ISSUE-352: Durability fails to deserialize rules containing condition…

…s with an empty constraint (#353)

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

@@ -259,8 +259,8 @@
          (throw (ex-info (str "Malformed variable binding for " variables ". No associated value.")
                          {:variables (map keyword variables)})))
 
-       (if binds-variables?
-
+       (cond
+         binds-variables?
          ;; Bind each variable with the first value we encounter.
          ;; The additional equality checks are handled below so which value
          ;; we bind to is not important. So an expression like (= ?x value-1 value-2) will
@@ -287,8 +287,14 @@
                compiled-rest)
             )
 
+         ;; A contraint that is empty doesn't need to be added as a check,
+         ;; simply move on to the rest
+         (empty? exp)
+         compiled-rest
+
          ;; No variables to unify, so simply check the expression and
          ;; move on to the rest.
+         :else
          `(if ~exp ~compiled-rest nil))))))
 
 

src/main/clojure/clara/rules/durability/fressian.clj

@@ -235,6 +235,23 @@
                 (read [_ rdr tag component-count]
                   (read-with-meta rdr #(apply list %))))}}
 
+   "clj/emptylist"
+   {:class clojure.lang.PersistentList$EmptyList
+    :writer (reify WriteHandler
+              (write [_ w o]
+                (let [m (meta o)]
+                  (do
+                    (.writeTag w "clj/emptylist" 1)
+                    (if m
+                      (.writeObject w m)
+                      (.writeNull w))))))
+    :readers {"clj/emptylist"
+              (reify ReadHandler
+                (read [_ rdr tag component-count]
+                  (let [m (read-meta rdr)]
+                    (cond-> '()
+                            m (with-meta m)))))}}
+
    "clj/aseq"
    {:class clojure.lang.ASeq
     :writer (reify WriteHandler
@@ -264,7 +281,7 @@
               (reify ReadHandler
                 (read [_ rdr tag component-count]
                   (read-with-meta rdr #(into {} %))))}}
-   
+
    "clj/treeset"
    {:class clojure.lang.PersistentTreeSet
     :writer (reify WriteHandler
@@ -289,7 +306,7 @@
                     (if m
                       (with-meta s m)
                       s))))}}
-   
+
    "clj/treemap"
    {:class clojure.lang.PersistentTreeMap
     :writer (reify WriteHandler
@@ -347,7 +364,7 @@
                   (let [s (symbol (.readObject rdr) (.readObject rdr))
                         m (read-meta rdr)]
                     (cond-> s
-                      m (with-meta m)))))}}
+                            m (with-meta m)))))}}
 
    "clj/record"
    {:class clojure.lang.IRecord

src/test/clojure/clara/durability_rules.clj

@@ -29,7 +29,12 @@
 
 (defrule find-wind-speeds-without-temp
   "Rule using NegationNode"
-  [?w <- WindSpeed (= ?loc location)]
+  [?w <- WindSpeed
+   ;; Empty constraint and a constraint containing an empty list to test serializing an EmptyList,
+   ;; see Issue 352 for more information
+   ()
+   (not= this ())
+   (= ?loc location)]
   [:not [Temperature (= ?loc location)]]
   =>
   (insert! (->UnpairedWindSpeed ?w)))

src/test/common/clara/test_dsl.cljc

@@ -10,7 +10,8 @@
                                     query]]
                [clara.rules.accumulators :as acc]
                [clara.rules.testfacts :refer [->Temperature ->Cold ->WindSpeed
-                                              ->ColdAndWindy map->FlexibleFields]]
+                                              ->ColdAndWindy map->FlexibleFields
+                                              ->First ->Second ->Third ->Fourth]]
                [clojure.test :refer [is deftest run-tests testing use-fixtures]]
                [clara.rules.accumulators]
                [schema.test :as st])
@@ -19,7 +20,11 @@
                Cold
                WindSpeed
                ColdAndWindy
-               FlexibleFields]))
+               FlexibleFields
+               First
+               Second
+               Third
+               Fourth]))
 
    :cljs
    (ns clara.test-dsl
@@ -34,7 +39,11 @@
                                               ->Temperature Temperature
                                               ->Cold Cold
                                               ->WindSpeed WindSpeed
-                                              ->ColdAndWindy ColdAndWindy]]
+                                              ->ColdAndWindy ColdAndWindy
+                                              ->First First
+                                              ->Second Second
+                                              ->Third Third
+                                              ->Fourth Fourth]]
                [clara.rules.accumulators :as acc]
                [clara.tools.testing-utils :as tu]
                [cljs.test]
@@ -440,3 +449,36 @@
       "Validate that the ?t binding from the previous accumulator result is used, rather
          than the binding in the ColdAndWindy condition that would create a ?t binding if one were
          not already present"))
+
+;; Test for https://github.com/cerner/clara-rules/issues/352
+;; A test to validate the construction of rules containing empty constraints
+(def-rules-test test-condition-with-empty-constraint
+  {:rules [rule-without-constraint [[[First]]
+                                    (swap! side-effect-holder conj :no-constraints)]
+           rule-with-an-empty [[[Second ()]]
+                               (swap! side-effect-holder conj :one-empty-constraint)]
+           rule-with-two-empty [[[Third () ()]]
+                                (swap! side-effect-holder conj :two-empty-constraint)]
+           rule-with-empty-and-non-empty [[[Fourth () (not= this ())]]
+                                          (swap! side-effect-holder conj :one-empty-one-populated)]
+           rule-with-non-empty-and-empty [[[Cold (not= this ()) ()]]
+                                          (swap! side-effect-holder conj :one-populated-one-empty)]]
+   :sessions [empty-session [rule-without-constraint
+                             rule-with-an-empty
+                             rule-with-two-empty
+                             rule-with-empty-and-non-empty
+                             rule-with-non-empty-and-empty] {}]}
+  (reset! side-effect-holder [])
+  (let [session (-> empty-session
+                    (insert (->First)
+                            (->Second)
+                            (->Third)
+                            (->Fourth)
+                            (->Cold -10))
+                    fire-rules)]
+    (is (= (frequencies @side-effect-holder)
+           (frequencies [:no-constraints
+                         :one-empty-constraint
+                         :two-empty-constraint
+                         :one-empty-one-populated
+                         :one-populated-one-empty])))))