Merge pull request #1766 from pguyot/w29/fix-lists-seq-2

Fix `lists:seq/2,3` when they should return an empty list

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

Author: bettio

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fixed a bug where binary matching could fail due to a missing preservation of the matched binary.
+- Fixed a bug where `lists:seq/2` wouldn't return the empty list in valid cases.
 
 ### Changed
 

libs/estdlib/src/lists.erl

@@ -601,7 +601,9 @@ join_1(_Sep, []) ->
 %%-----------------------------------------------------------------------------
 -spec seq(From :: integer(), To :: integer()) -> list().
 seq(From, To) when is_integer(From) andalso is_integer(To) andalso From =< To ->
-    seq_r(From, To, 1, []).
+    seq_r(From, To, 1, []);
+seq(From, To) when is_integer(From) andalso is_integer(To) andalso From =:= To + 1 ->
+    [].
 
 %%-----------------------------------------------------------------------------
 %% @param   From    from integer
@@ -623,6 +625,8 @@ seq(From, To, Incr) when
     error(badarg);
 seq(To, To, 0) ->
     [To];
+seq(From, To, Incr) when From =:= To + Incr ->
+    [];
 seq(From, To, Incr) ->
     Last = From + ((To - From) div Incr) * Incr,
     seq_r(From, Last, Incr, []).

tests/libs/estdlib/test_lists.erl

@@ -273,6 +273,8 @@ test_seq() ->
     ?ASSERT_MATCH(lists:seq(5, 1, -1), [5, 4, 3, 2, 1]),
     ?ASSERT_MATCH(lists:seq(1, 1, 0), [1]),
     ?ASSERT_MATCH(lists:seq(1, 1), [1]),
+    ?ASSERT_MATCH(lists:seq(1, 0), []),
+    ?ASSERT_MATCH(lists:seq(1, 0, 1), []),
 
     ?ASSERT_ERROR(lists:seq(foo, 1)),
     ?ASSERT_ERROR(lists:seq(1, bar)),