feat: hide caldav server settings if no app uses the caldav backend

[st3iny]

• Resolves: none

Summary

This PR introduces a dependency type to info.xml called backends which can be used by apps to express their intent to use a specific server-side backend. Currently, the only backend to be required is caldav.

The caldav server admin settings will be hidden if no app is requiring the caldav backend.

Exemplary info.xml

<?xml version="1.0"?>
<info xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance"
	  xsi:noNamespaceSchemaLocation="https://apps.nextcloud.com/schema/apps/info.xsd">
	<id>calendar</id>
	<name>Calendar</name>
	<summary>A Calendar app for Nextcloud</summary>
	<version>4.8.0-alpha.1</version>
	<namespace>Calendar</namespace>
	<!-- [...] -->
	<dependencies>
		<php min-version="8.0" max-version="8.3" />
		<nextcloud min-version="27" max-version="30" />
		<backend>caldav</backend>
	</dependencies>
	<!-- [...] -->
</info>

Hidden settings section

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[ChristophWurst]

This PR introduces a new top level key in info.xml called backends which can be used by apps to express their intent to use a specific server-side backend. Currently, the only backend to be required is caldav.

If we are changing info.xsd we can also move this into the dependencies element. I think that makes the meaning clearer. The current approach is ambiguous as it could mean that the apps that list caldav as backend are providing it.

[ChristophWurst]

Looks good so far!

[ChristophWurst]

don't forget to also submit these changes to the appstore repo

[st3iny]

nextcloud/appstore#1414

[tcitworld]

The caldav server admin settings will be hidden if no app is requiring the caldav backend.

So you won't be able to set the caldav settings if you want to use calendar sync with clients without the Calendar app? Apart from hiding the settings, is there any more consequences under consideration?

[ChristophWurst]

Yes, that is the behavior that was decided. We simply hide the settings. The case that someone uses the caldav backend without a Nextcloud frontend app is not covered.

[ChristophWurst]

I guess we should add a note to https://docs.nextcloud.com/server/latest/admin_manual/groupware/calendar.html for admins who can't find the settings

[nickvergessen]

@st3iny Please document in https://docs.nextcloud.com/server/latest/developer_manual/app_publishing_maintenance/app_upgrade_guide/upgrade_to_30.html#id1
(Saw the ticket, just putting it to all PRs)

[nickvergessen]

It's a bit problematic that we don't have CI in place to confirm this, but https://github.com/nextcloud/appstore/blob/master/nextcloudappstore/api/v1/release/info.xsd needs to be kept in sync.

[ChristophWurst]

nextcloud/appstore#1414