os: factor out newFileStatFromWin32FileAttributeData

The stat function is quite long on Windows. Simplify it a bit by
factoring out the creation of a fileStat from a Win32FileAttributeData.

This also makes it more consistent with the creation of fileStats
from other sources, which all have their own dedicated functions.

Change-Id: I0443f96d892b70ce7f3b5e92c5049e4e4a240c6c
Reviewed-on: https://go-review.googlesource.com/c/go/+/566435
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/os/stat_windows.go

@@ -33,6 +33,15 @@ func stat(funcname, name string, followSurrogates bool) (FileInfo, error) {
 	// See https://golang.org/issues/19922#issuecomment-300031421 for details.
 	var fa syscall.Win32FileAttributeData
 	err = syscall.GetFileAttributesEx(namep, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
+	if err == nil && fa.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT == 0 {
+		// Not a surrogate for another named entity, because it isn't any kind of reparse point.
+		// The information we got from GetFileAttributesEx is good enough for now.
+		fs := newFileStatFromWin32FileAttributeData(&fa)
+		if err := fs.saveInfoFromPath(name); err != nil {
+			return nil, err
+		}
+		return fs, nil
+	}
 
 	// GetFileAttributesEx fails with ERROR_SHARING_VIOLATION error for
 	// files like c:\pagefile.sys. Use FindFirstFile for such files.
@@ -53,23 +62,6 @@ func stat(funcname, name string, followSurrogates bool) (FileInfo, error) {
 		}
 	}
 
-	if err == nil && fa.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT == 0 {
-		// Not a surrogate for another named entity, because it isn't any kind of reparse point.
-		// The information we got from GetFileAttributesEx is good enough for now.
-		fs := &fileStat{
-			FileAttributes: fa.FileAttributes,
-			CreationTime:   fa.CreationTime,
-			LastAccessTime: fa.LastAccessTime,
-			LastWriteTime:  fa.LastWriteTime,
-			FileSizeHigh:   fa.FileSizeHigh,
-			FileSizeLow:    fa.FileSizeLow,
-		}
-		if err := fs.saveInfoFromPath(name); err != nil {
-			return nil, err
-		}
-		return fs, nil
-	}
-
 	// Use CreateFile to determine whether the file is a name surrogate and, if so,
 	// save information about the link target.
 	// Set FILE_FLAG_BACKUP_SEMANTICS so that CreateFile will create the handle

src/os/types_windows.go

@@ -76,6 +76,19 @@ func newFileStatFromGetFileInformationByHandle(path string, h syscall.Handle) (f
 	}, nil
 }
 
+// newFileStatFromWin32FileAttributeData copies all required information
+// from syscall.Win32FileAttributeData d into the newly created fileStat.
+func newFileStatFromWin32FileAttributeData(d *syscall.Win32FileAttributeData) *fileStat {
+	return &fileStat{
+		FileAttributes: d.FileAttributes,
+		CreationTime:   d.CreationTime,
+		LastAccessTime: d.LastAccessTime,
+		LastWriteTime:  d.LastWriteTime,
+		FileSizeHigh:   d.FileSizeHigh,
+		FileSizeLow:    d.FileSizeLow,
+	}
+}
+
 // newFileStatFromFileIDBothDirInfo copies all required information
 // from windows.FILE_ID_BOTH_DIR_INFO d into the newly created fileStat.
 func newFileStatFromFileIDBothDirInfo(d *windows.FILE_ID_BOTH_DIR_INFO) *fileStat {