rustc_trait_selection/traits/query/type_op/
implied_outlives_bounds.rs

1use std::ops::ControlFlow;
2
3use rustc_infer::infer::TypeOutlivesConstraint;
4use rustc_infer::infer::canonical::CanonicalQueryInput;
5use rustc_infer::traits::query::OutlivesBound;
6use rustc_infer::traits::query::type_op::ImpliedOutlivesBounds;
7use rustc_middle::infer::canonical::CanonicalQueryResponse;
8use rustc_middle::traits::ObligationCause;
9use rustc_middle::ty::outlives::{Component, push_outlives_components};
10use rustc_middle::ty::{self, ParamEnvAnd, Ty, TyCtxt, TypeVisitable, TypeVisitor, Unnormalized};
11use rustc_span::def_id::CRATE_DEF_ID;
12use rustc_span::{DUMMY_SP, Span, sym};
13use smallvec::{SmallVec, smallvec};
14
15use crate::traits::query::NoSolution;
16use crate::traits::{ObligationCtxt, wf};
17
18impl<'tcx> super::QueryTypeOp<'tcx> for ImpliedOutlivesBounds<'tcx> {
19    type QueryResponse = Vec<OutlivesBound<'tcx>>;
20
21    fn try_fast_path(
22        _tcx: TyCtxt<'tcx>,
23        key: &ParamEnvAnd<'tcx, Self>,
24    ) -> Option<Self::QueryResponse> {
25        // Don't go into the query for things that can't possibly have lifetimes.
26        match key.value.ty.kind() {
27            ty::Tuple(elems) if elems.is_empty() => Some(::alloc::vec::Vec::new()vec![]),
28            ty::Never | ty::Str | ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) => {
29                Some(::alloc::vec::Vec::new()vec![])
30            }
31            _ => None,
32        }
33    }
34
35    fn perform_query(
36        tcx: TyCtxt<'tcx>,
37        canonicalized: CanonicalQueryInput<'tcx, ParamEnvAnd<'tcx, Self>>,
38    ) -> Result<CanonicalQueryResponse<'tcx, Self::QueryResponse>, NoSolution> {
39        tcx.implied_outlives_bounds((canonicalized, false))
40    }
41
42    fn perform_locally_with_next_solver(
43        ocx: &ObligationCtxt<'_, 'tcx>,
44        key: ParamEnvAnd<'tcx, Self>,
45        span: Span,
46    ) -> Result<Self::QueryResponse, NoSolution> {
47        compute_implied_outlives_bounds_inner(ocx, key.param_env, key.value.ty, span, false)
48    }
49}
50
51pub fn compute_implied_outlives_bounds_inner<'tcx>(
52    ocx: &ObligationCtxt<'_, 'tcx>,
53    param_env: ty::ParamEnv<'tcx>,
54    ty: Ty<'tcx>,
55    span: Span,
56    disable_implied_bounds_hack: bool,
57) -> Result<Vec<OutlivesBound<'tcx>>, NoSolution> {
58    // Inside mir borrowck, each computation starts with an empty list.
59    if !ocx.infcx.inner.borrow().region_obligations().is_empty() {
    {
        ::core::panicking::panic_fmt(format_args!("compute_implied_outlives_bounds assumes region obligations are empty before starting"));
    }
};assert!(
60        ocx.infcx.inner.borrow().region_obligations().is_empty(),
61        "compute_implied_outlives_bounds assumes region obligations are empty before starting"
62    );
63
64    // FIXME: This doesn't seem right. All call sites already normalize `ty`:
65    // - `Ty`s from the `DefiningTy` in Borrowck: we have to normalize in the caller
66    //      in order to get implied bounds involving any unconstrained region vars
67    //      created as part of normalizing the sig. See #136547
68    // - `Ty`s from impl headers in Borrowck and in Non-Borrowck contexts: we have
69    //      to normalize in the caller as computing implied bounds from unnormalized
70    //      types would be unsound. See #100989
71    //
72    // We must normalize the type so we can compute the right outlives components.
73    // for example, if we have some constrained param type like `T: Trait<Out = U>`,
74    // and we know that `&'a T::Out` is WF, then we want to imply `U: 'a`.
75    let normalized_ty = ocx
76        .deeply_normalize(
77            &ObligationCause::dummy_with_span(span),
78            param_env,
79            Unnormalized::new_wip(ty),
80        )
81        .map_err(|_| NoSolution)?;
82
83    // Sometimes when we ask what it takes for T: WF, we get back that
84    // U: WF is required; in that case, we push U onto this stack and
85    // process it next. Because the resulting predicates aren't always
86    // guaranteed to be a subset of the original type, so we need to store the
87    // WF args we've computed in a set.
88    let mut checked_wf_args = rustc_data_structures::fx::FxHashSet::default();
89    let mut wf_args = ::alloc::boxed::box_assume_init_into_vec_unsafe(::alloc::intrinsics::write_box_via_move(::alloc::boxed::Box::new_uninit(),
        [ty.into(), normalized_ty.into()]))vec![ty.into(), normalized_ty.into()];
90
91    let mut outlives_bounds: Vec<OutlivesBound<'tcx>> = ::alloc::vec::Vec::new()vec![];
92
93    while let Some(arg) = wf_args.pop() {
94        if !checked_wf_args.insert(arg) {
95            continue;
96        }
97
98        // From the full set of obligations, just filter down to the region relationships.
99        for obligation in
100            wf::unnormalized_obligations(ocx.infcx, param_env, arg, DUMMY_SP, CRATE_DEF_ID)
101                .into_flat_iter()
102        {
103            let pred = ocx
104                .deeply_normalize(
105                    &ObligationCause::dummy_with_span(span),
106                    param_env,
107                    Unnormalized::new_wip(obligation.predicate),
108                )
109                .map_err(|_| NoSolution)?;
110            let Some(pred) = pred.kind().no_bound_vars() else {
111                continue;
112            };
113            match pred {
114                // FIXME(generic_const_parameter_types): Make sure that `<'a, 'b, const N: &'a &'b u32>`
115                // is sound if we ever support that
116                ty::PredicateKind::Clause(ty::ClauseKind::Trait(..))
117                | ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(..))
118                | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
119                | ty::PredicateKind::Subtype(..)
120                | ty::PredicateKind::Coerce(..)
121                | ty::PredicateKind::Clause(ty::ClauseKind::Projection(..))
122                | ty::PredicateKind::DynCompatible(..)
123                | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
124                | ty::PredicateKind::ConstEquate(..)
125                | ty::PredicateKind::Ambiguous
126                | ty::PredicateKind::NormalizesTo(..)
127                | ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_)) => {}
128
129                // We need to search through *all* WellFormed predicates
130                ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(term)) => {
131                    wf_args.push(term);
132                }
133
134                // We need to register region relationships
135                ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(
136                    ty::OutlivesPredicate(r_a, r_b),
137                )) => outlives_bounds.push(OutlivesBound::RegionSubRegion(r_b, r_a)),
138
139                ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
140                    ty_a,
141                    r_b,
142                ))) => {
143                    let mut components = ::smallvec::SmallVec::new()smallvec![];
144                    push_outlives_components(ocx.infcx.tcx, ty_a, &mut components);
145                    outlives_bounds.extend(implied_bounds_from_components(r_b, components))
146                }
147            }
148        }
149    }
150
151    // If we detect `bevy_ecs::*::ParamSet` in the WF args list (and `disable_implied_bounds_hack`
152    // or `-Zno-implied-bounds-compat` are not set), then use the registered outlives obligations
153    // as implied bounds.
154    if !disable_implied_bounds_hack
155        && !ocx.infcx.tcx.sess.opts.unstable_opts.no_implied_bounds_compat
156        && ty.visit_with(&mut ContainsBevyParamSet { tcx: ocx.infcx.tcx }).is_break()
157    {
158        for TypeOutlivesConstraint { sup_type, sub_region, .. } in
159            ocx.infcx.clone_registered_region_obligations()
160        {
161            let mut components = ::smallvec::SmallVec::new()smallvec![];
162            push_outlives_components(ocx.infcx.tcx, sup_type, &mut components);
163            outlives_bounds.extend(implied_bounds_from_components(sub_region, components));
164        }
165    }
166
167    Ok(outlives_bounds)
168}
169
170struct ContainsBevyParamSet<'tcx> {
171    tcx: TyCtxt<'tcx>,
172}
173
174impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ContainsBevyParamSet<'tcx> {
175    type Result = ControlFlow<()>;
176
177    fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
178        // We only care to match `ParamSet<T>` or `&ParamSet<T>`.
179        match t.kind() {
180            ty::Adt(def, _) => {
181                if self.tcx.item_name(def.did()) == sym::ParamSet
182                    && self.tcx.crate_name(def.did().krate) == sym::bevy_ecs
183                {
184                    return ControlFlow::Break(());
185                }
186            }
187            ty::Ref(_, ty, _) => ty.visit_with(self)?,
188            _ => {}
189        }
190
191        ControlFlow::Continue(())
192    }
193}
194
195/// When we have an implied bound that `T: 'a`, we can further break
196/// this down to determine what relationships would have to hold for
197/// `T: 'a` to hold. We get to assume that the caller has validated
198/// those relationships.
199fn implied_bounds_from_components<'tcx>(
200    sub_region: ty::Region<'tcx>,
201    sup_components: SmallVec<[Component<TyCtxt<'tcx>>; 4]>,
202) -> Vec<OutlivesBound<'tcx>> {
203    sup_components
204        .into_iter()
205        .filter_map(|component| {
206            match component {
207                Component::Region(r) => Some(OutlivesBound::RegionSubRegion(sub_region, r)),
208                Component::Param(p) => Some(OutlivesBound::RegionSubParam(sub_region, p)),
209                Component::Alias(p) => Some(OutlivesBound::RegionSubAlias(sub_region, p)),
210                Component::Placeholder(_p) => {
211                    // FIXME(non_lifetime_binders): Placeholders don't currently
212                    // imply anything for outlives, though they could easily.
213                    None
214                }
215                Component::EscapingAlias(_) =>
216                // If the projection has escaping regions, don't
217                // try to infer any implied bounds even for its
218                // free components. This is conservative, because
219                // the caller will still have to prove that those
220                // free components outlive `sub_region`. But the
221                // idea is that the WAY that the caller proves
222                // that may change in the future and we want to
223                // give ourselves room to get smarter here.
224                {
225                    None
226                }
227                Component::UnresolvedInferenceVariable(..) => None,
228            }
229        })
230        .collect()
231}
rustc_trait_selection/traits/query/type_op/implied_outlives_bounds.rs

rustc_trait_selection/traits/query/type_op/
implied_outlives_bounds.rs
