Refuse to translate if set1 is longer than set2 and set2 ends in a character class

tr [:lower:]a [:upper:]

fails in GNU tr, so print an error for tr too.

src/uu/tr/src/operation.rs

@@ -35,6 +35,7 @@ pub enum BadSequence {
     EmptySet2WhenNotTruncatingSet1,
     ClassExceptLowerUpperInSet2,
     ClassInSet2NotMatchedBySet1,
+    Set1LongerSet2EndsInClass,
 }
 
 impl Display for BadSequence {
@@ -62,6 +63,9 @@ impl Display for BadSequence {
             Self::ClassInSet2NotMatchedBySet1 => {
                 write!(f, "when translating, every 'upper'/'lower' in set2 must be matched by a 'upper'/'lower' in the same position in set1")
             }
+            Self::Set1LongerSet2EndsInClass => {
+                write!(f, "when translating with string1 longer than string2,\nthe latter string must not end with a character class")
+            }
         }
     }
 }
@@ -259,6 +263,15 @@ impl Sequence {
             .filter_map(to_u8)
             .collect();
 
+        if set2_solved.len() < set1_solved.len()
+            && !truncate_set1_flag
+            && matches!(
+                set2.last().copied(),
+                Some(Self::Class(Class::Upper)) | Some(Self::Class(Class::Lower))
+            )
+        {
+            return Err(BadSequence::Set1LongerSet2EndsInClass);
+        }
         //Truncation is done dead last. It has no influence on the other conversion steps
         if truncate_set1_flag {
             set1_solved.truncate(set2_solved.len());

tests/by-util/test_tr.rs

@@ -1374,3 +1374,15 @@ fn check_disallow_blank_in_set2_when_translating() {
 fn check_class_in_set2_must_be_matched_in_set1() {
     new_ucmd!().args(&["-t", "1[:upper:]", "[:upper:]"]).fails();
 }
+
+#[test]
+fn check_set1_longer_set2_ends_in_class() {
+    new_ucmd!().args(&["[:lower:]a", "[:upper:]"]).fails();
+}
+
+#[test]
+fn check_set1_longer_set2_ends_in_class_with_trunc() {
+    new_ucmd!()
+        .args(&["-t", "[:lower:]a", "[:upper:]"])
+        .succeeds();
+}