[Bug]: local folder are deleted by sync with read-only groupfolder

[HFlor]

⚠️ Before submitting, please verify the following: ⚠️

• This is a bug, not a question or a configuration issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server and Desktop Client are up to date. See Server Maintenance and Release Schedule and Desktop Releases for supported versions.
• I agree to follow Nextcloud's Code of Conduct

Bug description

without any question the local folder are deleted

Steps to reproduce

1. Creation of a group folder without write permission (via group)
2. A user in the group used above adds the folder synchronization with a local folder with subfolders and files
3. all local subfolders are deleted, only the files in the local folder (top level) are still there.

Expected behavior

at least a warning that all data should be deleted should be displayed

Which files are affected by this bug

no log entry

Operating system

Windows

Which version of the operating system you are running.

Windows 10

Package

Official Windows MSI

Nextcloud Server version

20.0.2

Nextcloud Desktop Client version

3.14.3

Is this bug present after an update or on a fresh install?

Fresh desktop client install

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

Are you using an external user-backend?

• Default internal user-backend
• LDAP/ Active Directory
• SSO - SAML
• Other

Nextcloud Server logs

Additional info

No response

[HFlor]

Server Version is 30.0.2

[Rello]

Hello @HFlor

I am not sure about this one
A user in the group used above adds the folder synchronization with a local folder with subfolders and files

do you mean that you select the group folder to be synced - but locally there was already a folder with that name and this one is then cleared?
If this is the case - then this is by design. Sync is sync. and if the server contains less files, the local version will be mirrored.

let me know if there is a misunderstanding

[HFlor]

No, it is when setting up a new synchronization of the local data. This has never been set up as a sync target. I recorded it:
https://youtu.be/UE6onK7TMjc