First, some context: CREATE_SUB_THREAD is a message that appears in the parent when a child chat is created. In contrast, CREATE_THREAD and CREATE_SIDEBAR messages appear in the newly created chat (more details on those two here).

Admittedly, this is rather confusing. We should probably add some code comments in the messageTypes definition to clarify this... probably best for a separate Linear task / diff, though.

Regarding your question – I initially suspected you were right, that this case is not used. It doesn't look like a messageTypes.CREATE_SUB_THREAD will get created if the child is a sidebar.

However, I then ran a query on my keyserver to confirm this:

SELECT m.*, t.* FROM messages m LEFT JOIN threads t ON t.id = m.content WHERE m.type = 3 AND t.type = 5;

It turns out that there is exactly one CREATE_SUB_THREAD that refers to a SIDEBAR, for some reason. This probably happened in the past when we were still iterating on the code for the sidebars feature. Perhaps this was the reason that D598 was created. Either way, it means we cannot remove this case here, I think.

After reading through this code I think you're right, we don't ever show See threads....

For everybody's context, this code refers to the inbox, which shows a list of chats. Underneath each "top-level" (not sidebar) chat, we show a list of sidebars. We don't show all sidebars, however... we have some special logic that decides which sidebars to show.

I think in the past, if there were any sidebars at all (even if we didn't have any to show) we would still show ChatThreadListSeeMoreSidebars. However, at some point I think we decided to stop doing this. I think it was in D1487.

Probably D1487 should have deleted showingSidebarsInline, but I forgot to do this / didn't realize I should. We should maybe delete it, but in a separate Linear task / diff.

Since the old version (left side) here shows up as "channel" instead of "full chat", I assume there is a dependency on D4539 here. We should specify the dependency relationship explicitly – see here for details