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Uplift push_outlives_components

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This commit is contained in:
Michael Goulet 2024-07-05 15:28:47 -04:00
parent 3bec61736a
commit 23c6f23b21
12 changed files with 386 additions and 300 deletions
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266
compiler/rustc_infer/src/infer/outlives/components.rs
View file

@ -1,266 +0,0 @@
// The outlines relation `T: 'a` or `'a: 'b`. This code frequently
// refers to rules defined in RFC 1214 (`OutlivesFooBar`), so see that
// RFC for reference.
use rustc_data_structures::sso::SsoHashSet;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{GenericArg, GenericArgKind};
use smallvec::{smallvec, SmallVec};
#[derive(Debug)]
pub enum Component<'tcx> {
Region(ty::Region<'tcx>),
Param(ty::ParamTy),
Placeholder(ty::PlaceholderType),
UnresolvedInferenceVariable(ty::InferTy),
// Projections like `T::Foo` are tricky because a constraint like
// `T::Foo: 'a` can be satisfied in so many ways. There may be a
// where-clause that says `T::Foo: 'a`, or the defining trait may
// include a bound like `type Foo: 'static`, or -- in the most
// conservative way -- we can prove that `T: 'a` (more generally,
// that all components in the projection outlive `'a`). This code
// is not in a position to judge which is the best technique, so
// we just product the projection as a component and leave it to
// the consumer to decide (but see `EscapingProjection` below).
Alias(ty::AliasTy<'tcx>),
// In the case where a projection has escaping regions -- meaning
// regions bound within the type itself -- we always use
// the most conservative rule, which requires that all components
// outlive the bound. So for example if we had a type like this:
//
// for<'a> Trait1< <T as Trait2<'a,'b>>::Foo >
// ~~~~~~~~~~~~~~~~~~~~~~~~~
//
// then the inner projection (underlined) has an escaping region
// `'a`. We consider that outer trait `'c` to meet a bound if `'b`
// outlives `'b: 'c`, and we don't consider whether the trait
// declares that `Foo: 'static` etc. Therefore, we just return the
// free components of such a projection (in this case, `'b`).
//
// However, in the future, we may want to get smarter, and
// actually return a "higher-ranked projection" here. Therefore,
// we mark that these components are part of an escaping
// projection, so that implied bounds code can avoid relying on
// them. This gives us room to improve the regionck reasoning in
// the future without breaking backwards compat.
EscapingAlias(Vec<Component<'tcx>>),
}
/// Push onto `out` all the things that must outlive `'a` for the condition
/// `ty0: 'a` to hold. Note that `ty0` must be a **fully resolved type**.
pub fn push_outlives_components<'tcx>(
tcx: TyCtxt<'tcx>,
ty0: Ty<'tcx>,
out: &mut SmallVec<[Component<'tcx>; 4]>,
) {
let mut visited = SsoHashSet::new();
compute_components(tcx, ty0, out, &mut visited);
debug!("components({:?}) = {:?}", ty0, out);
}
fn compute_components<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
out: &mut SmallVec<[Component<'tcx>; 4]>,
visited: &mut SsoHashSet<GenericArg<'tcx>>,
) {
// Descend through the types, looking for the various "base"
// components and collecting them into `out`. This is not written
// with `collect()` because of the need to sometimes skip subtrees
// in the `subtys` iterator (e.g., when encountering a
// projection).
match *ty.kind() {
ty::FnDef(_, args) => {
// HACK(eddyb) ignore lifetimes found shallowly in `args`.
// This is inconsistent with `ty::Adt` (including all args)
// and with `ty::Closure` (ignoring all args other than
// upvars, of which a `ty::FnDef` doesn't have any), but
// consistent with previous (accidental) behavior.
// See https://github.com/rust-lang/rust/issues/70917
// for further background and discussion.
for child in args {
match child.unpack() {
GenericArgKind::Type(ty) => {
compute_components(tcx, ty, out, visited);
}
GenericArgKind::Lifetime(_) => {}
GenericArgKind::Const(_) => {
compute_components_recursive(tcx, child, out, visited);
}
}
}
}
ty::Pat(element, _) |
ty::Array(element, _) => {
// Don't look into the len const as it doesn't affect regions
compute_components(tcx, element, out, visited);
}
ty::Closure(_, args) => {
let tupled_ty = args.as_closure().tupled_upvars_ty();
compute_components(tcx, tupled_ty, out, visited);
}
ty::CoroutineClosure(_, args) => {
let tupled_ty = args.as_coroutine_closure().tupled_upvars_ty();
compute_components(tcx, tupled_ty, out, visited);
}
ty::Coroutine(_, args) => {
// Same as the closure case
let tupled_ty = args.as_coroutine().tupled_upvars_ty();
compute_components(tcx, tupled_ty, out, visited);
// We ignore regions in the coroutine interior as we don't
// want these to affect region inference
}
// All regions are bound inside a witness
ty::CoroutineWitness(..) => (),
// OutlivesTypeParameterEnv -- the actual checking that `X:'a`
// is implied by the environment is done in regionck.
ty::Param(p) => {
out.push(Component::Param(p));
}
ty::Placeholder(p) => {
out.push(Component::Placeholder(p));
}
// For projections, we prefer to generate an obligation like
// `<P0 as Trait<P1...Pn>>::Foo: 'a`, because this gives the
// regionck more ways to prove that it holds. However,
// regionck is not (at least currently) prepared to deal with
// higher-ranked regions that may appear in the
// 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) => {
if !alias_ty.has_escaping_bound_vars() {
// best case: no escaping regions, so push the
// projection and skip the subtree (thus generating no
// constraints for Pi). This defers the choice between
// the rules OutlivesProjectionEnv,
// OutlivesProjectionTraitDef, and
// OutlivesProjectionComponents to regionck.
out.push(Component::Alias(alias_ty));
} else {
// fallback case: hard code
// OutlivesProjectionComponents. Continue walking
// through and constrain Pi.
let mut subcomponents = smallvec![];
let mut subvisited = SsoHashSet::new();
compute_alias_components_recursive(tcx, ty, &mut subcomponents, &mut subvisited);
out.push(Component::EscapingAlias(subcomponents.into_iter().collect()));
}
}
// We assume that inference variables are fully resolved.
// So, if we encounter an inference variable, just record
// the unresolved variable as a component.
ty::Infer(infer_ty) => {
out.push(Component::UnresolvedInferenceVariable(infer_ty));
}
// Most types do not introduce any region binders, nor
// involve any other subtle cases, and so the WF relation
// simply constraints any regions referenced directly by
// the type and then visits the types that are lexically
// contained within. (The comments refer to relevant rules
// from RFC1214.)
ty::Bool | // OutlivesScalar
ty::Char | // OutlivesScalar
ty::Int(..) | // OutlivesScalar
ty::Uint(..) | // OutlivesScalar
ty::Float(..) | // OutlivesScalar
ty::Never | // ...
ty::Adt(..) | // OutlivesNominalType
ty::Foreign(..) | // OutlivesNominalType
ty::Str | // OutlivesScalar (ish)
ty::Slice(..) | // ...
ty::RawPtr(..) | // ...
ty::Ref(..) | // OutlivesReference
ty::Tuple(..) | // ...
ty::FnPtr(_) | // OutlivesFunction (*)
ty::Dynamic(..) | // OutlivesObject, OutlivesFragment (*)
ty::Bound(..) |
ty::Error(_) => {
// (*) Function pointers and trait objects are both binders.
// In the RFC, this means we would add the bound regions to
// the "bound regions list". In our representation, no such
// list is maintained explicitly, because bound regions
// themselves can be readily identified.
compute_components_recursive(tcx, ty.into(), out, visited);
}
}
}
/// Collect [Component]s for *all* the args of `parent`.
///
/// This should not be used to get the components of `parent` itself.
/// Use [push_outlives_components] instead.
pub(super) fn compute_alias_components_recursive<'tcx>(
tcx: TyCtxt<'tcx>,
alias_ty: Ty<'tcx>,
out: &mut SmallVec<[Component<'tcx>; 4]>,
visited: &mut SsoHashSet<GenericArg<'tcx>>,
) {
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 { tcx.variances_of(alias_ty.def_id) } else { &[] };
for (index, child) in alias_ty.args.iter().enumerate() {
if opt_variances.get(index) == Some(&ty::Bivariant) {
continue;
}
if !visited.insert(child) {
continue;
}
match child.unpack() {
GenericArgKind::Type(ty) => {
compute_components(tcx, ty, out, visited);
}
GenericArgKind::Lifetime(lt) => {
// Ignore higher ranked regions.
if !lt.is_bound() {
out.push(Component::Region(lt));
}
}
GenericArgKind::Const(_) => {
compute_components_recursive(tcx, child, out, visited);
}
}
}
}
/// Collect [Component]s for *all* the args of `parent`.
///
/// This should not be used to get the components of `parent` itself.
/// Use [push_outlives_components] instead.
fn compute_components_recursive<'tcx>(
tcx: TyCtxt<'tcx>,
parent: GenericArg<'tcx>,
out: &mut SmallVec<[Component<'tcx>; 4]>,
visited: &mut SsoHashSet<GenericArg<'tcx>>,
) {
for child in parent.walk_shallow(visited) {
match child.unpack() {
GenericArgKind::Type(ty) => {
compute_components(tcx, ty, out, visited);
}
GenericArgKind::Lifetime(lt) => {
// Ignore higher ranked regions.
if !lt.is_bound() {
out.push(Component::Region(lt));
}
}
GenericArgKind::Const(_) => {
compute_components_recursive(tcx, child, out, visited);
}
}
}
}

3
compiler/rustc_infer/src/infer/outlives/mod.rs
View file

@ -7,8 +7,9 @@ use crate::infer::free_regions::RegionRelations;
use crate::infer::lexical_region_resolve;
use rustc_middle::traits::query::{NoSolution, OutlivesBound};
use rustc_middle::ty;
// TODO: Remove me
pub use rustc_type_ir::outlives as components;
pub mod components;
pub mod env;
pub mod for_liveness;
pub mod obligations;

2
compiler/rustc_infer/src/infer/outlives/obligations.rs
View file

@ -291,7 +291,7 @@ where
fn components_must_outlive(
&mut self,
origin: infer::SubregionOrigin<'tcx>,
components: &[Component<'tcx>],
components: &[Component<TyCtxt<'tcx>>],
region: ty::Region<'tcx>,
category: ConstraintCategory<'tcx>,
) {

4
compiler/rustc_infer/src/infer/outlives/verify.rs
View file

@ -139,7 +139,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
fn bound_from_components(
&self,
components: &[Component<'tcx>],
components: &[Component<TyCtxt<'tcx>>],
visited: &mut SsoHashSet<GenericArg<'tcx>>,
) -> VerifyBound<'tcx> {
let mut bounds = components
@ -158,7 +158,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
fn bound_from_single_component(
&self,
component: &Component<'tcx>,
component: &Component<TyCtxt<'tcx>>,
visited: &mut SsoHashSet<GenericArg<'tcx>>,
) -> VerifyBound<'tcx> {
match *component {