During the discussion of
SERVER-52914, we have noticed that OrMatchExpression::matchesSingleElement has a different handling of MatchDetails object compared to OrMatchExpression::matches. During the investigation we have started to wonder if this method ever gets called. It looks like query parser simply does not allow a query where this method would be called.
It is highly unlikely that our tests do not cover some case where OrMatchExpression::matchesSingleElement is used, so we concluded that this is a dead code. We should replace the body of this method with MONGO_UNREACHABLE_TASSERT to avoid further confusion.