Triagebot command to open associated zulip topic

[pnkfelix]

@spastorino and @pnkfelix were recently discussing ways to more readily link to associated zulip conversations, and to create fresh Zulip topcs when needed.

During that discussion, @spastorino suggested the idea of something like @triagebot discuss <optional-title>, which would be a way to ask triagebot to:

1. Create a zulip topic that links back to the current issue or PR (or, if a topic with the matching title and issue number already exists, then build a link to that pre-existing topic)
2. Add a comment that links to that topic to the issue/PR
3. Edit the issue/PR description to link to the Zulip discussion.

This would hopefully ease driving people towards Zulip for transient discussion (e.g. debating finer details of a posted comment, for example), and also help normalize the selection of Zulip topics (since right now the creation of associated Zulip topics is entirely up to the person creating the topic, and so it isn’t always easy for others to discover such pre-created topics)...

[pnkfelix]

Cc @Mark-Simulacrum

[Dylan-DPC-zz]

👍 This will also help us in the triage process

[spastorino]

Other "related" issues #12 and #1.
Related in the sense that we need to connect github issues with zulip topics and comments that we want to make in one of those places.
It would also be nice if we can easily discover links to zulip archive so we the bot can post on github when needed.

[mental32]

👋 Hi there!

I'm interested in implementing this :)
@pnkfelix could you direct me to the triagebot source/tracking issue where I can look into this further?

[LeSeulArtichaut]

@mental32 You can find the triagebot sources at https://github.com/rust-lang/triagebot
As for the implementation, you can probably get some ideas from the implementation of the notify-zulip feature

[apiraino]

@mental32 cool! For any question, don't hesitate to stop by our Zulip stream.

[camelid]

I believe this should be moved to rust-lang/triagebot – cc @Mark-Simulacrum

[spastorino]

@camelid as in the other issue, I guess we should open an issue on traigebot but still keep this one here and crosslink to the one in traigebot.