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, 12 insertions, 6 deletions

diff --git a/src/mongo/dbtests/replica_set_tests.cpp b/src/mongo/dbtests/replica_set_tests.cpp
index 91fa21f8800..e70a221fa57 100644
--- a/src/mongo/dbtests/replica_set_tests.cpp
+++ b/src/mongo/dbtests/replica_set_tests.cpp
@@ -93,14 +93,16 @@ TEST_F(ReplicaSetTest, ReplCoordExternalStateStoresLastVoteWithNewTerm) {
     auto opCtx = makeOpCtx();
     auto replCoordExternalState = getReplCoordExternalState();
 
-    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 1});
+    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 1})
+        .transitional_ignore();
 
     auto lastVote = replCoordExternalState->loadLocalLastVoteDocument(opCtx.get());
     ASSERT_OK(lastVote.getStatus());
     ASSERT_EQ(lastVote.getValue().getTerm(), 2);
     ASSERT_EQ(lastVote.getValue().getCandidateIndex(), 1);
 
-    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{3, 1});
+    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{3, 1})
+        .transitional_ignore();
 
     lastVote = replCoordExternalState->loadLocalLastVoteDocument(opCtx.get());
     ASSERT_OK(lastVote.getStatus());
@@ -112,14 +114,16 @@ TEST_F(ReplicaSetTest, ReplCoordExternalStateDoesNotStoreLastVoteWithOldTerm) {
     auto opCtx = makeOpCtx();
     auto replCoordExternalState = getReplCoordExternalState();
 
-    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 1});
+    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 1})
+        .transitional_ignore();
 
     auto lastVote = replCoordExternalState->loadLocalLastVoteDocument(opCtx.get());
     ASSERT_OK(lastVote.getStatus());
     ASSERT_EQ(lastVote.getValue().getTerm(), 2);
     ASSERT_EQ(lastVote.getValue().getCandidateIndex(), 1);
 
-    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{1, 1});
+    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{1, 1})
+        .transitional_ignore();
 
     lastVote = replCoordExternalState->loadLocalLastVoteDocument(opCtx.get());
     ASSERT_OK(lastVote.getStatus());
@@ -131,14 +135,16 @@ TEST_F(ReplicaSetTest, ReplCoordExternalStateDoesNotStoreLastVoteWithEqualTerm)
     auto opCtx = makeOpCtx();
     auto replCoordExternalState = getReplCoordExternalState();
 
-    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 1});
+    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 1})
+        .transitional_ignore();
 
     auto lastVote = replCoordExternalState->loadLocalLastVoteDocument(opCtx.get());
     ASSERT_OK(lastVote.getStatus());
     ASSERT_EQ(lastVote.getValue().getTerm(), 2);
     ASSERT_EQ(lastVote.getValue().getCandidateIndex(), 1);
 
-    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 2});
+    replCoordExternalState->storeLocalLastVoteDocument(opCtx.get(), repl::LastVote{2, 2})
+        .transitional_ignore();
 
     lastVote = replCoordExternalState->loadLocalLastVoteDocument(opCtx.get());
     ASSERT_OK(lastVote.getStatus());