Revert "SERVER-29135 Add post-image lookup to $changeNotification"

This reverts commit ad30a49a33b8773cbc07388bb257d605cbd6aa12.

23 files changed, 158 insertions, 916 deletions

diff --git a/src/mongo/db/pipeline/SConscript b/src/mongo/db/pipeline/SConscript
index 093cbb5a5c9..0d67ccbb2df 100644
--- a/src/mongo/db/pipeline/SConscript
+++ b/src/mongo/db/pipeline/SConscript
@@ -135,9 +135,7 @@ env.CppUnitTest(
         'document_source_geo_near_test.cpp',
         'document_source_group_test.cpp',
         'document_source_limit_test.cpp',
-        'document_source_lookup_change_post_image_test.cpp',
         'document_source_lookup_test.cpp',
-        'document_source_graph_lookup_test.cpp',
         'document_source_match_test.cpp',
         'document_source_mock_test.cpp',
         'document_source_project_test.cpp',
@@ -233,6 +231,7 @@ docSourceEnv.Library(
         'document_source_add_fields.cpp',
         'document_source_bucket.cpp',
         'document_source_bucket_auto.cpp',
+        'document_source_change_notification.cpp',
         'document_source_coll_stats.cpp',
         'document_source_count.cpp',
         'document_source_current_op.cpp',
@@ -263,7 +262,6 @@ docSourceEnv.Library(
         '$BUILD_DIR/mongo/db/matcher/expression_algo',
         '$BUILD_DIR/mongo/db/matcher/expressions',
         '$BUILD_DIR/mongo/db/pipeline/lite_parsed_document_source',
-        '$BUILD_DIR/mongo/db/repl/oplog_entry',
         '$BUILD_DIR/mongo/db/service_context',
         '$BUILD_DIR/mongo/db/stats/top',
         '$BUILD_DIR/mongo/db/storage/encryption_hooks',
@@ -311,10 +309,8 @@ env.Library(
 env.Library(
     target='document_source_lookup',
     source=[
-        'document_source_change_notification.cpp',
         'document_source_graph_lookup.cpp',
         'document_source_lookup.cpp',
-        'document_source_lookup_change_post_image.cpp',
     ],
     LIBDEPS=[
         'document_source',
@@ -322,6 +318,20 @@ env.Library(
     ],
 )
 
+env.CppUnitTest(
+    target='document_source_graph_lookup_test',
+    source='document_source_graph_lookup_test.cpp',
+    LIBDEPS=[
+        'document_source',
+        'document_source_lookup',
+        'document_value_test_util',
+        '$BUILD_DIR/mongo/db/auth/authorization_manager_mock_init',
+        '$BUILD_DIR/mongo/db/query/query_test_service_context',
+        '$BUILD_DIR/mongo/db/service_context_noop_init',
+        '$BUILD_DIR/mongo/s/is_mongos',
+    ],
+)
+
 env.Library(
     target='document_source_facet',
     source=[
diff --git a/src/mongo/db/pipeline/document_source.cpp b/src/mongo/db/pipeline/document_source.cpp
index a9d9f74181a..6e58adae2bf 100644
--- a/src/mongo/db/pipeline/document_source.cpp
+++ b/src/mongo/db/pipeline/document_source.cpp
@@ -41,7 +41,6 @@ namespace mongo {
 
 using Parser = DocumentSource::Parser;
 using boost::intrusive_ptr;
-using std::list;
 using std::string;
 using std::vector;
 
@@ -61,7 +60,7 @@ void DocumentSource::registerParser(string name, Parser parser) {
     parserMap[name] = parser;
 }
 
-list<intrusive_ptr<DocumentSource>> DocumentSource::parse(
+vector<intrusive_ptr<DocumentSource>> DocumentSource::parse(
     const intrusive_ptr<ExpressionContext>& expCtx, BSONObj stageObj) {
     uassert(16435,
             "A pipeline stage specification object must contain exactly one field.",
diff --git a/src/mongo/db/pipeline/document_source.h b/src/mongo/db/pipeline/document_source.h
index 383cd56e35f..2545f02d8de 100644
--- a/src/mongo/db/pipeline/document_source.h
+++ b/src/mongo/db/pipeline/document_source.h
@@ -85,7 +85,7 @@ class Document;
     MONGO_INITIALIZER(addToDocSourceParserMap_##key)(InitializerContext*) {                  \
         auto fullParserWrapper = [](BSONElement stageSpec,                                   \
                                     const boost::intrusive_ptr<ExpressionContext>& expCtx) { \
-            return std::list<boost::intrusive_ptr<DocumentSource>>{                          \
+            return std::vector<boost::intrusive_ptr<DocumentSource>>{                        \
                 (fullParser)(stageSpec, expCtx)};                                            \
         };                                                                                   \
         LiteParsedDocumentSource::registerParser("$" #key, liteParser);                      \
@@ -115,7 +115,7 @@ class Document;
 
 class DocumentSource : public IntrusiveCounterUnsigned {
 public:
-    using Parser = stdx::function<std::list<boost::intrusive_ptr<DocumentSource>>(
+    using Parser = stdx::function<std::vector<boost::intrusive_ptr<DocumentSource>>(
         BSONElement, const boost::intrusive_ptr<ExpressionContext>&)>;
 
     /**
@@ -303,7 +303,7 @@ public:
     /**
      * Create a DocumentSource pipeline stage from 'stageObj'.
      */
-    static std::list<boost::intrusive_ptr<DocumentSource>> parse(
+    static std::vector<boost::intrusive_ptr<DocumentSource>> parse(
         const boost::intrusive_ptr<ExpressionContext>& expCtx, BSONObj stageObj);
 
     /**
diff --git a/src/mongo/db/pipeline/document_source_bucket.cpp b/src/mongo/db/pipeline/document_source_bucket.cpp
index e209834b14d..853ef0aaa42 100644
--- a/src/mongo/db/pipeline/document_source_bucket.cpp
+++ b/src/mongo/db/pipeline/document_source_bucket.cpp
@@ -37,7 +37,6 @@ namespace mongo {
 
 using boost::intrusive_ptr;
 using std::vector;
-using std::list;
 
 REGISTER_MULTI_STAGE_ALIAS(bucket,
                            LiteParsedDocumentSourceDefault::parse,
@@ -53,7 +52,7 @@ intrusive_ptr<ExpressionConstant> getExpressionConstant(
 }
 }  // namespace
 
-list<intrusive_ptr<DocumentSource>> DocumentSourceBucket::createFromBson(
+vector<intrusive_ptr<DocumentSource>> DocumentSourceBucket::createFromBson(
     BSONElement elem, const intrusive_ptr<ExpressionContext>& pExpCtx) {
     uassert(40201,
             str::stream() << "Argument to $bucket stage must be an object, but found type: "
diff --git a/src/mongo/db/pipeline/document_source_bucket.h b/src/mongo/db/pipeline/document_source_bucket.h
index e059660fc99..aa83ee07cc2 100644
--- a/src/mongo/db/pipeline/document_source_bucket.h
+++ b/src/mongo/db/pipeline/document_source_bucket.h
@@ -40,7 +40,7 @@ public:
     /**
      * Returns a $group stage followed by a $sort stage.
      */
-    static std::list<boost::intrusive_ptr<DocumentSource>> createFromBson(
+    static std::vector<boost::intrusive_ptr<DocumentSource>> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
 private:
diff --git a/src/mongo/db/pipeline/document_source_bucket_test.cpp b/src/mongo/db/pipeline/document_source_bucket_test.cpp
index 26f18c4dca9..1a61934dcb5 100644
--- a/src/mongo/db/pipeline/document_source_bucket_test.cpp
+++ b/src/mongo/db/pipeline/document_source_bucket_test.cpp
@@ -47,22 +47,21 @@
 namespace mongo {
 namespace {
 
-using boost::intrusive_ptr;
-using std::list;
 using std::vector;
+using boost::intrusive_ptr;
 
 class BucketReturnsGroupAndSort : public AggregationContextFixture {
 public:
     void testCreateFromBsonResult(BSONObj bucketSpec, Value expectedGroupExplain) {
-        list<intrusive_ptr<DocumentSource>> result =
+        vector<intrusive_ptr<DocumentSource>> result =
             DocumentSourceBucket::createFromBson(bucketSpec.firstElement(), getExpCtx());
 
         ASSERT_EQUALS(result.size(), 2UL);
 
-        const auto* groupStage = dynamic_cast<DocumentSourceGroup*>(result.front().get());
+        const auto* groupStage = dynamic_cast<DocumentSourceGroup*>(result[0].get());
         ASSERT(groupStage);
 
-        const auto* sortStage = dynamic_cast<DocumentSourceSort*>(result.back().get());
+        const auto* sortStage = dynamic_cast<DocumentSourceSort*>(result[1].get());
         ASSERT(sortStage);
 
         // Serialize the DocumentSourceGroup and DocumentSourceSort from $bucket so that we can
@@ -155,7 +154,7 @@ TEST_F(BucketReturnsGroupAndSort, BucketSucceedsWithMultipleBoundaryValues) {
 
 class InvalidBucketSpec : public AggregationContextFixture {
 public:
-    list<intrusive_ptr<DocumentSource>> createBucket(BSONObj bucketSpec) {
+    vector<intrusive_ptr<DocumentSource>> createBucket(BSONObj bucketSpec) {
         auto sources = DocumentSourceBucket::createFromBson(bucketSpec.firstElement(), getExpCtx());
         return sources;
     }
@@ -268,14 +267,14 @@ TEST_F(InvalidBucketSpec, GroupFailsForBucketWithInvalidOutputField) {
 
 TEST_F(InvalidBucketSpec, SwitchFailsForBucketWhenNoDefaultSpecified) {
     const auto spec = fromjson("{$bucket : {groupBy : '$x', boundaries : [1, 2, 3]}}");
-    list<intrusive_ptr<DocumentSource>> bucketStages = createBucket(spec);
+    vector<intrusive_ptr<DocumentSource>> bucketStages = createBucket(spec);
 
     ASSERT_EQUALS(bucketStages.size(), 2UL);
 
-    auto* groupStage = dynamic_cast<DocumentSourceGroup*>(bucketStages.front().get());
+    auto* groupStage = dynamic_cast<DocumentSourceGroup*>(bucketStages[0].get());
     ASSERT(groupStage);
 
-    const auto* sortStage = dynamic_cast<DocumentSourceSort*>(bucketStages.back().get());
+    const auto* sortStage = dynamic_cast<DocumentSourceSort*>(bucketStages[1].get());
     ASSERT(sortStage);
 
     auto doc = Document{{"x", 4}};
diff --git a/src/mongo/db/pipeline/document_source_change_notification.cpp b/src/mongo/db/pipeline/document_source_change_notification.cpp
index d173d1183d5..dff06f05802 100644
--- a/src/mongo/db/pipeline/document_source_change_notification.cpp
+++ b/src/mongo/db/pipeline/document_source_change_notification.cpp
@@ -30,46 +30,30 @@
 
 #include "mongo/db/pipeline/document_source_change_notification.h"
 
-#include "mongo/bson/simple_bsonelement_comparator.h"
 #include "mongo/db/pipeline/document_source_limit.h"
-#include "mongo/db/pipeline/document_source_lookup_change_post_image.h"
 #include "mongo/db/pipeline/document_source_match.h"
 #include "mongo/db/pipeline/document_source_sort.h"
 #include "mongo/db/pipeline/expression.h"
 #include "mongo/db/pipeline/lite_parsed_document_source.h"
-#include "mongo/db/repl/oplog_entry.h"
-#include "mongo/db/repl/oplog_entry_gen.h"
 #include "mongo/util/log.h"
 
 namespace mongo {
 
 using boost::intrusive_ptr;
 using boost::optional;
-using std::list;
-using std::string;
 using std::vector;
+using std::string;
+
+constexpr StringData kNamespaceField = "ns"_sd;
+constexpr StringData kTimestmapField = "ts"_sd;
+constexpr StringData kOpTypeField = "op"_sd;
+constexpr StringData kOField = "o"_sd;
+constexpr StringData kIdField = "_id"_sd;
 
-// The $changeNotification stage is an alias for many stages, but we need to be able to serialize
-// and re-parse the pipeline. To make this work, the 'transformation' stage will serialize itself
-// with the original specification, and all other stages that are created during the alias expansion
-// will not serialize themselves.
 REGISTER_MULTI_STAGE_ALIAS(changeNotification,
                            DocumentSourceChangeNotification::LiteParsed::parse,
                            DocumentSourceChangeNotification::createFromBson);
 
-constexpr StringData DocumentSourceChangeNotification::kDocumentKeyField;
-constexpr StringData DocumentSourceChangeNotification::kFullDocumentField;
-constexpr StringData DocumentSourceChangeNotification::kIdField;
-constexpr StringData DocumentSourceChangeNotification::kNamespaceField;
-constexpr StringData DocumentSourceChangeNotification::kOperationTypeField;
-constexpr StringData DocumentSourceChangeNotification::kStageName;
-constexpr StringData DocumentSourceChangeNotification::kTimestmapField;
-constexpr StringData DocumentSourceChangeNotification::kUpdateOpType;
-constexpr StringData DocumentSourceChangeNotification::kDeleteOpType;
-constexpr StringData DocumentSourceChangeNotification::kReplaceOpType;
-constexpr StringData DocumentSourceChangeNotification::kInsertOpType;
-constexpr StringData DocumentSourceChangeNotification::kInvalidateOpType;
-
 namespace {
 
 static constexpr StringData kOplogMatchExplainName = "$_internalOplogMatch"_sd;
@@ -143,7 +127,7 @@ BSONObj DocumentSourceChangeNotification::buildMatchFilter(const NamespaceString
     return BSON("ts" << GT << Timestamp() << "$or" << BSON_ARRAY(opMatch << commandMatch));
 }
 
-list<intrusive_ptr<DocumentSource>> DocumentSourceChangeNotification::createFromBson(
+vector<intrusive_ptr<DocumentSource>> DocumentSourceChangeNotification::createFromBson(
     BSONElement elem, const intrusive_ptr<ExpressionContext>& expCtx) {
     // TODO: Add sharding support here (SERVER-29141).
     uassert(40470,
@@ -153,54 +137,17 @@ list<intrusive_ptr<DocumentSource>> DocumentSourceChangeNotification::createFrom
             "Only default collation is allowed when using a $changeNotification stage.",
             !expCtx->getCollator());
 
-    uassert(40573,
-            str::stream() << "the $changeNotification stage must be specified as an object, got "
-                          << typeName(elem.type()),
-            elem.type() == BSONType::Object);
-
-    bool shouldLookupPostImage = false;
-    for (auto&& option : elem.embeddedObject()) {
-        auto optionName = option.fieldNameStringData();
-        if (optionName == "fullDocument"_sd) {
-            uassert(40574,
-                    str::stream() << "the 'fullDocument' option to the $changeNotification stage "
-                                     "must be a string, got "
-                                  << typeName(option.type()),
-                    option.type() == BSONType::String);
-            auto fullDocOption = option.valueStringData();
-            uassert(40575,
-                    str::stream() << "unrecognized value for the 'fullDocument' option to the "
-                                     "$changeNotification stage. Expected \"none\" or "
-                                     "\"fullDocument\", got \""
-                                  << option.String()
-                                  << "\"",
-                    fullDocOption == "lookup"_sd || fullDocOption == "none"_sd);
-            shouldLookupPostImage = (fullDocOption == "lookup"_sd);
-        } else if (optionName == "resumeAfter"_sd) {
-            uasserted(
-                40576,
-                "the 'resumeAfter' option to the $changeNotification stage is not yet supported");
-        } else {
-            uasserted(40577,
-                      str::stream() << "unrecognized option to $changeNotification stage: \""
-                                    << optionName
-                                    << "\"");
-        }
-    }
+    BSONObj filter = buildMatchFilter(expCtx->ns);
 
-    auto oplogMatch = DocumentSourceOplogMatch::create(buildMatchFilter(expCtx->ns), expCtx);
-    auto transformation = createTransformationStage(elem.embeddedObject(), expCtx);
-    list<intrusive_ptr<DocumentSource>> stages = {oplogMatch, transformation};
-    if (shouldLookupPostImage) {
-        stages.push_back(DocumentSourceLookupChangePostImage::create(expCtx));
-    }
-    return stages;
+    auto oplogMatch = DocumentSourceOplogMatch::create(filter, expCtx);
+    auto transformation = createTransformationStage(expCtx);
+    return {oplogMatch, transformation};
 }
 
 intrusive_ptr<DocumentSource> DocumentSourceChangeNotification::createTransformationStage(
-    BSONObj changeNotificationSpec, const intrusive_ptr<ExpressionContext>& expCtx) {
+    const intrusive_ptr<ExpressionContext>& expCtx) {
     return intrusive_ptr<DocumentSource>(new DocumentSourceSingleDocumentTransformation(
-        expCtx, stdx::make_unique<Transformation>(changeNotificationSpec), kStageName.toString()));
+        expCtx, stdx::make_unique<Transformation>(), "$changeNotification"));
 }
 
 namespace {
@@ -220,103 +167,89 @@ Document DocumentSourceChangeNotification::Transformation::applyTransformation(
     MutableDocument doc;
 
     // Extract the fields we need.
-    checkValueType(input[repl::OplogEntry::kOpTypeFieldName],
-                   repl::OplogEntry::kOpTypeFieldName,
-                   BSONType::String);
-    string op = input[repl::OplogEntry::kOpTypeFieldName].getString();
-    Value ts = input[repl::OplogEntry::kTimestampFieldName];
-    Value ns = input[repl::OplogEntry::kNamespaceFieldName];
-    checkValueType(ns, repl::OplogEntry::kNamespaceFieldName, BSONType::String);
+    checkValueType(input[kOpTypeField], kOpTypeField, BSONType::String);
+    string op = input[kOpTypeField].getString();
+    Value ts = input[kTimestmapField];
+    Value ns = input[kNamespaceField];
+    checkValueType(ns, kNamespaceField, BSONType::String);
     NamespaceString nss(ns.getString());
     Value id = input.getNestedField("o._id");
     // Non-replace updates have the _id in field "o2".
     Value documentId = id.missing() ? input.getNestedField("o2._id") : id;
-    StringData operationType;
-    Value fullDocument = Value(BSONNULL);
+    string operationType;
+    Value newDocument;
     Value updateDescription;
 
     // Deal with CRUD operations and commands.
-    auto opType = repl::OpType_parse(IDLParserErrorContext("ChangeNotificationEntry.op"), op);
-    switch (opType) {
-        case repl::OpTypeEnum::kInsert: {
-            operationType = kInsertOpType;
-            fullDocument = input[repl::OplogEntry::kObjectFieldName];
-            break;
-        }
-        case repl::OpTypeEnum::kDelete: {
-            operationType = kDeleteOpType;
-            break;
-        }
-        case repl::OpTypeEnum::kUpdate: {
-            if (id.missing()) {
-                operationType = kUpdateOpType;
-                checkValueType(input[repl::OplogEntry::kObjectFieldName],
-                               repl::OplogEntry::kObjectFieldName,
-                               BSONType::Object);
-                Document opObject = input[repl::OplogEntry::kObjectFieldName].getDocument();
-                Value updatedFields = opObject["$set"];
-                Value removedFields = opObject["$unset"];
-
-                // Extract the field names of $unset document.
-                vector<Value> removedFieldsVector;
-                if (removedFields.getType() == BSONType::Object) {
-                    auto iter = removedFields.getDocument().fieldIterator();
-                    while (iter.more()) {
-                        removedFieldsVector.push_back(Value(iter.next().first));
-                    }
+    if (op == "i") {
+        operationType = "insert";
+        newDocument = input[kOField];
+    } else if (op == "d") {
+        operationType = "delete";
+    } else if (op == "u") {
+        if (id.missing()) {
+            operationType = "update";
+            checkValueType(input[kOField], kOField, BSONType::Object);
+            Document o = input[kOField].getDocument();
+            Value updatedFields = o["$set"];
+            Value removedFields = o["$unset"];
+
+            // Extract the field names of $unset document.
+            vector<Value> removedFieldsVector;
+            if (removedFields.getType() == BSONType::Object) {
+                auto iter = removedFields.getDocument().fieldIterator();
+                while (iter.more()) {
+                    removedFieldsVector.push_back(Value(iter.next().first));
                 }
-                updateDescription = Value(Document{
-                    {"updatedFields", updatedFields.missing() ? Value(Document()) : updatedFields},
-                    {"removedFields", removedFieldsVector}});
-            } else {
-                operationType = kReplaceOpType;
-                fullDocument = input[repl::OplogEntry::kObjectFieldName];
             }
-            break;
-        }
-        case repl::OpTypeEnum::kCommand: {
-            operationType = kInvalidateOpType;
-            // Make sure the result doesn't have a document id.
-            documentId = Value();
-            break;
+            updateDescription = Value(Document{
+                {"updatedFields", updatedFields.missing() ? Value(Document()) : updatedFields},
+                {"removedFields", removedFieldsVector}});
+        } else {
+            operationType = "replace";
+            newDocument = input[kOField];
         }
-        default: { MONGO_UNREACHABLE; }
+    } else if (op == "c") {
+        operationType = "invalidate";
+        // Make sure the result doesn't have a document id.
+        documentId = Value();
     }
 
-    // Construct the result document. Note that 'documentId' might be the missing value, in which
-    // case it will not appear in the output.
+    // Construct the result document. If document id is missing, it will not appear in the output.
     doc.addField(
         kIdField,
         Value(Document{{kTimestmapField, ts}, {kNamespaceField, ns}, {kIdField, documentId}}));
-    doc.addField(kOperationTypeField, Value(operationType));
-    doc.addField(kFullDocumentField, fullDocument);
+    doc.addField("operationType", Value(operationType));
 
     // "invalidate" entry has fewer fields.
-    if (opType == repl::OpTypeEnum::kCommand) {
+    if (op == "c") {
         return doc.freeze();
     }
 
+    // Add fields for normal operations.
     doc.addField(kNamespaceField, Value(Document{{"db", nss.db()}, {"coll", nss.coll()}}));
-    doc.addField(kDocumentKeyField, Value(Document{{kIdField, documentId}}));
+    doc.addField("documentKey", Value(Document{{kIdField, documentId}}));
 
-    // Note that 'updateDescription' might be the 'missing' value, in which case it will not be
-    // serialized.
+    // If newDocument or updateDescription is missing, it will not be serialized.
+    doc.addField("newDocument", newDocument);
     doc.addField("updateDescription", updateDescription);
     return doc.freeze();
 }
 
 Document DocumentSourceChangeNotification::Transformation::serializeStageOptions(
     boost::optional<ExplainOptions::Verbosity> explain) const {
-    return Document(_changeNotificationSpec);
+    // TODO SERVER-29135 Be sure to re-serialize the 'postImage' argument.
+    // TODO SERVER-29131 Be sure to re-serialize the 'resumeAfter' argument.
+    return Document();
 }
 
 DocumentSource::GetDepsReturn DocumentSourceChangeNotification::Transformation::addDependencies(
     DepsTracker* deps) const {
-    deps->fields.insert(repl::OplogEntry::kOpTypeFieldName.toString());
-    deps->fields.insert(repl::OplogEntry::kTimestampFieldName.toString());
-    deps->fields.insert(repl::OplogEntry::kNamespaceFieldName.toString());
-    deps->fields.insert(repl::OplogEntry::kObjectFieldName.toString());
-    deps->fields.insert(repl::OplogEntry::kObject2FieldName.toString());
+    deps->fields.insert(kOpTypeField.toString());
+    deps->fields.insert(kTimestmapField.toString());
+    deps->fields.insert(kNamespaceField.toString());
+    deps->fields.insert(kOField.toString());
+    deps->fields.insert("o2");
     return DocumentSource::GetDepsReturn::EXHAUSTIVE_ALL;
 }
 
diff --git a/src/mongo/db/pipeline/document_source_change_notification.h b/src/mongo/db/pipeline/document_source_change_notification.h
index ad10a5ad210..3b38a908626 100644
--- a/src/mongo/db/pipeline/document_source_change_notification.h
+++ b/src/mongo/db/pipeline/document_source_change_notification.h
@@ -51,8 +51,6 @@ public:
         }
 
         stdx::unordered_set<NamespaceString> getInvolvedNamespaces() const final {
-            // TODO SERVER-29138: we need to communicate that this stage will need to look up
-            // documents from different collections.
             return stdx::unordered_set<NamespaceString>();
         }
 
@@ -64,8 +62,6 @@ public:
 
     class Transformation : public DocumentSourceSingleDocumentTransformation::TransformerInterface {
     public:
-        Transformation(BSONObj changeNotificationSpec)
-            : _changeNotificationSpec(changeNotificationSpec.getOwned()) {}
         ~Transformation() = default;
         Document applyTransformation(const Document& input) final;
         TransformerType getType() const final {
@@ -76,48 +72,10 @@ public:
             boost::optional<ExplainOptions::Verbosity> explain) const final;
         DocumentSource::GetDepsReturn addDependencies(DepsTracker* deps) const final;
         DocumentSource::GetModPathsReturn getModifiedPaths() const final;
-
-    private:
-        BSONObj _changeNotificationSpec;
     };
 
-    // The name of the field where the document key (_id and shard key, if present) will be found
-    // after the transformation.
-    static constexpr StringData kDocumentKeyField = "documentKey"_sd;
-
-    // The name of the field where the full document will be found after the transformation. The
-    // full document is only present for certain types of operations, such as an insert.
-    static constexpr StringData kFullDocumentField = "fullDocument"_sd;
-
-    // The name of the field where the change identifier will be located after the transformation.
-    static constexpr StringData kIdField = "_id"_sd;
-
-    // The name of the field where the namespace of the change will be located after the
-    // transformation.
-    static constexpr StringData kNamespaceField = "ns"_sd;
-
-    // The name of the field where the type of the operation will be located after the
-    // transformation.
-    static constexpr StringData kOperationTypeField = "operationType"_sd;
-
-    // The name of this stage.
-    static constexpr StringData kStageName = "$changeNotification"_sd;
-
-    // The name of the field where the timestamp of the change will be located after the
-    // transformation. The timestamp will be located inside the change identifier, so the full path
-    // to the timestamp will be kIdField + "." + kTimestampField.
-    static constexpr StringData kTimestmapField = "ts"_sd;
-
-    // The different types of operations we can use for the operation type.
-    static constexpr StringData kUpdateOpType = "update"_sd;
-    static constexpr StringData kDeleteOpType = "delete"_sd;
-    static constexpr StringData kReplaceOpType = "replace"_sd;
-    static constexpr StringData kInsertOpType = "insert"_sd;
-    static constexpr StringData kInvalidateOpType = "invalidate"_sd;
-
     /**
-     * Produce the BSON object representing the filter for the $match stage to filter oplog entries
-     * to only those relevant for this $changeNotification stage.
+     * Produce the BSON for the $match stage based on a $changeNotification stage.
      */
     static BSONObj buildMatchFilter(const NamespaceString& nss);
 
@@ -125,11 +83,11 @@ public:
      * Parses a $changeNotification stage from 'elem' and produces the $match and transformation
      * stages required.
      */
-    static std::list<boost::intrusive_ptr<DocumentSource>> createFromBson(
+    static std::vector<boost::intrusive_ptr<DocumentSource>> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& expCtx);
 
     static boost::intrusive_ptr<DocumentSource> createTransformationStage(
-        BSONObj changeNotificationSpec, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
+        const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
 private:
     // It is illegal to construct a DocumentSourceChangeNotification directly, use createFromBson()
diff --git a/src/mongo/db/pipeline/document_source_change_notification_test.cpp b/src/mongo/db/pipeline/document_source_change_notification_test.cpp
index 9c08bd91637..b3595789577 100644
--- a/src/mongo/db/pipeline/document_source_change_notification_test.cpp
+++ b/src/mongo/db/pipeline/document_source_change_notification_test.cpp
@@ -49,18 +49,14 @@
 namespace mongo {
 namespace {
 
+using std::vector;
+using std::string;
 using boost::intrusive_ptr;
-using repl::OpTypeEnum;
 using repl::OplogEntry;
-using std::list;
-using std::string;
-using std::vector;
-
+using repl::OpTypeEnum;
 using D = Document;
 using V = Value;
 
-using DSChangeNotification = DocumentSourceChangeNotification;
-
 static const Timestamp ts(100, 1);
 static const repl::OpTime optime(ts, 1);
 static const NamespaceString nss("unittests.change_notification");
@@ -71,10 +67,10 @@ public:
 
     void checkTransformation(const OplogEntry& entry, const boost::optional<Document> expectedDoc) {
         const auto spec = fromjson("{$changeNotification: {}}");
-        list<intrusive_ptr<DocumentSource>> result =
-            DSChangeNotification::createFromBson(spec.firstElement(), getExpCtx());
+        vector<intrusive_ptr<DocumentSource>> result =
+            DocumentSourceChangeNotification::createFromBson(spec.firstElement(), getExpCtx());
 
-        auto match = dynamic_cast<DocumentSourceMatch*>(result.front().get());
+        auto match = dynamic_cast<DocumentSourceMatch*>(result[0].get());
         ASSERT(match);
         auto mock = DocumentSourceMock::create(D(entry.toBSON()));
         match->setSource(mock.get());
@@ -82,7 +78,7 @@ public:
         // Check the oplog entry is transformed correctly.
         auto transform = result.back().get();
         ASSERT(transform);
-        ASSERT_EQ(string(transform->getSourceName()), DSChangeNotification::kStageName);
+        ASSERT_EQ(string(transform->getSourceName()), "$changeNotification");
         transform->setSource(match);
 
         auto next = transform->getNext();
@@ -98,62 +94,16 @@ public:
     }
 };
 
-TEST_F(ChangeNotificationStageTest, ShouldRejectUnrecognizedOption) {
-    auto expCtx = getExpCtx();
-
-    ASSERT_THROWS_CODE(
-        DSChangeNotification::createFromBson(
-            BSON(DSChangeNotification::kStageName << BSON("unexpected" << 4)).firstElement(),
-            expCtx),
-        UserException,
-        40577);
-}
-
-TEST_F(ChangeNotificationStageTest, ShouldRejectResumeAfterOption) {
-    // TODO SERVER-29131 change this test to accept the option.
-    auto expCtx = getExpCtx();
-
-    ASSERT_THROWS_CODE(
-        DSChangeNotification::createFromBson(
-            BSON(DSChangeNotification::kStageName << BSON("resumeAfter" << ts)).firstElement(),
-            expCtx),
-        UserException,
-        40576);
-}
-
-TEST_F(ChangeNotificationStageTest, ShouldRejectNonStringFullDocumentOption) {
-    auto expCtx = getExpCtx();
-
-    ASSERT_THROWS_CODE(
-        DSChangeNotification::createFromBson(
-            BSON(DSChangeNotification::kStageName << BSON("fullDocument" << true)).firstElement(),
-            expCtx),
-        UserException,
-        40574);
-}
-
-TEST_F(ChangeNotificationStageTest, ShouldRejectUnrecognizedFullDocumentOption) {
-    auto expCtx = getExpCtx();
-
-    ASSERT_THROWS_CODE(DSChangeNotification::createFromBson(
-                           BSON(DSChangeNotification::kStageName << BSON("fullDocument"
-                                                                         << "unrecognized"))
-                               .firstElement(),
-                           expCtx),
-                       UserException,
-                       40575);
-}
-
 TEST_F(ChangeNotificationStageTest, StagesGeneratedCorrectly) {
     const auto spec = fromjson("{$changeNotification: {}}");
 
-    list<intrusive_ptr<DocumentSource>> result =
-        DSChangeNotification::createFromBson(spec.firstElement(), getExpCtx());
+    vector<intrusive_ptr<DocumentSource>> result =
+        DocumentSourceChangeNotification::createFromBson(spec.firstElement(), getExpCtx());
 
     ASSERT_EQUALS(result.size(), 2UL);
-    ASSERT_TRUE(dynamic_cast<DocumentSourceMatch*>(result.front().get()));
-    ASSERT_EQUALS(string(result.front()->getSourceName()), DSChangeNotification::kStageName);
-    ASSERT_EQUALS(string(result.back()->getSourceName()), DSChangeNotification::kStageName);
+    ASSERT_TRUE(dynamic_cast<DocumentSourceMatch*>(result[0].get()));
+    ASSERT_EQUALS(string(result[0]->getSourceName()), "$changeNotification");
+    ASSERT_EQUALS(string(result[1]->getSourceName()), "$changeNotification");
 
     // TODO: Check explain result.
 }
@@ -162,11 +112,11 @@ TEST_F(ChangeNotificationStageTest, TransformInsert) {
     OplogEntry insert(optime, 1, OpTypeEnum::kInsert, nss, BSON("_id" << 1 << "x" << 1));
     // Insert
     Document expectedInsert{
-        {DSChangeNotification::kIdField, D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
-        {DSChangeNotification::kOperationTypeField, DSChangeNotification::kInsertOpType},
-        {DSChangeNotification::kFullDocumentField, D{{"_id", 1}, {"x", 1}}},
-        {DSChangeNotification::kNamespaceField, D{{"db", nss.db()}, {"coll", nss.coll()}}},
-        {DSChangeNotification::kDocumentKeyField, D{{"_id", 1}}},
+        {"_id", D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
+        {"operationType", "insert"_sd},
+        {"ns", D{{"db", nss.db()}, {"coll", nss.coll()}}},
+        {"documentKey", D{{"_id", 1}}},
+        {"newDocument", D{{"_id", 1}, {"x", 1}}},
     };
     checkTransformation(insert, expectedInsert);
 }
@@ -176,15 +126,13 @@ TEST_F(ChangeNotificationStageTest, TransformUpdateFields) {
         optime, 1, OpTypeEnum::kUpdate, nss, BSON("$set" << BSON("y" << 1)), BSON("_id" << 1));
     // Update fields
     Document expectedUpdateField{
-        {DSChangeNotification::kIdField, D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
-        {DSChangeNotification::kOperationTypeField, DSChangeNotification::kUpdateOpType},
-        {DSChangeNotification::kFullDocumentField, BSONNULL},
-        {DSChangeNotification::kNamespaceField, D{{"db", nss.db()}, {"coll", nss.coll()}}},
-        {DSChangeNotification::kDocumentKeyField, D{{"_id", 1}}},
+        {"_id", D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
+        {"operationType", "update"_sd},
+        {"ns", D{{"db", nss.db()}, {"coll", nss.coll()}}},
+        {"documentKey", D{{"_id", 1}}},
         {
             "updateDescription", D{{"updatedFields", D{{"y", 1}}}, {"removedFields", vector<V>()}},
-        },
-    };
+        }};
     checkTransformation(updateField, expectedUpdateField);
 }
 
@@ -193,11 +141,10 @@ TEST_F(ChangeNotificationStageTest, TransformRemoveFields) {
         optime, 1, OpTypeEnum::kUpdate, nss, BSON("$unset" << BSON("y" << 1)), BSON("_id" << 1));
     // Remove fields
     Document expectedRemoveField{
-        {DSChangeNotification::kIdField, D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
-        {DSChangeNotification::kOperationTypeField, DSChangeNotification::kUpdateOpType},
-        {DSChangeNotification::kFullDocumentField, BSONNULL},
-        {DSChangeNotification::kNamespaceField, D{{"db", nss.db()}, {"coll", nss.coll()}}},
-        {DSChangeNotification::kDocumentKeyField, D{{"_id", 1}}},
+        {"_id", D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
+        {"operationType", "update"_sd},
+        {"ns", D{{"db", nss.db()}, {"coll", nss.coll()}}},
+        {"documentKey", D{{"_id", 1}}},
         {
             "updateDescription", D{{"updatedFields", D{}}, {"removedFields", vector<V>{V("y"_sd)}}},
         }};
@@ -209,11 +156,11 @@ TEST_F(ChangeNotificationStageTest, TransformReplace) {
         optime, 1, OpTypeEnum::kUpdate, nss, BSON("_id" << 1 << "y" << 1), BSON("_id" << 1));
     // Replace
     Document expectedReplace{
-        {DSChangeNotification::kIdField, D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
-        {DSChangeNotification::kOperationTypeField, DSChangeNotification::kReplaceOpType},
-        {DSChangeNotification::kFullDocumentField, D{{"_id", 1}, {"y", 1}}},
-        {DSChangeNotification::kNamespaceField, D{{"db", nss.db()}, {"coll", nss.coll()}}},
-        {DSChangeNotification::kDocumentKeyField, D{{"_id", 1}}},
+        {"_id", D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
+        {"operationType", "replace"_sd},
+        {"ns", D{{"db", nss.db()}, {"coll", nss.coll()}}},
+        {"documentKey", D{{"_id", 1}}},
+        {"newDocument", D{{"_id", 1}, {"y", 1}}},
     };
     checkTransformation(replace, expectedReplace);
 }
@@ -222,11 +169,10 @@ TEST_F(ChangeNotificationStageTest, TransformDelete) {
     OplogEntry deleteEntry(optime, 1, OpTypeEnum::kDelete, nss, BSON("_id" << 1));
     // Delete
     Document expectedDelete{
-        {DSChangeNotification::kIdField, D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
-        {DSChangeNotification::kOperationTypeField, DSChangeNotification::kDeleteOpType},
-        {DSChangeNotification::kFullDocumentField, BSONNULL},
-        {DSChangeNotification::kNamespaceField, D{{"db", nss.db()}, {"coll", nss.coll()}}},
-        {DSChangeNotification::kDocumentKeyField, D{{"_id", 1}}},
+        {"_id", D{{"ts", ts}, {"ns", nss.ns()}, {"_id", 1}}},
+        {"operationType", "delete"_sd},
+        {"ns", D{{"db", nss.db()}, {"coll", nss.coll()}}},
+        {"documentKey", D{{"_id", 1}}},
     };
     checkTransformation(deleteEntry, expectedDelete);
 }
@@ -241,9 +187,7 @@ TEST_F(ChangeNotificationStageTest, TransformInvalidate) {
 
     // Invalidate entry includes $cmd namespace in _id and doesn't have a document id.
     Document expectedInvalidate{
-        {DSChangeNotification::kIdField, D{{"ts", ts}, {"ns", nss.getCommandNS().ns()}}},
-        {DSChangeNotification::kOperationTypeField, DSChangeNotification::kInvalidateOpType},
-        {DSChangeNotification::kFullDocumentField, BSONNULL},
+        {"_id", D{{"ts", ts}, {"ns", nss.getCommandNS().ns()}}}, {"operationType", "invalidate"_sd},
     };
     for (auto& entry : {dropColl, dropDB, rename}) {
         checkTransformation(entry, expectedInvalidate);
@@ -259,9 +203,8 @@ TEST_F(ChangeNotificationStageTest, TransformInvalidateRenameDropTarget) {
                       otherColl.getCommandNS(),
                       BSON("renameCollection" << otherColl.ns() << "to" << nss.ns()));
     Document expectedInvalidate{
-        {DSChangeNotification::kIdField, D{{"ts", ts}, {"ns", otherColl.getCommandNS().ns()}}},
-        {DSChangeNotification::kOperationTypeField, DSChangeNotification::kInvalidateOpType},
-        {DSChangeNotification::kFullDocumentField, BSONNULL},
+        {"_id", D{{"ts", ts}, {"ns", otherColl.getCommandNS().ns()}}},
+        {"operationType", "invalidate"_sd},
     };
     checkTransformation(rename, expectedInvalidate);
 }
@@ -287,38 +230,5 @@ TEST_F(ChangeNotificationStageTest, MatchFiltersCreateIndex) {
     checkTransformation(createIndex, boost::none);
 }
 
-TEST_F(ChangeNotificationStageTest, TransformationShouldBeAbleToReParseSerializedStage) {
-    auto expCtx = getExpCtx();
-
-    auto originalSpec = BSON(DSChangeNotification::kStageName << BSONObj());
-    auto allStages = DSChangeNotification::createFromBson(originalSpec.firstElement(), expCtx);
-    ASSERT_EQ(allStages.size(), 2UL);
-    auto stage = allStages.back();
-    ASSERT(dynamic_cast<DocumentSourceSingleDocumentTransformation*>(stage.get()));
-
-    //
-    // Serialize the stage and confirm contents.
-    //
-    vector<Value> serialization;
-    stage->serializeToArray(serialization);
-    ASSERT_EQ(serialization.size(), 1UL);
-    ASSERT_EQ(serialization[0].getType(), BSONType::Object);
-    auto serializedDoc = serialization[0].getDocument();
-    ASSERT_BSONOBJ_EQ(serializedDoc.toBson(), originalSpec);
-
-    //
-    // Create a new stage from the serialization. Serialize the new stage and confirm that it is
-    // equivalent to the original serialization.
-    //
-    auto serializedBson = serializedDoc.toBson();
-    auto roundTripped = uassertStatusOK(Pipeline::create(
-        DSChangeNotification::createFromBson(serializedBson.firstElement(), expCtx), expCtx));
-
-    auto newSerialization = roundTripped->serialize();
-
-    ASSERT_EQ(newSerialization.size(), 1UL);
-    ASSERT_VALUE_EQ(newSerialization[0], serialization[0]);
-}
-
 }  // namespace
 }  // namespace mongo
diff --git a/src/mongo/db/pipeline/document_source_count.cpp b/src/mongo/db/pipeline/document_source_count.cpp
index 0a2d299200b..01c4044fece 100644
--- a/src/mongo/db/pipeline/document_source_count.cpp
+++ b/src/mongo/db/pipeline/document_source_count.cpp
@@ -39,14 +39,14 @@
 namespace mongo {
 
 using boost::intrusive_ptr;
-using std::list;
+using std::vector;
 using std::string;
 
 REGISTER_MULTI_STAGE_ALIAS(count,
                            LiteParsedDocumentSourceDefault::parse,
                            DocumentSourceCount::createFromBson);
 
-list<intrusive_ptr<DocumentSource>> DocumentSourceCount::createFromBson(
+vector<intrusive_ptr<DocumentSource>> DocumentSourceCount::createFromBson(
     BSONElement elem, const intrusive_ptr<ExpressionContext>& pExpCtx) {
     uassert(40156,
             str::stream() << "the count field must be a non-empty string",
diff --git a/src/mongo/db/pipeline/document_source_count.h b/src/mongo/db/pipeline/document_source_count.h
index e77ce3eb0ed..50fbccdf41b 100644
--- a/src/mongo/db/pipeline/document_source_count.h
+++ b/src/mongo/db/pipeline/document_source_count.h
@@ -40,7 +40,7 @@ public:
     /**
      * Returns a $group stage followed by a $project stage.
      */
-    static std::list<boost::intrusive_ptr<DocumentSource>> createFromBson(
+    static std::vector<boost::intrusive_ptr<DocumentSource>> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
 private:
diff --git a/src/mongo/db/pipeline/document_source_count_test.cpp b/src/mongo/db/pipeline/document_source_count_test.cpp
index 254f011ff1d..e083399b0fa 100644
--- a/src/mongo/db/pipeline/document_source_count_test.cpp
+++ b/src/mongo/db/pipeline/document_source_count_test.cpp
@@ -45,23 +45,22 @@
 
 namespace mongo {
 namespace {
-using boost::intrusive_ptr;
-using std::list;
 using std::vector;
+using boost::intrusive_ptr;
 
 class CountReturnsGroupAndProjectStages : public AggregationContextFixture {
 public:
     void testCreateFromBsonResult(BSONObj countSpec) {
-        list<intrusive_ptr<DocumentSource>> result =
+        vector<intrusive_ptr<DocumentSource>> result =
             DocumentSourceCount::createFromBson(countSpec.firstElement(), getExpCtx());
 
         ASSERT_EQUALS(result.size(), 2UL);
 
-        const auto* groupStage = dynamic_cast<DocumentSourceGroup*>(result.front().get());
+        const auto* groupStage = dynamic_cast<DocumentSourceGroup*>(result[0].get());
         ASSERT(groupStage);
 
         const auto* projectStage =
-            dynamic_cast<DocumentSourceSingleDocumentTransformation*>(result.back().get());
+            dynamic_cast<DocumentSourceSingleDocumentTransformation*>(result[1].get());
         ASSERT(projectStage);
 
         auto explain = ExplainOptions::Verbosity::kQueryPlanner;
@@ -95,7 +94,7 @@ TEST_F(CountReturnsGroupAndProjectStages, ValidStringSpec) {
 
 class InvalidCountSpec : public AggregationContextFixture {
 public:
-    list<intrusive_ptr<DocumentSource>> createCount(BSONObj countSpec) {
+    vector<intrusive_ptr<DocumentSource>> createCount(BSONObj countSpec) {
         auto specElem = countSpec.firstElement();
         return DocumentSourceCount::createFromBson(specElem, getExpCtx());
     }
diff --git a/src/mongo/db/pipeline/document_source_lookup_change_post_image.cpp b/src/mongo/db/pipeline/document_source_lookup_change_post_image.cpp
deleted file mode 100644
index ee605710a54..00000000000
--- a/src/mongo/db/pipeline/document_source_lookup_change_post_image.cpp
+++ /dev/null
@@ -1,125 +0,0 @@
-/**
- * Copyright (C) 2017 MongoDB Inc.
- *
- * This program is free software: you can redistribute it and/or  modify
- * it under the terms of the GNU Affero General Public License, version 3,
- * as published by the Free Software Foundation.
- *
- * 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
- * GNU Affero General Public License for more details.
- *
- * You should have received a copy of the GNU Affero General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
- * 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 GNU Affero General 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/platform/basic.h"
-
-#include "mongo/db/pipeline/document_source_lookup_change_post_image.h"
-
-#include "mongo/bson/simple_bsonelement_comparator.h"
-
-namespace mongo {
-
-constexpr StringData DocumentSourceLookupChangePostImage::kStageName;
-constexpr StringData DocumentSourceLookupChangePostImage::kFullDocumentFieldName;
-
-namespace {
-Value assertFieldHasType(const Document& fullDoc, StringData fieldName, BSONType expectedType) {
-    auto val = fullDoc[fieldName];
-    uassert(40578,
-            str::stream() << "failed to look up post image after change: expected \"" << fieldName
-                          << "\" field to have type "
-                          << typeName(expectedType)
-                          << ", instead found type "
-                          << typeName(val.getType())
-                          << ": "
-                          << val.toString()
-                          << ", full object: "
-                          << fullDoc.toString(),
-            val.getType() == expectedType);
-    return val;
-}
-}  // namespace
-
-DocumentSource::GetNextResult DocumentSourceLookupChangePostImage::getNext() {
-    pExpCtx->checkForInterrupt();
-
-    auto input = pSource->getNext();
-    if (!input.isAdvanced()) {
-        return input;
-    }
-    auto opTypeVal = assertFieldHasType(input.getDocument(),
-                                        DocumentSourceChangeNotification::kOperationTypeField,
-                                        BSONType::String);
-    if (opTypeVal.getString() != DocumentSourceChangeNotification::kUpdateOpType) {
-        return input;
-    }
-
-    MutableDocument output(input.releaseDocument());
-    output[kFullDocumentFieldName] = lookupPostImage(output.peek());
-    return output.freeze();
-}
-
-NamespaceString DocumentSourceLookupChangePostImage::assertNamespaceMatches(
-    const Document& inputDoc) const {
-    auto namespaceObject = assertFieldHasType(inputDoc,
-                                              DocumentSourceChangeNotification::kNamespaceField,
-                                              BSONType::Object)
-                               .getDocument();
-    auto dbName = assertFieldHasType(namespaceObject, "db"_sd, BSONType::String);
-    auto collectionName = assertFieldHasType(namespaceObject, "coll"_sd, BSONType::String);
-    NamespaceString nss(dbName.getString(), collectionName.getString());
-    uassert(40579,
-            str::stream() << "unexpected namespace during post image lookup: " << nss.ns()
-                          << ", expected "
-                          << pExpCtx->ns.ns(),
-            nss == pExpCtx->ns);
-    return nss;
-}
-
-Value DocumentSourceLookupChangePostImage::lookupPostImage(const Document& updateOp) const {
-    // Make sure we have a well-formed input.
-    auto nss = assertNamespaceMatches(updateOp);
-
-    auto documentKey = assertFieldHasType(
-        updateOp, DocumentSourceChangeNotification::kDocumentKeyField, BSONType::Object);
-    auto matchSpec = BSON("$match" << documentKey);
-
-    // TODO SERVER-29134 we need to extract the namespace from the document and set them on the new
-    // ExpressionContext if we're getting notifications from an entire database.
-    auto foreignExpCtx = pExpCtx->copyWith(nss);
-    auto pipeline = uassertStatusOK(_mongod->makePipeline({matchSpec}, foreignExpCtx));
-
-    if (auto first = pipeline->getNext()) {
-        auto lookedUpDocument = Value(*first);
-        if (auto next = pipeline->getNext()) {
-            uasserted(40580,
-                      str::stream() << "found more than document with documentKey "
-                                    << documentKey.toString()
-                                    << " while looking up post image after change: ["
-                                    << lookedUpDocument.toString()
-                                    << ", "
-                                    << next->toString()
-                                    << "]");
-        }
-        return lookedUpDocument;
-    }
-    // We couldn't find it with the documentKey, it may have been deleted.
-    return Value(BSONNULL);
-}
-
-}  // namespace mongo
diff --git a/src/mongo/db/pipeline/document_source_lookup_change_post_image.h b/src/mongo/db/pipeline/document_source_lookup_change_post_image.h
deleted file mode 100644
index ca14656a63c..00000000000
--- a/src/mongo/db/pipeline/document_source_lookup_change_post_image.h
+++ /dev/null
@@ -1,115 +0,0 @@
-/**
- * Copyright (C) 2017 MongoDB Inc.
- *
- * This program is free software: you can redistribute it and/or  modify
- * it under the terms of the GNU Affero General Public License, version 3,
- * as published by the Free Software Foundation.
- *
- * 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
- * GNU Affero General Public License for more details.
- *
- * You should have received a copy of the GNU Affero General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
- * 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 GNU Affero General 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.
- */
-
-#pragma once
-
-#include "mongo/db/pipeline/document_source.h"
-#include "mongo/db/pipeline/document_source_change_notification.h"
-
-namespace mongo {
-
-/**
- * Part of the change notification API machinery used to look up the post-image of a document. Uses
- * the "documentKey" field of the input to look up the new version of the document.
- *
- * Uses the ExpressionContext to determine what collection to look up into.
- * TODO SERVER-29134 When we allow change streams on multiple collections, this will need to change.
- */
-class DocumentSourceLookupChangePostImage final : public DocumentSourceNeedsMongod {
-public:
-    static constexpr StringData kStageName = "$_internalLookupChangePostImage"_sd;
-    static constexpr StringData kFullDocumentFieldName =
-        DocumentSourceChangeNotification::kFullDocumentField;
-
-    /**
-     * Creates a DocumentSourceLookupChangePostImage stage.
-     */
-    static boost::intrusive_ptr<DocumentSourceLookupChangePostImage> create(
-        const boost::intrusive_ptr<ExpressionContext>& expCtx) {
-        return new DocumentSourceLookupChangePostImage(expCtx);
-    }
-
-    /**
-     * Only modifies a single path: "fullDocument".
-     */
-    GetModPathsReturn getModifiedPaths() const final {
-        return {GetModPathsReturn::Type::kFiniteSet, {kFullDocumentFieldName.toString()}, {}};
-    }
-
-    StageConstraints constraints() const final {
-        StageConstraints constraints;
-        constraints.canSwapWithMatch = true;
-        constraints.isAllowedInsideFacetStage = false;
-        return constraints;
-    }
-
-    GetDepsReturn getDependencies(DepsTracker* deps) const {
-        // The namespace is not technically needed yet, but we will if there is more than one
-        // collection involved.
-        deps->fields.insert(DocumentSourceChangeNotification::kNamespaceField.toString());
-        deps->fields.insert(DocumentSourceChangeNotification::kDocumentKeyField.toString());
-        deps->fields.insert(DocumentSourceChangeNotification::kOperationTypeField.toString());
-        // This stage does not restrict the output fields to a finite set, and has no impact on
-        // whether metadata is available or needed.
-        return SEE_NEXT;
-    }
-
-    /**
-     * Performs the lookup to retrieve the full document.
-     */
-    GetNextResult getNext() final;
-
-    Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final {
-        if (explain) {
-            return Value{Document{{kStageName, Document()}}};
-        }
-        return Value();  // Do not serialize this stage unless we're explaining.
-    }
-
-    const char* getSourceName() const final {
-        return kStageName.rawData();
-    }
-
-private:
-    DocumentSourceLookupChangePostImage(const boost::intrusive_ptr<ExpressionContext>& expCtx)
-        : DocumentSourceNeedsMongod(expCtx) {}
-
-    /**
-     * Uses the "documentKey" field from 'updateOp' to look up the current version of the document.
-     * Returns Value(BSONNULL) if the document couldn't be found.
-     */
-    Value lookupPostImage(const Document& updateOp) const;
-
-    /**
-     * Throws a UserException if the namespace found in 'inputDoc' doesn't match the one on the
-     * ExpressionContext.
-     */
-    NamespaceString assertNamespaceMatches(const Document& inputDoc) const;
-};
-
-}  // namespace mongo
diff --git a/src/mongo/db/pipeline/document_source_lookup_change_post_image_test.cpp b/src/mongo/db/pipeline/document_source_lookup_change_post_image_test.cpp
deleted file mode 100644
index 728db433c55..00000000000
--- a/src/mongo/db/pipeline/document_source_lookup_change_post_image_test.cpp
+++ /dev/null
@@ -1,266 +0,0 @@
-/**
- * Copyright (C) 2017 MongoDB Inc.
- *
- * This program is free software: you can redistribute it and/or  modify
- * it under the terms of the GNU Affero General Public License, version 3,
- * as published by the Free Software Foundation.
- *
- * 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
- * GNU Affero General Public License for more details.
- *
- * You should have received a copy of the GNU Affero General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- *
- * 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 GNU Affero General 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/platform/basic.h"
-
-#include <boost/intrusive_ptr.hpp>
-#include <deque>
-#include <vector>
-
-#include "mongo/bson/bsonmisc.h"
-#include "mongo/bson/bsonobj.h"
-#include "mongo/bson/bsonobjbuilder.h"
-#include "mongo/db/pipeline/aggregation_context_fixture.h"
-#include "mongo/db/pipeline/document.h"
-#include "mongo/db/pipeline/document_source_change_notification.h"
-#include "mongo/db/pipeline/document_source_lookup_change_post_image.h"
-#include "mongo/db/pipeline/document_source_mock.h"
-#include "mongo/db/pipeline/document_value_test_util.h"
-#include "mongo/db/pipeline/field_path.h"
-#include "mongo/db/pipeline/stub_mongod_interface.h"
-#include "mongo/db/pipeline/value.h"
-
-namespace mongo {
-namespace {
-using boost::intrusive_ptr;
-using std::deque;
-using std::vector;
-
-// This provides access to getExpCtx(), but we'll use a different name for this test suite.
-using DocumentSourceLookupChangePostImageTest = AggregationContextFixture;
-
-/**
- * A mock MongodInterface which allows mocking a foreign pipeline.
- */
-class MockMongodInterface final : public StubMongodInterface {
-public:
-    MockMongodInterface(deque<DocumentSource::GetNextResult> mockResults)
-        : _mockResults(std::move(mockResults)) {}
-
-    bool isSharded(const NamespaceString& ns) final {
-        return false;
-    }
-
-    StatusWith<std::unique_ptr<Pipeline, Pipeline::Deleter>> makePipeline(
-        const std::vector<BSONObj>& rawPipeline,
-        const boost::intrusive_ptr<ExpressionContext>& expCtx) final {
-        auto pipeline = Pipeline::parse(rawPipeline, expCtx);
-        if (!pipeline.isOK()) {
-            return pipeline.getStatus();
-        }
-
-        pipeline.getValue()->addInitialSource(DocumentSourceMock::create(_mockResults));
-        pipeline.getValue()->optimizePipeline();
-
-        return pipeline;
-    }
-
-private:
-    deque<DocumentSource::GetNextResult> _mockResults;
-};
-
-TEST_F(DocumentSourceLookupChangePostImageTest, ShouldErrorIfMissingDocumentKeyOnUpdate) {
-    auto expCtx = getExpCtx();
-
-    // Set up the $lookup stage.
-    auto lookupChangeStage = DocumentSourceLookupChangePostImage::create(expCtx);
-
-    // Mock its input with a document without a "documentKey" field.
-    auto mockLocalSource = DocumentSourceMock::create(
-        Document{{"operationType", "update"_sd},
-                 {"fullDocument", Document{{"_id", 0}}},
-                 {"ns", Document{{"db", expCtx->ns.db()}, {"coll", expCtx->ns.coll()}}}});
-
-    lookupChangeStage->setSource(mockLocalSource.get());
-
-    // Mock out the foreign collection.
-    lookupChangeStage->injectMongodInterface(
-        std::make_shared<MockMongodInterface>(deque<DocumentSource::GetNextResult>{}));
-
-    ASSERT_THROWS_CODE(lookupChangeStage->getNext(), UserException, 40578);
-}
-
-TEST_F(DocumentSourceLookupChangePostImageTest, ShouldErrorIfMissingOperationType) {
-    auto expCtx = getExpCtx();
-
-    // Set up the $lookup stage.
-    auto lookupChangeStage = DocumentSourceLookupChangePostImage::create(expCtx);
-
-    // Mock its input with a document without a "ns" field.
-    auto mockLocalSource = DocumentSourceMock::create(
-        Document{{"documentKey", Document{{"_id", 0}}},
-                 {"fullDocument", Document{{"_id", 0}}},
-                 {"ns", Document{{"db", expCtx->ns.db()}, {"coll", expCtx->ns.coll()}}}});
-
-    lookupChangeStage->setSource(mockLocalSource.get());
-
-    // Mock out the foreign collection.
-    lookupChangeStage->injectMongodInterface(
-        std::make_shared<MockMongodInterface>(deque<DocumentSource::GetNextResult>{}));
-
-    ASSERT_THROWS_CODE(lookupChangeStage->getNext(), UserException, 40578);
-}
-
-TEST_F(DocumentSourceLookupChangePostImageTest, ShouldErrorIfMissingNamespace) {
-    auto expCtx = getExpCtx();
-
-    // Set up the $lookup stage.
-    auto lookupChangeStage = DocumentSourceLookupChangePostImage::create(expCtx);
-
-    // Mock its input with a document without a "ns" field.
-    auto mockLocalSource = DocumentSourceMock::create(Document{
-        {"documentKey", Document{{"_id", 0}}}, {"operationType", "update"_sd},
-    });
-
-    lookupChangeStage->setSource(mockLocalSource.get());
-
-    // Mock out the foreign collection.
-    lookupChangeStage->injectMongodInterface(
-        std::make_shared<MockMongodInterface>(deque<DocumentSource::GetNextResult>{}));
-
-    ASSERT_THROWS_CODE(lookupChangeStage->getNext(), UserException, 40578);
-}
-
-TEST_F(DocumentSourceLookupChangePostImageTest, ShouldErrorIfNsFieldHasWrongType) {
-    auto expCtx = getExpCtx();
-
-    // Set up the $lookup stage.
-    auto lookupChangeStage = DocumentSourceLookupChangePostImage::create(expCtx);
-
-    // Mock its input with a document without a "ns" field.
-    auto mockLocalSource = DocumentSourceMock::create(
-        Document{{"documentKey", Document{{"_id", 0}}}, {"operationType", "update"_sd}, {"ns", 4}});
-
-    lookupChangeStage->setSource(mockLocalSource.get());
-
-    // Mock out the foreign collection.
-    lookupChangeStage->injectMongodInterface(
-        std::make_shared<MockMongodInterface>(deque<DocumentSource::GetNextResult>{}));
-
-    ASSERT_THROWS_CODE(lookupChangeStage->getNext(), UserException, 40578);
-}
-
-TEST_F(DocumentSourceLookupChangePostImageTest, ShouldErrorIfNsFieldDoesNotMatchPipeline) {
-    auto expCtx = getExpCtx();
-
-    // Set up the $lookup stage.
-    auto lookupChangeStage = DocumentSourceLookupChangePostImage::create(expCtx);
-
-    // Mock its input with a document without a "ns" field.
-    auto mockLocalSource = DocumentSourceMock::create(
-        Document{{"documentKey", Document{{"_id", 0}}},
-                 {"operationType", "update"_sd},
-                 {"ns", Document{{"db", "DIFFERENT"_sd}, {"coll", expCtx->ns.coll()}}}});
-
-    lookupChangeStage->setSource(mockLocalSource.get());
-
-    // Mock out the foreign collection.
-    lookupChangeStage->injectMongodInterface(
-        std::make_shared<MockMongodInterface>(deque<DocumentSource::GetNextResult>{}));
-
-    ASSERT_THROWS_CODE(lookupChangeStage->getNext(), UserException, 40579);
-}
-
-TEST_F(DocumentSourceLookupChangePostImageTest, ShouldErrorIfDocumentKeyIsNotUnique) {
-    auto expCtx = getExpCtx();
-
-    // Set up the $lookup stage.
-    auto lookupChangeStage = DocumentSourceLookupChangePostImage::create(expCtx);
-
-    // Mock its input with an update document.
-    auto mockLocalSource = DocumentSourceMock::create(
-        Document{{"documentKey", Document{{"_id", 0}}},
-                 {"operationType", "update"_sd},
-                 {"ns", Document{{"db", expCtx->ns.db()}, {"coll", expCtx->ns.coll()}}}});
-
-    lookupChangeStage->setSource(mockLocalSource.get());
-
-    // Mock out the foreign collection to have two documents with the same document key.
-    deque<DocumentSource::GetNextResult> foreignCollection = {Document{{"_id", 0}},
-                                                              Document{{"_id", 0}}};
-    lookupChangeStage->injectMongodInterface(
-        std::make_shared<MockMongodInterface>(std::move(foreignCollection)));
-
-    ASSERT_THROWS_CODE(lookupChangeStage->getNext(), UserException, 40580);
-}
-
-TEST_F(DocumentSourceLookupChangePostImageTest, ShouldPropagatePauses) {
-    auto expCtx = getExpCtx();
-
-    // Set up the $lookup stage.
-    auto lookupChangeStage = DocumentSourceLookupChangePostImage::create(expCtx);
-
-    // Mock its input, pausing every other result.
-    auto mockLocalSource = DocumentSourceMock::create(
-        {Document{{"documentKey", Document{{"_id", 0}}},
-                  {"operationType", "insert"_sd},
-                  {"fullDocument", Document{{"_id", 0}}},
-                  {"ns", Document{{"db", expCtx->ns.db()}, {"coll", expCtx->ns.coll()}}}},
-         DocumentSource::GetNextResult::makePauseExecution(),
-         Document{{"documentKey", Document{{"_id", 1}}},
-                  {"operationType", "update"_sd},
-                  {"fullDocument", BSONNULL},
-                  {"ns", Document{{"db", expCtx->ns.db()}, {"coll", expCtx->ns.coll()}}}},
-         DocumentSource::GetNextResult::makePauseExecution()});
-
-    lookupChangeStage->setSource(mockLocalSource.get());
-
-    // Mock out the foreign collection.
-    deque<DocumentSource::GetNextResult> mockForeignContents{Document{{"_id", 0}},
-                                                             Document{{"_id", 1}}};
-    lookupChangeStage->injectMongodInterface(
-        std::make_shared<MockMongodInterface>(std::move(mockForeignContents)));
-
-    auto next = lookupChangeStage->getNext();
-    ASSERT_TRUE(next.isAdvanced());
-    ASSERT_DOCUMENT_EQ(
-        next.releaseDocument(),
-        (Document{{"documentKey", Document{{"_id", 0}}},
-                  {"operationType", "insert"_sd},
-                  {"fullDocument", Document{{"_id", 0}}},
-                  {"ns", Document{{"db", expCtx->ns.db()}, {"coll", expCtx->ns.coll()}}}}));
-
-    ASSERT_TRUE(lookupChangeStage->getNext().isPaused());
-
-    next = lookupChangeStage->getNext();
-    ASSERT_TRUE(next.isAdvanced());
-    ASSERT_DOCUMENT_EQ(
-        next.releaseDocument(),
-        (Document{{"documentKey", Document{{"_id", 1}}},
-                  {"operationType", "update"_sd},
-                  {"fullDocument", Document{{"_id", 1}}},
-                  {"ns", Document{{"db", expCtx->ns.db()}, {"coll", expCtx->ns.coll()}}}}));
-
-    ASSERT_TRUE(lookupChangeStage->getNext().isPaused());
-
-    ASSERT_TRUE(lookupChangeStage->getNext().isEOF());
-    ASSERT_TRUE(lookupChangeStage->getNext().isEOF());
-}
-
-}  // namespace
-}  // namespace mongo
diff --git a/src/mongo/db/pipeline/document_source_sort_by_count.cpp b/src/mongo/db/pipeline/document_source_sort_by_count.cpp
index 97c5e0f0297..48cfaa9f559 100644
--- a/src/mongo/db/pipeline/document_source_sort_by_count.cpp
+++ b/src/mongo/db/pipeline/document_source_sort_by_count.cpp
@@ -39,13 +39,13 @@
 namespace mongo {
 
 using boost::intrusive_ptr;
-using std::list;
+using std::vector;
 
 REGISTER_MULTI_STAGE_ALIAS(sortByCount,
                            LiteParsedDocumentSourceDefault::parse,
                            DocumentSourceSortByCount::createFromBson);
 
-list<intrusive_ptr<DocumentSource>> DocumentSourceSortByCount::createFromBson(
+vector<intrusive_ptr<DocumentSource>> DocumentSourceSortByCount::createFromBson(
     BSONElement elem, const intrusive_ptr<ExpressionContext>& pExpCtx) {
     if (elem.type() == Object) {
         // Make sure that the sortByCount field is an expression inside an object
diff --git a/src/mongo/db/pipeline/document_source_sort_by_count.h b/src/mongo/db/pipeline/document_source_sort_by_count.h
index c8196c9b498..69bf8d2c5e0 100644
--- a/src/mongo/db/pipeline/document_source_sort_by_count.h
+++ b/src/mongo/db/pipeline/document_source_sort_by_count.h
@@ -40,7 +40,7 @@ public:
     /**
      * Returns a $group stage followed by a $sort stage.
      */
-    static std::list<boost::intrusive_ptr<DocumentSource>> createFromBson(
+    static std::vector<boost::intrusive_ptr<DocumentSource>> createFromBson(
         BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
 
 private:
diff --git a/src/mongo/db/pipeline/document_source_sort_by_count_test.cpp b/src/mongo/db/pipeline/document_source_sort_by_count_test.cpp
index 12975e96149..3e0a007c59b 100644
--- a/src/mongo/db/pipeline/document_source_sort_by_count_test.cpp
+++ b/src/mongo/db/pipeline/document_source_sort_by_count_test.cpp
@@ -46,9 +46,8 @@
 
 namespace mongo {
 namespace {
-using boost::intrusive_ptr;
-using std::list;
 using std::vector;
+using boost::intrusive_ptr;
 
 /**
  * Fixture to test that $sortByCount returns a DocumentSourceGroup and DocumentSourceSort.
@@ -56,15 +55,15 @@ using std::vector;
 class SortByCountReturnsGroupAndSort : public AggregationContextFixture {
 public:
     void testCreateFromBsonResult(BSONObj sortByCountSpec, Value expectedGroupExplain) {
-        list<intrusive_ptr<DocumentSource>> result =
+        vector<intrusive_ptr<DocumentSource>> result =
             DocumentSourceSortByCount::createFromBson(sortByCountSpec.firstElement(), getExpCtx());
 
         ASSERT_EQUALS(result.size(), 2UL);
 
-        const auto* groupStage = dynamic_cast<DocumentSourceGroup*>(result.front().get());
+        const auto* groupStage = dynamic_cast<DocumentSourceGroup*>(result[0].get());
         ASSERT(groupStage);
 
-        const auto* sortStage = dynamic_cast<DocumentSourceSort*>(result.back().get());
+        const auto* sortStage = dynamic_cast<DocumentSourceSort*>(result[1].get());
         ASSERT(sortStage);
 
         // Serialize the DocumentSourceGroup and DocumentSourceSort from $sortByCount so that we can
@@ -112,7 +111,7 @@ TEST_F(SortByCountReturnsGroupAndSort, ExpressionInObjectSpec) {
  */
 class InvalidSortByCountSpec : public AggregationContextFixture {
 public:
-    list<intrusive_ptr<DocumentSource>> createSortByCount(BSONObj sortByCountSpec) {
+    vector<intrusive_ptr<DocumentSource>> createSortByCount(BSONObj sortByCountSpec) {
         auto specElem = sortByCountSpec.firstElement();
         return DocumentSourceSortByCount::createFromBson(specElem, getExpCtx());
     }
diff --git a/src/mongo/db/pipeline/expression_context.cpp b/src/mongo/db/pipeline/expression_context.cpp
index f5f42d197c0..d2a16a6ca87 100644
--- a/src/mongo/db/pipeline/expression_context.cpp
+++ b/src/mongo/db/pipeline/expression_context.cpp
@@ -73,7 +73,7 @@ void ExpressionContext::setCollator(std::unique_ptr<CollatorInterface> coll) {
 }
 
 intrusive_ptr<ExpressionContext> ExpressionContext::copyWith(NamespaceString ns) const {
-    intrusive_ptr<ExpressionContext> expCtx = new ExpressionContext(std::move(ns));
+    intrusive_ptr<ExpressionContext> expCtx = new ExpressionContext();
 
     expCtx->explain = explain;
     expCtx->inShard = inShard;
@@ -81,6 +81,7 @@ intrusive_ptr<ExpressionContext> ExpressionContext::copyWith(NamespaceString ns)
     expCtx->extSortAllowed = extSortAllowed;
     expCtx->bypassDocumentValidation = bypassDocumentValidation;
 
+    expCtx->ns = std::move(ns);
     expCtx->tempDir = tempDir;
 
     expCtx->opCtx = opCtx;
diff --git a/src/mongo/db/pipeline/expression_context.h b/src/mongo/db/pipeline/expression_context.h
index ba2690796f6..d04b095aa4b 100644
--- a/src/mongo/db/pipeline/expression_context.h
+++ b/src/mongo/db/pipeline/expression_context.h
@@ -134,9 +134,7 @@ public:
 
 protected:
     static const int kInterruptCheckPeriod = 128;
-
-    ExpressionContext(NamespaceString nss)
-        : ns(std::move(nss)), variablesParseState(variables.useIdGenerator()) {}
+    ExpressionContext() : variablesParseState(variables.useIdGenerator()) {}
 
     /**
      * Sets '_collator' and resets '_documentComparator' and '_valueComparator'.
diff --git a/src/mongo/db/pipeline/expression_context_for_test.h b/src/mongo/db/pipeline/expression_context_for_test.h
index 542e5b91eea..234b54e1a10 100644
--- a/src/mongo/db/pipeline/expression_context_for_test.h
+++ b/src/mongo/db/pipeline/expression_context_for_test.h
@@ -40,9 +40,7 @@ namespace mongo {
  */
 class ExpressionContextForTest : public ExpressionContext {
 public:
-    ExpressionContextForTest() : ExpressionContext(NamespaceString{"test"_sd, "namespace"_sd}) {}
-
-    ExpressionContextForTest(NamespaceString nss) : ExpressionContext(std::move(nss)) {}
+    ExpressionContextForTest() = default;
 
     ExpressionContextForTest(OperationContext* opCtx, const AggregationRequest& request)
         : ExpressionContext(opCtx, request, nullptr, {}) {}
diff --git a/src/mongo/db/pipeline/pipeline_test.cpp b/src/mongo/db/pipeline/pipeline_test.cpp
index 1402f6f504d..1f37b30fc90 100644
--- a/src/mongo/db/pipeline/pipeline_test.cpp
+++ b/src/mongo/db/pipeline/pipeline_test.cpp
@@ -37,11 +37,7 @@
 #include "mongo/db/pipeline/dependencies.h"
 #include "mongo/db/pipeline/document.h"
 #include "mongo/db/pipeline/document_source.h"
-#include "mongo/db/pipeline/document_source_change_notification.h"
-#include "mongo/db/pipeline/document_source_lookup_change_post_image.h"
-#include "mongo/db/pipeline/document_source_match.h"
 #include "mongo/db/pipeline/document_source_mock.h"
-#include "mongo/db/pipeline/document_source_project.h"
 #include "mongo/db/pipeline/document_value_test_util.h"
 #include "mongo/db/pipeline/expression_context_for_test.h"
 #include "mongo/db/pipeline/field_path.h"
@@ -56,8 +52,6 @@ using boost::intrusive_ptr;
 using std::string;
 using std::vector;
 
-const NamespaceString kTestNss = NamespaceString("a.collection");
-
 namespace Optimizations {
 using namespace mongo;
 
@@ -83,7 +77,7 @@ void assertPipelineOptimizesAndSerializesTo(std::string inputPipeJson,
         ASSERT_EQUALS(stageElem.type(), BSONType::Object);
         rawPipeline.push_back(stageElem.embeddedObject());
     }
-    AggregationRequest request(kTestNss, rawPipeline);
+    AggregationRequest request(NamespaceString("a.collection"), rawPipeline);
     intrusive_ptr<ExpressionContextForTest> ctx =
         new ExpressionContextForTest(opCtx.get(), request);
 
@@ -968,52 +962,6 @@ TEST(PipelineOptimizationTest, MatchOnMaxLengthShouldMoveAcrossRename) {
     assertPipelineOptimizesTo(inputPipe, outputPipe);
 }
 
-TEST(PipelineOptimizationTest, ChangeNotificationLookupSwapsWithIndependentMatch) {
-    QueryTestServiceContext testServiceContext;
-    auto opCtx = testServiceContext.makeOperationContext();
-
-    intrusive_ptr<ExpressionContext> expCtx(new ExpressionContextForTest(kTestNss));
-    expCtx->opCtx = opCtx.get();
-
-    auto spec = BSON("$changeNotification" << BSON("fullDocument"
-                                                   << "lookup"));
-    auto stages = DocumentSourceChangeNotification::createFromBson(spec.firstElement(), expCtx);
-    ASSERT_EQ(stages.size(), 3UL);
-    // Make sure the change lookup is at the end.
-    ASSERT(dynamic_cast<DocumentSourceLookupChangePostImage*>(stages.back().get()));
-
-    auto matchPredicate = BSON("extra"
-                               << "predicate");
-    stages.push_back(DocumentSourceMatch::create(matchPredicate, expCtx));
-    auto pipeline = uassertStatusOK(Pipeline::create(stages, expCtx));
-    pipeline->optimizePipeline();
-
-    // Make sure the $match stage has swapped before the change look up.
-    ASSERT(dynamic_cast<DocumentSourceLookupChangePostImage*>(pipeline->getSources().back().get()));
-}
-
-TEST(PipelineOptimizationTest, ChangeNotificationLookupDoesNotSwapWithMatchOnPostImage) {
-    QueryTestServiceContext testServiceContext;
-    auto opCtx = testServiceContext.makeOperationContext();
-
-    intrusive_ptr<ExpressionContext> expCtx(new ExpressionContextForTest(kTestNss));
-    expCtx->opCtx = opCtx.get();
-
-    auto spec = BSON("$changeNotification" << BSON("fullDocument"
-                                                   << "lookup"));
-    auto stages = DocumentSourceChangeNotification::createFromBson(spec.firstElement(), expCtx);
-    ASSERT_EQ(stages.size(), 3UL);
-    // Make sure the change lookup is at the end.
-    ASSERT(dynamic_cast<DocumentSourceLookupChangePostImage*>(stages.back().get()));
-
-    stages.push_back(DocumentSourceMatch::create(
-        BSON(DocumentSourceLookupChangePostImage::kFullDocumentFieldName << BSONNULL), expCtx));
-    auto pipeline = uassertStatusOK(Pipeline::create(stages, expCtx));
-    pipeline->optimizePipeline();
-
-    // Make sure the $match stage stays at the end.
-    ASSERT(dynamic_cast<DocumentSourceMatch*>(pipeline->getSources().back().get()));
-}
 }  // namespace Local
 
 namespace Sharded {
@@ -1038,7 +986,7 @@ public:
             ASSERT_EQUALS(stageElem.type(), BSONType::Object);
             rawPipeline.push_back(stageElem.embeddedObject());
         }
-        AggregationRequest request(kTestNss, rawPipeline);
+        AggregationRequest request(NamespaceString("a.collection"), rawPipeline);
         intrusive_ptr<ExpressionContextForTest> ctx =
             new ExpressionContextForTest(&_opCtx, request);
 
@@ -1443,7 +1391,7 @@ TEST_F(PipelineInitialSourceNSTest, CollectionNSNotValidIfInitialStageIsCollecti
     auto collectionlessSource = DocumentSourceCollectionlessMock::create();
     auto ctx = getExpCtx();
 
-    ctx->ns = kTestNss;
+    ctx->ns = NamespaceString("a.collection");
 
     ASSERT_NOT_OK(Pipeline::create({collectionlessSource}, ctx).getStatus());
 }
diff --git a/src/mongo/db/pipeline/value.h b/src/mongo/db/pipeline/value.h
index 04e396dc58d..9f7a357f677 100644
--- a/src/mongo/db/pipeline/value.h
+++ b/src/mongo/db/pipeline/value.h
@@ -117,9 +117,6 @@ public:
     explicit Value(const MaxKeyLabeler&) : _storage(MaxKey) {}        // MAXKEY
     explicit Value(const Date_t& date) : _storage(Date, date.toMillisSinceEpoch()) {}
 
-    explicit Value(const char*) = delete;  // Use StringData instead to prevent accidentally
-                                           // terminating the string at the first null byte.
-
     // TODO: add an unsafe version that can share storage with the BSONElement
     /// Deep-convert from BSONElement to Value
     explicit Value(const BSONElement& elem);