feat(tracing): use hook to log errors on panics

The two bugs raised in issues #1 and #2 were due to panics that were not
visible in the logs, which left the process hanging and unresponsive,
ultimately needing to be force killed with a command like 'Stop-Process
-Name komorebi'.

The only way to even verify that a panic had taken place and what the
panic related to, was to run '$env:RUST_BACKTRACE ='full';
komorebi.exe', wait for the panic, then restore the now-hidden window
with 'komorebic restore-windows' to finally see the panic message.

This commit integrates an example from the 'tracing' repo,  which
through the addition of a panic hook, logs out panics as errors.
Hopefully this will debugging much easier in the future.

re #1, re #2

komorebi/src/main.rs

@@ -82,6 +82,31 @@ fn setup() -> Result<WorkerGuard> {
             ),
     )?;
 
+    // https://github.com/tokio-rs/tracing/blob/master/examples/examples/panic_hook.rs
+    // Set a panic hook that records the panic as a `tracing` event at the
+    // `ERROR` verbosity level.
+    //
+    // If we are currently in a span when the panic occurred, the logged event
+    // will include the current span, allowing the context in which the panic
+    // occurred to be recorded.
+    std::panic::set_hook(Box::new(|panic| {
+        // If the panic has a source location, record it as structured fields.
+        if let Some(location) = panic.location() {
+            // On nightly Rust, where the `PanicInfo` type also exposes a
+            // `message()` method returning just the message, we could record
+            // just the message instead of the entire `fmt::Display`
+            // implementation, avoiding the duplciated location
+            tracing::error!(
+                message = %panic,
+                panic.file = location.file(),
+                panic.line = location.line(),
+                panic.column = location.column(),
+            );
+        } else {
+            tracing::error!(message = %panic);
+        }
+    }));
+
     Ok(guard)
 }