Production Elixir Not Finding Existing Atoms

Question

I'm using a library that parses input into maps using already-existing keys (Poison). For whatever reason, in production, it thinks the keys don't exist, and I can't figure out why. I do have a few pieces of information that I'm hoping someone who isn't a rookie is willing to help me figure out what's going on:

1:

If I do an IEX session (iex -S mix), I can run :erlang.binary_to_existing_atom("first_name", :"utf8") without trouble. But in production, instead I get

** (ArgumentError) argument error
  :erlang.binary_to_existing_atom("first_name", :utf8)

2:

I can run :first_name immediately before :erlang.binary_to_existing_atom on production, and it works fine, since by then, the atom has been created. BUT , I can't run :first_name followed by the library's method: Poison.Parser.parse!(~s(#{body}), keys: :atoms!) as it throws the error, which I find to be strange.

3:

I'm using Heroku, not sure if that matters. The atoms are defined within an Ecto model, also not sure if that matters. Any help would be greatly appreciated - thanks in advance!

Answer 1

You'll note that the Erlang documentation says:

binary_to_existing_atom(Binary, Encoding) -> atom()

Types:

Binary = binary() Encoding = latin1 | unicode | utf8 Works like binary_to_atom/2, but the atom must already exist.

Failure: badarg if the atom does not already exist.

If I were you I'd try to figure out why the :first_name atom isn't there before the call is run.

Answer 2

Erlang compiler optimizes away known pure function calls and replaces them with the call result. This omits the original atom from the module, thus making it non-existent. The bug is here https://bugs.erlang.org/browse/ERL-453 and I might be fixing it.