Basic fix for #384

In escript we can not find our elixir executable, so warn
and default to true (most things should have protocol consolidation
turned on)

lib/benchee/system.ex

@@ -185,11 +185,18 @@ defmodule Benchee.System do
     end
   end
 
-  defp all_protocols_consolidated? do
-    path = :code.lib_dir(:elixir, :ebin)
-
-    [path]
-    |> Protocol.extract_protocols()
-    |> Enum.all?(&Protocol.consolidated?/1)
+  # just made public for easy testing purposes
+  @doc false
+  def all_protocols_consolidated?(lib_dir_fun \\ &:code.lib_dir/2) do
+    case lib_dir_fun.(:elixir, :ebin) do
+      # do we get a good old erlang charlist?
+      path when is_list(path) ->
+        [path]
+        |> Protocol.extract_protocols()
+        |> Enum.all?(&Protocol.consolidated?/1)
+      _error ->
+        IO.puts("Could not check if protocols are consolidated. Running as escript? Defaulting to they are consolidated.")
+        true
+    end
   end
 end

test/benchee/system_test.exs

@@ -99,4 +99,24 @@ defmodule Benchee.SystemTest do
       assert system_cmd("cat", "dev/null", system_func) == "N/A"
     end)
   end
+
+  describe "all_protocols_consolidated?/1" do
+    test "normally it just works and is true for Bechee and does not log a warning" do
+      warning = capture_io(fn ->
+        assert true == all_protocols_consolidated?()
+      end)
+
+      assert warning == ""
+    end
+
+    test "when it borks out it warns and defaults to true, see #384" do
+      fake_lib_dir = fn _, _ -> {:error, :bad_name} end
+
+      warning = capture_io(fn ->
+        assert true == all_protocols_consolidated?(fake_lib_dir)
+      end)
+
+      assert warning =~ ~r/not.*check.*protocol.*consolidat/i
+    end
+  end
 end