Changes after comments from Saleem.

Use idiomatic Swift notation, not `Optional<Bool>`.

Prefer Win32 APIs to UCRT APIs.

rdar://125087707

Author: al45tair

Sources/System/FilePath/FilePathTemp.swift

@@ -29,8 +29,8 @@ internal func getTemporaryDirectory() throws -> FilePath {
                                            capacity: Int(MAX_PATH) + 1) {
     buffer in
 
-    let count = GetTempPath2W(DWORD(buffer.count), buffer.baseAddress)
-    if count == 0 {
+    guard let count = GetTempPath2W(DWORD(buffer.count), buffer.baseAddress),
+          count != 0 else {
       throw Errno(windowsError: GetLastError())
     }
 
@@ -116,7 +116,7 @@ internal func getTemporaryDirectory() throws -> FilePath {
   while true {
     let path: FilePath? = withUnsafeTemporaryAllocation(
       of: CInterop.PlatformChar.self,
-      capacity: 1024) { buffer in
+      capacity: capacity) { buffer in
       let len = system_confstr(SYSTEM_CS_DARWIN_USER_TEMP_DIR,
                                buffer.baseAddress!,
                                buffer.count)

Sources/System/Internals/Mocking.swift

@@ -110,7 +110,7 @@ private var contextualMockingEnabled: Bool {
 extension MockingDriver {
   internal static var enabled: Bool { mockingEnabled }
 
-  internal static var forceWindowsPaths: Optional<Bool> {
+  internal static var forceWindowsPaths: Bool? {
     currentMockingDriver?.forceWindowsSyntaxForPaths
   }
 }
@@ -128,7 +128,7 @@ internal var mockingEnabled: Bool {
 }
 
 @inline(__always)
-internal var forceWindowsPaths: Optional<Bool> {
+internal var forceWindowsPaths: Bool? {
   #if !ENABLE_MOCKING
   return false
   #else

Sources/System/Internals/WindowsSyscallAdapters.swift

@@ -160,14 +160,25 @@ internal func mkdir(
   _ path: UnsafePointer<CInterop.PlatformChar>,
   _ mode: CInterop.Mode
 ) -> CInt {
-  return _wmkdir(path)
+  // TODO: Read/write permissions (these need mapping to a SECURITY_DESCRIPTOR).
+  if !CreateDirectoryW(path, nil) {
+    ucrt._set_errno(mapWindowsErrorToErrno(GetLastError()))
+    return -1
+  }
+
+  return 0;
 }
 
 @inline(__always)
 internal func rmdir(
   _ path: UnsafePointer<CInterop.PlatformChar>
 ) -> CInt {
-  return _wrmdir(path)
+  if !RemoveDirectoryW(path) {
+    ucrt._set_errno(mapWindowsErrorToErrno(GetLastError()))
+    return -1
+  }
+
+  return 0;
 }
 
 @usableFromInline