os: return an error when the argument of Mkdir on Windows is os.DevNull

Test added.

Fixes #24556

Change-Id: I4d1cd4513142edeea1a983fbfde46c2fccecab2a
Reviewed-on: https://go-review.googlesource.com/c/go/+/186139
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

1 files changed, 2 insertions, 20 deletions

diff --git a/src/os/stat_windows.go b/src/os/stat_windows.go
index fd22ef21ab..3e0e0a59ed 100644
--- a/src/os/stat_windows.go
+++ b/src/os/stat_windows.go
@@ -10,24 +10,6 @@ import (
 	"unsafe"
 )
 
-// isNulName reports whether name is NUL file name.
-// For example, it returns true for both "NUL" and "nul".
-func isNulName(name string) bool {
-	if len(name) != 3 {
-		return false
-	}
-	if name[0] != 'n' && name[0] != 'N' {
-		return false
-	}
-	if name[1] != 'u' && name[1] != 'U' {
-		return false
-	}
-	if name[2] != 'l' && name[2] != 'L' {
-		return false
-	}
-	return true
-}
-
 // Stat returns the FileInfo structure describing file.
 // If there is an error, it will be of type *PathError.
 func (file *File) Stat() (FileInfo, error) {
@@ -39,7 +21,7 @@ func (file *File) Stat() (FileInfo, error) {
 		// I don't know any better way to do that for directory
 		return Stat(file.dirinfo.path)
 	}
-	if isNulName(file.name) {
+	if isWindowsNulName(file.name) {
 		return &devNullStat, nil
 	}
 
@@ -65,7 +47,7 @@ func stat(funcname, name string, createFileAttrs uint32) (FileInfo, error) {
 	if len(name) == 0 {
 		return nil, &PathError{funcname, name, syscall.Errno(syscall.ERROR_PATH_NOT_FOUND)}
 	}
-	if isNulName(name) {
+	if isWindowsNulName(name) {
 		return &devNullStat, nil
 	}
 	namep, err := syscall.UTF16PtrFromString(fixLongPath(name))