selfupdate: abort if updating would discard fuse semantics

cmd/cmount/arch.go

@@ -0,0 +1,7 @@
+package cmount
+
+// ProvidedBy returns true if the rclone build for the given OS
+// provides support for lib/cgo-fuse
+func ProvidedBy(osName string) bool {
+	return osName == "windows" || osName == "darwin"
+}

cmd/cmount/mount.go

@@ -26,7 +26,7 @@ import (
 
 func init() {
 	name := "cmount"
-	cmountOnly := runtime.GOOS == "windows" || runtime.GOOS == "darwin"
+	cmountOnly := ProvidedBy(runtime.GOOS)
 	if cmountOnly {
 		name = "mount"
 	}

cmd/selfupdate/help.go

@@ -37,6 +37,10 @@ your OS) to update these too. This command with the default |--package zip|
 will update only the rclone executable so the local manual may become
 inaccurate after it.
 
+The |rclone mount| command (https://rclone.org/commands/rclone_mount/) may
+or may not support extended FUSE options depending on the build and OS.
+|selfupdate| will refuse to update if the capability would be discarded.
+
 Note: Windows forbids deletion of a currently running executable so this
 command will rename the old executable to 'rclone.old.exe' upon success.
 

cmd/selfupdate/selfupdate.go

@@ -21,9 +21,11 @@ import (
 
 	"github.com/pkg/errors"
 	"github.com/rclone/rclone/cmd"
+	"github.com/rclone/rclone/cmd/cmount"
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config/flags"
 	"github.com/rclone/rclone/fs/fshttp"
+	"github.com/rclone/rclone/lib/buildinfo"
 	"github.com/rclone/rclone/lib/random"
 	"github.com/spf13/cobra"
 
@@ -141,6 +143,17 @@ func InstallUpdate(ctx context.Context, opt *Options) error {
 		return errors.New("--stable and --beta are mutually exclusive")
 	}
 
+	gotCmount := false
+	for _, tag := range buildinfo.Tags {
+		if tag == "cmount" {
+			gotCmount = true
+			break
+		}
+	}
+	if gotCmount && !cmount.ProvidedBy(runtime.GOOS) {
+		return errors.New("updating would discard the mount FUSE capability, aborting")
+	}
+
 	newVersion, siteURL, err := GetVersion(ctx, opt.Beta, opt.Version)
 	if err != nil {
 		return errors.Wrap(err, "unable to detect new version")