Fix collision-detection regression with convex polyhedron caused by the internal edges handling

src/query/contact_manifolds/contact_manifolds_pfm_pfm.rs

@@ -92,13 +92,17 @@ pub fn contact_manifold_pfm_pfm<'a, ManifoldData, ContactData, S1, S2>(
                 false,
             );
 
-            if manifold.points.is_empty() {
-                // cfg!(feature = "dim3") || (cfg!(feature = "dim2") && manifold.points.is_empty()) {
+            if (cfg!(feature = "dim2") && manifold.points.is_empty())
+                // TODO: this test is a workaround until we figure-out a way to
+                //       determine the feature ids for the GJK/EPA contact.
+                || pfm1.is_convex_polyhedron()
+                || pfm2.is_convex_polyhedron()
+            {
                 let contact = TrackedContact::new(
                     p1,
                     pos12.inverse_transform_point(&p2_1),
-                    PackedFeatureId::UNKNOWN, // FIXME: We don't know what features are involved.
-                    PackedFeatureId::UNKNOWN, // FIXME
+                    PackedFeatureId::UNKNOWN, // TODO: We don't know what features are involved.
+                    PackedFeatureId::UNKNOWN,
                     (p2_1 - p1).dot(&dir),
                 );
                 manifold.points.push(contact);

src/shape/convex_polyhedron.rs

@@ -558,6 +558,10 @@ impl PolygonalFeatureMap for ConvexPolyhedron {
         out_feature.fid = PackedFeatureId::face(best_fid as u32);
         out_feature.num_vertices = num_vertices as usize;
     }
+
+    fn is_convex_polyhedron(&self) -> bool {
+        true
+    }
 }
 
 /*

src/shape/polygonal_feature_map.rs

@@ -17,6 +17,14 @@ use na::{ComplexField, RealField}; // for .abs() and .copysign()
 pub trait PolygonalFeatureMap: SupportMap {
     /// Compute the support polygonal face of `self` towards the `dir`.
     fn local_support_feature(&self, dir: &Unit<Vector<Real>>, out_feature: &mut PolygonalFeature);
+
+    // TODO: this is currently just a workaround for https://github.com/dimforge/rapier/issues/417
+    //       until we get a better way to deal with the issue without breaking internal edges
+    //       handling.
+    /// Is this shape a `ConvexPolyhedron`?
+    fn is_convex_polyhedron(&self) -> bool {
+        false
+    }
 }
 
 impl PolygonalFeatureMap for Segment {