Check for just ... in stack etc, and raise with a useful error message

[dcherian]

Is your feature request related to a problem? Please describe.

The following doesn't work

import xarray as xr

da = xr.DataArray([[1,2],[1,2]], dims=("x", "y"))
da.stack(flat=...)

Describe the solution you'd like
This could be equivalent to

da.stack(flat=da.dims)

I think using ds.dims it should be fine for datasets too.

[max-sixty]

It still needs to be in a list! Otherwise it would be funky to do flat=[x, ...]

In [2]: import xarray as xr
   ...:
   ...: da = xr.DataArray([[1,2],[1,2]], dims=("x", "y"))
   ...: da.stack(flat=[...])

[dcherian]

Can we special-case ... and convert it to [...]?

[max-sixty]

I see @mathause agrees, so I am v happy to be voted into the minority, but I would vote against it — ... stands for x, y, not [x, y], and we're better to hold that line rather than have ... be a "mood of 'etc'".

I would def be up for updating the error message to check for this mistake.

(I worry that when people disagree we can stay with the status quo, so I really would be fine doing this if you think it's better. Also I didn't get the release done yesterday so I should be downweighted 😁 )

[dcherian]

— ... stands for x, y, not [x, y], and we're better to hold that line rather than have ... be a "mood of 'etc'".

Sounds good to me. "mood of 'etc'". is a great phrase!

I also agree with checking for ... and raising an error asking the user to enter [...]