Rollup merge of rust-lang#88893 - Mark-Simulacrum:relnotes, r=pietroa…

…lbini

Add 1.56.0 release notes

Notable things:

* Rustdoc section currently absent, for lack of things to call out that I could find. It seems like rust-lang#87451 is the only potential candidate, but that seems like more of a bugfix and doesn't seem to warrant inclusion to me. But we can add it if desired.

As with the 1.55.0 release notes, my intent is to leave this open for approximately 1-2 weeks at the early part of the cycle, and then merge it in (after fixing any feedback). Further iteration can happen in subsequent issues (and PRs).

[Rendered](https://github.com/Mark-Simulacrum/rust/blob/relnotes/RELEASES.md)

RELEASES.md

@@ -1,3 +1,188 @@
+Rust 1.56.0 (2021-10-21)
+========================
+
+Language
+--------
+
+- [The 2021 Edition is now stable.][rust#88100]
+  See [the edition guide][rust-2021-edition-guide] for more details.
+- [You can now specify explicit discriminant values on any Rust enum.][rust#86860]
+- [The pattern in `binding @ pattern` can now also introduce new bindings.][rust#85305]
+- [Union field access is permitted in `const fn`.][rust#85769]
+
+[rust-2021-edition-guide]: https://doc.rust-lang.org/nightly/edition-guide/rust-2021/index.html
+
+Compiler
+--------
+
+- [Upgrade to LLVM 13.][rust#87570]
+- [Support memory, address, and thread sanitizers on aarch64-unknown-freebsd.][rust#88023]
+- [Allow specifying an deployment target version for all iOS targets][rust#87699]
+- [Warnings can be forced on with `--force-warn`.][rust#87472]
+  This feature is primarily intended for usage by `cargo fix`, rather than end users.
+- [Promote `aarch64-apple-ios-sim` to Tier 2\*.][rust#87760]
+- [Add `powerpc-unknown-freebsd` at Tier 3\*.][rust#87370]
+
+\* Refer to Rust's [platform support page][platform-support-doc] for more
+information on Rust's tiered platform support.
+
+Libraries
+---------
+
+- [Allow writing of incomplete UTF-8 sequences via stdout/stderr on Windows.][rust#83342]
+  The Windows console still requires valid Unicode, but this change allows
+  splitting a UTF-8 character across multiple write calls. This allows, for
+  instance, programs that just read and write data buffers (e.g. copying a file
+  to stdout) without regard for Unicode or character boundaries.
+- [Prefer `AtomicU{64,128}` over Mutex for Instant backsliding protection.][rust#83093]
+  For this use case, atomics scale much better under contention.
+- [Implement `Extend<(A, B)>` for `(Extend<A>, Extend<B>)`][rust#85835]
+- [impl Default, Copy, Clone for std::io::Sink and std::io::Empty][rust#86744]
+- [`impl From<[(K, V); N]>` for all collections.][rust#84111]
+- [Remove `P: Unpin` bound on impl Future for Pin.][rust#81363]
+- [Treat invalid environment variable names as non-existent.][rust#86183]
+  Previously, the environment functions would panic if given a variable name
+  with an internal null character or equal sign (`=`). Now, these functions will
+  just treat such names as non-existent variables, since the OS cannot represent
+  the existence of a variable with such a name.
+
+Stabilised APIs
+---------------
+
+- [`std::os::unix::fs::chroot`]
+- [`Iterator::intersperse`]
+- [`Iterator::intersperse_with`]
+- [`UnsafeCell::raw_get`]
+- [`BufWriter::into_parts`]
+- [`core::panic::{UnwindSafe, RefUnwindSafe, AssertUnwindSafe}`]
+  These APIs were previously stable in `std`, but are now also available in `core`.
+- [`Vec::shrink_to`]
+- [`String::shrink_to`]
+- [`OsString::shrink_to`]
+- [`PathBuf::shrink_to`]
+- [`BinaryHeap::shrink_to`]
+- [`VecDeque::shrink_to`]
+- [`HashMap::shrink_to`]
+- [`HashSet::shrink_to`]
+- [`task::ready!`]
+
+These APIs are now usable in const contexts:
+
+- [`std::mem::transmute`]
+- [`[T]::first`][`slice::first`]
+- [`[T]::split_first`][`slice::split_first`]
+- [`[T]::last`][`slice::last`]
+- [`[T]::split_last`][`slice::split_last`]
+
+Cargo
+-----
+
+- [Cargo supports specifying a minimum supported Rust version in Cargo.toml.][`rust-version`]
+  This has no effect at present on dependency version selection.
+  We encourage crates to specify their minimum supported Rust version, and we encourage CI systems
+  that support Rust code to include a crate's specified minimum version in the text matrix for that
+  crate by default.
+
+Compatibility notes
+-------------------
+
+- [Update to new argument parsing rules on Windows.][rust#87580]
+  This adjusts Rust's standard library to match the behavior of the standard
+  libraries for C/C++. The rules have changed slightly over time, and this PR
+  brings us to the latest set of rules (changed in 2008).
+- [Disallow the aapcs calling convention on aarch64][rust#88399]
+  This was already not supported by LLVM; this change surfaces this lack of
+  support with a better error message.
+- [Make `SEMICOLON_IN_EXPRESSIONS_FROM_MACROS` warn by default][rust#87385]
+- [Warn when an escaped newline skips multiple lines.][rust#87671]
+- [Calls to `libc::getpid` / `std::process::id` from `Command::pre_exec`
+   may return different values on glibc <= 2.24.][rust#81825]
+   Rust now invokes the `clone3` system call directly, when available, to use new functionality
+   available via that system call. Older versions of glibc cache the result of `getpid`, and only
+   update that cache when calling glibc's clone/fork functions, so a direct system call bypasses
+   that cache update. glibc 2.25 and newer no longer cache `getpid` for exactly this reason.
+
+Internal changes
+----------------
+These changes provide no direct user facing benefits, but represent significant
+improvements to the internals and overall performance of rustc
+and related tools.
+
+- [LLVM is compiled with PGO in published x86_64-unknown-linux-gnu artifacts.][rust#88069]
+  This improves the performance of most Rust builds.
+- [Unify representation of macros in internal data structures.][rust#88019]
+  This change fixes a host of bugs with the handling of macros by the compiler,
+  as well as rustdoc.
+
+[`std::os::unix::fs::chroot`]: https://doc.rust-lang.org/stable/std/os/unix/fs/fn.chroot.html
+[`Iterator::intersperse`]: https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html#method.intersperse
+[`Iterator::intersperse_with`]: https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html#method.intersperse
+[`UnsafeCell::raw_get`]: https://doc.rust-lang.org/stable/std/cell/struct.UnsafeCell.html#method.raw_get
+[`BufWriter::into_parts`]: https://doc.rust-lang.org/stable/std/io/struct.BufWriter.html#method.into_parts
+[`core::panic::{UnwindSafe, RefUnwindSafe, AssertUnwindSafe}`]: https://github.com/rust-lang/rust/pull/84662
+[`Vec::shrink_to`]: https://doc.rust-lang.org/stable/std/vec/struct.Vec.html#method.shrink_to
+[`String::shrink_to`]: https://doc.rust-lang.org/stable/std/string/struct.String.html#method.shrink_to
+[`OsString::shrink_to`]: https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html#method.shrink_to
+[`PathBuf::shrink_to`]: https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#method.shrink_to
+[`BinaryHeap::shrink_to`]: https://doc.rust-lang.org/stable/std/collections/struct.BinaryHeap.html#method.shrink_to
+[`VecDeque::shrink_to`]: https://doc.rust-lang.org/stable/std/collections/struct.VecDeque.html#method.shrink_to
+[`HashMap::shrink_to`]: https://doc.rust-lang.org/stable/std/collections/hash_map/struct.HashMap.html#method.shrink_to
+[`HashSet::shrink_to`]: https://doc.rust-lang.org/stable/std/collections/hash_set/struct.HashSet.html#method.shrink_to
+[`task::ready!`]: https://doc.rust-lang.org/stable/std/task/macro.ready.html
+[`std::mem::transmute`]: https://doc.rust-lang.org/stable/std/mem/fn.transmute.html
+[`slice::first`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.first
+[`slice::split_first`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.split_first
+[`slice::last`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.last
+[`slice::split_last`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.split_last
+[`rust-version`]: https://doc.rust-lang.org/nightly/cargo/reference/manifest.html#the-rust-version-field
+[rust#87671]: https://github.com/rust-lang/rust/pull/87671
+[rust#86183]: https://github.com/rust-lang/rust/pull/86183
+[rust#87385]: https://github.com/rust-lang/rust/pull/87385
+[rust#88100]: https://github.com/rust-lang/rust/pull/88100
+[rust#86860]: https://github.com/rust-lang/rust/pull/86860
+[rust#84039]: https://github.com/rust-lang/rust/pull/84039
+[rust#86492]: https://github.com/rust-lang/rust/pull/86492
+[rust#88363]: https://github.com/rust-lang/rust/pull/88363
+[rust#85305]: https://github.com/rust-lang/rust/pull/85305
+[rust#87832]: https://github.com/rust-lang/rust/pull/87832
+[rust#88069]: https://github.com/rust-lang/rust/pull/88069
+[rust#87472]: https://github.com/rust-lang/rust/pull/87472
+[rust#87699]: https://github.com/rust-lang/rust/pull/87699
+[rust#87570]: https://github.com/rust-lang/rust/pull/87570
+[rust#88023]: https://github.com/rust-lang/rust/pull/88023
+[rust#87760]: https://github.com/rust-lang/rust/pull/87760
+[rust#87370]: https://github.com/rust-lang/rust/pull/87370
+[rust#87580]: https://github.com/rust-lang/rust/pull/87580
+[rust#83342]: https://github.com/rust-lang/rust/pull/83342
+[rust#83093]: https://github.com/rust-lang/rust/pull/83093
+[rust#88177]: https://github.com/rust-lang/rust/pull/88177
+[rust#88548]: https://github.com/rust-lang/rust/pull/88548
+[rust#88551]: https://github.com/rust-lang/rust/pull/88551
+[rust#88299]: https://github.com/rust-lang/rust/pull/88299
+[rust#88220]: https://github.com/rust-lang/rust/pull/88220
+[rust#85835]: https://github.com/rust-lang/rust/pull/85835
+[rust#86879]: https://github.com/rust-lang/rust/pull/86879
+[rust#86744]: https://github.com/rust-lang/rust/pull/86744
+[rust#84662]: https://github.com/rust-lang/rust/pull/84662
+[rust#86593]: https://github.com/rust-lang/rust/pull/86593
+[rust#81050]: https://github.com/rust-lang/rust/pull/81050
+[rust#81363]: https://github.com/rust-lang/rust/pull/81363
+[rust#84111]: https://github.com/rust-lang/rust/pull/84111
+[rust#85769]: https://github.com/rust-lang/rust/pull/85769#issuecomment-854363720
+[rust#88490]: https://github.com/rust-lang/rust/pull/88490
+[rust#88269]: https://github.com/rust-lang/rust/pull/88269
+[rust#84176]: https://github.com/rust-lang/rust/pull/84176
+[rust#88399]: https://github.com/rust-lang/rust/pull/88399
+[rust#88227]: https://github.com/rust-lang/rust/pull/88227
+[rust#88200]: https://github.com/rust-lang/rust/pull/88200
+[rust#82776]: https://github.com/rust-lang/rust/pull/82776
+[rust#88077]: https://github.com/rust-lang/rust/pull/88077
+[rust#87728]: https://github.com/rust-lang/rust/pull/87728
+[rust#87050]: https://github.com/rust-lang/rust/pull/87050
+[rust#87619]: https://github.com/rust-lang/rust/pull/87619
+[rust#81825]: https://github.com/rust-lang/rust/pull/81825#issuecomment-808406918
+[rust#88019]: https://github.com/rust-lang/rust/pull/88019
+
 Version 1.55.0 (2021-09-09)
 ============================