Type issue on decode!()

[lucianoengel]

Hello, I'm trying to shift from Jason to Jsonrs but I'm hitting some weird type issues. Dialyzer is going crazy overall. One example is the code below:

@spec deserialize(binary) :: {term, Metadata.t() | nil} | :error
 def deserialize(message) do
    case Jsonrs.decode!(message) do
      %{"route" => route, "reference" => reference, "payload" => payload} ->
        {payload, %Metadata{reference: reference, route: route}}
      %{"d" => payload} ->
        {payload, nil}
      _ ->
        :error
    end
 end

Dialyzer just give me this for the first case clause line

The pattern can never match the type.

Pattern:
%{
  <<114, 101, 102, 101, 114, 101, 110, 99, 101>> => _reference,
  <<114, 111, 117, 116, 101>> => _route,
  <<112, 97, 121, 108, 111, 97, 100>> => _payload
}

Type:
binary()

I don't understand how decode!() can be expecting a binary() type as return for the dialyzer run?

I did look at Jsonrs typing and everything seems correct, specs says decode!() should return term so I'm in a bit of a loss...

Important to notice is that I had no dialyzer issues at all with Jason and the only thing that changed in that function was the decode function module name

[benhaney]

Thanks for reporting this. Looks like the typespec for nif_decode!/1 was wrong, and dialyzer was appropriately narrowing the return type of decode!/2 because of that.
0.1.4 should fix this. Let me know.

[lucianoengel]

@benhaney thanks for the quick reply! That did silence dialyzer around, closing :)