expand, unexpand: preserve bare - as stdin

src/uu/expand/src/expand.rs

@@ -193,11 +193,12 @@ fn expand_shortcuts(args: Vec<OsString>) -> Vec<OsString> {
     let mut processed_args = Vec::with_capacity(args.len());
 
     for arg in args {
-        if let Some(arg) = arg.to_str()
-            && arg.starts_with('-')
-            && arg[1..].chars().all(is_digit_or_comma)
+        if let Some(shortcut) = arg
+            .to_str()
+            .and_then(|arg| arg.strip_prefix('-'))
+            .filter(|shortcut| !shortcut.is_empty() && shortcut.chars().all(is_digit_or_comma))
         {
-            arg[1..]
+            shortcut
                 .split(',')
                 .filter(|s| !s.is_empty())
                 .for_each(|s| processed_args.push(OsString::from(format!("--tabs={s}"))));

src/uu/unexpand/src/unexpand.rs

@@ -201,8 +201,11 @@ fn expand_shortcuts(args: Vec<OsString>) -> Vec<OsString> {
 
     for arg in args {
         if let Some(arg) = arg.to_str() {
-            if arg.starts_with('-') && arg[1..].chars().all(is_digit_or_comma) {
-                arg[1..]
+            if let Some(shortcut) = arg
+                .strip_prefix('-')
+                .filter(|shortcut| !shortcut.is_empty() && shortcut.chars().all(is_digit_or_comma))
+            {
+                shortcut
                     .split(',')
                     .filter(|s| !s.is_empty())
                     .for_each(|s| processed_args.push(OsString::from(format!("--tabs={s}"))));

tests/by-util/test_expand.rs

@@ -7,13 +7,24 @@
 
 use rstest::rstest;
 use uucore::display::Quotable;
-use uutests::new_ucmd;
+use uutests::{at_and_ucmd, new_ucmd};
 
 #[test]
 fn test_invalid_arg() {
     new_ucmd!().arg("--definitely-invalid").fails_with_code(1);
 }
 
+#[test]
+fn test_bare_dash_reads_stdin_in_file_list() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.write("file", "file\n");
+
+    ucmd.args(&["-", "file"])
+        .pipe_in("stdin\n")
+        .succeeds()
+        .stdout_is("stdin\nfile\n");
+}
+
 #[test]
 fn test_with_tab() {
     new_ucmd!()

tests/by-util/test_unexpand.rs

@@ -13,6 +13,35 @@ fn test_invalid_arg() {
     new_ucmd!().arg("--definitely-invalid").fails_with_code(1);
 }
 
+#[test]
+fn test_bare_dash_reads_stdin_in_file_list() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.write("file", "file\n");
+
+    ucmd.args(&["-", "file"])
+        .pipe_in("stdin\n")
+        .succeeds()
+        .stdout_is("stdin\nfile\n");
+}
+
+#[test]
+fn test_bare_dash_does_not_force_first_only() {
+    new_ucmd!()
+        .args(&["-t", "3", "-"])
+        .pipe_in("a  b\n")
+        .succeeds()
+        .stdout_is("a\tb\n");
+}
+
+#[test]
+fn test_first_only_with_bare_stdin_operand() {
+    new_ucmd!()
+        .args(&["--first-only", "-"])
+        .pipe_in("        A     B\n")
+        .succeeds()
+        .stdout_is("\tA     B\n");
+}
+
 #[rstest]
 #[case::unexpand_init_0(&["-t4"], " 1\n  2\n   3\n    4\n", " 1\n  2\n   3\n\t4\n")]
 #[case::unexpand_init_1(&["-t4"], "     5\n      6\n       7\n        8\n", "\t 5\n\t  6\n\t   7\n\t\t8\n")]