From ec29d3342381bf36cd6ce3196d9aafd83f0959e2 Mon Sep 17 00:00:00 2001
From: can1357 <me@can.ac>
Date: Wed, 18 Mar 2026 23:58:00 +0100
Subject: [PATCH] tr: fix complemented class truncation ordering

---
 src/uu/tr/src/operation.rs | 21 +++++++++++++++++++--
 tests/by-util/test_tr.rs   |  8 ++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/uu/tr/src/operation.rs b/src/uu/tr/src/operation.rs
index 2f45bc9b990..e7b90cb9e12 100644
--- a/src/uu/tr/src/operation.rs
+++ b/src/uu/tr/src/operation.rs
@@ -292,11 +292,12 @@ impl Sequence {
         set2_uniques.sort_unstable();
         set2_uniques.dedup();
 
+        let set1_has_class = set1.iter().any(|x| matches!(x, Self::Class(_)));
         // If the complement flag is used in translate mode, only one unique
         // character may appear in set2. Validate this with the set of uniques
         // in set2 that we just generated.
         // Also, set2 must not overgrow set1, otherwise the mapping can't be 1:1.
-        if set1.iter().any(|x| matches!(x, Self::Class(_)))
+        if set1_has_class
             && translating
             && complement_flag
             && (set2_uniques.len() > 1 || set2_solved.len() > set1_len)
@@ -306,7 +307,23 @@ impl Sequence {
 
         if set2_solved.len() < set1_solved.len() {
             if truncate_set1_flag {
-                set1_solved.truncate(set2_solved.len());
+                if complement_flag && set1_has_class {
+                    // GNU applies -t before complementing a character class.
+                    // That means we must first truncate the expanded, non-complemented
+                    // source set, then complement the truncated prefix to recover the
+                    // final translation domain. Complementing first would incorrectly
+                    // shrink the complemented domain to the prefix length.
+                    let truncated_set1: Vec<_> = set1
+                        .iter()
+                        .flat_map(Self::flatten)
+                        .take(set2_solved.len())
+                        .collect();
+                    set1_solved = (0..=u8::MAX)
+                        .filter(|x| !truncated_set1.contains(x))
+                        .collect();
+                } else {
+                    set1_solved.truncate(set2_solved.len());
+                }
             } else if matches!(
                 set2.last().copied(),
                 Some(Self::Class(Class::Upper | Class::Lower))
diff --git a/tests/by-util/test_tr.rs b/tests/by-util/test_tr.rs
index 4a7c266b92a..84f62cd90b0 100644
--- a/tests/by-util/test_tr.rs
+++ b/tests/by-util/test_tr.rs
@@ -341,6 +341,14 @@ fn test_truncate_with_set1_shorter_than_set2() {
         .stdout_is("xycde");
 }
 
+#[test]
+fn test_truncate_applies_before_complement_with_class() {
+    new_ucmd!()
+        .args(&["-ct", "[:digit:]", "X"])
+        .pipe_in("A")
+        .succeeds()
+        .stdout_is("X");
+}
 #[test]
 fn missing_args_fails() {
     let (_, mut ucmd) = at_and_ucmd!();