I’m trying to reduce the number of Elixir 1.17 warnings in my projects, and I have questions with optional dependencies.

One example that triggers a new warning is Jason’s optional dependency on Decimal. If you create an empty project, add :jason to the dependencies and compile, you’ll see this:

==> jason
    warning: Decimal.new/1 is undefined (module Decimal is not available or is yet to be defined)
    │
 94 │         decimal.new(string)
    │                 ~
    │
    └─ (jason 1.4.3) lib/decoder.ex:94:17: Jason.Decoder.float_decode_function/1

warning: struct Decimal.Error is undefined (module Decimal.Error is not available or is yet to be defined)
└─ (jason 1.4.3) lib/decoder.ex: Jason.Decoder.float_decode_function/1

     warning: Decimal.to_string/2 is undefined (module Decimal is not available or is yet to be defined)
     │
 242 │     [?", decimal.to_string(value, :normal), ?"]
     │                  ~
     │
     └─ (jason 1.4.3) lib/encode.ex:242:18: Jason.Encode.struct/4

     warning: Decimal.to_string/1 is undefined (module Decimal is not available or is yet to be defined)
     │
 231 │     [?", decimal.to_string(value), ?"]
     │                  ~
     │
     └─ (jason 1.4.3) lib/encoder.ex:231:18: Jason.Encoder.Decimal.encode/2

There’s code that silenced a similar warning previously, but Elixir 1.17 is smarter. This is really cool that it can be detected, but I was wondering if there was preferred way of resolving warnings like this.

For example, placing the following compile-time checks around the Decimal-using functions would silence the Jason warnings:

if Code.ensure_loaded(Decimal) == {:module, Decimal} do
  def fun_that_uses_decimal() do
    ...
  end
end

Since this comes up with other libraries too, I’d like to be consistent and I’m not sure if there are subtle gotchas that this introduces.