uucore: fall back to '~' when the backup suffix is empty

src/uucore/src/lib/features/backup_control.rs

@@ -245,7 +245,8 @@ pub mod arguments {
 ///
 /// 1. From the '-S' or '--suffix' CLI argument, if present
 /// 2. From the "SIMPLE_BACKUP_SUFFIX" environment variable, if present
-/// 3. By using the default '~' if none of the others apply, or if they contained slashes
+/// 3. By using the default '~' if none of the others apply, or if the
+///    resolved suffix is empty or contains slashes
 ///
 /// This function directly takes [`ArgMatches`] as argument and looks for
 /// the '-S' and '--suffix' arguments itself.
@@ -256,7 +257,7 @@ pub fn determine_backup_suffix(matches: &ArgMatches) -> String {
     } else {
         env::var("SIMPLE_BACKUP_SUFFIX").unwrap_or_else(|_| DEFAULT_BACKUP_SUFFIX.to_owned())
     };
-    if suffix.contains('/') {
+    if suffix.is_empty() || suffix.contains('/') {
         DEFAULT_BACKUP_SUFFIX.to_owned()
     } else {
         suffix
@@ -710,6 +711,15 @@ mod tests {
         assert_eq!(result, DEFAULT_BACKUP_SUFFIX);
     }
 
+    #[test]
+    fn test_suffix_empty_defaults_to_tilde() {
+        let _dummy = TEST_MUTEX.lock().unwrap();
+        let matches = make_app().get_matches_from(vec!["command", "-b", "--suffix", ""]);
+
+        let result = determine_backup_suffix(&matches);
+        assert_eq!(result, DEFAULT_BACKUP_SUFFIX);
+    }
+
     #[test]
     fn test_numbered_backup_path() {
         assert_eq!(numbered_backup_path(Path::new("")), PathBuf::from(".~1~"));

tests/by-util/test_cp.rs

@@ -1156,6 +1156,23 @@ fn test_cp_arg_suffix_hyphen_value() {
     );
 }
 
+#[test]
+fn test_cp_arg_suffix_empty_defaults_to_tilde() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    ucmd.arg(TEST_HELLO_WORLD_SOURCE)
+        .arg("-b")
+        .arg("--suffix=")
+        .arg(TEST_HOW_ARE_YOU_SOURCE)
+        .succeeds();
+
+    assert_eq!(at.read(TEST_HOW_ARE_YOU_SOURCE), "Hello, World!\n");
+    assert_eq!(
+        at.read(&format!("{TEST_HOW_ARE_YOU_SOURCE}~")),
+        "How are you?\n"
+    );
+}
+
 #[test]
 fn test_cp_custom_backup_suffix_via_env() {
     let (at, mut ucmd) = at_and_ucmd!();

tests/by-util/test_install.rs

@@ -1309,6 +1309,30 @@ fn test_install_backup_short_custom_suffix() {
     assert!(at.file_exists(format!("{file_b}{suffix}")));
 }
 
+#[test]
+fn test_install_backup_empty_suffix_defaults_to_tilde() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    let file_a = "test_install_backup_empty_suffix_file_a";
+    let file_b = "test_install_backup_empty_suffix_file_b";
+
+    at.touch(file_a);
+    at.touch(file_b);
+    scene
+        .ucmd()
+        .arg("-b")
+        .arg("--suffix=")
+        .arg(file_a)
+        .arg(file_b)
+        .succeeds()
+        .no_stderr();
+
+    assert!(at.file_exists(file_a));
+    assert!(at.file_exists(file_b));
+    assert!(at.file_exists(format!("{file_b}~")));
+}
+
 #[test]
 fn test_install_suffix_without_backup_option() {
     let scene = TestScenario::new(util_name!());

tests/by-util/test_ln.rs

@@ -244,6 +244,25 @@ fn test_symlink_custom_backup_suffix() {
     assert_eq!(at.resolve_link(backup), file);
 }
 
+#[test]
+fn test_ln_backup_empty_suffix_defaults_to_tilde() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+
+    at.write("a", "a\n");
+    at.write("b", "b2\n");
+
+    scene
+        .ucmd()
+        .args(&["-b", "--suffix=", "a", "b"])
+        .succeeds()
+        .no_stderr();
+
+    // b is now a hard link to a, and the original b was backed up to b~
+    assert_eq!(at.read("b"), "a\n");
+    assert_eq!(at.read("b~"), "b2\n");
+}
+
 #[test]
 fn test_symlink_suffix_without_backup_option() {
     let scene = TestScenario::new(util_name!());