Don't make top-level spaces their own children (#1100)

* Don't make top-level spaces their own children
* Allow view coordinates to be logged at the root

crates/re_viewer/src/misc/space_info.rs

@@ -190,7 +190,15 @@ impl SpaceInfoCollection {
                 .child_spaces
                 .insert(tree.path.clone(), transform);
 
-            add_children(entity_db, &mut spaces_info, &mut space_info, tree, &query);
+            for child_tree in tree.children.values() {
+                add_children(
+                    entity_db,
+                    &mut spaces_info,
+                    &mut space_info,
+                    child_tree,
+                    &query,
+                );
+            }
             spaces_info.spaces.insert(tree.path.clone(), space_info);
         }
         spaces_info

rerun_py/src/python_bridge.rs

@@ -443,9 +443,8 @@ fn log_transform(
     timeless: bool,
 ) -> PyResult<()> {
     let entity_path = parse_entity_path(entity_path)?;
-    if entity_path.len() == 1 {
-        // Stop people from logging a transform to a root-entity, such as "world" (which doesn't have a parent).
-        return Err(PyTypeError::new_err("Transforms are between a child entity and its parent, so root entities cannot have transforms"));
+    if entity_path.is_root() {
+        return Err(PyTypeError::new_err("Transforms are between a child entity and its parent, so the root cannot have a transform"));
     }
     let mut session = global_session();
     let time_point = time(timeless);
@@ -517,16 +516,22 @@ fn log_view_coordinates_up_handedness(
 }
 
 fn log_view_coordinates(
-    entity_path: &str,
+    entity_path_str: &str,
     coordinates: ViewCoordinates,
     timeless: bool,
 ) -> PyResult<()> {
     if coordinates.handedness() == Some(coordinates::Handedness::Left) {
         re_log::warn_once!("Left-handed coordinate systems are not yet fully supported by Rerun");
     }
 
+    // We normally disallow logging to root, but we make an exception for view_coordinates
+    let entity_path = if entity_path_str == "/" {
+        EntityPath::root()
+    } else {
+        parse_entity_path(entity_path_str)?
+    };
+
     let mut session = global_session();
-    let entity_path = parse_entity_path(entity_path)?;
     let time_point = time(timeless);
 
     // We currently log view coordinates from inside the bridge because the code