Comment (by Samuel Cupp):

Looking more closely at the thorn, I feel its important to point out that it doesn’t have any READ or WRITE declarations. This means that no one has updated it to use the PreSync features. So even if you resolve the boundary warnings, it won’t really benefit you because the READ/WRITE declarations aren’t there yet. I’m sure the maintainers of Lean would be appreciative if you added them. However, if you don’t have the time to add those to the schedule.ccl, then none of the presync_mode settings can actually be used.

I do think I have found the source of the issue, though. The issue is that the PreSync feature isn’t being informed of what the BCs are. The old boundary thorn uses Boundary_SelectGroupForBC to control how BCs are applied, while PreSync depends on the driver function Driver_SelectGroupForBC. At some point, I had suggested that this call be added to the Boundary_SelectGroupForBC as well for the sake of old thorns, but that doesn’t seem to have happened.

I did a pretty ugly edit real quick by duplicating the boundary f’n calls with driver calls. This runs until it hits an error because PreSync tries to apply boundary conditions on something that isn’t valid in the interior (and nothing is valid anywhere because of paragraph 1).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2723/no-boundary-conditions-registered-for