fix(forms): clearing a field's length limit leaves it with none, not its parent field's

/MaxLen is inheritable (ISO 32000-2 12.7.5.3). Clearing a kid's limit removed its own key, so
the parent's limit came back. When an ancestor sets /MaxLen, write /MaxLen 0, which read.rs
already reads as no limit and which overrides the inherited one (#3323). Follow-up to #4991.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SqmHYx8FiWM5PcsoiErgp9

crates/automation/tests/it/automation.rs

@@ -9433,6 +9433,31 @@ fn changing_a_lists_options_through_tools_keeps_its_saved_selection_on_the_same_
     assert_eq!(saved_selection_indices(&dir.join("letters.pdf"), "letters"), Some(vec![0, 1]), "B and C are now items 0 and 1");
 }
 
+/// Clearing a field's length limit through `form_set_props` (`"max_length": 0`) leaves it with
+/// none, even when its parent field has one it would otherwise inherit.
+#[test]
+fn clearing_a_kids_length_limit_through_tools_does_not_bring_back_its_parents() {
+    let objs = [
+        "<< /Type /Catalog /Pages 2 0 R /AcroForm 4 0 R >>",
+        "<< /Type /Pages /Kids [3 0 R] /Count 1 /MediaBox [0 0 400 300] >>",
+        "<< /Type /Page /Parent 2 0 R /Annots [6 0 R] >>",
+        "<< /Fields [5 0 R] /DA (/Helv 12 Tf 0 g) /DR << /Font << /Helv 7 0 R >> >> >>",
+        "<< /T (address) /FT /Tx /MaxLen 3 /Kids [6 0 R] >>",
+        "<< /Type /Annot /Subtype /Widget /T (city) /Parent 5 0 R /MaxLen 8 /Rect [10 250 150 268] /P 3 0 R >>",
+        "<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >>",
+    ];
+    let dir = workdir("kid-max-len");
+    std::fs::write(dir.join("form.pdf"), pdf_of(&objs)).unwrap();
+    let mut a = auto(&dir);
+    let doc = ok(&mut a, "doc_open", json!({ "path": "form.pdf" }))["doc"].as_u64().unwrap();
+    ok(&mut a, "form_set_props", json!({ "doc": doc, "field": "address.city", "max_length": 0 }));
+    ok(&mut a, "form_fill", json!({ "doc": doc, "values": { "address.city": "Absalom" } }));
+    let fields = ok(&mut a, "form_fields", json!({ "doc": doc }));
+    let city = fields["fields"].as_array().unwrap().iter().find(|f| f["name"] == "address.city").unwrap().clone();
+    assert!(city.get("max_length").is_none(), "no limit, not the parent's 3: {city}");
+    assert_eq!(city["value"], "Absalom", "the value is not cut to the parent's 3 characters");
+}
+
 /// Clearing a field's default through `form_set_props` (`"default": ""`) leaves it with none,
 /// even when its parent field has one it would otherwise inherit.
 #[test]

crates/forms/src/author/edit.rs

@@ -189,6 +189,7 @@ pub fn set_props(doc: &mut Document, name: &str, props: &FieldProps) -> Result<S
     let mut list_picked = None;
     let (sort_items, old_selection) = items_to_sort(doc, &f, props);
     let parent_default = ancestor_sets(doc, f.obj, b"DV");
+    let parent_limit = ancestor_sets(doc, f.obj, b"MaxLen");
     doc.update_dict(f.obj, |d| {
         d.set(b"Ff".to_vec(), Object::Int(ff as i64));
         if let Some(t) = &props.tooltip {
@@ -201,6 +202,8 @@ pub fn set_props(doc: &mut Document, name: &str, props: &FieldProps) -> Result<S
         if let Some(m) = props.max_len {
             match m {
                 Some(m) => d.set(b"MaxLen".to_vec(), Object::Int(m as i64)),
+                // An absent key would inherit the parent's limit; zero is "no limit" (`read.rs`).
+                None if parent_limit => d.set(b"MaxLen".to_vec(), Object::Int(0)),
                 None => {
                     d.remove(b"MaxLen");
                 }

crates/forms/src/tests.rs

@@ -5271,6 +5271,29 @@ fn sorting_keeps_which_of_two_items_with_one_export_value_is_selected() {
     assert_eq!(selection_indices(&doc, &list), Some(vec![2]));
 }
 
+#[test]
+fn clearing_a_kids_length_limit_does_not_bring_back_its_parents() {
+    let mut doc = fixture();
+    let city = field(&fields(&doc), "address.city").clone();
+    let parent = doc.get(city.obj).as_dict().unwrap().reference(b"Parent").unwrap();
+    doc.update_dict(parent, |d| d.set(b"MaxLen".to_vec(), Object::Int(3))).unwrap();
+    set_props(&mut doc, "address.city", &FieldProps { max_len: Some(Some(8)), ..FieldProps::default() }).unwrap();
+    assert_eq!(field(&fields(&doc), "address.city").max_len, Some(8));
+    set_props(&mut doc, "address.city", &FieldProps { max_len: Some(None), ..FieldProps::default() }).unwrap();
+    let mut doc = reopen(&doc);
+    let f = field(&fields(&doc), "address.city").clone();
+    assert_eq!(f.max_len, None, "no limit, not the parent's 3");
+    let own = doc.get(f.obj).as_dict().and_then(|d| d.get(b"MaxLen")).and_then(Object::as_int);
+    assert_eq!(own, Some(0), "the kid holds an explicit unlimited of its own");
+    set_value(&mut doc, "address.city", &FieldValue::Text("Absalom".into())).unwrap();
+    assert_eq!(field(&fields(&reopen(&doc)), "address.city").value, ["Absalom"], "not cut to 3 characters");
+    // Without a parent limit, clearing still removes the key.
+    set_props(&mut doc, "name", &FieldProps { max_len: Some(Some(4)), ..FieldProps::default() }).unwrap();
+    set_props(&mut doc, "name", &FieldProps { max_len: Some(None), ..FieldProps::default() }).unwrap();
+    let name = field(&fields(&doc), "name").clone();
+    assert!(doc.get(name.obj).as_dict().unwrap().get(b"MaxLen").is_none());
+}
+
 #[test]
 fn clearing_a_kids_default_does_not_bring_back_its_parents() {
     let mut doc = fixture();

parity/acrobat-features.toml

@@ -5003,8 +5003,8 @@ milestone = "M6"
 status = "shipped"
 commands = ["form.field.properties"]
 tools = ["form_set_props"]
-evidence = ["crates/forms/src/tests.rs::button_caption_preserves_other_widgets_and_shared_dictionaries", "crates/forms/src/tests.rs::a_button_caption_is_drawn_in_its_fields_font_size_and_color", "crates/ui-egui/tests/it/prepare.rs::button_label_is_editable_without_renaming_the_field", "crates/automation/tests/it/button_caption.rs::button_caption_can_be_changed_after_creation", "crates/forms/src/tests.rs::properties_rename_and_delete", "crates/automation/tests/it/automation.rs::preparing_a_form_through_tools", "crates/forms/src/tests.rs::options_tab_flags_alignment_and_defaults", "crates/ui-egui/tests/it/prepare.rs::options_tab_sets_flags_alignment_and_defaults", "crates/automation/tests/it/form_bulk.rs::bulk_options_apply_per_field_and_refuse_an_invalid_comb_atomically", "crates/forms/src/tests.rs::changing_a_lists_options_repoints_its_selected_indices", "crates/forms/src/tests.rs::shrinking_a_lists_options_scrolls_a_widget_with_its_own_top_row", "crates/forms/src/tests.rs::each_widget_with_its_own_top_row_scrolls_by_itself", "crates/forms/src/tests.rs::a_list_boxs_top_row_follows_a_font_size_changed_with_its_items", "crates/forms/src/tests.rs::sorting_a_combo_boxs_items_repoints_its_selected_index", "crates/automation/tests/it/automation.rs::changing_a_lists_options_through_tools_keeps_its_saved_selection_on_the_same_items", "crates/forms/src/tests.rs::clearing_a_kids_default_does_not_bring_back_its_parents", "crates/forms/src/tests.rs::clearing_a_buttons_default_under_a_parent_with_one_leaves_it_off", "crates/automation/tests/it/automation.rs::clearing_a_kids_default_through_tools_does_not_bring_back_its_parents"]
-notes = "push buttons: per-widget normal label independent of the field name, including clearing and save/reopen, drawn in the font, size and color of the button's /DA (the form's /DR font, else Helvetica; an automatic size fits the button) and centered by Helvetica's widths; icon-only layout retained, rollover/down labels and icon layout editing remain unavailable; text: alignment, default (clearing it leaves none, not a parent field's), multi-line, scroll, rich text flag, limit, password, file selection, spell check, comb; choices: items (the selected indices /I follow their items when the list is edited or sorted), default, sort, custom text, multiple selection, commit immediately; check boxes and radios: checked by default, radios in unison. Shared GUI offers applicable text/choice flags, alignment, text limits and check styles; choices/defaults remain individual GUI edits"
+evidence = ["crates/forms/src/tests.rs::button_caption_preserves_other_widgets_and_shared_dictionaries", "crates/forms/src/tests.rs::a_button_caption_is_drawn_in_its_fields_font_size_and_color", "crates/ui-egui/tests/it/prepare.rs::button_label_is_editable_without_renaming_the_field", "crates/automation/tests/it/button_caption.rs::button_caption_can_be_changed_after_creation", "crates/forms/src/tests.rs::properties_rename_and_delete", "crates/automation/tests/it/automation.rs::preparing_a_form_through_tools", "crates/forms/src/tests.rs::options_tab_flags_alignment_and_defaults", "crates/ui-egui/tests/it/prepare.rs::options_tab_sets_flags_alignment_and_defaults", "crates/automation/tests/it/form_bulk.rs::bulk_options_apply_per_field_and_refuse_an_invalid_comb_atomically", "crates/forms/src/tests.rs::changing_a_lists_options_repoints_its_selected_indices", "crates/forms/src/tests.rs::shrinking_a_lists_options_scrolls_a_widget_with_its_own_top_row", "crates/forms/src/tests.rs::each_widget_with_its_own_top_row_scrolls_by_itself", "crates/forms/src/tests.rs::a_list_boxs_top_row_follows_a_font_size_changed_with_its_items", "crates/forms/src/tests.rs::sorting_a_combo_boxs_items_repoints_its_selected_index", "crates/automation/tests/it/automation.rs::changing_a_lists_options_through_tools_keeps_its_saved_selection_on_the_same_items", "crates/forms/src/tests.rs::clearing_a_kids_default_does_not_bring_back_its_parents", "crates/forms/src/tests.rs::clearing_a_kids_length_limit_does_not_bring_back_its_parents", "crates/automation/tests/it/automation.rs::clearing_a_kids_length_limit_through_tools_does_not_bring_back_its_parents", "crates/forms/src/tests.rs::clearing_a_buttons_default_under_a_parent_with_one_leaves_it_off", "crates/automation/tests/it/automation.rs::clearing_a_kids_default_through_tools_does_not_bring_back_its_parents"]
+notes = "push buttons: per-widget normal label independent of the field name, including clearing and save/reopen, drawn in the font, size and color of the button's /DA (the form's /DR font, else Helvetica; an automatic size fits the button) and centered by Helvetica's widths; icon-only layout retained, rollover/down labels and icon layout editing remain unavailable; text: alignment, default (clearing it leaves none, not a parent field's), multi-line, scroll, rich text flag, limit (clearing it leaves none, not a parent field's), password, file selection, spell check, comb; choices: items (the selected indices /I follow their items when the list is edited or sorted), default, sort, custom text, multiple selection, commit immediately; check boxes and radios: checked by default, radios in unison. Shared GUI offers applicable text/choice flags, alignment, text limits and check styles; choices/defaults remain individual GUI edits"
 
 [[feature]]
 id = "form.props-actions"