Fix process handle leak on Windows

- Add a missing CloseHandle as part of the process termination handling
- Enable Process tests on Windows

Author: daveinglis

Package.swift

@@ -349,7 +349,7 @@ let package = Package(
                 "FoundationNetworking",
                 "XCTest",
                 "Testing",
-                .target(name: "xdgTestHelper", condition: .when(platforms: [.linux, .android]))
+                .target(name: "xdgTestHelper", condition: .when(platforms: [.linux, .android, .windows]))
             ],
             resources: [
                 .copy("Foundation/Resources")

Sources/Foundation/Process.swift

@@ -1198,10 +1198,21 @@ open class Process: NSObject, @unchecked Sendable {
         }
 
         if let handler = self.terminationHandler {
-            let thread: Thread = Thread { handler(self) }
+            let thread: Thread = Thread {
+                handler(self)
+                self.closeHandle()
+            }
             thread.start()
+        } else {
+            closeHandle()
         }
     }
+    
+    private func closeHandle() {
+#if os(Windows)
+        CloseHandle(self.processHandle)
+#endif
+    }
 }
 
 extension Process {

Tests/Foundation/TestBundle.swift

@@ -43,15 +43,7 @@ internal func testBundleName() -> String {
 }
 
 internal func xdgTestHelperURL() throws -> URL {
-    #if os(Windows)
-    // Adding the xdgTestHelper as a dependency of TestFoundation causes its object files (including the main function) to be linked into the test runner executable as well
-    // While this works on Linux due to special linker functionality, this doesn't work on Windows and results in a collision between the two main symbols
-    // SwiftPM also cannot support depending on this executable (to ensure it is built) without also linking its objects into the test runner
-    // For those reasons, using the xdgTestHelper on Windows is currently unsupported and tests that rely on it must be skipped
-    throw XCTSkip("xdgTestHelper is not supported during testing on Windows (test executables are not supported by SwiftPM on Windows)")
-    #else
     testBundle().bundleURL.deletingLastPathComponent().appendingPathComponent("xdgTestHelper")
-    #endif
 }
 
 

Tests/Foundation/TestFileManager.swift

@@ -1235,6 +1235,9 @@ class TestFileManager : XCTestCase {
     }
 
     func test_fetchXDGPathsFromHelper() throws {
+        #if os(Windows)
+        throw XCTSkip("This test is disabled on Windows, needs investigation.")
+        #endif
         let prefix = NSHomeDirectory() + "/_Foundation_Test_"
 
         let configuration = """

Tests/Foundation/TestProcess.swift

@@ -363,11 +363,13 @@ class TestProcess : XCTestCase {
         process.arguments = ["--cat"]
         _ = try? process.run()
         XCTAssertTrue(process.isRunning)
-        XCTAssertTrue(process.processIdentifier > 0)
+        XCTAssertGreaterThan(process.processIdentifier, 0)
         process.terminate()
         process.waitUntilExit()
         XCTAssertFalse(process.isRunning)
-        XCTAssertTrue(process.processIdentifier > 0)
+        #if !os(Windows) // Since the processHandle is Closed on terminate, this cannot be determined.
+        XCTAssertGreaterThan(process.processIdentifier, 0)
+        #endif
         XCTAssertEqual(process.terminationReason, .uncaughtSignal)
         XCTAssertEqual(process.terminationStatus, SIGTERM)
     }
@@ -635,7 +637,7 @@ class TestProcess : XCTestCase {
             let one: String.Index = directory.index(zero, offsetBy: 1)
             XCTAssertTrue(directory[zero].isLetter)
             XCTAssertEqual(directory[one], ":")
-            directory = "/" + String(directory.dropFirst(2))
+            directory = String(directory.dropFirst(2))
 #endif
             XCTAssertEqual(URL(fileURLWithPath: directory).absoluteURL,
                            URL(fileURLWithPath: "/").absoluteURL)