windows: fix hang while reading from directory

changelog/unreleased/pull-21796

@@ -1,6 +1,8 @@
 Change: Update dependencies and require Go 1.25 or newer
 
 We have updated all dependencies. Restic now requires Go 1.25 or newer to build.
+In addition, the Windows build of restic using Go 1.26 was fixed.
 
 https://github.com/restic/restic/pull/21796
 https://github.com/restic/restic/pull/5619
+https://github.com/restic/restic/issues/21791

internal/fs/const_unix.go

@@ -9,3 +9,9 @@ const O_NOFOLLOW int = syscall.O_NOFOLLOW
 
 // O_DIRECTORY instructs the kernel to only open directories.
 const O_DIRECTORY int = syscall.O_DIRECTORY
+
+// sanitizeFlags cleans up flags that conflict with actual OS API flags.
+// Must only be used right before passing the flags to the go stdlib.
+func sanitizeFlags(flags int) int {
+	return flags
+}

internal/fs/const_windows.go

@@ -11,3 +11,9 @@ const O_NOFOLLOW int = 0x40000000
 
 // O_DIRECTORY is a noop on Windows.
 const O_DIRECTORY int = 0
+
+// sanitizeFlags cleans up flags that conflict with actual OS API flags
+// Must only be used right before passing the flags to the go stdlib.
+func sanitizeFlags(flags int) int {
+	return flags &^ O_NOFOLLOW
+}

internal/fs/file.go

@@ -3,7 +3,6 @@ package fs
 import (
 	"fmt"
 	"os"
-	"runtime"
 )
 
 // MkdirAll creates a directory named path, along with any necessary parents,
@@ -48,10 +47,7 @@ func Lstat(name string) (os.FileInfo, error) {
 // methods on the returned File can be used for I/O.
 // If there is an error, it will be of type *PathError.
 func OpenFile(name string, flag int, perm os.FileMode) (*os.File, error) {
-	if runtime.GOOS == "windows" {
-		flag &^= O_NOFOLLOW
-	}
-	return os.OpenFile(fixpath(name), flag, perm)
+	return os.OpenFile(fixpath(name), sanitizeFlags(flag), perm)
 }
 
 // IsAccessDenied checks if the error is due to permission error.

internal/fs/fs_local.go

@@ -106,7 +106,7 @@ func newLocalFile(name string, flag int, metadataOnly bool) (*localFile, error)
 	var f *os.File
 	if !metadataOnly {
 		var err error
-		f, err = os.OpenFile(fixpath(name), flag, 0)
+		f, err = os.OpenFile(fixpath(name), sanitizeFlags(flag), 0)
 		if err != nil {
 			return nil, err
 		}