Fatal compiler bug when compiling BitArray pattern to Erlang about gleam

[DanielleMaywood]

It does not break any of my projects, no. I discovered this when experimenting.

[lpil]

Thank you. Does this break any of your projects?

[Acepie]

FYI looks like this is the same issue as #3251 as for actually solving this, my erlang isn't great but as far as I understand from reading docs/looking online, erlang doesn't allow assignments in bitarray matches right? So we can't produce something like the below because the assignment is a syntax error. I assume we can't make this a regular compilation error since that gleam code is valid when compiled to javascript? In Javascript we make this work by doing the assignment inside the block so I guess we could try to do the same thing for this case? lmk if this sounds reasonable or if I'm totally off the mark

-module(test_gleam).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([main/0]).

-spec main() -> bitstring().
main() ->
    _assert_subject = <<65>>,
    <<65 = A, _/binary>> = case _assert_subject of
        <<65, _/binary>> -> _assert_subject;
        _assert_fail ->
            erlang:error(#{gleam_error => let_assert,
                        message => <<"Assertion pattern match failed"/utf8>>,
                        value => _assert_fail,
                        module => <<"test_gleam"/utf8>>,
                        function => <<"main"/utf8>>,
                        line => 2})
    end.

[lpil]

Bit array patterns are so tricky! Lots of weird restrictions I didn't realise.

We could remove the 65 = and push a guard of A =:= 65 perhaps? Seems like it could get a bit complicated.

Shall we close the other issue and track this one here? Seeing as it has more context?