feat: throw condition node exception

CONTRIBUTORS.md

@@ -11,6 +11,7 @@ Community
 - David Goeke [@dgoeke]
 - Dave Dixon [@sparkofreason]
 - Baptiste Fontaine [@bfontaine]
+- Jose Gomez [@k13gomez]
 
 [@rbrush]: https://github.com/rbrush
 [@mrrodriguez]: https://github.com/mrrodriguez

src/main/clojure/clara/rules/engine.cljc

@@ -144,30 +144,47 @@
   (retract-elements [transport memory listener nodes elements])
   (retract-tokens [transport memory listener nodes tokens]))
 
+(declare get-conditions-and-rule-names)
+(declare single-condition-message)
+
+(defn- throw-condition-node-exception
+  "Adds a useful error message when executing a constraint node raises an exception."
+  [{:keys [cause node]}]
+  (let [conditions-and-rules (get-conditions-and-rule-names node)
+        condition-messages (->> conditions-and-rules
+                                (map-indexed single-condition-message)
+                                (string/join "\n"))
+        message (str "Condition exception raised.\n" condition-messages)]
+    (throw (ex-info message
+                    {:conditions-and-rules conditions-and-rules}
+                    cause))))
+
 (defn- propagate-items-to-nodes [transport memory listener nodes items propagate-fn]
   (doseq [node nodes
           :let [join-keys (get-join-keys node)]]
-
-    (if (pos? (count join-keys))
-
-      ;; Group by the join keys for the activation.
-      (doseq [[join-bindings item-group] (platform/group-by-seq #(select-keys (:bindings %) join-keys) items)]
-        (propagate-fn node
-                      join-bindings
-                      item-group
-                      memory
-                      transport
-                      listener))
-
-      ;; The node has no join keys, so just send everything at once
-      ;; (if there is something to send.)
-      (when (seq items)
-        (propagate-fn node
-                      {}
-                      items
-                      memory
-                      transport
-                      listener)))))
+    (try
+      (if (pos? (count join-keys))
+
+        ;; Group by the join keys for the activation.
+        (doseq [[join-bindings item-group] (platform/group-by-seq #(select-keys (:bindings %) join-keys) items)]
+          (propagate-fn node
+                        join-bindings
+                        item-group
+                        memory
+                        transport
+                        listener))
+
+        ;; The node has no join keys, so just send everything at once
+        ;; (if there is something to send.)
+        (when (seq items)
+          (propagate-fn node
+                        {}
+                        items
+                        memory
+                        transport
+                        listener)))
+      (catch #?(:clj Exception :cljs :default) e
+        (throw-condition-node-exception {:cause e :node node})))))
 
 ;; Simple, in-memory transport.
 (deftype LocalTransport []