loops: Use Void for infinite loops

src/actors/external/debug.rs

@@ -3,12 +3,13 @@
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
-use std::thread;
-use zbus::{Connection, ObjectServer, dbus_interface, fdo};
-
 use crate::main;
 use crate::state;
 
+use std::thread;
+use zbus::{Connection, ObjectServer, dbus_interface, fdo};
+
+use super::Void;
 
 use std::convert::TryInto;
 
@@ -37,7 +38,7 @@ impl Manager {
     }
 }
 
-fn start(mgr: Manager) -> Result<(), Box<dyn std::error::Error>> {
+fn start(mgr: Manager) -> Result<Void, Box<dyn std::error::Error>> {
     let connection = Connection::new_session()?;
     fdo::DBusProxy::new(&connection)?.request_name(
         "sm.puri.SqueekDebug",

src/actors/external/mod.rs

@@ -8,4 +8,7 @@
  
 pub mod debug;
 #[cfg(feature = "zbus_v1_5")]
-pub mod screensaver;
+pub mod screensaver;
+
+/// The uninhabited type. Cannot be created or returned; means "will never return" as return type. Useful for infinite loops.
+enum Void {}

src/actors/external/screensaver.rs

@@ -3,10 +3,11 @@
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
+use crate::logging;
 use std::thread;
 use zbus::{Connection, dbus_proxy};
 
-use crate::logging;
+use super::Void;
 
 
 #[derive(Debug)]
@@ -45,7 +46,7 @@ pub fn init(destination: Destination) {
     });
 }
 
-fn start(destination: Destination) -> Result<(), zbus::Error> {
+fn start(destination: Destination) -> Result<Void, zbus::Error> {
     let conn = Connection::new_session()?;
     let manager = ManagerProxy::new(&conn)?;