From 4902bee69fdf8cfbac263e1e8fe522efbe177f53 Mon Sep 17 00:00:00 2001
From: Lukasz Samson <lukaszsamson@gmail.com>
Date: Sun, 13 Sep 2026 14:05:38 +0200
Subject: [PATCH] Fix typechecker crash on non elixir struct module in defimpl

Ensure the module exports __info__/1
Mimic check from struct_info/6
---
 lib/elixir/lib/module/types/of.ex             |  6 ++++-
 .../elixir/module/types/integration_test.exs  | 25 +++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/lib/elixir/lib/module/types/of.ex b/lib/elixir/lib/module/types/of.ex
index ed1de24a80..44599256cf 100644
--- a/lib/elixir/lib/module/types/of.ex
+++ b/lib/elixir/lib/module/types/of.ex
@@ -291,7 +291,11 @@ defmodule Module.Types.Of do
     # so we need to deal with such cases accordingly.
     # TODO: Assume implementation is available on Elixir v2.0.
     # A warning is emitted since v1.19+.
-    if info = mode == :closed && Code.ensure_loaded?(struct) && struct.__info__(:struct) do
+    info =
+      mode == :closed and Code.ensure_loaded?(struct) and
+        function_exported?(struct, :__info__, 1) and struct.__info__(:struct)
+
+    if info do
       struct_type(struct, info)
     else
       open_map(__struct__: {atom([struct]), false})
diff --git a/lib/elixir/test/elixir/module/types/integration_test.exs b/lib/elixir/test/elixir/module/types/integration_test.exs
index a9cca324da..8da5403acc 100644
--- a/lib/elixir/test/elixir/module/types/integration_test.exs
+++ b/lib/elixir/test/elixir/module/types/integration_test.exs
@@ -163,6 +163,31 @@ defmodule Module.Types.IntegrationTest do
                dynamic(open_map(__struct__: {atom([Unknown]), false}))
     end
 
+    test "writes exports for implementations of Erlang modules" do
+      files = %{
+        "pe.ex" => """
+        defprotocol Erl do
+          def erl(data)
+        end
+
+        defimpl Erl, for: :gen_server do
+          def erl(data), do: data
+        end
+        """
+      }
+
+      modules = compile_modules(files)
+
+      {_, %{sig: {:infer, nil, [{[domain], _return}]}}} =
+        List.keyfind(
+          read_chunk(modules[Module.concat(Erl, :gen_server)]).exports,
+          {:erl, 1},
+          0
+        )
+
+      assert domain == open_map(__struct__: {atom([:gen_server]), false})
+    end
+
     test "ignores additional callbacks on implementations" do
       files = %{
         "p.ex" => """