MessageListView could be disposed twice

[gnprice]

This is the issue thread for the bug fixed by:

• store: Ensure sole ownership of MessageListView #1340

See also chat thread:
https://chat.zulip.org/#narrow/channel/243-mobile-team/topic/MessageListView.20lifecycle/near/2083074

I believe this was a crash bug — the stack trace in #1340 was while the Flutter framework is updating the element tree, and I think an exception there can leave things in an inconsistent state where the app no longer responds normally. Not sure of that, though.

OTOH it's probably hard to trigger: as far as I know we never heard from someone running into symptoms from it, and learned about it instead because @PIG208 was studying the code as part of work on #1183.

[gnprice]

@PIG208 do you know what the symptom was for this bug? (Did you happen to try triggering it in the app at some point, and see the effect?)

If you don't already know, no need to spend time investigating; the bug's already fixed at this point. (And it's not among the few kinds of bug that need followup after that.)

[PIG208]

This only happens when you are on a message list page and log out. At the time I triggered on a draft branch #1183 before we have the fix in #1340, by invalidating the API key. The error dialog would show up, and the app become unusable afterwards with runtime errors about references to inactive/out-of-tree elements, but I'm not sure about the details. This was on a development build, though.

[gnprice]

Thanks. OK, and I believe the condition "you are on a message list page and log out" is impossible in main in the actual app, right? I think the only way to get logged out is by using the UI for that on the choose-account page, and that can't be above a message-list page on the stack.

So in that case this was a latent bug: it wasn't actually possible to trigger in the app given the whole rest of the codebase.

[PIG208]

You can probably be on a message list page, follow notification for another account to see the loading screen, and navigate to the choose-account page from there. But that's of course not a common situation.

[gnprice]

Yeah, and I don't think the notification would get you a way to navigate to the choose-account page anyway — that's a special feature of the HomePage loading page.

(With the MessageListPage that gets pushed by following a notification, if the loading takes a long time and you want to bail out you can just hit back. That's not an option on HomePage, which is why we added that wrinkle.)