1 files changed, 27 insertions, 1 deletions
diff --git a/src/mongo/db/query/canonical_query_encoder.cpp b/src/mongo/db/query/canonical_query_encoder.cpp
index c8a8cd29d48..ccbcce36635 100644
--- a/src/mongo/db/query/canonical_query_encoder.cpp
+++ b/src/mongo/db/query/canonical_query_encoder.cpp
@@ -74,6 +74,32 @@ bool isQueryNegatingEqualToNull(const mongo::MatchExpression* tree) {
 
 namespace {
 
+// Delimiters for cache key encoding.
+const char kEncodeChildrenBegin = '[';
+const char kEncodeChildrenEnd = ']';
+const char kEncodeChildrenSeparator = ',';
+const char kEncodeCollationSection = '#';
+const char kEncodeProjectionSection = '|';
+const char kEncodeProjectionRequirementSeparator = '-';
+const char kEncodeRegexFlagsSeparator = '/';
+const char kEncodeSortSection = '~';
+const char kEncodeEngineSection = '@';
+
+// These special bytes are used in the encoding of auto-parameterized match expressions in the SBE
+// plan cache key.
+
+// Precedes the id number of a parameter marker.
+const char kEncodeParamMarker = '?';
+// Precedes the encoding of a constant when that constant has not been auto-paramterized. The
+// constant is typically encoded as a BSON type byte followed by a BSON value (without the
+// BSONElement's field name).
+const char kEncodeConstantLiteralMarker = ':';
+// Precedes a byte which encodes the bounds tightness associated with a predicate. The structure of
+// the plan (i.e. presence of filters) is affected by bounds tightness. Therefore, if different
+// parameter values can result in different tightnesses, this must be explicitly encoded into the
+// plan cache key.
+const char kEncodeBoundsTightnessDiscriminator = ':';
+
 /**
  * AppendChar provides the compiler with a type for a "appendChar(...)" member function.
  */
@@ -558,7 +584,7 @@ void encodeKeyForProj(const projection_ast::Projection* proj, StringBuilder* key
         return;
     }
 
-    auto requiredFields = proj->getRequiredFields();
+    std::set<std::string> requiredFields = proj->getRequiredFields();
 
     // If the only requirement is that $sortKey be included with some value, we just act as if the
     // entire document is needed.