Rollup of 8 pull requests #85685
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Rollup of 8 pull requests #85685
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Clarify error returns from Mutex::try_lock, RwLock::try_read, RwLock::try_write to make it more obvious that both poisoning and the lock being already locked are possible errors.
Use "the `WouldBlock` error" instead of "the error `WouldBlock`", etc.
…raints-61997, r=jackh726 stabilize member constraints Stabilizes the use of "member constraints" in solving `impl Trait` bindings. This is a step towards stabilizing a "MVP" of "named impl Trait". # Member constraint stabilization report | Info | | | --- | --- | | Tracking issue | [rust-lang#61997](rust-lang#61997) | | Implementation history | [rust-lang#61775] | | rustc-dev-guide coverage | [link](https://rustc-dev-guide.rust-lang.org/borrow_check/region_inference/member_constraints.html) | | Complications | [rust-lang#61773] | [rust-lang#61775]: rust-lang#61775 [rust-lang#61773]: rust-lang#61773 ## Background Member constraints are an extension to our region solver that was introduced to make async fn region solving tractable. There are used in situations like the following: ```rust fn foo<'a, 'b>(...) -> impl Trait<'a, 'b> { .. } ``` The problem here is that every region R in the hidden type must be equal to *either* `'a` *or* `'b` (or `'static`). This cannot be expressed simply via 'outlives constriants' like `R: 'a`. Therefore, we introduce a 'member constraint' `R member of ['a, 'b]`. These constraints were introduced in [rust-lang#61775]. At the time, we kept them feature gated and used them only for `impl Trait` return types that are derived from `async fn`. The intention, however, was always to support them in other contexts once we had time to gain more experience with them. **In the time since their introduction, we have encountered no surprises or bugs due to these member constraints.** They are tested extensively as part of every async function that involves multiple unrelated lifetimes in its arguments. ## Tests The behavior of member constraints is covered by the following tests: * [`src/test/ui/async-await/multiple-lifetimes`](https://github.com/rust-lang/rust/tree/20e032e65007ff1376e8480c1fbdb0a5068028fa/src/test/ui/async-await/multiple-lifetimes) -- tests using the async await, which are mostly already stabilized * [`src/test/ui/impl-trait/multiple-lifetimes.rs`](https://github.com/rust-lang/rust/blob/20e032e65007ff1376e8480c1fbdb0a5068028fa/src/test/ui/impl-trait/multiple-lifetimes.rs) * [`src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unsuited.rs`](https://github.com/rust-lang/rust/blob/20e032e65007ff1376e8480c1fbdb0a5068028fa/src/test/ui/impl-trait/multiple-lifetimes/ordinary-bounds-unsuited.rs) * [`src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-fg.rs`](https://github.com/rust-lang/rust/blob/20e032e65007ff1376e8480c1fbdb0a5068028fa/src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-fg.rs) * [`src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.rs`](https://github.com/rust-lang/rust/blob/20e032e65007ff1376e8480c1fbdb0a5068028fa/src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.rs) These tests cover a number of scenarios: * `-> implTrait<'a, 'b>` with unrelated lifetimes `'a` and `'b`, as described above * `async fn` that returns an `impl Trait` like the previous case, which desugars to a kind of "nested" impl trait like `impl Future<Output = impl Trait<'a, 'b>>` ## Potential concerns There is a potential interaction with `impl Trait` on local variables, described in [rust-lang#61773]. The challenge is that if you have a program like: ```rust= trait Foo<'_> { } impl Foo<'_> for &u32 { } fn bar() { let x: impl Foo<'_> = &44; // let's call the region variable for `'_` `'1` } ``` then we would wind up with `'0 member of ['1, 'static]`, where `'0` is the region variable in the hidden type (`&'0 u32`) and `'1` is the region variable in the bounds `Foo<'1>`. This is tricky because both `'0` and `'1` are being inferred -- so making them equal may have other repercussions. That said, `impl Trait` in bindings are not stable, and the implementation is pretty far from stabilization. Moreover, the difficulty highlighted here is not due to the presence of member constraints -- it's inherent to the design of the language. In other words, stabilizing member constraints does not actually cause us to accept anything that would make this problem any harder. So I don't see this as a blocker to stabilization of member constraints; it is potentially a blocker to stablization of `impl trait` in let bindings.
doc: clarify Mutex::try_lock, etc. errors Clarify error returns from Mutex::try_lock, RwLock::try_read, RwLock::try_write to make it more obvious that both poisoning and the lock being already locked are possible errors.
Weak's type parameter may dangle on drop Way back in rust-lang@34076bc, #\[may_dangle\] was added to Rc\<T\> and Arc\<T\>'s Drop impls. That appears to have been because a test added in rust-lang#28929 used Arc and Rc with dangling references at drop time. However, Weak was not covered by that test, and therefore no #\[may_dangle\] was forced to be added at the time. As far as dropping, Weak has *even less need* to interact with the T than Rc and Arc do. Roughly speaking #\[may_dangle\] describes generic parameters that the outer type's Drop impl does not interact with except by possibly dropping them; no other interaction (such as trait method calls on the generic type) is permissible. It's clear this applies to Rc's and Arc's drop impl, which sometimes drop T but otherwise do not interact with one. It applies *even more* to Weak. Dropping a Weak cannot ever cause T's drop impl to run. Either there are strong references still in existence, in which case better not drop the T. Or there are no strong references still in existence, in which case the T would already have been dropped previously by the drop of the last strong count.
…e, r=oli-obk Fix pointer provenance in <[T]>::copy_within Previously the `self.as_mut_ptr()` invalidated the pointer created by the first `self.as_ptr()`. This also triggered miri when run with `-Zmiri-track-raw-pointers`
Demote `ControlFlow::{from|into}_try` to `pub(crate)`
They have mediocre names and non-obvious semantics, so personally I don't think they're worth trying to stabilize, and thus might as well just be internal (they're used for convenience in iterator adapters), not something shown in the rustdocs.
I don't think anyone actually wanted to use them outside `core` -- they just got made public-but-unstable along with the whole type in rust-lang#76204 that promoted `LoopState` from an internal type to the exposed `ControlFlow` type.
cc rust-lang#75744, the tracking issue they mention.
…nd, r=jyn514 Revert "Move llvm submodule updates to rustbuild" Reverts rust-lang#81601 This updates LLVM a bit too eagerly -- and particularly on Windows, this can be slow. See discussion on [Zulip]. [Zulip]: https://rust-lang.zulipchat.com/#narrow/stream/182449-t-compiler.2Fhelp/topic/x.2Epy.20always.20updates.20LLVM.20submodule
… r=dtolnay Document shared_from_cow functions
…Simulacrum Fix tasklist example in rustdoc book. There were a few issues with the tasklist example in the rustdoc book: * Misspelled "incomplete" * Checkmarks were backwards * Didn't show the text for each item * Used HTML which renders differently from how markdown renders it (which uses "disabled" marks) * Didn't use blockquotes to offset the example like the other extensions do * Missing a colon Before: <img width="160" alt="image" src="https://user-images.githubusercontent.com/43198/119503519-e7787880-bd1f-11eb-9f13-1c67754ce001.png"> After: <img width="220" alt="image" src="https://user-images.githubusercontent.com/43198/119503449-d6c80280-bd1f-11eb-9ab5-fe4a6df82124.png">
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@bors r+ p=8 rollup=never |
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📌 Commit b922253 has been approved by |
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⌛ Testing commit b922253 with merge 6fc49b5958a03b6c96d02f9e864cc5728d45932f... |
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The job Click to see the possible cause of the failure (guessed by this bot) |
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💔 Test failed - checks-actions |
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Successful merges:
ControlFlow::{from|into}_trytopub(crate)#85645 (DemoteControlFlow::{from|into}_trytopub(crate))Failed merges:
r? @ghost
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