#417: Duplicate unifications within the same condition cause rebinding (

#424)

CHANGELOG.md

@@ -1,5 +1,8 @@
 This is a history of changes to clara-rules.
 
+# 0.20.0 SNAPSHOT
+* Correct duplicate bindings within the same condition. See [issue 417](https://github.com/cerner/clara-rules/issues/417)
+
 # 0.19.1
 * Added a new field to the clara.rules.engine/Accumulator record.  This could be a breaking change for any user durability implementations with low-level performance optimizations.  See [PR 410](https://github.com/cerner/clara-rules/pull/410) for details.
 * Performance improvements for :exists conditions.  See [issue 298](https://github.com/cerner/clara-rules/issues/298).

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

@@ -255,7 +255,6 @@
    (if (empty? exp-seq)
      `(deref ~'?__bindings__)
      (let [ [exp & rest-exp] exp-seq
-            compiled-rest (compile-constraints rest-exp equality-only-variables)
             variables (into #{}
                             (filter (fn [item]
                                       (and (symbol? item)
@@ -264,7 +263,17 @@
                                     exp))
             expression-values (remove variables (rest exp))
             binds-variables? (and (equality-expression? exp)
-                                  (seq variables))]
+                                  (seq variables))
+
+           ;; if we intend on binding any variables at this level of the
+           ;; expression then future layers should not be able to rebind them.
+           ;; see https://github.com/cerner/clara-rules/issues/417 for more info
+           equality-only-variables (if binds-variables?
+                                     (into equality-only-variables
+                                           variables)
+                                     equality-only-variables)
+
+           compiled-rest (compile-constraints rest-exp equality-only-variables)]
 
        (when (and binds-variables?
                   (empty? expression-values))

src/test/common/clara/test_bindings.cljc

@@ -369,3 +369,44 @@
              fire-rules
              (query cold-query)))
       "The query results should not be empty for a matching location"))
+
+;; https://github.com/cerner/clara-rules/issues/417
+(def-rules-test test-duplicate-unification
+
+  {:queries [single-condition [[]
+                               [[?temp <- Temperature (= ?t temperature)
+                                 (= ?t -10)]]]
+             multi-condition-expression [[]
+                                         [[?temp <- Temperature (= ?t temperature)
+                                           (= ?t -10)]
+                                          [ColdAndWindy (< ?t temperature)]]]
+
+             multi-condition-equality [[]
+                                       [[?temp <- Temperature (= ?t temperature)
+                                         (= ?t -14)]
+                                        [ColdAndWindy (= ?t temperature)]]]]
+
+   :sessions [empty-session [single-condition
+                             multi-condition-expression
+                             multi-condition-equality] {}]}
+
+  (let [session (-> empty-session
+                    (insert (->Temperature -10 "MCI"))
+                    (insert (->Temperature 10 "LAX"))
+                    (insert (->Temperature 30 "ATL"))
+                    fire-rules)
+
+        multi-condition (-> empty-session
+                            (insert (->Temperature -10 "ATL"))
+                            (insert (->Temperature -14 "MCI"))
+                            (insert (->ColdAndWindy -9 "ATL"))
+                            (insert (->ColdAndWindy -14 "MCI"))
+                            fire-rules)]
+    (is (= [(->Temperature -10 "MCI")]
+           (map :?temp (query session single-condition))))
+
+    (is (= [(->Temperature -10 "ATL")]
+           (map :?temp (query multi-condition multi-condition-expression))))
+
+    (is (= [(->Temperature -14 "MCI")]
+           (map :?temp (query multi-condition multi-condition-equality))))))