It is generated from Explorer.Chain.MapCache when it is used by the module.
Long story short, if you are new to elixir, this are more advanced topics related to metaprogramming. Usually tracking down code generated at compile-time can be pretty difficult, one thing you can do is use the following from iex:
Module.__info__/1 callback to get the list of all functions:
Explorer.Chain.Cache.Block.__info__(:functions)
Or you can try to use beam_file to get the elixir code after all the macros were expanded: How to view module source after code generation? - #13 by Marcus
