Failed to parse warning for a binary pattern

[axelson]

Failed to parse warning:
[{:"<<", 1}, {:int, 1, 67}, {:":", 1}, {:int, 1, 8}, {:atom_part, 1, '/'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 't'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'g'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'r'}, {:atom_part, 1, '-'}, {:atom_part, 1, 'u'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 't'}, {:":", 1}, {:int, 1, 1}, {:",", 1}, {:int, 1, 111}, {:":", 1}, {:int, 1, 8}, {:atom_part, 1, '/'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 't'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'g'}, {:atom_part, 1, 'e'}, {:atom_part, 1, 'r'}, {:atom_part, 1, '-'}, {:atom_part, 1, 'u'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 't'}, {:":", 1}, {:int, 1, 1}, {:",", 1}, {:int, 1, 110}, {:":", 1}, {:int, 1, 8}, {:atom_part, 1, '/'}, {:atom_part, 1, 'i'}, {:atom_part, 1, 'n'}, {:atom_part, 1, 't'}, {:atom_part, 1, 'e'}, {:atom_part, 1, ...}, {:atom_part, ...}, {...}, ...]

Legacy warning:
lib/ls_proxy/cli.ex:44: The pattern <<67:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,116:8/integer-unit:1,101:8/integer-unit:1,110:8/integer-unit:1,116:8/integer-unit:1,45:8/integer-unit:1,76:8/integer-unit:1,101:8/integer-unit:1,110:8/integer-unit:1,103:8/integer-unit:1,116:8/integer-unit:1,104:8/integer-unit:1,58:8/integer-unit:1,32:8/integer-unit:1,_value@1/binary-unit:8>> can never match the type [binary()]

I think this code should reproduce the error:

defmodule Example do
  @header_fields %{"Content-Length" => :content_length, "Content-Type" => :content_type}

  for {field_name, field_atom} <- @header_fields do
    defp parse_header_field("#{unquote(field_name)}: " <> value) do
      {unquote(field_atom), value}
    end
  end

[asummers]

Related to #263 (comment)