Merge pull request #640 from CosmWasm/aw/improve-panics

Improve panic messages when VM panicks

Author: aumetra

libwasmvm/src/handle_vm_panic.rs

@@ -5,8 +5,14 @@ use std::any::Any;
 /// We want to provide as much debug information as possible
 /// as those cases are not expected to happen during healthy operations.
 pub fn handle_vm_panic(what: &str, err: Box<dyn Any + Send + 'static>) {
+    let err = match (err.downcast_ref::<&str>(), err.downcast_ref::<String>()) {
+        (Some(str), ..) => *str,
+        (.., Some(str)) => str,
+        (None, None) => "[unusable panic payload]",
+    };
+
     eprintln!("Panic in {what}:");
-    eprintln!("{err:?}"); // Does not show useful information, see https://users.rust-lang.org/t/return-value-from-catch-unwind-is-a-useless-any/89134/6
+    eprintln!("{err:?}");
     eprintln!(
         "This indicates a panic in during the operations of libwasmvm/cosmwasm-vm.
 Such panics must not happen and are considered bugs. If you see this in any real-world or
@@ -31,4 +37,13 @@ mod tests {
         let err = catch_unwind(nice_try).unwrap_err();
         handle_vm_panic("nice_try", err);
     }
+
+    #[test]
+    fn can_handle_random_payloads() {
+        fn nice_try() {
+            std::panic::panic_any(());
+        }
+        let err = catch_unwind(nice_try).unwrap_err();
+        handle_vm_panic("nice_try", err);
+    }
 }