SERVER-126799: Filter NaN from $percentile/$median window function inputs (#53849)

GitOrigin-RevId: 37e218058da9f66347691c029f86de3e045fdd8e

src/mongo/db/pipeline/BUILD.bazel

@@ -1367,6 +1367,7 @@ mongo_cc_unit_test(
         "//src/mongo/db/pipeline/window_function:window_function_min_max_scaler_util_test.cpp",
         "//src/mongo/db/pipeline/window_function:window_function_min_max_test.cpp",
         "//src/mongo/db/pipeline/window_function:window_function_n_test.cpp",
+        "//src/mongo/db/pipeline/window_function:window_function_percentile_test.cpp",
         "//src/mongo/db/pipeline/window_function:window_function_push_test.cpp",
         "//src/mongo/db/pipeline/window_function:window_function_set_union_test.cpp",
         "//src/mongo/db/pipeline/window_function:window_function_std_dev_test.cpp",

src/mongo/db/pipeline/window_function/window_function_percentile.cpp

@@ -29,6 +29,8 @@
 
 #include "mongo/db/pipeline/window_function/window_function_percentile.h"
 
+#include <cmath>
+
 namespace mongo {
 
 void WindowFunctionPercentileCommon::add(Value value) {
@@ -36,7 +38,13 @@ void WindowFunctionPercentileCommon::add(Value value) {
     if (!value.numeric()) {
         return;
     }
-    _values.insert(value.coerceToDouble());
+    const double d = value.coerceToDouble();
+    // NaN violates the strict-weak-ordering required by boost::container::flat_multiset
+    // and would corrupt _values, so skip it (matching AccuratePercentile::incorporate).
+    if (std::isnan(d)) {
+        return;
+    }
+    _values.insert(d);
     _memUsageTracker.add(sizeof(double));
 }
 
@@ -45,8 +53,12 @@ void WindowFunctionPercentileCommon::remove(Value value) {
     if (!value.numeric()) {
         return;
     }
+    const double d = value.coerceToDouble();
+    if (std::isnan(d)) {
+        return;
+    }
 
-    auto iter = _values.find(value.coerceToDouble());
+    auto iter = _values.find(d);
     tassert(7455904,
             "Cannot remove a value not tracked by WindowFunctionPercentile",
             iter != _values.end());

src/mongo/db/pipeline/window_function/window_function_percentile_test.cpp

@@ -0,0 +1,86 @@
+/**
+ *    Copyright (C) 2026-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/pipeline/window_function/window_function_percentile.h"
+
+#include "mongo/db/exec/document_value/document_value_test_util.h"
+#include "mongo/db/pipeline/aggregation_context_fixture.h"
+#include "mongo/platform/decimal128.h"
+#include "mongo/unittest/unittest.h"
+
+#include <limits>
+
+namespace mongo {
+namespace {
+
+class WindowFunctionPercentileTest : public AggregationContextFixture {
+public:
+    WindowFunctionPercentileTest()
+        : expCtx(getExpCtx()),
+          medianApprox(expCtx.get(), PercentileMethodEnum::kApproximate),
+          medianDiscrete(expCtx.get(), PercentileMethodEnum::kDiscrete) {}
+
+    const double kNaN = std::numeric_limits<double>::quiet_NaN();
+
+    boost::intrusive_ptr<ExpressionContext> expCtx;
+    WindowFunctionMedian medianApprox;
+    WindowFunctionMedian medianDiscrete;
+};
+
+TEST_F(WindowFunctionPercentileTest, NaNOnlyWindowReturnsNull) {
+    medianApprox.add(Value(kNaN));
+    medianApprox.add(Value(kNaN));
+    ASSERT_VALUE_EQ(medianApprox.getValue(), Value{BSONNULL});
+}
+
+TEST_F(WindowFunctionPercentileTest, NaNMixedWithFiniteFiltered) {
+    medianApprox.add(Value(1.0));
+    medianApprox.add(Value(kNaN));
+    medianApprox.add(Value(2.0));
+    ASSERT_VALUE_EQ(medianApprox.getValue(), Value(1.0));
+}
+
+TEST_F(WindowFunctionPercentileTest, RemoveFiniteAfterNaNDoesNotCorrupt) {
+    medianDiscrete.add(Value(1.0));
+    medianDiscrete.add(Value(kNaN));
+    medianDiscrete.remove(Value(1.0));
+    medianDiscrete.add(Value(3.0));
+    ASSERT_VALUE_EQ(medianDiscrete.getValue(), Value(3.0));
+}
+
+TEST_F(WindowFunctionPercentileTest, DecimalNaNIsFiltered) {
+    medianApprox.add(Value(1.0));
+    medianApprox.add(Value(Decimal128::kPositiveNaN));
+    medianApprox.add(Value(3.0));
+    medianApprox.remove(Value(Decimal128::kPositiveNaN));
+    ASSERT_VALUE_EQ(medianApprox.getValue(), Value(1.0));
+}
+
+}  // namespace
+}  // namespace mongo