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, 17 insertions, 15 deletions

diff --git a/src/mongo/db/repl/sync_source_resolver.cpp b/src/mongo/db/repl/sync_source_resolver.cpp
index 1218ffa2cc2..77579cc24ad 100644
--- a/src/mongo/db/repl/sync_source_resolver.cpp
+++ b/src/mongo/db/repl/sync_source_resolver.cpp
@@ -256,12 +256,13 @@ void SyncSourceResolver::_firstOplogEntryFetcherCallback(
         _finishCallback(Status(ErrorCodes::CallbackCanceled,
                                str::stream()
                                    << "sync source resolver shut down while probing candidate: "
-                                   << candidate));
+                                   << candidate))
+            .transitional_ignore();
         return;
     }
 
     if (ErrorCodes::CallbackCanceled == queryResult.getStatus()) {
-        _finishCallback(queryResult.getStatus());
+        _finishCallback(queryResult.getStatus()).transitional_ignore();
         return;
     }
 
@@ -272,14 +273,14 @@ void SyncSourceResolver::_firstOplogEntryFetcherCallback(
               << "' for " << kFetcherErrorBlacklistDuration << " until: " << until;
         _syncSourceSelector->blacklistSyncSource(candidate, until);
 
-        _chooseAndProbeNextSyncSource(earliestOpTimeSeen);
+        _chooseAndProbeNextSyncSource(earliestOpTimeSeen).transitional_ignore();
         return;
     }
 
     const auto& queryResponse = queryResult.getValue();
     const auto remoteEarliestOpTime = _parseRemoteEarliestOpTime(candidate, queryResponse);
     if (remoteEarliestOpTime.isNull()) {
-        _chooseAndProbeNextSyncSource(earliestOpTimeSeen);
+        _chooseAndProbeNextSyncSource(earliestOpTimeSeen).transitional_ignore();
         return;
     }
 
@@ -306,7 +307,7 @@ void SyncSourceResolver::_firstOplogEntryFetcherCallback(
             earliestOpTimeSeen = remoteEarliestOpTime;
         }
 
-        _chooseAndProbeNextSyncSource(earliestOpTimeSeen);
+        _chooseAndProbeNextSyncSource(earliestOpTimeSeen).transitional_ignore();
         return;
     }
 
@@ -323,7 +324,7 @@ void SyncSourceResolver::_scheduleRBIDRequest(HostAndPort candidate, OpTime earl
                    stdx::placeholders::_1));
 
     if (!handle.isOK()) {
-        _finishCallback(handle.getStatus());
+        _finishCallback(handle.getStatus()).transitional_ignore();
         return;
     }
 
@@ -339,7 +340,7 @@ void SyncSourceResolver::_rbidRequestCallback(
     OpTime earliestOpTimeSeen,
     const executor::TaskExecutor::RemoteCommandCallbackArgs& rbidReply) {
     if (rbidReply.response.status == ErrorCodes::CallbackCanceled) {
-        _finishCallback(rbidReply.response.status);
+        _finishCallback(rbidReply.response.status).transitional_ignore();
         return;
     }
 
@@ -352,7 +353,7 @@ void SyncSourceResolver::_rbidRequestCallback(
         log() << "Blacklisting " << candidate << " due to error: '" << ex << "' for "
               << kFetcherErrorBlacklistDuration << " until: " << until;
         _syncSourceSelector->blacklistSyncSource(candidate, until);
-        _chooseAndProbeNextSyncSource(earliestOpTimeSeen);
+        _chooseAndProbeNextSyncSource(earliestOpTimeSeen).transitional_ignore();
         return;
     }
 
@@ -361,11 +362,11 @@ void SyncSourceResolver::_rbidRequestCallback(
         // Unittest requires that this kind of failure be handled specially.
         auto status = _scheduleFetcher(_makeRequiredOpTimeFetcher(candidate, earliestOpTimeSeen));
         if (!status.isOK()) {
-            _finishCallback(status);
+            _finishCallback(status).transitional_ignore();
         }
         return;
     }
-    _finishCallback(candidate);
+    _finishCallback(candidate).transitional_ignore();
 }
 
 Status SyncSourceResolver::_compareRequiredOpTimeWithQueryResponse(
@@ -405,12 +406,13 @@ void SyncSourceResolver::_requiredOpTimeFetcherCallback(
                                                 "required optime "
                                              << _requiredOpTime.toString()
                                              << " in candidate's oplog: "
-                                             << candidate));
+                                             << candidate))
+            .transitional_ignore();
         return;
     }
 
     if (ErrorCodes::CallbackCanceled == queryResult.getStatus()) {
-        _finishCallback(queryResult.getStatus());
+        _finishCallback(queryResult.getStatus()).transitional_ignore();
         return;
     }
 
@@ -422,7 +424,7 @@ void SyncSourceResolver::_requiredOpTimeFetcherCallback(
               << " until: " << until << ". required optime: " << _requiredOpTime;
         _syncSourceSelector->blacklistSyncSource(candidate, until);
 
-        _chooseAndProbeNextSyncSource(earliestOpTimeSeen);
+        _chooseAndProbeNextSyncSource(earliestOpTimeSeen).transitional_ignore();
         return;
     }
 
@@ -439,11 +441,11 @@ void SyncSourceResolver::_requiredOpTimeFetcherCallback(
                   << " until: " << until;
         _syncSourceSelector->blacklistSyncSource(candidate, until);
 
-        _chooseAndProbeNextSyncSource(earliestOpTimeSeen);
+        _chooseAndProbeNextSyncSource(earliestOpTimeSeen).transitional_ignore();
         return;
     }
 
-    _finishCallback(candidate);
+    _finishCallback(candidate).transitional_ignore();
 }
 
 Status SyncSourceResolver::_chooseAndProbeNextSyncSource(OpTime earliestOpTimeSeen) {