SERVER-24392 Remove invalid invariant in expression::isSubsetOf()

2 files changed, 20 insertions, 4 deletions

diff --git a/src/mongo/db/matcher/expression_algo.cpp b/src/mongo/db/matcher/expression_algo.cpp
index 966c727501f..1b130592597 100644
--- a/src/mongo/db/matcher/expression_algo.cpp
+++ b/src/mongo/db/matcher/expression_algo.cpp
@@ -95,14 +95,16 @@ bool _isSubsetOf(const ComparisonMatchExpression* lhs, const ComparisonMatchExpr
         return false;
     }
 
-    // Either collator may be used by compareElementValues() here. If lhs (the query) contains
-    // string comparison, then _isSubsetOf will only be called if lhs and rhs have the same
-    // collator. Otherwise, the collator will not be used by compareElementValues().
     if (!CollatorInterface::collatorsMatch(lhs->getCollator(), rhs->getCollator())) {
         // TODO SERVER-23172: Check that lhsData does not contain string comparison in nested
         // objects or arrays.
-        invariant(lhsData.type() != BSONType::String);
+        if (lhsData.type() == BSONType::String) {
+            return false;
+        }
     }
+
+    // Either collator may be used by compareElementValues() here, since either the collators are
+    // the same or lhsData does not contain string comparison.
     int cmp = compareElementValues(lhsData, rhsData, rhs->getCollator());
 
     // Check whether the two expressions are equivalent.
diff --git a/src/mongo/db/matcher/expression_algo_test.cpp b/src/mongo/db/matcher/expression_algo_test.cpp
index ead421bc76e..1eccce190bb 100644
--- a/src/mongo/db/matcher/expression_algo_test.cpp
+++ b/src/mongo/db/matcher/expression_algo_test.cpp
@@ -663,6 +663,20 @@ TEST(ExpressionAlgoIsSubsetOf, CollationAwareStringComparison) {
     ASSERT_FALSE(expression::isSubsetOf(lhsLT.get(), rhsLT.get()));
 }
 
+TEST(ExpressionAlgoIsSubsetOf, NonMatchingCollationsStringComparison) {
+    CollatorInterfaceMock collatorAlwaysEqual(CollatorInterfaceMock::MockType::kAlwaysEqual);
+    CollatorInterfaceMock collatorReverseString(CollatorInterfaceMock::MockType::kReverseString);
+    ParsedMatchExpression lhs("{a: {$gt: 'abc'}}", &collatorAlwaysEqual);
+    ParsedMatchExpression rhs("{a: {$gt: 'cba'}}", &collatorReverseString);
+
+    ASSERT_FALSE(expression::isSubsetOf(lhs.get(), rhs.get()));
+
+    ParsedMatchExpression lhsLT("{a: {$lt: 'abc'}}", &collatorAlwaysEqual);
+    ParsedMatchExpression rhsLT("{a: {$lt: 'cba'}}", &collatorReverseString);
+
+    ASSERT_FALSE(expression::isSubsetOf(lhsLT.get(), rhsLT.get()));
+}
+
 TEST(ExpressionAlgoIsSubsetOf, CollationAwareStringComparisonIn) {
     CollatorInterfaceMock collator(CollatorInterfaceMock::MockType::kReverseString);
     ParsedMatchExpression lhsAllGTcba("{a: {$in: ['abc', 'cbc']}}", &collator);