Allow swift-build to have async entrypoint (#7369)

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.

This change is a prerequisite for
#7367.

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/SwiftBuildCommand.swift

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

Sources/Commands/SwiftRunCommand.swift

@@ -90,7 +90,7 @@ struct RunCommandOptions: ParsableArguments {
 }
 
 /// swift-run command namespace
-public struct SwiftRunCommand: SwiftCommand {
+public struct SwiftRunCommand: AsyncSwiftCommand {
     public static var configuration = CommandConfiguration(
         commandName: "run",
         _superCommandName: "swift",
@@ -109,7 +109,7 @@ public struct SwiftRunCommand: SwiftCommand {
         return .init(wantsREPLProduct: options.mode == .repl)
     }
 
-    public func run(_ swiftCommandState: SwiftCommandState) throws {
+    public func run(_ swiftCommandState: SwiftCommandState) async throws {
         if options.shouldBuildTests && options.shouldSkipBuild {
             swiftCommandState.observabilityScope.emit(
               .mutuallyExclusiveArgumentsError(arguments: ["--build-tests", "--skip-build"])
@@ -284,9 +284,20 @@ public struct SwiftRunCommand: SwiftCommand {
     /// A safe wrapper of TSCBasic.exec.
     private func execute(path: String, args: [String]) throws -> Never {
         #if !os(Windows)
-        // On platforms other than Windows, signal(SIGINT, SIG_IGN) is used for handling SIGINT by DispatchSourceSignal,
-        // but this process is about to be replaced by exec, so SIG_IGN must be returned to default.
-        signal(SIGINT, SIG_DFL)
+        // Dispatch will disable almost all asynchronous signals on its worker threads, and this is called from `async`
+        // context. To correctly `exec` a freshly built binary, we will need to:
+        // 1. reset the signal masks
+        for i in 1..<NSIG {
+            signal(i, SIG_DFL)
+        }
+        var sig_set_all = sigset_t()
+        sigfillset(&sig_set_all)
+        sigprocmask(SIG_UNBLOCK, &sig_set_all, nil)
+        
+        // 2. close all file descriptors.
+        for i in 3..<getdtablesize() {
+            close(i)
+        }
         #endif
 
         try TSCBasic.exec(path: path, args: args)

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

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

Sources/swift-package-manager/SwiftPM.swift

@@ -17,29 +17,43 @@ import PackageCollectionsCommand
 import PackageRegistryCommand
 
 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 {
+        // 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 baseNameWithoutExtension == "swift-package-manager" {
+            await main(execName: EnvironmentVariables.process()["SWIFTPM_EXEC_NAME"])
+        } else {
+            await main(execName: baseNameWithoutExtension)
+        }
+    }
+
+    @discardableResult
+    private static func main(execName: String?) async -> Bool {
         switch execName {
         case "swift-package":
             await SwiftPackageCommand.main()
         case "swift-build":
-            SwiftBuildCommand.main()
+            await SwiftBuildCommand.main()
         case "swift-experimental-sdk":
             await SwiftSDKCommand.main()
         case "swift-test":
             SwiftTestCommand.main()
         case "swift-run":
-            SwiftRunCommand.main()
+            await SwiftRunCommand.main()
         case "swift-package-collection":
             await PackageCollectionsCommand.main()
         case "swift-package-registry":
             await PackageRegistryCommand.main()
         default:
             fatalError("swift-package-manager launched with unexpected name: \(execName ?? "(unknown)")")
         }
+
+        return true
     }
 }

Sources/swift-run/CMakeLists.txt

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

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

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

Tests/CommandsTests/RunCommandTests.swift

@@ -16,6 +16,7 @@ import SPMTestSupport
 import XCTest
 
 import class TSCBasic.Process
+import enum TSCBasic.ProcessEnv
 
 final class RunCommandTests: CommandsTestCase {
     private func execute(
@@ -121,8 +122,12 @@ final class RunCommandTests: CommandsTestCase {
 
             let sync = DispatchGroup()
             let outputHandler = OutputHandler(sync: sync)
+
+            var environmentBlock = ProcessEnv.block
+            environmentBlock["SWIFTPM_EXEC_NAME"] = "swift-run"
             let process = Process(
                 arguments: [SwiftPM.Run.xctestBinaryPath.pathString, "--package-path", fixturePath.pathString],
+                environmentBlock: environmentBlock,
                 outputRedirection: .stream(stdout: outputHandler.handle(bytes:), stderr: outputHandler.handle(bytes:))
             )