Allow swift-build to have async entrypoint

Due to a bug in Swift 5.9, we can't have multiple executables with `async` entrypoints linked into test products. This was the reason why we weren't able to make `swift-build` entrypoint `async`. Since we have a single `swift-package-manager` executable anyway, we can link that one into tests instead, and pass "simulated" executable name via an environment variable. This allows us to work around the bug and start using structured concurrency from `swift-build` entrypoint.

Author: MaxDesiatov

Package.swift

@@ -681,9 +681,7 @@ package.targets.append(contentsOf: [
     .testTarget(
         name: "FunctionalPerformanceTests",
         dependencies: [
-            "swift-build",
-            "swift-package",
-            "swift-test",
+            "swift-package-manager",
             "SPMTestSupport"
         ]
     ),
@@ -695,9 +693,7 @@ if ProcessInfo.processInfo.environment["SWIFTCI_DISABLE_SDK_DEPENDENT_TESTS"] ==
         .testTarget(
             name: "FunctionalTests",
             dependencies: [
-                "swift-build",
-                "swift-package",
-                "swift-test",
+                "swift-package-manager",
                 "PackageModel",
                 "SPMTestSupport"
             ]
@@ -713,10 +709,7 @@ if ProcessInfo.processInfo.environment["SWIFTCI_DISABLE_SDK_DEPENDENT_TESTS"] ==
         .testTarget(
             name: "CommandsTests",
             dependencies: [
-                "swift-build",
-                "swift-package",
-                "swift-test",
-                "swift-run",
+                "swift-package-manager",
                 "Basics",
                 "Build",
                 "Commands",

Sources/Commands/SwiftBuildTool.swift

@@ -95,7 +95,7 @@ struct BuildToolOptions: ParsableArguments {
 }
 
 /// swift-build tool namespace
-public struct SwiftBuildTool: SwiftCommand {
+public struct SwiftBuildTool: AsyncSwiftCommand {
     public static var configuration = CommandConfiguration(
         commandName: "build",
         _superCommandName: "swift",
@@ -110,7 +110,7 @@ public struct SwiftBuildTool: SwiftCommand {
     @OptionGroup()
     var options: BuildToolOptions
 
-    public func run(_ swiftTool: SwiftTool) throws {
+    public func run(_ swiftTool: SwiftTool) async throws {
         if options.shouldPrintBinPath {
             return try print(swiftTool.productsBuildParameters.buildPath.description)
         }

Sources/SPMTestSupport/SwiftPMProduct.swift

@@ -29,7 +29,7 @@ public enum SwiftPM {
 
 extension SwiftPM {
     /// Executable name.
-    private var executableName: RelativePath {
+    private var executableName: String {
         switch self {
         case .Build:
             return "swift-build"
@@ -45,7 +45,7 @@ extension SwiftPM {
     }
 
     public var xctestBinaryPath: AbsolutePath {
-        Self.xctestBinaryPath(for: executableName)
+        Self.xctestBinaryPath(for: RelativePath("swift-package-manager"))
     }
 
     public static func xctestBinaryPath(for executableName: RelativePath) -> AbsolutePath {
@@ -114,11 +114,12 @@ extension SwiftPM {
 #endif
         // FIXME: We use this private environment variable hack to be able to
         // create special conditions in swift-build for swiftpm tests.
-        environment["SWIFTPM_TESTS_MODULECACHE"] = xctestBinaryPath.parentDirectory.pathString
-        
+        environment["SWIFTPM_TESTS_MODULECACHE"] = self.xctestBinaryPath.parentDirectory.pathString
+
         // Unset the internal env variable that allows skipping certain tests.
         environment["_SWIFTPM_SKIP_TESTS_LIST"] = nil
-        
+        environment["SWIFTPM_EXEC_NAME"] = self.executableName
+
         for (key, value) in env ?? [:] {
             environment[key] = value
         }

Sources/swift-build/CMakeLists.txt

@@ -7,9 +7,12 @@
 # See http://swift.org/CONTRIBUTORS.txt for Swift project authors
 
 add_executable(swift-build
-    main.swift)
+    Entrypoint.swift)
 target_link_libraries(swift-build PRIVATE
     Commands)
 
+target_compile_options(swift-build PRIVATE
+  -parse-as-library)
+
 install(TARGETS swift-build
   DESTINATION bin)

Sources/swift-build/main.swift renamed to Sources/swift-build/Entrypoint.swift

@@ -12,4 +12,9 @@
 
 import Commands
 
-SwiftBuildTool.main()
+@main
+struct Entrypoint {
+    static func main() async {
+        await SwiftBuildTool.main()
+    }
+}

Sources/swift-package-manager/SwiftPM.swift

@@ -17,17 +17,22 @@ import PackageCollectionsTool
 import PackageRegistryTool
 
 let firstArg = CommandLine.arguments[0]
-let execName = (try? AbsolutePath(validating: firstArg).basenameWithoutExt) ??
+let baseNameWithoutExtension = (try? AbsolutePath(validating: firstArg).basenameWithoutExt) ??
     (try? RelativePath(validating: firstArg).basenameWithoutExt)
 
 @main
 struct SwiftPM {
     static func main() async {
+        await main(execName: baseNameWithoutExtension)
+    }
+
+    @discardableResult
+    private static func main(execName: String?) async -> Bool {
         switch execName {
         case "swift-package":
             await SwiftPackageTool.main()
         case "swift-build":
-            SwiftBuildTool.main()
+            await SwiftBuildTool.main()
         case "swift-experimental-sdk":
             await SwiftSDKTool.main()
         case "swift-test":
@@ -39,7 +44,14 @@ struct SwiftPM {
         case "swift-package-registry":
             await SwiftPackageRegistryTool.main()
         default:
-            fatalError("swift-package-manager launched with unexpected name: \(execName ?? "(unknown)")")
+            // Workaround a bug in Swift 5.9, where multiple executables with an `async` main entrypoint can't be linked
+            // into the same test bundle. We're then linking single `swift-package-manager` binary instead and passing
+            // executable name via `SWIFTPM_EXEC_NAME`.
+            if await !main(execName: EnvironmentVariables.process()["SWIFTPM_EXEC_NAME"]) {
+                fatalError("swift-package-manager launched with unexpected name: \(execName ?? "(unknown)")")
+            }
         }
+
+        return true
     }
 }