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f035d41b XL |
1 | //! Candidate assembly. |
2 | //! | |
3 | //! The selection process begins by examining all in-scope impls, | |
4 | //! caller obligations, and so forth and assembling a list of | |
5 | //! candidates. See the [rustc dev guide] for more details. | |
6 | //! | |
7 | //! [rustc dev guide]:https://rustc-dev-guide.rust-lang.org/traits/resolution.html#candidate-assembly | |
5e7ed085 | 8 | use hir::LangItem; |
f035d41b | 9 | use rustc_hir as hir; |
c295e0f8 XL |
10 | use rustc_hir::def_id::DefId; |
11 | use rustc_infer::traits::TraitEngine; | |
f035d41b | 12 | use rustc_infer::traits::{Obligation, SelectionError, TraitObligation}; |
c295e0f8 | 13 | use rustc_lint_defs::builtin::DEREF_INTO_DYN_SUPERTRAIT; |
1b1a35ee | 14 | use rustc_middle::ty::print::with_no_trimmed_paths; |
a2a8927a | 15 | use rustc_middle::ty::{self, ToPredicate, Ty, TypeFoldable}; |
f035d41b XL |
16 | use rustc_target::spec::abi::Abi; |
17 | ||
c295e0f8 | 18 | use crate::traits; |
1b1a35ee | 19 | use crate::traits::coherence::Conflict; |
c295e0f8 | 20 | use crate::traits::query::evaluate_obligation::InferCtxtExt; |
f035d41b | 21 | use crate::traits::{util, SelectionResult}; |
3c0e092e | 22 | use crate::traits::{Ambiguous, ErrorReporting, Overflow, Unimplemented}; |
f035d41b XL |
23 | |
24 | use super::BuiltinImplConditions; | |
1b1a35ee XL |
25 | use super::IntercrateAmbiguityCause; |
26 | use super::OverflowError; | |
f035d41b | 27 | use super::SelectionCandidate::{self, *}; |
1b1a35ee | 28 | use super::{EvaluatedCandidate, SelectionCandidateSet, SelectionContext, TraitObligationStack}; |
f035d41b XL |
29 | |
30 | impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { | |
29967ef6 | 31 | #[instrument(level = "debug", skip(self))] |
f035d41b XL |
32 | pub(super) fn candidate_from_obligation<'o>( |
33 | &mut self, | |
34 | stack: &TraitObligationStack<'o, 'tcx>, | |
35 | ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> { | |
36 | // Watch out for overflow. This intentionally bypasses (and does | |
37 | // not update) the cache. | |
38 | self.check_recursion_limit(&stack.obligation, &stack.obligation)?; | |
39 | ||
40 | // Check the cache. Note that we freshen the trait-ref | |
41 | // separately rather than using `stack.fresh_trait_ref` -- | |
42 | // this is because we want the unbound variables to be | |
43 | // replaced with fresh types starting from index 0. | |
44 | let cache_fresh_trait_pred = self.infcx.freshen(stack.obligation.predicate); | |
29967ef6 | 45 | debug!(?cache_fresh_trait_pred); |
f035d41b XL |
46 | debug_assert!(!stack.obligation.predicate.has_escaping_bound_vars()); |
47 | ||
48 | if let Some(c) = | |
49 | self.check_candidate_cache(stack.obligation.param_env, cache_fresh_trait_pred) | |
50 | { | |
29967ef6 | 51 | debug!(candidate = ?c, "CACHE HIT"); |
f035d41b XL |
52 | return c; |
53 | } | |
54 | ||
55 | // If no match, compute result and insert into cache. | |
56 | // | |
57 | // FIXME(nikomatsakis) -- this cache is not taking into | |
58 | // account cycles that may have occurred in forming the | |
59 | // candidate. I don't know of any specific problems that | |
60 | // result but it seems awfully suspicious. | |
61 | let (candidate, dep_node) = | |
62 | self.in_task(|this| this.candidate_from_obligation_no_cache(stack)); | |
63 | ||
29967ef6 | 64 | debug!(?candidate, "CACHE MISS"); |
f035d41b XL |
65 | self.insert_candidate_cache( |
66 | stack.obligation.param_env, | |
67 | cache_fresh_trait_pred, | |
68 | dep_node, | |
69 | candidate.clone(), | |
70 | ); | |
71 | candidate | |
72 | } | |
73 | ||
1b1a35ee XL |
74 | fn candidate_from_obligation_no_cache<'o>( |
75 | &mut self, | |
76 | stack: &TraitObligationStack<'o, 'tcx>, | |
77 | ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> { | |
78 | if let Some(conflict) = self.is_knowable(stack) { | |
79 | debug!("coherence stage: not knowable"); | |
80 | if self.intercrate_ambiguity_causes.is_some() { | |
81 | debug!("evaluate_stack: intercrate_ambiguity_causes is some"); | |
82 | // Heuristics: show the diagnostics when there are no candidates in crate. | |
83 | if let Ok(candidate_set) = self.assemble_candidates(stack) { | |
84 | let mut no_candidates_apply = true; | |
85 | ||
86 | for c in candidate_set.vec.iter() { | |
87 | if self.evaluate_candidate(stack, &c)?.may_apply() { | |
88 | no_candidates_apply = false; | |
89 | break; | |
90 | } | |
91 | } | |
92 | ||
93 | if !candidate_set.ambiguous && no_candidates_apply { | |
94 | let trait_ref = stack.obligation.predicate.skip_binder().trait_ref; | |
95 | let self_ty = trait_ref.self_ty(); | |
5e7ed085 | 96 | let (trait_desc, self_desc) = with_no_trimmed_paths!({ |
1b1a35ee XL |
97 | let trait_desc = trait_ref.print_only_trait_path().to_string(); |
98 | let self_desc = if self_ty.has_concrete_skeleton() { | |
99 | Some(self_ty.to_string()) | |
100 | } else { | |
101 | None | |
102 | }; | |
103 | (trait_desc, self_desc) | |
104 | }); | |
105 | let cause = if let Conflict::Upstream = conflict { | |
106 | IntercrateAmbiguityCause::UpstreamCrateUpdate { trait_desc, self_desc } | |
107 | } else { | |
108 | IntercrateAmbiguityCause::DownstreamCrate { trait_desc, self_desc } | |
109 | }; | |
29967ef6 | 110 | debug!(?cause, "evaluate_stack: pushing cause"); |
1b1a35ee XL |
111 | self.intercrate_ambiguity_causes.as_mut().unwrap().push(cause); |
112 | } | |
113 | } | |
114 | } | |
115 | return Ok(None); | |
116 | } | |
117 | ||
118 | let candidate_set = self.assemble_candidates(stack)?; | |
119 | ||
120 | if candidate_set.ambiguous { | |
121 | debug!("candidate set contains ambig"); | |
122 | return Ok(None); | |
123 | } | |
124 | ||
3c0e092e | 125 | let candidates = candidate_set.vec; |
1b1a35ee | 126 | |
29967ef6 | 127 | debug!(?stack, ?candidates, "assembled {} candidates", candidates.len()); |
1b1a35ee XL |
128 | |
129 | // At this point, we know that each of the entries in the | |
130 | // candidate set is *individually* applicable. Now we have to | |
131 | // figure out if they contain mutual incompatibilities. This | |
132 | // frequently arises if we have an unconstrained input type -- | |
133 | // for example, we are looking for `$0: Eq` where `$0` is some | |
134 | // unconstrained type variable. In that case, we'll get a | |
135 | // candidate which assumes $0 == int, one that assumes `$0 == | |
136 | // usize`, etc. This spells an ambiguity. | |
137 | ||
3c0e092e XL |
138 | let mut candidates = self.filter_impls(candidates, stack.obligation); |
139 | ||
1b1a35ee XL |
140 | // If there is more than one candidate, first winnow them down |
141 | // by considering extra conditions (nested obligations and so | |
142 | // forth). We don't winnow if there is exactly one | |
143 | // candidate. This is a relatively minor distinction but it | |
144 | // can lead to better inference and error-reporting. An | |
145 | // example would be if there was an impl: | |
146 | // | |
147 | // impl<T:Clone> Vec<T> { fn push_clone(...) { ... } } | |
148 | // | |
149 | // and we were to see some code `foo.push_clone()` where `boo` | |
150 | // is a `Vec<Bar>` and `Bar` does not implement `Clone`. If | |
151 | // we were to winnow, we'd wind up with zero candidates. | |
152 | // Instead, we select the right impl now but report "`Bar` does | |
153 | // not implement `Clone`". | |
154 | if candidates.len() == 1 { | |
3c0e092e | 155 | return self.filter_reservation_impls(candidates.pop().unwrap(), stack.obligation); |
1b1a35ee XL |
156 | } |
157 | ||
158 | // Winnow, but record the exact outcome of evaluation, which | |
159 | // is needed for specialization. Propagate overflow if it occurs. | |
160 | let mut candidates = candidates | |
161 | .into_iter() | |
162 | .map(|c| match self.evaluate_candidate(stack, &c) { | |
163 | Ok(eval) if eval.may_apply() => { | |
164 | Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval })) | |
165 | } | |
166 | Ok(_) => Ok(None), | |
5e7ed085 | 167 | Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)), |
c295e0f8 | 168 | Err(OverflowError::ErrorReporting) => Err(ErrorReporting), |
5e7ed085 | 169 | Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))), |
1b1a35ee XL |
170 | }) |
171 | .flat_map(Result::transpose) | |
172 | .collect::<Result<Vec<_>, _>>()?; | |
173 | ||
29967ef6 | 174 | debug!(?stack, ?candidates, "winnowed to {} candidates", candidates.len()); |
1b1a35ee | 175 | |
29967ef6 | 176 | let needs_infer = stack.obligation.predicate.has_infer_types_or_consts(); |
1b1a35ee XL |
177 | |
178 | // If there are STILL multiple candidates, we can further | |
179 | // reduce the list by dropping duplicates -- including | |
180 | // resolving specializations. | |
181 | if candidates.len() > 1 { | |
182 | let mut i = 0; | |
183 | while i < candidates.len() { | |
184 | let is_dup = (0..candidates.len()).filter(|&j| i != j).any(|j| { | |
185 | self.candidate_should_be_dropped_in_favor_of( | |
186 | &candidates[i], | |
187 | &candidates[j], | |
188 | needs_infer, | |
189 | ) | |
190 | }); | |
191 | if is_dup { | |
29967ef6 | 192 | debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len()); |
1b1a35ee XL |
193 | candidates.swap_remove(i); |
194 | } else { | |
29967ef6 | 195 | debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len()); |
1b1a35ee XL |
196 | i += 1; |
197 | ||
198 | // If there are *STILL* multiple candidates, give up | |
199 | // and report ambiguity. | |
200 | if i > 1 { | |
201 | debug!("multiple matches, ambig"); | |
3c0e092e XL |
202 | return Err(Ambiguous( |
203 | candidates | |
204 | .into_iter() | |
205 | .filter_map(|c| match c.candidate { | |
206 | SelectionCandidate::ImplCandidate(def_id) => Some(def_id), | |
207 | _ => None, | |
208 | }) | |
209 | .collect(), | |
210 | )); | |
1b1a35ee XL |
211 | } |
212 | } | |
213 | } | |
214 | } | |
215 | ||
216 | // If there are *NO* candidates, then there are no impls -- | |
217 | // that we know of, anyway. Note that in the case where there | |
218 | // are unbound type variables within the obligation, it might | |
219 | // be the case that you could still satisfy the obligation | |
220 | // from another crate by instantiating the type variables with | |
221 | // a type from another crate that does have an impl. This case | |
222 | // is checked for in `evaluate_stack` (and hence users | |
223 | // who might care about this case, like coherence, should use | |
224 | // that function). | |
225 | if candidates.is_empty() { | |
226 | // If there's an error type, 'downgrade' our result from | |
227 | // `Err(Unimplemented)` to `Ok(None)`. This helps us avoid | |
228 | // emitting additional spurious errors, since we're guaranteed | |
229 | // to have emitted at least one. | |
04454e1e FG |
230 | if stack.obligation.predicate.references_error() { |
231 | debug!(?stack.obligation.predicate, "found error type in predicate, treating as ambiguous"); | |
1b1a35ee XL |
232 | return Ok(None); |
233 | } | |
234 | return Err(Unimplemented); | |
235 | } | |
236 | ||
237 | // Just one candidate left. | |
3c0e092e | 238 | self.filter_reservation_impls(candidates.pop().unwrap().candidate, stack.obligation) |
1b1a35ee XL |
239 | } |
240 | ||
c295e0f8 | 241 | #[instrument(skip(self, stack), level = "debug")] |
f035d41b XL |
242 | pub(super) fn assemble_candidates<'o>( |
243 | &mut self, | |
244 | stack: &TraitObligationStack<'o, 'tcx>, | |
245 | ) -> Result<SelectionCandidateSet<'tcx>, SelectionError<'tcx>> { | |
246 | let TraitObligationStack { obligation, .. } = *stack; | |
247 | let obligation = &Obligation { | |
248 | param_env: obligation.param_env, | |
249 | cause: obligation.cause.clone(), | |
250 | recursion_depth: obligation.recursion_depth, | |
fc512014 | 251 | predicate: self.infcx().resolve_vars_if_possible(obligation.predicate), |
f035d41b XL |
252 | }; |
253 | ||
254 | if obligation.predicate.skip_binder().self_ty().is_ty_var() { | |
5e7ed085 | 255 | debug!(ty = ?obligation.predicate.skip_binder().self_ty(), "ambiguous inference var or opaque type"); |
f035d41b XL |
256 | // Self is a type variable (e.g., `_: AsRef<str>`). |
257 | // | |
258 | // This is somewhat problematic, as the current scheme can't really | |
259 | // handle it turning to be a projection. This does end up as truly | |
260 | // ambiguous in most cases anyway. | |
261 | // | |
262 | // Take the fast path out - this also improves | |
263 | // performance by preventing assemble_candidates_from_impls from | |
264 | // matching every impl for this trait. | |
265 | return Ok(SelectionCandidateSet { vec: vec![], ambiguous: true }); | |
266 | } | |
267 | ||
268 | let mut candidates = SelectionCandidateSet { vec: Vec::new(), ambiguous: false }; | |
269 | ||
3c0e092e XL |
270 | // The only way to prove a NotImplemented(T: Foo) predicate is via a negative impl. |
271 | // There are no compiler built-in rules for this. | |
272 | if obligation.polarity() == ty::ImplPolarity::Negative { | |
273 | self.assemble_candidates_for_trait_alias(obligation, &mut candidates); | |
5869c6ff | 274 | self.assemble_candidates_from_impls(obligation, &mut candidates); |
f035d41b | 275 | } else { |
3c0e092e XL |
276 | self.assemble_candidates_for_trait_alias(obligation, &mut candidates); |
277 | ||
278 | // Other bounds. Consider both in-scope bounds from fn decl | |
279 | // and applicable impls. There is a certain set of precedence rules here. | |
280 | let def_id = obligation.predicate.def_id(); | |
281 | let lang_items = self.tcx().lang_items(); | |
282 | ||
283 | if lang_items.copy_trait() == Some(def_id) { | |
284 | debug!(obligation_self_ty = ?obligation.predicate.skip_binder().self_ty()); | |
285 | ||
286 | // User-defined copy impls are permitted, but only for | |
287 | // structs and enums. | |
288 | self.assemble_candidates_from_impls(obligation, &mut candidates); | |
289 | ||
290 | // For other types, we'll use the builtin rules. | |
291 | let copy_conditions = self.copy_clone_conditions(obligation); | |
292 | self.assemble_builtin_bound_candidates(copy_conditions, &mut candidates); | |
293 | } else if lang_items.discriminant_kind_trait() == Some(def_id) { | |
294 | // `DiscriminantKind` is automatically implemented for every type. | |
295 | candidates.vec.push(DiscriminantKindCandidate); | |
296 | } else if lang_items.pointee_trait() == Some(def_id) { | |
297 | // `Pointee` is automatically implemented for every type. | |
298 | candidates.vec.push(PointeeCandidate); | |
299 | } else if lang_items.sized_trait() == Some(def_id) { | |
300 | // Sized is never implementable by end-users, it is | |
301 | // always automatically computed. | |
302 | let sized_conditions = self.sized_conditions(obligation); | |
303 | self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates); | |
304 | } else if lang_items.unsize_trait() == Some(def_id) { | |
305 | self.assemble_candidates_for_unsizing(obligation, &mut candidates); | |
5e7ed085 FG |
306 | } else if lang_items.destruct_trait() == Some(def_id) { |
307 | self.assemble_const_destruct_candidates(obligation, &mut candidates); | |
3c0e092e XL |
308 | } else { |
309 | if lang_items.clone_trait() == Some(def_id) { | |
310 | // Same builtin conditions as `Copy`, i.e., every type which has builtin support | |
311 | // for `Copy` also has builtin support for `Clone`, and tuples/arrays of `Clone` | |
312 | // types have builtin support for `Clone`. | |
313 | let clone_conditions = self.copy_clone_conditions(obligation); | |
314 | self.assemble_builtin_bound_candidates(clone_conditions, &mut candidates); | |
315 | } | |
f035d41b | 316 | |
3c0e092e XL |
317 | self.assemble_generator_candidates(obligation, &mut candidates); |
318 | self.assemble_closure_candidates(obligation, &mut candidates); | |
319 | self.assemble_fn_pointer_candidates(obligation, &mut candidates); | |
320 | self.assemble_candidates_from_impls(obligation, &mut candidates); | |
321 | self.assemble_candidates_from_object_ty(obligation, &mut candidates); | |
322 | } | |
f035d41b | 323 | |
3c0e092e XL |
324 | self.assemble_candidates_from_projected_tys(obligation, &mut candidates); |
325 | self.assemble_candidates_from_caller_bounds(stack, &mut candidates)?; | |
326 | // Auto implementations have lower priority, so we only | |
327 | // consider triggering a default if there is no other impl that can apply. | |
328 | if candidates.vec.is_empty() { | |
329 | self.assemble_candidates_from_auto_impls(obligation, &mut candidates); | |
330 | } | |
f035d41b XL |
331 | } |
332 | debug!("candidate list size: {}", candidates.vec.len()); | |
333 | Ok(candidates) | |
334 | } | |
335 | ||
5099ac24 | 336 | #[tracing::instrument(level = "debug", skip(self, candidates))] |
f035d41b XL |
337 | fn assemble_candidates_from_projected_tys( |
338 | &mut self, | |
339 | obligation: &TraitObligation<'tcx>, | |
340 | candidates: &mut SelectionCandidateSet<'tcx>, | |
341 | ) { | |
f035d41b XL |
342 | // Before we go into the whole placeholder thing, just |
343 | // quickly check if the self-type is a projection at all. | |
1b1a35ee | 344 | match obligation.predicate.skip_binder().trait_ref.self_ty().kind() { |
f035d41b XL |
345 | ty::Projection(_) | ty::Opaque(..) => {} |
346 | ty::Infer(ty::TyVar(_)) => { | |
347 | span_bug!( | |
348 | obligation.cause.span, | |
349 | "Self=_ should have been handled by assemble_candidates" | |
350 | ); | |
351 | } | |
352 | _ => return, | |
353 | } | |
354 | ||
355 | let result = self | |
356 | .infcx | |
357 | .probe(|_| self.match_projection_obligation_against_definition_bounds(obligation)); | |
358 | ||
a2a8927a | 359 | candidates.vec.extend(result.into_iter().map(ProjectionCandidate)); |
f035d41b XL |
360 | } |
361 | ||
362 | /// Given an obligation like `<SomeTrait for T>`, searches the obligations that the caller | |
363 | /// supplied to find out whether it is listed among them. | |
364 | /// | |
365 | /// Never affects the inference environment. | |
5099ac24 | 366 | #[tracing::instrument(level = "debug", skip(self, stack, candidates))] |
f035d41b XL |
367 | fn assemble_candidates_from_caller_bounds<'o>( |
368 | &mut self, | |
369 | stack: &TraitObligationStack<'o, 'tcx>, | |
370 | candidates: &mut SelectionCandidateSet<'tcx>, | |
371 | ) -> Result<(), SelectionError<'tcx>> { | |
5099ac24 | 372 | debug!(?stack.obligation); |
f035d41b XL |
373 | |
374 | let all_bounds = stack | |
375 | .obligation | |
376 | .param_env | |
377 | .caller_bounds() | |
378 | .iter() | |
a2a8927a | 379 | .filter_map(|o| o.to_opt_poly_trait_pred()); |
f035d41b XL |
380 | |
381 | // Micro-optimization: filter out predicates relating to different traits. | |
382 | let matching_bounds = | |
a2a8927a | 383 | all_bounds.filter(|p| p.def_id() == stack.obligation.predicate.def_id()); |
f035d41b XL |
384 | |
385 | // Keep only those bounds which may apply, and propagate overflow if it occurs. | |
f035d41b | 386 | for bound in matching_bounds { |
a2a8927a XL |
387 | // FIXME(oli-obk): it is suspicious that we are dropping the constness and |
388 | // polarity here. | |
5e7ed085 | 389 | let wc = self.where_clause_may_apply(stack, bound.map_bound(|t| t.trait_ref))?; |
f035d41b | 390 | if wc.may_apply() { |
a2a8927a | 391 | candidates.vec.push(ParamCandidate(bound)); |
f035d41b XL |
392 | } |
393 | } | |
394 | ||
f035d41b XL |
395 | Ok(()) |
396 | } | |
397 | ||
398 | fn assemble_generator_candidates( | |
399 | &mut self, | |
400 | obligation: &TraitObligation<'tcx>, | |
401 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5869c6ff | 402 | ) { |
f035d41b | 403 | if self.tcx().lang_items().gen_trait() != Some(obligation.predicate.def_id()) { |
5869c6ff | 404 | return; |
f035d41b XL |
405 | } |
406 | ||
407 | // Okay to skip binder because the substs on generator types never | |
408 | // touch bound regions, they just capture the in-scope | |
409 | // type/region parameters. | |
410 | let self_ty = obligation.self_ty().skip_binder(); | |
1b1a35ee | 411 | match self_ty.kind() { |
f035d41b | 412 | ty::Generator(..) => { |
29967ef6 | 413 | debug!(?self_ty, ?obligation, "assemble_generator_candidates",); |
f035d41b XL |
414 | |
415 | candidates.vec.push(GeneratorCandidate); | |
416 | } | |
417 | ty::Infer(ty::TyVar(_)) => { | |
418 | debug!("assemble_generator_candidates: ambiguous self-type"); | |
419 | candidates.ambiguous = true; | |
420 | } | |
421 | _ => {} | |
422 | } | |
f035d41b XL |
423 | } |
424 | ||
425 | /// Checks for the artificial impl that the compiler will create for an obligation like `X : | |
426 | /// FnMut<..>` where `X` is a closure type. | |
427 | /// | |
428 | /// Note: the type parameters on a closure candidate are modeled as *output* type | |
429 | /// parameters and hence do not affect whether this trait is a match or not. They will be | |
430 | /// unified during the confirmation step. | |
431 | fn assemble_closure_candidates( | |
432 | &mut self, | |
433 | obligation: &TraitObligation<'tcx>, | |
434 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5869c6ff | 435 | ) { |
5e7ed085 FG |
436 | let Some(kind) = self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()) else { |
437 | return; | |
f035d41b XL |
438 | }; |
439 | ||
440 | // Okay to skip binder because the substs on closure types never | |
441 | // touch bound regions, they just capture the in-scope | |
442 | // type/region parameters | |
1b1a35ee | 443 | match *obligation.self_ty().skip_binder().kind() { |
f035d41b | 444 | ty::Closure(_, closure_substs) => { |
29967ef6 | 445 | debug!(?kind, ?obligation, "assemble_unboxed_candidates"); |
f035d41b XL |
446 | match self.infcx.closure_kind(closure_substs) { |
447 | Some(closure_kind) => { | |
29967ef6 | 448 | debug!(?closure_kind, "assemble_unboxed_candidates"); |
f035d41b XL |
449 | if closure_kind.extends(kind) { |
450 | candidates.vec.push(ClosureCandidate); | |
451 | } | |
452 | } | |
453 | None => { | |
454 | debug!("assemble_unboxed_candidates: closure_kind not yet known"); | |
455 | candidates.vec.push(ClosureCandidate); | |
456 | } | |
457 | } | |
458 | } | |
459 | ty::Infer(ty::TyVar(_)) => { | |
460 | debug!("assemble_unboxed_closure_candidates: ambiguous self-type"); | |
461 | candidates.ambiguous = true; | |
462 | } | |
463 | _ => {} | |
464 | } | |
f035d41b XL |
465 | } |
466 | ||
467 | /// Implements one of the `Fn()` family for a fn pointer. | |
468 | fn assemble_fn_pointer_candidates( | |
469 | &mut self, | |
470 | obligation: &TraitObligation<'tcx>, | |
471 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5869c6ff | 472 | ) { |
f035d41b XL |
473 | // We provide impl of all fn traits for fn pointers. |
474 | if self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()).is_none() { | |
5869c6ff | 475 | return; |
f035d41b XL |
476 | } |
477 | ||
478 | // Okay to skip binder because what we are inspecting doesn't involve bound regions. | |
479 | let self_ty = obligation.self_ty().skip_binder(); | |
1b1a35ee | 480 | match *self_ty.kind() { |
f035d41b XL |
481 | ty::Infer(ty::TyVar(_)) => { |
482 | debug!("assemble_fn_pointer_candidates: ambiguous self-type"); | |
483 | candidates.ambiguous = true; // Could wind up being a fn() type. | |
484 | } | |
485 | // Provide an impl, but only for suitable `fn` pointers. | |
486 | ty::FnPtr(_) => { | |
487 | if let ty::FnSig { | |
488 | unsafety: hir::Unsafety::Normal, | |
489 | abi: Abi::Rust, | |
490 | c_variadic: false, | |
491 | .. | |
492 | } = self_ty.fn_sig(self.tcx()).skip_binder() | |
493 | { | |
c295e0f8 | 494 | candidates.vec.push(FnPointerCandidate { is_const: false }); |
f035d41b XL |
495 | } |
496 | } | |
497 | // Provide an impl for suitable functions, rejecting `#[target_feature]` functions (RFC 2396). | |
498 | ty::FnDef(def_id, _) => { | |
499 | if let ty::FnSig { | |
500 | unsafety: hir::Unsafety::Normal, | |
501 | abi: Abi::Rust, | |
502 | c_variadic: false, | |
503 | .. | |
504 | } = self_ty.fn_sig(self.tcx()).skip_binder() | |
505 | { | |
506 | if self.tcx().codegen_fn_attrs(def_id).target_features.is_empty() { | |
c295e0f8 XL |
507 | candidates |
508 | .vec | |
509 | .push(FnPointerCandidate { is_const: self.tcx().is_const_fn(def_id) }); | |
f035d41b XL |
510 | } |
511 | } | |
512 | } | |
513 | _ => {} | |
514 | } | |
f035d41b XL |
515 | } |
516 | ||
517 | /// Searches for impls that might apply to `obligation`. | |
518 | fn assemble_candidates_from_impls( | |
519 | &mut self, | |
520 | obligation: &TraitObligation<'tcx>, | |
521 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5869c6ff | 522 | ) { |
29967ef6 | 523 | debug!(?obligation, "assemble_candidates_from_impls"); |
f035d41b XL |
524 | |
525 | // Essentially any user-written impl will match with an error type, | |
526 | // so creating `ImplCandidates` isn't useful. However, we might | |
527 | // end up finding a candidate elsewhere (e.g. a `BuiltinCandidate` for `Sized) | |
528 | // This helps us avoid overflow: see issue #72839 | |
529 | // Since compilation is already guaranteed to fail, this is just | |
530 | // to try to show the 'nicest' possible errors to the user. | |
3c0e092e XL |
531 | // We don't check for errors in the `ParamEnv` - in practice, |
532 | // it seems to cause us to be overly aggressive in deciding | |
533 | // to give up searching for candidates, leading to spurious errors. | |
534 | if obligation.predicate.references_error() { | |
5869c6ff | 535 | return; |
f035d41b XL |
536 | } |
537 | ||
538 | self.tcx().for_each_relevant_impl( | |
539 | obligation.predicate.def_id(), | |
540 | obligation.predicate.skip_binder().trait_ref.self_ty(), | |
541 | |impl_def_id| { | |
923072b8 FG |
542 | // Before we create the substitutions and everything, first |
543 | // consider a "quick reject". This avoids creating more types | |
544 | // and so forth that we need to. | |
545 | let impl_trait_ref = self.tcx().bound_impl_trait_ref(impl_def_id).unwrap(); | |
546 | if self.fast_reject_trait_refs(obligation, &impl_trait_ref.0) { | |
547 | return; | |
548 | } | |
549 | ||
f035d41b | 550 | self.infcx.probe(|_| { |
923072b8 | 551 | if let Ok(_substs) = self.match_impl(impl_def_id, impl_trait_ref, obligation) { |
f035d41b XL |
552 | candidates.vec.push(ImplCandidate(impl_def_id)); |
553 | } | |
554 | }); | |
555 | }, | |
556 | ); | |
f035d41b XL |
557 | } |
558 | ||
559 | fn assemble_candidates_from_auto_impls( | |
560 | &mut self, | |
561 | obligation: &TraitObligation<'tcx>, | |
562 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5869c6ff | 563 | ) { |
f035d41b XL |
564 | // Okay to skip binder here because the tests we do below do not involve bound regions. |
565 | let self_ty = obligation.self_ty().skip_binder(); | |
29967ef6 | 566 | debug!(?self_ty, "assemble_candidates_from_auto_impls"); |
f035d41b XL |
567 | |
568 | let def_id = obligation.predicate.def_id(); | |
569 | ||
570 | if self.tcx().trait_is_auto(def_id) { | |
1b1a35ee | 571 | match self_ty.kind() { |
f035d41b XL |
572 | ty::Dynamic(..) => { |
573 | // For object types, we don't know what the closed | |
574 | // over types are. This means we conservatively | |
575 | // say nothing; a candidate may be added by | |
576 | // `assemble_candidates_from_object_ty`. | |
577 | } | |
578 | ty::Foreign(..) => { | |
579 | // Since the contents of foreign types is unknown, | |
580 | // we don't add any `..` impl. Default traits could | |
581 | // still be provided by a manual implementation for | |
582 | // this trait and type. | |
583 | } | |
584 | ty::Param(..) | ty::Projection(..) => { | |
585 | // In these cases, we don't know what the actual | |
586 | // type is. Therefore, we cannot break it down | |
587 | // into its constituent types. So we don't | |
588 | // consider the `..` impl but instead just add no | |
589 | // candidates: this means that typeck will only | |
590 | // succeed if there is another reason to believe | |
591 | // that this obligation holds. That could be a | |
592 | // where-clause or, in the case of an object type, | |
593 | // it could be that the object type lists the | |
594 | // trait (e.g., `Foo+Send : Send`). See | |
5869c6ff | 595 | // `ui/typeck/typeck-default-trait-impl-send-param.rs` |
f035d41b XL |
596 | // for an example of a test case that exercises |
597 | // this path. | |
598 | } | |
599 | ty::Infer(ty::TyVar(_)) => { | |
600 | // The auto impl might apply; we don't know. | |
601 | candidates.ambiguous = true; | |
602 | } | |
603 | ty::Generator(_, _, movability) | |
604 | if self.tcx().lang_items().unpin_trait() == Some(def_id) => | |
605 | { | |
606 | match movability { | |
607 | hir::Movability::Static => { | |
608 | // Immovable generators are never `Unpin`, so | |
609 | // suppress the normal auto-impl candidate for it. | |
610 | } | |
611 | hir::Movability::Movable => { | |
612 | // Movable generators are always `Unpin`, so add an | |
613 | // unconditional builtin candidate. | |
614 | candidates.vec.push(BuiltinCandidate { has_nested: false }); | |
615 | } | |
616 | } | |
617 | } | |
618 | ||
619 | _ => candidates.vec.push(AutoImplCandidate(def_id)), | |
620 | } | |
621 | } | |
f035d41b XL |
622 | } |
623 | ||
624 | /// Searches for impls that might apply to `obligation`. | |
625 | fn assemble_candidates_from_object_ty( | |
626 | &mut self, | |
627 | obligation: &TraitObligation<'tcx>, | |
628 | candidates: &mut SelectionCandidateSet<'tcx>, | |
629 | ) { | |
630 | debug!( | |
29967ef6 XL |
631 | self_ty = ?obligation.self_ty().skip_binder(), |
632 | "assemble_candidates_from_object_ty", | |
f035d41b XL |
633 | ); |
634 | ||
635 | self.infcx.probe(|_snapshot| { | |
636 | // The code below doesn't care about regions, and the | |
637 | // self-ty here doesn't escape this probe, so just erase | |
638 | // any LBR. | |
fc512014 | 639 | let self_ty = self.tcx().erase_late_bound_regions(obligation.self_ty()); |
1b1a35ee | 640 | let poly_trait_ref = match self_ty.kind() { |
f035d41b XL |
641 | ty::Dynamic(ref data, ..) => { |
642 | if data.auto_traits().any(|did| did == obligation.predicate.def_id()) { | |
643 | debug!( | |
644 | "assemble_candidates_from_object_ty: matched builtin bound, \ | |
645 | pushing candidate" | |
646 | ); | |
647 | candidates.vec.push(BuiltinObjectCandidate); | |
648 | return; | |
649 | } | |
650 | ||
651 | if let Some(principal) = data.principal() { | |
652 | if !self.infcx.tcx.features().object_safe_for_dispatch { | |
653 | principal.with_self_ty(self.tcx(), self_ty) | |
654 | } else if self.tcx().is_object_safe(principal.def_id()) { | |
655 | principal.with_self_ty(self.tcx(), self_ty) | |
656 | } else { | |
657 | return; | |
658 | } | |
659 | } else { | |
660 | // Only auto trait bounds exist. | |
661 | return; | |
662 | } | |
663 | } | |
664 | ty::Infer(ty::TyVar(_)) => { | |
665 | debug!("assemble_candidates_from_object_ty: ambiguous"); | |
666 | candidates.ambiguous = true; // could wind up being an object type | |
667 | return; | |
668 | } | |
669 | _ => return, | |
670 | }; | |
671 | ||
29967ef6 XL |
672 | debug!(?poly_trait_ref, "assemble_candidates_from_object_ty"); |
673 | ||
fc512014 | 674 | let poly_trait_predicate = self.infcx().resolve_vars_if_possible(obligation.predicate); |
29967ef6 | 675 | let placeholder_trait_predicate = |
fc512014 | 676 | self.infcx().replace_bound_vars_with_placeholders(poly_trait_predicate); |
f035d41b XL |
677 | |
678 | // Count only those upcast versions that match the trait-ref | |
679 | // we are looking for. Specifically, do not only check for the | |
680 | // correct trait, but also the correct type parameters. | |
681 | // For example, we may be trying to upcast `Foo` to `Bar<i32>`, | |
682 | // but `Foo` is declared as `trait Foo: Bar<u32>`. | |
29967ef6 XL |
683 | let candidate_supertraits = util::supertraits(self.tcx(), poly_trait_ref) |
684 | .enumerate() | |
685 | .filter(|&(_, upcast_trait_ref)| { | |
686 | self.infcx.probe(|_| { | |
687 | self.match_normalize_trait_ref( | |
688 | obligation, | |
689 | upcast_trait_ref, | |
690 | placeholder_trait_predicate.trait_ref, | |
691 | ) | |
692 | .is_ok() | |
693 | }) | |
f035d41b | 694 | }) |
29967ef6 | 695 | .map(|(idx, _)| ObjectCandidate(idx)); |
f035d41b | 696 | |
29967ef6 | 697 | candidates.vec.extend(candidate_supertraits); |
f035d41b XL |
698 | }) |
699 | } | |
700 | ||
c295e0f8 XL |
701 | /// Temporary migration for #89190 |
702 | fn need_migrate_deref_output_trait_object( | |
703 | &mut self, | |
704 | ty: Ty<'tcx>, | |
705 | cause: &traits::ObligationCause<'tcx>, | |
706 | param_env: ty::ParamEnv<'tcx>, | |
707 | ) -> Option<(Ty<'tcx>, DefId)> { | |
708 | let tcx = self.tcx(); | |
709 | if tcx.features().trait_upcasting { | |
710 | return None; | |
711 | } | |
712 | ||
713 | // <ty as Deref> | |
714 | let trait_ref = ty::TraitRef { | |
715 | def_id: tcx.lang_items().deref_trait()?, | |
716 | substs: tcx.mk_substs_trait(ty, &[]), | |
717 | }; | |
718 | ||
719 | let obligation = traits::Obligation::new( | |
720 | cause.clone(), | |
721 | param_env, | |
722 | ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx), | |
723 | ); | |
724 | if !self.infcx.predicate_may_hold(&obligation) { | |
725 | return None; | |
726 | } | |
727 | ||
728 | let mut fulfillcx = traits::FulfillmentContext::new_in_snapshot(); | |
729 | let normalized_ty = fulfillcx.normalize_projection_type( | |
730 | &self.infcx, | |
731 | param_env, | |
732 | ty::ProjectionTy { | |
733 | item_def_id: tcx.lang_items().deref_target()?, | |
734 | substs: trait_ref.substs, | |
735 | }, | |
736 | cause.clone(), | |
737 | ); | |
738 | ||
3c0e092e | 739 | let ty::Dynamic(data, ..) = normalized_ty.kind() else { |
c295e0f8 XL |
740 | return None; |
741 | }; | |
742 | ||
743 | let def_id = data.principal_def_id()?; | |
744 | ||
745 | return Some((normalized_ty, def_id)); | |
746 | } | |
747 | ||
f035d41b XL |
748 | /// Searches for unsizing that might apply to `obligation`. |
749 | fn assemble_candidates_for_unsizing( | |
750 | &mut self, | |
751 | obligation: &TraitObligation<'tcx>, | |
752 | candidates: &mut SelectionCandidateSet<'tcx>, | |
753 | ) { | |
754 | // We currently never consider higher-ranked obligations e.g. | |
755 | // `for<'a> &'a T: Unsize<Trait+'a>` to be implemented. This is not | |
756 | // because they are a priori invalid, and we could potentially add support | |
757 | // for them later, it's just that there isn't really a strong need for it. | |
758 | // A `T: Unsize<U>` obligation is always used as part of a `T: CoerceUnsize<U>` | |
759 | // impl, and those are generally applied to concrete types. | |
760 | // | |
761 | // That said, one might try to write a fn with a where clause like | |
762 | // for<'a> Foo<'a, T>: Unsize<Foo<'a, Trait>> | |
763 | // where the `'a` is kind of orthogonal to the relevant part of the `Unsize`. | |
764 | // Still, you'd be more likely to write that where clause as | |
765 | // T: Trait | |
766 | // so it seems ok if we (conservatively) fail to accept that `Unsize` | |
767 | // obligation above. Should be possible to extend this in the future. | |
5e7ed085 FG |
768 | let Some(source) = obligation.self_ty().no_bound_vars() else { |
769 | // Don't add any candidates if there are bound regions. | |
770 | return; | |
f035d41b XL |
771 | }; |
772 | let target = obligation.predicate.skip_binder().trait_ref.substs.type_at(1); | |
773 | ||
29967ef6 | 774 | debug!(?source, ?target, "assemble_candidates_for_unsizing"); |
f035d41b | 775 | |
94222f64 | 776 | match (source.kind(), target.kind()) { |
f035d41b XL |
777 | // Trait+Kx+'a -> Trait+Ky+'b (upcasts). |
778 | (&ty::Dynamic(ref data_a, ..), &ty::Dynamic(ref data_b, ..)) => { | |
94222f64 | 779 | // Upcast coercions permit several things: |
f035d41b XL |
780 | // |
781 | // 1. Dropping auto traits, e.g., `Foo + Send` to `Foo` | |
782 | // 2. Tightening the region bound, e.g., `Foo + 'a` to `Foo + 'b` if `'a: 'b` | |
94222f64 | 783 | // 3. Tightening trait to its super traits, eg. `Foo` to `Bar` if `Foo: Bar` |
f035d41b | 784 | // |
94222f64 XL |
785 | // Note that neither of the first two of these changes requires any |
786 | // change at runtime. The third needs to change pointer metadata at runtime. | |
f035d41b | 787 | // |
94222f64 | 788 | // We always perform upcasting coercions when we can because of reason |
f035d41b | 789 | // #2 (region bounds). |
94222f64 XL |
790 | let auto_traits_compatible = data_b |
791 | .auto_traits() | |
792 | // All of a's auto traits need to be in b's auto traits. | |
793 | .all(|b| data_a.auto_traits().any(|a| a == b)); | |
794 | if auto_traits_compatible { | |
795 | let principal_def_id_a = data_a.principal_def_id(); | |
796 | let principal_def_id_b = data_b.principal_def_id(); | |
797 | if principal_def_id_a == principal_def_id_b { | |
798 | // no cyclic | |
799 | candidates.vec.push(BuiltinUnsizeCandidate); | |
800 | } else if principal_def_id_a.is_some() && principal_def_id_b.is_some() { | |
801 | // not casual unsizing, now check whether this is trait upcasting coercion. | |
802 | let principal_a = data_a.principal().unwrap(); | |
803 | let target_trait_did = principal_def_id_b.unwrap(); | |
804 | let source_trait_ref = principal_a.with_self_ty(self.tcx(), source); | |
c295e0f8 XL |
805 | if let Some((deref_output_ty, deref_output_trait_did)) = self |
806 | .need_migrate_deref_output_trait_object( | |
807 | source, | |
808 | &obligation.cause, | |
809 | obligation.param_env, | |
810 | ) | |
811 | { | |
812 | if deref_output_trait_did == target_trait_did { | |
813 | self.tcx().struct_span_lint_hir( | |
814 | DEREF_INTO_DYN_SUPERTRAIT, | |
815 | obligation.cause.body_id, | |
816 | obligation.cause.span, | |
817 | |lint| { | |
818 | lint.build(&format!( | |
819 | "`{}` implements `Deref` with supertrait `{}` as output", | |
820 | source, | |
821 | deref_output_ty | |
822 | )).emit(); | |
823 | }, | |
824 | ); | |
825 | return; | |
826 | } | |
827 | } | |
828 | ||
94222f64 XL |
829 | for (idx, upcast_trait_ref) in |
830 | util::supertraits(self.tcx(), source_trait_ref).enumerate() | |
831 | { | |
832 | if upcast_trait_ref.def_id() == target_trait_did { | |
833 | candidates.vec.push(TraitUpcastingUnsizeCandidate(idx)); | |
834 | } | |
835 | } | |
836 | } | |
837 | } | |
f035d41b XL |
838 | } |
839 | ||
840 | // `T` -> `Trait` | |
94222f64 XL |
841 | (_, &ty::Dynamic(..)) => { |
842 | candidates.vec.push(BuiltinUnsizeCandidate); | |
843 | } | |
f035d41b XL |
844 | |
845 | // Ambiguous handling is below `T` -> `Trait`, because inference | |
846 | // variables can still implement `Unsize<Trait>` and nested | |
847 | // obligations will have the final say (likely deferred). | |
848 | (&ty::Infer(ty::TyVar(_)), _) | (_, &ty::Infer(ty::TyVar(_))) => { | |
849 | debug!("assemble_candidates_for_unsizing: ambiguous"); | |
850 | candidates.ambiguous = true; | |
f035d41b XL |
851 | } |
852 | ||
853 | // `[T; n]` -> `[T]` | |
94222f64 XL |
854 | (&ty::Array(..), &ty::Slice(_)) => { |
855 | candidates.vec.push(BuiltinUnsizeCandidate); | |
856 | } | |
f035d41b XL |
857 | |
858 | // `Struct<T>` -> `Struct<U>` | |
859 | (&ty::Adt(def_id_a, _), &ty::Adt(def_id_b, _)) if def_id_a.is_struct() => { | |
94222f64 XL |
860 | if def_id_a == def_id_b { |
861 | candidates.vec.push(BuiltinUnsizeCandidate); | |
862 | } | |
f035d41b XL |
863 | } |
864 | ||
865 | // `(.., T)` -> `(.., U)` | |
94222f64 XL |
866 | (&ty::Tuple(tys_a), &ty::Tuple(tys_b)) => { |
867 | if tys_a.len() == tys_b.len() { | |
868 | candidates.vec.push(BuiltinUnsizeCandidate); | |
869 | } | |
870 | } | |
f035d41b | 871 | |
94222f64 | 872 | _ => {} |
f035d41b | 873 | }; |
f035d41b XL |
874 | } |
875 | ||
5099ac24 | 876 | #[tracing::instrument(level = "debug", skip(self, obligation, candidates))] |
f035d41b XL |
877 | fn assemble_candidates_for_trait_alias( |
878 | &mut self, | |
879 | obligation: &TraitObligation<'tcx>, | |
880 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5869c6ff | 881 | ) { |
f035d41b XL |
882 | // Okay to skip binder here because the tests we do below do not involve bound regions. |
883 | let self_ty = obligation.self_ty().skip_binder(); | |
5099ac24 | 884 | debug!(?self_ty); |
f035d41b XL |
885 | |
886 | let def_id = obligation.predicate.def_id(); | |
887 | ||
888 | if self.tcx().is_trait_alias(def_id) { | |
889 | candidates.vec.push(TraitAliasCandidate(def_id)); | |
890 | } | |
f035d41b XL |
891 | } |
892 | ||
893 | /// Assembles the trait which are built-in to the language itself: | |
894 | /// `Copy`, `Clone` and `Sized`. | |
5099ac24 | 895 | #[tracing::instrument(level = "debug", skip(self, candidates))] |
f035d41b XL |
896 | fn assemble_builtin_bound_candidates( |
897 | &mut self, | |
898 | conditions: BuiltinImplConditions<'tcx>, | |
899 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5869c6ff | 900 | ) { |
f035d41b XL |
901 | match conditions { |
902 | BuiltinImplConditions::Where(nested) => { | |
f035d41b XL |
903 | candidates |
904 | .vec | |
905 | .push(BuiltinCandidate { has_nested: !nested.skip_binder().is_empty() }); | |
906 | } | |
907 | BuiltinImplConditions::None => {} | |
908 | BuiltinImplConditions::Ambiguous => { | |
f035d41b XL |
909 | candidates.ambiguous = true; |
910 | } | |
911 | } | |
f035d41b | 912 | } |
c295e0f8 | 913 | |
5e7ed085 | 914 | fn assemble_const_destruct_candidates( |
c295e0f8 XL |
915 | &mut self, |
916 | obligation: &TraitObligation<'tcx>, | |
917 | candidates: &mut SelectionCandidateSet<'tcx>, | |
5099ac24 | 918 | ) { |
5e7ed085 | 919 | // If the predicate is `~const Destruct` in a non-const environment, we don't actually need |
5099ac24 | 920 | // to check anything. We'll short-circuit checking any obligations in confirmation, too. |
5e7ed085 FG |
921 | if !obligation.is_const() { |
922 | candidates.vec.push(ConstDestructCandidate(None)); | |
5099ac24 FG |
923 | return; |
924 | } | |
c295e0f8 | 925 | |
5099ac24 FG |
926 | let self_ty = self.infcx().shallow_resolve(obligation.self_ty()); |
927 | match self_ty.skip_binder().kind() { | |
928 | ty::Opaque(..) | |
929 | | ty::Dynamic(..) | |
930 | | ty::Error(_) | |
931 | | ty::Bound(..) | |
932 | | ty::Param(_) | |
933 | | ty::Placeholder(_) | |
934 | | ty::Projection(_) => { | |
5e7ed085 | 935 | // We don't know if these are `~const Destruct`, at least |
5099ac24 FG |
936 | // not structurally... so don't push a candidate. |
937 | } | |
c295e0f8 | 938 | |
5099ac24 FG |
939 | ty::Bool |
940 | | ty::Char | |
941 | | ty::Int(_) | |
942 | | ty::Uint(_) | |
943 | | ty::Float(_) | |
944 | | ty::Infer(ty::IntVar(_)) | |
945 | | ty::Infer(ty::FloatVar(_)) | |
946 | | ty::Str | |
947 | | ty::RawPtr(_) | |
948 | | ty::Ref(..) | |
949 | | ty::FnDef(..) | |
950 | | ty::FnPtr(_) | |
951 | | ty::Never | |
952 | | ty::Foreign(_) | |
953 | | ty::Array(..) | |
954 | | ty::Slice(_) | |
955 | | ty::Closure(..) | |
956 | | ty::Generator(..) | |
957 | | ty::Tuple(_) | |
958 | | ty::GeneratorWitness(_) => { | |
5e7ed085 FG |
959 | // These are built-in, and cannot have a custom `impl const Destruct`. |
960 | candidates.vec.push(ConstDestructCandidate(None)); | |
5099ac24 | 961 | } |
c295e0f8 | 962 | |
5099ac24 FG |
963 | ty::Adt(..) => { |
964 | // Find a custom `impl Drop` impl, if it exists | |
965 | let relevant_impl = self.tcx().find_map_relevant_impl( | |
5e7ed085 | 966 | self.tcx().require_lang_item(LangItem::Drop, None), |
5099ac24 FG |
967 | obligation.predicate.skip_binder().trait_ref.self_ty(), |
968 | Some, | |
969 | ); | |
c295e0f8 | 970 | |
5099ac24 FG |
971 | if let Some(impl_def_id) = relevant_impl { |
972 | // Check that `impl Drop` is actually const, if there is a custom impl | |
923072b8 | 973 | if self.tcx().constness(impl_def_id) == hir::Constness::Const { |
5e7ed085 | 974 | candidates.vec.push(ConstDestructCandidate(Some(impl_def_id))); |
c295e0f8 | 975 | } |
5099ac24 FG |
976 | } else { |
977 | // Otherwise check the ADT like a built-in type (structurally) | |
5e7ed085 | 978 | candidates.vec.push(ConstDestructCandidate(None)); |
c295e0f8 XL |
979 | } |
980 | } | |
c295e0f8 | 981 | |
5099ac24 FG |
982 | ty::Infer(_) => { |
983 | candidates.ambiguous = true; | |
984 | } | |
985 | } | |
c295e0f8 | 986 | } |
f035d41b | 987 | } |