Add a helper tool for swift-testing

Since the xctest and swift-testing are being unified into one product
we need an additional tool (just like `swiftpm-xctest-helper`) to load
and run swift-testing tests from the unified bundle.

Author: xedin

Package.swift

@@ -738,6 +738,16 @@ let package = Package(
     swiftLanguageVersions: [.v5]
 )
 
+#if canImport(Darwin)
+package.targets.append(contentsOf: [
+    .executableTarget(
+      name: "swiftpm-testing-helper",
+      dependencies: ["Commands"],
+      exclude: ["CMakeLists.txt"]
+    )
+])
+#endif
+
 // Workaround SPM's attempt to link in executables which does not work on all
 // platforms.
 #if !os(Windows)

Sources/swiftpm-testing-helper/Entrypoint.swift

@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2014-2017 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 Commands
+import Darwin.C
+
+@main
+struct Entrypoint {
+    static func main() async throws {
+        // HACK: use the swift-test executable as a host for the .xctest bundle
+        // when running Swift Testing tests.
+        let args = CommandLine.arguments
+        if args.count >= 3, args[1] == "--test-bundle-path" {
+            let bundlePath = args[2]
+            guard let image = dlopen(bundlePath, RTLD_LAZY) else {
+                let errorMessage: String = dlerror().flatMap {
+                    #if compiler(>=6)
+                    String(validatingCString: $0)
+                    #else
+                    String(validatingUTF8: $0)
+                    #endif
+                } ?? "An unknown error occurred."
+                fatalError("Failed to open test bundle at path \(bundlePath): \(errorMessage)")
+            }
+            defer {
+                dlclose(image)
+            }
+
+            // Find and call the main function from the image. This function may
+            // link to the copy of Swift Testing included with Xcode, or may link to
+            // a copy that's included as a package dependency.
+            let main = dlsym(image, "main").map {
+                unsafeBitCast(
+                    $0,
+                    to: (@convention(c) (CInt, UnsafeMutablePointer<UnsafeMutablePointer<CChar>?>) -> CInt).self
+                )
+            }
+            if let main {
+                exit(main(CommandLine.argc, CommandLine.unsafeArgv))
+            }
+        }
+
+        await SwiftTestCommand.main()
+    }
+}

Utilities/bootstrap

@@ -435,7 +435,11 @@ def install(args):
 def install_swiftpm(prefix, args):
     # Install the swift-package-manager tool and create symlinks to it.
     cli_tool_dest = os.path.join(prefix, "bin")
+    aux_tool_dest = os.path.join(prefix, "usr", "libexec", "swift", "pm")
+
     install_binary(args, "swift-package-manager", os.path.join(cli_tool_dest, "swift-package"), destination_is_directory=False)
+    install_binary(args, "swiftpm-testing-helper", aux_tool_dest, destination_is_directory=True)
+
     for tool in ["swift-build", "swift-test", "swift-run", "swift-package-collection", "swift-package-registry", "swift-sdk", "swift-experimental-sdk"]:
         src = "swift-package"
         dest = os.path.join(cli_tool_dest, tool)