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, 2 insertions, 1 deletions

diff --git a/src/mongo/db/repl/databases_cloner_test.cpp b/src/mongo/db/repl/databases_cloner_test.cpp
index 36020cea9a8..5e7ceacae2b 100644
--- a/src/mongo/db/repl/databases_cloner_test.cpp
+++ b/src/mongo/db/repl/databases_cloner_test.cpp
@@ -176,7 +176,8 @@ protected:
                     log() << "reusing collection during test which may cause problems, ns:" << nss;
                 }
                 (collInfo->loader = new CollectionBulkLoaderMock(&collInfo->stats))
-                    ->init(secondaryIndexSpecs);
+                    ->init(secondaryIndexSpecs)
+                    .transitional_ignore();
 
                 return StatusWith<std::unique_ptr<CollectionBulkLoader>>(
                     std::unique_ptr<CollectionBulkLoader>(collInfo->loader));