rustc_trait_selection/solve/
delegate.rs

1use std::ops::Deref;
2
3use rustc_data_structures::fx::FxHashSet;
4use rustc_hir::LangItem;
5use rustc_hir::def_id::{CRATE_DEF_ID, DefId};
6use rustc_infer::infer::canonical::query_response::make_query_region_constraints;
7use rustc_infer::infer::canonical::{
8    Canonical, CanonicalExt as _, CanonicalQueryInput, CanonicalVarKind, CanonicalVarValues,
9};
10use rustc_infer::infer::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TyCtxtInferExt};
11use rustc_infer::traits::solve::Goal;
12use rustc_middle::traits::query::NoSolution;
13use rustc_middle::traits::solve::Certainty;
14use rustc_middle::ty::{
15    self, Ty, TyCtxt, TypeFlags, TypeFoldable, TypeVisitableExt as _, TypingMode,
16};
17use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
18
19use crate::traits::{EvaluateConstErr, ObligationCause, specialization_graph};
20
21#[repr(transparent)]
22pub struct SolverDelegate<'tcx>(InferCtxt<'tcx>);
23
24impl<'a, 'tcx> From<&'a InferCtxt<'tcx>> for &'a SolverDelegate<'tcx> {
25    fn from(infcx: &'a InferCtxt<'tcx>) -> Self {
26        // SAFETY: `repr(transparent)`
27        unsafe { std::mem::transmute(infcx) }
28    }
29}
30
31impl<'tcx> Deref for SolverDelegate<'tcx> {
32    type Target = InferCtxt<'tcx>;
33
34    fn deref(&self) -> &Self::Target {
35        &self.0
36    }
37}
38
39impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<'tcx> {
40    type Infcx = InferCtxt<'tcx>;
41    type Interner = TyCtxt<'tcx>;
42
43    fn cx(&self) -> TyCtxt<'tcx> {
44        self.0.tcx
45    }
46
47    fn build_with_canonical<V>(
48        interner: TyCtxt<'tcx>,
49        canonical: &CanonicalQueryInput<'tcx, V>,
50    ) -> (Self, V, CanonicalVarValues<'tcx>)
51    where
52        V: TypeFoldable<TyCtxt<'tcx>>,
53    {
54        let (infcx, value, vars) = interner
55            .infer_ctxt()
56            .with_next_trait_solver(true)
57            .build_with_canonical(DUMMY_SP, canonical);
58        (SolverDelegate(infcx), value, vars)
59    }
60
61    fn compute_goal_fast_path(
62        &self,
63        goal: Goal<'tcx, ty::Predicate<'tcx>>,
64        span: Span,
65    ) -> Option<Certainty> {
66        if let Some(trait_pred) = goal.predicate.as_trait_clause() {
67            if trait_pred.polarity() == ty::PredicatePolarity::Positive {
68                match self.0.tcx.as_lang_item(trait_pred.def_id()) {
69                    Some(LangItem::Sized)
70                        if self
71                            .resolve_vars_if_possible(trait_pred.self_ty().skip_binder())
72                            .is_trivially_sized(self.0.tcx) =>
73                    {
74                        return Some(Certainty::Yes);
75                    }
76                    Some(LangItem::Copy | LangItem::Clone) => {
77                        let self_ty =
78                            self.resolve_vars_if_possible(trait_pred.self_ty().skip_binder());
79                        // Unlike `Sized` traits, which always prefer the built-in impl,
80                        // `Copy`/`Clone` may be shadowed by a param-env candidate which
81                        // could force a lifetime error or guide inference. While that's
82                        // not generally desirable, it is observable, so for now let's
83                        // ignore this fast path for types that have regions or infer.
84                        if !self_ty
85                            .has_type_flags(TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_INFER)
86                            && self_ty.is_trivially_pure_clone_copy()
87                        {
88                            return Some(Certainty::Yes);
89                        }
90                    }
91                    _ => {}
92                }
93            }
94        }
95
96        let pred = goal.predicate.kind();
97        match pred.no_bound_vars()? {
98            ty::PredicateKind::DynCompatible(def_id) if self.0.tcx.is_dyn_compatible(def_id) => {
99                Some(Certainty::Yes)
100            }
101            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(outlives)) => {
102                self.0.sub_regions(
103                    SubregionOrigin::RelateRegionParamBound(span, None),
104                    outlives.1,
105                    outlives.0,
106                );
107                Some(Certainty::Yes)
108            }
109            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(outlives)) => {
110                self.0.register_type_outlives_constraint(
111                    outlives.0,
112                    outlives.1,
113                    &ObligationCause::dummy_with_span(span),
114                );
115
116                Some(Certainty::Yes)
117            }
118            _ => None,
119        }
120    }
121
122    fn fresh_var_for_kind_with_span(
123        &self,
124        arg: ty::GenericArg<'tcx>,
125        span: Span,
126    ) -> ty::GenericArg<'tcx> {
127        match arg.kind() {
128            ty::GenericArgKind::Lifetime(_) => {
129                self.next_region_var(RegionVariableOrigin::MiscVariable(span)).into()
130            }
131            ty::GenericArgKind::Type(_) => self.next_ty_var(span).into(),
132            ty::GenericArgKind::Const(_) => self.next_const_var(span).into(),
133        }
134    }
135
136    fn leak_check(&self, max_input_universe: ty::UniverseIndex) -> Result<(), NoSolution> {
137        self.0.leak_check(max_input_universe, None).map_err(|_| NoSolution)
138    }
139
140    fn evaluate_const(
141        &self,
142        param_env: ty::ParamEnv<'tcx>,
143        uv: ty::UnevaluatedConst<'tcx>,
144    ) -> Option<ty::Const<'tcx>> {
145        let ct = ty::Const::new_unevaluated(self.tcx, uv);
146
147        match crate::traits::try_evaluate_const(&self.0, ct, param_env) {
148            Ok(ct) => Some(ct),
149            Err(EvaluateConstErr::EvaluationFailure(e)) => Some(ty::Const::new_error(self.tcx, e)),
150            Err(
151                EvaluateConstErr::InvalidConstParamTy(_) | EvaluateConstErr::HasGenericsOrInfers,
152            ) => None,
153        }
154    }
155
156    fn well_formed_goals(
157        &self,
158        param_env: ty::ParamEnv<'tcx>,
159        term: ty::Term<'tcx>,
160    ) -> Option<Vec<Goal<'tcx, ty::Predicate<'tcx>>>> {
161        crate::traits::wf::unnormalized_obligations(
162            &self.0,
163            param_env,
164            term,
165            DUMMY_SP,
166            CRATE_DEF_ID,
167        )
168        .map(|obligations| obligations.into_iter().map(|obligation| obligation.as_goal()).collect())
169    }
170
171    fn make_deduplicated_outlives_constraints(
172        &self,
173    ) -> Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>> {
174        // Cannot use `take_registered_region_obligations` as we may compute the response
175        // inside of a `probe` whenever we have multiple choices inside of the solver.
176        let region_obligations = self.0.inner.borrow().region_obligations().to_owned();
177        let region_constraints = self.0.with_region_constraints(|region_constraints| {
178            make_query_region_constraints(
179                self.tcx,
180                region_obligations
181                    .iter()
182                    .map(|r_o| (r_o.sup_type, r_o.sub_region, r_o.origin.to_constraint_category())),
183                region_constraints,
184            )
185        });
186
187        let mut seen = FxHashSet::default();
188        region_constraints
189            .outlives
190            .into_iter()
191            .filter(|&(outlives, _)| seen.insert(outlives))
192            .map(|(outlives, _)| outlives)
193            .collect()
194    }
195
196    fn instantiate_canonical<V>(
197        &self,
198        canonical: Canonical<'tcx, V>,
199        values: CanonicalVarValues<'tcx>,
200    ) -> V
201    where
202        V: TypeFoldable<TyCtxt<'tcx>>,
203    {
204        canonical.instantiate(self.tcx, &values)
205    }
206
207    fn instantiate_canonical_var_with_infer(
208        &self,
209        kind: CanonicalVarKind<'tcx>,
210        span: Span,
211        universe_map: impl Fn(ty::UniverseIndex) -> ty::UniverseIndex,
212    ) -> ty::GenericArg<'tcx> {
213        self.0.instantiate_canonical_var(span, kind, universe_map)
214    }
215
216    fn add_item_bounds_for_hidden_type(
217        &self,
218        def_id: DefId,
219        args: ty::GenericArgsRef<'tcx>,
220        param_env: ty::ParamEnv<'tcx>,
221        hidden_ty: Ty<'tcx>,
222        goals: &mut Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
223    ) {
224        self.0.add_item_bounds_for_hidden_type(def_id, args, param_env, hidden_ty, goals);
225    }
226
227    fn fetch_eligible_assoc_item(
228        &self,
229        goal_trait_ref: ty::TraitRef<'tcx>,
230        trait_assoc_def_id: DefId,
231        impl_def_id: DefId,
232    ) -> Result<Option<DefId>, ErrorGuaranteed> {
233        let node_item = specialization_graph::assoc_def(self.tcx, impl_def_id, trait_assoc_def_id)?;
234
235        let eligible = if node_item.is_final() {
236            // Non-specializable items are always projectable.
237            true
238        } else {
239            // Only reveal a specializable default if we're past type-checking
240            // and the obligation is monomorphic, otherwise passes such as
241            // transmute checking and polymorphic MIR optimizations could
242            // get a result which isn't correct for all monomorphizations.
243            match self.typing_mode() {
244                TypingMode::Coherence
245                | TypingMode::Analysis { .. }
246                | TypingMode::Borrowck { .. }
247                | TypingMode::PostBorrowckAnalysis { .. } => false,
248                TypingMode::PostAnalysis => {
249                    let poly_trait_ref = self.resolve_vars_if_possible(goal_trait_ref);
250                    !poly_trait_ref.still_further_specializable()
251                }
252            }
253        };
254
255        // FIXME: Check for defaultness here may cause diagnostics problems.
256        if eligible { Ok(Some(node_item.item.def_id)) } else { Ok(None) }
257    }
258
259    // FIXME: This actually should destructure the `Result` we get from transmutability and
260    // register candidates. We probably need to register >1 since we may have an OR of ANDs.
261    fn is_transmutable(
262        &self,
263        dst: Ty<'tcx>,
264        src: Ty<'tcx>,
265        assume: ty::Const<'tcx>,
266    ) -> Result<Certainty, NoSolution> {
267        // Erase regions because we compute layouts in `rustc_transmute`,
268        // which will ICE for region vars.
269        let (dst, src) = self.tcx.erase_regions((dst, src));
270
271        let Some(assume) = rustc_transmute::Assume::from_const(self.tcx, assume) else {
272            return Err(NoSolution);
273        };
274
275        // FIXME(transmutability): This really should be returning nested goals for `Answer::If*`
276        match rustc_transmute::TransmuteTypeEnv::new(self.0.tcx)
277            .is_transmutable(rustc_transmute::Types { src, dst }, assume)
278        {
279            rustc_transmute::Answer::Yes => Ok(Certainty::Yes),
280            rustc_transmute::Answer::No(_) | rustc_transmute::Answer::If(_) => Err(NoSolution),
281        }
282    }
283}
rustc_trait_selection/solve/delegate.rs

rustc_trait_selection/solve/
delegate.rs
