unexpand: reject too-large --tabs increment instead of overflowing

src/uu/unexpand/src/unexpand.rs

@@ -117,7 +117,11 @@ fn parse_tabstops(s: &str) -> Result<TabConfig, ParseError> {
     // Only add an extra tab stop if increment is non-zero
     if let Some(inc) = increment_size.filter(|&i| i > 0) {
         let last = *nums.last().unwrap();
-        nums.push(last + inc);
+        // A near-maximal last stop plus the increment can exceed `usize::MAX`.
+        // Reject it as too large (matching GNU) instead of overflowing, which
+        // aborts under overflow checks and wraps to a bogus stop otherwise.
+        let next = last.checked_add(inc).ok_or(ParseError::TabSizeTooLarge)?;
+        nums.push(next);
     }
 
     if let (false, _) = nums

tests/by-util/test_unexpand.rs

@@ -252,6 +252,18 @@ fn test_tabs_shortcut_with_too_large_size() {
     new_ucmd!().arg(arg).fails().stderr_contains(expected_error);
 }
 
+#[test]
+fn test_extended_tabstop_increment_overflow() {
+    // `--tabs=N,+M` adds one stop at `N + M`. When `N` is near `usize::MAX`,
+    // that sum must be rejected as too large rather than overflowing (which
+    // aborts under overflow checks and wraps to a bogus stop otherwise).
+    let arg = format!("--tabs={},+1", usize::MAX);
+    new_ucmd!()
+        .arg(arg)
+        .fails()
+        .stderr_contains("tab stop value is too large");
+}
+
 #[test]
 fn test_is_directory() {
     let (at, mut ucmd) = at_and_ucmd!();