SERVER-19758 add support for "executionStats" and "allPlansExecution" to agg explain

Like other explainable commands, aggregate can now be
explained using the explain command, e.g.
db.runCommand({explain: {aggregate: ...}, verbosity:
"executionStats"}). The existing explain:true flag
corresponds to "queryPlanner" mode and is still supported.
However, explain:true cannot be specified when explaining
aggregate via the explain command.

Additional execution information is provided only in the
$cursor section of the aggregation explain output. Having
aggregation stages themselves track and report execution
info is further work.

1 files changed, 5 insertions, 6 deletions

diff --git a/src/mongo/s/commands/cluster_explain_cmd.cpp b/src/mongo/s/commands/cluster_explain_cmd.cpp
index 4031a45c02a..099d6233a60 100644
--- a/src/mongo/s/commands/cluster_explain_cmd.cpp
+++ b/src/mongo/s/commands/cluster_explain_cmd.cpp
@@ -112,10 +112,9 @@ public:
                      int options,
                      std::string& errmsg,
                      BSONObjBuilder& result) {
-        ExplainCommon::Verbosity verbosity;
-        Status parseStatus = ExplainCommon::parseCmdBSON(cmdObj, &verbosity);
-        if (!parseStatus.isOK()) {
-            return appendCommandStatus(result, parseStatus);
+        auto verbosity = ExplainOptions::parseCmdBSON(cmdObj);
+        if (!verbosity.isOK()) {
+            return appendCommandStatus(result, verbosity.getStatus());
         }
 
         // This is the nested command which we are explaining.
@@ -139,8 +138,8 @@ public:
         rpc::ServerSelectionMetadata metadata(secondaryOk, readPref.getValue());
 
         // Actually call the nested command's explain(...) method.
-        Status explainStatus =
-            commToExplain->explain(opCtx, dbName, explainObj, verbosity, metadata, &result);
+        Status explainStatus = commToExplain->explain(
+            opCtx, dbName, explainObj, verbosity.getValue(), metadata, &result);
         if (!explainStatus.isOK()) {
             return appendCommandStatus(result, explainStatus);
         }