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 self.shallow_resolve(trait_pred.self_ty().skip_binder()).is_ty_var()
68                // We don't do this fast path when opaques are defined since we may
69                // eventually use opaques to incompletely guide inference via ty var
70                // self types.
71                // FIXME: Properly consider opaques here.
72                && self.inner.borrow_mut().opaque_types().is_empty()
73            {
74                return Some(Certainty::AMBIGUOUS);
75            }
76
77            if trait_pred.polarity() == ty::PredicatePolarity::Positive {
78                match self.0.tcx.as_lang_item(trait_pred.def_id()) {
79                    Some(LangItem::Sized)
80                        if self
81                            .resolve_vars_if_possible(trait_pred.self_ty().skip_binder())
82                            .is_trivially_sized(self.0.tcx) =>
83                    {
84                        return Some(Certainty::Yes);
85                    }
86                    Some(LangItem::Copy | LangItem::Clone) => {
87                        let self_ty =
88                            self.resolve_vars_if_possible(trait_pred.self_ty().skip_binder());
89                        // Unlike `Sized` traits, which always prefer the built-in impl,
90                        // `Copy`/`Clone` may be shadowed by a param-env candidate which
91                        // could force a lifetime error or guide inference. While that's
92                        // not generally desirable, it is observable, so for now let's
93                        // ignore this fast path for types that have regions or infer.
94                        if !self_ty
95                            .has_type_flags(TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_INFER)
96                            && self_ty.is_trivially_pure_clone_copy()
97                        {
98                            return Some(Certainty::Yes);
99                        }
100                    }
101                    _ => {}
102                }
103            }
104        }
105
106        let pred = goal.predicate.kind();
107        match pred.no_bound_vars()? {
108            ty::PredicateKind::DynCompatible(def_id) if self.0.tcx.is_dyn_compatible(def_id) => {
109                Some(Certainty::Yes)
110            }
111            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(outlives)) => {
112                self.0.sub_regions(
113                    SubregionOrigin::RelateRegionParamBound(span, None),
114                    outlives.1,
115                    outlives.0,
116                );
117                Some(Certainty::Yes)
118            }
119            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(outlives)) => {
120                self.0.register_type_outlives_constraint(
121                    outlives.0,
122                    outlives.1,
123                    &ObligationCause::dummy_with_span(span),
124                );
125
126                Some(Certainty::Yes)
127            }
128            ty::PredicateKind::Subtype(ty::SubtypePredicate { a, b, .. })
129            | ty::PredicateKind::Coerce(ty::CoercePredicate { a, b }) => {
130                if self.shallow_resolve(a).is_ty_var() && self.shallow_resolve(b).is_ty_var() {
131                    // FIXME: We also need to register a subtype relation between these vars
132                    // when those are added, and if they aren't in the same sub root then
133                    // we should mark this goal as `has_changed`.
134                    Some(Certainty::AMBIGUOUS)
135                } else {
136                    None
137                }
138            }
139            _ => None,
140        }
141    }
142
143    fn fresh_var_for_kind_with_span(
144        &self,
145        arg: ty::GenericArg<'tcx>,
146        span: Span,
147    ) -> ty::GenericArg<'tcx> {
148        match arg.kind() {
149            ty::GenericArgKind::Lifetime(_) => {
150                self.next_region_var(RegionVariableOrigin::MiscVariable(span)).into()
151            }
152            ty::GenericArgKind::Type(_) => self.next_ty_var(span).into(),
153            ty::GenericArgKind::Const(_) => self.next_const_var(span).into(),
154        }
155    }
156
157    fn leak_check(&self, max_input_universe: ty::UniverseIndex) -> Result<(), NoSolution> {
158        self.0.leak_check(max_input_universe, None).map_err(|_| NoSolution)
159    }
160
161    fn evaluate_const(
162        &self,
163        param_env: ty::ParamEnv<'tcx>,
164        uv: ty::UnevaluatedConst<'tcx>,
165    ) -> Option<ty::Const<'tcx>> {
166        let ct = ty::Const::new_unevaluated(self.tcx, uv);
167
168        match crate::traits::try_evaluate_const(&self.0, ct, param_env) {
169            Ok(ct) => Some(ct),
170            Err(EvaluateConstErr::EvaluationFailure(e)) => Some(ty::Const::new_error(self.tcx, e)),
171            Err(
172                EvaluateConstErr::InvalidConstParamTy(_) | EvaluateConstErr::HasGenericsOrInfers,
173            ) => None,
174        }
175    }
176
177    fn well_formed_goals(
178        &self,
179        param_env: ty::ParamEnv<'tcx>,
180        term: ty::Term<'tcx>,
181    ) -> Option<Vec<Goal<'tcx, ty::Predicate<'tcx>>>> {
182        crate::traits::wf::unnormalized_obligations(
183            &self.0,
184            param_env,
185            term,
186            DUMMY_SP,
187            CRATE_DEF_ID,
188        )
189        .map(|obligations| obligations.into_iter().map(|obligation| obligation.as_goal()).collect())
190    }
191
192    fn make_deduplicated_outlives_constraints(
193        &self,
194    ) -> Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>> {
195        // Cannot use `take_registered_region_obligations` as we may compute the response
196        // inside of a `probe` whenever we have multiple choices inside of the solver.
197        let region_obligations = self.0.inner.borrow().region_obligations().to_owned();
198        let region_constraints = self.0.with_region_constraints(|region_constraints| {
199            make_query_region_constraints(
200                self.tcx,
201                region_obligations
202                    .iter()
203                    .map(|r_o| (r_o.sup_type, r_o.sub_region, r_o.origin.to_constraint_category())),
204                region_constraints,
205            )
206        });
207
208        let mut seen = FxHashSet::default();
209        region_constraints
210            .outlives
211            .into_iter()
212            .filter(|&(outlives, _)| seen.insert(outlives))
213            .map(|(outlives, _)| outlives)
214            .collect()
215    }
216
217    fn instantiate_canonical<V>(
218        &self,
219        canonical: Canonical<'tcx, V>,
220        values: CanonicalVarValues<'tcx>,
221    ) -> V
222    where
223        V: TypeFoldable<TyCtxt<'tcx>>,
224    {
225        canonical.instantiate(self.tcx, &values)
226    }
227
228    fn instantiate_canonical_var_with_infer(
229        &self,
230        kind: CanonicalVarKind<'tcx>,
231        span: Span,
232        universe_map: impl Fn(ty::UniverseIndex) -> ty::UniverseIndex,
233    ) -> ty::GenericArg<'tcx> {
234        self.0.instantiate_canonical_var(span, kind, universe_map)
235    }
236
237    fn add_item_bounds_for_hidden_type(
238        &self,
239        def_id: DefId,
240        args: ty::GenericArgsRef<'tcx>,
241        param_env: ty::ParamEnv<'tcx>,
242        hidden_ty: Ty<'tcx>,
243        goals: &mut Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
244    ) {
245        self.0.add_item_bounds_for_hidden_type(def_id, args, param_env, hidden_ty, goals);
246    }
247
248    fn fetch_eligible_assoc_item(
249        &self,
250        goal_trait_ref: ty::TraitRef<'tcx>,
251        trait_assoc_def_id: DefId,
252        impl_def_id: DefId,
253    ) -> Result<Option<DefId>, ErrorGuaranteed> {
254        let node_item = specialization_graph::assoc_def(self.tcx, impl_def_id, trait_assoc_def_id)?;
255
256        let eligible = if node_item.is_final() {
257            // Non-specializable items are always projectable.
258            true
259        } else {
260            // Only reveal a specializable default if we're past type-checking
261            // and the obligation is monomorphic, otherwise passes such as
262            // transmute checking and polymorphic MIR optimizations could
263            // get a result which isn't correct for all monomorphizations.
264            match self.typing_mode() {
265                TypingMode::Coherence
266                | TypingMode::Analysis { .. }
267                | TypingMode::Borrowck { .. }
268                | TypingMode::PostBorrowckAnalysis { .. } => false,
269                TypingMode::PostAnalysis => {
270                    let poly_trait_ref = self.resolve_vars_if_possible(goal_trait_ref);
271                    !poly_trait_ref.still_further_specializable()
272                }
273            }
274        };
275
276        // FIXME: Check for defaultness here may cause diagnostics problems.
277        if eligible { Ok(Some(node_item.item.def_id)) } else { Ok(None) }
278    }
279
280    // FIXME: This actually should destructure the `Result` we get from transmutability and
281    // register candidates. We probably need to register >1 since we may have an OR of ANDs.
282    fn is_transmutable(
283        &self,
284        dst: Ty<'tcx>,
285        src: Ty<'tcx>,
286        assume: ty::Const<'tcx>,
287    ) -> Result<Certainty, NoSolution> {
288        // Erase regions because we compute layouts in `rustc_transmute`,
289        // which will ICE for region vars.
290        let (dst, src) = self.tcx.erase_regions((dst, src));
291
292        let Some(assume) = rustc_transmute::Assume::from_const(self.tcx, assume) else {
293            return Err(NoSolution);
294        };
295
296        // FIXME(transmutability): This really should be returning nested goals for `Answer::If*`
297        match rustc_transmute::TransmuteTypeEnv::new(self.0.tcx)
298            .is_transmutable(rustc_transmute::Types { src, dst }, assume)
299        {
300            rustc_transmute::Answer::Yes => Ok(Certainty::Yes),
301            rustc_transmute::Answer::No(_) | rustc_transmute::Answer::If(_) => Err(NoSolution),
302        }
303    }
304}