Show rooms in common with another user

[Half-Shot]

This PR adds the ability to show the rooms you have in common with another user.

As far as I'm aware, there is no design for this yet so it would be good to get some input at some point. This is inspired by Telegram's "groups in common" feature.

Additionally, this now shows a subset of those rooms (up to 3) in the invite room preview screen:

Meta-issue: https://github.com/vector-im/riot-web/issues/14339
JS-SDK PR: matrix-org/matrix-js-sdk#1417
Synapse PR: matrix-org/synapse#7785

[nadonomy]

Definitely want this functionality, but need to think about how to expose it in the right panel in more detail so we don't add to the stockpile of design debt. Will look at this in earnest but more like a p2-1 where we have a few p1's in flight atm.

[Half-Shot]

@jryans sadly it looks like the preview doesn't show labs by default, which makes them a bit useless :(

[ShadowJonathan]

@Half-Shot What's the next step with this? What're we waiting for here?

[Half-Shot]

Waiting for Design to get back to me on feedback and possibly a mockup to work against. I don't think there is any dev task for me.

[Half-Shot]

N4d has got back to me with feedback, and I shall begin implementing :)

The headlines were:

• Make the shared users list a button, that when clicked will show you a memberlist like thing except with a rooms.
• Same for the invite dialogue

[nadonomy]

@Half-Shot just checking in on this as it's still on my list. :) If I'm blocking anything on this it may have slipped through the cracks on my side, so please DM if so.

[Half-Shot]

@nadonomy it's still on me to do the changes we talked about :)

[Half-Shot]

I've made some changes so that the shared room list now appears in the right panel. There is a lot left to do though:

• Design on invite / user info panel for the shared users button needs work
• No way to search / paginate the shared room list atm
• Dispatching right panel actions from the invite dialogue doesn't work

[tulir]

The new panel for shared rooms seems to be missing a back button to go back to the profile view or member list. The x button just closes the whole panel.

[t3chguy]

So looks like the API doesn't work on m.org which is quite a downer to this getting any further traction:

[tulir]

That looks like a misconfiguration on matrix.org, likely related to workers and routing requests

[t3chguy]

Blocked on matrix-org/synapse#10339

[aaronraimist]

Presumably the PR will fail gracefully if the server doesn't support it?

Why does matrix.org have to support the feature for it to go into Element? m.org doesn't support presence but Element does.

[t3chguy]

The PR gracefully fails with a user-presented error, as conditionally showing a section in the user info panel would be confusing

[MurzNN]

Instead of "Shared rooms" maybe better to use phrase "Mutual rooms"? Because we already use "Share" therm to share room action, and current "Shared rooms" looks like this person has shared those rooms personally for you.

[ShadowJonathan]

This is more a MSC comment, but yes, it has already been noted on the MSC; matrix-org/matrix-spec-proposals#2666 (comment)

After unblocking this on synapse's side, im interested in working on this PR, as half-shot is currently unavailable to finish this work.

[turt2live]

This has been open for so long I'm not really sure how to make it go forward at all.

It's clear we want this feature (per design review), but the implementation is subject to design iteration. The code is also almost certainly bitrotted to a point of no return - even if the merge conflicts can be dealt with, there's non-trivial architectural changes and modern code style to adhere to.

I think the best thing for this PR is to probably close it and if someone wants to reuse the code then it'll still be here. However, I will note that design work needs to be completed before someone can reasonably pick this up again.

If an issue hasn't been opened, please open one so it can get added to the design backlog.