Don't panic when collaborating with older Zed versions (#7162)

Older Zed versions may send a buffer id of 0, which is no-longer
supported. (as of #6993)

This doesn't fix that, but it does ensure that we don't panic in the
workspace by maintaining the invariant that from_proto_state returns
Some(Task) if the variant matches.

It also converts the panic to an error should something similar happen
again in the future.


Release Notes:

- N/A

crates/editor/src/items.rs

@@ -73,18 +73,16 @@ impl FollowableItem for Editor {
             .iter()
             .map(|excerpt| excerpt.buffer_id)
             .collect::<HashSet<_>>();
-        let buffers = project
-            .update(cx, |project, cx| {
-                buffer_ids
-                    .iter()
-                    .map(|id| BufferId::new(*id).map(|id| project.open_buffer_by_id(id, cx)))
-                    .collect::<Result<Vec<_>>>()
-            })
-            .ok()?;
+        let buffers = project.update(cx, |project, cx| {
+            buffer_ids
+                .iter()
+                .map(|id| BufferId::new(*id).map(|id| project.open_buffer_by_id(id, cx)))
+                .collect::<Result<Vec<_>>>()
+        });
 
         let pane = pane.downgrade();
         Some(cx.spawn(|mut cx| async move {
-            let mut buffers = futures::future::try_join_all(buffers)
+            let mut buffers = futures::future::try_join_all(buffers?)
                 .await
                 .debug_assert_ok("leaders don't share views for unshared buffers")?;
             let editor = pane.update(&mut cx, |pane, cx| {

crates/workspace/src/workspace.rs

@@ -2784,8 +2784,10 @@ impl Workspace {
                         item_tasks.push(task);
                         leader_view_ids.push(id);
                         break;
-                    } else {
-                        assert!(variant.is_some());
+                    } else if variant.is_none() {
+                        Err(anyhow!(
+                            "failed to construct view from leader (maybe from a different version of zed?)"
+                        ))?;
                     }
                 }
             }