Add core::future::{pending,ready}
Adds two future constructors to `core`: `future::ready` and `future::pending`. These functions enable constructing futures of any type that either immediately resolve, or never resolve which is an incredible useful tool when writing documentation.
These functions have prior art in both the `futures` and `async-std` crates. This implementation has been adapted from the `futures` crate.
## Examples
In https://github.com/rust-lang/rust/pull/70817 we propose adding the `ready!` macro. In the example we use an `async fn` which does not return a future that implements `Unpin`, which leads to the use of `unsafe`. Instead had we had `future::ready` available, we could've written the same example without using `unsafe`:
```rust
use core::task::{Context, Poll};
use core::future::{self, Future};
use core::pin::Pin;
pub fn do_poll(cx: &mut Context<'_>) -> Poll<()> {
let mut fut = future::ready(42_u8);
let num = ready!(Pin::new(fut).poll(cx));
// ... use num
Poll::Ready(())
}
```
## Why future::ready?
Arguably `future::ready` and `async {}` can be considered equivalent. The main differences are that `future::ready` returns a future that implements `Unpin`, and the returned future is a concrete type. This is useful for traits that require a future as an associated type that can sometimes be a no-op ([example](https://docs.rs/http-service/0.4.0/http_service/trait.HttpService.html#associatedtype.ConnectionFuture)).
The final, minor argument is that `future::ready` and `future::pending` form a counterpart to the enum members of `Poll`: `Ready` and `Pending`. These functions form a conceptual bridge between `Poll` and `Future`, and can be used as a useful teaching device.
## References
- [`futures::future::ready`](https://docs.rs/futures/0.3.4/futures/future/fn.ready.html)
- [`futures::future::pending`](https://docs.rs/futures/0.3.4/futures/future/fn.pending.html)
- [`async_std::future::pending`](https://docs.rs/async-std/1.5.0/async_std/future/fn.pending.html)
- [`async_std::future::ready`](https://docs.rs/async-std/1.5.0/async_std/future/fn.ready.html)
Work around ICEs during cross-compilation for target, ast, & attr
This applies the fix for #72003 to work around #56935 to three more libraries. With these additional fixes, I'm able to use rustfmt_lib from wasm (https://github.com/rust-lang/rustfmt/issues/4132#issuecomment-616587989), which was my goal.
To get it working locally and to test, I copied the `.cargo/registry/src` and applied the fix and replaced the reference in my project:
``` toml
[replace]
"rustc-ap-rustc_span:656.0.0" = { path = "../rustc-ap-rustc_span" }
"rustc-ap-rustc_target:656.0.0" = { path = "../rustc-ap-rustc_target" }
"rustc-ap-rustc_ast:656.0.0" = { path = "../rustc-ap-rustc_ast" }
"rustc-ap-rustc_attr:656.0.0" = { path = "../rustc-ap-rustc_attr" }
```
allow wasm target for rustc-ap-rustc_span
This fixes#71998 by applying the work-a-round. The root cause is probably #56935, as @petrochenkov pointed out.
I reproduced the bug by:
```
cd ~/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-ap-rustc_span-657.0.0/
cargo build --target wasm32-unknown-unknown
```
Adding this line fixes it.
Reduce `TypedArena` creations in `check_match`.
`check_match` creates a new `TypedArena` for every call to
`create_and_enter`. DHAT tells me that each `TypedArena` typically is
barely used, with typically a single allocation per arena.
This commit moves the `TypedArena` creation outwards a bit, into
`check_match`, and then passes it into `create_and_enter`. This reduces
the number of arenas created by about 4-5x, for a very small perf win.
(Moving the arena creation further outwards is hard because
`check_match` is a query.)
r? @oli-obk
Improve bitcode generation for Apple platforms
Some improvements for iOS bitcode support suggested by Alex over at https://github.com/getditto/rust-bitcode/issues/9. r? @alexcrichton
This improves Rust's bitcode generation so that provided you have a compatible LLVM version, Rust targeting iOS should work out of the box when compiled into bitcode-enabled apps, and when submitted to the App Store. I've tested these changes using Xcode 11.4.1 and Apple's vendored LLVM, [tag `swift-5.2.3-RELEASE`](https://github.com/apple/llvm-project/releases/tag/swift-5.2.3-RELEASE).
1. Force `aarch64-apple-ios` and `aarch64-apple-tvos` targets to always emit full bitcode sections, even when cargo is trying to optimise by invoking `rustc` with `-Cembed-bitcode=no`. Since Apple recommends bitcode on iOS and requires it on tvOS it is likely that this is what developers intend. Currently you need to override the codegen options with `RUSTFLAGS`, which is far from obvious.
2. Provide an LLVM cmdline in the target spec. Apple's bitcode verification process looks for some arguments. For Rust modules to be accepted we must pretend they were produced similarly. A suitable default is provided in `TargetOptions` for iOS, copied directly from the a clang equivalent section.
In the context of Apple platforms, the predominant purpose of bitcode is App Store submissions, so simulator and 32-bit targets are not relevant. I'm hoping that the cmdline strings will not be a maintenance burden to keep up-to-date. If the event of any future incompatibilities, hopefully a custom target config would offer enough flexibility to work around it. It's impossible to say for sure.
Due to unrelated build errors I haven't been able to build and test a full tvOS toolchain. I've stopped short of providing a similar `bitcode_llvm_cmdline` until I can actually test it.
Unify lints handling in rustdoc
This is a small cleanup. The goal is to unify a bit things to make the reading simpler.
r? @kinnison
cc @rust-lang/rustdoc
Rollup of 6 pull requests
Successful merges:
- #71989 (Use a single enum for the kind of a const context)
- #71993 (Remove old `util/liveness.rs` module)
- #71999 (Add myself to mailmap.)
- #72001 (Adjust cfg(version) to lang team decision)
- #72007 (Fix some tests failing in `--pass check` mode)
- #72008 (Add const-generics test)
Failed merges:
r? @ghost
Remove old `util/liveness.rs` module
The liveness dataflow analysis now lives in the `dataflow` module, so this one is no longer necessary. I've copied the relevant bits of the module docs for `util::liveness` to `MaybeLiveLocals`. The example in the docs is now a `mir-dataflow` test: a08c47310c/src/test/ui/mir-dataflow/liveness-ptr.rs (L6-L26)
The borrow-checker used the same notion of "defs" and "uses", so I've moved it into a submodule. I would have moved it to `util/def_use.rs`, since it seems generally useful, but there's already a slightly [different version](https://github.com/rust-lang/rust/blob/master/src/librustc_mir/util/def_use.rs) of the same abstraction needed for copy propagation.
Use a single enum for the kind of a const context
This adds a `ConstContext` enum to the `rustc_hir` crate and method that can be called via `tcx.hir()` to get the `ConstContext` for a given body owner. This arose from discussion in #71824.
r? @oli-obk
[CI] Use the latest Python available on Windows
This PR changes our Windows CI to always use the latest Python interpreter available in the GHA tool cache instead of hardcoding Python 3.7.6. This is needed because occasionally GitHub bumps the installed version, deleting the previous one.
This fixes the current GHA outage we're having. I fully expect the outage to propagate to Azure Pipelines in the coming days if we don't merge this, as both GHA and Azure use the same underlying image. Once the PR is merged we can re-enabled the double-gating.
r? @Mark-Simulacrum
This commit changes our Windows CI to always use the latest Python
interpreter available in the GHA tool cache instead of hardcoding Python
3.7.6. This is needed because occasionally GitHub bumps the installed
version, deleting the previous one.
The liveness dataflow analysis now lives in
`librustc_mir/dataflow/impls/liveness.rs`. The borrow-checker has an
abstraction around of "defs" and "uses" that I've made module private. I
would have moved it to `util/def_use.rs`, but there's a slightly
different abstraction used for copy propagation with that name.
reword "possible candidate" import suggestion
This suggestion has always read a bit awkwardly to me, particularly the "possible better candidate" variant.
This commit rewords the suggestion to be more concise and mention the kind of the suggested item. There isn't a nice way to label individual suggestions, so I opted to use "items" in the case of multiple suggestions.
Allow a few warnings.
On Windows, these types were causing warnings to be emitted during the
build. These types are allowed to not have idiomatic names, so the
warning should be supressed.
use hex for pointers in Miri error messages
Also refine vtable error message: distinguish between "drop fn does not point to a function" and "drop fn points to a function with the wrong signature".
Grammar
I've split this into individual changes so that people can veto individually. I'm not attached to most of them.
`zeroes` vs. `zeros` is why I took the effort to run this through app.grammarly (which disappointingly didn't even notice).
Dylan DPC
bors
Cameron Taggart
Bastian Kauschke
Vadim Petrochenkov
Charles Lew
Tom Karpiniec
mibac138
Nicholas Nethercote
Ralf Jung
Pietro Albini
Dylan MacKenzie
Esteban Küber
Yuki Okushi