More verbosity on NetCDF errors

[mikekryjak]

One of the most common gotchas for new users is not having the grid in their current directory (so common that I would say about half the users I know have been confused about this). This currently returns an unhelpful NetCDF error saying no such file or directory. The reason this is not very helpful is because A) it doesn't tell the user how to fix it and B) missing restart files give the same error message. This could be improved by:

• Changing the message to Grid not found in the current working directory
• Adding a separate message for restart files: Restart files not found in simulation directory

[dschwoerer]

The issue is that netCDF is raising that error.

So you should really report this with netCDF, that they should raise a more helpful error.
If they would include the full path that is requested and the current working directory, that should resolve this.

[ZedThree]

This isn't really a netCDF issue, we should definitely be able to raise more helpful exceptions on our side

[dschwoerer]

We can certainly also catch that and raise our own error. But netCDF should probably also include more details when raising that error. That would be helpful for all consumers of netCDF. I can submit a patch to netCDF, if they reject that, I do agree we should improve the message in BOUT++.

[mikekryjak]

I think a helpful message would be e.g. Cannot read grid file. We can't expect netCDF to know that we are trying to load a grid file. I think it's more than sufficient to just say there was a file-related error to do with the grid or with the restart files. Sure, if netCDF also said "can't read " that would be helpful, but it's not necessary to make a big improvement.

[dschwoerer]

Indeed, only BOUT++ can say Cannot read grid file, but netCDF can say no such File or directory 'grid-name.nc' with current working directory '/path/to/hermes-3' or no such File or directory 'examples/transport/BOUT.restart.3.nc' with current working directory '/path/to/hermes-3'

That would also tell you what you need to know?

[mikekryjak]

Yes, sure, that would obviously be very helpful too.