Pin stabilization
This implements the changes suggested in https://github.com/rust-lang/rust/issues/55766#issue-378417538 and stabilizes the `pin` feature. @alexcrichton also listed several "blockers" in that issue, but then in [this comment](https://github.com/rust-lang/rust/issues/55766#issuecomment-445074980) mentioned that they're more "TODO items":
> In that vein I think it's fine for a stabilization PR to be posted at any time now with FCP lapsed for a week or so now. The final points about self/pin/pinned can be briefly discussed there (if even necessary, they could be left as the proposal above).
Let's settle these last bits here and get this thing stabilized! :)
r? @alexcrichton
cc @withoutboats
deny intra-doc link resolution failures in libstd
Fixes#56693.
Until we land a fix for the underlying issue (#56922), we can at least fix the failures in libstd so they don't propagate to downstream crates.
This lets you write methods using `self: Rc<Self>`, `self: Arc<Self>`, `self: Pin<&mut Self>`, `self: Pin<Box<Self>`, and other combinations involving `Pin` and another stdlib receiver type, without needing the `arbitrary_self_types`. Other user-created receiver types can be used, but they still require the feature flag to use.
This is implemented by introducing a new trait, `Receiver`, which the method receiver's type must implement if the `arbitrary_self_types` feature is not enabled. To keep composed receiver types such as `&Arc<Self>` unstable, the receiver type is also required to implement `Deref<Target=Self>` when the feature flag is not enabled.
This lets you use `self: Rc<Self>` and `self: Arc<Self>` in stable Rust, which was not allowed previously. It was agreed that they would be stabilized in #55786. `self: Pin<&Self>` and other pinned receiver types do not require the `arbitrary_self_types` feature, but they cannot be used on stable because `Pin` still requires the `pin` feature.
Rename `CoerceSized` to `DispatchFromDyn`, and reverse the direction so that, for example, you write
```
impl<T: Unsize<U>, U> DispatchFromDyn<*const U> for *const T {}
```
instead of
```
impl<T: Unsize<U>, U> DispatchFromDyn<*const T> for *const U {}
```
this way the trait is really just a subset of `CoerceUnsized`.
The checks in object_safety.rs are updated for the new trait, and some documentation and method names in there are updated for the new trait name — e.g. `receiver_is_coercible` is now called `receiver_is_dispatchable`. Since the trait now works in the opposite direction, some code had to updated here for that too.
I did not update the error messages for invalid `CoerceSized` (now `DispatchFromDyn`) implementations, except to find/replace `CoerceSized` with `DispatchFromDyn`. Will ask for suggestions in the PR thread.
Update to a new pinning API.
~~Blocked on #53843 because of method resolution problems with new pin type.~~
@r? @cramertj
cc @RalfJung @pythonesque anyone interested in #49150
move the Pin API into its own module for centralized documentation
This implements the change proposed by @withoutboats in #49150, as suggested by @RalfJung in the review of #53104,
along with the documentation that was originally in it, that was deemed more appropriate in module-level documentation.
r? @RalfJung
It contains the re-exports that are in `std::prelude::v1`
but not in `core::prelude::v1`.
Calling it prelude is somewhat of a misnomer since (unlike those modules
in `std` or `core`) its contents are never implicitly imported in modules.
Rather it is intended to be used with an explicit glob import like
`use alloc::prelude::*;`.
However there is precedent for the same misnomer with `std::io::prelude`,
for example.
This new module is unstable with the same feature name as the `alloc` care.
They are proposed for stabilization together in RFC
https://github.com/rust-lang/rfcs/pull/2480
closes#45085
this commit adds an `atomic_cas` target option and an unstable `#[cfg(target_has_atomic_cas)]`
attribute to enable a subset of the `Atomic*` API on architectures that don't support atomic CAS
natively, like MSP430 and ARMv6-M.
