Check if parent variable is an array in readblock!

[tiemvanderdeure]

Implement a check to determine if the parent variable is an array in readblock!

readblock! normally isn't called for variables with array parent, but in rafaqz/Rasters.jl#966 we found a case where it is and this immediately errors.

This is a bit of a temporary fix to avoid that error. In the long term 1) CDM changes will affect this a little bit, 2) maybe we want to change DA.@implement_diskarray Variable to `DA.@implement_diskarray Variable{<:Any,<:Any,DiskValues}?, 3) maybe we could avoid eagerly reading some values.

[tcarion]

Thanks for the PR!

I need to catch up a little bit with this issue and investigate a little bit what could be done better in GRIBDatasets, but let's stick to this fix for now

[tcarion]

I'm realizing that these lines were already dispatching properly between normal Array and DiskArray

And this doesn't seem to fix the Rasters issue

[tiemvanderdeure]

I'm realizing that these lines were already dispatching properly between normal Array and DiskArray

The problem occurs only when a Variable is wrapped in something else (in the case of Rasters, a ModifiedDiskArray), then you index into the wrapper, which forwards to readblock! on the wrapper, which forwards to readblock! on the Variable, which then errors. And those getindex dispatches never get called.

There are a few other Rasters bugs but this should help

[tcarion]

Ok I understand better now, thank you for the clarification!

I don't know what would be the cleanest long-term solution here. Given the design of GRIB files (as shortly described here), I don't see how non-horizontal dimensions lookups could be something else than memory arrays. But the choice of loading horizontal dimension lookups into memory was pretty arbitrary, and if it's causing issues, I can try to modify the GRIBDatasets design to keep them on disk.