sort: reject conflicting -t separators

src/uu/sort/locales/en-US.ftl

@@ -24,6 +24,7 @@ sort-file-operands-combined = extra operand {$file}
     file operands cannot be combined with --files0-from
     Try '{$help} --help' for more information.
 sort-multiple-output-files = multiple output files specified
+sort-incompatible-tabs = incompatible tabs
 sort-minus-in-stdin = when reading file names from standard input, no file name of '-' allowed
 sort-no-input-from = no input from {$file}
 sort-random-source-end-of-file = {$path}: end of file

src/uu/sort/locales/fr-FR.ftl

@@ -24,6 +24,7 @@ sort-file-operands-combined = opérande supplémentaire {$file}
     les opérandes de fichier ne peuvent pas être combinées avec --files0-from
     Essayez '{$help} --help' pour plus d'informations.
 sort-multiple-output-files = plusieurs fichiers de sortie spécifiés
+sort-incompatible-tabs = tabulations incompatibles
 sort-minus-in-stdin = lors de la lecture des noms de fichiers depuis l'entrée standard, aucun nom de fichier '-' n'est autorisé
 sort-no-input-from = aucune entrée depuis {$file}
 sort-invalid-zero-length-filename = {$file}:{$line_num} : nom de fichier de longueur zéro invalide

src/uu/sort/src/sort.rs

@@ -182,6 +182,9 @@ pub enum SortError {
     #[error("{}", translate!("sort-multiple-output-files"))]
     MultipleOutputFiles,
 
+    #[error("{}", translate!("sort-incompatible-tabs"))]
+    IncompatibleTabs,
+
     #[error("{}", translate!("sort-minus-in-stdin"))]
     MinusInStdIn,
 
@@ -2137,6 +2140,19 @@ fn emit_debug_warnings(
     }
 }
 
+/// Whether option `id` was given several times with differing values.
+/// Repeating an option is fine as long as every occurrence has the same value.
+fn has_conflicting_values<T>(matches: &ArgMatches, id: &str) -> bool
+where
+    T: Clone + PartialEq + Send + Sync + 'static,
+{
+    matches.get_many::<T>(id).is_some_and(|mut values| {
+        values
+            .next()
+            .is_some_and(|first| values.any(|value| value != first))
+    })
+}
+
 #[uucore::main]
 #[allow(clippy::cognitive_complexity)]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
@@ -2177,18 +2193,16 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         uucore::clap_localization::handle_clap_result_with_exit_code(uu_app(), processed_args, 2)?;
 
     // Prevent -o/--output to be specified multiple times
-    if matches
-        .get_many::<OsString>(options::OUTPUT)
-        .is_some_and(|mut outputs| {
-            outputs
-                .next()
-                .as_ref()
-                .is_some_and(|first| outputs.any(|out| out != *first))
-        })
-    {
+    if has_conflicting_values::<OsString>(&matches, options::OUTPUT) {
         return Err(SortError::MultipleOutputFiles.into());
     }
 
+    // Prevent -t/--field-separator from being given different values. Raw
+    // values suffice: `\0` is the only spelling rewritten later, and argv cannot hold a NUL.
+    if has_conflicting_values::<OsString>(&matches, options::SEPARATOR) {
+        return Err(SortError::IncompatibleTabs.into());
+    }
+
     settings.debug = matches.get_flag(options::DEBUG);
     if let Some(path) = matches.get_one::<OsString>(options::RANDOM_SOURCE) {
         settings.random_source = Some(PathBuf::from(path));
@@ -2691,7 +2705,9 @@ pub fn uu_app() -> Command {
             .short('t')
             .long(options::SEPARATOR)
             .help(translate!("sort-help-separator"))
-            .value_parser(ValueParser::os_string()),
+            .value_parser(ValueParser::os_string())
+            // To detect differing occurrences and raise an error
+            .action(ArgAction::Append),
     )
     .arg(
         Arg::new(options::ZERO_TERMINATED)

tests/by-util/test_sort.rs

@@ -2080,6 +2080,36 @@ fn test_separator_attached_equals_multi_char() {
         .stderr_contains("separator must be exactly one character long: '=a'");
 }
 
+#[test]
+fn test_error_on_incompatible_separators() {
+    let cases: [&[&str]; 3] = [
+        &["-t@", "-t!"],
+        &["-t", "@", "-t", "!"],
+        &["--field-separator=@", "-t", "!"],
+    ];
+    for args in cases {
+        new_ucmd!()
+            .args(args)
+            .fails_with_code(2)
+            .stderr_only("sort: incompatible tabs\n");
+    }
+}
+
+#[test]
+fn test_same_separator_twice_ok() {
+    let cases: [&[&str]; 2] = [
+        &["-t:", "-t:", "-k2"],
+        &["--field-separator=:", "-t", ":", "-k2"],
+    ];
+    for args in cases {
+        new_ucmd!()
+            .args(args)
+            .pipe_in("a:2\nb:1\n")
+            .succeeds()
+            .stdout_only("b:1\na:2\n");
+    }
+}
+
 #[test]
 fn test_output_is_input() {
     let input = "a\nb\nc\n";