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Christopher Di Bella
05a7ecbd34
Determining that a type has trivial destruction requires checking whether all of its subobjects have trivial destruction and whether its type has a custom witness for `Destroy.Op`. This isn't possible when `Destroy` is the custodian for `Destroy.Op` and `SubobjectDestroy.Op`, so we need to make `SubobjectDestroy` its own interface. `Destroy.SelfDestruct` becomes a standalone function because it depends on `SubobjectDestroy` and `Destroy` being implemented, and is also responsible for generating any custom witnesses for both interfaces. Making `SelfDestruct` an interface was experimented with, but this required a blanket impl that caused issues for facet types. `Destroy` depends on `SubobjectDestroy` to be implemented. We'd ideally use `require impls SubobjectDestroy`, but it isn't complete yet, and it also causes problems when `Destroy` is implemented inside the class definition. We work around this by temporarily renaming the `Destroy` interface to `DestroyImpl`, and introducing a constraint called `Destroy` so that user code doesn't need to write `Core.SubobjectDestroy & Core.Destroy`.