I don't fully agree. IMs are a great place to discuss issues in a semi-synchronous way. Telecon or face-to-face meetings are sometimes better in velocity, but IMs have some edge on bringing random people happen to be online into the discussion. And it can also bring a different audience into the issue than bug reporting tools or mailing list.

When this issue was brought into the group, it just took several hours for curious people there to collaboratively find the conclusion. This is something unlikely to happen in any other form of discussions based on my experience.

But I agree that group chat is not a great way to record it, and that's why the findings are recorded on the GitHub issue, and group members also encouraged the author to write this up. Then it got posted on HN and on /r/rust by two different group members as well. (The author's initial posting on HN was mysteriously taken down, so the op here helped posting it again.)