Summary:
Added code for generically handing structs to OptionTypeInfo. A struct is a collection of variables handled by their own map of OptionTypeInfos. Examples of structs include Compaction and Cache options.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6425
Reviewed By: siying
Differential Revision: D21668789
Pulled By: zhichao-cao
fbshipit-source-id: 064b110de39dadf82361ed4663f7ac1a535b0b07