Merge pull request #685 from camunda/mob-582-filter-null

feat: Improve null handling in filter expressions
camunda · Jul 21, 2023 · 2fe6c5e · 2fe6c5e
2 parents 0d85ebb + 96aa1e9
commit 2fe6c5e
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Showing 2 changed files with 40 additions and 10 deletions.
diff --git a/src/main/scala/org/camunda/feel/impl/interpreter/FeelInterpreter.scala b/src/main/scala/org/camunda/feel/impl/interpreter/FeelInterpreter.scala
@@ -789,9 +789,9 @@ class FeelInterpreter {
     val withBooleanFilter = (list: List[Val]) => mapEither[Val, Val](
       list,
       item =>
-        withBoolean(filter(item), {
-          case true => item
-          case false => conditionNotFulfilled
+        (filter(item) match {
+          case ValBoolean(true) => item
+          case _ => conditionNotFulfilled
         }).toEither,
       items => ValList(items.filterNot(_ == conditionNotFulfilled))
     )
@@ -809,7 +809,10 @@ class FeelInterpreter {
           case fulFilledItems: ValList => fulFilledItems
           case error => error
         }
-        case other => error(s"Expected boolean filter or number but found '$other'")
+        case _ => withBooleanFilter(list.tail) match {
+          case ValList(fulFilledItems) => ValList(fulFilledItems)
+          case error => error
+        }
       })
     ).getOrElse(
       // Return always an empty list if the given list is empty. Note that we would return `null`

diff --git a/src/test/scala/org/camunda/feel/impl/interpreter/InterpreterListExpressionTest.scala b/src/test/scala/org/camunda/feel/impl/interpreter/InterpreterListExpressionTest.scala
@@ -108,6 +108,36 @@ class InterpreterListExpressionTest
       ValList(List(ValNumber(3), ValNumber(4))))
   }
 
+  it should "be filtered via comparison with null" in {
+    // items that are not comparable to null are ignored
+    eval("[1,2,3,4][item > null]") should be(
+      ValList(List()))
+
+    // items that are not comparable to null are ignored
+    eval("[1,2,3,4][item < null]") should be(
+      ValList(List()))
+  }
+
+  it should "be filtered via comparison with null elements" in {
+    // null is not comparable to 2, so it's ignored
+    eval("[1,2,null,4][item > 2]") should be(
+      ValList(List(ValNumber(4))))
+
+    // null is the only item for which the comparison returns true
+    eval("[1,2,null,4][item = null]") should be(
+      ValList(List(ValNull)))
+  }
+
+  ignore should "be filtered via comparison with missing variable" in {
+    // null is the only item for which the comparison returns true
+    eval("[1,2,x,4][item = null]") should be(
+      ValList(List(ValNull)))
+
+    // missing variable becomes null, so same as direct null item
+    eval("[1,2,x,4][item > 2]") should be(
+      ValList(List(ValNumber(4))))
+  }
+
   it should "be filtered via index" in {
 
     eval("[1,2,3,4][1]") should be(ValNumber(1))
@@ -234,15 +264,12 @@ class InterpreterListExpressionTest
       ValNumber(1))
   }
 
-  it should "fail if the filter doesn't return a boolean or a number" in {
+  it should "be filtered if the filter doesn't always return a boolean or a number" in {
     eval(""" [1,2,3,4]["not a valid filter"] """) should be (
-      ValError("Expected boolean filter or number but found 'ValString(not a valid filter)'")
+      ValList(List())
     )
-  }
-
-  it should "fail if the filter doesn't return always a boolean" in {
     eval("[1,2,3,4][if item < 3 then true else null]") should be (
-      ValError("Expected Boolean but found 'ValNull'")
+      ValList(List(ValNumber(1), ValNumber(2)))
     )
   }