Incorrect warning for @derive Jason.Encoder

[Ch4s3]

Environment

• Elixir & Erlang versions (elixir --version):
  Erlang/OTP 21 [erts-10.0] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe]
  Elixir (1.6.6)

• Operating system:
  macOS 10.13.5

• Client (editor or IDE):
  vsCode 1.25.1

Basically an Ecto schema with a derive macro for Jason will show an incorrect error. Unfortunately, I missed grabbing the dev logs.

Code:

defmodule MyApp.MailData do
  @derive {Jason.Encoder,
           only: [:to, :subject, :sendgrid_template, :extra_data, :send_attempts, :priority]}
  schema "mail_data" do
    field(:to, :string)
    field(:subject, :string)
    field(:sendgrid_template, :string, default: "")
    field(:extra_data, :map, default: %{})
    field(:send_attempts, :integer, default: 0)
    field(:priority, :integer, default: 0)
  end
end

Error:

[Elixir]
** (BadArityError) #Function<1.119002335/3 in Jason.Codegen.encode_pair/2> with arity 3 called with 4 arguments ("to", "to", 0, [])
    lib/encode.ex:239: Jason.Encode.key/2
    lib/codegen.ex:126: Jason.Codegen.encode_pair/2
    (elixir) lib/enum.ex:1294: Enum."-map/2-lists^map/1-0-"/2
    lib/codegen.ex:48: Jason.Codegen.build_kv_iodata/2
    expanding macro: Jason.Encoder.Any.__deriving__/3
    lib/emails/mail_data.ex:21: MyApp.MailData (module)
    (elixir) lib/module.ex:516: Module.eval_quoted/4

The hot fix was uninstalling ElixirLS and reinstalling it, but @michalmuskala and I thought it might be worth filing an issue here. Thanks!

[JakeBecker]

This is most likely an unfortunate side effect of having Jason included in ElixirLS. If your project depends on a different version of it, it's a bit unpredictable which one ElixirLS will use in compilation.

I haven't thought of a good fix for this, but probably the simplest thing to mitigate it would be to keep up with Jason's minor releases so compilation is more likely to succeed.

[Ch4s3]

Interesting... I'll give this some thought.

[michalmuskala]

The only solution I could think of would be vendoring Jason inside the elixir-ls by copying the code and renaming modules. It's not ideal from the maintenance perspective, but should solve all such issues.

[JakeBecker]

This project has moved!

It's now being maintained by proactive volunteers from the Elixir community over at elixir-lsp/elixir-ls. Updates will continue to be published from that repo to the original VS Code extension, so no need to switch plugins if you're using VS Code.

To avoid inundating the new maintainers with issues, please verify that your issue persists with the latest version of the extension (which is published from the new repo) before re-filing your issue there.

Thanks for using ElixirLS!