This is one more step towards completing #13231
This series of commits add support for default trait implementations. The changes in this PR don't break existing code and they are expected to preserve the existing behavior in the compiler as far as built-in bounds checks go.
The PR adds negative implementations of `Send`/`Sync` for some types and it removes the special cases for `Send`/`Sync` during the trait obligations checks. That is, it now fully relies on the traits check rather than lang items.
Once this patch lands and a new snapshot is created, it'll be possible to add default impls for `Send` and `Sync` and remove entirely the use of `BuiltinBound::{BoundSend,BoundSync}` for positive implementations as well.
This PR also removes the restriction on negative implementations. That is, it is now possible to add negative implementations for traits other than `Send`/`Sync`
This is not a complete implementation of the RFC:
- only existing methods got updated, no new ones added
- doc comments are not extensive enough yet
- optimizations got lost and need to be reimplemented
See https://github.com/rust-lang/rfcs/pull/528
Technically a
[breaking-change]
- Don't allow multiple default trait implementations
- Allow positive trait implementations just for structs and enums when
there's a default implementation for such trait.
This commit stabilizes `std::borrow`, making the following modifications
to catch up the API with language changes:
* It renames `BorrowFrom` to `Borrow`, as was originally intended (but
blocked for technical reasons), and reorders the parameters
accordingly.
* It moves the type parameter of `ToOwned` to an associated type. This
is somewhat less flexible, in that each borrowed type must have a
unique owned type, but leads to a significant simplification for
`Cow`. Flexibility can be regained by using newtyped slices, which is
advisable for other reasons anyway.
* It removes the owned type parameter from `Cow`, making the type much
less verbose.
* Deprecates the `is_owned` and `is_borrowed` predicates in favor of
direct matching.
The above API changes are relatively minor; the basic functionality
remains the same, and essentially the whole module is now marked
`#[stable]`.
[breaking-change]
This commit is an implementation of [RFC 823][rfc] which is another pass over
the `std::hash` module for stabilization. The contents of the module were not
entirely marked stable, but some portions which remained quite similar to the
previous incarnation are now marked `#[stable]`. Specifically:
[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0823-hash-simplification.md
* `std::hash` is now stable (the name)
* `Hash` is now stable
* `Hash::hash` is now stable
* `Hasher` is now stable
* `SipHasher` is now stable
* `SipHasher::new` and `new_with_keys` are now stable
* `Hasher for SipHasher` is now stable
* Many `Hash` implementations are now stable
All other portions of the `hash` module remain `#[unstable]` as they are less
commonly used and were recently redesigned.
This commit is a breaking change due to the modifications to the `std::hash` API
and more details can be found on the [RFC][rfc].
Closes#22467
[breaking-change]
The big change here is that we update the object-safety rules to prohibit references to `Self` in the supertrait listing. See #22040 for the motivation. The other change is to handle the interaction of defaults that reference `Self` and object types (where `Self` is erased). We force users to give an explicit type in that scenario.
r? @aturon
Take 2. This PR includes a bunch of refactoring that was part of an experimental branch implementing [implied bounds]. That particular idea isn't ready to go yet, but the refactoring proved useful for fixing #22246. The implied bounds branch also exposed #22110 so a simple fix for that is included here. I still think some more refactoring would be a good idea here -- in particular I think most of the code in wf.rs is kind of duplicating the logic in implicator and should go, but I decided to post this PR and call it a day before diving into that. I'll write a bit more details about the solutions I adopted in the various bugs. I patched the two issues I was concerned about, which was the handling of supertraits and HRTB (the latter turned out to be fine, so I added a comment explaining why.)
r? @pnkfelix (for now, anyway)
cc @aturon
[implied bounds]: http://smallcultfollowing.com/babysteps/blog/2014/07/06/implied-bounds/
This overlaps with #22276 (I left make check running overnight) but covers a number of additional cases and has a few rewrites where the clones are not even necessary.
This also implements `RandomAccessIterator` for `iter::Cloned`
cc @steveklabnik, you may want to glance at this before #22281 gets the bors treatment
