From 03c40b2db24aeb8c37575b9375f23e22f17e0919 Mon Sep 17 00:00:00 2001
From: Terts Diepraam <terts.diepraam@gmail.com>
Date: Sat, 12 Nov 2022 15:02:52 +0100
Subject: [PATCH] sort: allow a sort mode to appear multiple times

A test case for this is `sort -k 2n,2n` which should be accepted, because `n` is
compatible with itself.

Resolves issue #4129.
---
 src/uu/sort/src/sort.rs    | 2 +-
 tests/by-util/test_sort.rs | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/uu/sort/src/sort.rs b/src/uu/sort/src/sort.rs
index 9d23034ad44..e7ca996771c 100644
--- a/src/uu/sort/src/sort.rs
+++ b/src/uu/sort/src/sort.rs
@@ -458,7 +458,7 @@ impl KeySettings {
     }
 
     fn set_sort_mode(&mut self, mode: SortMode) -> Result<(), String> {
-        if self.mode != SortMode::Default {
+        if self.mode != SortMode::Default && self.mode != mode {
             return Err(format!(
                 "options '-{}{}' are incompatible",
                 self.mode.get_short_name().unwrap(),
diff --git a/tests/by-util/test_sort.rs b/tests/by-util/test_sort.rs
index 5c753470aa4..fe63eb2c7fb 100644
--- a/tests/by-util/test_sort.rs
+++ b/tests/by-util/test_sort.rs
@@ -1156,3 +1156,8 @@ fn test_tmp_files_deleted_on_sigint() {
     // `sort` should have deleted the temporary directory again.
     assert!(read_dir(at.plus("tmp_dir")).unwrap().next().is_none());
 }
+
+#[test]
+fn test_same_sort_mode_twice() {
+    new_ucmd!().args(&["-k", "2n,2n", "empty.txt"]).succeeds();
+}