'nets argument to convert must be a signal' when working with records and functions

[Schottkyc137]

Not sure what the underlying issue is but this is as far broken down as I could:

entity A is
  port (din : BIT_VECTOR(4 downto 0));
end A;

architecture arch of A is
begin
end architecture;

package pkg_B is
  function init return natural;
end pkg_B;

package body pkg_B is
  function init return natural is
  begin
    return 1;
  end init;
end pkg_B;

use work.pkg_B.init;

package pkg_C is
	type bar is record
		field  : BIT_VECTOR(init downto 0);
	end record;
end package pkg_C;

use work.pkg_C.bar;

entity B is
end entity B;

architecture rtl of B is

  signal foo : bar;

  function bar_to_bitvector(bar_obj: bar) return BIT_VECTOR is
	begin
		return (4 downto 0 => '0');
	end;

begin

  test_inst: entity work.A
  port map(din => bar_to_bitvector(foo));
end architecture;

[nickg]

I've fixed the crash but found another bug which will prevent this from working properly.