Rib: accept a Project feature as its sketch ref

Rib guarded with `sk.type != CadFeatureType::Sketch`, while every other
sketch consumer — Extrude, SurfaceExtrude, SurfaceRevolve, the loft paths —
tests `!= Sketch && != Project`. A Project feature carries a plane and Line
entities, which is all a rib reads, so the guard blocked "project a body
edge, then rib along it" for no stated reason.

The picker in the Design tab offered Sketch features only, so it is widened
to match: a kernel that accepts Project refs and a GUI that never lists them
would have left the path unreachable anyway.

Worth recording for whoever hits this next: Rib also needs a sketch carrying
EXPLICIT entities. A parametric Rectangle sketch (add_sketch with
width/height) has an empty entities vector — build_sketch_wire synthesises
its profile on demand — so rib_entity 0 is out of range there and it fails
with "rib: bad entity". That is why Rib could not be driven headlessly at
all before this change; a Project feature is now the one programmatic way to
produce a ribbable line.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/libslic3r/CadDocument.cpp

@@ -2273,7 +2273,10 @@ void CadDocument::apply_feature(TopoDS_Shape& result, bool& have_body,
         if (f.rib_sketch_ref < 0 || f.rib_sketch_ref >= (int)features.size())
             throw std::runtime_error("rib: bad sketch ref");
         const CadFeature& sk = features[f.rib_sketch_ref];
-        if (sk.type != CadFeatureType::Sketch)
+        // Project counts as sketch-like here exactly as it does for Extrude, SurfaceExtrude
+        // and SurfaceRevolve: it carries plane + Line entities, which is all a rib reads.
+        // Ribbing along a projected body edge is otherwise unreachable.
+        if (sk.type != CadFeatureType::Sketch && sk.type != CadFeatureType::Project)
             throw std::runtime_error("rib: ref is not a sketch");
         if (f.rib_entity < 0 || f.rib_entity >= (int)sk.entities.size())
             throw std::runtime_error("rib: bad entity");

src/slic3r/GUI/DesignPanel.cpp

@@ -596,7 +596,10 @@ DesignPanel::DesignPanel(wxWindow* parent)
                     for (int i = 0; i < int(m_doc.features.size()); ++i) {
                         // 3-arg Append: ComboBox's own Append(text, bitmap) hides
                         // wxItemContainer's (text, void*) — see the Sweep picker.
-                        if (m_doc.features[i].type == CadFeatureType::Sketch)
+                        // Project features too: they carry Line entities the kernel ribs from
+                        // just like a drawn sketch, so a projected body edge is a valid path.
+                        if (m_doc.features[i].type == CadFeatureType::Sketch ||
+                            m_doc.features[i].type == CadFeatureType::Project)
                             m_rib_sketch->Append(wxString::FromUTF8(m_doc.features[i].name), wxNullBitmap,
                                                  reinterpret_cast<void*>(intptr_t(i)));
                     }

tests/libslic3r/test_caddocument.cpp

@@ -4048,6 +4048,30 @@ TEST_CASE("rib adds material to a box", "[CadDocument][rib]")
     REQUIRE_FALSE(bad.recompute());
 }
 
+TEST_CASE("rib accepts a Project feature as its sketch ref", "[CadDocument][rib]")
+{
+    // Project carries plane + Line entities, which is all a rib reads. Every other consumer
+    // (Extrude, SurfaceExtrude, SurfaceRevolve) already accepts it; Rib used to reject it,
+    // which made "project a body edge, then rib along it" unreachable.
+    CadDocument doc;
+    int sk = doc.add_sketch(SketchShape::Rectangle, SketchPlane::XY(), 40, 40, 10, "Box");
+    doc.add_extrude(sk, 10.0, false, BooleanMode::New, "Extrude");
+    REQUIRE(doc.recompute());
+    double Vbox = double(doc.display_mesh.volume());
+
+    // Project the whole body onto XY: the 4 top and 4 bottom edges survive as Lines.
+    int proj = doc.add_project_edges(0, {}, -1, SketchPlane::XY(), "Proj");
+    REQUIRE(proj >= 0);
+    REQUIRE(doc.recompute());
+    REQUIRE(doc.features[proj].entities.size() == 8);
+
+    int fi = doc.add_rib(proj, 0, 3.0, 12.0, 0, "RibFromProjection");
+    REQUIRE(fi >= 0);
+    REQUIRE(doc.recompute());
+    REQUIRE(doc.error.empty());
+    REQUIRE(double(doc.display_mesh.volume()) > Vbox);
+}
+
 TEST_CASE("rib non-line entity rejected safely", "[CadDocument][rib]")
 {