1 files changed, 34 insertions, 1 deletions
diff --git a/src/mongo/db/pipeline/abt/utils.cpp b/src/mongo/db/pipeline/abt/utils.cpp
index c4d6093cc1b..9911e090305 100644
--- a/src/mongo/db/pipeline/abt/utils.cpp
+++ b/src/mongo/db/pipeline/abt/utils.cpp
@@ -30,7 +30,7 @@
 #include "mongo/db/pipeline/abt/utils.h"
 
 #include "mongo/db/exec/sbe/values/bson.h"
-
+#include "mongo/db/query/optimizer/utils/utils.h"
 
 namespace mongo::optimizer {
 
@@ -81,6 +81,39 @@ ABT translateFieldPath(const FieldPath& fieldPath,
     return result;
 }
 
+ABT translateFieldRef(const FieldRef& fieldRef, ABT initial) {
+    ABT result = std::move(initial);
+
+    const size_t fieldPathLength = fieldRef.numParts();
+
+    // Handle empty field paths separately.
+    if (fieldPathLength == 0) {
+        return make<PathGet>("", std::move(result));
+    }
+
+    for (size_t i = fieldPathLength; i-- > 0;) {
+        // A single empty field path will parse to a FieldRef with 0 parts but should
+        // logically be considered a single part with an empty string.
+        if (i != fieldPathLength - 1) {
+            // For field paths with empty elements such as 'x.', we should traverse the
+            // array 'x' but not reach into any sub-objects. So a predicate such as {'x.':
+            // {$eq: 5}} should match {x: [5]} and {x: {"": 5}} but not {x: [{"": 5}]}.
+            const bool trailingEmptyPath =
+                (fieldPathLength >= 2u && i == fieldPathLength - 2u) && (fieldRef[i + 1] == ""_sd);
+            if (trailingEmptyPath) {
+                auto arrCase = make<PathArr>();
+                maybeComposePath(arrCase, result.cast<PathGet>()->getPath());
+                maybeComposePath<PathComposeA>(result, arrCase);
+            } else {
+                result = make<PathTraverse>(std::move(result), PathTraverse::kSingleLevel);
+            }
+        }
+        result = make<PathGet>(fieldRef[i].toString(), std::move(result));
+    }
+
+    return result;
+}
+
 std::pair<boost::optional<ABT>, bool> getMinMaxBoundForType(const bool isMin,
                                                             const sbe::value::TypeTags& tag) {
     switch (tag) {