expand: allow specifier only with last value

src/uu/expand/src/expand.rs

@@ -41,6 +41,7 @@ static DEFAULT_TABSTOP: usize = 8;
 
 /// The mode to use when replacing tabs beyond the last one specified in
 /// the `--tabs` argument.
+#[derive(PartialEq)]
 enum RemainingMode {
     None,
     Slash,
@@ -65,6 +66,7 @@ fn is_space_or_comma(c: char) -> bool {
 enum ParseError {
     InvalidCharacter(String),
     SpecifierNotAtStartOfNumber(String, String),
+    SpecifierOnlyAllowedWithLastValue(String),
     TabSizeCannotBeZero,
     TabSizeTooLarge(String),
     TabSizesMustBeAscending,
@@ -85,6 +87,11 @@ impl fmt::Display for ParseError {
                 specifier.quote(),
                 s.quote(),
             ),
+            Self::SpecifierOnlyAllowedWithLastValue(specifier) => write!(
+                f,
+                "{} specifier only allowed with the last value",
+                specifier.quote()
+            ),
             Self::TabSizeCannotBeZero => write!(f, "tab size cannot be 0"),
             Self::TabSizeTooLarge(s) => write!(f, "tab stop is too large {}", s.quote()),
             Self::TabSizesMustBeAscending => write!(f, "tab sizes must be ascending"),
@@ -112,6 +119,7 @@ fn tabstops_parse(s: &str) -> Result<(RemainingMode, Vec<usize>), ParseError> {
 
     let mut nums = vec![];
     let mut remaining_mode = RemainingMode::None;
+    let mut is_specifier_already_used = false;
     for word in s.split(is_space_or_comma) {
         let bytes = word.as_bytes();
         for i in 0..bytes.len() {
@@ -139,6 +147,19 @@ fn tabstops_parse(s: &str) -> Result<(RemainingMode, Vec<usize>), ParseError> {
                                 }
                             }
 
+                            if is_specifier_already_used {
+                                let specifier = if remaining_mode == RemainingMode::Slash {
+                                    "/".to_string()
+                                } else {
+                                    "+".to_string()
+                                };
+                                return Err(ParseError::SpecifierOnlyAllowedWithLastValue(
+                                    specifier,
+                                ));
+                            } else if remaining_mode != RemainingMode::None {
+                                is_specifier_already_used = true;
+                            }
+
                             // Append this tab stop to the list of all tabstops.
                             nums.push(num);
                             break;

tests/by-util/test_expand.rs

@@ -226,6 +226,24 @@ fn test_tabs_with_specifier_not_at_start() {
     run_cmd("--tabs=1+2", "+", "+2");
 }
 
+#[test]
+fn test_tabs_with_specifier_only_allowed_with_last_value() {
+    fn run_cmd(arg: &str, specifier: &str) {
+        let expected_msg = format!(
+            "{} specifier only allowed with the last value",
+            specifier.quote()
+        );
+        new_ucmd!().arg(arg).fails().stderr_contains(expected_msg);
+    }
+    run_cmd("--tabs=/1,2,3", "/");
+    run_cmd("--tabs=1,/2,3", "/");
+    new_ucmd!().arg("--tabs=1,2,/3").succeeds();
+
+    run_cmd("--tabs=+1,2,3", "+");
+    run_cmd("--tabs=1,+2,3", "+");
+    new_ucmd!().arg("--tabs=1,2,+3").succeeds();
+}
+
 #[test]
 fn test_tabs_with_invalid_chars() {
     new_ucmd!()