1 files changed, 64 insertions, 4 deletions

diff --git a/src/os/types_windows.go b/src/os/types_windows.go
index 9a3d508783..6b9fef6c12 100644
--- a/src/os/types_windows.go
+++ b/src/os/types_windows.go
@@ -16,7 +16,7 @@ import (
 type fileStat struct {
 	name string
 
-	// from ByHandleFileInformation, Win32FileAttributeData and Win32finddata
+	// from ByHandleFileInformation, Win32FileAttributeData, Win32finddata, and GetFileInformationByHandleEx
 	FileAttributes uint32
 	CreationTime   syscall.Filetime
 	LastAccessTime syscall.Filetime
@@ -24,7 +24,7 @@ type fileStat struct {
 	FileSizeHigh   uint32
 	FileSizeLow    uint32
 
-	// from Win32finddata
+	// from Win32finddata and GetFileInformationByHandleEx
 	ReparseTag uint32
 
 	// what syscall.GetFileType returns
@@ -80,6 +80,40 @@ func newFileStatFromGetFileInformationByHandle(path string, h syscall.Handle) (f
 	}, nil
 }
 
+// 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 {
+	// The FILE_ID_BOTH_DIR_INFO MSDN documentations isn't completely correct.
+	// FileAttributes can contain any file attributes that is currently set on the file,
+	// not just the ones documented.
+	// EaSize contains the reparse tag if the file is a reparse point.
+	return &fileStat{
+		FileAttributes: d.FileAttributes,
+		CreationTime:   d.CreationTime,
+		LastAccessTime: d.LastAccessTime,
+		LastWriteTime:  d.LastWriteTime,
+		FileSizeHigh:   uint32(d.EndOfFile >> 32),
+		FileSizeLow:    uint32(d.EndOfFile),
+		ReparseTag:     d.EaSize,
+		idxhi:          uint32(d.FileID >> 32),
+		idxlo:          uint32(d.FileID),
+	}
+}
+
+// newFileStatFromFileFullDirInfo copies all required information
+// from windows.FILE_FULL_DIR_INFO d into the newly created fileStat.
+func newFileStatFromFileFullDirInfo(d *windows.FILE_FULL_DIR_INFO) *fileStat {
+	return &fileStat{
+		FileAttributes: d.FileAttributes,
+		CreationTime:   d.CreationTime,
+		LastAccessTime: d.LastAccessTime,
+		LastWriteTime:  d.LastWriteTime,
+		FileSizeHigh:   uint32(d.EndOfFile >> 32),
+		FileSizeLow:    uint32(d.EndOfFile),
+		ReparseTag:     d.EaSize,
+	}
+}
+
 // newFileStatFromWin32finddata copies all required information
 // from syscall.Win32finddata d into the newly created fileStat.
 func newFileStatFromWin32finddata(d *syscall.Win32finddata) *fileStat {
@@ -101,6 +135,16 @@ func newFileStatFromWin32finddata(d *syscall.Win32finddata) *fileStat {
 	return fs
 }
 
+// isReparseTagNameSurrogate determines whether a tag's associated
+// reparse point is a surrogate for another named entity (for example, a mounted folder).
+//
+// See https://learn.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-isreparsetagnamesurrogate
+// and https://learn.microsoft.com/en-us/windows/win32/fileio/reparse-point-tags.
+func (fs *fileStat) isReparseTagNameSurrogate() bool {
+	// True for IO_REPARSE_TAG_SYMLINK and IO_REPARSE_TAG_MOUNT_POINT.
+	return fs.ReparseTag&0x20000000 != 0
+}
+
 func (fs *fileStat) isSymlink() bool {
 	// As of https://go.dev/cl/86556, we treat MOUNT_POINT reparse points as
 	// symlinks because otherwise certain directory junction tests in the
@@ -141,7 +185,23 @@ func (fs *fileStat) Mode() (m FileMode) {
 		m |= ModeDevice | ModeCharDevice
 	}
 	if fs.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT != 0 && m&ModeType == 0 {
-		m |= ModeIrregular
+		if fs.ReparseTag == windows.IO_REPARSE_TAG_DEDUP {
+			// If the Data Deduplication service is enabled on Windows Server, its
+			// Optimization job may convert regular files to IO_REPARSE_TAG_DEDUP
+			// whenever that job runs.
+			//
+			// However, DEDUP reparse points remain similar in most respects to
+			// regular files: they continue to support random-access reads and writes
+			// of persistent data, and they shouldn't add unexpected latency or
+			// unavailability in the way that a network filesystem might.
+			//
+			// Go programs may use ModeIrregular to filter out unusual files (such as
+			// raw device files on Linux, POSIX FIFO special files, and so on), so
+			// to avoid files changing unpredictably from regular to irregular we will
+			// consider DEDUP files to be close enough to regular to treat as such.
+		} else {
+			m |= ModeIrregular
+		}
 	}
 	return m
 }
@@ -171,7 +231,7 @@ func (fs *fileStat) loadFileId() error {
 	}
 	var path string
 	if fs.appendNameToPath {
-		path = fs.path + `\` + fs.name
+		path = fixLongPath(fs.path + `\` + fs.name)
 	} else {
 		path = fs.path
 	}