From e703e955a5cd3cfd413cfd8797970b128c1e220b Mon Sep 17 00:00:00 2001
From: Mislav Bradac <mislav.bradac@memgraph.io>
Date: Tue, 14 Nov 2017 14:42:58 +0100
Subject: [PATCH] Fix bug in InListOperator

Reviewers: florijan, teon.banek

Reviewed By: florijan

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D981
---
 src/query/interpret/eval.hpp              | 11 ++++++++---
 tests/unit/query_expression_evaluator.cpp | 15 +++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/query/interpret/eval.hpp b/src/query/interpret/eval.hpp
index 3c5c6263e..d0927b30d 100644
--- a/src/query/interpret/eval.hpp
+++ b/src/query/interpret/eval.hpp
@@ -157,9 +157,14 @@ class ExpressionEvaluator : public TreeVisitor<TypedValue> {
                                   _list.type());
     }
     auto list = _list.Value<std::vector<TypedValue>>();
-    if (literal.IsNull()) {
-      return TypedValue::Null;
-    }
+
+    // If literal is NULL there is no need to try to compare it with every
+    // element in the list since result of every comparison will be NULL. There
+    // is one special case that we must test explicitly: if list is empty then
+    // result is false since no comparison will be performed.
+    if (list.size() == 0U) return false;
+    if (literal.IsNull()) return TypedValue::Null;
+
     auto has_null = false;
     for (const auto &element : list) {
       auto result = literal == element;
diff --git a/tests/unit/query_expression_evaluator.cpp b/tests/unit/query_expression_evaluator.cpp
index 14cc3e71d..a4f881978 100644
--- a/tests/unit/query_expression_evaluator.cpp
+++ b/tests/unit/query_expression_evaluator.cpp
@@ -344,6 +344,21 @@ TEST(ExpressionEvaluator, InListOperator) {
     auto value = op->Accept(eval.eval);
     EXPECT_TRUE(value.IsNull());
   }
+  {
+    // Null literal.
+    auto *op = storage.Create<InListOperator>(
+        storage.Create<PrimitiveLiteral>(TypedValue::Null), list_literal);
+    auto value = op->Accept(eval.eval);
+    EXPECT_TRUE(value.IsNull());
+  }
+  {
+    // Null literal, empty list.
+    auto *op = storage.Create<InListOperator>(
+        storage.Create<PrimitiveLiteral>(TypedValue::Null),
+        storage.Create<ListLiteral>(std::vector<Expression *>()));
+    auto value = op->Accept(eval.eval);
+    EXPECT_FALSE(value.ValueBool());
+  }
 }
 
 TEST(ExpressionEvaluator, ListMapIndexingOperator) {