deltas: updated delta issued after pruned delta

[oliver-sanders]

When a workflow is removed we would expect a single pruned delta with the ID of the workflow.

• pruned(id)

However, we currently get two deltas:

• updated(id), pruned(id)
• updated(id)

The first delta contains an update for the workflow which is erroneous in this case as nothing should have changed in the workflow data, however this update is probably harmless (as we apply updated before pruned).

The second delta is more of a problem as it contains updates for a workflow which no longer exists.

This is a major problem for cylc/cylc-ui#1108 which avoids issues like cylc/cylc-ui#903 by treating added & updated deltas as the same, inserting any missing nodes in the process.

Steps to reproduce:

Open GraphiQL to the following subscription:

subscription {
  deltas {
    added {
      workflow {
        id
      }
    }
    updated {
      workflow {
        id
      }
    }
    pruned {
      workflow
    }
  }
}

Install a workflow (I'm using cp rather than cylc install to reduce the number of moving parts and ensure the addition is atomic):

cp -r ~/cylc-src/my-workflow ~/cylc-run

You should get an added delta for the workflow.

Remove the workflow (I'm using rm rather than cylc clean to reduce the number of moving parts and ensure the removal is atomic):

rm -r ~/cylc-run/my-workflow

Evidence:

[hjoliver]

Ping @dwsutherland !

[dwsutherland]

Unregister was also disconnecting with additional contact update (and hence delta).. #394

[hjoliver]

Closed by #394