Expand use of Win32Error

Have its string representation print the actual error message for improved debuggability.

Author: jakepetroules

Sources/SWBUtil/CMakeLists.txt

@@ -100,6 +100,7 @@ add_library(SWBUtil
   VFS.swift
   WaitCondition.swift
   WeakRef.swift
+  Win32Error.swift
   XCBuildDataArchive.swift
   Xcode.swift)
 set_target_properties(SWBUtil PROPERTIES

Sources/SWBUtil/FSProxy.swift

@@ -621,15 +621,15 @@ class LocalFS: FSProxy, @unchecked Sendable {
                         DWORD(OPEN_EXISTING), DWORD(FILE_FLAG_BACKUP_SEMANTICS), nil)
         }
         if handle == INVALID_HANDLE_VALUE {
-            throw StubError.error("Failed to update file time")
+            throw Win32Error(GetLastError())
         }
         try handle.closeAfter {
             var ft = FILETIME()
             var st = SYSTEMTIME()
             GetSystemTime(&st)
             SystemTimeToFileTime(&st, &ft)
             if !SetFileTime(handle, nil, &ft, &ft) {
-                throw StubError.error("Failed to update file time")
+                Win32Error(GetLastError())
             }
         }
         #else
@@ -648,7 +648,7 @@ class LocalFS: FSProxy, @unchecked Sendable {
                         DWORD(OPEN_EXISTING), DWORD(FILE_FLAG_BACKUP_SEMANTICS), nil)
         }
         if handle == INVALID_HANDLE_VALUE {
-            throw StubError.error("Failed to update file time")
+            throw Win32Error(GetLastError())
         }
         try handle.closeAfter {
             // Number of 100ns intervals between 1601 and 1970 epochs
@@ -663,7 +663,7 @@ class LocalFS: FSProxy, @unchecked Sendable {
             ft.dwLowDateTime = timeInt.LowPart
             ft.dwHighDateTime = timeInt.HighPart
             if !SetFileTime(handle, nil, &ft, &ft) {
-                throw StubError.error("Failed to update file time")
+                throw Win32Error(GetLastError())
             }
         }
         #else
@@ -887,7 +887,7 @@ class LocalFS: FSProxy, @unchecked Sendable {
             return try withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(dwLength)) {
                 guard GetFinalPathNameByHandleW(handle, $0.baseAddress!, DWORD($0.count),
                                                 DWORD(FILE_NAME_NORMALIZED)) == dwLength - 1 else {
-                    throw StubError.error("GetFinalPathNameByHandleW failed")
+                    throw Win32Error(GetLastError())
                 }
                 let path = String(platformString: $0.baseAddress!)
                 // Drop UNC prefix if present
@@ -1643,13 +1643,6 @@ extension HANDLE {
         }
     }
 }
-
-fileprivate struct Win32Error: Error {
-    let error: DWORD
-    init(_ error: DWORD) {
-        self.error = error
-    }
-}
 #endif
 
 extension FileDescriptor {

Sources/SWBUtil/Library.swift

@@ -34,7 +34,7 @@ public enum Library: Sendable {
     public static func open(_ path: Path) throws -> LibraryHandle {
         #if os(Windows)
         guard let handle = path.withPlatformString(LoadLibraryW) else {
-            throw LibraryOpenError(message: "LoadLibraryW returned \(GetLastError())")
+            throw LibraryOpenError(message: Win32Error(GetLastError()).description)
         }
         return LibraryHandle(rawValue: handle)
         #else

Sources/SWBUtil/Win32Error.swift

@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#if os(Windows)
+public import WinSDK
+import Foundation
+
+public struct Win32Error: Error, CustomStringConvertible {
+    public let error: DWORD
+
+    public init(_ error: DWORD) {
+        self.error = error
+    }
+
+    public var description: String {
+        let flags: DWORD = DWORD(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS)
+        var buffer: UnsafeMutablePointer<WCHAR>?
+        let length: DWORD = withUnsafeMutablePointer(to: &buffer) {
+            $0.withMemoryRebound(to: WCHAR.self, capacity: 2) {
+                FormatMessageW(flags, nil, error, 0, $0, 0, nil)
+            }
+        }
+        guard let buffer, length > 0 else {
+            return "Win32 Error Code \(error)"
+        }
+        defer { LocalFree(buffer) }
+        return String(decodingCString: buffer, as: UTF16.self).trimmingCharacters(in: .whitespacesAndNewlines)
+    }
+}
+#endif

Tests/SwiftBuildTests/ConsoleCommands/CLIConnection.swift

@@ -165,11 +165,11 @@ final class CLIConnection {
     static func terminate(processIdentifier: Int32) throws {
         #if os(Windows)
         guard let proc = OpenProcess(DWORD(PROCESS_TERMINATE), false, DWORD(processIdentifier)) else {
-            throw StubError.error("OpenProcess failed with error \(GetLastError())")
+            throw Win32Error(GetLastError())
         }
         defer { CloseHandle(proc) }
         if !TerminateProcess(proc, UINT(0xC0000000 | DWORD(9))) {
-            throw StubError.error("TerminateProcess returned \(GetLastError())")
+            throw Win32Error(GetLastError())
         }
         #else
         if SWBLibc.kill(processIdentifier, SIGKILL) != 0 {
@@ -317,7 +317,7 @@ fileprivate func swiftRuntimePath() throws -> Path? {
     let name = "swiftCore.dll"
     return try name.withCString(encodedAs: CInterop.PlatformUnicodeEncoding.self) { wName in
         guard let handle = GetModuleHandleW(wName) else {
-            throw POSIXError(errno, context: "GetModuleHandleW", name)
+            throw Win32Error(GetLastError())
         }
 
         var capacity = MAX_PATH
@@ -327,7 +327,7 @@ fileprivate func swiftRuntimePath() throws -> Path? {
                 let dwLength = GetModuleFileNameW(handle, $0.baseAddress!, DWORD($0.count))
                 switch dwLength {
                 case 0:
-                    throw POSIXError(errno, context: "GetModuleFileNameW", String(dwLength))
+                    throw Win32Error(GetLastError())
                 default:
                     if GetLastError() == ERROR_INSUFFICIENT_BUFFER {
                         capacity *= 2
@@ -348,12 +348,12 @@ fileprivate func systemRoot() throws -> Path? {
     #if os(Windows)
     let dwLength: DWORD = GetWindowsDirectoryW(nil, 0)
     if dwLength == 0 {
-        throw POSIXError(errno, context: "GetWindowsDirectoryW")
+        throw Win32Error(GetLastError())
     }
     return try withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(dwLength)) {
         switch GetWindowsDirectoryW($0.baseAddress!, DWORD($0.count)) {
         case 0:
-            throw POSIXError(errno, context: "GetWindowsDirectoryW", String($0.count))
+            throw Win32Error(GetLastError())
         default:
             return Path(String(decodingCString: $0.baseAddress!, as: CInterop.PlatformUnicodeEncoding.self))
         }

Tests/SwiftBuildTests/ConsoleCommands/ServiceConsoleTests.swift

@@ -131,12 +131,12 @@ extension Processes {
         let promise = Promise<Void, any Error>()
         #if os(Windows)
         guard let proc: HANDLE = OpenProcess(SYNCHRONIZE, false, DWORD(pid)) else {
-            throw StubError.error("OpenProcess failed with error \(GetLastError())")
+            throw Win32Error(GetLastError())
         }
         defer { CloseHandle(proc) }
         Thread.detachNewThread {
             if WaitForSingleObject(proc, INFINITE) == WAIT_FAILED {
-                promise.fail(throwing: StubError.error("WaitForSingleObject failed with error \(GetLastError())"))
+                promise.fail(throwing: Win32Error(GetLastError()))
                 return
             }
             promise.fulfill(with: ())