From 69990a5d1d3cd00ed0422a87b49841c27e16ff15 Mon Sep 17 00:00:00 2001
From: Jean Klingler <sabiwara@gmail.com>
Date: Fri, 21 Feb 2025 23:08:36 +0900
Subject: [PATCH] Fix regression when diffing nested improper lists (#14292)

Close https://github.com/elixir-lang/elixir/issues/14291
---
 lib/ex_unit/lib/ex_unit/diff.ex             |  1 +
 lib/ex_unit/test/ex_unit/diff_test.exs      |  2 ++
 lib/ex_unit/test/ex_unit/formatter_test.exs | 11 +++++++++++
 3 files changed, 14 insertions(+)

diff --git a/lib/ex_unit/lib/ex_unit/diff.ex b/lib/ex_unit/lib/ex_unit/diff.ex
index 170e988c35a..93fe0113727 100644
--- a/lib/ex_unit/lib/ex_unit/diff.ex
+++ b/lib/ex_unit/lib/ex_unit/diff.ex
@@ -1156,6 +1156,7 @@ defmodule ExUnit.Diff do
     else
       other
       |> Map.to_list()
+      |> Enum.map(&escape_pair/1)
       |> build_map_or_struct(struct)
     end
   end
diff --git a/lib/ex_unit/test/ex_unit/diff_test.exs b/lib/ex_unit/test/ex_unit/diff_test.exs
index a2317cf73e2..87474a2324c 100644
--- a/lib/ex_unit/test/ex_unit/diff_test.exs
+++ b/lib/ex_unit/test/ex_unit/diff_test.exs
@@ -330,6 +330,8 @@ defmodule ExUnit.DiffTest do
       "[[[[], \"Hello-,- \"] | \"world\"] | \"!\"]",
       "[[[[], \"Hello \"] | \"world\"] | \"!\"]"
     )
+
+    refute_diff(:foo = %{bar: [:a | :b]}, "", "")
   end
 
   test "proper lists" do
diff --git a/lib/ex_unit/test/ex_unit/formatter_test.exs b/lib/ex_unit/test/ex_unit/formatter_test.exs
index a1e5506c1f6..6d115da9bc0 100644
--- a/lib/ex_unit/test/ex_unit/formatter_test.exs
+++ b/lib/ex_unit/test/ex_unit/formatter_test.exs
@@ -503,6 +503,17 @@ defmodule ExUnit.FormatterTest do
            """
   end
 
+  test "formats assertions with nested improper list diffing" do
+    failure = [{:error, catch_assertion(assert :foo = %{bar: [1 | 2]}), []}]
+
+    assert format_test_all_failure(test_module(), failure, 1, :infinity, &diff_formatter/2) =~ """
+           match (=) failed
+                code:  assert :foo = %{bar: [1 | 2]}
+                left:  :foo
+                right: %{bar: [1 | 2]}
+           """
+  end
+
   defmodule BadInspect do
     defstruct key: 0