Raise ArgumentError when defdelegating points to the delegating module (#11545)

2 files changed, 17 insertions, 0 deletions

diff --git a/lib/elixir/lib/kernel.ex b/lib/elixir/lib/kernel.ex
index b9af22f89..47c58565a 100644
--- a/lib/elixir/lib/kernel.ex
+++ b/lib/elixir/lib/kernel.ex
@@ -5562,6 +5562,13 @@ defmodule Kernel do
       target =
         Keyword.get(opts, :to) || raise ArgumentError, "expected to: to be given as argument"
 
+      as = Keyword.get(opts, :as)
+
+      if target == __MODULE__ and is_nil(as) do
+        raise ArgumentError,
+              "defdelegate function is calling itself, which will lead to an infinite loop. You should either change the value of the :to option or specify the :as option"
+      end
+
       if is_list(funs) do
         IO.warn(
           "passing a list to Kernel.defdelegate/2 is deprecated, please define each delegate separately",
diff --git a/lib/elixir/test/elixir/kernel_test.exs b/lib/elixir/test/elixir/kernel_test.exs
index 01760982e..9ce715846 100644
--- a/lib/elixir/test/elixir/kernel_test.exs
+++ b/lib/elixir/test/elixir/kernel_test.exs
@@ -896,6 +896,16 @@ defmodule KernelTest do
       end
     end
 
+    test "raises when :to targeting the delegating module is given without the :as option" do
+      assert_raise ArgumentError,
+                   ~r/defdelegate function is calling itself, which will lead to an infinite loop. You should either change the value of the :to option or specify the :as option/,
+                   fn ->
+                     defmodule ImplAttributes do
+                       defdelegate foo(), to: __MODULE__
+                     end
+                   end
+    end
+
     defdelegate my_reverse(list \\ []), to: :lists, as: :reverse
     defdelegate my_get(map \\ %{}, key, default \\ ""), to: Map, as: :get