[WIP] Build Swift Testing and XCTest content in a single product.

This PR refactors the previously-experimental Swift Testing support logic so
that only a single build product is produced when using both XCTest and Swift
Testing, and detection of Swift Testing usage is no longer needed at compile
time.

On macOS, Xcode 16 is responsible for hosting Swift Testing content, so
additional changes may be needed in Xcode to support this refactoring. Such
changes are beyond the purview of the Swift open source project.

Author: grynspan

Sources/Build/BuildManifest/LLBuildManifestBuilder.swift

@@ -112,9 +112,7 @@ public class LLBuildManifestBuilder {
             }
         }
 
-        if self.plan.destinationBuildParameters.testingParameters.library == .xctest {
-            try self.addTestDiscoveryGenerationCommand()
-        }
+        try self.addTestDiscoveryGenerationCommand()
         try self.addTestEntryPointGenerationCommand()
 
         // Create command for all products in the plan.
@@ -310,9 +308,7 @@ extension LLBuildManifestBuilder {
 
             let outputs = testEntryPointTarget.target.sources.paths
 
-            let mainFileName = TestEntryPointTool.mainFileName(
-                for: self.plan.destinationBuildParameters.testingParameters.library
-            )
+            let mainFileName = TestEntryPointTool.mainFileName
             guard let mainOutput = (outputs.first { $0.basename == mainFileName }) else {
                 throw InternalError("main output (\(mainFileName)) not found")
             }

Sources/Build/BuildPlan/BuildPlan+Test.swift

@@ -116,7 +116,7 @@ extension BuildPlan {
                 resolvedTargetDependencies: [ResolvedModule.Dependency]
             ) throws -> SwiftModuleBuildDescription {
                 let entryPointDerivedDir = destinationBuildParameters.buildPath.appending(components: "\(testProduct.name).derived")
-                let entryPointMainFileName = TestEntryPointTool.mainFileName(for: destinationBuildParameters.testingParameters.library)
+                let entryPointMainFileName = TestEntryPointTool.mainFileName
                 let entryPointMainFile = entryPointDerivedDir.appending(component: entryPointMainFileName)
                 let entryPointSources = Sources(paths: [entryPointMainFile], root: entryPointDerivedDir)
 
@@ -153,16 +153,9 @@ extension BuildPlan {
             let swiftTargetDependencies: [Module.Dependency]
             let resolvedTargetDependencies: [ResolvedModule.Dependency]
 
-            switch destinationBuildParameters.testingParameters.library {
-            case .xctest:
-                discoveryTargets = try generateDiscoveryTargets()
-                swiftTargetDependencies = [.module(discoveryTargets!.target, conditions: [])]
-                resolvedTargetDependencies = [.module(discoveryTargets!.resolved, conditions: [])]
-            case .swiftTesting:
-                discoveryTargets = nil
-                swiftTargetDependencies = testProduct.modules.map { .module($0.underlying, conditions: []) }
-                resolvedTargetDependencies = testProduct.modules.map { .module($0, conditions: []) }
-            }
+            discoveryTargets = try generateDiscoveryTargets()
+            swiftTargetDependencies = [.module(discoveryTargets!.target, conditions: [])]
+            resolvedTargetDependencies = [.module(discoveryTargets!.resolved, conditions: [])]
 
             if let entryPointResolvedTarget = testProduct.testEntryPointModule {
                 if isEntryPointPathSpecifiedExplicitly || explicitlyEnabledDiscovery {

Sources/Build/LLBuildCommands.swift

@@ -50,8 +50,8 @@ extension IndexStore.TestCaseClass.TestMethod {
 }
 
 extension TestEntryPointTool {
-    public static func mainFileName(for library: BuildParameters.Testing.Library) -> String {
-        "runner-\(library).swift"
+    public static var mainFileName: String {
+        "runner.swift"
     }
 }
 
@@ -105,74 +105,67 @@ final class TestDiscoveryCommand: CustomLLBuildCommand, TestBuildCommand {
     private func execute(fileSystem: Basics.FileSystem, tool: TestDiscoveryTool) throws {
         let outputs = tool.outputs.compactMap { try? AbsolutePath(validating: $0.name) }
 
-        switch self.context.productsBuildParameters.testingParameters.library {
-        case .swiftTesting:
-            for file in outputs {
-                try fileSystem.writeIfChanged(path: file, string: "")
-            }
-        case .xctest:
-            let index = self.context.productsBuildParameters.indexStore
-            let api = try self.context.indexStoreAPI.get()
-            let store = try IndexStore.open(store: TSCAbsolutePath(index), api: api)
-
-            // FIXME: We can speed this up by having one llbuild command per object file.
-            let tests = try store
-                .listTests(in: tool.inputs.map { try TSCAbsolutePath(AbsolutePath(validating: $0.name)) })
-
-            let testsByModule = Dictionary(grouping: tests, by: { $0.module.spm_mangledToC99ExtendedIdentifier() })
-
-            // Find the main file path.
-            guard let mainFile = outputs.first(where: { path in
-                path.basename == TestDiscoveryTool.mainFileName
-            }) else {
-                throw InternalError("main output (\(TestDiscoveryTool.mainFileName)) not found")
-            }
+        let index = self.context.productsBuildParameters.indexStore
+        let api = try self.context.indexStoreAPI.get()
+        let store = try IndexStore.open(store: TSCAbsolutePath(index), api: api)
 
-            // Write one file for each test module.
-            //
-            // We could write everything in one file but that can easily run into type conflicts due
-            // in complex packages with large number of test modules.
-            for file in outputs where file != mainFile {
-                // FIXME: This is relying on implementation detail of the output but passing the
-                // the context all the way through is not worth it right now.
-                let module = file.basenameWithoutExt.spm_mangledToC99ExtendedIdentifier()
-
-                guard let tests = testsByModule[module] else {
-                    // This module has no tests so just write an empty file for it.
-                    try fileSystem.writeFileContents(file, bytes: "")
-                    continue
-                }
-                try write(
-                    tests: tests,
-                    forModule: module,
-                    fileSystem: fileSystem,
-                    path: file
-                )
+        // FIXME: We can speed this up by having one llbuild command per object file.
+        let tests = try store
+            .listTests(in: tool.inputs.map { try TSCAbsolutePath(AbsolutePath(validating: $0.name)) })
+
+        let testsByModule = Dictionary(grouping: tests, by: { $0.module.spm_mangledToC99ExtendedIdentifier() })
+
+        // Find the main file path.
+        guard let mainFile = outputs.first(where: { path in
+            path.basename == TestDiscoveryTool.mainFileName
+        }) else {
+            throw InternalError("main output (\(TestDiscoveryTool.mainFileName)) not found")
+        }
+
+        // Write one file for each test module.
+        //
+        // We could write everything in one file but that can easily run into type conflicts due
+        // in complex packages with large number of test modules.
+        for file in outputs where file != mainFile {
+            // FIXME: This is relying on implementation detail of the output but passing the
+            // the context all the way through is not worth it right now.
+            let module = file.basenameWithoutExt.spm_mangledToC99ExtendedIdentifier()
+
+            guard let tests = testsByModule[module] else {
+                // This module has no tests so just write an empty file for it.
+                try fileSystem.writeFileContents(file, bytes: "")
+                continue
             }
+            try write(
+                tests: tests,
+                forModule: module,
+                fileSystem: fileSystem,
+                path: file
+            )
+        }
 
-            let testsKeyword = tests.isEmpty ? "let" : "var"
+        let testsKeyword = tests.isEmpty ? "let" : "var"
 
-            // Write the main file.
-            let stream = try LocalFileOutputByteStream(mainFile)
+        // Write the main file.
+        let stream = try LocalFileOutputByteStream(mainFile)
 
-            stream.send(
-                #"""
-                import XCTest
+        stream.send(
+            #"""
+            import XCTest
 
-                @available(*, deprecated, message: "Not actually deprecated. Marked as deprecated to allow inclusion of deprecated tests (which test deprecated functionality) without warnings")
-                @MainActor
-                public func __allDiscoveredTests() -> [XCTestCaseEntry] {
-                    \#(testsKeyword) tests = [XCTestCaseEntry]()
+            @available(*, deprecated, message: "Not actually deprecated. Marked as deprecated to allow inclusion of deprecated tests (which test deprecated functionality) without warnings")
+            @MainActor
+            public func __allDiscoveredTests() -> [XCTestCaseEntry] {
+                \#(testsKeyword) tests = [XCTestCaseEntry]()
 
-                    \#(testsByModule.keys.map { "tests += __\($0)__allTests()" }.joined(separator: "\n    "))
+                \#(testsByModule.keys.map { "tests += __\($0)__allTests()" }.joined(separator: "\n    "))
 
-                    return tests
-                }
-                """#
-            )
+                return tests
+            }
+            """#
+        )
 
-            stream.flush()
-        }
+        stream.flush()
     }
 
     override func execute(
@@ -201,9 +194,7 @@ final class TestEntryPointCommand: CustomLLBuildCommand, TestBuildCommand {
         let outputs = tool.outputs.compactMap { try? AbsolutePath(validating: $0.name) }
 
         // Find the main output file
-        let mainFileName = TestEntryPointTool.mainFileName(
-            for: self.context.productsBuildParameters.testingParameters.library
-        )
+        let mainFileName = TestEntryPointTool.mainFileName
         guard let mainFile = outputs.first(where: { path in
             path.basename == mainFileName
         }) else {
@@ -213,62 +204,67 @@ final class TestEntryPointCommand: CustomLLBuildCommand, TestBuildCommand {
         // Write the main file.
         let stream = try LocalFileOutputByteStream(mainFile)
 
-        switch self.context.productsBuildParameters.testingParameters.library {
-        case .swiftTesting:
-            stream.send(
-                #"""
-                #if canImport(Testing)
-                import Testing
-                #endif
+        // Find the inputs, which are the names of the test discovery module(s)
+        let inputs = tool.inputs.compactMap { try? AbsolutePath(validating: $0.name) }
+        let discoveryModuleNames = inputs.map(\.basenameWithoutExt)
 
-                @main struct Runner {
-                    static func main() async {
-                #if canImport(Testing)
-                        await Testing.__swiftPMEntryPoint() as Never
-                #endif
-                    }
-                }
-                """#
-            )
-        case .xctest:
-            // Find the inputs, which are the names of the test discovery module(s)
-            let inputs = tool.inputs.compactMap { try? AbsolutePath(validating: $0.name) }
-            let discoveryModuleNames = inputs.map(\.basenameWithoutExt)
-
-            let testObservabilitySetup: String
-            let buildParameters = self.context.productsBuildParameters
-            if buildParameters.testingParameters.experimentalTestOutput && buildParameters.triple.supportsTestSummary {
-                testObservabilitySetup = "_ = SwiftPMXCTestObserver()\n"
-            } else {
-                testObservabilitySetup = ""
-            }
+        let testObservabilitySetup: String
+        let buildParameters = self.context.productsBuildParameters
+        if buildParameters.testingParameters.experimentalTestOutput && buildParameters.triple.supportsTestSummary {
+            testObservabilitySetup = "_ = SwiftPMXCTestObserver()\n"
+        } else {
+            testObservabilitySetup = ""
+        }
 
-            stream.send(
-                #"""
-                \#(generateTestObservationCode(buildParameters: buildParameters))
+        stream.send(
+            #"""
+            #if canImport(Testing)
+            import Testing
+            #endif
 
-                import XCTest
-                \#(discoveryModuleNames.map { "import \($0)" }.joined(separator: "\n"))
+            #if canImport(XCTest)
+            \#(generateTestObservationCode(buildParameters: buildParameters))
 
-                @main
-                @available(*, deprecated, message: "Not actually deprecated. Marked as deprecated to allow inclusion of deprecated tests (which test deprecated functionality) without warnings")
-                struct Runner {
-                    #if os(WASI)
-                    /// On WASI, we can't block the main thread, so XCTestMain is defined as async.
-                    static func main() async {
-                        \#(testObservabilitySetup)
-                        await XCTMain(__allDiscoveredTests()) as Never
+            import XCTest
+            \#(discoveryModuleNames.map { "import \($0)" }.joined(separator: "\n"))
+            #endif
+
+            @main
+            @available(*, deprecated, message: "Not actually deprecated. Marked as deprecated to allow inclusion of deprecated tests (which test deprecated functionality) without warnings")
+            struct Runner {
+                static func which() -> String {
+                    // HACK: abstract this check properly!
+                    let args = CommandLine.arguments
+                    if args.contains("--testing-library=swift-testing") {
+                        return "swift-testing" 
+                    } else if args.contains("--testing-library=xctest") {
+                        return "XCTest"
+                    }
+                    // Fallback if not specified: run XCTest (legacy behavior)
+                    return "XCTest"
+                }
+                static func main() async {
+                    let which = Self.which()
+            #if canImport(Testing)
+                    if which == "swift-testing" {
+                        await Testing.__swiftPMEntryPoint() as Never
                     }
-                    #else
-                    static func main() {
+            #endif
+            #if canImport(XCTest)
+                    if which == "XCTest" {
                         \#(testObservabilitySetup)
+            #if os(WASI)
+                        /// On WASI, we can't block the main thread, so XCTestMain is defined as async.
+                        await XCTMain(__allDiscoveredTests()) as Never
+            #else
                         XCTMain(__allDiscoveredTests()) as Never
+            #endif
                     }
-                    #endif
+            #endif
                 }
-                """#
-            )
-        }
+            }
+            """#
+        )
 
         stream.flush()
     }

Sources/Build/LLBuildDescription.swift

@@ -140,8 +140,7 @@ public struct BuildDescription: Codable {
             try BuiltTestProduct(
                 productName: desc.product.name,
                 binaryPath: desc.binaryPath,
-                packagePath: desc.package.path,
-                library: desc.buildParameters.testingParameters.library
+                packagePath: desc.package.path
             )
         }
         self.pluginDescriptions = pluginDescriptions

Sources/Commands/PackageCommands/Init.swift

@@ -54,20 +54,11 @@ extension SwiftPackageCommand {
                 throw InternalError("Could not find the current working directory")
             }
 
-            // NOTE: Do not use testLibraryOptions.enabledTestingLibraries(swiftCommandState:) here
-            // because the package doesn't exist yet, so there are no dependencies for it to query.
-            var testingLibraries: Set<BuildParameters.Testing.Library> = []
-            if testLibraryOptions.enableXCTestSupport {
-                testingLibraries.insert(.xctest)
-            }
-            if testLibraryOptions.explicitlyEnableSwiftTestingLibrarySupport == true {
-                testingLibraries.insert(.swiftTesting)
-            }
             let packageName = self.packageName ?? cwd.basename
             let initPackage = try InitPackage(
                 name: packageName,
                 packageType: initMode,
-                supportedTestingLibraries: testingLibraries,
+                supportedTestingLibraries: testLibraryOptions.enabledTestingLibraries,
                 destinationPath: cwd,
                 installedSwiftPMConfiguration: swiftCommandState.getHostToolchain().installedSwiftPMConfiguration,
                 fileSystem: swiftCommandState.fileSystem

Sources/Commands/SwiftBuildCommand.swift

@@ -175,23 +175,20 @@ public struct SwiftBuildCommand: AsyncSwiftCommand {
         }
 
         if case .allIncludingTests = subset {
-            func updateTestingParameters(of buildParameters: inout BuildParameters, library: BuildParameters.Testing.Library) {
+            func updateTestingParameters(of buildParameters: inout BuildParameters) {
                 buildParameters.testingParameters = .init(
                     configuration: buildParameters.configuration,
                     targetTriple: buildParameters.triple,
                     enableCodeCoverage: buildParameters.testingParameters.enableCodeCoverage,
                     enableTestability: buildParameters.testingParameters.enableTestability,
                     experimentalTestOutput: buildParameters.testingParameters.experimentalTestOutput,
                     forceTestDiscovery: globalOptions.build.enableTestDiscovery,
-                    testEntryPointPath: globalOptions.build.testEntryPointPath,
-                    library: library
+                    testEntryPointPath: globalOptions.build.testEntryPointPath
                 )
             }
-            for library in try options.testLibraryOptions.enabledTestingLibraries(swiftCommandState: swiftCommandState) {
-                updateTestingParameters(of: &productsBuildParameters, library: library)
-                updateTestingParameters(of: &toolsBuildParameters, library: library)
-                try build(swiftCommandState, subset: subset, productsBuildParameters: productsBuildParameters, toolsBuildParameters: toolsBuildParameters)
-            }
+            updateTestingParameters(of: &productsBuildParameters)
+            updateTestingParameters(of: &toolsBuildParameters)
+            try build(swiftCommandState, subset: subset, productsBuildParameters: productsBuildParameters, toolsBuildParameters: toolsBuildParameters)
         } else {
             try build(swiftCommandState, subset: subset, productsBuildParameters: productsBuildParameters, toolsBuildParameters: toolsBuildParameters)
         }