From 1447859bd1518d7c626ed72e87184f5ca326557b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fabian=20N=2EC=2E=20van=20=C2=B4t=20Hooft?=
 <fnchooft@gmail.com>
Date: Wed, 19 Jul 2023 14:00:47 -0300
Subject: [PATCH] Add erlang-module support

The code is deemed a module definition if the first line
start with "-module(".

In this case the entire code-block is interpreted as
erlang-module and if there are no errors the module is compiled
and loaded.

Basic error handling has been added
Basic test has been added ( TODO add failure cases )
---
 lib/livebook/runtime/evaluator.ex        | 92 ++++++++++++++++++++++++
 test/livebook/runtime/evaluator_test.exs | 13 ++++
 2 files changed, 105 insertions(+)

diff --git a/lib/livebook/runtime/evaluator.ex b/lib/livebook/runtime/evaluator.ex
index 7043eb5b7021..2baa9e0d96a6 100644
--- a/lib/livebook/runtime/evaluator.ex
+++ b/lib/livebook/runtime/evaluator.ex
@@ -674,7 +674,99 @@ defmodule Livebook.Runtime.Evaluator do
     {result, code_markers}
   end
 
+  # main entry point to decide between erlang-statements vs module
   defp eval(:erlang, code, binding, env) do
+    is_module = String.starts_with?(code, "-module(")
+
+    case is_module do
+      true -> eval_module(:erlang, code, binding, env)
+      false -> eval_statements(:erlang, code, binding, env)
+    end
+  end
+
+  # Simple Erlang Module - helper functions
+  # ------------------------------------------------------------------------
+  # In order to handle the expression in their forms - separate per {:dot,_}
+  defp not_dot({:dot, _}) do
+    false
+  end
+
+  defp not_dot(_) do
+    true
+  end
+
+  # A list of scanned token - must be seperated per dot, in order to feed them
+  # into the :erl_parse.parse_form function.
+  defp tokens_to_forms(tokens) do
+    {:ok, tokens_to_forms(tokens, [])}
+  end
+
+  defp tokens_to_forms([], acc) do
+    :lists.reverse(acc)
+  end
+
+  defp tokens_to_forms(tokens, acc) do
+    form = :lists.takewhile(&not_dot/1, tokens)
+    [dot | rest] = :lists.dropwhile(&not_dot/1, tokens)
+    tokens_to_forms(rest, [{form ++ [dot]}] ++ acc)
+  end
+
+  defp parse_forms(form_statements) do
+    try do
+      res =
+        Enum.map(
+          form_statements,
+          fn {form_statement} ->
+            case :erl_parse.parse_form(form_statement) do
+              {:ok, form} -> form
+              err -> throw({:parse_fail, err})
+            end
+          end
+        )
+
+      {:ok, res}
+    catch
+      {:parse_fail, err} -> err
+    end
+  end
+
+  # Create module - tokens from string
+  # Based on: https://stackoverflow.com/questions/2160660/how-to-compile-erlang-code-loaded-into-a-string
+  # The function will first assume that code starting with -module( is a erlang module definition
+
+  # Step 1: Scan the code
+  # Step 2: Convert to forms
+  # Step 3: Extract module name
+  # Step 4: Compile and load
+  defp eval_module(:erlang, code, binding, env) do
+    try do
+      with {:ok, tokens, _} <- :erl_scan.string(String.to_charlist(code), {1, 1}, [:text]),
+           {:ok, form_statements} <- tokens_to_forms(tokens),
+           {:ok, forms} <- parse_forms(form_statements) do
+        # First statement - form = module definition
+        {:attribute, _, :module, module_name} = hd(forms)
+
+        # Compile the forms from the code-block
+        {:ok, _, binary_module} = :compile.forms(forms)
+        :code.load_binary(module_name, ~c"nofile", binary_module)
+        {{:ok, ~c"erlang module successfully compiled", binding, env}, []}
+      else
+        # Tokenizer error - https://www.erlang.org/doc/man/erl_scan.html#string-3
+        {:error, {location, module, description}, _end_loc} ->
+          process_erlang_error(env, code, location, module, description)
+
+        # Parser error - https://www.erlang.org/doc/man/erl_parse.html#parse_form-1
+        {:error, {location, module, description}} ->
+          process_erlang_error(env, code, location, module, description)
+      end
+    catch
+      kind, error ->
+        stacktrace = prune_stacktrace(:erl_eval, __STACKTRACE__)
+        {{:error, kind, error, stacktrace}, []}
+    end
+  end
+
+  defp eval_statements(:erlang, code, binding, env) do
     try do
       erl_binding =
         Enum.reduce(binding, %{}, fn {name, value}, erl_binding ->
diff --git a/test/livebook/runtime/evaluator_test.exs b/test/livebook/runtime/evaluator_test.exs
index 3d0ac4ec04b4..767ce636b326 100644
--- a/test/livebook/runtime/evaluator_test.exs
+++ b/test/livebook/runtime/evaluator_test.exs
@@ -1227,6 +1227,19 @@ defmodule Livebook.Runtime.EvaluatorTest do
       assert_receive {:runtime_evaluation_response, :code_1, {:text, "6"}, metadata()}
     end
 
+    test "evaluate erlang-module code", %{evaluator: evaluator} do
+      Evaluator.evaluate_code(
+        evaluator,
+        :erlang,
+        "-module(tryme). -export([go/0]). go() ->{ok,went}.",
+        :code_4,
+        []
+      )
+
+      assert_receive {:runtime_evaluation_response, :code_4,
+                      {:text, "\"erlang module successfully compiled\""}, metadata()}
+    end
+
     test "mixed erlang/elixir bindings", %{evaluator: evaluator} do
       Evaluator.evaluate_code(evaluator, :elixir, "x = 1", :code_1, [])
       Evaluator.evaluate_code(evaluator, :erlang, "Y = X.", :code_2, [:code_1])