Implement Weak::{strong_count, weak_count}
The counters are also useful on `Weak`, not just on strong references (`Rc` or `Arc`).
In situations where there are still strong references around, you can also get these counts by temporarily upgrading and adjusting the values accordingly. Using the methods introduced here is simpler to do, less error-prone (since you can't forget to adjust the counts), can also be used when no strong references are around anymore, and might be more efficient due to not having to temporarily create an `Rc`.
This is mainly useful in assertions or tests of complex data structures. Data structures might have internal invariants that make them the sole owner of a `Weak` pointer, and an assertion on the weak count could be used to ensure that this indeed happens as expected. Due to the presence of `Weak::upgrade`, the `strong_count` becomes less useful, but it still seems worthwhile to mirror the API of `Rc`.
TODO:
* [X] Tracking issue - https://github.com/rust-lang/rust/issues/57977
Closes https://github.com/rust-lang/rust/issues/50158
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.
In the comments of (closed, defunct) pull request #54884, Mazdak
"Centril" Farrokhzad noted that must-use annotations didn't work on an
associated function (what other communities might call a "static
method"). Subsequent logging revealed that in this case we have a
`Def::Method`, whereas the lint pass was only matching on
`Def::Fn`. (One could argue that those def-names are thereby
misleading—must-use for self-ful methods have always worked—but
documenting or reworking that can be left to another day.)
This commit introduces language items for `Arc` and `Rc` so that types
can later be checked to be `Arc` or `Rc` in the NLL borrow checker. The
`lang` attribute is currently limited to `stage1` as it requires a
compiler built with knowledge of the expected language items.
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
Add some more wording to module documentation regarding how
`Arc::clone()` works, as some users have assumed cloning Arc's
to work via dereferencing to inner value as follows:
use std::sync::Arc;
let myarc = Arc::new(1);
let myarcref = myarc.clone();
assert!(1 == myarcref);
Instead of the actual mechanic of referencing the existing
Arc value:
use std::sync::Arg;
let myarc = Arc::new(1);
let myarcref = myarc.clone();
assert!(myarcref == &myarc); // not sure if assert could assert this
in the real world
Previously, `is_unique` would not synchronize at all with a `drop` that returned
early because it was not the last reference, leading to a data race.
Fixes#51780
