Can’t assign a marker to types wrapped by async functions

[JustusAdam]

This came up when testing DFPP on Lemmy for our Eurosys submission. There was a label applied to type LocalUserView. DFPP can see that

LocalUserView::find_by_email_or_name(conn, &username_or_email) returns type LocalUserView and apply the label correctly, but when it’s wrapped in the blocking() function, it can’t anymore.

// problem with async blocking function (we use a type walk, need to go handle impl Future structure to infer the type here)
let local_user_view = apply_localuserview_label(blocking(context.pool(), move |conn| {
  LocalUserView::find_by_email_or_name(conn, &username_or_email)
})
.await?)
.map_err(|e| LemmyError::from_error_message(e, "couldnt_find_that_username_or_email"))?;

Also ran into this error with Flowistry intermittently when running DFPP on Lemmy:

thread 'rustc' panicked at 'internal error: entered unreachable code', 
/Users/carolynzech/.cargo/git/checkouts/flowistry-58afecc4a577121d/6e1de04/crates/flowistry/src/mir/borrowck_facts.rs:93:38

I couldn’t establish any clear pattern for when it was happening, and cargo clean always fixed it, so maybe not a huge deal.