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, 3 insertions, 3 deletions

diff --git a/src/mongo/bson/mutable/algorithm.h b/src/mongo/bson/mutable/algorithm.h
index 768469deff4..9e4ffd278e4 100644
--- a/src/mongo/bson/mutable/algorithm.h
+++ b/src/mongo/bson/mutable/algorithm.h
@@ -140,9 +140,9 @@ void sortChildren(Element parent, Comparator comp) {
     const std::vector<Element>::iterator end = children.end();
     for (; where != end; ++where) {
         // Detach from its current location.
-        where->remove();
+        where->remove().transitional_ignore();
         // Make it the new rightmost element.
-        parent.pushBack(*where);
+        parent.pushBack(*where).transitional_ignore();
     }
 }
 
@@ -156,7 +156,7 @@ void deduplicateChildren(Element parent, EqualityComparator equal) {
     while (current.ok()) {
         Element next = current.rightSibling();
         if (next.ok() && equal(current, next)) {
-            next.remove();
+            next.remove().transitional_ignore();
         } else {
             current = next;
         }