M12: an XFA label or button without a width is as wide as its text

A draw or a button with no width took all the width available, so a
right-aligned label slid to the far side of its subform and a button
spread over what lay beside it: DA Form 31's Instructions button covered
its header and the email line, and its PERSONNEL/FINANCE line ran into
the field after it. They now grow to their text, unwrapped, within what
is available and never below their minimum width, as containers do.

crates/xfa/src/layout.rs

@@ -912,7 +912,8 @@ impl Layouter<'_> {
         let ctx = ctx.with_som(c, 0);
         let som = ctx.som.clone();
         // A container without a width is as wide as its content (a radio group beside its
-        // question, say); a leaf without one takes what is available.
+        // question, say), and so is a text label or a button (as wide as its caption), within
+        // what is available; any other field without one takes what is available.
         let w = match c.w {
             Some(w) => w,
             None => match node {
@@ -920,7 +921,13 @@ impl Layouter<'_> {
                     let inner = (avail_w - c.margin.horizontal()).max(1.0);
                     (self.content_width(node, inner, &ctx, depth) + c.margin.horizontal()).min(avail_w)
                 }
-                Node::Field(_) | Node::Draw(_) => avail_w,
+                Node::Draw(d) => self.natural_width(&d.value, &ctx.font, &ctx.para).map_or(avail_w, |t| (t + c.margin.horizontal()).min(avail_w)),
+                Node::Field(f) if f.ui == Ui::Button => f
+                    .caption
+                    .as_ref()
+                    .and_then(|cap| self.natural_width(&cap.value, &ctx.font.apply(&cap.font), &ctx.para.apply(&cap.para)))
+                    .map_or(avail_w, |t| (t + c.margin.horizontal() + f.ui_margin.horizontal()).min(avail_w)),
+                Node::Field(_) => avail_w,
             },
         };
         let w = clamp_opt(w, c.min_w, c.max_w);
@@ -1004,6 +1011,17 @@ impl Layouter<'_> {
         }
     }
 
+    /// How wide text `v` is unwrapped, in `font` and `para`, with a hair to spare so that laying
+    /// it out at that width keeps it on its lines; `None` for what isn't text.
+    fn natural_width(&self, v: &Value, font: &Font, para: &Para) -> Option<f64> {
+        let rich = match v {
+            Value::Text(t) => text::plain(t),
+            Value::Rich(r) => r.clone(),
+            _ => return None,
+        };
+        Some(text::natural_width(&rich, para, &Face::of(font), &|id| self.embed(id)) + 0.01)
+    }
+
     fn value_height(&self, v: &Value, w: f64, ctx: &Ctx) -> f64 {
         match v {
             Value::Text(t) => text::measure_height(&text::plain(t), w, &ctx.para, &Face::of(&ctx.font), &|id| self.embed(id)),

crates/xfa/src/tests.rs

@@ -1195,6 +1195,63 @@ fn repeating_subforms_inside_positioned_content_get_their_instances() {
 /// treated like a subform (at most once), so once the first body page was out the layout fell
 /// back to the last page area, here one limited to a single use, and drew its content over every
 /// body page (and listed a copy of its fields per page).
+/// A positioned subform holding `body`, laid out; its page's items.
+fn positioned(body: &str) -> Vec<Item> {
+    let xdp = format!(
+        r##"<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">
+ <pageSet><pageArea name="front"><contentArea x="0.5in" y="0.5in" w="7.5in" h="10in"/><medium short="8.5in" long="11in"/></pageArea></pageSet>
+ <subform name="box" w="7.5in" h="3in">{body}</subform>
+</subform>
+</template></xdp:xdp>"##
+    );
+    layout_xml(&xdp).unwrap().pages.into_iter().next().unwrap().items
+}
+
+#[test]
+fn a_label_without_a_width_is_as_wide_as_its_text() {
+    const TEXT: &str = "PERSONNEL ONLY: from date (YYYYMMDD):";
+    let natural = pdfcraft_fonts::helvetica_width(TEXT, 8.0);
+    // Right-aligned, with a minimum narrower than the text: the box is as wide as the text and
+    // starts where it is placed, so the text does too (not at the far right of the subform).
+    let items = positioned(&format!(
+        r#"<draw name="a" x="1in" y="0" minW="50pt"><value><text>{TEXT}</text></value><font typeface="Arial" size="8pt"/><para hAlign="right"/></draw>"#
+    ));
+    let span = items.iter().find_map(|i| if let Item::Text(s) = i { Some(s) } else { None }).expect("the text");
+    assert!((span.x - (36.0 + 72.0)).abs() < 0.05, "starts at its x: {}", span.x);
+    // With a minimum wider than the text, the box is that wide and the text ends at its right.
+    let items = positioned(&format!(
+        r#"<draw name="a" x="1in" y="0" minW="{}pt"><value><text>{TEXT}</text></value><font typeface="Arial" size="8pt"/><para hAlign="right"/></draw>"#,
+        natural + 40.0
+    ));
+    let span = items.iter().find_map(|i| if let Item::Text(s) = i { Some(s) } else { None }).expect("the text");
+    assert!((span.x + span.face.width(&span.text) - (36.0 + 72.0 + natural + 40.0)).abs() < 0.05, "ends at its right: {}", span.x);
+    // Text longer than the room left still wraps at the container's width.
+    let long = "word ".repeat(200);
+    let items = positioned(&format!(r#"<draw name="a" x="0" y="0"><value><text>{long}</text></value><font typeface="Arial" size="8pt"/></draw>"#));
+    let lines: std::collections::BTreeSet<i64> =
+        items.iter().filter_map(|i| if let Item::Text(s) = i { Some((s.baseline * 100.0).round() as i64) } else { None }).collect();
+    assert!(lines.len() > 1, "wraps: {} line(s)", lines.len());
+}
+
+#[test]
+fn a_button_without_a_width_is_as_wide_as_its_caption() {
+    // No width, a minimum narrower than its caption: as wide as the caption, not the subform.
+    let caption = "Open the instructions for this form";
+    let items = positioned(&format!(
+        r#"<field name="help" x="1in" y="0" minW="40pt" minH="12pt"><ui><button/></ui><caption><value><text>{caption}</text></value><font typeface="Arial" size="8pt"/></caption></field>"#
+    ));
+    let button = items.iter().find_map(|i| if let Item::Widget(w) = i { Some(w) } else { None }).expect("the button");
+    let natural = pdfcraft_fonts::helvetica_width(caption, 8.0);
+    assert!(button.rect.w >= natural && button.rect.w < natural + 10.0, "{} for a caption of {natural}", button.rect.w);
+    // A minimum wider than the caption wins.
+    let items = positioned(
+        r#"<field name="help" x="1in" y="0" minW="200pt" minH="12pt"><ui><button/></ui><caption><value><text>Help</text></value><font typeface="Arial" size="8pt"/></caption></field>"#,
+    );
+    let button = items.iter().find_map(|i| if let Item::Widget(w) = i { Some(w) } else { None }).expect("the button");
+    assert!((button.rect.w - 200.0).abs() < 0.05, "{}", button.rect.w);
+}
+
 #[test]
 fn page_area_without_occur_serves_every_body_page() {
     let section = |n: u32| {

crates/xfa/src/text.rs

@@ -280,6 +280,14 @@ pub fn layout(rich: &RichText, rect: Rect, para: &Para, base: &Face, embed: &dyn
     Block { spans, height: total }
 }
 
+/// The width `rich` takes with no line wrapped (its longest paragraph, with the paragraph's
+/// margins and first-line indent): how wide a box without an explicit width grows.
+pub fn natural_width(rich: &RichText, para: &Para, base: &Face, embed: &dyn Fn(&str) -> String) -> f64 {
+    let indent = para.text_indent.max(0.0);
+    let widest = rich.paragraphs.iter().map(|p| words(&p.runs, base, embed).iter().map(|w| w.width).sum::<f64>()).fold(0.0, f64::max);
+    (para.margin_left + indent + widest + para.margin_right).max(0.0)
+}
+
 /// Height `rich` needs at `width` (for boxes without an explicit height).
 pub fn measure_height(rich: &RichText, width: f64, para: &Para, base: &Face, embed: &dyn Fn(&str) -> String) -> f64 {
     let p = Para { v_align: crate::model::VAlign::Top, ..para.clone() };