Can not set the bitstring value in a struct definition

[Eiji7]

Elixir and Erlang/OTP versions

$ elixir --version
Erlang/OTP 27 [erts-15.2.3] [source] [64-bit] [smp:32:32] [ds:32:32:10] [async-threads:1] [jit:ns]

Elixir 1.18.3 (compiled with Erlang/OTP 27)

Operating system

Gentoo Linux with default/linux/amd64/23.0/desktop/plasma profile and 6.12.16 kernel version.

Current behavior

Defining a struct with default bitstring value raises ArgumentError with message argument error. It happens only if the size is not a multiple of 8.

The following examples are failing:

defmodule Example1, do: defstruct value: <<0::1>>
defmodule Example2, do: defstruct value: <<0::2>>
defmodule Example3, do: defstruct value: <<0::3>>
defmodule Example4, do: defstruct value: <<0::4>>
defmodule Example5, do: defstruct value: <<0::5>>
defmodule Example6, do: defstruct value: <<0::6>>
defmodule Example7, do: defstruct value: <<0::7>>

defmodule Example9, do: defstruct value: <<0::9>>
defmodule Example10, do: defstruct value: <<0::10>>
defmodule Example11, do: defstruct value: <<0::11>>
defmodule Example12, do: defstruct value: <<0::12>>
defmodule Example13, do: defstruct value: <<0::13>>
defmodule Example14, do: defstruct value: <<0::14>>
defmodule Example15, do: defstruct value: <<0::15>>

The following examples are working:

defmodule Example8, do: defstruct value: <<0::8>>
defmodule Example16, do: defstruct value: <<0::16>>
defmodule Example24, do: defstruct value: <<0::24>>
defmodule Example32, do: defstruct value: <<0::32>>
defmodule Example40, do: defstruct value: <<0::40>>
defmodule Example48, do: defstruct value: <<0::48>>
defmodule Example56, do: defstruct value: <<0::56>>

Here is a complete error with stacktrace for Example1:

** (ArgumentError) argument error
    (elixir 1.18.3) src/elixir_erl.erl:109: :elixir_erl.elixir_to_erl(<<0::size(1)>>, 0)
    (elixir 1.18.3) src/elixir_erl.erl:70: :elixir_erl."-elixir_to_erl/2-lc$^1/1-0-"/2
    (elixir 1.18.3) src/elixir_erl.erl:71: :elixir_erl.elixir_to_erl/2
    (elixir 1.18.3) src/elixir_erl.erl:111: :elixir_erl.elixir_to_erl_cons/2
    (elixir 1.18.3) src/elixir_erl.erl:339: :elixir_erl.struct_info/1
    (elixir 1.18.3) src/elixir_erl.erl:311: :elixir_erl.add_info_function/6
    (elixir 1.18.3) src/elixir_erl.erl:286: :elixir_erl.functions_form/8
    iex:15: (file)

Expected behavior

I don't see why bitstring as a default value may be not supported especially that it works in version 1.17.3.

What's interesting is that the below call also does not work:

iex> :elixir_erl.elixir_to_erl(<<0::size(1)>>, 0)
** (ArgumentError) argument error
    (elixir 1.17.3) src/elixir_erl.erl:96: :elixir_erl.elixir_to_erl/2
    iex:1: (file)

which means that either :elixir_erl.elixir_to_erl/2 does not support non UTF-8 bitstrings or if it's expected then this call is incorrectly used since Elixir version 1.18.0-rc.0.

---

I've tried to search for a root issue. I believe I found a commit that introduces this bug: cb2e036. To be even more precise it happened in the first commit of #13984 which is: 792e604

1. Looks like a module paraller checker is now calling a :elixir_erl.debug_info/4:
   

   elixir/lib/elixir/lib/module/parallel_checker.ex

   Lines 65 to 79 in 66c5908

   	module_tuple =
   	cond do
   	is_tuple(info) ->
   	info
   	is_binary(info) ->
   	with {:ok, binary} <- File.read(info),
   	{:ok, {_, [debug_info: chunk]}} <- :beam_lib.chunks(binary, [:debug_info]),
   	{:debug_info_v1, backend, data} = chunk,
   	{:ok, module_map} <- backend.debug_info(:elixir_v1, module, data, []) do
   	cache_from_module_map(table, module_map)
   	else
   	_ -> nil
   	end
   	end

2. which calls :elixir_erl.dynamic_form/1:
   

   elixir/lib/elixir/src/elixir_erl.erl

   Lines 9 to 37 in 66c5908

   	%% debug_info callback
   	debug_info(elixir_v1, _Module, none, _Opts) ->
   	{error, missing};
   	debug_info(elixir_v1, _Module, {elixir_v1, Map, _Specs}, _Opts) ->
   	{ok, Map};
   	debug_info(erlang_v1, _Module, {elixir_v1, Map, Specs}, _Opts) ->
   	{Prefix, Forms, _, _, _} = dynamic_form(Map),
   	{ok, Prefix ++ Specs ++ Forms};
   	debug_info(core_v1, _Module, {elixir_v1, Map, Specs}, Opts) ->
   	{Prefix, Forms, _, _, _} = dynamic_form(Map),
   	#{compile_opts := CompileOpts} = Map,
   	AllOpts = CompileOpts ++ Opts,
   	%% Do not rely on elixir_erl_compiler because we don't warn
   	%% warnings nor the other functionality provided there.
   	case elixir_erl_compiler:erl_to_core(Prefix ++ Specs ++ Forms, AllOpts) of
   	{ok, CoreForms, _} ->
   	try compile:noenv_forms(CoreForms, [no_spawn_compiler_process, from_core, to_core, return | AllOpts]) of
   	{ok, _, Core, _} -> {ok, Core};
   	_What -> {error, failed_conversion}
   	catch
   	error:_ -> {error, failed_conversion}
   	end;
   	_ ->
   	{error, failed_conversion}
   	end;
   	debug_info(_, _, _, _) ->
   	{error, unknown_format}.

3. which calls :elixir_erl.functions_form/8:
   

   elixir/lib/elixir/src/elixir_erl.erl

   Lines 156 to 178 in 66c5908

   	dynamic_form(#{module := Module, relative_file := RelativeFile,
   	attributes := Attributes, definitions := Definitions, unreachable := Unreachable,
   	deprecated := Deprecated, compile_opts := Opts} = Map) ->
   	%% TODO: Match on anno directly in Elixir v1.22+
   	Line = case Map of
   	#{anno := AnnoValue} -> erl_anno:line(AnnoValue);
   	#{line := LineValue} -> LineValue
   	end,
   	{Def, Defmacro, Macros, Exports, Functions} =
   	split_definition(Definitions, Unreachable, Line, [], [], [], [], {[], []}),
   	FilteredOpts = lists:filter(fun({no_warn_undefined, _}) -> false; (_) -> true end, Opts),
   	Location = {elixir_utils:characters_to_list(RelativeFile), Line},
   	Prefix = [{attribute, Line, file, Location},
   	{attribute, Line, module, Module},
   	{attribute, Line, compile, [no_auto_import | FilteredOpts]}],
   	Struct = maps:get(struct, Map, nil),
   	Forms0 = functions_form(Line, Module, Def, Defmacro, Exports, Functions, Deprecated, Struct),
   	Forms1 = attributes_form(Line, Attributes, Forms0),
   	{Prefix, Forms1, Def, Defmacro, Macros}.

4. (rest is in the stacktrace above)

If I'm correct the changes in type system caused a bug in struct definition. Since we want to keep a backwards compatibility we have to add bitstring support for the :elixir_erl.elixir_to_erl/2 function.

Related forum topic:
https://elixirforum.com/t/can-not-set-bitstring-value-in-defstruct-in-elixir-1-18-is-this-a-bug/70121?u=eiji