[Bug]: Deduplicate VALARM creates duplicate calendar notification

[ChristophWurst]

⚠️ This issue respects the following points: ⚠️

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

Bug description

I have an event that has tons of VALARM components. It's probably caused by a bug in Evolution.

BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-PT15M
DESCRIPTION:Default Mozilla Description
X-EVOLUTION-ALARM-UID:7db2b9aea6d9ed8e3d05d090e24df8e399eb5cad
END:VALARM
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-PT15M
DESCRIPTION:Default Mozilla Description
X-EVOLUTION-ALARM-UID:0fbb4a0653e314ed123803620b490b44ed4c5be8
END:VALARM
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-PT15M
DESCRIPTION:Default Mozilla Description
X-EVOLUTION-ALARM-UID:73644b7baac717bbfea098df0e5fedc1cd6e92de
END:VALARM
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-PT15M
DESCRIPTION:Default Mozilla Description
X-EVOLUTION-ALARM-UID:cc7b0ab01d25278f0e1cf450107048ca6828e9dd
END:VALARM
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-PT15M
DESCRIPTION:Default Mozilla Description
X-EVOLUTION-ALARM-UID:b77009d5b1d879da58d2da8c4fd5307155b0a62b
END:VALARM
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER:-PT15M
DESCRIPTION:Default Mozilla Description
X-EVOLUTION-ALARM-UID:88363f16b6d74cd3b0e98f1cbbc351d7c7c60aef
END:VALARM

15 minutes before this event starts, I get overloaded with duplicate notifications.

Let's try to deduplicate identical notifications to work around these kind of client bugs.

Steps to reproduce

1. Import an event with two identical VALARMs
2. Wait for the alarm time to be reached

Expected behavior

See one single notification

Installation method

None

Nextcloud Server version

28

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

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

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response