SERVER-41257 Disallow persisting new 4.2 expressions in FCV 4.0

3 files changed, 45 insertions, 4 deletions

diff --git a/src/mongo/db/pipeline/expression.cpp b/src/mongo/db/pipeline/expression.cpp
index 0e8984a81fa..d6068398342 100644
--- a/src/mongo/db/pipeline/expression.cpp
+++ b/src/mongo/db/pipeline/expression.cpp
@@ -4924,7 +4924,10 @@ Value ExpressionRound::evaluate(const Document& root) const {
         root, _children, getOpName(), Decimal128::kRoundTiesToEven, &std::round);
 }
 
-REGISTER_EXPRESSION(round, ExpressionRound::parse);
+REGISTER_EXPRESSION_WITH_MIN_VERSION(
+    round,
+    ExpressionRound::parse,
+    ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
 const char* ExpressionRound::getOpName() const {
     return "$round";
 }
@@ -4934,6 +4937,30 @@ Value ExpressionTrunc::evaluate(const Document& root) const {
         root, _children, getOpName(), Decimal128::kRoundTowardZero, &std::trunc);
 }
 
+intrusive_ptr<Expression> ExpressionTrunc::parse(const intrusive_ptr<ExpressionContext>& expCtx,
+                                                 BSONElement elem,
+                                                 const VariablesParseState& vps) {
+    // In version 4.2 we added new arguments. In all previous versions the expression existed but
+    // only supported a single argument.
+    const bool newArgumentsAllowed =
+        (!expCtx->maxFeatureCompatibilityVersion ||
+         (*expCtx->maxFeatureCompatibilityVersion >=
+          ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42));
+    uassert(
+        ErrorCodes::QueryFeatureNotAllowed,
+        // TODO SERVER-31968 we would like to include the current version and the required minimum
+        // version in this error message, but using FeatureCompatibilityVersion::toString() would
+        // introduce a dependency cycle.
+        str::stream()
+            << elem.fieldNameStringData()
+            << " with >1 argument is not allowed in the current feature compatibility version. See "
+            << feature_compatibility_version_documentation::kCompatibilityLink
+            << " for more information.",
+        // Allow non-arrays since they will be rejected anyway by the parser below.
+        elem.type() != BSONType::Array || elem.Array().size() <= 1 || newArgumentsAllowed);
+    return ExpressionRangedArity<ExpressionTrunc, 1, 2>::parse(expCtx, elem, vps);
+}
+
 REGISTER_EXPRESSION(trunc, ExpressionTrunc::parse);
 const char* ExpressionTrunc::getOpName() const {
     return "$trunc";
@@ -6015,7 +6042,10 @@ void ExpressionRegex::_doAddDependencies(DepsTracker* deps) const {
 
 /* -------------------------- ExpressionRegexFind ------------------------------ */
 
-REGISTER_EXPRESSION(regexFind, ExpressionRegexFind::parse);
+REGISTER_EXPRESSION_WITH_MIN_VERSION(
+    regexFind,
+    ExpressionRegexFind::parse,
+    ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
 boost::intrusive_ptr<Expression> ExpressionRegexFind::parse(
     const boost::intrusive_ptr<ExpressionContext>& expCtx,
     BSONElement expr,
@@ -6036,7 +6066,10 @@ Value ExpressionRegexFind::evaluate(const Document& root) const {
 
 /* -------------------------- ExpressionRegexFindAll ------------------------------ */
 
-REGISTER_EXPRESSION(regexFindAll, ExpressionRegexFindAll::parse);
+REGISTER_EXPRESSION_WITH_MIN_VERSION(
+    regexFindAll,
+    ExpressionRegexFindAll::parse,
+    ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
 boost::intrusive_ptr<Expression> ExpressionRegexFindAll::parse(
     const boost::intrusive_ptr<ExpressionContext>& expCtx,
     BSONElement expr,
@@ -6097,7 +6130,10 @@ Value ExpressionRegexFindAll::evaluate(const Document& root) const {
 
 /* -------------------------- ExpressionRegexMatch ------------------------------ */
 
-REGISTER_EXPRESSION(regexMatch, ExpressionRegexMatch::parse);
+REGISTER_EXPRESSION_WITH_MIN_VERSION(
+    regexMatch,
+    ExpressionRegexMatch::parse,
+    ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
 boost::intrusive_ptr<Expression> ExpressionRegexMatch::parse(
     const boost::intrusive_ptr<ExpressionContext>& expCtx,
     BSONElement expr,
diff --git a/src/mongo/db/pipeline/expression.h b/src/mongo/db/pipeline/expression.h
index 7033ee717d1..7ec1700afb3 100644
--- a/src/mongo/db/pipeline/expression.h
+++ b/src/mongo/db/pipeline/expression.h
@@ -2325,6 +2325,10 @@ public:
     explicit ExpressionTrunc(const boost::intrusive_ptr<ExpressionContext>& expCtx)
         : ExpressionRangedArity<ExpressionTrunc, 1, 2>(expCtx) {}
 
+    static boost::intrusive_ptr<Expression> parse(
+        const boost::intrusive_ptr<ExpressionContext>& expCtx,
+        BSONElement elem,
+        const VariablesParseState& vps);
     Value evaluate(const Document& root) const final;
     const char* getOpName() const final;
 
diff --git a/src/mongo/db/pipeline/expression_context.cpp b/src/mongo/db/pipeline/expression_context.cpp
index 0054e0de98c..9f65c12669f 100644
--- a/src/mongo/db/pipeline/expression_context.cpp
+++ b/src/mongo/db/pipeline/expression_context.cpp
@@ -160,6 +160,7 @@ intrusive_ptr<ExpressionContext> ExpressionContext::copyWith(
     expCtx->inMongos = inMongos;
     expCtx->allowDiskUse = allowDiskUse;
     expCtx->bypassDocumentValidation = bypassDocumentValidation;
+    expCtx->maxFeatureCompatibilityVersion = maxFeatureCompatibilityVersion;
     expCtx->subPipelineDepth = subPipelineDepth;
 
     expCtx->tempDir = tempDir;