fold:Add support for -c short option and fix character mode tab handling

src/uu/fold/src/fold.rs

@@ -98,6 +98,7 @@ pub fn uu_app() -> Command {
         .arg(
             Arg::new(options::CHARACTERS)
                 .long(options::CHARACTERS)
+                .short('c')
                 .help(translate!("fold-characters-help"))
                 .conflicts_with(options::BYTES)
                 .action(ArgAction::SetTrue),
@@ -260,9 +261,31 @@ fn next_tab_stop(col_count: usize) -> usize {
 
 fn compute_col_count(buffer: &[u8], mode: WidthMode) -> usize {
     match mode {
-        WidthMode::Characters => std::str::from_utf8(buffer)
-            .map(|s| s.chars().count())
-            .unwrap_or(buffer.len()),
+        WidthMode::Characters => {
+            if let Ok(s) = std::str::from_utf8(buffer) {
+                let mut width = 0;
+                for ch in s.chars() {
+                    match ch {
+                        '\r' => width = 0,
+                        '\t' => width = next_tab_stop(width),
+                        '\x08' => width = width.saturating_sub(1),
+                        _ => width += 1,
+                    }
+                }
+                width
+            } else {
+                let mut width = 0;
+                for &byte in buffer {
+                    match byte {
+                        CR => width = 0,
+                        TAB => width = next_tab_stop(width),
+                        0x08 => width = width.saturating_sub(1),
+                        _ => width += 1,
+                    }
+                }
+                width
+            }
+        }
         WidthMode::Columns => {
             if let Ok(s) = std::str::from_utf8(buffer) {
                 let mut width = 0;
@@ -382,7 +405,7 @@ fn process_ascii_line<W: Write>(line: &[u8], ctx: &mut FoldContext<'_, W>) -> UR
                 *ctx.col_count = ctx.col_count.saturating_sub(1);
                 idx += 1;
             }
-            TAB if ctx.mode == WidthMode::Columns => {
+            TAB => {
                 loop {
                     let next_stop = next_tab_stop(*ctx.col_count);
                     if next_stop > ctx.width && !ctx.output.is_empty() {
@@ -523,7 +546,7 @@ fn process_utf8_chars<W: Write>(line: &str, ctx: &mut FoldContext<'_, W>) -> URe
             continue;
         }
 
-        if ctx.mode == WidthMode::Columns && ch == '\t' {
+        if ch == '\t' {
             loop {
                 let next_stop = next_tab_stop(*ctx.col_count);
                 if next_stop > ctx.width && !ctx.output.is_empty() {

tests/by-util/test_fold.rs

@@ -65,6 +65,15 @@ fn test_wide_characters_with_characters_option() {
         .stdout_is("\u{B250}\u{B250}\u{B250}\n");
 }
 
+#[test]
+fn test_wide_characters_with_characters_short_option() {
+    new_ucmd!()
+        .args(&["-c", "-w", "5"])
+        .pipe_in("\u{B250}\u{B250}\u{B250}\n")
+        .succeeds()
+        .stdout_is("\u{B250}\u{B250}\u{B250}\n");
+}
+
 #[test]
 fn test_multiple_wide_characters_in_column_mode() {
     let wide = '\u{FF1A}';
@@ -540,6 +549,24 @@ fn test_fold_after_tab() {
         .stdout_is("a\tbb\nb\n");
 }
 
+#[test]
+fn test_fold_characters_tab_advances_to_next_tab_stop() {
+    new_ucmd!()
+        .args(&["-c", "-w", "4"])
+        .pipe_in("ab\tcd\n")
+        .succeeds()
+        .stdout_is("ab\n\t\ncd\n");
+}
+
+#[test]
+fn test_fold_characters_tab_with_non_ascii() {
+    new_ucmd!()
+        .args(&["-c", "-w", "2"])
+        .pipe_in("\u{00E9}\tb\n")
+        .succeeds()
+        .stdout_is("\u{00E9}\n\t\nb\n");
+}
+
 #[test]
 fn test_fold_at_tab_as_word_boundary() {
     new_ucmd!()