Use of HdDependencySchema etc to track prim removal - brilliant or terrible?

Community Hydra
1

Much like Storm and RenderMan, we’re looking at adding custom Scene Indexes for our renderers to feed the DependencyForwardingSceneIndex with dependencies specific to our needs.

One of the dependencies we’re currently looking at, however, is not a “when X is dirty, Y should be dirty” dependency but, rather, “when X is removed, Y should be dirty”. We’ve found we can still use a HdDependencySchema to achieve this, with:

    static HdLocatorDataSourceHandle dependedOnLocatorDataSource =
        HdRetainedTypedSampledDataSource<HdDataSourceLocator>::New(
            HdDataSourceLocator(TfToken("__no_locator__")));
    builder.SetDependedOnDataSourceLocator(dependedOnLocatorDataSource);

Since __no_locator__ doesn’t exist, we won’t generate any unnecessary dirtying, but since DependencyForwardingSceneIndex handles prim removal and does a blanket dirtying for all registered dependencies irrespective of the locator, we do get the dirtying for deletion - what we want.

So the question is: is this a brilliant/clever/sensible (ab)use of the dependency system, or is this a terrible horrible idea and I should really really be handling this in our scene index via _PrimsRemoved and sending a _SendPrimsDirtied ourselves?