Revert "SERVER-54049 Add translation phase for accumulator-style window functions"

This reverts commit 8b27b6710d4db7cefb840309903462ed40007402.

7 files changed, 19 insertions, 137 deletions

diff --git a/src/mongo/db/pipeline/window_function/partition_iterator.cpp b/src/mongo/db/pipeline/window_function/partition_iterator.cpp
index 9f2034c80f5..435cb7a765b 100644
--- a/src/mongo/db/pipeline/window_function/partition_iterator.cpp
+++ b/src/mongo/db/pipeline/window_function/partition_iterator.cpp
@@ -125,7 +125,7 @@ void PartitionIterator::getNextDocument() {
 
     auto doc = getNextRes.releaseDocument();
     if (_partitionExpr) {
-        auto curKey = (*_partitionExpr)->evaluate(doc, &_expCtx->variables);
+        auto curKey = _partitionExpr->evaluate(doc, &_expCtx->variables);
         uassert(ErrorCodes::TypeMismatch,
                 "Cannot 'partitionBy' an expression of type array",
                 !curKey.isArray());
diff --git a/src/mongo/db/pipeline/window_function/partition_iterator.h b/src/mongo/db/pipeline/window_function/partition_iterator.h
index 3e645d8a768..bf7f0bd1097 100644
--- a/src/mongo/db/pipeline/window_function/partition_iterator.h
+++ b/src/mongo/db/pipeline/window_function/partition_iterator.h
@@ -42,7 +42,7 @@ class PartitionIterator {
 public:
     PartitionIterator(ExpressionContext* expCtx,
                       DocumentSource* source,
-                      boost::optional<boost::intrusive_ptr<Expression>> partitionExpr)
+                      boost::optional<const ExpressionFieldPath&> partitionExpr)
         : _expCtx(expCtx),
           _source(source),
           _partitionExpr(partitionExpr),
@@ -75,13 +75,6 @@ public:
         return _currentIndex;
     }
 
-    /**
-     * Sets the input DocumentSource for this iterator to 'source'.
-     */
-    void setSource(DocumentSource* source) {
-        _source = source;
-    }
-
 private:
     /**
      * Retrieves the next document from the prior stage and updates the state accordingly.
@@ -105,7 +98,7 @@ private:
 
     ExpressionContext* _expCtx;
     DocumentSource* _source;
-    boost::optional<boost::intrusive_ptr<Expression>> _partitionExpr;
+    boost::optional<const ExpressionFieldPath&> _partitionExpr;
     std::vector<Document> _cache;
     int _currentIndex = 0;
     Value _partitionKey;
diff --git a/src/mongo/db/pipeline/window_function/partition_iterator_test.cpp b/src/mongo/db/pipeline/window_function/partition_iterator_test.cpp
index 7c6f80b3031..f0666f12f39 100644
--- a/src/mongo/db/pipeline/window_function/partition_iterator_test.cpp
+++ b/src/mongo/db/pipeline/window_function/partition_iterator_test.cpp
@@ -84,8 +84,7 @@ TEST_F(PartitionIteratorTest, LookaheadOutOfRangeAccessNewPartition) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_DOCUMENT_EQ(docs[0].getDocument(), *partIter[0]);
     ASSERT_DOCUMENT_EQ(docs[1].getDocument(), *partIter[1]);
     ASSERT_FALSE(partIter[2]);
@@ -99,8 +98,7 @@ TEST_F(PartitionIteratorTest, AdvanceMovesCurrent) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_DOCUMENT_EQ(docs[0].getDocument(), *partIter[0]);
     ASSERT_DOCUMENT_EQ(docs[1].getDocument(), *partIter[1]);
     ASSERT_FALSE(partIter[2]);
@@ -118,8 +116,7 @@ TEST_F(PartitionIteratorTest, AdvanceOverPartitionBoundary) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_DOCUMENT_EQ(docs[0].getDocument(), *partIter[0]);
     // First advance to the final document in partition with key "1".
     ASSERT_ADVANCE_RESULT(PartitionIterator::AdvanceResult::kAdvanced, partIter.advance());
@@ -136,8 +133,7 @@ TEST_F(PartitionIteratorTest, AdvanceResultsInEof) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_DOCUMENT_EQ(docs[0].getDocument(), *partIter[0]);
     ASSERT_ADVANCE_RESULT(PartitionIterator::AdvanceResult::kEOF, partIter.advance());
 
@@ -153,8 +149,7 @@ TEST_F(PartitionIteratorTest, CurrentReturnsCorrectDocumentAsIteratorAdvances) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_DOCUMENT_EQ(docs[0].getDocument(), *partIter[0]);
     partIter.advance();
     ASSERT_DOCUMENT_EQ(docs[1].getDocument(), *partIter[0]);
@@ -167,8 +162,7 @@ TEST_F(PartitionIteratorTest, EmptyCollectionReturnsEOF) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_FALSE(partIter[0]);
     ASSERT_ADVANCE_RESULT(PartitionIterator::AdvanceResult::kEOF, partIter.advance());
 }
@@ -179,8 +173,7 @@ TEST_F(PartitionIteratorTest, PartitionByArrayErrs) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_DOCUMENT_EQ(docs[0].getDocument(), *partIter[0]);
     ASSERT_THROWS_CODE(*partIter[1], AssertionException, ErrorCodes::TypeMismatch);
 }
@@ -191,8 +184,7 @@ TEST_F(PartitionIteratorTest, CurrentOffsetIsCorrectAfterDocumentsAreAccessed) {
     const auto mock = DocumentSourceMock::createForTest(docs, getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "a", getExpCtx()->variablesParseState);
-    auto partIter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto partIter = PartitionIterator(getExpCtx().get(), mock.get(), *key);
     ASSERT_EQ(0, partIter.getCurrentOffset());
     auto doc = partIter[0];
     partIter.advance();
diff --git a/src/mongo/db/pipeline/window_function/window_function_exec.cpp b/src/mongo/db/pipeline/window_function/window_function_exec.cpp
deleted file mode 100644
index a6ff3438df7..00000000000
--- a/src/mongo/db/pipeline/window_function/window_function_exec.cpp
+++ /dev/null
@@ -1,80 +0,0 @@
-/**
- *    Copyright (C) 2021-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_exec.h"
-#include "mongo/db/pipeline/window_function/window_function_exec_non_removable.h"
-
-namespace mongo {
-
-namespace {
-
-std::unique_ptr<WindowFunctionExec> translateDocumentWindow(
-    PartitionIterator* iter,
-    boost::intrusive_ptr<window_function::Expression> expr,
-    const WindowBounds::DocumentBased& bounds) {
-    uassert(5397904,
-            "Only 'unbounded' lower bound is currently supported",
-            stdx::holds_alternative<WindowBounds::Unbounded>(bounds.lower));
-    uassert(5397903,
-            "Only 'current' upper bound is currently supported",
-            stdx::holds_alternative<WindowBounds::Current>(bounds.upper));
-
-    // A left unbounded window will always be non-removable regardless of the upper
-    // bound.
-    return std::make_unique<WindowFunctionExecNonRemovable<AccumulatorState>>(
-        iter, std::move(expr->input()), expr->buildAccumulatorOnly(), bounds.upper);
-}
-
-}  // namespace
-
-std::unique_ptr<WindowFunctionExec> WindowFunctionExec::create(
-    PartitionIterator* iter, const WindowFunctionStatement& functionStmt) {
-    uassert(5397905,
-            "Window functions cannot set to dotted paths",
-            functionStmt.fieldName.find('.') == std::string::npos);
-
-    // Use a sentinel variable to avoid a compilation error when some cases of std::visit don't
-    // return a value.
-    std::unique_ptr<WindowFunctionExec> exec;
-    stdx::visit(
-        visit_helper::Overloaded{
-            [&](const WindowBounds::DocumentBased& docBase) {
-                exec = translateDocumentWindow(iter, functionStmt.expr, docBase);
-            },
-            [&](const WindowBounds::RangeBased& rangeBase) {
-                uasserted(5397901, "Ranged based windows not currently supported");
-            },
-            [&](const WindowBounds::TimeBased& timeBase) {
-                uasserted(5397902, "Time based windows are not currently supported");
-            }},
-        functionStmt.expr->bounds().bounds);
-    return exec;
-}
-
-}  // namespace mongo
diff --git a/src/mongo/db/pipeline/window_function/window_function_exec.h b/src/mongo/db/pipeline/window_function/window_function_exec.h
index 0a83de32595..4dfcbdd8356 100644
--- a/src/mongo/db/pipeline/window_function/window_function_exec.h
+++ b/src/mongo/db/pipeline/window_function/window_function_exec.h
@@ -32,7 +32,6 @@
 #include <queue>
 
 #include "mongo/db/pipeline/document_source.h"
-#include "mongo/db/pipeline/document_source_set_window_fields.h"
 #include "mongo/db/pipeline/expression.h"
 #include "mongo/db/pipeline/window_function/partition_iterator.h"
 #include "mongo/db/pipeline/window_function/window_bounds.h"
@@ -40,8 +39,6 @@
 
 namespace mongo {
 
-struct WindowFunctionStatement;
-
 /**
  * An interface for an executor class capable of evaluating a function over a given window
  * definition. The function must expose an accumulate-type interface and potentially a remove
@@ -52,12 +49,7 @@ struct WindowFunctionStatement;
  */
 class WindowFunctionExec {
 public:
-    /**
-     * Creates an appropriate WindowFunctionExec that is capable of evaluating the window function
-     * over the given bounds, both found within the WindowFunctionStatement.
-     */
-    static std::unique_ptr<WindowFunctionExec> create(PartitionIterator* iter,
-                                                      const WindowFunctionStatement& functionStmt);
+    WindowFunctionExec(PartitionIterator* iter) : _iter(iter){};
 
     /**
      * Retrieve the next value computed by the window function.
@@ -70,8 +62,6 @@ public:
     virtual void reset() = 0;
 
 protected:
-    WindowFunctionExec(PartitionIterator* iter) : _iter(iter){};
-
     PartitionIterator* _iter;
 };
 
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 0892d7d164c..bdc773ee131 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
@@ -152,8 +152,7 @@ TEST_F(WindowFunctionExecNonRemovableTest, AccumulateOnlyWithMultiplePartitions)
     auto mock = DocumentSourceMock::createForTest(std::move(docs), getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto iter = PartitionIterator(
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key));
+    auto iter = PartitionIterator{getExpCtx().get(), mock.get(), *key};
     auto input =
         ExpressionFieldPath::parse(getExpCtx().get(), "$a", getExpCtx()->variablesParseState);
     auto mgr = WindowFunctionExecNonRemovable<AccumulatorState>(
@@ -329,8 +328,7 @@ TEST_F(WindowFunctionExecRemovableDocumentTest, CanResetFunction) {
     auto mock = DocumentSourceMock::createForTest(std::move(docs), getExpCtx());
     auto key = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    auto iter = PartitionIterator{
-        getExpCtx().get(), mock.get(), boost::optional<boost::intrusive_ptr<Expression>>(key)};
+    auto iter = PartitionIterator{getExpCtx().get(), mock.get(), *key};
     auto input =
         ExpressionFieldPath::parse(getExpCtx().get(), "$a", getExpCtx()->variablesParseState);
     CollatorInterfaceMock collator = CollatorInterfaceMock::MockType::kToLowerString;
@@ -357,8 +355,7 @@ TEST_F(WindowFunctionExecRemovableDocumentTest, CanResetFunction) {
     auto mockTwo = DocumentSourceMock::createForTest(std::move(docsTwo), getExpCtx());
     auto keyTwo = ExpressionFieldPath::createPathFromString(
         getExpCtx().get(), "key", getExpCtx()->variablesParseState);
-    iter = PartitionIterator{
-        getExpCtx().get(), mockTwo.get(), boost::optional<boost::intrusive_ptr<Expression>>(key)};
+    iter = PartitionIterator{getExpCtx().get(), mockTwo.get(), *key};
     input = ExpressionFieldPath::parse(getExpCtx().get(), "$a", getExpCtx()->variablesParseState);
     maxFunc = std::make_unique<WindowFunctionMax>(cmp);
     mgr = WindowFunctionExecRemovableDocument(
diff --git a/src/mongo/db/pipeline/window_function/window_function_expression.h b/src/mongo/db/pipeline/window_function/window_function_expression.h
index f02445314ee..bf1fc38a55e 100644
--- a/src/mongo/db/pipeline/window_function/window_function_expression.h
+++ b/src/mongo/db/pipeline/window_function/window_function_expression.h
@@ -29,7 +29,6 @@
 
 #pragma once
 
-#include "mongo/db/pipeline/accumulator.h"
 #include "mongo/db/pipeline/document_source.h"
 #include "mongo/db/pipeline/document_source_set_window_fields_gen.h"
 #include "mongo/db/pipeline/window_function/window_bounds.h"
@@ -93,13 +92,10 @@ public:
 
     virtual boost::intrusive_ptr<::mongo::Expression> input() const = 0;
 
-    virtual boost::intrusive_ptr<AccumulatorState> buildAccumulatorOnly() const = 0;
-
 private:
     static StringMap<Parser> parserMap;
 };
 
-template <typename NonRemovableType>
 class ExpressionFromAccumulator : public Expression {
 public:
     static boost::intrusive_ptr<Expression> parse(BSONElement elem,
@@ -118,8 +114,8 @@ public:
                                   << " found an unknown argument: " << arg.fieldNameStringData(),
                     allowedFields.find(arg.fieldNameStringData()) != allowedFields.end());
         }
-        return make_intrusive<ExpressionFromAccumulator<NonRemovableType>>(
-            expCtx, std::move(accumulatorName), std::move(input), std::move(bounds));
+        return make_intrusive<ExpressionFromAccumulator>(
+            std::move(accumulatorName), std::move(input), std::move(bounds));
     }
     Value serialize(boost::optional<ExplainOptions::Verbosity> explain) const final {
         MutableDocument args;
@@ -132,12 +128,10 @@ public:
         }};
     }
 
-    ExpressionFromAccumulator(ExpressionContext* expCtx,
-                              std::string accumulatorName,
+    ExpressionFromAccumulator(std::string accumulatorName,
                               boost::intrusive_ptr<::mongo::Expression> input,
                               WindowBounds bounds)
-        : _expCtx(expCtx),
-          _accumulatorName(std::move(accumulatorName)),
+        : _accumulatorName(std::move(accumulatorName)),
           _input(std::move(input)),
           _bounds(std::move(bounds)) {}
 
@@ -153,12 +147,8 @@ public:
         return _bounds;
     }
 
-    boost::intrusive_ptr<AccumulatorState> buildAccumulatorOnly() const {
-        return NonRemovableType::create(_expCtx);
-    }
 
 private:
-    ExpressionContext* _expCtx;
     std::string _accumulatorName;
     boost::intrusive_ptr<::mongo::Expression> _input;
     WindowBounds _bounds;