M6: treat imported MaxLen zero as unlimited

crates/forms/src/lib.rs

@@ -754,7 +754,10 @@ fn walk(
         inh.q = Some(q);
     }
     if let Some(m) = d.get(b"MaxLen").and_then(|o| doc.resolve(o).as_int()) {
-        inh.max_len = usize::try_from(m).ok();
+        // Compatibility: some writers emit zero for an unlimited text field. Keep /MaxLen
+        // untouched in the object graph, but expose only positive limits to both UI and API.
+        // An explicit zero also clears an inherited limit rather than inheriting it again.
+        inh.max_len = usize::try_from(m).ok().filter(|limit| *limit > 0);
     }
     let kids: Vec<ObjRef> =
         d.get(b"Kids").map(|k| doc.resolve(k)).and_then(|k| k.as_array().cloned()).unwrap_or_default().iter().filter_map(|k| k.as_ref()).collect();

crates/forms/src/tests.rs

@@ -2239,6 +2239,22 @@ fn page_shapes_closes_only_last_stroked_subpath_but_all_filled_subpaths() {
     assert!(filled.rules.is_empty());
 }
 
+#[test]
+fn zero_max_len_is_unlimited_and_overrides_inherited_limit() {
+    let mut doc = fixture();
+    let city = fields(&doc).into_iter().find(|f| f.name == "address.city").unwrap();
+    let parent = doc.get(city.obj).as_dict().unwrap().get(b"Parent").unwrap().as_ref().unwrap();
+    doc.update_dict(parent, |d| d.set(b"MaxLen".to_vec(), Object::Int(3))).unwrap();
+    assert_eq!(fields(&doc).into_iter().find(|f| f.name == "address.city").unwrap().max_len, Some(3));
+    doc.update_dict(city.obj, |d| d.set(b"MaxLen".to_vec(), Object::Int(0))).unwrap();
+    assert_eq!(fields(&doc).into_iter().find(|f| f.name == "address.city").unwrap().max_len, None);
+    set_value(&mut doc, "address.city", &FieldValue::Text("Absalom".into())).unwrap();
+    let again = reopen(&doc);
+    assert_eq!(field(&fields(&again), "address.city").value, ["Absalom"]);
+    assert_eq!(again.get(city.obj).as_dict().unwrap().int(b"MaxLen"), Some(0), "preserve the original entry");
+    assert!(set_value(&mut doc, "zip", &FieldValue::Text("123456".into())).is_err(), "positive limits still apply");
+}
+
 #[test]
 fn auto_text_size_fits_single_and_multiline_text() {
     use crate::appearance::auto_text_size;