Fix panic message being printed twice (godot_error! + eprintln!)

Author: Bromeon

godot-core/src/meta/error/call_error.rs

@@ -301,7 +301,11 @@ impl CallError {
 
     #[doc(hidden)]
     pub fn failed_by_user_panic(call_ctx: &CallContext, reason: String) -> Self {
-        Self::new(call_ctx, reason, None)
+        // This can cause the panic message to be printed twice in some scenarios (e.g. bind_mut() borrow failure).
+        // But in other cases (e.g. itest `dynamic_call_with_panic`), it is only printed once.
+        // Would need some work to have a consistent experience.
+
+        Self::new(call_ctx, format!("function panicked: {reason}"), None)
     }
 
     fn new(

godot-core/src/private.rs

@@ -296,11 +296,14 @@ where
 
         let message = format_panic_message(panic_info);
         if godot_print() {
+            // Also prints to stdout/stderr -- do not print twice.
             godot_error!("{message}");
+        } else {
+            eprintln!("{message}");
         }
 
         let backtrace = format_backtrace!("panic backtrace");
-        eprintln!("{message}{backtrace}");
+        eprintln!("{backtrace}");
         let _ignored_result = std::io::stderr().flush();
     }));
 }

itest/rust/src/object_tests/dynamic_call_test.rs

@@ -163,7 +163,7 @@ fn dynamic_call_with_panic() {
 
     let expected_error_message = "godot-rust function call failed: Object::call(&\"do_panic\")\
         \n  Source: ObjPayload::do_panic()\
-        \n    Reason: do_panic exploded"
+        \n    Reason: function panicked: do_panic exploded"
         .to_string();
 
     assert_eq!(call_error.to_string(), expected_error_message);