From 61d0d7555376ea261f1ddfc06d7d3a4dc2fdfc70 Mon Sep 17 00:00:00 2001
From: Paul Guyot <pguyot@kallisys.net>
Date: Sun, 13 Jul 2025 17:49:02 +0200
Subject: [PATCH] Add `lists:keysort/2`

Signed-off-by: Paul Guyot <pguyot@kallisys.net>
---
 CHANGELOG.md                      |  4 ++++
 libs/estdlib/src/lists.erl        | 12 ++++++++++++
 tests/libs/estdlib/test_lists.erl | 13 +++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9a9759e699..e128d458b9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [0.6.7] - Unreleased
 
+### Added
+
+- Added `lists:keysort/2`
+
 ### Fixed
 
 - Fixed a bug where binary matching could fail due to a missing preservation of the matched binary.
diff --git a/libs/estdlib/src/lists.erl b/libs/estdlib/src/lists.erl
index 9aecce8342..2fc12a3e93 100644
--- a/libs/estdlib/src/lists.erl
+++ b/libs/estdlib/src/lists.erl
@@ -43,6 +43,7 @@
     keyfind/3,
     keymember/3,
     keyreplace/4,
+    keysort/2,
     keystore/4,
     keytake/3,
     foldl/3,
@@ -330,6 +331,17 @@ keyreplace(Key, N, [H | Tail], _OrigL, NewTuple, Acc) when element(N, H) =:= Key
 keyreplace(Key, N, [H | Tail], OrigL, NewTuple, Acc) ->
     keyreplace(Key, N, Tail, OrigL, NewTuple, [H | Acc]).
 
+%%-----------------------------------------------------------------------------
+%% @param   N           the position in the tuple to compare (1..tuple_size)
+%% @param   L           the list to sort
+%% @returns The list L sorted by Nth element
+%% @doc     Sort a list of tuples by Nth element.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec keysort(N :: pos_integer(), L :: [tuple()]) -> [tuple()].
+keysort(N, TupleList) ->
+    sort(fun(E1, E2) -> element(N, E1) < element(N, E2) end, TupleList).
+
 %%-----------------------------------------------------------------------------
 %% @param   Key         the key to match
 %% @param   N           the position in the tuple to compare (1..tuple_size)
diff --git a/tests/libs/estdlib/test_lists.erl b/tests/libs/estdlib/test_lists.erl
index 72dc3bf494..b45c4f47f5 100644
--- a/tests/libs/estdlib/test_lists.erl
+++ b/tests/libs/estdlib/test_lists.erl
@@ -32,6 +32,7 @@ test() ->
     ok = test_keyfind(),
     ok = test_keydelete(),
     ok = test_keyreplace(),
+    ok = test_keysort(),
     ok = test_keystore(),
     ok = test_keytake(),
     ok = test_foldl(),
@@ -120,6 +121,18 @@ test_keyreplace() ->
     ]),
     ok.
 
+test_keysort() ->
+    ?ASSERT_MATCH(lists:keysort(1, [{2, foo}, {1, bar}]), [{1, bar}, {2, foo}]),
+    ?ASSERT_MATCH(lists:keysort(1, [{2, foobar}, {1, foo}, {1, bar}]), [
+        {1, foo}, {1, bar}, {2, foobar}
+    ]),
+    ?ASSERT_MATCH(lists:keysort(1, [{2, foo, zot}, {1, bar}]), [{1, bar}, {2, foo, zot}]),
+    ?ASSERT_MATCH(lists:keysort(1, []), []),
+    ?ASSERT_MATCH(lists:keysort(2, [{foo, 2}, {bar, 1}]), [{bar, 1}, {foo, 2}]),
+    ?ASSERT_ERROR(lists:keysort(1, [1, 2])),
+    ?ASSERT_ERROR(lists:keysort(3, [{1, bar}, {2, foo}])),
+    ok.
+
 test_keystore() ->
     ?ASSERT_MATCH(lists:keystore(a, 1, [], {foo, bar}), [{foo, bar}]),
     ?ASSERT_MATCH(lists:keystore(a, 1, [{a, x}, b, []], {1, 2}), [{1, 2}, b, []]),