tr: align [:upper:]/[:lower:] the way GNU does, and say so

src/uu/tr/locales/en-US.ftl

@@ -13,7 +13,7 @@ tr-error-missing-operand = missing operand
 tr-error-missing-operand-translating = missing operand after { $set }
   Two strings must be given when translating.
 tr-error-missing-operand-deleting-squeezing = missing operand after { $set }
-  Two strings must be given when deleting and squeezing.
+  Two strings must be given when both deleting and squeezing repeats.
 tr-error-extra-operand-deleting-without-squeezing = extra operand { $operand }
   Only one string may be given when deleting without squeezing repeats.
 tr-error-extra-operand-simple = extra operand { $operand }
@@ -34,7 +34,7 @@ tr-error-char-repeat-in-set1 = the [c*] repeat construct may not appear in strin
 tr-error-invalid-repeat-count = invalid repeat count { $count } in [c*n] construct
 tr-error-empty-set2-when-not-truncating = when not truncating set1, string2 must be non-empty
 tr-error-class-except-lower-upper-in-set2 = when translating, the only character classes that may appear in set2 are 'upper' and 'lower'
-tr-error-class-in-set2-not-matched = when translating, every 'upper'/'lower' in set2 must be matched by a 'upper'/'lower' in the same position in set1
+tr-error-class-in-set2-not-matched = misaligned [:upper:] and/or [:lower:] construct
 tr-error-set1-longer-set2-ends-in-class = when translating with string1 longer than string2,
   the latter string must not end with a character class
 tr-error-complement-more-than-one-unique = when translating with complemented character classes,

src/uu/tr/locales/fr-FR.ftl

@@ -13,7 +13,7 @@ tr-error-missing-operand = opérande manquant
 tr-error-missing-operand-translating = opérande manquant après { $set }
   Deux chaînes doivent être données lors de la traduction.
 tr-error-missing-operand-deleting-squeezing = opérande manquant après { $set }
-  Deux chaînes doivent être données lors de la suppression et compression.
+  Deux chaînes doivent être données lors de la suppression et de la compression des répétitions.
 tr-error-extra-operand-deleting-without-squeezing = opérande supplémentaire { $operand }
   Une seule chaîne peut être donnée lors de la suppression sans compression des répétitions.
 tr-error-extra-operand-simple = opérande supplémentaire { $operand }
@@ -35,7 +35,7 @@ tr-error-char-repeat-in-set1 = la construction de répétition [c*] ne peut pas
 tr-error-invalid-repeat-count = nombre de répétitions invalide { $count } dans la construction [c*n]
 tr-error-empty-set2-when-not-truncating = quand on ne tronque pas set1, string2 doit être non-vide
 tr-error-class-except-lower-upper-in-set2 = lors de la traduction, les seules classes de caractères qui peuvent apparaître dans set2 sont 'upper' et 'lower'
-tr-error-class-in-set2-not-matched = lors de la traduction, chaque 'upper'/'lower' dans set2 doit être associé à un 'upper'/'lower' à la même position dans set1
+tr-error-class-in-set2-not-matched = les structures [:upper:] ou [:lower:] ne sont pas alignées correctement
 tr-error-set1-longer-set2-ends-in-class = lors de la traduction avec string1 plus long que string2,
   cette dernière chaîne ne doit pas se terminer par une classe de caractères
 tr-error-complement-more-than-one-unique = lors de la traduction avec des classes de caractères complémentées,

src/uu/tr/src/operation.rs

@@ -318,9 +318,10 @@ impl Sequence {
             })
             .collect();
 
-        // For every upper/lower in set2, there must be an upper/lower in set1 at the same position. The position is calculated by expanding everything before the upper/lower in both sets
+        // For every upper/lower in set2, there must be an upper/lower in set1 at the same position. The position is calculated by expanding everything before the upper/lower in both sets.
+        // Only when translating: with -d, set2 is the squeeze set and lines up with nothing.
         for (set2_pos, set2_item) in set2.iter().enumerate() {
-            if matches!(set2_item, Self::Class(_)) {
+            if translating && matches!(set2_item, Self::Class(_)) {
                 let mut set2_part_solved_len = 0;
                 if set2_pos >= 1 {
                     set2_part_solved_len =
@@ -329,7 +330,10 @@ impl Sequence {
 
                 let mut class_matches = false;
                 for (set1_pos, set1_item) in set1.iter().enumerate() {
-                    if matches!(set1_item, Self::Class(_)) {
+                    // Only an 'upper'/'lower' in set1 can line up with one in
+                    // set2: any other class there leaves the mapping
+                    // undefined, so GNU rejects it.
+                    if matches!(set1_item, Self::Class(Class::Upper | Class::Lower)) {
                         let mut set1_part_solved_len = 0;
                         if set1_pos >= 1 {
                             set1_part_solved_len =
@@ -401,10 +405,12 @@ impl Sequence {
                 } else {
                     set1_solved.truncate(set2_solved.len());
                 }
-            } else if matches!(
-                set2.last().copied(),
-                Some(Self::Class(Class::Upper | Class::Lower))
-            ) {
+            } else if translating
+                && matches!(
+                    set2.last().copied(),
+                    Some(Self::Class(Class::Upper | Class::Lower))
+                )
+            {
                 return Err(SequenceError::whole_set(
                     BadSequence::Set1LongerSet2EndsInClass,
                     1,

tests/by-util/test_tr.rs

@@ -299,13 +299,55 @@ fn test_translate_and_squeeze_multiple_lines() {
         .stdout_is("yaay\nyaay"); // spell-checker:disable-line
 }
 
+/// An 'upper'/'lower' in SET2 must line up with an 'upper'/'lower' in SET1;
+/// any other class there leaves the mapping undefined. GNU calls that a
+/// misaligned construct.
+#[test]
+fn test_misaligned_upper_lower_construct() {
+    for sets in [
+        ["[:alpha:]", "[:upper:]"],
+        ["[:digit:]", "[:upper:]"],
+        ["abc", "[:upper:]"],
+        ["a[:lower:]", "[:upper:]b"],
+        ["[:lower:]", "[:upper:][:lower:]"],
+    ] {
+        new_ucmd!()
+            .args(&sets)
+            .pipe_in("aZ1")
+            .fails_with_code(1)
+            .no_stdout()
+            .stderr_contains("tr: misaligned [:upper:] and/or [:lower:] construct\n");
+    }
+}
+
+/// The alignment rule is about translating only: with -d, SET2 is the squeeze
+/// set and lines up with nothing.
+#[test]
+fn test_misaligned_construct_not_checked_when_deleting() {
+    new_ucmd!()
+        .args(&["-ds", "[:alpha:]", "[:upper:]"])
+        .pipe_in("aZ1")
+        .succeeds()
+        .stdout_is("1");
+}
+
+/// SET1 longer than SET2 keeps its own message, which GNU also has.
+#[test]
+fn test_set1_longer_than_set2_ending_in_class() {
+    new_ucmd!()
+        .args(&["[:upper:][:lower:]", "[:lower:]"])
+        .pipe_in("aZ1")
+        .fails_with_code(1)
+        .stderr_contains("when translating with string1 longer than string2,\n");
+}
+
 #[test]
 fn test_delete_and_squeeze_one_set() {
     new_ucmd!()
         .args(&["-ds", "a-z"])
         .fails()
         .stderr_contains("missing operand after 'a-z'")
-        .stderr_contains("Two strings must be given when deleting and squeezing.");
+        .stderr_contains("Two strings must be given when both deleting and squeezing repeats.");
 }
 
 #[test]