What should be the default diff (if no arguments are given)?

[aawsome]

Hi everybody!

I just made #1639 which handles all kind of possible arguments for the diff command in an (hopefully) meaningful and understandable way.

There is however one open case (which is currently not supported): What should be the output of rustic diff (i.e. without any argument)?

IMO, there are three possible options which make sense:

1. let it behave like rustic diff latest latest~1, like in Feature request: Diff - show changes for latest backup by default restic/restic#1965
2. let it behave like rustic diff latest, i.e. compare the latest snapshot with local path (see fix: handle all arg combinations for diff command #1639)
3. don't support it as it is kind of ambiguous

What are your opinions? Are there additional sensible defaults?

[aawsome]

Here we have 3:1 for rustic diff latest latest~1.
On discord, we had a majority of 13 votes for rustic diff latest and 3 votes for rustic diff latest latest~1.

So, altogether rustic diff latest is the favorite, which will be implemented.