AREA, Object: an open polyline's perimeter is its length, without the closing side (fixes #1168) (#1188)

crates/engine/src/cmd/inquiry.rs

@@ -211,8 +211,10 @@ fn object_area(s: &Session, h: Handle) -> Result<(f64, f64)> {
     Ok(match &e.kind {
         EntityKind::Circle(c) => (c.radius * c.radius * cadcraft_geom::PI, c.radius * cadcraft_geom::TAU),
         EntityKind::LwPolyline(pl) => {
+            // An open polyline is measured as if closed for the area, but its perimeter is its own length (AutoCAD's AREA help).
             let g = Polyline { vertices: pl.vertices.clone(), closed: true };
-            (g.area().abs(), g.len())
+            let drawn = Polyline { vertices: pl.vertices.clone(), closed: pl.closed };
+            (g.area().abs(), drawn.len())
         }
         EntityKind::Ellipse(el) => {
             let arc = cadcraft_geom::Ellipse { center: el.center.xy(), major: el.major.xy(), ratio: el.ratio, start: el.start, end: el.end };

crates/engine/tests/inquiry_keywords.rs

@@ -33,6 +33,13 @@ fn area_object_add_and_subtract_keep_a_running_total() {
     assert!(s.running.is_none(), "{}", s.prompt_text());
 }
 
+#[test]
+fn area_object_on_an_open_polyline_closes_the_area_but_not_the_perimeter() {
+    // Open, 160 long; the closing side back to 0,0 would add 116.619.
+    let (_, log) = run(&["pline", "0,0", "100,0", "100,60", "", "area", "o", "50,0"]);
+    assert!(has(&log, "Area = 3000.0000, Perimeter = 160.0000"), "{log:?}");
+}
+
 #[test]
 fn area_unsupported_keywords_say_so_and_length_extends_the_last_segment() {
     let (s, log) = run(&["area", "0,0", "a"]);