Empty groups in addressbook silently not exported

[respiranto]

Prerequisites

• [X] I have searched for duplicate or closed issues
• [X] I can recreate the issue with all plugins disabled

Describe the issue

When exporting an addressbook via the Roundcube web UI ("Export all"), any group without members is silently ignored.

What I would expect is either that empty groups are exported, or a warning message indicating that the respective groups without members could not be exported and why.

In particular, I would expect that the result of "Export all" (if no error is indicated) can be used with "Import" to recreate the original addressbook.

Given that Roundcube exports to the vCard 3.0 format (c.f. RFC 2426), and represents groups as values of CATEGORIES for each group member, it seems impossible to actually export a group without members.

Hence, I suggest a warning message specifying that certain to be named groups could not be exported because not having any members if that is the case.

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Originally reported at the Debian BTS as Bug 1078777, where I was asked to report the bug here instead.

What browser(s) are you seeing the problem on?

Firefox

What version of PHP are you using?

v8.2

What version of Roundcube are you using?

master / 58721e3037671888f82d75fd8e91a8622405af45

JavaScript errors

No response

PHP errors

No response

[alecpl]

vCard 4.0 solves the problem, but of course it's not a simple solution. A warning makes sense.

[respiranto]

Is vCard 4.0 support planned?

Relatedly, might I suggest using an external vCard library (e.g., sabre/vobject) to help address this and the other vCard-related issues?