Remove stacktrace warning

lib/display/failure.ex

@@ -49,8 +49,7 @@ defmodule Display.Failure do
   end
 
   defp format_error(error) do
-    trace = System.stacktrace() |> Enum.take(2)
-    Paint.red(Exception.format(:error, error, trace))
+    Paint.red(Exception.format(:error, error, []))
   end
 
   def show_compile_error(error) do

lib/execute.ex

@@ -31,26 +31,20 @@ defmodule Execute do
   end
 
   defp exec(module, name, args, parent) do
-    result = apply(module, name, args)
-    send(parent, expand(result, module))
+    case apply(module, name, args) do
+      :ok  -> send(parent, :ok)
+      err -> send(parent, expand(err))
+    end
     Process.exit(self(), :kill)
   end
 
-  defp expand(:ok, _), do: :ok
-
-  defp expand({:error, stacktrace, exception}, module) do
-    {file, line} =
-      stacktrace
-      |> Enum.drop_while(&(!in_koan?(&1, module)))
-      |> List.first()
-      |> extract_file_and_line
-
-    %{error: exception, file: file, line: line}
+  defp expand({:error, error, {:location, file_path, line}}) do
+   %{error: error, file: make_relative(file_path), line: line}
   end
 
-  defp in_koan?({module, _, _, _}, koan), do: module == koan
-
-  defp extract_file_and_line({_, _, _, [file: file, line: line]}) do
-    {file, line}
+  defp make_relative(path) do
+    path
+    |> Path.relative_to_cwd()
+    |> to_string()
   end
 end

lib/koans.ex

@@ -22,7 +22,7 @@ defmodule Koans do
           unquote(compiled_body)
           :ok
         rescue
-          e -> {:error, __STACKTRACE__, e}
+          e -> {:error, e, {:location, __ENV__.file, __ENV__.line}}
         end
       end
     end
@@ -39,7 +39,7 @@ defmodule Koans do
           unquote(single_var)
           :ok
         rescue
-          e -> {:error, __STACKTRACE__, e}
+          e -> {:error, e, {:location, __ENV__.file, __ENV__.line}}
         end
       end
     end
@@ -57,7 +57,7 @@ defmodule Koans do
           unquote(multi_var)
           :ok
         rescue
-          e -> {:error, __STACKTRACE__, e}
+          e -> {:error, e, {:location, __ENV__.file, __ENV__.line}}
         end
       end
     end
@@ -98,8 +98,8 @@ defmodule Koans do
     end
   end
 
-  defp koans(env) do
-    env.module
+  defp koans(%{module: module}) do
+    module
     |> Module.get_attribute(:koans)
     |> Enum.reverse()
   end

test/display/failure_test.exs

@@ -39,13 +39,31 @@ defmodule FailureTests do
 
   test "only offending lines are displayed for errors" do
     [koan] = SingleArity.all_koans()
-    error = apply(SingleArity, koan, []) |> Tuple.to_list |> List.last |> error
+    error = apply(SingleArity, koan, []) |> error()
 
     assert Failure.format_failure(error) == """
-           Assertion failed in some_file.ex:42\nmatch?(:foo, ___)
+           Assertion failed in some_file.ex:42
+           match?(:foo, ___)
+           """
+  end
+
+  test "formats errors such as arity mismatches as such" do
+    e = error({:error, %FunctionClauseError{args: nil, arity: 1, clauses: nil, function: :chardata_to_string, kind: nil, module: IO}, nil})
+
+    assert Failure.format_failure(e) == """
+           Error in some_file.ex:42
+           ** (FunctionClauseError) no function clause matching in IO.chardata_to_string/1
            """
   end
 
+  defp error({:error, error, _}) do
+    %{
+      error: error,
+      file: "some_file.ex",
+      line: 42
+    }
+  end
+
   defp error(error) do
     %{
       error: error,

test/executor_test.exs

@@ -7,7 +7,7 @@ defmodule ExecuteTest do
 
   test "stops at the first failing koan" do
     {:failed, %{file: file, line: line}, SampleKoan, _name} = Execute.run_module(SampleKoan)
-    assert file == 'test/support/sample_koan.ex'
+    assert file == "test/support/sample_koan.ex"
     assert line == 8
   end