From 9a5fd32bfcdbf356a35961e45ed3d6693e85b89e Mon Sep 17 00:00:00 2001
From: Dianna Hohensee <dianna.hohensee@10gen.com>
Date: Thu, 22 Feb 2018 16:37:38 -0500
Subject: SERVER-33014 Remove unreachable featureCompatibilityVersion document
 op observers

---
 .../db/commands/feature_compatibility_version.cpp  | 26 ----------------------
 .../db/commands/feature_compatibility_version.h    | 12 ----------
 src/mongo/db/op_observer_impl.cpp                  | 14 +++++++-----
 3 files changed, 9 insertions(+), 43 deletions(-)

diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index 60014e63785..1781a956435 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -335,32 +335,6 @@ void FeatureCompatibilityVersion::onInsertOrUpdate(OperationContext* opCtx, cons
     });
 }
 
-void FeatureCompatibilityVersion::onDelete(OperationContext* opCtx, const BSONObj& doc) {
-    auto idElement = doc["_id"];
-    if (idElement.type() != BSONType::String ||
-        idElement.String() != FeatureCompatibilityVersion::kParameterName) {
-        return;
-    }
-
-    log() << "setting featureCompatibilityVersion to "
-          << FeatureCompatibilityVersionCommandParser::kVersion34;
-    opCtx->recoveryUnit()->onCommit([]() {
-        serverGlobalParams.featureCompatibility.setVersion(
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo34);
-        updateMinWireVersion();
-    });
-}
-
-void FeatureCompatibilityVersion::onDropCollection(OperationContext* opCtx) {
-    log() << "setting featureCompatibilityVersion to "
-          << FeatureCompatibilityVersionCommandParser::kVersion36;
-    opCtx->recoveryUnit()->onCommit([]() {
-        serverGlobalParams.featureCompatibility.setVersion(
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36);
-        updateMinWireVersion();
-    });
-}
-
 void FeatureCompatibilityVersion::updateMinWireVersion() {
     WireSpec& spec = WireSpec::instance();
 
diff --git a/src/mongo/db/commands/feature_compatibility_version.h b/src/mongo/db/commands/feature_compatibility_version.h
index aab764f7ea9..1c3916565b0 100644
--- a/src/mongo/db/commands/feature_compatibility_version.h
+++ b/src/mongo/db/commands/feature_compatibility_version.h
@@ -151,18 +151,6 @@ public:
      */
     static void onInsertOrUpdate(OperationContext* opCtx, const BSONObj& doc);
 
-    /**
-     * Examines the _id of a document removed from admin.system.version. If it is the
-     * featureCompatibilityVersion document, resets the server parameter to its default value
-     * on commit.
-     */
-    static void onDelete(OperationContext* opCtx, const BSONObj& doc);
-
-    /**
-     * Resets the server parameter to its default value on commit.
-     */
-    static void onDropCollection(OperationContext* opCtx);
-
     /**
      * Sets the server's outgoing and incomingInternalClient minWireVersions according to the
      * current featureCompatibilityVersion value.
diff --git a/src/mongo/db/op_observer_impl.cpp b/src/mongo/db/op_observer_impl.cpp
index 8ba3bfd13be..4a1977ebf7d 100644
--- a/src/mongo/db/op_observer_impl.cpp
+++ b/src/mongo/db/op_observer_impl.cpp
@@ -602,9 +602,11 @@ void OpObserverImpl::onDropDatabase(OperationContext* opCtx, const std::string&
                 kUninitializedStmtId,
                 {});
 
-    if (dbName == FeatureCompatibilityVersion::kDatabase) {
-        FeatureCompatibilityVersion::onDropCollection(opCtx);
-    } else if (dbName == NamespaceString::kSessionTransactionsTableNamespace.db()) {
+    uassert(50714,
+            "dropping the admin database is not allowed.",
+            dbName != FeatureCompatibilityVersion::kDatabase);
+
+    if (dbName == NamespaceString::kSessionTransactionsTableNamespace.db()) {
         SessionCatalog::get(opCtx)->invalidateSessions(opCtx, boost::none);
     }
 
@@ -636,10 +638,12 @@ repl::OpTime OpObserverImpl::onDropCollection(OperationContext* opCtx,
                                  {});
     }
 
+    uassert(50715,
+            "dropping the admin.system.version collection is not allowed.",
+            collectionName.ns() != FeatureCompatibilityVersion::kCollection);
+
     if (collectionName.coll() == DurableViewCatalog::viewsCollectionName()) {
         DurableViewCatalog::onExternalChange(opCtx, collectionName);
-    } else if (collectionName.ns() == FeatureCompatibilityVersion::kCollection) {
-        FeatureCompatibilityVersion::onDropCollection(opCtx);
     } else if (collectionName == NamespaceString::kSessionTransactionsTableNamespace) {
         SessionCatalog::get(opCtx)->invalidateSessions(opCtx, boost::none);
     }
-- 
cgit v1.2.1