local: when using -l fix setting modification times of symlinks #1152

Before this change it was setting the modification times of the things
that the symlinks pointed to.

Note that this is only implemented for unix style OSes.  Other OSes
will not attempt to set the modification time of a symlink.

backend/local/lchtimes.go

@@ -0,0 +1,20 @@
+// +build windows plan9
+
+package local
+
+import (
+	"time"
+)
+
+const haveLChtimes = false
+
+// lChtimes changes the access and modification times of the named
+// link, similar to the Unix utime() or utimes() functions.
+//
+// The underlying filesystem may truncate or round the values to a
+// less precise time unit.
+// If there is an error, it will be of type *PathError.
+func lChtimes(name string, atime time.Time, mtime time.Time) error {
+	// Does nothing
+	return nil
+}

backend/local/lchtimes_unix.go

@@ -0,0 +1,28 @@
+// +build !windows,!plan9
+
+package local
+
+import (
+	"os"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+const haveLChtimes = true
+
+// lChtimes changes the access and modification times of the named
+// link, similar to the Unix utime() or utimes() functions.
+//
+// The underlying filesystem may truncate or round the values to a
+// less precise time unit.
+// If there is an error, it will be of type *PathError.
+func lChtimes(name string, atime time.Time, mtime time.Time) error {
+	var utimes [2]unix.Timespec
+	utimes[0] = unix.NsecToTimespec(atime.UnixNano())
+	utimes[1] = unix.NsecToTimespec(mtime.UnixNano())
+	if e := unix.UtimesNanoAt(unix.AT_FDCWD, name, utimes[0:], unix.AT_SYMLINK_NOFOLLOW); e != nil {
+		return &os.PathError{Op: "lchtimes", Path: name, Err: e}
+	}
+	return nil
+}

backend/local/local.go

@@ -744,7 +744,12 @@ func (o *Object) ModTime() time.Time {
 
 // SetModTime sets the modification time of the local fs object
 func (o *Object) SetModTime(modTime time.Time) error {
-	err := os.Chtimes(o.path, modTime, modTime)
+	var err error
+	if o.translatedLink {
+		err = lChtimes(o.path, modTime, modTime)
+	} else {
+		err = os.Chtimes(o.path, modTime, modTime)
+	}
 	if err != nil {
 		return err
 	}