Work around miscompilation of entry point function on Windows with Swift 5.10. (#381)

This PR works around two apparent miscompiles of the entry point
function added with #360. These workarounds are only necessary on
Windows when using the Swift 5.10 compiler (I've seen no indication of
issues on other platforms or with the Swift 6 compiler.) We can revert
this change once we no longer provide any support for the Swift 5.10
toolchain.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/EntryPoints/ABIEntryPoint.swift

@@ -60,12 +60,12 @@ public typealias ABIEntryPoint_v0 = @Sendable (
 @usableFromInline
 func abiEntryPoint_v0(_ outEntryPoint: UnsafeMutableRawPointer) {
   outEntryPoint.initializeMemory(as: ABIEntryPoint_v0.self) { argumentsJSON, eventHandler in
-    let args = try! argumentsJSON.map { argumentsJSON in
+    var args = try! argumentsJSON.map { argumentsJSON in
       try JSON.decode(__CommandLineArguments_v0.self, from: argumentsJSON)
     }
 
     let eventHandler = eventHandlerForStreamingEvents_v0(to: eventHandler)
-    return await entryPoint(passing: args, eventHandler: eventHandler)
+    return await entryPoint(passing: &args, eventHandler: eventHandler)
   }
 }
 #endif

Sources/Testing/EntryPoints/EntryPoint.swift

@@ -26,7 +26,8 @@ private import TestingInternals
 /// - Warning: This function is used by Swift Package Manager. Do not call it
 ///   directly.
 @_disfavoredOverload public func __swiftPMEntryPoint(passing args: __CommandLineArguments_v0? = nil) async -> CInt {
-  await entryPoint(passing: args, eventHandler: nil)
+  var args = args
+  return await entryPoint(passing: &args, eventHandler: nil)
 }
 
 /// The entry point to the testing library used by Swift Package Manager.
@@ -55,12 +56,17 @@ public func __swiftPMEntryPoint(passing args: __CommandLineArguments_v0? = nil)
 ///   - args: A previously-parsed command-line arguments structure to interpret.
 ///     If `nil`, a new instance is created from the command-line arguments to
 ///     the current process.
-///   - eventHandler: An event handler
-func entryPoint(passing args: __CommandLineArguments_v0?, eventHandler: Event.Handler?) async -> CInt {
+///   - eventHandler: An event handler.
+///
+/// - Bug: This function takes `args` as a pointer in order to work around a
+///   code generation bug when using the Swift 5.10 toolchain on Windows. This
+///   function should be updated to take `args` directly when Swift 5.10
+///   support is removed.
+func entryPoint(passing args: UnsafePointer<__CommandLineArguments_v0?>, eventHandler: Event.Handler?) async -> CInt {
   let exitCode = Locked(rawValue: EXIT_SUCCESS)
 
   do {
-    let args = try args ?? parseCommandLineArguments(from: CommandLine.arguments())
+    let args = try args.pointee ?? parseCommandLineArguments(from: CommandLine.arguments())
     if args.listTests {
       for testID in await listTestsForSwiftPM(Test.all) {
 #if SWT_TARGET_OS_APPLE && !SWT_NO_FILE_IO

Sources/Testing/EntryPoints/XCTestScaffold.swift

@@ -144,8 +144,9 @@ public enum XCTestScaffold: Sendable {
       functionName[...]
     }
     args.xcTestCaseHostIdentifier = "\(typeName)/\(functionName)"
+    var argsCopy: __CommandLineArguments_v0? = args
 
-    _ = await entryPoint(passing: args) { event, _ in
+    _ = await entryPoint(passing: &argsCopy) { event, _ in
       guard case let .issueRecorded(issue) = event.kind else {
         return
       }

Tests/TestingTests/ABIEntryPointTests.swift

@@ -28,9 +28,11 @@ struct ABIEntryPointTests {
       }
     )
 #endif
-    let abiEntryPoint = withUnsafeTemporaryAllocation(of: ABIEntryPoint_v0.self, capacity: 1) { buffer in
-      copyABIEntryPoint(buffer.baseAddress!)
-      return buffer.baseAddress!.move()
+    let abiEntryPoint = UnsafeMutablePointer<ABIEntryPoint_v0>.allocate(capacity: 1)
+    copyABIEntryPoint(abiEntryPoint)
+    defer {
+      abiEntryPoint.deinitialize(count: 1)
+      abiEntryPoint.deallocate()
     }
 
     // Construct arguments and convert them to JSON.
@@ -46,7 +48,7 @@ struct ABIEntryPointTests {
     }
 
     // Call the entry point function.
-    let result = await abiEntryPoint(.init(argumentsJSON)) { eventAndContextJSON in
+    let result = await abiEntryPoint.pointee(.init(argumentsJSON)) { eventAndContextJSON in
       let eventAndContext = try! JSON.decode(EventAndContextSnapshot.self, from: eventAndContextJSON)
       _ = (eventAndContext.event, eventAndContext.eventContext)
     }