Primitive support for a rescue trace event

Discussed in CRuby core developer meeting May 10, 2023 at
RubyKaigi.

Experimental, do not merge until semantics are worked out in CRuby
(and until we actually populate the rest of TracePoint with file
and line etc).

core/src/main/java/org/jruby/ir/runtime/IRRuntimeHelpers.java

@@ -452,6 +452,10 @@ public static IRubyObject isExceptionHandled(ThreadContext context, IRubyObject
         boolean ret = IRRuntimeHelpers.isRubyExceptionHandled(context, excType, excObj)
             || IRRuntimeHelpers.isJavaExceptionHandled(context, excType, excObj, false);
 
+        if (ret) {
+            context.runtime.getTraceEvents().callEventHooks(context, RubyEvent.RESCUE, "dummy", -1, "dummy", (IRubyObject) excObj);
+        }
+
         return RubyBoolean.newBoolean(context, ret);
     }
 

core/src/main/java/org/jruby/runtime/RubyEvent.java

@@ -29,7 +29,8 @@ public enum RubyEvent {
     // A_CALL is CALL + B_CALL + C_CALL
     A_CALL   ("a_call"),
     // A_RETURN is RETURN + B_RETURN + C_RETURN
-    A_RETURN ("a_return");
+    A_RETURN ("a_return"),
+    RESCUE ("rescue", false);
 
     public static final Set<RubyEvent> ALL_EVENTS = Collections.synchronizedSet(EnumSet.allOf(RubyEvent.class));
     public static final EnumSet ALL_EVENTS_ENUMSET = EnumSet.copyOf(RubyEvent.ALL_EVENTS);