Compilation Error with invalid bit pattern

[dmorn]

Elixir and Erlang/OTP versions

Erlang/OTP 27 [erts-15.2.1] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]

Elixir 1.18.3 (compiled with Erlang/OTP 27)

Operating system

MacOS 15.3.2 (24D81)

Current behavior

Compiler's output

Compiling 5 files (.ex)
    warning: variable "rest" is unused (if the variable is not meant to be used, prefix it with an underscore)
    │
 43 │          @start_code_4b <> <<0::1, prio::2, type::5, rest::bitstring>>,
    │                                                      ~~~~
    │
    └─ lib/vt/sub_proxy/nalu/parser.ex:43:54: VT.SubProxy.NALU.Parser.split_nalu/3


== Compilation error in file lib/vt/sub_proxy/nalu/parser.ex ==
** (RuntimeError) found error while checking types for VT.SubProxy.NALU.Parser.handle_buffer/4:

** (RuntimeError) found error while checking types for VT.SubProxy.NALU.Parser.parse_and_forward/1:

** (RuntimeError) found error while checking types for VT.SubProxy.NALU.Parser.split_nalu/3:

** (MatchError) no match of right hand side value: nil
The exception happened while checking this code:

defp split_nalu(
       <<"\0\0\0\x01"::binary,
         <<0::integer-size(1), prio::integer-size(2), type::integer-size(5), rest::bitstring>>::binary>>,
       _next,
       _acc
     ) do
  IO.inspect(type, label: "TYPE")
  IO.inspect(prio, label: "PRIO")
  :erlang.error(RuntimeError.exception([]), :none, error_info: %{module: Exception})
end

Please report this bug at: https://github.com/elixir-lang/elixir/issues

The exception happened while checking this code:

defp parse_and_forward(state = %{buffer: payload, next: next}) do
  _ = split_nalu(payload, next, [])
  {[], state}
end

Please report this bug at: https://github.com/elixir-lang/elixir/issues

The exception happened while checking this code:

def handle_buffer(:input, buffer, _ctx, state) do
  parse_and_forward(
    Kernel.update_in(state, [:buffer], fn x -> <<x::binary, buffer.payload::binary>> end)
  )
end

Please report this bug at: https://github.com/elixir-lang/elixir/issues

    (elixir 1.18.3) lib/module/types/pattern.ex:495: Module.Types.Pattern.of_pattern/4
    (elixir 1.18.3) lib/module/types/pattern.ex:57: Module.Types.Pattern.of_pattern_args_index/5
    (elixir 1.18.3) lib/module/types/pattern.ex:46: Module.Types.Pattern.of_pattern_args/5
    (elixir 1.18.3) lib/module/types/pattern.ex:35: Module.Types.Pattern.of_head/7
    (elixir 1.18.3) lib/module/types.ex:242: anonymous fn/6 in Module.Types.local_handler/7
    (elixir 1.18.3) lib/enum.ex:2546: Enum."-reduce/3-lists^foldl/2-0-"/3
    (elixir 1.18.3) lib/module/types.ex:236: Module.Types.local_handler/7
    (elixir 1.18.3) lib/module/types.ex:218: Module.Types.local_handler/5

For reference, the compilation error appears from 1.18.0-opt27. On 1.17.3-otp27 we get:

Compiling 5 files (.ex)
    warning: variable "rest" is unused (if the variable is not meant to be used, prefix it with an underscore)
    │
 43 │          @start_code_4b <> <<0::1, prio::2, type::5, rest::bitstring>>,
    │                                                      ~~~~
    │
    └─ lib/vt/sub_proxy/nalu/parser.ex:43:54: VT.SubProxy.NALU.Parser.split_nalu/3


== Compilation error in file lib/vt/sub_proxy/nalu/parser.ex ==
** (CompileError) Elixir.VT.SubProxy.NALU.Parser: expecting pattern in split_nalu/3
    (stdlib 6.2) lists.erl:2310: :lists.foreach_1/2

Expected behavior

It is a compiler error, I expect it to either report that the code cannot be compiled and why. I know the code is invalid, the bit-pattern should be written as <<0, 0, 0, 1, 0::1, prio::2, type::5, rest::bitstring>> instead of what I'm doing there, but anyway I think it's worth reporting.

[josevalim]

Fixed in main and v1.18. Thank you.