M6: a radio button without its /Parent link leaves its group's /Kids too

Deleting one widget took it out of the field tree through its /Parent,
which a damaged file can leave out or point at another field; the group
kept the widget in its /Kids with no page showing it, and the delete
reported success. The field that owns the widget drops it from its own
/Kids as well (CodeRabbit on #4631).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GbuSKAS2k5248LGFEapMUR

crates/forms/src/author/lifecycle.rs

@@ -219,6 +219,15 @@ pub fn delete_widget(doc: &mut Document, name: &str, widget: usize) -> Result<()
     drop_from_calculation_order(doc, |r| r == w.obj)?;
     let mut d = doc.get(f.obj).as_dict().cloned().unwrap_or_default();
     let mut changed = false;
+    // The field's own `/Kids` is what made the widget its: `detach` follows the widget's
+    // `/Parent`, which a damaged file can leave out or point elsewhere, so the field would keep
+    // a widget no page shows.
+    if let Some(kids) = d.get(b"Kids").map(|o| doc.resolve(o)).and_then(|o| o.as_array().cloned())
+        && kids.iter().any(|k| k.as_ref() == Some(w.obj))
+    {
+        d.set(b"Kids".to_vec(), Object::Array(kids.into_iter().filter(|k| k.as_ref() != Some(w.obj)).collect()));
+        changed = true;
+    }
     if per_widget_opt
         && let Some(opt) = d.get(b"Opt").map(|o| doc.resolve(o)).and_then(|o| o.as_array().cloned())
         && opt.len() == f.widgets.len()

crates/forms/src/tests.rs

@@ -4693,6 +4693,29 @@ fn deleting_one_copy_of_a_field_keeps_the_field_and_its_value() {
     assert_eq!(annots(&doc), [6, 7, 8]);
 }
 
+#[test]
+fn deleting_a_radio_button_without_its_parent_link_takes_it_out_of_the_group() {
+    // A damaged file: the group lists Medium in its /Kids, but Medium has no /Parent.
+    for parent in [None, Some(Object::Ref(ObjRef::new(9, 0)))] {
+        let mut doc = radio_group_form();
+        let medium = ObjRef::new(7, 0);
+        let mut w = doc.get(medium).as_dict().cloned().unwrap();
+        w.remove(b"Parent");
+        if let Some(p) = parent.clone() {
+            w.set(b"Parent".to_vec(), p);
+        }
+        doc.set(medium, Object::Dict(w));
+        delete_widget(&mut doc, "size", 1).unwrap();
+        let doc = reopen(&doc);
+        let all = fields(&doc);
+        assert_eq!(field(&all, "size").widgets.iter().map(|w| w.obj.num).collect::<Vec<_>>(), [6, 8], "/Parent {parent:?}");
+        let kids = doc.resolve(doc.get(ObjRef::new(5, 0)).as_dict().unwrap().get(b"Kids").unwrap()).as_array().cloned().unwrap();
+        assert!(!kids.iter().any(|k| k.as_ref() == Some(medium)), "/Parent {parent:?}: {kids:?}");
+        assert_eq!(field(&all, "name").widgets.len(), 2, "/Parent {parent:?}: the other field is untouched");
+        assert_eq!(annots(&doc), [6, 8, 10, 11]);
+    }
+}
+
 #[test]
 fn deleting_a_widget_that_is_not_there_changes_nothing() {
     let mut doc = radio_group_form();