SERVER-27244 Status usage compile-time facilities.

There are numerous places in the codebase where `mongo::Status` or
`mongo::StatusWith< T >` objects are returned and never checked.
Many of these are innocuous, but many of them are potentially
severe bugs.  This change introduces facilities to permit
compile-time warning of unchecked `Status` and `StatusWith` usage
on clang compilers.  It introduces an `ignore` function which is
useful to state that a specific "ignored status" case was
intentional.  It not presently an error, in clang builds, to
forget to check a `Status` -- this will come in a later commit.

This also introduces a `transitional_ignore` function, which allows
for easy continual auditing of the codebase for current "whitelisted"
unchecked-status instances.  All present "ignored status" cases
have been marked `transitional_ignore`.

1 files changed, 8 insertions, 5 deletions

diff --git a/src/mongo/db/repl/replication_coordinator_impl_elect_v1.cpp b/src/mongo/db/repl/replication_coordinator_impl_elect_v1.cpp
index d227f78b76b..394878e52ec 100644
--- a/src/mongo/db/repl/replication_coordinator_impl_elect_v1.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl_elect_v1.cpp
@@ -149,8 +149,10 @@ void ReplicationCoordinatorImpl::_startElectSelfV1_inlock() {
         return;
     }
     fassert(28685, nextPhaseEvh.getStatus());
-    _replExecutor->onEvent(nextPhaseEvh.getValue(),
-                           stdx::bind(&ReplicationCoordinatorImpl::_onDryRunComplete, this, term));
+    _replExecutor
+        ->onEvent(nextPhaseEvh.getValue(),
+                  stdx::bind(&ReplicationCoordinatorImpl::_onDryRunComplete, this, term))
+        .status_with_transitional_ignore();
     lossGuard.dismiss();
 }
 
@@ -244,9 +246,10 @@ void ReplicationCoordinatorImpl::_startVoteRequester_inlock(long long newTerm) {
         return;
     }
     fassert(28643, nextPhaseEvh.getStatus());
-    _replExecutor->onEvent(
-        nextPhaseEvh.getValue(),
-        stdx::bind(&ReplicationCoordinatorImpl::_onVoteRequestComplete, this, newTerm));
+    _replExecutor
+        ->onEvent(nextPhaseEvh.getValue(),
+                  stdx::bind(&ReplicationCoordinatorImpl::_onVoteRequestComplete, this, newTerm))
+        .status_with_transitional_ignore();
 }
 
 void ReplicationCoordinatorImpl::_onVoteRequestComplete(long long originalTerm) {