From 4d0159cfe61fa54e3a61a902df430ad316c13974 Mon Sep 17 00:00:00 2001
From: Jon Rowe <hello@jonrowe.co.uk>
Date: Mon, 4 Feb 2019 18:52:14 +0000
Subject: [PATCH] Prevent default Kernel imports from conflicting with allowed
 functions

---
 lib/double.ex               | 9 ++++++++-
 test/double_test.exs        | 8 ++++++++
 test/support/test_module.ex | 1 +
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/lib/double.ex b/lib/double.ex
index 2b004e0..34165b3 100644
--- a/lib/double.ex
+++ b/lib/double.ex
@@ -187,6 +187,7 @@ defmodule Double do
     code = Enum.reduce(funcs, code, fn({function_name, func}, acc) ->
       {signature, message} = function_parts(function_name, func)
       acc <> """
+        #{unimport_if_needed(function_name, func)}
         def #{function_name}(#{signature}) do
           #{function_body(mod, message, function_name, signature)}
         end
@@ -211,7 +212,7 @@ defmodule Double do
   defp function_body(double_id, message, function_name, signature) do
     """
     test_pid = Double.Registry.whereis_test(\"#{double_id}\")
-    send(test_pid, #{message})
+    Kernel.send(test_pid, #{message})
     pid = Double.Registry.whereis_double(\"#{double_id}\")
     func_list = Double.func_list(pid)
     Double.FuncList.apply(func_list, :#{function_name}, [#{signature}])
@@ -234,6 +235,12 @@ defmodule Double do
     {signature, message}
   end
 
+  defp unimport_if_needed(function_name, func) do
+    if Enum.member?(Kernel.__info__(:functions), {function_name, func_arity = arity(func)}) do
+      "import Kernel, except: [#{function_name}: #{func_arity}]"
+    end
+  end
+
   defp arity(func) do
     :erlang.fun_info(func)[:arity]
   end
diff --git a/test/double_test.exs b/test/double_test.exs
index 1d9c9f5..04e9ffc 100644
--- a/test/double_test.exs
+++ b/test/double_test.exs
@@ -161,6 +161,14 @@ defmodule DoubleTest do
       assert dbl.loaded_applications() == :ok
     end
 
+    test "can override kernel functions" do
+      dbl =
+        double(TestModule)
+        |> allow(:send, fn _, _ -> :ok end)
+
+      assert dbl.send(:a, :b) == :ok
+    end
+
     test "verifies valid behavior doubles" do
       dbl =
         TestBehaviour
diff --git a/test/support/test_module.ex b/test/support/test_module.ex
index 9ffe38f..33c9a3a 100644
--- a/test/support/test_module.ex
+++ b/test/support/test_module.ex
@@ -6,4 +6,5 @@ defmodule TestModule do
   def process(x, y, z), do: {x, y, z}
   def another_function, do: nil
   def another_function(x), do: x
+  def send(a, b), do: {a, b}
 end