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9c376795 FG |
1 | use crate::traits::{specialization_graph, translate_substs}; |
2 | ||
3 | use super::assembly::{self, Candidate, CandidateSource}; | |
4 | use super::infcx_ext::InferCtxtExt; | |
5 | use super::trait_goals::structural_traits; | |
6 | use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult}; | |
7 | use rustc_errors::ErrorGuaranteed; | |
8 | use rustc_hir::def::DefKind; | |
9 | use rustc_hir::def_id::DefId; | |
10 | use rustc_infer::infer::InferCtxt; | |
11 | use rustc_infer::traits::query::NoSolution; | |
12 | use rustc_infer::traits::specialization_graph::LeafDef; | |
13 | use rustc_infer::traits::Reveal; | |
14 | use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams}; | |
15 | use rustc_middle::ty::{self, Ty, TyCtxt}; | |
16 | use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor}; | |
17 | use rustc_middle::ty::{ToPredicate, TypeVisitable}; | |
18 | use rustc_span::DUMMY_SP; | |
19 | use std::iter; | |
20 | use std::ops::ControlFlow; | |
21 | ||
22 | impl<'tcx> EvalCtxt<'_, 'tcx> { | |
23 | pub(super) fn compute_projection_goal( | |
24 | &mut self, | |
25 | goal: Goal<'tcx, ProjectionPredicate<'tcx>>, | |
26 | ) -> QueryResult<'tcx> { | |
27 | // To only compute normalization once for each projection we only | |
28 | // normalize if the expected term is an unconstrained inference variable. | |
29 | // | |
30 | // E.g. for `<T as Trait>::Assoc = u32` we recursively compute the goal | |
31 | // `exists<U> <T as Trait>::Assoc = U` and then take the resulting type for | |
32 | // `U` and equate it with `u32`. This means that we don't need a separate | |
33 | // projection cache in the solver. | |
34 | if self.term_is_fully_unconstrained(goal) { | |
35 | let candidates = self.assemble_and_evaluate_candidates(goal); | |
36 | self.merge_project_candidates(candidates) | |
37 | } else { | |
38 | let predicate = goal.predicate; | |
39 | let unconstrained_rhs = match predicate.term.unpack() { | |
40 | ty::TermKind::Ty(_) => self.infcx.next_ty_infer().into(), | |
41 | ty::TermKind::Const(ct) => self.infcx.next_const_infer(ct.ty()).into(), | |
42 | }; | |
43 | let unconstrained_predicate = ty::Clause::Projection(ProjectionPredicate { | |
44 | projection_ty: goal.predicate.projection_ty, | |
45 | term: unconstrained_rhs, | |
46 | }); | |
47 | let (_has_changed, normalize_certainty) = | |
48 | self.evaluate_goal(goal.with(self.tcx(), unconstrained_predicate))?; | |
49 | ||
50 | let nested_eq_goals = | |
51 | self.infcx.eq(goal.param_env, unconstrained_rhs, predicate.term)?; | |
52 | let eval_certainty = self.evaluate_all(nested_eq_goals)?; | |
53 | self.make_canonical_response(normalize_certainty.unify_and(eval_certainty)) | |
54 | } | |
55 | } | |
56 | ||
57 | /// Is the projection predicate is of the form `exists<T> <Ty as Trait>::Assoc = T`. | |
58 | /// | |
59 | /// This is the case if the `term` is an inference variable in the innermost universe | |
60 | /// and does not occur in any other part of the predicate. | |
61 | fn term_is_fully_unconstrained(&self, goal: Goal<'tcx, ProjectionPredicate<'tcx>>) -> bool { | |
62 | let infcx = self.infcx; | |
63 | let term_is_infer = match goal.predicate.term.unpack() { | |
64 | ty::TermKind::Ty(ty) => { | |
65 | if let &ty::Infer(ty::TyVar(vid)) = ty.kind() { | |
66 | match infcx.probe_ty_var(vid) { | |
67 | Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"), | |
68 | Err(universe) => universe == infcx.universe(), | |
69 | } | |
70 | } else { | |
71 | false | |
72 | } | |
73 | } | |
74 | ty::TermKind::Const(ct) => { | |
75 | if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = ct.kind() { | |
76 | match self.infcx.probe_const_var(vid) { | |
77 | Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"), | |
78 | Err(universe) => universe == infcx.universe(), | |
79 | } | |
80 | } else { | |
81 | false | |
82 | } | |
83 | } | |
84 | }; | |
85 | ||
86 | // Guard against `<T as Trait<?0>>::Assoc = ?0>`. | |
87 | struct ContainsTerm<'tcx> { | |
88 | term: ty::Term<'tcx>, | |
89 | } | |
90 | impl<'tcx> TypeVisitor<'tcx> for ContainsTerm<'tcx> { | |
91 | type BreakTy = (); | |
92 | fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { | |
93 | if t.needs_infer() { | |
94 | if ty::Term::from(t) == self.term { | |
95 | ControlFlow::BREAK | |
96 | } else { | |
97 | t.super_visit_with(self) | |
98 | } | |
99 | } else { | |
100 | ControlFlow::CONTINUE | |
101 | } | |
102 | } | |
103 | ||
104 | fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> { | |
105 | if c.needs_infer() { | |
106 | if ty::Term::from(c) == self.term { | |
107 | ControlFlow::BREAK | |
108 | } else { | |
109 | c.super_visit_with(self) | |
110 | } | |
111 | } else { | |
112 | ControlFlow::CONTINUE | |
113 | } | |
114 | } | |
115 | } | |
116 | ||
117 | let mut visitor = ContainsTerm { term: goal.predicate.term }; | |
118 | ||
119 | term_is_infer | |
120 | && goal.predicate.projection_ty.visit_with(&mut visitor).is_continue() | |
121 | && goal.param_env.visit_with(&mut visitor).is_continue() | |
122 | } | |
123 | ||
124 | fn merge_project_candidates( | |
125 | &mut self, | |
126 | mut candidates: Vec<Candidate<'tcx>>, | |
127 | ) -> QueryResult<'tcx> { | |
128 | match candidates.len() { | |
129 | 0 => return Err(NoSolution), | |
130 | 1 => return Ok(candidates.pop().unwrap().result), | |
131 | _ => {} | |
132 | } | |
133 | ||
134 | if candidates.len() > 1 { | |
135 | let mut i = 0; | |
136 | 'outer: while i < candidates.len() { | |
137 | for j in (0..candidates.len()).filter(|&j| i != j) { | |
138 | if self.project_candidate_should_be_dropped_in_favor_of( | |
139 | &candidates[i], | |
140 | &candidates[j], | |
141 | ) { | |
142 | debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len()); | |
143 | candidates.swap_remove(i); | |
144 | continue 'outer; | |
145 | } | |
146 | } | |
147 | ||
148 | debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len()); | |
149 | // If there are *STILL* multiple candidates, give up | |
150 | // and report ambiguity. | |
151 | i += 1; | |
152 | if i > 1 { | |
153 | debug!("multiple matches, ambig"); | |
154 | // FIXME: return overflow if all candidates overflow, otherwise return ambiguity. | |
155 | unimplemented!(); | |
156 | } | |
157 | } | |
158 | } | |
159 | ||
160 | Ok(candidates.pop().unwrap().result) | |
161 | } | |
162 | ||
163 | fn project_candidate_should_be_dropped_in_favor_of( | |
164 | &self, | |
165 | candidate: &Candidate<'tcx>, | |
166 | other: &Candidate<'tcx>, | |
167 | ) -> bool { | |
168 | // FIXME: implement this | |
169 | match (candidate.source, other.source) { | |
170 | (CandidateSource::Impl(_), _) | |
171 | | (CandidateSource::ParamEnv(_), _) | |
172 | | (CandidateSource::BuiltinImpl, _) | |
173 | | (CandidateSource::AliasBound(_), _) => unimplemented!(), | |
174 | } | |
175 | } | |
176 | } | |
177 | ||
178 | impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> { | |
179 | fn self_ty(self) -> Ty<'tcx> { | |
180 | self.self_ty() | |
181 | } | |
182 | ||
183 | fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self { | |
184 | self.with_self_ty(tcx, self_ty) | |
185 | } | |
186 | ||
187 | fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId { | |
188 | self.trait_def_id(tcx) | |
189 | } | |
190 | ||
191 | fn consider_impl_candidate( | |
192 | ecx: &mut EvalCtxt<'_, 'tcx>, | |
193 | goal: Goal<'tcx, ProjectionPredicate<'tcx>>, | |
194 | impl_def_id: DefId, | |
195 | ) -> QueryResult<'tcx> { | |
196 | let tcx = ecx.tcx(); | |
197 | ||
198 | let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx); | |
199 | let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); | |
200 | let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder }; | |
201 | if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs) | |
202 | .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp)) | |
203 | { | |
204 | return Err(NoSolution); | |
205 | } | |
206 | ||
207 | ecx.infcx.probe(|_| { | |
208 | let impl_substs = ecx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id); | |
209 | let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs); | |
210 | ||
211 | let mut nested_goals = ecx.infcx.eq(goal.param_env, goal_trait_ref, impl_trait_ref)?; | |
212 | let where_clause_bounds = tcx | |
213 | .predicates_of(impl_def_id) | |
214 | .instantiate(tcx, impl_substs) | |
215 | .predicates | |
216 | .into_iter() | |
217 | .map(|pred| goal.with(tcx, pred)); | |
218 | ||
219 | nested_goals.extend(where_clause_bounds); | |
220 | let trait_ref_certainty = ecx.evaluate_all(nested_goals)?; | |
221 | ||
222 | // In case the associated item is hidden due to specialization, we have to | |
223 | // return ambiguity this would otherwise be incomplete, resulting in | |
224 | // unsoundness during coherence (#105782). | |
225 | let Some(assoc_def) = fetch_eligible_assoc_item_def( | |
226 | ecx.infcx, | |
227 | goal.param_env, | |
228 | goal_trait_ref, | |
229 | goal.predicate.def_id(), | |
230 | impl_def_id | |
231 | )? else { | |
232 | let certainty = Certainty::Maybe(MaybeCause::Ambiguity); | |
233 | return ecx.make_canonical_response(trait_ref_certainty.unify_and(certainty)); | |
234 | }; | |
235 | ||
236 | if !assoc_def.item.defaultness(tcx).has_value() { | |
237 | tcx.sess.delay_span_bug( | |
238 | tcx.def_span(assoc_def.item.def_id), | |
239 | "missing value for assoc item in impl", | |
240 | ); | |
241 | } | |
242 | ||
243 | // Getting the right substitutions here is complex, e.g. given: | |
244 | // - a goal `<Vec<u32> as Trait<i32>>::Assoc<u64>` | |
245 | // - the applicable impl `impl<T> Trait<i32> for Vec<T>` | |
246 | // - and the impl which defines `Assoc` being `impl<T, U> Trait<U> for Vec<T>` | |
247 | // | |
248 | // We first rebase the goal substs onto the impl, going from `[Vec<u32>, i32, u64]` | |
249 | // to `[u32, u64]`. | |
250 | // | |
251 | // And then map these substs to the substs of the defining impl of `Assoc`, going | |
252 | // from `[u32, u64]` to `[u32, i32, u64]`. | |
253 | let impl_substs_with_gat = goal.predicate.projection_ty.substs.rebase_onto( | |
254 | tcx, | |
255 | goal_trait_ref.def_id, | |
256 | impl_substs, | |
257 | ); | |
258 | let substs = translate_substs( | |
259 | ecx.infcx, | |
260 | goal.param_env, | |
261 | impl_def_id, | |
262 | impl_substs_with_gat, | |
263 | assoc_def.defining_node, | |
264 | ); | |
265 | ||
266 | // Finally we construct the actual value of the associated type. | |
267 | let is_const = matches!(tcx.def_kind(assoc_def.item.def_id), DefKind::AssocConst); | |
268 | let ty = tcx.bound_type_of(assoc_def.item.def_id); | |
269 | let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const { | |
270 | let identity_substs = | |
271 | ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id); | |
272 | let did = ty::WithOptConstParam::unknown(assoc_def.item.def_id); | |
273 | let kind = | |
274 | ty::ConstKind::Unevaluated(ty::UnevaluatedConst::new(did, identity_substs)); | |
275 | ty.map_bound(|ty| tcx.mk_const(kind, ty).into()) | |
276 | } else { | |
277 | ty.map_bound(|ty| ty.into()) | |
278 | }; | |
279 | ||
280 | // The term of our goal should be fully unconstrained, so this should never fail. | |
281 | // | |
282 | // It can however be ambiguous when the resolved type is a projection. | |
283 | let nested_goals = ecx | |
284 | .infcx | |
285 | .eq(goal.param_env, goal.predicate.term, term.subst(tcx, substs)) | |
286 | .expect("failed to unify with unconstrained term"); | |
287 | let rhs_certainty = | |
288 | ecx.evaluate_all(nested_goals).expect("failed to unify with unconstrained term"); | |
289 | ||
290 | ecx.make_canonical_response(trait_ref_certainty.unify_and(rhs_certainty)) | |
291 | }) | |
292 | } | |
293 | ||
294 | fn consider_assumption( | |
295 | ecx: &mut EvalCtxt<'_, 'tcx>, | |
296 | goal: Goal<'tcx, Self>, | |
297 | assumption: ty::Predicate<'tcx>, | |
298 | ) -> QueryResult<'tcx> { | |
299 | if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() { | |
300 | ecx.infcx.probe(|_| { | |
301 | let assumption_projection_pred = | |
302 | ecx.infcx.instantiate_bound_vars_with_infer(poly_projection_pred); | |
303 | let nested_goals = ecx.infcx.eq( | |
304 | goal.param_env, | |
305 | goal.predicate.projection_ty, | |
306 | assumption_projection_pred.projection_ty, | |
307 | )?; | |
308 | let subst_certainty = ecx.evaluate_all(nested_goals)?; | |
309 | ||
310 | // The term of our goal should be fully unconstrained, so this should never fail. | |
311 | // | |
312 | // It can however be ambiguous when the resolved type is a projection. | |
313 | let nested_goals = ecx | |
314 | .infcx | |
315 | .eq(goal.param_env, goal.predicate.term, assumption_projection_pred.term) | |
316 | .expect("failed to unify with unconstrained term"); | |
317 | let rhs_certainty = ecx | |
318 | .evaluate_all(nested_goals) | |
319 | .expect("failed to unify with unconstrained term"); | |
320 | ||
321 | ecx.make_canonical_response(subst_certainty.unify_and(rhs_certainty)) | |
322 | }) | |
323 | } else { | |
324 | Err(NoSolution) | |
325 | } | |
326 | } | |
327 | ||
328 | fn consider_auto_trait_candidate( | |
329 | _ecx: &mut EvalCtxt<'_, 'tcx>, | |
330 | goal: Goal<'tcx, Self>, | |
331 | ) -> QueryResult<'tcx> { | |
332 | bug!("auto traits do not have associated types: {:?}", goal); | |
333 | } | |
334 | ||
335 | fn consider_trait_alias_candidate( | |
336 | _ecx: &mut EvalCtxt<'_, 'tcx>, | |
337 | goal: Goal<'tcx, Self>, | |
338 | ) -> QueryResult<'tcx> { | |
339 | bug!("trait aliases do not have associated types: {:?}", goal); | |
340 | } | |
341 | ||
342 | fn consider_builtin_sized_candidate( | |
343 | _ecx: &mut EvalCtxt<'_, 'tcx>, | |
344 | goal: Goal<'tcx, Self>, | |
345 | ) -> QueryResult<'tcx> { | |
346 | bug!("`Sized` does not have an associated type: {:?}", goal); | |
347 | } | |
348 | ||
349 | fn consider_builtin_copy_clone_candidate( | |
350 | _ecx: &mut EvalCtxt<'_, 'tcx>, | |
351 | goal: Goal<'tcx, Self>, | |
352 | ) -> QueryResult<'tcx> { | |
353 | bug!("`Copy`/`Clone` does not have an associated type: {:?}", goal); | |
354 | } | |
355 | ||
356 | fn consider_builtin_pointer_sized_candidate( | |
357 | _ecx: &mut EvalCtxt<'_, 'tcx>, | |
358 | goal: Goal<'tcx, Self>, | |
359 | ) -> QueryResult<'tcx> { | |
360 | bug!("`PointerSized` does not have an associated type: {:?}", goal); | |
361 | } | |
362 | ||
363 | fn consider_builtin_fn_trait_candidates( | |
364 | ecx: &mut EvalCtxt<'_, 'tcx>, | |
365 | goal: Goal<'tcx, Self>, | |
366 | goal_kind: ty::ClosureKind, | |
367 | ) -> QueryResult<'tcx> { | |
368 | if let Some(tupled_inputs_and_output) = | |
369 | structural_traits::extract_tupled_inputs_and_output_from_callable( | |
370 | ecx.tcx(), | |
371 | goal.predicate.self_ty(), | |
372 | goal_kind, | |
373 | )? | |
374 | { | |
375 | let pred = tupled_inputs_and_output | |
376 | .map_bound(|(inputs, output)| ty::ProjectionPredicate { | |
377 | projection_ty: ecx | |
378 | .tcx() | |
379 | .mk_alias_ty(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]), | |
380 | term: output.into(), | |
381 | }) | |
382 | .to_predicate(ecx.tcx()); | |
383 | Self::consider_assumption(ecx, goal, pred) | |
384 | } else { | |
385 | ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity)) | |
386 | } | |
387 | } | |
388 | ||
389 | fn consider_builtin_tuple_candidate( | |
390 | _ecx: &mut EvalCtxt<'_, 'tcx>, | |
391 | goal: Goal<'tcx, Self>, | |
392 | ) -> QueryResult<'tcx> { | |
393 | bug!("`Tuple` does not have an associated type: {:?}", goal); | |
394 | } | |
395 | } | |
396 | ||
397 | /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code. | |
398 | /// | |
399 | /// FIXME: We should merge these 3 implementations as it's likely that they otherwise | |
400 | /// diverge. | |
401 | #[instrument(level = "debug", skip(infcx, param_env), ret)] | |
402 | fn fetch_eligible_assoc_item_def<'tcx>( | |
403 | infcx: &InferCtxt<'tcx>, | |
404 | param_env: ty::ParamEnv<'tcx>, | |
405 | goal_trait_ref: ty::TraitRef<'tcx>, | |
406 | trait_assoc_def_id: DefId, | |
407 | impl_def_id: DefId, | |
408 | ) -> Result<Option<LeafDef>, NoSolution> { | |
409 | let node_item = specialization_graph::assoc_def(infcx.tcx, impl_def_id, trait_assoc_def_id) | |
410 | .map_err(|ErrorGuaranteed { .. }| NoSolution)?; | |
411 | ||
412 | let eligible = if node_item.is_final() { | |
413 | // Non-specializable items are always projectable. | |
414 | true | |
415 | } else { | |
416 | // Only reveal a specializable default if we're past type-checking | |
417 | // and the obligation is monomorphic, otherwise passes such as | |
418 | // transmute checking and polymorphic MIR optimizations could | |
419 | // get a result which isn't correct for all monomorphizations. | |
420 | if param_env.reveal() == Reveal::All { | |
421 | let poly_trait_ref = infcx.resolve_vars_if_possible(goal_trait_ref); | |
422 | !poly_trait_ref.still_further_specializable() | |
423 | } else { | |
424 | debug!(?node_item.item.def_id, "not eligible due to default"); | |
425 | false | |
426 | } | |
427 | }; | |
428 | ||
429 | if eligible { Ok(Some(node_item)) } else { Ok(None) } | |
430 | } |