refactor: reuse built-ins and shared helpers

crates/chanora_audio/src/ptt_backends/mod.rs

@@ -22,6 +22,7 @@
 use core::fmt;
 
 use crate::ptt::{AudioTransmitGate, PttBackendDescriptor};
+use thiserror::Error;
 
 mod focused;
 
@@ -108,35 +109,51 @@ impl fmt::Display for PttInputClass {
 }
 
 /// Errors raised by a desktop PTT backend.
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum PttBackendError {
     /// The OS rejected the backend initialisation (e.g. Raw Input
     /// registration failed, event tap creation failed).
+    #[error("init failed: {0}")]
     Init(String),
     /// The user-granted permission required for global capture is
     /// not granted (typically macOS Input Monitoring / Accessibility).
+    #[error("permission denied")]
     PermissionDenied,
     /// The display server or compositor does not expose the
     /// expected interface (typically a non-tested Linux compositor).
+    #[error("unsupported environment")]
     UnsupportedEnvironment,
     /// Caller submitted a binding whose `platform_key` cannot be
     /// parsed in the active OS.
+    #[error("invalid binding: {0}")]
     InvalidBinding(String),
 }
 
-impl fmt::Display for PttBackendError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::Init(s) => write!(f, "init failed: {s}"),
-            Self::PermissionDenied => f.write_str("permission denied"),
-            Self::UnsupportedEnvironment => f.write_str("unsupported environment"),
-            Self::InvalidBinding(s) => write!(f, "invalid binding: {s}"),
-        }
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ptt_backend_error_display_strings_stay_stable() {
+        assert_eq!(
+            PttBackendError::Init("rawinput".into()).to_string(),
+            "init failed: rawinput"
+        );
+        assert_eq!(
+            PttBackendError::PermissionDenied.to_string(),
+            "permission denied"
+        );
+        assert_eq!(
+            PttBackendError::UnsupportedEnvironment.to_string(),
+            "unsupported environment"
+        );
+        assert_eq!(
+            PttBackendError::InvalidBinding("bad key".into()).to_string(),
+            "invalid binding: bad key"
+        );
     }
 }
 
-impl std::error::Error for PttBackendError {}
-
 /// Cross-platform desktop PTT backend (SDD-081).
 ///
 /// All implementations call exactly the audio transmit gate's