mv --backup=simple a b on hard links should not fail

touch a
ln a b
./target/debug/coreutils mv --backup=simple a b

GNU: tests/mv/hard-4.sh

src/uu/mv/src/mv.rs

@@ -255,7 +255,9 @@ fn handle_two_paths(source: &Path, target: &Path, b: &Behavior) -> UResult<()> {
         return Err(MvError::NoSuchFile(source.quote().to_string()).into());
     }
 
-    if source.eq(target) || are_hardlinks_to_same_file(source, target) {
+    if (source.eq(target) || are_hardlinks_to_same_file(source, target))
+        && b.backup != BackupMode::SimpleBackup
+    {
         if source.eq(Path::new(".")) || source.ends_with("/.") || source.is_file() {
             return Err(
                 MvError::SameFile(source.quote().to_string(), target.quote().to_string()).into(),

tests/by-util/test_mv.rs

@@ -417,6 +417,23 @@ fn test_mv_same_hardlink() {
         .stderr_is(format!("mv: '{file_a}' and '{file_b}' are the same file\n",));
 }
 
+#[test]
+#[cfg(unix)]
+fn test_mv_same_hardlink_backup_simple() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    let file_a = "test_mv_same_file_a";
+    let file_b = "test_mv_same_file_b";
+    at.touch(file_a);
+
+    at.hard_link(file_a, file_b);
+
+    at.touch(file_a);
+    ucmd.arg(file_a)
+        .arg(file_b)
+        .arg("--backup=simple")
+        .succeeds();
+}
+
 #[test]
 fn test_mv_same_file_not_dot_dir() {
     let (at, mut ucmd) = at_and_ucmd!();