Running dialiyzer with rustler 0.30.0 results in "The pattern can never match the type""

[neosimsim]

Running dialiyzer with rustler 0.30.0 fails with "The pattern can never match the type"

$ mix deps.get && mix dialyzer
Resolving Hex dependencies...
Resolution completed in 0.042s
Unchanged:
  dialyxir 1.4.1
  erlex 0.2.6
  jason 1.4.1
  rustler 0.30.0
  toml 0.7.0
All dependencies are up to date
Compiling 1 file (.ex)
Finding suitable PLTs
Checking PLT...
[:compiler, :eex, :elixir, :kernel, :logger, :rustler, :stdlib]
PLT is up to date!
No :ignore_warnings opt specified in mix.exs and default does not exist.

Starting Dialyzer
[
  check_plt: false,
  init_plt: '/home/neosimsim/tmp/rustler_and_dialyzer/rustler_and_dialyzer/_build/dev/dialyxir_erlang-25.3.2.2_elixir-1.14.5_deps-dev.plt',
  files: ['/home/neosimsim/tmp/rustler_and_dialyzer/rustler_and_dialyzer/_build/dev/lib/foo/ebin/Elixir.Foo.Application.beam',
   '/home/neosimsim/tmp/rustler_and_dialyzer/rustler_and_dialyzer/_build/dev/lib/foo/ebin/Elixir.Foo.beam'],
  warnings: [:unknown]
]
Total errors: 1, Skipped: 0, Unnecessary Skips: 0
done in 0m0.91s
lib/foo.ex:1:pattern_match
The pattern can never match the type.

Pattern:
{_, {_, _}}

Type:
{0, nil}

________________________________________________________________________________
done (warnings were emitted)
Halting VM with exit status 2

The same works with rustler 0.29.0.

Here is the an example module file that fails.

defmodule Foo do
  use Rustler,
    otp_app: :foo,
    crate: "bar",
    mode: :release,
    target_dir:
      Mix.Project.build_path()
      |> Path.join("rustler_crates")
      |> Path.expand()
end

[neosimsim]

I looked at the diff between 0.29.0 and 0.30.0 and couldn't find anything strange. I wonder if this might be a bug in dialyzer?

[evnu]

I think this is called by this change. Dialyzer is technically right, the case will always access only one of the clauses, as this is hardcoded into the module. Note that this happens exactly once when loading the library, so this should not really be an issue. I see two options:

1. make dialyzer ignore the problem
2. expand the case statement during compile time

[evnu]

@neosimsim can you give #570 a try?

[neosimsim]

@neosimsim can you give #570 a try?

That works. Thanks.