: fs,
+              manifests: [
+                Manifest.createRootManifest(
+                  displayName: "Pkg",
+                  path: "/Pkg",
+                  toolsVersion: toolsVersion,
+                  targets: [
+                    TargetDescription(
+                      name: "foo"
+                    ),
+                  ]
+                ),
+              ],
+              observabilityScope: observability.topScope
+            )
+
+            let result = try BuildPlanResult(plan: BuildPlan(
+              buildParameters: mockBuildParameters(),
+              graph: graph,
+              fileSystem: fs,
+              observabilityScope: observability.topScope
+            ))
+
+            XCTAssertMatch(
+              try result.target(for: "foo").swiftTarget().compileArguments(),
+              [
+                "-swift-version", .equal(expectedVersionString)
+              ]
+            )
+        }
+    }
 }

Tests/BuildTests/BuildSystemDelegateTests.swift

@@ -17,7 +17,8 @@ import XCTest
 import var TSCBasic.localFileSystem
 
 final class BuildSystemDelegateTests: XCTestCase {
-    func testDoNotFilterLinkerDiagnostics() throws {
+    func testDoNotFilterLinkerDiagnostics() async throws {
+        try await UserToolchain.default.skipUnlessAtLeastSwift6()
         try XCTSkipIf(!UserToolchain.default.supportsSDKDependentTests(), "skipping because test environment doesn't support this test")
         try fixture(name: "Miscellaneous/DoNotFilterLinkerDiagnostics") { fixturePath in
             #if !os(macOS)

Tests/FunctionalTests/PluginTests.swift

@@ -178,7 +178,9 @@ final class PluginTests: XCTestCase {
         }
     }
 
-    func testBuildToolWithoutOutputs() throws {
+    func testBuildToolWithoutOutputs() async throws {
+        try await UserToolchain.default.skipUnlessAtLeastSwift6()
+
         // Only run the test if the environment in which we're running actually supports Swift concurrency (which the plugin APIs require).
         try XCTSkipIf(!UserToolchain.default.supportsSwiftConcurrency(), "skipping because test environment doesn't support concurrency")
 
@@ -1155,7 +1157,9 @@ final class PluginTests: XCTestCase {
         }
     }
 
-    func testURLBasedPluginAPI() throws {
+    func testURLBasedPluginAPI() async throws {
+        try await UserToolchain.default.skipUnlessAtLeastSwift6()
+
         // Only run the test if the environment in which we're running actually supports Swift concurrency (which the plugin APIs require).
         try XCTSkipIf(!UserToolchain.default.supportsSwiftConcurrency(), "skipping because test environment doesn't support concurrency")
 
@@ -1165,7 +1169,9 @@ final class PluginTests: XCTestCase {
         }
     }
 
-    func testDependentPlugins() throws {
+    func testDependentPlugins() async throws {
+        try await UserToolchain.default.skipUnlessAtLeastSwift6()
+
         try XCTSkipIf(!UserToolchain.default.supportsSwiftConcurrency(), "skipping because test environment doesn't support concurrency")
 
         try fixture(name: "Miscellaneous/Plugins/DependentPlugins") { fixturePath in

Tests/FunctionalTests/ResourcesTests.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 import Basics
+import PackageModel
 import SPMTestSupport
 import XCTest
 
@@ -126,7 +127,9 @@ class ResourcesTests: XCTestCase {
         }
     }
 
-    func testResourcesOutsideOfTargetCanBeIncluded() throws {
+    func testResourcesOutsideOfTargetCanBeIncluded() async throws {
+        try await UserToolchain.default.skipUnlessAtLeastSwift6()
+
         try testWithTemporaryDirectory { tmpPath in
             let packageDir = tmpPath.appending(components: "MyPackage")