Support using `Self` or projections inside an RPIT/async fn
I reuse the same idea as https://github.com/rust-lang/rust/pull/103449 to use variances to encode whether a lifetime parameter is captured by impl-trait.
The current implementation of async and RPIT replace all lifetimes from the parent generics by `'static`. This PR changes the scheme
```rust
impl<'a> Foo<'a> {
fn foo<'b, T>() -> impl Into<Self> + 'b { ... }
}
opaque Foo::<'_a>::foo::<'_b, T>::opaque<'b>: Into<Foo<'_a>> + 'b;
impl<'a> Foo<'a> {
// OLD
fn foo<'b, T>() -> Foo::<'static>::foo::<'static, T>::opaque::<'b> { ... }
^^^^^^^ the `Self` becomes `Foo<'static>`
// NEW
fn foo<'b, T>() -> Foo::<'a>::foo::<'b, T>::opaque::<'b> { ... }
^^ the `Self` stays `Foo<'a>`
}
```
There is the same issue with projections. In the example, substitute `Self` by `<T as Trait<'b>>::Assoc` in the sugared version, and `Foo<'_a>` by `<T as Trait<'_b>>::Assoc` in the desugared one.
This allows to support `Self` in impl-trait, since we do not replace lifetimes by `'static` any more. The same trick allows to use projections like `T::Assoc` where `Self` is allowed. The feature is gated behind a `impl_trait_projections` feature gate.
The implementation relies on 2 tweaking rules for opaques in 2 places:
- we only relate substs that correspond to captured lifetimes during TypeRelation;
- we only list captured lifetimes in choice region computation.
For simplicity, I encoded the "capturedness" of lifetimes as a variance, `Bivariant` vs `Invariant` for unused vs captured lifetimes. The `variances_of` query used to ICE for opaques.
Impl-trait that do not reference `Self` or projections will have their variances as:
- `o` (invariant) for each parent type or const;
- `*` (bivariant) for each parent lifetime --> will not participate in borrowck;
- `o` (invariant) for each own lifetime.
Impl-trait that does reference `Self` and/or projections will have some parent lifetimes marked as `o` (as the example above), and participate in type relation and borrowck. In the example above, `variances_of(opaque) = ['_a: o, '_b: *, T: o, 'b: o]`.
r? types
cc `@compiler-errors` , as you asked about the issue with `Self` and projections.
Add `rustc_deny_explicit_impl`
Also adjust `E0322` error message to be more general, since it's used for `DiscriminantKind` and `Pointee` as well.
Also add `rustc_deny_explicit_impl` on the `Tuple` and `Destruct` marker traits.
Fix broken link in description of error code E0706
Corresponding subsection in async book is `07.05` not `07.06`.
The information on the linked page is the same so it may be reasonable to remove the whole sentence.
Mention const and lifetime parameters in error E0207
Error Index for E0207 must mention const and lifetime parameters. In addition, add code examples for these situations.
Fixes#80862
Corresponding subsection in async book is not `07.05` not `07.06`.
The information on the linked page is the same so it may be reasonable to remove the whole sentence.
E0045: Use a stable non-C ABI instead
E0092: Use an atomic intrinsic that actually exists
E0161: Don't use box_syntax
E0579: Format ranges in the rustfmt style
E0622: Use the rustfmt style
E0743: Remove feature gate as it's not needed
Add `#[rustc_safe_intrinsic]`
This PR adds the `#[rustc_safe_intrinsic]` attribute as mentionned on Zulip. The goal of this attribute is to avoid keeping a list of symbols as the source for stable intrinsics, and instead rely on an attribute. This is similar to `#[rustc_const_stable]` and `#[rustc_const_unstable]`, which among other things, are used to mark the constness of intrinsic functions.
- use the simpler minimum working example from the review
- add an alterate "fix" that helps make the cause of the error more
clear
- attempt to add an improved description of what is going on
There was a partial rust code block in the readme that was invalid
because of a missing line. I inlined the code snippet into the text to
fix the error. This also improves readability a bit.
Improve the function pointer docs
This is #97842 but for function pointers instead of tuples. The concept is basically the same.
* Reduce duplicate impls; show `fn (T₁, T₂, …, Tₙ)` and include a sentence saying that there exists up to twelve of them.
* Show `Copy` and `Clone`.
* Show auto traits like `Send` and `Sync`, and blanket impls like `Any`.
https://notriddle.com/notriddle-rustdoc-test/std/primitive.fn.html
* Reduce duplicate impls; show only the `fn (T)` and include a sentence
saying that there exists up to twelve of them.
* Show `Copy` and `Clone`.
* Show auto traits like `Send` and `Sync`, and blanket impls like `Any`.
Simplify memory ordering intrinsics
This changes the names of the atomic intrinsics to always fully include their memory ordering arguments.
```diff
- atomic_cxchg
+ atomic_cxchg_seqcst_seqcst
- atomic_cxchg_acqrel
+ atomic_cxchg_acqrel_release
- atomic_cxchg_acqrel_failrelaxed
+ atomic_cxchg_acqrel_relaxed
// And so on.
```
- `seqcst` is no longer implied
- The failure ordering on chxchg is no longer implied in some cases, but now always explicitly part of the name.
- `release` is no longer shortened to just `rel`. That was especially confusing, since `relaxed` also starts with `rel`.
- `acquire` is no longer shortened to just `acq`, such that the names now all match the `std::sync::atomic::Ordering` variants exactly.
- This now allows for more combinations on the compare exchange operations, such as `atomic_cxchg_acquire_release`, which is necessary for #68464.
- This PR only exposes the new possibilities through unstable intrinsics, but not yet through the stable API. That's for [a separate PR](https://github.com/rust-lang/rust/pull/98383) that requires an FCP.
Suffixes for operations with a single memory order:
| Order | Before | After |
|---------|--------------|------------|
| Relaxed | `_relaxed` | `_relaxed` |
| Acquire | `_acq` | `_acquire` |
| Release | `_rel` | `_release` |
| AcqRel | `_acqrel` | `_acqrel` |
| SeqCst | (none) | `_seqcst` |
Suffixes for compare-and-exchange operations with two memory orderings:
| Success | Failure | Before | After |
|---------|---------|--------------------------|--------------------|
| Relaxed | Relaxed | `_relaxed` | `_relaxed_relaxed` |
| Relaxed | Acquire | ❌ | `_relaxed_acquire` |
| Relaxed | SeqCst | ❌ | `_relaxed_seqcst` |
| Acquire | Relaxed | `_acq_failrelaxed` | `_acquire_relaxed` |
| Acquire | Acquire | `_acq` | `_acquire_acquire` |
| Acquire | SeqCst | ❌ | `_acquire_seqcst` |
| Release | Relaxed | `_rel` | `_release_relaxed` |
| Release | Acquire | ❌ | `_release_acquire` |
| Release | SeqCst | ❌ | `_release_seqcst` |
| AcqRel | Relaxed | `_acqrel_failrelaxed` | `_acqrel_relaxed` |
| AcqRel | Acquire | `_acqrel` | `_acqrel_acquire` |
| AcqRel | SeqCst | ❌ | `_acqrel_seqcst` |
| SeqCst | Relaxed | `_failrelaxed` | `_seqcst_relaxed` |
| SeqCst | Acquire | `_failacq` | `_seqcst_acquire` |
| SeqCst | SeqCst | (none) | `_seqcst_seqcst` |
Remove migrate borrowck mode
Closes#58781Closes#43234
# Stabilization proposal
This PR proposes the stabilization of `#![feature(nll)]` and the removal of `-Z borrowck`. Current borrow checking behavior of item bodies is currently done by first infering regions *lexically* and reporting any errors during HIR type checking. If there *are* any errors, then MIR borrowck (NLL) never occurs. If there *aren't* any errors, then MIR borrowck happens and any errors there would be reported. This PR removes the lexical region check of item bodies entirely and only uses MIR borrowck. Because MIR borrowck could never *not* be run for a compiled program, this should not break any programs. It does, however, change diagnostics significantly and allows a slightly larger set of programs to compile.
Tracking issue: #43234
RFC: https://github.com/rust-lang/rfcs/blob/master/text/2094-nll.md
Version: 1.63 (2022-06-30 => beta, 2022-08-11 => stable).
## Motivation
Over time, the Rust borrow checker has become "smarter" and thus allowed more programs to compile. There have been three different implementations: AST borrowck, MIR borrowck, and polonius (well, in progress). Additionally, there is the "lexical region resolver", which (roughly) solves the constraints generated through HIR typeck. It is not a full borrow checker, but does emit some errors.
The AST borrowck was the original implementation of the borrow checker and was part of the initially stabilized Rust 1.0. In mid 2017, work began to implement the current MIR borrow checker and that effort ompleted by the end of 2017, for the most part. During 2018, efforts were made to migrate away from the AST borrow checker to the MIR borrow checker - eventually culminating into "migrate" mode - where HIR typeck with lexical region resolving following by MIR borrow checking - being active by default in the 2018 edition.
In early 2019, migrate mode was turned on by default in the 2015 edition as well, but with MIR borrowck errors emitted as warnings. By late 2019, these warnings were upgraded to full errors. This was followed by the complete removal of the AST borrow checker.
In the period since, various errors emitted by the MIR borrow checker have been improved to the point that they are mostly the same or better than those emitted by the lexical region resolver.
While there do remain some degradations in errors (tracked under the [NLL-diagnostics tag](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-diagnostics), those are sufficiently small and rare enough that increased flexibility of MIR borrow check-only is now a worthwhile tradeoff.
## What is stabilized
As said previously, this does not fundamentally change the landscape of accepted programs. However, there are a [few](https://github.com/rust-lang/rust/issues?q=is%3Aopen+is%3Aissue+label%3ANLL-fixed-by-NLL) cases where programs can compile under `feature(nll)`, but not otherwise.
There are two notable patterns that are "fixed" by this stabilization. First, the `scoped_threads` feature, which is a continutation of a pre-1.0 API, can sometimes emit a [weird lifetime error](https://github.com/rust-lang/rust/issues/95527) without NLL. Second, actually seen in the standard library. In the `Extend` impl for `HashMap`, there is an implied bound of `K: 'a` that is available with NLL on but not without - this is utilized in the impl.
As mentioned before, there are a large number of diagnostic differences. Most of them are better, but some are worse. None are serious or happen often enough to need to block this PR. The biggest change is the loss of error code for a number of lifetime errors in favor of more general "lifetime may not live long enough" error. While this may *seem* bad, the former error codes were just attempts to somewhat-arbitrarily bin together lifetime errors of the same type; however, on paper, they end up being roughly the same with roughly the same kinds of solutions.
## What isn't stabilized
This PR does not completely remove the lexical region resolver. In the future, it may be possible to remove that (while still keeping HIR typeck) or to remove it together with HIR typeck.
## Tests
Many test outputs get updated by this PR. However, there are number of tests specifically geared towards NLL under `src/test/ui/nll`
## History
* On 2017-07-14, [tracking issue opened](https://github.com/rust-lang/rust/issues/43234)
* On 2017-07-20, [initial empty MIR pass added](https://github.com/rust-lang/rust/pull/43271)
* On 2017-08-29, [RFC opened](https://github.com/rust-lang/rfcs/pull/2094)
* On 2017-11-16, [Integrate MIR type-checker with NLL](https://github.com/rust-lang/rust/pull/45825)
* On 2017-12-20, [NLL feature complete](https://github.com/rust-lang/rust/pull/46862)
* On 2018-07-07, [Don't run AST borrowck on mir mode](https://github.com/rust-lang/rust/pull/52083)
* On 2018-07-27, [Add migrate mode](https://github.com/rust-lang/rust/pull/52681)
* On 2019-04-22, [Enable migrate mode on 2015 edition](https://github.com/rust-lang/rust/pull/59114)
* On 2019-08-26, [Don't downgrade errors on 2015 edition](https://github.com/rust-lang/rust/pull/64221)
* On 2019-08-27, [Remove AST borrowck](https://github.com/rust-lang/rust/pull/64790)
Add E0788 for improper #[no_coverage] usage
Essentially, this adds proper checking for the attribute (tracking issue #84605) and throws errors when it's put in obviously-wrong places, like on struct or const definitions. Most of the code is taken directly from the checks for the `#[inline]` attribute, since it's very similar.
Right now, the code only checks at the function level, but it seems reasonable to allow adding `#[no_coverage]` to individual blocks or expressions, so, for now those just throw `unused_attributes` warnings. Similarly, since there was a lot of desire to eventually allow recursive definitions as well on modules and impl blocks, these also throw `unused_attributes` instead of an error.
I'm not sure if anything has to be done since this error is technically for an unstable feature, but since an error for using unstable features will show up anyway, I think it's okay.
This is the first big piece needed for stabilising this attribute, although I personally would like to explore renaming it to `#[coverage(never)]` on a separate PR, which I will offer soon. There's a lot of discussion still to be had about that, which is why it will be kept separate.
I don't think much is needed besides adding this simple check and a UI test, but let me know if there's something else that should be added to make this happen.
Remove `#[rustc_deprecated]`
This removes `#[rustc_deprecated]` and introduces diagnostics to help users to the right direction (that being `#[deprecated]`). All uses of `#[rustc_deprecated]` have been converted. CI is expected to fail initially; this requires #95958, which includes converting `stdarch`.
I plan on following up in a short while (maybe a bootstrap cycle?) removing the diagnostics, as they're only intended to be short-term.
Inherit lifetimes for async fn instead of duplicating them.
The current desugaring of `async fn foo<'a>(&usize) -> &u8` is equivalent to
```rust
fn foo<'a, '0>(&'0 usize) -> foo<'static, 'static>::Opaque<'a, '0, '_>;
type foo<'_a, '_0>::Opaque<'a, '0, '1> = impl Future<Output = &'1 u8>;
```
following the RPIT model.
Duplicating all the inherited lifetime parameters and setting the inherited version to `'static` makes lowering more complex and causes issues like #61949. This PR removes the duplication of inherited lifetimes to directly use
```rust
fn foo<'a, '0>(&'0 usize) -> foo<'a, '0>::Opaque<'_>;
type foo<'a, '0>::Opaque<'1> = impl Future<Output = &'1 u8>;
```
following the TAIT model.
Fixes https://github.com/rust-lang/rust/issues/61949
Transition unsupported naked functions future incompatibility lint into
an error:
* Naked functions must contain a single inline assembly block.
Introduced as future incompatibility lint in 1.50 #79653.
Change into an error fixes a soundness issue described in #32489.
* Naked functions must not use any forms of inline attribute.
Introduced as future incompatibility lint in 1.56 #87652.
This usually describes either an error in the compiler itself or some
sort of IO error. Either way, we should report it to the user rather
than just saying "crate not found".
This only gives an error if the crate couldn't be loaded at all - if the
compiler finds another .rlib or .rmeta file which was valid, it will
continue to compile the crate.
Example output:
```
error[E0785]: found invalid metadata files for crate `foo`
--> bar.rs:3:24
|
3 | println!("{}", foo::FOO_11_49[0]);
| ^^^
|
= warning: failed to parse rlib '/home/joshua/test-rustdoc/libfoo.rlib': Invalid archive extended name offset
```
Update E0637 description to mention `&` w/o an explicit lifetime name
Deal with https://github.com/rust-lang/rust/issues/89824#issuecomment-941598647. Another solution would be splitting the error code into two as (I think) it's a bit unclear to users why they have the same error code.
Rollup of 7 pull requests
Successful merges:
- #86011 (move implicit `Sized` predicate to end of list)
- #89821 (Add a strange test for `unsafe_code` lint.)
- #89859 (add dedicated error variant for writing the discriminant of an uninhabited enum variant)
- #89870 (Suggest Box::pin when Pin::new is used instead)
- #89880 (Use non-checking TLS relocation in aarch64 asm! sym test.)
- #89885 (add long explanation for E0183)
- #89894 (Remove unused dependencies from rustc_const_eval)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
The test is copied from `src/test/ui/crate-loading/crateresolve1.rs` and
its auxiliary tests. I added it to the `compile_fail` code example check
exemption list since it's hard if not impossible to reproduce this error
in a standalone code example.
