SERVER-69909: [CQF] Explain of Constant should be lossess and display tag/value

2 files changed, 21 insertions, 4 deletions

diff --git a/src/mongo/db/query/optimizer/explain.cpp b/src/mongo/db/query/optimizer/explain.cpp
index de32dc051fe..5796de6f03a 100644
--- a/src/mongo/db/query/optimizer/explain.cpp
+++ b/src/mongo/db/query/optimizer/explain.cpp
@@ -1895,10 +1895,16 @@ public:
 
     ExplainPrinter transport(const Constant& expr) {
         ExplainPrinter printer("Const");
-        printer.separator(" [")
-            .fieldName("value", ExplainVersion::V3)
-            .print(expr.get())
-            .separator("]");
+        printer.separator(" [").fieldName("tag", ExplainVersion::V3);
+
+        if (version == ExplainVersion::V3) {
+            std::stringstream ss;
+            ss << expr.get().first;
+            std::string tagAsString = ss.str();
+            printer.print(tagAsString);
+        }
+
+        printer.fieldName("value", ExplainVersion::V3).print(expr.get()).separator("]");
         return printer;
     }
 
diff --git a/src/mongo/db/query/optimizer/optimizer_test.cpp b/src/mongo/db/query/optimizer/optimizer_test.cpp
index 4f5fa788eac..d52b84470a1 100644
--- a/src/mongo/db/query/optimizer/optimizer_test.cpp
+++ b/src/mongo/db/query/optimizer/optimizer_test.cpp
@@ -744,5 +744,16 @@ TEST(Explain, ExplainV2Compact) {
         evalNode);
 }
 
+TEST(Explain, ExplainBsonForConstant) {
+    ABT cNode = Constant::int64(3);
+    auto [tag, val] = ExplainGenerator::explainBSON(cNode);
+    sbe::value::ValueGuard vg(tag, val);
+    ASSERT_EQ(
+        "{\n    nodeType: \"Const\", \n"
+        "    tag: \"NumberInt64\", \n"
+        "    value: 3\n}\n",
+        ExplainGenerator::printBSON(tag, val));
+}
+
 }  // namespace
 }  // namespace mongo::optimizer