better error handling using Result instead of panic

Cargo.lock

@@ -192,7 +192,7 @@ dependencies = [
 
 [[package]]
 name = "swayout"
-version = "1.2.1"
+version = "1.2.2"
 dependencies = [
  "kdl",
  "serde",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "swayout"
-version = "1.2.1"
+version = "1.2.2"
 edition = "2021"
 description = "A tool to configure sway outputs"
 authors = ["Stephen Byrne"]

src/lib.rs

@@ -135,7 +135,7 @@ pub fn print_layout_names() {
 /// or the name of an output.
 /// Return true of any outputs were enabled.
 /// Return false if there were no outputs to enable and thus nothing was done.
-pub fn apply_layout(layout_name: &String) -> bool {
+pub fn apply_layout(layout_name: &String) -> Result<(), String> {
     let config = get_config();
     let outputs = get_outputs();
     let monitor_states = get_monitor_states(&config, &outputs);
@@ -151,15 +151,21 @@ pub fn apply_layout(layout_name: &String) -> bool {
         .find(|layout| &layout.name == layout_name)
     {
         // The layout is defined in the config.
-        layout
-            .outputs
-            .iter()
-            .for_each(|(monitor_name, output_config)| {
-                let monitor_state = get_monitor_state_by_name(&monitor_states, &monitor_name)
-                    .unwrap_or_else(||panic!("Cannot find monitor '{}' for layout '{}'", monitor_name, layout_name));
+        for (monitor_name, output_config) in &layout.outputs {
+            // there is probably a syntactic sugar for this?
+            let monitor_state = if let Some(monitor_state) =
+                get_monitor_state_by_name(&monitor_states, &monitor_name)
+            {
+                monitor_state
+            } else {
+                return Err(format!(
+                    "Cannot find monitor '{}' for layout '{}'",
+                    monitor_name, layout_name
+                ));
+            };
 
             if monitor_state.is_lid_closed {
-                    panic!("Monitor '{}' is closed", monitor_name);
+                return Err(format!("Monitor '{}' is closed.", monitor_name));
             }
 
             // find the output for the monitor to get the output name.
@@ -169,15 +175,18 @@ pub fn apply_layout(layout_name: &String) -> bool {
             if let Some(output) = output_opt {
                 output_config_map.insert(&output.name, &output_config);
             } else {
-                    panic!("Missing output for monitor '{monitor_name}'");
+                return Err(format!("Missing output for monitor '{}'.", monitor_name));
+            }
         }
-            });
     } else {
         // The layout is not defined in the rules.
         // See if it is a monitor name...
         if let Some(monitor_state) = get_monitor_state_by_name(&monitor_states, &layout_name) {
             if monitor_state.is_lid_closed {
-                panic!("Monitor '{}' is closed", &monitor_state.monitor.name);
+                return Err(format!(
+                    "Monitor '{}' is closed.",
+                    &monitor_state.monitor.name
+                ));
             }
 
             // It is a monitor name. Find the matching output...
@@ -187,29 +196,34 @@ pub fn apply_layout(layout_name: &String) -> bool {
             {
                 output_config_map.insert(&output.name, &output.output_config);
             } else {
-                panic!("Could not find output for monitor '{layout_name}'")
+                return Err(format!(
+                    "Could not find output for monitor '{}'.",
+                    layout_name
+                ));
             }
         } else {
             // See if it is an output name...
             if let Some(output) = outputs.iter().find(|output| &output.name == layout_name) {
                 output_config_map.insert(&output.name, &output.output_config);
             } else {
-                panic!("Could not find layout, monitor, or output '{layout_name}'")
+                return Err(format!(
+                    "Could not find layout, monitor, or output '{}.'",
+                    layout_name
+                ));
             }
         }
     }
 
-    if ! output_config_map.is_empty() {
-        apply_outputs(&outputs, &output_config_map);
-        true
-    } else {
-        false
+    if output_config_map.is_empty() {
+        return Err("No outputs would be enabled. Do nothing.".to_string());
     }
+
+    apply_outputs(&outputs, &output_config_map)
 }
 
 /// Apply the first automatic layout for which all outputs are available.
 /// Return the name of the layout applied or None if no automatic layout was available.
-pub fn apply_automatic() -> Option<String> {
+pub fn apply_automatic() -> Result<String,String> {
     let outputs = get_outputs();
 
     let config = get_config();
@@ -219,12 +233,10 @@ pub fn apply_automatic() -> Option<String> {
         .iter()
         .find(|layout| layout.automatic)
     {
-        if apply_layout(&layout.name) {
-            Some(String::from(&layout.name))
+
+        apply_layout(&layout.name)?;
+        Ok(String::from(&layout.name))
     } else {
-            None
-        }
-    } else {
-        None
+        Err("No automatic layouts available.".to_string())
     }
 }

src/main.rs

@@ -8,14 +8,18 @@ fn main() {
     } else if args.len() == 2 {
         let arg = &args[1];
         if arg == "--automatic" {
-            if let Some(layout_name) = swayout::apply_automatic() {
+            match swayout::apply_automatic() {
+                Ok(layout_name) => {
                     println!("{}", layout_name);
-            } else {
-                eprintln!("no automatic layout available");
+                }
+                Err(e) => {
+                    eprintln!("{}", e);
                     process::exit(2)
                 }
+            }
         } else {
-            if ! swayout::apply_layout(&args[1]) {
+            if let Err(e) = swayout::apply_layout(&args[1]) {
+                eprintln!("{}", e);
                 process::exit(3)
             }
         }

src/sway.rs

@@ -67,7 +67,10 @@ fn get_mode(output: &Value) -> String {
 }
 
 /// Apply the specified outputs. Enable all outputs in [outputs], disable others.
-pub fn apply_outputs(all_outputs: &Vec<Output>, outputs: &HashMap<&String, &OutputConfig>) {
+pub fn apply_outputs(
+    all_outputs: &Vec<Output>,
+    outputs: &HashMap<&String, &OutputConfig>,
+) -> Result<(), String> {
     // set enabled outputs first, then set disabled outputs.
     // That way if some work before an error, you have at least one output enabled.
 
@@ -85,7 +88,7 @@ pub fn apply_outputs(all_outputs: &Vec<Output>, outputs: &HashMap<&String, &Outp
     });
 
     if enabled.is_empty() {
-        panic!("No enabled outputs!");
+        return Err("No enabled outputs!".to_string());
     }
 
     let mut cmd = Command::new("swaymsg");
@@ -117,4 +120,6 @@ pub fn apply_outputs(all_outputs: &Vec<Output>, outputs: &HashMap<&String, &Outp
         .for_each(|arg| print!("{} ", arg.to_str().unwrap()));
 
     cmd.output().expect("swaymsg output failed");
+
+    Ok(())
 }