new solver: remove provisional cache
The provisional cache is a performance optimization if there are large, interleaving cycles. Such cycles generally do not exist. It is incredibly complex and unsound in all trait solvers which have one: the old solver, chalk, and the new solver ([link](https://github.com/rust-lang/rust/blob/master/tests/ui/traits/new-solver/cycles/inductive-not-on-stack.rs)).
Given the assumption that it is not perf-critical and also incredibly complex, remove it from the new solver, only checking whether a goal is on the stack. While writing this, I uncovered two additional soundness bugs, see the inline comments for them.
r? `@compiler-errors`
Stabilize `impl_trait_projections`
Closes#115659
## TL;DR:
This allows us to mention `Self` and `T::Assoc` in async fn and return-position `impl Trait`, as you would expect you'd be able to.
Some examples:
```rust
#![feature(return_position_impl_trait_in_trait, async_fn_in_trait)]
// (just needed for final tests below)
// ---------------------------------------- //
struct Wrapper<'a, T>(&'a T);
impl Wrapper<'_, ()> {
async fn async_fn() -> Self {
//^ Previously rejected because it returns `-> Self`, not `-> Wrapper<'_, ()>`.
Wrapper(&())
}
fn impl_trait() -> impl Iterator<Item = Self> {
//^ Previously rejected because it mentions `Self`, not `Wrapper<'_, ()>`.
std::iter::once(Wrapper(&()))
}
}
// ---------------------------------------- //
trait Trait<'a> {
type Assoc;
fn new() -> Self::Assoc;
}
impl Trait<'_> for () {
type Assoc = ();
fn new() {}
}
impl<'a, T: Trait<'a>> Wrapper<'a, T> {
async fn mk_assoc() -> T::Assoc {
//^ Previously rejected because `T::Assoc` doesn't mention `'a` in the HIR,
// but ends up resolving to `<T as Trait<'a>>::Assoc`, which does rely on `'a`.
// That's the important part -- the elided trait.
T::new()
}
fn a_few_assocs() -> impl Iterator<Item = T::Assoc> {
//^ Previously rejected for the same reason
[T::new(), T::new(), T::new()].into_iter()
}
}
// ---------------------------------------- //
trait InTrait {
async fn async_fn() -> Self;
fn impl_trait() -> impl Iterator<Item = Self>;
}
impl InTrait for &() {
async fn async_fn() -> Self { &() }
//^ Previously rejected just like inherent impls
fn impl_trait() -> impl Iterator<Item = Self> {
//^ Previously rejected just like inherent impls
[&()].into_iter()
}
}
```
## Technical:
Lifetimes in return-position `impl Trait` (and `async fn`) are duplicated as early-bound generics local to the opaque in order to make sure we are able to substitute any late-bound lifetimes from the function in the opaque's hidden type. (The [dev guide](https://rustc-dev-guide.rust-lang.org/return-position-impl-trait-in-trait.html#aside-opaque-lifetime-duplication) has a small section about why this is necessary -- this was written for RPITITs, but it applies to all RPITs)
Prior to #103491, all of the early-bound lifetimes not local to the opaque were replaced with `'static` to avoid issues where relating opaques caused their *non-captured* lifetimes to be related. This `'static` replacement led to strange and possibly unsound behaviors (https://github.com/rust-lang/rust/issues/61949#issuecomment-508836314) (https://github.com/rust-lang/rust/issues/53613) when referencing the `Self` type alias in an impl or indirectly referencing a lifetime parameter via a projection type (via a `T::Assoc` projection without an explicit trait), since lifetime resolution is performed on the HIR, when neither `T::Assoc`-style projections or `Self` in impls are expanded.
Therefore an error was implemented in #62849 to deny this subtle behavior as a known limitation of the compiler. It was attempted by `@cjgillot` to fix this in #91403, which was subsequently unlanded. Then it was re-attempted to much success (🎉) in #103491, which is where we currently are in the compiler.
The PR above (#103491) fixed this issue technically by *not* replacing the opaque's parent lifetimes with `'static`, but instead using variance to properly track which lifetimes are captured and are not. The PR gated any of the "side-effects" of the PR behind a feature gate (`impl_trait_projections`) presumably to avoid having to involve T-lang or T-types in the PR as well. `@cjgillot` can clarify this if I'm misunderstanding what their intention was with the feature gate.
Since we're not replacing (possibly *invariant*!) lifetimes with `'static` anymore, there are no more soundness concerns here. Therefore, this PR removes the feature gate.
Tests:
* `tests/ui/async-await/feature-self-return-type.rs`
* `tests/ui/impl-trait/feature-self-return-type.rs`
* `tests/ui/async-await/issues/issue-78600.rs`
* `tests/ui/impl-trait/capture-lifetime-not-in-hir.rs`
---
r? cjgillot on the impl (not much, just removing the feature gate)
I'm gonna mark this as FCP for T-lang and T-types.
Simplify some of the logic in the `invalid_reference_casting` lint
This PR simplifies 2 areas of the logic for the `invalid_reference_casting` lint:
- The init detection: we now use the newly added `expr_or_init` function instead of a manual detection
- The ref-to-mut-ptr casting detection logic: I simplified this logic by caring less hardly about the order of the casting operations
Those two simplifications permits us to detect more cases, as can be seen in the test output changes.
Anonymize binders for `refining_impl_trait` check
We're naively using the equality impl for `ty::Clause` in the refinement check, which is okay *except* for binders, which carry some information about where they come from in the AST. Those locations are not gonna be equal between traits and impls, so anonymize those clauses so that this doesn't matter.
Fixes#116135
Don't store lazyness in `DefKind::TyAlias`
1. Don't store lazyness of a type alias in its `DefKind`, but instead via a query.
2. This allows us to treat type aliases as lazy if `#[feature(lazy_type_alias)]` *OR* if the alias contains a TAIT, rather than having checks for both in separate parts of the codebase.
r? `@oli-obk` cc `@fmease`
Only prevent field projections into opaque types, not types containing opaque types
fixes https://github.com/rust-lang/rust/issues/115778
I did not think that original condition through properly... I'll also need to check the similar check around the other `ProjectionKind::OpaqueCast` creation site (this one is in hir, the other one is in mir), but I'll do that change in another PR that doesn't go into a beta backport.
Gate and validate `#[rustc_safe_intrinsic]`
Copied over from #116159:
> This was added as ungated in https://github.com/rust-lang/rust/pull/100719/files#diff-09c366d3ad3ec9a42125253b610ca83cad6b156aa2a723f6c7e83eddef7b1e8fR502, probably because the author looked at the surrounding attributes, which are ungated because they are gated specially behind the staged_api feature.
>
> I don't think we need to crater this, the attribute is entirely useless without the intrinsics feature, which is already unstable..
r? ``@Nilstrieb``
lint towards rejecting consts in patterns that do not implement PartialEq
I think we definitely don't want to allow such consts, so even while the general plan around structural matching is up in the air, we can start the process of getting non-PartialEq matches out of the ecosystem.
ConstParamTy: require Eq as supertrait
As discussed with `@BoxyUwu` [on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/260443-project-const-generics/topic/.60ConstParamTy.60.20and.20.60Eq.60).
We want to say that valtree equality on const generic params agrees with `==`, but that only makes sense if `==` actually exists, hence we should have an appropriate bound. Valtree equality is an equivalence relation, so such a type can always be `Eq` and not just `PartialEq`.
Properly print cstr literals in `proc_macro::Literal::to_string`
Previously we printed the contents of the string, rather than the actual string literal (e.g. `the c string` instead of `c"the c string"`).
Fixes#112820
cc #105723
Use placeholders to prevent using inferred RPITIT types to imply their own well-formedness
The issue here is that we use the same signature to do RPITIT inference as we do to compute implied bounds. To fix this, when gathering the assumed wf types for the method, we replace all of the infer vars (that will be eventually used to infer RPITIT types) with type placeholders, which imply nothing about lifetime bounds.
This solution kind of sucks, but I'm not certain there's another feasible way to fix this. If anyone has a better solution, I'd be glad to hear it.
My naive first solution was, instead of using placeholders, to replace the signature with the RPITIT projections that it originally started out with. But turns out that we can't just use the unnormalized signature of the trait method in `implied_outlives_bounds` since we normalize during WF computation -- that would cause a query cycle in `collect_return_position_impl_trait_in_trait_tys`.
idk who to request review...
r? `@lcnr` or `@aliemjay` i guess.
Fixes#116060
Point at more causes of expectation of break value when possible
Follow up to #116071.
r? `@compiler-errors`
Disregard the first commit, which is in the other PR.
Rollup of 5 pull requests
Successful merges:
- #116073 (Allow higher-ranked fn sigs in `ValuePairs`)
- #116082 (Tweak expected message to explain what it's actually signifying)
- #116086 (More accurate suggestion for `self.` and `Self::`)
- #116104 (Reuse calculate_debuginfo_offset for fragments.)
- #116106 (Migrate GUI colors test to original CSS color format)
r? `@ghost`
`@rustbot` modify labels: rollup
More accurate suggestion for `self.` and `Self::`
Detect that we can't suggest `self.` in an associated function without `&self` receiver.
Partially address #115992.
r? ``@compiler-errors``
implement Literal::byte_character
without this, the only way to create a `LitKind::Byte` is by
doing `"b'a'".parse::<Literal>()`, this solves that by enabling
`Literal::byte_character(b'a')`
cc #71358
The tracking issue is #115268
Pietro Albini