Fix #1679: a filled pencil path keeps a stroke of None

The Pencil gave every path a black stroke when the stroke was None. With Fill
new pencil strokes on and a fill set, the path now keeps no stroke; only a path
that would show nothing (no fill, no stroke) still gets black.

crates/engine/src/cmd/draw2.rs

@@ -615,7 +615,10 @@ fn freehand(s: &mut Session, p: &Value) -> Result<Value> {
     }
     let sp = fit_freehand(&pts, tol, closed);
     let fill = if bool_or(p, "fill", false) { s.paint.fill.clone() } else { Paint::None };
-    let mut look = s.new_art_look(fill, stroke_paint(s), s.paint.stroke_width.max(0.1));
+    // A pencil path with a fill keeps a stroke of None (#1679); only one that would show nothing
+    // gets black. A brush is its stroke.
+    let stroke = if brush || fill.is_none() { stroke_paint(s) } else { s.paint.stroke.clone() };
+    let mut look = s.new_art_look(fill, stroke, s.paint.stroke_width.max(0.1));
     if let Some(st) = look.appearance.stroke_mut() {
         st.pressure = pressure;
     }

crates/engine/src/tests_draw2.rs

@@ -1235,3 +1235,21 @@ fn pen_with_alt_converts_the_anchors_of_a_path_in_a_selected_group() {
         assert_eq!(paths(&s).len(), 1, "{wrap}: no new path");
     }
 }
+
+/// #1679: a filled pencil path keeps a stroke of None; an unfilled one with no stroke gets black,
+/// or it would show nothing.
+#[test]
+fn a_filled_pencil_path_keeps_no_stroke() {
+    let mut s = Session::new();
+    s.execute("file.new", &json!({"width": 200, "height": 200})).unwrap();
+    s.execute("select.none", &json!({})).unwrap();
+    s.execute("paint.setFill", &json!({"color": "#ff0000"})).unwrap();
+    s.execute("paint.setStroke", &json!({"none": true})).unwrap();
+    let pts = json!([[10, 10], [60, 20], [90, 80], [20, 90]]);
+    let id = NodeId(s.execute("path.freehand", &json!({"points": pts, "fill": true})).unwrap()["id"].as_u64().unwrap());
+    let n = s.doc().unwrap().doc.node(id).unwrap().clone();
+    assert!(n.appearance.stroke_paint().is_none(), "{:?}", n.appearance);
+    assert!(!n.appearance.fill_paint().is_none());
+    let id = NodeId(s.execute("path.freehand", &json!({"points": pts})).unwrap()["id"].as_u64().unwrap());
+    assert!(!s.doc().unwrap().doc.node(id).unwrap().appearance.stroke_paint().is_none());
+}