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};
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(vec![]),
28            ty::Never | ty::Str | ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) => {
29                Some(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    let normalize_ty = |ty| -> Result<_, NoSolution> {
59        // We must normalize the type so we can compute the right outlives components.
60        // for example, if we have some constrained param type like `T: Trait<Out = U>`,
61        // and we know that `&'a T::Out` is WF, then we want to imply `U: 'a`.
62        let ty = ocx
63            .deeply_normalize(&ObligationCause::dummy_with_span(span), param_env, ty)
64            .map_err(|_| NoSolution)?;
65        Ok(ty)
66    };
67
68    // Sometimes when we ask what it takes for T: WF, we get back that
69    // U: WF is required; in that case, we push U onto this stack and
70    // process it next. Because the resulting predicates aren't always
71    // guaranteed to be a subset of the original type, so we need to store the
72    // WF args we've computed in a set.
73    let mut checked_wf_args = rustc_data_structures::fx::FxHashSet::default();
74    let mut wf_args = vec![ty.into(), normalize_ty(ty)?.into()];
75
76    let mut outlives_bounds: Vec<OutlivesBound<'tcx>> = vec![];
77
78    while let Some(arg) = wf_args.pop() {
79        if !checked_wf_args.insert(arg) {
80            continue;
81        }
82
83        // From the full set of obligations, just filter down to the region relationships.
84        for obligation in
85            wf::unnormalized_obligations(ocx.infcx, param_env, arg, DUMMY_SP, CRATE_DEF_ID)
86                .into_iter()
87                .flatten()
88        {
89            let pred = ocx
90                .deeply_normalize(
91                    &ObligationCause::dummy_with_span(span),
92                    param_env,
93                    obligation.predicate,
94                )
95                .map_err(|_| NoSolution)?;
96            let Some(pred) = pred.kind().no_bound_vars() else {
97                continue;
98            };
99            match pred {
100                // FIXME(const_generics): Make sure that `<'a, 'b, const N: &'a &'b u32>` is sound
101                // if we ever support that
102                ty::PredicateKind::Clause(ty::ClauseKind::Trait(..))
103                | ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(..))
104                | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
105                | ty::PredicateKind::Subtype(..)
106                | ty::PredicateKind::Coerce(..)
107                | ty::PredicateKind::Clause(ty::ClauseKind::Projection(..))
108                | ty::PredicateKind::DynCompatible(..)
109                | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
110                | ty::PredicateKind::ConstEquate(..)
111                | ty::PredicateKind::Ambiguous
112                | ty::PredicateKind::NormalizesTo(..)
113                | ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_))
114                | ty::PredicateKind::AliasRelate(..) => {}
115
116                // We need to search through *all* WellFormed predicates
117                ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(term)) => {
118                    wf_args.push(term);
119                }
120
121                // We need to register region relationships
122                ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(
123                    ty::OutlivesPredicate(r_a, r_b),
124                )) => outlives_bounds.push(OutlivesBound::RegionSubRegion(r_b, r_a)),
125
126                ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
127                    ty_a,
128                    r_b,
129                ))) => {
130                    let mut components = smallvec![];
131                    push_outlives_components(ocx.infcx.tcx, ty_a, &mut components);
132                    outlives_bounds.extend(implied_bounds_from_components(r_b, components))
133                }
134            }
135        }
136    }
137
138    // If we detect `bevy_ecs::*::ParamSet` in the WF args list (and `disable_implied_bounds_hack`
139    // or `-Zno-implied-bounds-compat` are not set), then use the registered outlives obligations
140    // as implied bounds.
141    if !disable_implied_bounds_hack
142        && !ocx.infcx.tcx.sess.opts.unstable_opts.no_implied_bounds_compat
143        && ty.visit_with(&mut ContainsBevyParamSet { tcx: ocx.infcx.tcx }).is_break()
144    {
145        for TypeOutlivesConstraint { sup_type, sub_region, .. } in
146            ocx.infcx.take_registered_region_obligations()
147        {
148            let mut components = smallvec![];
149            push_outlives_components(ocx.infcx.tcx, sup_type, &mut components);
150            outlives_bounds.extend(implied_bounds_from_components(sub_region, components));
151        }
152    }
153
154    Ok(outlives_bounds)
155}
156
157struct ContainsBevyParamSet<'tcx> {
158    tcx: TyCtxt<'tcx>,
159}
160
161impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ContainsBevyParamSet<'tcx> {
162    type Result = ControlFlow<()>;
163
164    fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
165        // We only care to match `ParamSet<T>` or `&ParamSet<T>`.
166        match t.kind() {
167            ty::Adt(def, _) => {
168                if self.tcx.item_name(def.did()) == sym::ParamSet
169                    && self.tcx.crate_name(def.did().krate) == sym::bevy_ecs
170                {
171                    return ControlFlow::Break(());
172                }
173            }
174            ty::Ref(_, ty, _) => ty.visit_with(self)?,
175            _ => {}
176        }
177
178        ControlFlow::Continue(())
179    }
180}
181
182/// When we have an implied bound that `T: 'a`, we can further break
183/// this down to determine what relationships would have to hold for
184/// `T: 'a` to hold. We get to assume that the caller has validated
185/// those relationships.
186fn implied_bounds_from_components<'tcx>(
187    sub_region: ty::Region<'tcx>,
188    sup_components: SmallVec<[Component<TyCtxt<'tcx>>; 4]>,
189) -> Vec<OutlivesBound<'tcx>> {
190    sup_components
191        .into_iter()
192        .filter_map(|component| {
193            match component {
194                Component::Region(r) => Some(OutlivesBound::RegionSubRegion(sub_region, r)),
195                Component::Param(p) => Some(OutlivesBound::RegionSubParam(sub_region, p)),
196                Component::Alias(p) => Some(OutlivesBound::RegionSubAlias(sub_region, p)),
197                Component::Placeholder(_p) => {
198                    // FIXME(non_lifetime_binders): Placeholders don't currently
199                    // imply anything for outlives, though they could easily.
200                    None
201                }
202                Component::EscapingAlias(_) =>
203                // If the projection has escaping regions, don't
204                // try to infer any implied bounds even for its
205                // free components. This is conservative, because
206                // the caller will still have to prove that those
207                // free components outlive `sub_region`. But the
208                // idea is that the WAY that the caller proves
209                // that may change in the future and we want to
210                // give ourselves room to get smarter here.
211                {
212                    None
213                }
214                Component::UnresolvedInferenceVariable(..) => None,
215            }
216        })
217        .collect()
218}
rustc_trait_selection/traits/query/type_op/implied_outlives_bounds.rs

rustc_trait_selection/traits/query/type_op/
implied_outlives_bounds.rs
