From 2c4e1f55c68fcb0f227b86a6d423a5947fe52693 Mon Sep 17 00:00:00 2001
From: Felipe Sere <felipesere@gmail.com>
Date: Sat, 12 Oct 2019 12:03:27 +0200
Subject: [PATCH 1/2] Remove stacktrace warning

---
 lib/display/failure.ex | 2 +-
 lib/execute.ex         | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/display/failure.ex b/lib/display/failure.ex
index ced1046c..7fe9311d 100644
--- a/lib/display/failure.ex
+++ b/lib/display/failure.ex
@@ -49,7 +49,7 @@ defmodule Display.Failure do
   end
 
   defp format_error(error) do
-    trace = System.stacktrace() |> Enum.take(2)
+    trace = :erlang.get_stacktrace() |> Enum.take(2)
     Paint.red(Exception.format(:error, error, trace))
   end
 
diff --git a/lib/execute.ex b/lib/execute.ex
index 485e0c59..2f677470 100644
--- a/lib/execute.ex
+++ b/lib/execute.ex
@@ -40,7 +40,7 @@ defmodule Execute do
 
   defp expand({:error, stacktrace, exception}, module) do
     {file, line} =
-      stacktrace
+      :erlang.get_stacktrace()
       |> Enum.drop_while(&(!in_koan?(&1, module)))
       |> List.first()
       |> extract_file_and_line

From 804406c298c637a6500078ddfdd5a34a78ebcd59 Mon Sep 17 00:00:00 2001
From: Felipe Sere <felipesere@gmail.com>
Date: Fri, 19 Jun 2020 09:45:17 +0200
Subject: [PATCH 2/2] Extract file/line from koan and make stacktrace obsolete

---
 lib/display/failure.ex        |  3 +--
 lib/execute.ex                | 26 ++++++++++----------------
 lib/koans.ex                  | 10 +++++-----
 test/display/failure_test.exs | 22 ++++++++++++++++++++--
 test/executor_test.exs        |  2 +-
 5 files changed, 37 insertions(+), 26 deletions(-)

diff --git a/lib/display/failure.ex b/lib/display/failure.ex
index 7fe9311d..6ecf8420 100644
--- a/lib/display/failure.ex
+++ b/lib/display/failure.ex
@@ -49,8 +49,7 @@ defmodule Display.Failure do
   end
 
   defp format_error(error) do
-    trace = :erlang.get_stacktrace() |> Enum.take(2)
-    Paint.red(Exception.format(:error, error, trace))
+    Paint.red(Exception.format(:error, error, []))
   end
 
   def show_compile_error(error) do
diff --git a/lib/execute.ex b/lib/execute.ex
index 2f677470..c6ae4922 100644
--- a/lib/execute.ex
+++ b/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} =
-      :erlang.get_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
diff --git a/lib/koans.ex b/lib/koans.ex
index 5ab03b38..5c42d60a 100644
--- a/lib/koans.ex
+++ b/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
diff --git a/test/display/failure_test.exs b/test/display/failure_test.exs
index addce2cd..a527e8bb 100644
--- a/test/display/failure_test.exs
+++ b/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,
diff --git a/test/executor_test.exs b/test/executor_test.exs
index d989123d..fd028ea8 100644
--- a/test/executor_test.exs
+++ b/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