Wrong undefined function warning

[dominicletz]

Elixir and Erlang/OTP versions

elixir 1.18.0-rc.0
erlang 26.2.5.3

Operating system

Linux

Current behavior

Compiling:

defmodule TypeBug do
  def file_monitor_backened?() do
    case :os.type() do
      {:unix, :darwin} -> :fsevents
      {:unix, :linux} -> :inotifywait
      {:win32, :nt} -> :inotifywait_win32
      _ -> nil
    end
    |> case do
      nil -> false
      backend -> backend.find_executable() != false
    end
  end
end

produces this warning:

   warning: nil.find_executable/0 is undefined (module nil is not available or is yet to be defined)
    │
 14 │         backend.find_executable() != false
    │                 ~
    │
    └─ lib/type_bug.ex:11:26: TypeBug.has_file_monitor_backened?/0

Expected behavior

There should be no warning, since the nil case is handled already.

[josevalim]

This is similar to #14043. You should tag the results instead, it will be addressed on v1.19:

defmodule TypeBug do
  def file_monitor_backened?() do
    case :os.type() do
      {:unix, :darwin} -> {:ok, :fsevents}
      {:unix, :linux} -> {:ok, :inotifywait}
      {:win32, :nt} -> {:ok, :inotifywait_win32}
      _ -> :error
    end
    |> case do
      :error -> false
      {:ok, backend} -> backend.find_executable() != false
    end
  end
end

[harrisi]

I think there's a slight error in the second case match in the corrected code.

[josevalim]

Thank you, addressed!

[josevalim]

Closing this for now (as it was open for guidance).