Issue 284: Improve multi-child negation exception (#488)

Issue 284: Include faulty expression in compilation exception for multi-child negations

CHANGELOG.md

@@ -4,6 +4,7 @@ This is a history of changes to clara-rules.
 * extract clara.rules.compiler/compile-test-handler from clara.rules.compiler/compile-test
 * add support for `env` inside of test expressions
 * use `.clj_kondo` extension for clj-kondo hook code for better tool compatibility (clj-kondo support now requires clj-kondo 2022.04.25 or higher)
+* Include the invalid constraint in the exception thrown at session compilation time when negations have multiple children.  See [Issue 284](https://github.com/cerner/clara-rules/issues/284).
 
 # 0.22.1
 * fix incorrent lint warning triggered when this binding is not used in clj-kondo hooks

src/main/clojure/clara/rules/compiler.clj

@@ -584,7 +584,7 @@
           child (first children)]
 
       (when (not= 1 (count children))
-        (throw (RuntimeException. "Negation must have only one child.")))
+        (throw (ex-info "Negation must have only one child." {:illegal-negation expression})))
 
       (condp = (expr-type child)
 

src/test/clojure/clara/test_rules.clj

@@ -2424,3 +2424,15 @@
                                                                :name :clara.rules.test-rules-data/is-cold-and-windy-data
                                                                :lhs  []
                                                                :rhs  '(println "I have no meaning outside of this test")}))) {})))
+
+(deftest test-negation-multiple-children-exception
+  (let [not-rule (dsl/parse-rule [[:not
+                                   [Hot (= ?t temperature)]
+                                   [Temperature (> temperature 0)]]]
+                                 (insert! (->LousyWeather)))]
+    (assert-ex-data
+     {:illegal-negation [:not {:type clara.rules.testfacts.Hot
+                               :constraints ['(= ?t temperature)]}
+                         {:type clara.rules.testfacts.Temperature
+                          :constraints ['(> temperature 0)]}]}
+     (mk-session [not-rule] :cache false))))