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Add opt_alias_variances and use it in outlives code

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This commit is contained in:
Michael Goulet 2025-02-05 18:03:26 +00:00
parent 2f92f050e8
commit d17a4a7f9a
12 changed files with 117 additions and 50 deletions
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12
compiler/rustc_borrowck/src/type_check/opaque_types.rs
View File

@ -284,7 +284,7 @@ where
return;
}
match ty.kind() {
match *ty.kind() {
ty::Closure(_, args) => {
// Skip lifetime parameters of the enclosing item(s)
@ -316,10 +316,12 @@ where
args.as_coroutine().resume_ty().visit_with(self);
}
ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
// Skip lifetime parameters that are not captures.
let variances = self.tcx.variances_of(*def_id);
ty::Alias(kind, ty::AliasTy { def_id, args, .. })
if let Some(variances) = self.tcx.opt_alias_variances(kind, def_id) =>
{
// Skip lifetime parameters that are not captured, since they do
// not need member constraints registered for them; we'll erase
// them (and hopefully in the future replace them with placeholders).
for (v, s) in std::iter::zip(variances, args.iter()) {
if *v != ty::Bivariant {
s.visit_with(self);

10
compiler/rustc_infer/src/infer/outlives/for_liveness.rs
View File

@ -48,7 +48,7 @@ where
return ty.super_visit_with(self);
}
match ty.kind() {
match *ty.kind() {
// We can prove that an alias is live two ways:
// 1. All the components are live.
//
@ -95,11 +95,9 @@ where
assert!(r.type_flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS));
r.visit_with(self);
} else {
// Skip lifetime parameters that are not captures.
let variances = match kind {
ty::Opaque => Some(self.tcx.variances_of(*def_id)),
_ => None,
};
// Skip lifetime parameters that are not captured, since they do
// not need to be live.
let variances = tcx.opt_alias_variances(kind, def_id);
for (idx, s) in args.iter().enumerate() {
if variances.map(|variances| variances[idx]) != Some(ty::Bivariant) {

6
compiler/rustc_infer/src/infer/outlives/obligations.rs
View File

@ -392,13 +392,13 @@ where
// the problem is to add `T: 'r`, which isn't true. So, if there are no
// inference variables, we use a verify constraint instead of adding
// edges, which winds up enforcing the same condition.
let is_opaque = alias_ty.kind(self.tcx) == ty::Opaque;
let kind = alias_ty.kind(self.tcx);
if approx_env_bounds.is_empty()
&& trait_bounds.is_empty()
&& (alias_ty.has_infer_regions() || is_opaque)
&& (alias_ty.has_infer_regions() || kind == ty::Opaque)
{
debug!("no declared bounds");
let opt_variances = is_opaque.then(|| self.tcx.variances_of(alias_ty.def_id));
let opt_variances = self.tcx.opt_alias_variances(kind, alias_ty.def_id);
self.args_must_outlive(alias_ty.args, origin, region, opt_variances);
return;
}

8
compiler/rustc_infer/src/infer/outlives/verify.rs
View File

@ -102,12 +102,11 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
#[instrument(level = "debug", skip(self))]
pub(crate) fn alias_bound(&self, alias_ty: ty::AliasTy<'tcx>) -> VerifyBound<'tcx> {
let alias_ty_as_ty = alias_ty.to_ty(self.tcx);
// Search the env for where clauses like `P: 'a`.
let env_bounds = self.approx_declared_bounds_from_env(alias_ty).into_iter().map(|binder| {
if let Some(ty::OutlivesPredicate(ty, r)) = binder.no_bound_vars()
&& ty == alias_ty_as_ty
&& let ty::Alias(_, alias_ty_from_bound) = *ty.kind()
&& alias_ty_from_bound == alias_ty
{
// Micro-optimize if this is an exact match (this
// occurs often when there are no region variables
@ -127,7 +126,8 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
// see the extensive comment in projection_must_outlive
let recursive_bound = {
let mut components = smallvec![];
compute_alias_components_recursive(self.tcx, alias_ty_as_ty, &mut components);
let kind = alias_ty.kind(self.tcx);
compute_alias_components_recursive(self.tcx, kind, alias_ty, &mut components);
self.bound_from_components(&components)
};

8
compiler/rustc_middle/src/ty/context.rs
View File

@ -194,6 +194,14 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
self.variances_of(def_id)
}
fn opt_alias_variances(
self,
kind: impl Into<ty::AliasTermKind>,
def_id: DefId,
) -> Option<&'tcx [ty::Variance]> {
self.opt_alias_variances(kind, def_id)
}
fn type_of(self, def_id: DefId) -> ty::EarlyBinder<'tcx, Ty<'tcx>> {
self.type_of(def_id)
}

23
compiler/rustc_middle/src/ty/util.rs
View File

@ -951,6 +951,29 @@ impl<'tcx> TyCtxt<'tcx> {
ty
}
// Computes the variances for an alias (opaque or RPITIT) that represent
// its (un)captured regions.
pub fn opt_alias_variances(
self,
kind: impl Into<ty::AliasTermKind>,
def_id: DefId,
) -> Option<&'tcx [ty::Variance]> {
match kind.into() {
ty::AliasTermKind::ProjectionTy => {
if self.is_impl_trait_in_trait(def_id) {
Some(self.variances_of(def_id))
} else {
None
}
}
ty::AliasTermKind::OpaqueTy => Some(self.variances_of(def_id)),
ty::AliasTermKind::InherentTy
| ty::AliasTermKind::WeakTy
| ty::AliasTermKind::UnevaluatedConst
| ty::AliasTermKind::ProjectionConst => None,
}
}
}
struct OpaqueTypeExpander<'tcx> {

6
compiler/rustc_type_ir/src/interner.rs
View File

@ -141,6 +141,12 @@ pub trait Interner:
type VariancesOf: Copy + Debug + SliceLike<Item = ty::Variance>;
fn variances_of(self, def_id: Self::DefId) -> Self::VariancesOf;
fn opt_alias_variances(
self,
kind: impl Into<ty::AliasTermKind>,
def_id: Self::DefId,
) -> Option<Self::VariancesOf>;
fn type_of(self, def_id: Self::DefId) -> ty::EarlyBinder<Self, Self::Ty>;
type AdtDef: AdtDef<Self>;

18
compiler/rustc_type_ir/src/outlives.rs
View File

@ -148,7 +148,7 @@ impl<I: Interner> TypeVisitor<I> for OutlivesCollector<'_, I> {
// trait-ref. Therefore, if we see any higher-ranked regions,
// we simply fallback to the most restrictive rule, which
// requires that `Pi: 'a` for all `i`.
ty::Alias(_, alias_ty) => {
ty::Alias(kind, alias_ty) => {
if !alias_ty.has_escaping_bound_vars() {
// best case: no escaping regions, so push the
// projection and skip the subtree (thus generating no
@ -162,7 +162,7 @@ impl<I: Interner> TypeVisitor<I> for OutlivesCollector<'_, I> {
// OutlivesProjectionComponents. Continue walking
// through and constrain Pi.
let mut subcomponents = smallvec![];
compute_alias_components_recursive(self.cx, ty, &mut subcomponents);
compute_alias_components_recursive(self.cx, kind, alias_ty, &mut subcomponents);
self.out.push(Component::EscapingAlias(subcomponents.into_iter().collect()));
}
}
@ -217,21 +217,17 @@ impl<I: Interner> TypeVisitor<I> for OutlivesCollector<'_, I> {
}
}
/// Collect [Component]s for *all* the args of `parent`.
/// Collect [Component]s for *all* the args of `alias_ty`.
///
/// This should not be used to get the components of `parent` itself.
/// This should not be used to get the components of `alias_ty` itself.
/// Use [push_outlives_components] instead.
pub fn compute_alias_components_recursive<I: Interner>(
cx: I,
alias_ty: I::Ty,
kind: ty::AliasTyKind,
alias_ty: ty::AliasTy<I>,
out: &mut SmallVec<[Component<I>; 4]>,
) {
let ty::Alias(kind, alias_ty) = alias_ty.kind() else {
unreachable!("can only call `compute_alias_components_recursive` on an alias type")
};
let opt_variances =
if kind == ty::Opaque { Some(cx.variances_of(alias_ty.def_id)) } else { None };
let opt_variances = cx.opt_alias_variances(kind, alias_ty.def_id);
let mut visitor = OutlivesCollector { cx, out, visited: Default::default() };

11
compiler/rustc_type_ir/src/predicate.rs
View File

@ -469,6 +469,17 @@ impl AliasTermKind {
}
}
impl From<ty::AliasTyKind> for AliasTermKind {
fn from(value: ty::AliasTyKind) -> Self {
match value {
ty::Projection => AliasTermKind::ProjectionTy,
ty::Opaque => AliasTermKind::OpaqueTy,
ty::Weak => AliasTermKind::WeakTy,
ty::Inherent => AliasTermKind::InherentTy,
}
}
}
/// Represents the unprojected term of a projection goal.
///
/// * For a projection, this would be `<Ty as Trait<...>>::N<...>`.

28
compiler/rustc_type_ir/src/relate.rs
View File

@ -236,28 +236,14 @@ impl<I: Interner> Relate<I> for ty::AliasTy<I> {
ExpectedFound::new(a, b)
}))
} else {
let args = match a.kind(relation.cx()) {
ty::Opaque => relate_args_with_variances(
relation,
a.def_id,
relation.cx().variances_of(a.def_id),
a.args,
b.args,
let cx = relation.cx();
let args = if let Some(variances) = cx.opt_alias_variances(a.kind(cx), a.def_id) {
relate_args_with_variances(
relation, a.def_id, variances, a.args, b.args,
false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle
)?,
ty::Projection if relation.cx().is_impl_trait_in_trait(a.def_id) => {
relate_args_with_variances(
relation,
a.def_id,
relation.cx().variances_of(a.def_id),
a.args,
b.args,
false, // do not fetch `type_of(a_def_id)`, as it will cause a cycle
)?
}
ty::Projection | ty::Weak | ty::Inherent => {
relate_args_invariantly(relation, a.args, b.args)?
}
)?
} else {
relate_args_invariantly(relation, a.args, b.args)?
};
Ok(ty::AliasTy::new_from_args(relation.cx(), a.def_id, args))
}

19
tests/ui/impl-trait/precise-capturing/rpitit-outlives-2.rs Normal file
View File

@ -0,0 +1,19 @@
//@ check-pass
// Ensure that we skip uncaptured args from RPITITs when comptuing outlives.
#![feature(precise_capturing_in_traits)]
struct Invariant<T>(*mut T);
trait Foo {
fn hello<'s: 's>(&'s self) -> Invariant<impl Sized + use<Self>>;
}
fn outlives_static(_: impl Sized + 'static) {}
fn hello<'s, T: Foo + 'static>(x: &'s T) {
outlives_static(x.hello());
}
fn main() {}

18
tests/ui/impl-trait/precise-capturing/rpitit-outlives.rs Normal file
View File

@ -0,0 +1,18 @@
//@ check-pass
// Ensure that we skip uncaptured args from RPITITs when collecting the regions
// to enforce member constraints in opaque type inference.
#![feature(precise_capturing_in_traits)]
struct Invariant<T>(*mut T);
trait Foo {
fn hello<'s: 's>(&'s self) -> Invariant<impl Sized + use<Self>>;
}
fn hello<'s, T: Foo>(x: &'s T) -> Invariant<impl Sized> {
x.hello()
}
fn main() {}