`process_predicates` returns a
`Result<Option<Vec<PredicateObligation>>>`. `process_obligation` calls
it and then fiddles with the output (using `map`, `map`, `into_iter`,
`collect`) to produce a a
`Result<Option<Vec<PendingPredicateObligation>>>`.
This function is sufficiently hot that the fiddling is expensive. It's
much better for `process_predicate` to directly return a
`Result<Option<Vec<PendingPredicateObligation>>>` because `Ok(None)`
accounts for ~90% of the results, and `Ok(vec![])` accounts for another
~5%.
Add Future and task system to the standard library
This adds preliminary versions of the `std::future` and `std::task` modules in order to unblock development of async/await (https://github.com/rust-lang/rust/issues/50547). These shouldn't be considered as final forms of these libraries-- design questions about the libraries should be left on https://github.com/rust-lang/rfcs/pull/2418. Once that RFC (or a successor) is merged, these APIs will be adjusted as necessary.
r? @aturon
Accept `..` in incorrect position to avoid further errors
We currently give a specific message when encountering a `..` anywhere
other than the end of a pattern. Modify the parser to accept it (while
still emitting the error) so that we don't also trigger "missing fields
in pattern" errors afterwards.
Add suggestions to either remove trailing `,` or moving the `..` to the
end.
Follow up to #49268.
Closes#49137, the tracking issue for `NonZero*`,
as this was the last remaining open question.
Note that `ptr::NonNull<T>` already documents a similar guarantee.
Refactor the const eval diagnostic API
* no longer report "const eval error" for things that have typeck errors
* errors and lints have saner spans and messages
* unified the diagnostic logic (const eval errors were slightly different depending on where they were reported, and there was also code duplication between the different reporters)
* report errors if an erroneous constant is used inside a promoted (fixes most of #50814)
