Only try to create Component -> Component connections when both are i…

…n the current change set

Since we display "virtual" Components of some things that aren't
actually in the current change set, we need to make sure that we don't
try to create a connection to them as that would effectively be a
dangling pointer.

lib/dal/src/component.rs

@@ -1939,14 +1939,34 @@ impl Component {
         destination_input_socket_id: InputSocketId,
     ) -> ComponentResult<Option<AttributePrototypeArgumentId>> {
         let total_start = std::time::Instant::now();
+        // Make sure both source & destination Components exist in the "current" change set.
+        // Eventually, this should probably be reported as an error actionable by the frontend, but
+        // for now, this is a no-op so we don't end up creating a broken graph.
+        let (_source_component, destination_component) = match (
+            Component::try_get_by_id(ctx, source_component_id).await?,
+            Component::try_get_by_id(ctx, destination_component_id).await?,
+        ) {
+            (Some(source), Some(destination)) => (source, destination),
+            (source, destination) => {
+                warn!(
+                    "Not creating edge; either source or destination component does not exist in current change set: {:?}, {:?}",
+                    source,
+                    destination,
+                );
+                return Ok(None);
+            }
+        };
         // Already have this connection? Nothing to do.
-        let destination_component = Component::get_by_id(ctx, destination_component_id).await?;
         for connection in destination_component.incoming_connections(ctx).await? {
             if connection.from_component_id == source_component_id
                 && connection.from_output_socket_id == source_output_socket_id
                 && connection.to_component_id == destination_component_id
                 && connection.to_input_socket_id == destination_input_socket_id
             {
+                warn!(
+                    "Not creating edge; already have this connection in change set: {:?}",
+                    connection
+                );
                 return Ok(None);
             }
         }