fix(sort): fix case-insensitive sorting to order punctuation after letters

Changed ascii_case_insensitive_cmp to fold characters to uppercase instead of lowercase, ensuring that in ASCII case-insensitive sorting, letters are ordered before punctuation. Added tests to verify the correct behavior.

Author: mattsu2020

src/uu/sort/src/sort.rs

@@ -2622,13 +2622,13 @@ fn compare_by<'a>(
 /// untouched and we avoid locale-sensitive routines such as `strcasecmp`.
 fn ascii_case_insensitive_cmp(a: &[u8], b: &[u8]) -> Ordering {
     #[inline]
-    fn lower(byte: u8) -> u8 {
-        byte.to_ascii_lowercase()
+    fn fold(byte: u8) -> u8 {
+        byte.to_ascii_uppercase()
     }
 
     for (lhs, rhs) in a.iter().copied().zip(b.iter().copied()) {
-        let l = lower(lhs);
-        let r = lower(rhs);
+        let l = fold(lhs);
+        let r = fold(rhs);
         if l != r {
             return l.cmp(&r);
         }

tests/by-util/test_sort.rs

@@ -208,6 +208,24 @@ fn test_version_sort_stable() {
         .stdout_is("0.1\n0.02\n0.2\n0.002\n0.3\n");
 }
 
+#[test]
+fn test_ignore_case_orders_punctuation_after_letters() {
+    new_ucmd!()
+        .arg("-f")
+        .pipe_in("A\na\n_\n")
+        .succeeds()
+        .stdout_is("A\na\n_\n");
+}
+
+#[test]
+fn test_ignore_case_unique_orders_punctuation_after_letters() {
+    new_ucmd!()
+        .arg("-fu")
+        .pipe_in("a\n_\n")
+        .succeeds()
+        .stdout_is("a\n_\n");
+}
+
 #[test]
 fn test_human_numeric_whitespace() {
     test_helper(