SERVER-50640 listCommands should list isMaster in addition to hello

(cherry picked from commit 2756fa678945f890c73318efa72d3793c6e918d8)

7 files changed, 27 insertions, 16 deletions

diff --git a/jstests/core/list_commands.js b/jstests/core/list_commands.js
index 2310d7d9a0a..e9c021ff32b 100644
--- a/jstests/core/list_commands.js
+++ b/jstests/core/list_commands.js
@@ -22,6 +22,7 @@
     // Test that result contains basic commands.
     assert(commands.hasOwnProperty("commands"));
     assert(commands["commands"].hasOwnProperty("hello"));
+    assert(commands["commands"].hasOwnProperty("isMaster"));
     assert(commands["commands"].hasOwnProperty("insert"));
     assert(commands["commands"].hasOwnProperty("ping"));
 })();
diff --git a/jstests/core/views/views_all_commands.js b/jstests/core/views/views_all_commands.js
index 46f161bf122..59d5d0be518 100644
--- a/jstests/core/views/views_all_commands.js
+++ b/jstests/core/views/views_all_commands.js
@@ -305,6 +305,7 @@
         insert: {command: {insert: "view", documents: [{x: 1}]}, expectFailure: true},
         invalidateUserCache: {skip: isUnrelated},
         isdbgrid: {skip: isUnrelated},
+        isMaster: {skip: isUnrelated},
         journalLatencyTest: {skip: isUnrelated},
         killCursors: {
             setup: function(conn) {
diff --git a/jstests/replsets/db_reads_while_recovering_all_commands.js b/jstests/replsets/db_reads_while_recovering_all_commands.js
index 036fecbc6e6..06be14ffe96 100644
--- a/jstests/replsets/db_reads_while_recovering_all_commands.js
+++ b/jstests/replsets/db_reads_while_recovering_all_commands.js
@@ -205,6 +205,7 @@
         insert: {skip: isPrimaryOnly},
         internalRenameIfOptionsAndIndexesMatch: {skip: isAnInternalCommand},
         invalidateUserCache: {skip: isNotAUserDataRead},
+        isMaster: {skip: isNotAUserDataRead},
         journalLatencyTest: {skip: isNotAUserDataRead},
         killAllSessions: {skip: isNotAUserDataRead},
         killAllSessionsByPattern: {skip: isNotAUserDataRead},
diff --git a/jstests/sharding/safe_secondary_reads_drop_recreate.js b/jstests/sharding/safe_secondary_reads_drop_recreate.js
index e9794244aca..24f104bfc03 100644
--- a/jstests/sharding/safe_secondary_reads_drop_recreate.js
+++ b/jstests/sharding/safe_secondary_reads_drop_recreate.js
@@ -234,6 +234,7 @@
         insert: {skip: "primary only"},
         invalidateUserCache: {skip: "does not return user data"},
         isdbgrid: {skip: "does not return user data"},
+        isMaster: {skip: "does not return user data"},
         journalLatencyTest: {skip: "does not return user data"},
         killAllSessions: {skip: "does not return user data"},
         killAllSessionsByPattern: {skip: "does not return user data"},
diff --git a/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js b/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js
index ab5fe6ae322..b65e7fabae4 100644
--- a/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js
+++ b/jstests/sharding/safe_secondary_reads_single_migration_suspend_range_deletion.js
@@ -274,6 +274,7 @@
         insert: {skip: "primary only"},
         invalidateUserCache: {skip: "does not return user data"},
         isdbgrid: {skip: "does not return user data"},
+        isMaster: {skip: "does not return user data"},
         journalLatencyTest: {skip: "does not return user data"},
         killCursors: {skip: "does not return user data"},
         killAllSessions: {skip: "does not return user data"},
diff --git a/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js b/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js
index af12768b14d..126ace906a9 100644
--- a/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js
+++ b/jstests/sharding/safe_secondary_reads_single_migration_waitForDelete.js
@@ -238,6 +238,7 @@
         insert: {skip: "primary only"},
         invalidateUserCache: {skip: "does not return user data"},
         isdbgrid: {skip: "does not return user data"},
+        isMaster: {skip: "does not return user data"},
         journalLatencyTest: {skip: "does not return user data"},
         killAllSessions: {skip: "does not return user data"},
         killAllSessionsByPattern: {skip: "does not return user data"},
diff --git a/src/mongo/db/commands/generic.cpp b/src/mongo/db/commands/generic.cpp
index 22a54ca1be4..4940d1106dd 100644
--- a/src/mongo/db/commands/generic.cpp
+++ b/src/mongo/db/commands/generic.cpp
@@ -34,6 +34,7 @@
 
 #include <time.h>
 
+#include "mongo/base/string_data.h"
 #include "mongo/bson/util/bson_extract.h"
 #include "mongo/bson/util/builder.h"
 #include "mongo/client/dbclient_rs.h"
@@ -72,6 +73,8 @@ using std::string;
 using std::stringstream;
 using std::vector;
 
+constexpr auto kIsMasterString = "isMaster"_sd;
+
 class CmdBuildInfo : public BasicCommand {
 public:
     CmdBuildInfo() : BasicCommand("buildInfo", "buildinfo") {}
@@ -278,33 +281,35 @@ public:
                      const string& ns,
                      const BSONObj& cmdObj,
                      BSONObjBuilder& result) {
-        // sort the commands before building the result BSON
-        std::vector<Command*> commands;
+        // Sort the command names before building the result BSON.
+        std::vector<std::string> commandNames;
         for (const auto command : allCommands()) {
-            // don't show oldnames
-            if (command.first == command.second->getName())
-                commands.push_back(command.second);
+            // Don't show oldnames unless it's "isMaster". The output of the listCommands command
+            // must include "isMaster," even though it's an alias for the "hello" command, in order
+            // to preserve backwards compatibility with Ops Manager 4.4.
+            if (command.first == command.second->getName() || command.first == kIsMasterString)
+                commandNames.push_back(command.first);
         }
-        std::sort(commands.begin(), commands.end(), [](Command* lhs, Command* rhs) {
-            return (lhs->getName()) < (rhs->getName());
-        });
+        std::sort(commandNames.begin(), commandNames.end());
 
         BSONObjBuilder b(result.subobjStart("commands"));
-        for (const auto& c : commands) {
-            BSONObjBuilder temp(b.subobjStart(c->getName()));
-
+        for (const auto& c : commandNames) {
+            const auto command = findCommand(c);
+            auto name = (c == kIsMasterString) ? kIsMasterString : command->getName();
+            BSONObjBuilder temp(b.subobjStart(name));
             {
                 stringstream help;
-                c->help(help);
+                command->help(help);
                 temp.append("help", help.str());
             }
-            temp.append("slaveOk", c->slaveOk());
-            temp.append("adminOnly", c->adminOnly());
+            temp.append("slaveOk", command->slaveOk());
+            temp.append("adminOnly", command->adminOnly());
             // optionally indicates that the command can be forced to run on a slave/secondary
-            if (c->slaveOverrideOk())
-                temp.append("slaveOverrideOk", c->slaveOverrideOk());
+            if (command->slaveOverrideOk())
+                temp.append("slaveOverrideOk", command->slaveOverrideOk());
             temp.done();
         }
+
         b.done();
 
         return 1;