README.md

StartSpan

Demonstrates a problem with :opencensus typing.

To reproduce: mix dialyzer.

To reproduce from the gist:

cd `mktemp -d`
git clone https://gist.github.com/garthk/fb0d89181372136f150d7adc539356c3
cd fb0d89181372136f150d7adc539356c3
docker build -t start_span .
docker run --rm -ti start_span

Output after rebuilding PLTs:

lib/start_span.ex:13:no_return
Function fail/0 has no local return.
________________________________________________________________________________
lib/start_span.ex:14:call
The function call will not succeed.

StartSpan.start_span(<<102, 97, 105, 108>>, :undefined, [{:kind, :SERVER}])

will never return since it differs in arguments with
positions 2nd from the success typing arguments:

(
  binary(),
  {:span_ctx, :undefined | non_neg_integer(), :undefined | non_neg_integer(),
   :undefined | integer(), :undefined | {:tracestate, [any()]}},
  Keyword.t()
)

Dockerfile

# docker build -t start_span .
# docker run --rm -ti start_span

FROM elixir:1.10.3-alpine
RUN cd /usr/local/src && mix new start_span
WORKDIR /usr/local/src/start_span
COPY mix.exs README.md ./
COPY start_span.ex lib/
RUN mix local.hex --force && mix local.rebar --force && mix deps.get
CMD ["mix", "dialyzer"]

mix.exs

defmodule StartSpan.MixProject do
  use Mix.Project

  def project do
    [
      app: :start_span,
      version: "0.1.0",
      elixir: "~> 1.10",
      start_permanent: Mix.env() == :prod,
      deps: [
        {:dialyxir, "~> 1.0.0", only: [:dev], runtime: false},
        {:opencensus, "~> 0.9.3", override: true}
      ],
      dialyzer: [plt_add_deps: [:app_tree]]
    ]
  end

  def application, do: [extra_applications: [:logger]]
end

start_span.ex

# lib/start_span.ex

defmodule StartSpan do
  @moduledoc """
  Demonstrates a problem with `:opencensus` typing.

  To reproduce: `mix dialyzer`.
  """

  @doc """
  Call `start_span/3` with an `:undefined` parent.
  """
  def fail do
    start_span("fail", :undefined, kind: :SERVER)
  end

  @doc """
  Start a new span with `:oc_trace.start_span/3`.
  """
  @spec start_span(
          name :: binary(),
          parent_span_ctx :: :undefined | :opencensus.span_ctx(),
          opts :: [
            {:attributes, :opencensus.attributes()}
            | {:kind, :SERVER | :CLIENT | :SPAN_KIND_UNSPECIFIED}
          ]
        ) :: :opencensus.span_ctx()
  def start_span(name, parent_span_ctx, opts \\ []) do
    {attributeses, opts} = Keyword.pop_values(opts, :attributes)
    {kind, opts} = Keyword.pop(opts, :kind, :SPAN_KIND_UNSPECIFIED)
    for {k, _} <- opts, do: raise(ArgumentError, "no such option: #{k}")

    :oc_trace.start_span(
      name,
      parent_span_ctx,
      %{
        kind: kind,
        attributes: attributeses |> Enum.flat_map(& &1) |> Enum.into(%{})
      }
    )
  end
end