How to derive Jason.Encoder in Livebook

11 February 2025

• #elixir
• #livebook

I ran into the issue of trying to include @derive Jason.Encoer in a struct while working Livebook.

My code was simple enough:

defmodule ContentPart do
  @derive Jason.Encoder
  defstruct [:text]
end

but I was getting a warning:

warning: the Jason.Encoder protocol has already been consolidated, an implementation for ContentPart has no effect.

I found a simple fix in a comment by Wojtek Mach:

Mix.install([:jason], consolidate_protocols: true)