1 files changed, 136 insertions, 0 deletions
diff --git a/src/mongo/db/cst/c_node_validation.cpp b/src/mongo/db/cst/c_node_validation.cpp
new file mode 100644
index 00000000000..338c8e198eb
--- /dev/null
+++ b/src/mongo/db/cst/c_node_validation.cpp
@@ -0,0 +1,136 @@
+/**
+ *    Copyright (C) 2020-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 <iterator>
+
+#include "mongo/base/status.h"
+#include "mongo/db/cst/c_node_validation.h"
+
+namespace mongo::c_node_validation {
+namespace {
+
+template <typename Iter, typename EndFun>
+StatusWith<IsInclusion> processAdditionalFieldsInclusionAssumed(const Iter& iter,
+                                                                const EndFun& isEnd);
+template <typename Iter, typename EndFun>
+StatusWith<IsInclusion> processAdditionalFieldsExclusionAssumed(const Iter& iter,
+                                                                const EndFun& isEnd);
+
+auto isInclusionField(const CNode& project) {
+    if (project.isInclusionKeyValue())
+        // This is an inclusion Key.
+        return true;
+    else if (stdx::holds_alternative<KeyValue>(project.payload))
+        // This is an exclusion Key.
+        return false;
+    else
+        // This is an arbitrary expression to produce a computed field (this counts as inclusion).
+        return true;
+}
+
+template <typename Iter, typename EndFun>
+StatusWith<IsInclusion> processAdditionalFieldsInclusionConfirmed(const Iter& iter,
+                                                                  const EndFun& isEnd) {
+    if (!isEnd(iter)) {
+        if (CNode::fieldnameIsId(iter->first)) {
+            return processAdditionalFieldsInclusionConfirmed(std::next(iter), isEnd);
+        } else {
+            if (isInclusionField(iter->second))
+                return processAdditionalFieldsInclusionConfirmed(std::next(iter), isEnd);
+            else
+                return Status{ErrorCodes::FailedToParse,
+                              "$project containing inclusion and/or computed fields must"
+                              "contain no exclusion fields"};
+        }
+    } else {
+        return IsInclusion::yes;
+    }
+}
+
+template <typename Iter, typename EndFun>
+StatusWith<IsInclusion> processAdditionalFieldsExclusionConfirmed(const Iter& iter,
+                                                                  const EndFun& isEnd) {
+    if (!isEnd(iter)) {
+        if (CNode::fieldnameIsId(iter->first)) {
+            return processAdditionalFieldsExclusionConfirmed(std::next(iter), isEnd);
+        } else {
+            if (isInclusionField(iter->second))
+                return Status{ErrorCodes::FailedToParse,
+                              "$project containing exclusion fields must contain no"
+                              "inclusion and/or computed fields"};
+            else
+                return processAdditionalFieldsExclusionConfirmed(std::next(iter), isEnd);
+        }
+    } else {
+        return IsInclusion::no;
+    }
+}
+
+template <typename Iter, typename EndFun>
+StatusWith<IsInclusion> processAdditionalFieldsWhenAssuming(const Iter& iter, const EndFun& isEnd) {
+    if (CNode::fieldnameIsId(iter->first)) {
+        if (isInclusionField(iter->second))
+            return processAdditionalFieldsInclusionAssumed(std::next(iter), isEnd);
+        else
+            return processAdditionalFieldsExclusionAssumed(std::next(iter), isEnd);
+    } else {
+        if (isInclusionField(iter->second))
+            return processAdditionalFieldsInclusionConfirmed(std::next(iter), isEnd);
+        else
+            return processAdditionalFieldsExclusionConfirmed(std::next(iter), isEnd);
+    }
+}
+
+template <typename Iter, typename EndFun>
+StatusWith<IsInclusion> processAdditionalFieldsInclusionAssumed(const Iter& iter,
+                                                                const EndFun& isEnd) {
+    if (!isEnd(iter))
+        return processAdditionalFieldsWhenAssuming(iter, isEnd);
+    else
+        return IsInclusion::yes;
+}
+
+template <typename Iter, typename EndFun>
+StatusWith<IsInclusion> processAdditionalFieldsExclusionAssumed(const Iter& iter,
+                                                                const EndFun& isEnd) {
+    if (!isEnd(iter))
+        return processAdditionalFieldsWhenAssuming(iter, isEnd);
+    else
+        return IsInclusion::no;
+}
+
+}  // namespace
+
+StatusWith<IsInclusion> validateProjectionAsInclusionOrExclusion(const CNode& projects) {
+    return processAdditionalFieldsInclusionAssumed(
+        projects.objectChildren().cbegin(),
+        [&](auto&& iter) { return iter == projects.objectChildren().cend(); });
+}
+
+}  // namespace mongo::c_node_validation