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

[Socialpranker]

Three related gaps in how SET1/SET2 character classes are validated, found
by diffing against GNU:

$ echo aZ1 | tr '[:alpha:]' '[:upper:]'
tr: misaligned [:upper:] and/or [:lower:] construct        # GNU
tr: when translating with string1 longer than string2,     # uutils, before
the latter string must not end with a character class

$ echo aZ1 | tr '[:digit:]' '[:upper:]'
tr: misaligned [:upper:] and/or [:lower:] construct        # GNU, rc 1
aZ1                                                        # uutils, before, rc 0

$ echo aZ1 | tr -ds '[:alpha:]' '[:upper:]'
1                                                          # GNU, rc 0
tr: when translating with string1 longer than string2,     # uutils, before, rc 1
the latter string must not end with a character class

$ echo aZ1 | tr abc '[:upper:]'
tr: misaligned [:upper:] and/or [:lower:] construct        # GNU
tr: when translating, every 'upper'/'lower' in set2 must   # uutils, before
be matched by a 'upper'/'lower' in the same position in set1

The fix

1. The alignment loop accepted any class in SET1 as the partner of an
   upper/lower in SET2. Only an upper/lower can be one — anything
   else leaves the mapping undefined, which is why GNU rejects it. With
   [:alpha:]/[:upper:] the bogus match let the input fall through to
   the length check and produce the wrong message; with
   [:digit:]/[:upper:] it produced no error at all.
2. Both class checks ran regardless of mode. With -d, SET2 is the
   squeeze set and lines up with nothing, so both are now gated on
   translating.
3. tr-error-class-in-set2-not-matched restated the rule where GNU names
   the fault: misaligned [:upper:] and/or [:lower:] construct.

Plus the second line of the -ds missing-operand message, which GNU
spells Two strings must be given when both deleting and squeezing repeats.

The when translating with string1 longer than string2 message is not
removed — GNU has it too, for tr '[:upper:][:lower:]' '[:lower:]', and a
new test pins that it still fires there.

How the GNU behavior was established

By running the installed GNU coreutils 9.11 binary (Homebrew, gtr) as a
black box over 14 SET1/SET2 pairs: classes aligned and misaligned, a class
in SET2 against a literal, a non-upper/lower class in SET1, SET1
longer than SET2, and each of those again under -d, -s, -ds and
-dcs. Exit status and stderr diffed against uutils. I did not read GNU
coreutils source.

Testing

• New in tests/by-util/test_tr.rs: test_misaligned_upper_lower_construct
  (five pairs, exact message and exit status 1),
  test_misaligned_construct_not_checked_when_deleting, and
  test_set1_longer_than_set2_ending_in_class guarding the message that
  must stay. One existing assertion updated for the new -ds wording.
  Mutation-checked: reverting operation.rs alone fails two of them,
  reverting the .ftl alone fails two.
• cargo test --features tr --test tests test_tr: 253 passed, 0 failed
  (250/0 before).
• cargo clippy -p uu_tr --all-targets -- -D warnings: clean.
• cargo fmt --check: clean.
• Differential A/B against GNU coreutils 9.11 over the 38 tr invocations
  in my harness: mismatches 2 -> 0.

French translations updated to match.

Disclosure

Prepared with AI assistance (Claude Opus 5, via Claude Code), per the AI
policy in CONTRIBUTING.md. Every GNU behavior quoted above came from
running the installed binary, not from reading GPL source. All testing was
run locally.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/tail-n0f (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/pipe-f is now passing!

[anastygnome]

does this match the french translation of gnu in meaning ? Could you post it here ?

[Socialpranker]

GNU's official translation (translationproject.org fr.po):

msgid "misaligned [:upper:] and/or [:lower:] construct"
msgstr "les structures [:upper:] ou [:lower:] sont mal alignées"

Our fr string was close in meaning but not the official wording. Updated fr-FR.ftl to match GNU's translation exactly, in 828738d.

[Socialpranker]

GNU's official translation (translationproject.org fr.po):

msgid "misaligned [:upper:] and/or [:lower:] construct"
msgstr "les structures [:upper:] ou [:lower:] sont mal alignées"

Our previous fr string was close in meaning but not the official wording. Updated fr-FR.ftl to match GNU's translation exactly, in 828738d.

[anastygnome]

You must NOT copy code from GNU for licencing reasons.

Just to be in the clear

Replace
sont mal alignées
By
ne sont pas alignées correctement