SERVER-54607 Add support for right unbounded windows in removable document executor

2 files changed, 31 insertions, 9 deletions

diff --git a/src/mongo/db/pipeline/window_function/window_function_exec_removable_document.cpp b/src/mongo/db/pipeline/window_function/window_function_exec_removable_document.cpp
index 571c06eac30..2a724589360 100644
--- a/src/mongo/db/pipeline/window_function/window_function_exec_removable_document.cpp
+++ b/src/mongo/db/pipeline/window_function/window_function_exec_removable_document.cpp
@@ -53,7 +53,7 @@ WindowFunctionExecRemovableDocument::WindowFunctionExecRemovableDocument(
     stdx::visit(
         visit_helper::Overloaded{
             [](const WindowBounds::Unbounded&) {
-                uasserted(5339801, "Right unbounded windows are not yet supported");
+                // Pass. _upperBound defaults to boost::none which represents no upper bound.
             },
             [&](const WindowBounds::Current&) { _upperBound = 0; },
             [&](const int& upperIndex) { _upperBound = upperIndex; },
@@ -63,7 +63,9 @@ WindowFunctionExecRemovableDocument::WindowFunctionExecRemovableDocument(
 
 void WindowFunctionExecRemovableDocument::initialize() {
     int lowerBoundForInit = _lowerBound > 0 ? _lowerBound : 0;
-    for (int i = lowerBoundForInit; i <= _upperBound; ++i) {
+    // Run the loop until we hit the out of partition break (right unbounded) or we hit the upper
+    // bound.
+    for (int i = lowerBoundForInit; !_upperBound || i <= _upperBound.get(); ++i) {
         // If this is false, we're over the end of the partition.
         if (auto doc = (*this->_iter)[i]) {
             addValue(_input->evaluate(*doc, nullptr));
diff --git a/src/mongo/db/pipeline/window_function/window_function_exec_test.cpp b/src/mongo/db/pipeline/window_function/window_function_exec_test.cpp
index a3238d8594e..3f36d25123d 100644
--- a/src/mongo/db/pipeline/window_function/window_function_exec_test.cpp
+++ b/src/mongo/db/pipeline/window_function/window_function_exec_test.cpp
@@ -270,14 +270,34 @@ TEST_F(WindowFunctionExecRemovableDocumentTest, DefaultValueWorksAsExpected) {
     ASSERT(mgr.getNext().nullish());  // Default value
 }
 
-TEST_F(WindowFunctionExecRemovableDocumentTest, FunctionalityNotSupported) {
+TEST_F(WindowFunctionExecRemovableDocumentTest, RightUnboundedDoesNotAddDocumentsDuringWindow) {
     const auto docs = std::deque<DocumentSource::GetNextResult>{
-        Document{{"a", 3}}, Document{{"a", 2}}, Document{{"a", 1}}};
-    ASSERT_THROWS_CODE(
-        createForFieldPath(
-            std::move(docs), "$a", WindowBounds::DocumentBased{1, WindowBounds::Unbounded{}}),
-        AssertionException,
-        5339801);
+        Document{{"a", 3}}, Document{{"a", 2}}, Document{{"a", 1}}, Document{{"a", 17}}};
+    auto mgr = createForFieldPath(
+        std::move(docs),
+        "$a",
+        WindowBounds::DocumentBased{WindowBounds::Current{}, WindowBounds::Unbounded{}});
+    ASSERT_VALUE_EQ(Value(17), mgr.getNext());
+    advanceIterator();
+    ASSERT_VALUE_EQ(Value(17), mgr.getNext());
+    advanceIterator();
+    ASSERT_VALUE_EQ(Value(17), mgr.getNext());
+    advanceIterator();
+    ASSERT_VALUE_EQ(Value(17), mgr.getNext());
+    advanceIterator();
+
+    const auto docsTwo = std::deque<DocumentSource::GetNextResult>{
+        Document{{"a", 18}}, Document{{"a", 2}}, Document{{"a", 1}}, Document{{"a", 17}}};
+    mgr = createForFieldPath(
+        std::move(docsTwo), "$a", WindowBounds::DocumentBased{-1, WindowBounds::Unbounded{}});
+    ASSERT_VALUE_EQ(Value(18), mgr.getNext());
+    advanceIterator();
+    ASSERT_VALUE_EQ(Value(18), mgr.getNext());
+    advanceIterator();
+    ASSERT_VALUE_EQ(Value(17), mgr.getNext());
+    advanceIterator();
+    ASSERT_VALUE_EQ(Value(17), mgr.getNext());
+    advanceIterator();
 }
 
 TEST_F(WindowFunctionExecRemovableDocumentTest, EnsureFirstDocumentIsNotRemovedEarly) {