Compile error for function definition via macro

[Nazari]

Environment

• Elixir & Erlang/OTP versions (elixir --version):
  Erlang/OTP 23 [erts-11.0.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace]

Elixir 1.10.4 (compiled with Erlang/OTP 23)

• Operating system:
  macOS Catalina 10.15.6

Current behavior

Compiler complains with this message:
== Compilation error in file lib/problem1.ex ==
** (ArgumentError) argument error
(stdlib 3.13) :lists.keyfind(:counter, 1, :b)
(elixir 1.10.4) src/elixir_utils.erl:45: :elixir_utils.var_context/2
(stdlib 3.13) lists.erl:1354: :lists.mapfoldl/3
for this code:
`
defmodule Problem1 do
def sample,
do: {
:fname,
{:a, :cmd,
[
{:a, :b, :reqres},
{:a, :c, :req},
]}
}

defmacro res_cmd() do
  {fnname, {namespace,container,lista}} = sample()
  quote do
      def unquote(fnname)(:res, pars) do
        {
          unquote(namespace),
          unquote(container),
          unquote(lista)
          |> Enum.filter(fn {_, _, ty} -> ty == :res or ty == :reqres end)
          |> Enum.map(fn {a,b,_c} -> { a, b, pars[b]} end)
        }
    end
  end
end

end

defmodule Injected1 do
require Problem1
Problem1.res_cmd()
end
`

Expected behavior

As this version of the code. It works as desired defining a function in module Injected2:
`
defmodule Problem2 do
def sample,
do: {
:fname,
{:a, :cmd,
[
{:a, :b, :reqres},
{:a, :c, :req},
]}
}

defmacro res_cmd() do
  {fnname, {namespace,container,lista}} = sample()
  filtered = lista
    |> Enum.filter(fn {_, _, ty} -> ty == :res or ty == :reqres end)
    |> Enum.map(fn {a,b,_c} -> {a,b} end)
  quote do
      def unquote(fnname)(:res, pars) do
        {
          unquote(namespace),
          unquote(container),
          unquote(filtered)
            |> Enum.map(fn {a,b} -> { a, b, pars[b]} end)
        }
    end
  end
end

end

defmodule Injected2 do
require Problem2
Problem2.res_cmd()
end
`

[fuelen]

You use three-element tuples which are used for calls in AST representation.
Replace

unquote(lista)

with

unquote(Macro.escape(lista))

[josevalim]

Thanks @fuelen for debugging this. I have recently pushed some guards to the code base to make these errors easier to spot, thanks for the report!