respond to SIGUSR1 by reloading config (#3952)

* respond to SIGUSR1 by reloading config

* document USR1 signal handling

book/src/configuration.md

@@ -28,6 +28,10 @@ hidden = false
 You may also specify a file to use for configuration with the `-c` or
 `--config` CLI argument: `hx -c path/to/custom-config.toml`.
 
+It is also possible to trigger configuration file reloading by sending the `USR1`
+signal to the helix process, e.g. via `pkill -USR1 hx`. This is only supported 
+on unix operating systems.
+
 ## Editor
 
 ### `[editor]` Section

helix-term/src/application.rs

@@ -224,8 +224,8 @@ impl Application {
         #[cfg(windows)]
         let signals = futures_util::stream::empty();
         #[cfg(not(windows))]
-        let signals =
-            Signals::new(&[signal::SIGTSTP, signal::SIGCONT]).context("build signal handler")?;
+        let signals = Signals::new(&[signal::SIGTSTP, signal::SIGCONT, signal::SIGUSR1])
+            .context("build signal handler")?;
 
         let app = Self {
             compositor,
@@ -426,6 +426,10 @@ impl Application {
                 self.compositor.load_cursor();
                 self.render();
             }
+            signal::SIGUSR1 => {
+                self.refresh_config();
+                self.render();
+            }
             _ => unreachable!(),
         }
     }