M6: fields that don't scroll stop taking text when full

crates/engine/src/lib.rs

@@ -787,6 +787,17 @@ impl Document {
         self.editable() && self.permissions().is_none_or(|p| p.modify())
     }
 
+    /// How widget `widget` of text field `name` lays its value out, for asking whether a typed
+    /// value fits it ([`form_appearance::TextBox::fits`]): a field that doesn't scroll takes no
+    /// more than fits. `None` without such a field or widget, or when the document can't be
+    /// edited.
+    pub fn field_text_box(&self, name: &str, widget: usize) -> Option<form_appearance::TextBox> {
+        let cos = &self.editor.as_ref()?.cos;
+        let f = self.form.iter().find(|f| f.name == name)?;
+        let w = f.widgets.get(widget)?;
+        Some(form_appearance::text_box(cos, f, w))
+    }
+
     /// Filling in form fields is allowed (Table 22, bits 6 and 9).
     pub fn allows_form_filling(&self) -> bool {
         self.editable() && self.permissions().is_none_or(|p| p.fill_forms())

crates/engine/src/tests.rs

@@ -4675,6 +4675,25 @@ fn measurement_edits_are_transactional_and_honour_annotation_permissions() {
     );
 }
 
+/// A laid-out XFA field that doesn't scroll (`hScrollPolicy="off"`) opens as a text field with
+/// DoNotScroll, and its text box says what fits it: what the editor takes no more than.
+#[test]
+fn an_xfa_field_that_doesnt_scroll_opens_with_do_not_scroll_and_a_text_box() {
+    let xdp = r##"<?xml version="1.0" encoding="UTF-8"?>
+<xdp:xdp xmlns:xdp="http://ns.adobe.com/xdp/"><template xmlns="http://www.xfa.org/schema/xfa-template/3.3/"><subform name="form" layout="tb">
+<field name="code" w="1in" h="0.3in"><ui><textEdit hScrollPolicy="off"/></ui><font typeface="Arial" size="10pt"/></field>
+<field name="note" w="1in" h="0.3in"><ui><textEdit/></ui><font typeface="Arial" size="10pt"/></field>
+</subform></template></xdp:xdp>"##;
+    let mut s = Session::new();
+    let id = s.open("form.pdf", None, Arc::new(pdfcraft_xfa::fixtures::shell(xdp)), None).expect("opens");
+    let doc = s.get(id).unwrap();
+    let field = |end: &str| doc.form.iter().find(|f| f.name.ends_with(end)).unwrap_or_else(|| panic!("no field {end}"));
+    assert!(field("code").has(field_flags::DO_NOT_SCROLL) && !field("note").has(field_flags::DO_NOT_SCROLL));
+    let tb = doc.field_text_box(&field("code").name, 0).expect("a text box");
+    assert!(tb.fits("A1B2") && !tb.fits(&"W".repeat(40)), "a 1-inch field at 10 pt");
+    assert!(doc.field_text_box("no such field", 0).is_none() && doc.field_text_box(&field("code").name, 5).is_none());
+}
+
 #[test]
 fn dynamic_xfa_forms_are_laid_out_on_open_filled_and_saved_incrementally() {
     let original = Arc::new(pdfcraft_xfa::fixtures::shell(&pdfcraft_xfa::fixtures::template(3)));