SERVER-30582 Permit 'local' readConcern for aggregation explain.

5 files changed, 26 insertions, 21 deletions

diff --git a/src/mongo/db/commands/run_aggregate.cpp b/src/mongo/db/commands/run_aggregate.cpp
index 1077d65a0d2..2ad882ef2f5 100644
--- a/src/mongo/db/commands/run_aggregate.cpp
+++ b/src/mongo/db/commands/run_aggregate.cpp
@@ -57,6 +57,7 @@
 #include "mongo/db/query/get_executor.h"
 #include "mongo/db/query/plan_summary_stats.h"
 #include "mongo/db/repl/oplog.h"
+#include "mongo/db/repl/read_concern_args.h"
 #include "mongo/db/service_context.h"
 #include "mongo/db/storage/storage_options.h"
 #include "mongo/db/views/view.h"
@@ -297,6 +298,14 @@ Status runAggregate(OperationContext* opCtx,
     // For operations on views, this will be the underlying namespace.
     NamespaceString nss = request.getNamespaceString();
 
+    if (request.getExplain() &&
+        repl::ReadConcernArgs::get(opCtx).getLevel() != repl::ReadConcernLevel::kLocalReadConcern) {
+        return {ErrorCodes::InvalidOptions,
+                str::stream() << "Explain for the aggregate command "
+                                 "does not support non-local "
+                                 "readConcern levels"};
+    }
+
     // Parse the user-specified collation, if any.
     std::unique_ptr<CollatorInterface> userSpecifiedCollator = request.getCollation().isEmpty()
         ? nullptr
diff --git a/src/mongo/db/pipeline/aggregation_request.cpp b/src/mongo/db/pipeline/aggregation_request.cpp
index 7c0e6401cd2..88bb2352a60 100644
--- a/src/mongo/db/pipeline/aggregation_request.cpp
+++ b/src/mongo/db/pipeline/aggregation_request.cpp
@@ -254,13 +254,6 @@ StatusWith<AggregationRequest> AggregationRequest::parseFromBSON(
                     << "' option is required, except for aggregate with the explain argument"};
     }
 
-    if (request.getExplain() && !request.getReadConcern().isEmpty()) {
-        return {ErrorCodes::FailedToParse,
-                str::stream() << "Aggregation explain does not support the '"
-                              << repl::ReadConcernArgs::kReadConcernFieldName
-                              << "' option"};
-    }
-
     if (request.getExplain() && cmdObj[WriteConcernOptions::kWriteConcernField]) {
         return {ErrorCodes::FailedToParse,
                 str::stream() << "Aggregation explain does not support the'"
diff --git a/src/mongo/db/pipeline/aggregation_request_test.cpp b/src/mongo/db/pipeline/aggregation_request_test.cpp
index 312e8158121..112d1d3fb17 100644
--- a/src/mongo/db/pipeline/aggregation_request_test.cpp
+++ b/src/mongo/db/pipeline/aggregation_request_test.cpp
@@ -126,6 +126,19 @@ TEST(AggregationRequestTest, ShouldParseWithSeparateQueryPlannerExplainModeArgAn
     ASSERT_EQ(request.getBatchSize(), 10);
 }
 
+TEST(AggregationRequestTest, ShouldParseExplainFlagWithReadConcern) {
+    NamespaceString nss("a.collection");
+    // Non-local readConcern should not be allowed with the explain flag, but this is checked
+    // elsewhere to avoid having to parse the readConcern in AggregationRequest.
+    const BSONObj inputBson =
+        fromjson("{pipeline: [], explain: true, readConcern: {level: 'majority'}}");
+    auto request = unittest::assertGet(AggregationRequest::parseFromBSON(nss, inputBson));
+    ASSERT_TRUE(request.getExplain());
+    ASSERT_BSONOBJ_EQ(request.getReadConcern(),
+                      BSON("level"
+                           << "majority"));
+}
+
 //
 // Serialization
 //
@@ -399,13 +412,6 @@ TEST(AggregationRequestTest, ShouldRejectExplainFalseWithSeparateExplainArg) {
             .getStatus());
 }
 
-TEST(AggregationRequestTest, ShouldRejectExplainWithReadConcernMajority) {
-    NamespaceString nss("a.collection");
-    const BSONObj inputBson =
-        fromjson("{pipeline: [], explain: true, readConcern: {level: 'majority'}}");
-    ASSERT_NOT_OK(AggregationRequest::parseFromBSON(nss, inputBson).getStatus());
-}
-
 TEST(AggregationRequestTest, ShouldRejectExplainExecStatsVerbosityWithReadConcernMajority) {
     NamespaceString nss("a.collection");
     const BSONObj inputBson = fromjson("{pipeline: [], readConcern: {level: 'majority'}}");
diff --git a/src/mongo/s/commands/cluster_aggregate.cpp b/src/mongo/s/commands/cluster_aggregate.cpp
index a70227b99a4..864e9d457ac 100644
--- a/src/mongo/s/commands/cluster_aggregate.cpp
+++ b/src/mongo/s/commands/cluster_aggregate.cpp
@@ -80,6 +80,10 @@ Document wrapAggAsExplain(Document aggregateCommand, ExplainOptions::Verbosity v
     explainCommandBuilder[QueryRequest::kUnwrappedReadPrefField] =
         Value(aggregateCommand[QueryRequest::kUnwrappedReadPrefField]);
 
+    // readConcern needs to be promoted to the top-level of the request.
+    explainCommandBuilder[repl::ReadConcernArgs::kReadConcernFieldName] =
+        Value(aggregateCommand[repl::ReadConcernArgs::kReadConcernFieldName]);
+
     // Add explain command options.
     for (auto&& explainOption : ExplainOptions::toBSON(verbosity)) {
         explainCommandBuilder[explainOption.fieldNameStringData()] = Value(explainOption);
diff --git a/src/mongo/shell/session.js b/src/mongo/shell/session.js
index 7db8f47fbc2..aa1d56afb01 100644
--- a/src/mongo/shell/session.js
+++ b/src/mongo/shell/session.js
@@ -132,13 +132,6 @@ var {
                 return false;
             }
 
-            if (cmdName === "aggregate" && cmdObjUnwrapped.explain) {
-                // TODO SERVER-30582: Aggregation's explain doesn't support the "readConcern"
-                // option. Note that an aggregation with a $out stage as its last stage still
-                // supports a read concern level of "local".
-                return false;
-            }
-
             if (cmdName === "explain") {
                 return kCommandsThatSupportReadConcern.has(Object.keys(cmdObjUnwrapped.explain)[0]);
             }