SERVER-59432 tassert for group system var optimize

(cherry picked from commit 5cf8a293567989fcc970fb21cde4a1af111c8b58)

2 files changed, 11 insertions, 2 deletions

diff --git a/src/mongo/db/pipeline/document_source_group.cpp b/src/mongo/db/pipeline/document_source_group.cpp
index fdcacba50e5..f5a187ed7fc 100644
--- a/src/mongo/db/pipeline/document_source_group.cpp
+++ b/src/mongo/db/pipeline/document_source_group.cpp
@@ -832,7 +832,9 @@ DocumentSourceGroup::rewriteGroupAsTransformOnFirstDocument() const {
         // each document has a unique _id, it will just return the entire collection). We only
         // apply the rewrite when grouping by a single field, so we cannot apply it in this case,
         // where we are grouping by the entire document.
-        invariant(fieldPath.getFieldName(0) == "CURRENT" || fieldPath.getFieldName(0) == "ROOT");
+        tassert(5943200,
+                "Optimization attempted on group by always-dissimilar system variable",
+                fieldPath.getFieldName(0) == "CURRENT" || fieldPath.getFieldName(0) == "ROOT");
         return nullptr;
     }
 
diff --git a/src/mongo/db/pipeline/expression.cpp b/src/mongo/db/pipeline/expression.cpp
index 8f03f21c2f9..599837bb631 100644
--- a/src/mongo/db/pipeline/expression.cpp
+++ b/src/mongo/db/pipeline/expression.cpp
@@ -2348,7 +2348,14 @@ intrusive_ptr<ExpressionFieldPath> ExpressionFieldPath::createVarFromString(
 ExpressionFieldPath::ExpressionFieldPath(ExpressionContext* const expCtx,
                                          const string& theFieldPath,
                                          Variables::Id variable)
-    : Expression(expCtx), _fieldPath(theFieldPath), _variable(variable) {}
+    : Expression(expCtx), _fieldPath(theFieldPath), _variable(variable) {
+    const auto varName = theFieldPath.substr(0, theFieldPath.find('.'));
+    tassert(5943201,
+            std::string{"Variable with $$ROOT's id is not $$CURRENT or $$ROOT as expected, "
+                        "field path is actually '"} +
+                theFieldPath + "'",
+            _variable != Variables::kRootId || varName == "CURRENT" || varName == "ROOT");
+}
 
 intrusive_ptr<Expression> ExpressionFieldPath::optimize() {
     if (_variable == Variables::kRemoveId) {