handle unmatched return dialyzer errors

[jjcarstens]

Dialyzer fails with unmatched_return errors in my apps using slipstream. I happen to use that everywhere, so this is prob more of a convenience for me, but dialyzer passes after this.

Dialyzer log

``` jonjon@bender:~/repos/nerves_hub_link$ mix dialyzer Compiling 11 files (.ex) Generated nerves_hub_link app Finding suitable PLTs Checking PLT... [:asn1, :atecc508a, :castore, :certifi, :compiler, :cowlib, :crypto, :elixir, :extty, :fwup, :gun, :hackney, :idna, :iex, :inets, :jason, :kernel, :logger, :metrics, :mimerl, :mint, :nerves_hub_link_common, :nerves_key, :nerves_key_pkcs11, :nerves_runtime, :nimble_options, :parse_trans, :public_key, :slipstream, :ssl, :ssl_verify_fun, :stdlib, :syntax_tools, :system_registry, :telemetry, :uboot_env, :unicode_util_compat, :x509] Looking up modules in dialyxir_erlang-23.2.5_elixir-1.11.3_deps-dev.plt Finding applications for dialyxir_erlang-23.2.5_elixir-1.11.3_deps-dev.plt Finding modules for dialyxir_erlang-23.2.5_elixir-1.11.3_deps-dev.plt Checking 932 modules in dialyxir_erlang-23.2.5_elixir-1.11.3_deps-dev.plt Adding 42 modules to dialyxir_erlang-23.2.5_elixir-1.11.3_deps-dev.plt done in 0m4.44s No :ignore_warnings opt specified in mix.exs and default does not exist. Starting Dialyzer [ check_plt: false, init_plt: '/home/jonjon/repos/nerves_hub_link/_build/dev/dialyxir_erlang-23.2.5_elixir-1.11.3_deps-dev.plt', files: ['/home/jonjon/repos/nerves_hub_link/_build/dev/lib/nerves_hub_link/ebin/Elixir.NervesHubLink.Application.beam', '/home/jonjon/repos/nerves_hub_link/_build/dev/lib/nerves_hub_link/ebin/Elixir.NervesHubLink.Certificate.beam', '/home/jonjon/repos/nerves_hub_link/_build/dev/lib/nerves_hub_link/ebin/Elixir.NervesHubLink.Client.Default.beam', '/home/jonjon/repos/nerves_hub_link/_build/dev/lib/nerves_hub_link/ebin/Elixir.NervesHubLink.Client.beam', '/home/jonjon/repos/nerves_hub_link/_build/dev/lib/nerves_hub_link/ebin/Elixir.NervesHubLink.Configurator.Config.beam', ...], warnings: [:race_conditions, :error_handling, :underspecs, :unmatched_returns, ...] ] Total errors: 2, Skipped: 0, Unnecessary Skips: 0 done in 0m1.57s lib/slipstream.ex:1494:unmatched_return The expression produces a value of type: :ignore | :ok | {:error, _} | {:ok, _} | {:ok, pid(), _} | %Slipstream.Socket{ :assigns => map(), :channel_config => nil | %Slipstream.Configuration{ :gun_open_options => _, :headers => [{_, _}], :heartbeat_interval_msec => non_neg_integer(), :json_parser => atom(), :reconnect_after_msec => [non_neg_integer()], :rejoin_after_msec => [non_neg_integer()], :test_mode? => _, :uri => %URI{ :authority => _, :fragment => _, :host => _, :path => _, :port => _, :query => _, :scheme => _, :userinfo => _ } }, :channel_pid => nil | pid(), :joins => %{ binary() => %Slipstream.Socket.Join{ :params => _, :rejoin_counter => _, :status => _, :topic => _ } }, :metadata => %{atom() => binary() | %{binary() => binary()}}, :reconnect_counter => non_neg_integer(), :response_headers => _, :socket_pid => pid() } but this value is unmatched. ________________________________________________________________________________ lib/slipstream.ex:1507:unmatched_return The expression produces a value of type: :ignore | :ok | {:error, _} | {:ok, _} | {:ok, pid(), _} | %Slipstream.Socket{ :assigns => map(), :channel_config => nil | %Slipstream.Configuration{ :gun_open_options => _, :headers => [{_, _}], :heartbeat_interval_msec => non_neg_integer(), :json_parser => atom(), :reconnect_after_msec => [non_neg_integer()], :rejoin_after_msec => [non_neg_integer()], :test_mode? => _, :uri => %URI{ :authority => _, :fragment => _, :host => _, :path => _, :port => _, :query => _, :scheme => _, :userinfo => _ } }, :channel_pid => nil | pid(), :joins => %{ binary() => %Slipstream.Socket.Join{ :params => _, :rejoin_counter => _, :status => _, :topic => _ } }, :metadata => %{atom() => binary() | %{binary() => binary()}}, :reconnect_counter => non_neg_integer(), :response_headers => _, :socket_pid => pid() } but this value is unmatched. ________________________________________________________________________________ done (warnings were emitted) Halting VM with exit status 2 ```