os: use FindFirstFile when GetFileAttributesEx fails in Stat

Fixes #15355

Change-Id: Idbab7a627c5de249bb62d519c5a47f3d2f6c82a7
Reviewed-on: https://go-review.googlesource.com/22796Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/internal/syscall/windows/syscall_windows.go

@@ -7,6 +7,7 @@ package windows
 import "syscall"
 
 const (
+	ERROR_SHARING_VIOLATION      syscall.Errno = 32
 	ERROR_NO_UNICODE_TRANSLATION syscall.Errno = 1113
 )
 

src/os/os_windows_test.go

@@ -630,3 +630,14 @@ func TestReadStdin(t *testing.T) {
 		}
 	}
 }
+
+func TestStatPagefile(t *testing.T) {
+	_, err := os.Stat(`c:\pagefile.sys`)
+	if err == nil {
+		return
+	}
+	if os.IsNotExist(err) {
+		t.Skip(`skipping because c:\pagefile.sys is not found`)
+	}
+	t.Fatal(err)
+}

src/os/stat_windows.go

@@ -5,6 +5,7 @@
 package os
 
 import (
+	"internal/syscall/windows"
 	"syscall"
 	"unsafe"
 )
@@ -95,7 +96,23 @@ func Lstat(name string) (FileInfo, error) {
 	}
 	e = syscall.GetFileAttributesEx(namep, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fs.sys)))
 	if e != nil {
-		return nil, &PathError{"GetFileAttributesEx", name, e}
+		if e != windows.ERROR_SHARING_VIOLATION {
+			return nil, &PathError{"GetFileAttributesEx", name, e}
+		}
+		// try FindFirstFile now that GetFileAttributesEx failed
+		var fd syscall.Win32finddata
+		h, e2 := syscall.FindFirstFile(namep, &fd)
+		if e2 != nil {
+			return nil, &PathError{"FindFirstFile", name, e}
+		}
+		syscall.FindClose(h)
+
+		fs.sys.FileAttributes = fd.FileAttributes
+		fs.sys.CreationTime = fd.CreationTime
+		fs.sys.LastAccessTime = fd.LastAccessTime
+		fs.sys.LastWriteTime = fd.LastWriteTime
+		fs.sys.FileSizeHigh = fd.FileSizeHigh
+		fs.sys.FileSizeLow = fd.FileSizeLow
 	}
 	fs.path = name
 	if !isAbs(fs.path) {