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Jonathan Brouwer
53e67f248d
Eliminate `QueryLatchInfo`. The boolean `complete` flag indicates whether the `waiters` vec is still in use, which means the `waiters` vec must be empty when `complete` is true. This is achieved by using `drain` on the waiters just after `complete` is set. We can do better by using the type system to make invalid combinations impossible. This commit removes `complete` and puts the waiters inside an `Option`. `Some` means the query job is still active, and `None` once it is complete. And `QueryLatchInfo` is eliminated. (The `Arc<Mutex<Option<Vec<Arc<QueryWaiter<'tcx>>>>>>` type is a mouthful, but when it's all in one place I find it easier to understand than when it's split across two types. And we can use `Option` methods like `as_ref`, `as_mut`, and `take`, which is nice.) r? @petrochenkov
For more information about how the query system works, see the rustc dev guide.