Use m.fully_read to implement "Jump to first unread message"

[krombel]

Sync contains the following data which riot uses to identify what the latest read message is to implement "Jump to first unread message" and to eventually show a bar between read and unread messages when opening a room
That data is tracked user-only and independent of m.receipt.

Here a snippet:

{
    "rooms": {
        "join": {
            "!roomID123456:matrix.org": {
                "unread_notifications": {
                    "highlight_count": 0,
                    "notification_count": 0
                },
                "account_data": {
                    "events": [{
                        "content": {
                            "event_id": "$messageIDofLastReadMessage:matrix.org"
                        },
                    "type": "m.fully_read"
                    }]
                }
            }
        }
    }
}

Hint:
You have to allow m.fully_read as type in account_data for rooms in default_filter

[t3chguy]

Riot doesn't use the RM (m.fully_read) for calculating number of unreads, it uses the Read Receipt

[t3chguy]

the RM is used to Jump to first unread message. only.

[t3chguy]

Relevant: element-hq/riot-meta#66

[krombel]

I updated the description to match the real goal of m.fully_read