Deserialize custom workspaces using a placeholder

CHANGELOG.md

@@ -1,3 +1,12 @@
+## Unreleased
+
+### Modified
+
+- Deserializing a `ContactManifoldsWorkspace` that was serialized by a custom contact-manifolds
+  algorithm no longer fails with `"Cannot deserialize custom shape."`. It now yields the new
+  `UnknownContactManifoldsWorkspace`, which the relevant algorithm can replace with a workspace
+  of the correct type at its next execution.
+
 ## 0.31.1
 
 ### Modified

src/query/contact_manifolds/contact_manifolds_workspace.rs

@@ -60,37 +60,59 @@ enum DeserializableWorkspaceData {
 
 #[cfg(feature = "serde-serialize")]
 impl DeserializableWorkspaceData {
-    pub fn into_contact_manifold_workspace(self) -> Option<ContactManifoldsWorkspace> {
+    pub fn into_contact_manifold_workspace(self) -> ContactManifoldsWorkspace {
         match self {
             DeserializableWorkspaceData::TriMeshShapeContactManifoldsWorkspace(w) => {
-                Some(ContactManifoldsWorkspace(Box::new(w)))
+                ContactManifoldsWorkspace(Box::new(w))
             }
             DeserializableWorkspaceData::HeightfieldShapeContactManifoldsWorkspace(w) => {
-                Some(ContactManifoldsWorkspace(Box::new(w)))
+                ContactManifoldsWorkspace(Box::new(w))
             }
             DeserializableWorkspaceData::HeightfieldCompositeShapeContactManifoldsWorkspace(w) => {
-                Some(ContactManifoldsWorkspace(Box::new(w)))
+                ContactManifoldsWorkspace(Box::new(w))
             }
             DeserializableWorkspaceData::CompositeShapeCompositeShapeContactManifoldsWorkspace(
                 w,
-            ) => Some(ContactManifoldsWorkspace(Box::new(w))),
+            ) => ContactManifoldsWorkspace(Box::new(w)),
             DeserializableWorkspaceData::CompositeShapeShapeContactManifoldsWorkspace(w) => {
-                Some(ContactManifoldsWorkspace(Box::new(w)))
+                ContactManifoldsWorkspace(Box::new(w))
             }
             DeserializableWorkspaceData::VoxelsShapeContactManifoldsWorkspace(w) => {
-                Some(ContactManifoldsWorkspace(Box::new(w)))
+                ContactManifoldsWorkspace(Box::new(w))
             }
             DeserializableWorkspaceData::VoxelsCompositeShapeContactManifoldsWorkspace(w) => {
-                Some(ContactManifoldsWorkspace(Box::new(w)))
+                ContactManifoldsWorkspace(Box::new(w))
             }
             DeserializableWorkspaceData::VoxelsVoxelsContactManifoldsWorkspace(w) => {
-                Some(ContactManifoldsWorkspace(Box::new(w)))
+                ContactManifoldsWorkspace(Box::new(w))
+            }
+            // The data of a custom workspace is unknown to parry, so we fall back to a placeholder.
+            // This can later be overwritten by algorithms that need the workspace and know its type.
+            DeserializableWorkspaceData::Custom => {
+                ContactManifoldsWorkspace(Box::new(UnknownContactManifoldsWorkspace))
             }
-            DeserializableWorkspaceData::Custom => None,
         }
     }
 }
 
+/// A placeholder workspace used for custom workspace types unknown to parry.
+///
+/// This is yielded when deserializing a custom [`ContactManifoldsWorkspace`],
+/// as its data is lost during serialization. Algorithms that access the workspace
+/// can replace the placeholder with the correct workspace type on their next call.
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
+pub struct UnknownContactManifoldsWorkspace;
+
+impl WorkspaceData for UnknownContactManifoldsWorkspace {
+    fn as_typed_workspace_data(&self) -> TypedWorkspaceData<'_> {
+        TypedWorkspaceData::Custom
+    }
+
+    fn clone_dyn(&self) -> Box<dyn WorkspaceData> {
+        Box::new(*self)
+    }
+}
+
 /// Data from a [`ContactManifoldsWorkspace`].
 pub trait WorkspaceData: DowncastSync {
     /// Gets the underlying workspace as an enum.
@@ -134,9 +156,7 @@ impl<'de> serde::Deserialize<'de> for ContactManifoldsWorkspace {
     where
         D: serde::Deserializer<'de>,
     {
-        use crate::serde::de::Error;
-        DeserializableWorkspaceData::deserialize(deserializer)?
-            .into_contact_manifold_workspace()
-            .ok_or(D::Error::custom("Cannot deserialize custom shape."))
+        Ok(DeserializableWorkspaceData::deserialize(deserializer)?
+            .into_contact_manifold_workspace())
     }
 }

src/query/contact_manifolds/mod.rs

@@ -178,7 +178,7 @@ pub use self::contact_manifolds_voxels_voxels::{
     contact_manifolds_voxels_voxels, contact_manifolds_voxels_voxels_shapes,
 };
 pub use self::contact_manifolds_workspace::{
-    ContactManifoldsWorkspace, TypedWorkspaceData, WorkspaceData,
+    ContactManifoldsWorkspace, TypedWorkspaceData, UnknownContactManifoldsWorkspace, WorkspaceData,
 };
 pub use self::normals_constraint::{NormalConstraints, NormalConstraintsPair};
 

src/query/mod.rs

@@ -29,7 +29,8 @@ pub use self::closest_points::{closest_points, ClosestPoints};
 pub use self::contact::{contact, Contact};
 #[cfg(feature = "alloc")]
 pub use self::contact_manifolds::{
-    ContactManifold, ContactManifoldsWorkspace, TrackedContact, TypedWorkspaceData, WorkspaceData,
+    ContactManifold, ContactManifoldsWorkspace, TrackedContact, TypedWorkspaceData,
+    UnknownContactManifoldsWorkspace, WorkspaceData,
 };
 pub use self::default_query_dispatcher::DefaultQueryDispatcher;
 pub use self::distance::{distance, ShapeDistance};