feat(calc): Inform user if qalc is not installed

plugins/src/calc/mod.rs

@@ -107,13 +107,23 @@ async fn qcalc(regex: &mut Regex, expression: &str, decimal_comma: bool) -> Opti
         command.args(&["-set", "decimal comma on"]);
     }
 
-    let mut child = command
+    let spawn = command
         .env("LANG", "C")
         .stdin(Stdio::piped())
         .stdout(Stdio::piped())
         .stderr(Stdio::null())
-        .spawn()
-        .ok()?;
+        .spawn();
+
+    let mut child = match spawn {
+        Ok(child) => child,
+        Err(why) => {
+            return Some(if why.kind() == io::ErrorKind::NotFound {
+                String::from("qalc command is not installed")
+            } else {
+                format!("qalc command failed to spawn: {}", why)
+            })
+        }
+    };
 
     if let Some(mut stdin) = child.stdin.take() {
         let _ = stdin
@@ -121,7 +131,15 @@ async fn qcalc(regex: &mut Regex, expression: &str, decimal_comma: bool) -> Opti
             .await;
     }
 
-    if let Some(stdout) = child.stdout.take() {
+    let stdout = match child.stdout.take() {
+        Some(stdout) => stdout,
+        None => {
+            return Some(String::from(
+                "qalc lacks stdout pipe: did you get hit by a cosmic ray?",
+            ));
+        }
+    };
+
     let mut reader = smol::io::BufReader::new(stdout).lines().skip(2);
     let mut output = String::new();
 
@@ -179,10 +197,7 @@ async fn qcalc(regex: &mut Regex, expression: &str, decimal_comma: bool) -> Opti
         };
     }
 
-        return Some(output);
-    }
-
-    None
+    Some(output)
 }
 
 pub async fn uses_decimal_comma() -> bool {