STEP export: shelled revolved bodies export instead of panicking (#1496)

A scale across a revolution's axis keeps the face a surface of revolution and is written as one; any other refusal from the writer is an export error, not a panic.

crates/engine/tests/step_export_regressions.rs

@@ -0,0 +1,68 @@
+//! STEP export regressions found by round-tripping the robustness designs: a body the app built
+//! must export, and read back as the same solid.
+
+use serde_json::{Value, json};
+use solidcraft_engine::Session;
+use solidcraft_kernel::{measure, step_export, step_import};
+
+fn run(s: &mut Session, script: Value) {
+    for c in script.as_array().into_iter().flatten() {
+        let (id, p) = (c["command"].as_str().unwrap_or_default(), &c["params"]);
+        if let Err(e) = s.execute(id, p) {
+            panic!("{id} {p}: {e}");
+        }
+    }
+}
+
+/// The design's one body exports, and reads back closed with the same volume and area.
+fn round_trips(s: &Session) {
+    let st = s.model.state();
+    assert_eq!(st.bodies.len(), 1);
+    let body = &st.bodies[0].body;
+    let text = step_export(&[body], "test").unwrap_or_else(|e| panic!("export: {e}"));
+    let imp = step_import(&text).unwrap_or_else(|e| panic!("import: {e}"));
+    assert_eq!(imp.bodies.len(), 1, "{:?}", imp.warnings);
+    assert!(imp.bodies[0].closed && imp.warnings.is_empty(), "{:?}", imp.warnings);
+    let (a, b) = (measure(body).unwrap(), measure(&imp.bodies[0].body).unwrap());
+    assert!((a.volume - b.volume).abs() < 1e-3 * a.volume, "volume {} -> {}", a.volume, b.volume);
+    assert!((a.area - b.area).abs() < 1e-3 * a.area, "area {} -> {}", a.area, b.area);
+}
+
+/// Robustness seed 19, shrunk: a three-quarter turn of a rectangle, a sphere cut, a 1 mm shell.
+/// The shell moves revolved faces by a scale across their axis; export refused them and the
+/// refusal surfaced as a panic ("a Display implementation returned an error").
+#[test]
+fn shelled_revolve_with_a_sphere_cut_exports() {
+    let mut s = Session::default();
+    run(
+        &mut s,
+        json!([
+            {"command":"sketch.create","params":{"plane":"XZ"}},
+            {"command":"sketch.rectangle.two_point","params":{"p0":[5.0,0],"p1":[25.0,5.0]}},
+            {"command":"sketch.finish","params":{}},
+            {"command":"solid.revolve","params":{"angle":"270 deg","axis":"Z"}},
+            {"command":"solid.sphere","params":{"center":[-2.5,5.0,-2.5],"operation":"cut","radius":10.0}},
+            {"command":"solid.shell","params":{"faces":[[-2.7554552980815448e-15,-15.0,-2.5000000000000004]],"thickness":1.0}}
+        ]),
+    );
+    round_trips(&s);
+}
+
+/// Robustness seed 24, shrunk: a three-quarter turn of a rectangle, a chamfer of two edges, a
+/// 1.5 mm shell. The same refusal as seed 19's, reached through a chamfer.
+#[test]
+fn shelled_chamfered_revolve_exports() {
+    let mut s = Session::default();
+    run(
+        &mut s,
+        json!([
+            {"command":"sketch.create","params":{"plane":"XZ"}},
+            {"command":"sketch.rectangle.two_point","params":{"p0":[10.0,0],"p1":[27.5,22.5]}},
+            {"command":"sketch.finish","params":{}},
+            {"command":"solid.revolve","params":{"angle":"270 deg","axis":"Z"}},
+            {"command":"solid.chamfer","params":{"distance":2.0,"edges":[[7.0710678118654755,7.0710678118654755,0.0],[-19.445436482630054,19.44543648263006,0.0]]}},
+            {"command":"solid.shell","params":{"faces":[[18.75,0.0,-11.358616634594824]],"thickness":1.5}}
+        ]),
+    );
+    round_trips(&s);
+}