cipd: Make it work on Windows.

go/src/infra/tools/cipd/local/rename_windows.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// +build windows
+
+package local
+
+import (
+        "syscall"
+        "unsafe"
+)
+
+// See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365240(v=vs.85).aspx
+
+var (
+        kernel32        = syscall.NewLazyDLL("kernel32.dll")
+        procMoveFileExW = kernel32.NewProc("MoveFileExW")
+)
+
+const (
+        moveFileReplaceExisting = 1
+        moveFileWriteThrough    = 8
+)
+
+func moveFileEx(source, target *uint16, flags uint32) error {
+        ret, _, err := procMoveFileExW.Call(uintptr(unsafe.Pointer(source)), uintptr(unsafe.Pointer(target)), uintptr(flags))
+        if ret == 0 {
+                if err != nil {
+                        return err
+                }
+                return syscall.EINVAL
+        }
+        return nil
+}
+
+func atomicRename(source, target string) error {
+        lpReplacedFileName, err := syscall.UTF16PtrFromString(target)
+        if err != nil {
+                return err
+        }
+        lpReplacementFileName, err := syscall.UTF16PtrFromString(source)
+        if err != nil {
+                return err
+        }
+        return moveFileEx(lpReplacementFileName, lpReplacedFileName, moveFileReplaceExisting|moveFileWriteThrough)
+}