Add support for running commands on BEL

Adds a new configuration option under `visual_bell` called
`bell_command` that reuses the command formatting of the keybindings.

This allows for things like playing a notification sound.
See alacritty#1528 (comment)

Closes alacritty#1528

src/config/mod.rs

@@ -215,6 +215,9 @@ pub struct VisualBellConfig {
     /// Visual bell flash color
     #[serde(deserialize_with = "rgb_from_hex")]
     color: Rgb,
+
+    #[serde(deserialize_with = "failure_default")]
+    bell_command: Option<CommandWrapper>,
 }
 
 impl Default for VisualBellConfig {
@@ -223,6 +226,7 @@ impl Default for VisualBellConfig {
             animation: Default::default(),
             duration: Default::default(),
             color: default_visual_bell_color(),
+            bell_command: None,
         }
     }
 }
@@ -249,6 +253,12 @@ impl VisualBellConfig {
     pub fn color(&self) -> Rgb {
         self.color
     }
+
+    /// Visual bell command
+    #[inline]
+    pub fn bell_command(&self) -> Option<CommandWrapper> {
+        self.bell_command.clone()
+    }
 }
 
 #[derive(Debug, Deserialize, PartialEq, Eq)]

src/term/mod.rs

@@ -25,7 +25,7 @@ use unicode_width::UnicodeWidthChar;
 use crate::ansi::{
     self, Attr, CharsetIndex, Color, CursorStyle, Handler, NamedColor, StandardCharset,
 };
-use crate::config::{Config, VisualBellAnimation};
+use crate::config::{Config, VisualBellAnimation, CommandWrapper};
 use crate::grid::{
     BidirectionalIterator, DisplayIter, Grid, GridCell, IndexRegion, Indexed, Scroll,
     ViewportPosition,
@@ -37,6 +37,7 @@ use crate::selection::{self, Locations, Selection};
 use crate::term::cell::{Cell, Flags, LineLength};
 use crate::term::color::Rgb;
 use crate::url::{Url, UrlParser};
+use crate::util::start_daemon;
 use copypasta::{Clipboard, Load, Store};
 use font::{self, Size};
 
@@ -632,6 +633,9 @@ pub struct VisualBell {
 
     /// The last time the visual bell rang, if at all
     start_time: Option<Instant>,
+
+    /// Command to run when bell is rang
+    bell_command: Option<CommandWrapper>,
 }
 
 fn cubic_bezier(p0: f64, p1: f64, p2: f64, p3: f64, x: f64) -> f64 {
@@ -647,6 +651,7 @@ impl VisualBell {
         VisualBell {
             animation: visual_bell_config.animation(),
             duration: visual_bell_config.duration(),
+            bell_command: visual_bell_config.bell_command(),
             start_time: None,
         }
     }
@@ -737,10 +742,20 @@ impl VisualBell {
         }
     }
 
+    pub fn run_bell_command(&self) {
+        if let Some(ref cmd) = self.bell_command {
+            match start_daemon(cmd.program(), cmd.args()) {
+                Ok(_) => debug!("Launched {} with args {:?} on bell", cmd.program(), cmd.args()),
+                Err(_) => warn!("Unable to launch {} with args {:?} on bell", cmd.program(), cmd.args()),
+            }
+        }
+    }
+
     pub fn update_config(&mut self, config: &Config) {
         let visual_bell_config = config.visual_bell();
         self.animation = visual_bell_config.animation();
         self.duration = visual_bell_config.duration();
+        self.bell_command = visual_bell_config.bell_command();
     }
 }
 
@@ -1708,6 +1723,7 @@ impl ansi::Handler for Term {
     fn bell(&mut self) {
         trace!("Bell");
         self.visual_bell.ring();
+        self.visual_bell.run_bell_command();
         self.next_is_urgent = Some(true);
     }