Unhelpful concatenate failure message

[PAGWatson]

Hello, I just spent a fair amount of time tracking down why two cubes with differing time dimensions would not concatenate. The error message printed by concatenate_cube() was simply:

ConcatenateError: failed to concatenate into a single cube. An unexpected problem prevented concatenation. Expected only a single cube, found 2.

The error turned out to be that the time series overlapped by one day - my silly fault, of course, but it would be useful if a check for dimensions overlapping could be added in concatenate_cube().

[DPeterK]

Hi @PAGWatson, thanks for raising this. This is a known shortcoming in concatenate, which unfortunately is simply endemic of the fact that concatenate is less advanced than merge. The error message you've hit here is the general catch-all case when something outside of what the concatenate framework can check for is nevertheless preventing the concatenate process from returning only a single cube.

Unfortunately then there's not really a short fix for this - concatenate would require some significant effort to improve this situation. This does add weight to the argument that we should consider a more significant change to the processes used to join cubes in Iris to try and make it more general, more robust, and less separated.

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