MSC3015: Room state personal overrides

proposals/3015-room-personal-overrides.md

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+# MSC3015: Room state personal overrides 
+
+Very often users want to personally rename rooms to see it in list like they wants, especially for DM rooms. But room
+name is shared thing, so if they rename it for yourself, all other members will see this rename too. 
+
+Examples of problem: 
+
+1. Very often other people want to rename DM rooms with me and can do this, because we both are admins. So they set the
+   alternative name of that DM room (eg `Korepov Alexey` instead of `Alexey Murz Korepov`) - this works well on their
+   side. But, as result on my side, I see that room in my rooms list with my name, instead of remote user name.
+
+2. The user has two DM rooms with different Matrix users, but both have name "Alice" without avatar. As result they see
+   two identical rooms in the list with same name and it is unclear which room is which.
+   If attempting to solve this problem via renaming rooms, the problem described in 1 occurs.
+
+3. This problem often happens for rooms from bridged networks, when we talk with same person via different networks, and
+   want to mark each room personally. This can be solved via adding suffixes with remote network name to room name on
+   Bridge side, but people want to change other parts of room name too. For example, one person can have different names
+   in each network (eg "Alexey Korepov" on VK, "Korepov Alexey" on Skype, "Alex" on WhatsApp, "Murz" on Telegram), and I
+   want to see all rooms with him as similar names, and also maybe attach personal avatar to that rooms.
+
+4. Some networks (eg IRC, Slack) also have no per-room avatars, so they are bridged with empty or identical avatars, that
+   makes harder to diffirentiate them in avatar-only list of rooms, so users want to override the avatars personally too.
+
+Most of other modern messengers (Telegram, Skype, Viber, WhatsApp) already have this feature, but only for DM rooms via
+reusing smartphone's addressbook to store personal names of contacts. And moving from that messengers to Matrix confuses
+the people, because they can't rename personal chats in his own list like before.
+
+# Proposal
+
+For solve this problem I propose to use [room's account
+data](https://matrix.org/docs/spec/client_server/r0.6.0#put-matrix-client-r0-user-userid-rooms-roomid-account-data-type)
+item with same key as overriden state event type, but with `override.` prefix, to store personal overrides of needed 
+state any room for each user individually, and overriden content, here is example for room name and avatar overrides:
+
+**`override.m.room.name`**
+```json
+{
+  "name": "The room name"
+}
+```
+**`override.m.room.avatar`**
+```json
+{
+  "info": {
+    "h": 398,
+     "mimetype": "image/jpeg",
+     "size": 31037,
+     "w": 394
+  },
+  "url": "mxc://example.org/JWEIFJgwEIhweiWJE"
+}
+```
+
+By default those items are absent. They are added only when user make the personal override, and cleared if user
+remove the personal name for room (or make it empty). Regarding to spec, the account data's key can't be deleted,
+so if user wants to remove the personal override (aka "Reset to default"), the value of the key should become 
+empty (`{}`).
+
+Those overrides can be used for all types of rooms: DMs (to rename personal contacts or set custom photo to avatar, 
+add notes to topic), public rooms (to set desired personal name, eg in user's native language), public Spaces, etc.
+
+For not allow to override bad things, I think we must define an allowlist of state types, that can be overriden:
+- `m.room.name`
+- `m.room.avatar`
+- `m.room.topic`
+- and maybe also `m.room.pinned_events` for implement personal pinning?
+
+Also we can allow even `m.room.member` for personally override room members names and avatars too. But for this task
+may be better to wait for user profiles implementation from [MSC1769: Extensible profiles as rooms](https://github.com/matrix-org/matrix-doc/pull/1769),
+to override profile info values via same technic like in regular rooms, this will allow even complements the remote 
+profiles: add personal phone number for your contact, that missed in public profile and know only by you, leave personal
+notes about that contact, etc.
+
+# Client support
+
+## Displaying:
+
+When client displays the room information (eg in room list), for all allowlisted state keys it should lookup the 
+corresponding room's account data key with `override.` prefix, if it exists and not empty - replace the content
+of that state event to overriden before rendering. Clients may show both values (global and personal) and explain
+that this room have an overriden personal value, that is seen only for current user.
+
+## Adding, removing, renaming:
+
+Clients should provide a way to privately override allowed room state values and clearly explain the difference 
+between global and personally overriden values.
+
+In room list this can be implemented via "Rename room personally" or "Set personal name for room" menu item in
+right-click menu, and similar way for avatar.
+
+In room settings page personal name can be implemented via button "Set personal name for this room", which will be
+available even if user have no permission to change the room name, and same for avatar. If personal value is filled,
+it should be shown near the global room value, with ability to remove it.
+
+# Server support
+
+This MSC does not need any changes on server side.
+
+# Potential issues
+
+1. User can set a personal value that is identical to the current global room value. This may cause confusion as the
+   client will not see future global value changes. Clients should consider providing the user a suggestion to remove
+   personal override for follow future renames of room. And for other renames - explain that personal override will not 
+   follow the future changing of global value.
+
+# Alternatives
+
+1. Instead of setting personal name for rooms via
+   [room's account_data](https://matrix.org/docs/spec/client_server/r0.6.0#put-matrix-client-r0-user-userid-rooms-roomid-account-data-type)
+   we can set personal names directly for Matrix users (mxid), like other messengers (Telegram, WhatsApp, etc) doing.
+   This will give similar behavior for DM rooms, but will make impossible to set personal names of rooms with several
+   users (or DM rooms with bots), and intersects with per-room display names feature. And this way will be better to
+   implement together with "[Contacts](https://github.com/vector-im/roadmap/issues/10)" feature, which is planned in
+   Element and in issue [Contact List & Renaming Contacts](https://github.com/matrix-org/matrix-doc/issues/2936).
+
+# Unstable prefix
+
+Clients should use `org.matrix.msc3015.[m.state.type].override` for room account data key instead of proposed, while this
+MSC has not been included in a spec release.