From 3d90896472391c05cd5f60c497891f88f4668d3a Mon Sep 17 00:00:00 2001
From: sabiwara <sabiwara@gmail.com>
Date: Fri, 9 Aug 2024 10:17:34 +0900
Subject: [PATCH 1/2] Add List.ends_with?/2

---
 CHANGELOG.md                         |  1 +
 lib/elixir/lib/list.ex               | 38 +++++++++++++++++++++++++++
 lib/elixir/test/elixir/list_test.exs | 39 ++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 235f36f6fdc..3ca40239939 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ This release no longer supports WERL (a graphical user interface for the Erlang
   * [Exception] Add `MissingApplicationsError` exception to denote missing applications
   * [Kernel] Update source code parsing to match [UTS #55](https://www.unicode.org/reports/tr55/) latest recommendations. In particular, mixed script is allowed in identifiers as long as they are separate by underscores (`_`), such as `http_сервер`. Previously allowed highly restrictive identifiers, which mixed Latin and other scripts, such as the japanese word for t-shirt, `Tシャツ`, now require the underscore as well
   * [Kernel] Warn on bidirectional confusability in identifiers
+  * [List] Add `List.ends_with?/2`
   * [Macro] Improve `dbg` handling of `if/2`, `unless/2`, and code blocks
   * [Process] Handle arbitrarily high integer values in `Process.sleep/1`
   * [String] Inspect special whitespace and zero-width characters using their Unicode representation
diff --git a/lib/elixir/lib/list.ex b/lib/elixir/lib/list.ex
index cc396213ef5..4bb6f621164 100644
--- a/lib/elixir/lib/list.ex
+++ b/lib/elixir/lib/list.ex
@@ -908,6 +908,44 @@ defmodule List do
   def starts_with?(list, []) when is_list(list), do: true
   def starts_with?(list, [_ | _]) when is_list(list), do: false
 
+  @doc """
+  Returns `true` if `list` ends with the given `suffix` list, otherwise returns `false`.
+
+  If `suffix` is an empty list, it returns `true`.
+
+  ### Examples
+
+      iex> List.ends_with?([1, 2, 3], [2, 3])
+      true
+
+      iex> List.ends_with?([1, 2], [1, 2, 3])
+      false
+
+      iex> List.ends_with?([:alpha], [])
+      true
+
+      iex> List.ends_with?([], [:alpha])
+      false
+
+  """
+  @doc since: "1.18.0"
+  @spec ends_with?(nonempty_list, nonempty_list) :: boolean
+  @spec ends_with?(list, []) :: true
+  @spec ends_with?([], nonempty_list) :: false
+  def ends_with?(list, suffix) do
+    case ends_with_offset(list, suffix) do
+      nil -> false
+      n -> :lists.nthtail(n, list) === suffix
+    end
+  end
+
+  defp ends_with_offset([], [_ | _]), do: nil
+  defp ends_with_offset(rest, []), do: length(rest)
+
+  defp ends_with_offset([_ | tail], [_ | suffix_tail]) do
+    ends_with_offset(tail, suffix_tail)
+  end
+
   @doc """
   Converts a charlist to an atom.
 
diff --git a/lib/elixir/test/elixir/list_test.exs b/lib/elixir/test/elixir/list_test.exs
index 368e0d6b9ea..20b237c98ce 100644
--- a/lib/elixir/test/elixir/list_test.exs
+++ b/lib/elixir/test/elixir/list_test.exs
@@ -285,6 +285,45 @@ defmodule ListTest do
     end
   end
 
+  describe "ends_with?/2" do
+    test "list and prefix are equal" do
+      assert List.ends_with?([], [])
+      assert List.ends_with?([1], [1])
+      assert List.ends_with?([1, 2, 3], [1, 2, 3])
+    end
+
+    test "proper lists" do
+      refute List.ends_with?([2], [1, 2])
+      assert List.ends_with?([1, 2, 3], [2, 3])
+      refute List.ends_with?([2, 3, 4], [1, 2, 3, 4])
+    end
+
+    test "list is empty" do
+      refute List.ends_with?([], [1])
+      refute List.ends_with?([], [1, 2])
+    end
+
+    test "prefix is empty" do
+      assert List.ends_with?([1], [])
+      assert List.ends_with?([1, 2], [])
+      assert List.ends_with?([1, 2, 3], [])
+    end
+
+    test "only accepts proper lists" do
+      message = "no function clause matching in List.ends_with_offset/2"
+
+      assert_raise FunctionClauseError, message, fn ->
+        List.ends_with?([1 | 2], [1 | 2])
+      end
+
+      message = "no function clause matching in List.ends_with_offset/2"
+
+      assert_raise FunctionClauseError, message, fn ->
+        List.ends_with?([1, 2], 1)
+      end
+    end
+  end
+
   test "to_string/1" do
     assert List.to_string([?æ, ?ß]) == "æß"
     assert List.to_string([?a, ?b, ?c]) == "abc"

From 906a69a9e4dd60edf88cc2165586d7fdbf046ae3 Mon Sep 17 00:00:00 2001
From: sabiwara <sabiwara@gmail.com>
Date: Fri, 9 Aug 2024 17:02:07 +0900
Subject: [PATCH 2/2] Delegate to :lists.suffix/2

---
 lib/elixir/lib/list.ex               | 12 +-----------
 lib/elixir/test/elixir/list_test.exs |  8 ++------
 2 files changed, 3 insertions(+), 17 deletions(-)

diff --git a/lib/elixir/lib/list.ex b/lib/elixir/lib/list.ex
index 4bb6f621164..f8fe874bbeb 100644
--- a/lib/elixir/lib/list.ex
+++ b/lib/elixir/lib/list.ex
@@ -933,17 +933,7 @@ defmodule List do
   @spec ends_with?(list, []) :: true
   @spec ends_with?([], nonempty_list) :: false
   def ends_with?(list, suffix) do
-    case ends_with_offset(list, suffix) do
-      nil -> false
-      n -> :lists.nthtail(n, list) === suffix
-    end
-  end
-
-  defp ends_with_offset([], [_ | _]), do: nil
-  defp ends_with_offset(rest, []), do: length(rest)
-
-  defp ends_with_offset([_ | tail], [_ | suffix_tail]) do
-    ends_with_offset(tail, suffix_tail)
+    :lists.suffix(suffix, list)
   end
 
   @doc """
diff --git a/lib/elixir/test/elixir/list_test.exs b/lib/elixir/test/elixir/list_test.exs
index 20b237c98ce..12676c126f1 100644
--- a/lib/elixir/test/elixir/list_test.exs
+++ b/lib/elixir/test/elixir/list_test.exs
@@ -310,15 +310,11 @@ defmodule ListTest do
     end
 
     test "only accepts proper lists" do
-      message = "no function clause matching in List.ends_with_offset/2"
-
-      assert_raise FunctionClauseError, message, fn ->
+      assert_raise ArgumentError, ~r/not a list/, fn ->
         List.ends_with?([1 | 2], [1 | 2])
       end
 
-      message = "no function clause matching in List.ends_with_offset/2"
-
-      assert_raise FunctionClauseError, message, fn ->
+      assert_raise ArgumentError, ~r/not a list/, fn ->
         List.ends_with?([1, 2], 1)
       end
     end