cli/discover: remove local collections if the remote collection is deleted

[dilyanpalauzov]

This works when the destination backend is 'filesystem' and the source is CalDAV-calendar-home-set.

[lgtm-com]

This pull request introduces 1 alert when merging fc49ba8 into a42906b - view on LGTM.com

new alerts:

• 1 for Except block handles 'BaseException'

[WhyNotHugo]

I'm not a fan of doing this by default.

I've several times deleted a remote collection with the intent of pushing my local copy elsewhere. If my local copy were auto-deleted, I would have lost it permanently.

I'm sure there's other scenarios where it might lead to people inadvertently losing data. I don't want people finding out about this feature the hard way 😅

I'd be okay with this with any of these changes a dedicated flag to enable / disable the behaviour. For example, something like:

[pair calendars]
# ...
prune_collections = true

[dilyanpalauzov]

I am utterly fine in anyway this is implemented. I provided my way of doing it. I have also

diff --git a/vdirsyncer/cli/utils.py b/vdirsyncer/cli/utils.py
--- a/vdirsyncer/cli/utils.py
+++ b/vdirsyncer/cli/utils.py
@@ -404,7 +404,7 @@ def handle_collection_not_found(config, collection, e=None):
                        .format(f'{e}\n' if e else '',
                                json.dumps(collection), storage_name))
 
-    if click.confirm('Should vdirsyncer attempt to create it?'):
+    if True or click.confirm('Should vdirsyncer attempt to create it?'):
         storage_type = config['type']
         cls, config = storage_class_from_config(config)
         config['collection'] = collection

to create automatically Calendars, once they are created on the server. I want to have a system that periodically syncs and gets the state on the server (incl. creating new calendars and deleting old ones). For implicit calendar creation, the name prune_collection is not good, if both options will get the same name.

[dilyanpalauzov]

Moved to #869.