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94b46f34 XL |
1 | //! Support code for rustdoc and external tools . You really don't |
2 | //! want to be using this unless you need to. | |
3 | ||
4 | use super::*; | |
5 | ||
6 | use std::collections::hash_map::Entry; | |
7 | use std::collections::VecDeque; | |
8 | ||
9fa01778 XL |
9 | use crate::infer::region_constraints::{Constraint, RegionConstraintData}; |
10 | use crate::infer::InferCtxt; | |
0bf4aa26 | 11 | use rustc_data_structures::fx::{FxHashMap, FxHashSet}; |
94b46f34 | 12 | |
9fa01778 XL |
13 | use crate::ty::fold::TypeFolder; |
14 | use crate::ty::{Region, RegionVid}; | |
94b46f34 XL |
15 | |
16 | // FIXME(twk): this is obviously not nice to duplicate like that | |
17 | #[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)] | |
18 | pub enum RegionTarget<'tcx> { | |
19 | Region(Region<'tcx>), | |
20 | RegionVid(RegionVid), | |
21 | } | |
22 | ||
23 | #[derive(Default, Debug, Clone)] | |
24 | pub struct RegionDeps<'tcx> { | |
25 | larger: FxHashSet<RegionTarget<'tcx>>, | |
26 | smaller: FxHashSet<RegionTarget<'tcx>>, | |
27 | } | |
28 | ||
29 | pub enum AutoTraitResult<A> { | |
30 | ExplicitImpl, | |
31 | PositiveImpl(A), | |
32 | NegativeImpl, | |
33 | } | |
34 | ||
35 | impl<A> AutoTraitResult<A> { | |
36 | fn is_auto(&self) -> bool { | |
37 | match *self { | |
38 | AutoTraitResult::PositiveImpl(_) | AutoTraitResult::NegativeImpl => true, | |
39 | _ => false, | |
40 | } | |
41 | } | |
42 | } | |
43 | ||
44 | pub struct AutoTraitInfo<'cx> { | |
45 | pub full_user_env: ty::ParamEnv<'cx>, | |
46 | pub region_data: RegionConstraintData<'cx>, | |
94b46f34 XL |
47 | pub vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'cx>>, |
48 | } | |
49 | ||
dc9dc135 XL |
50 | pub struct AutoTraitFinder<'tcx> { |
51 | tcx: TyCtxt<'tcx>, | |
94b46f34 XL |
52 | } |
53 | ||
dc9dc135 XL |
54 | impl<'tcx> AutoTraitFinder<'tcx> { |
55 | pub fn new(tcx: TyCtxt<'tcx>) -> Self { | |
94b46f34 XL |
56 | AutoTraitFinder { tcx } |
57 | } | |
58 | ||
9fa01778 | 59 | /// Makes a best effort to determine whether and under which conditions an auto trait is |
94b46f34 XL |
60 | /// implemented for a type. For example, if you have |
61 | /// | |
62 | /// ``` | |
63 | /// struct Foo<T> { data: Box<T> } | |
64 | /// ``` | |
0bf4aa26 | 65 | /// |
94b46f34 XL |
66 | /// then this might return that Foo<T>: Send if T: Send (encoded in the AutoTraitResult type). |
67 | /// The analysis attempts to account for custom impls as well as other complex cases. This | |
68 | /// result is intended for use by rustdoc and other such consumers. | |
0bf4aa26 | 69 | /// |
94b46f34 XL |
70 | /// (Note that due to the coinductive nature of Send, the full and correct result is actually |
71 | /// quite simple to generate. That is, when a type has no custom impl, it is Send iff its field | |
72 | /// types are all Send. So, in our example, we might have that Foo<T>: Send if Box<T>: Send. | |
73 | /// But this is often not the best way to present to the user.) | |
0bf4aa26 | 74 | /// |
94b46f34 XL |
75 | /// Warning: The API should be considered highly unstable, and it may be refactored or removed |
76 | /// in the future. | |
77 | pub fn find_auto_trait_generics<A>( | |
78 | &self, | |
48663c56 XL |
79 | ty: Ty<'tcx>, |
80 | orig_env: ty::ParamEnv<'tcx>, | |
94b46f34 | 81 | trait_did: DefId, |
dc9dc135 | 82 | auto_trait_callback: impl Fn(&InferCtxt<'_, 'tcx>, AutoTraitInfo<'tcx>) -> A, |
94b46f34 XL |
83 | ) -> AutoTraitResult<A> { |
84 | let tcx = self.tcx; | |
94b46f34 XL |
85 | |
86 | let trait_ref = ty::TraitRef { | |
87 | def_id: trait_did, | |
88 | substs: tcx.mk_substs_trait(ty, &[]), | |
89 | }; | |
90 | ||
91 | let trait_pred = ty::Binder::bind(trait_ref); | |
92 | ||
93 | let bail_out = tcx.infer_ctxt().enter(|infcx| { | |
94 | let mut selcx = SelectionContext::with_negative(&infcx, true); | |
95 | let result = selcx.select(&Obligation::new( | |
96 | ObligationCause::dummy(), | |
48663c56 | 97 | orig_env, |
94b46f34 XL |
98 | trait_pred.to_poly_trait_predicate(), |
99 | )); | |
0bf4aa26 | 100 | |
94b46f34 XL |
101 | match result { |
102 | Ok(Some(Vtable::VtableImpl(_))) => { | |
103 | debug!( | |
48663c56 | 104 | "find_auto_trait_generics({:?}): \ |
94b46f34 | 105 | manual impl found, bailing out", |
48663c56 | 106 | trait_ref |
94b46f34 | 107 | ); |
0bf4aa26 | 108 | true |
94b46f34 | 109 | } |
0bf4aa26 XL |
110 | _ => false |
111 | } | |
94b46f34 XL |
112 | }); |
113 | ||
114 | // If an explicit impl exists, it always takes priority over an auto impl | |
115 | if bail_out { | |
116 | return AutoTraitResult::ExplicitImpl; | |
117 | } | |
118 | ||
119 | return tcx.infer_ctxt().enter(|mut infcx| { | |
0bf4aa26 | 120 | let mut fresh_preds = FxHashSet::default(); |
94b46f34 XL |
121 | |
122 | // Due to the way projections are handled by SelectionContext, we need to run | |
123 | // evaluate_predicates twice: once on the original param env, and once on the result of | |
124 | // the first evaluate_predicates call. | |
125 | // | |
126 | // The problem is this: most of rustc, including SelectionContext and traits::project, | |
0731742a | 127 | // are designed to work with a concrete usage of a type (e.g., Vec<u8> |
94b46f34 XL |
128 | // fn<T>() { Vec<T> }. This information will generally never change - given |
129 | // the 'T' in fn<T>() { ... }, we'll never know anything else about 'T'. | |
130 | // If we're unable to prove that 'T' implements a particular trait, we're done - | |
131 | // there's nothing left to do but error out. | |
132 | // | |
133 | // However, synthesizing an auto trait impl works differently. Here, we start out with | |
134 | // a set of initial conditions - the ParamEnv of the struct/enum/union we're dealing | |
135 | // with - and progressively discover the conditions we need to fulfill for it to | |
136 | // implement a certain auto trait. This ends up breaking two assumptions made by trait | |
137 | // selection and projection: | |
138 | // | |
139 | // * We can always cache the result of a particular trait selection for the lifetime of | |
140 | // an InfCtxt | |
141 | // * Given a projection bound such as '<T as SomeTrait>::SomeItem = K', if 'T: | |
142 | // SomeTrait' doesn't hold, then we don't need to care about the 'SomeItem = K' | |
143 | // | |
144 | // We fix the first assumption by manually clearing out all of the InferCtxt's caches | |
145 | // in between calls to SelectionContext.select. This allows us to keep all of the | |
146 | // intermediate types we create bound to the 'tcx lifetime, rather than needing to lift | |
147 | // them between calls. | |
148 | // | |
149 | // We fix the second assumption by reprocessing the result of our first call to | |
150 | // evaluate_predicates. Using the example of '<T as SomeTrait>::SomeItem = K', our first | |
151 | // pass will pick up 'T: SomeTrait', but not 'SomeItem = K'. On our second pass, | |
152 | // traits::project will see that 'T: SomeTrait' is in our ParamEnv, allowing | |
153 | // SelectionContext to return it back to us. | |
154 | ||
155 | let (new_env, user_env) = match self.evaluate_predicates( | |
156 | &mut infcx, | |
94b46f34 XL |
157 | trait_did, |
158 | ty, | |
48663c56 XL |
159 | orig_env, |
160 | orig_env, | |
94b46f34 XL |
161 | &mut fresh_preds, |
162 | false, | |
163 | ) { | |
164 | Some(e) => e, | |
165 | None => return AutoTraitResult::NegativeImpl, | |
166 | }; | |
167 | ||
168 | let (full_env, full_user_env) = self.evaluate_predicates( | |
169 | &mut infcx, | |
94b46f34 XL |
170 | trait_did, |
171 | ty, | |
48663c56 | 172 | new_env, |
94b46f34 XL |
173 | user_env, |
174 | &mut fresh_preds, | |
175 | true, | |
176 | ).unwrap_or_else(|| { | |
177 | panic!( | |
178 | "Failed to fully process: {:?} {:?} {:?}", | |
48663c56 | 179 | ty, trait_did, orig_env |
94b46f34 XL |
180 | ) |
181 | }); | |
182 | ||
183 | debug!( | |
48663c56 | 184 | "find_auto_trait_generics({:?}): fulfilling \ |
94b46f34 | 185 | with {:?}", |
48663c56 | 186 | trait_ref, full_env |
94b46f34 XL |
187 | ); |
188 | infcx.clear_caches(); | |
189 | ||
190 | // At this point, we already have all of the bounds we need. FulfillmentContext is used | |
191 | // to store all of the necessary region/lifetime bounds in the InferContext, as well as | |
192 | // an additional sanity check. | |
193 | let mut fulfill = FulfillmentContext::new(); | |
194 | fulfill.register_bound( | |
195 | &infcx, | |
196 | full_env, | |
197 | ty, | |
198 | trait_did, | |
9fa01778 | 199 | ObligationCause::misc(DUMMY_SP, hir::DUMMY_HIR_ID), |
94b46f34 XL |
200 | ); |
201 | fulfill.select_all_or_error(&infcx).unwrap_or_else(|e| { | |
202 | panic!( | |
203 | "Unable to fulfill trait {:?} for '{:?}': {:?}", | |
204 | trait_did, ty, e | |
205 | ) | |
206 | }); | |
207 | ||
0bf4aa26 | 208 | let body_id_map: FxHashMap<_, _> = infcx |
94b46f34 XL |
209 | .region_obligations |
210 | .borrow() | |
211 | .iter() | |
0bf4aa26 | 212 | .map(|&(id, _)| (id, vec![])) |
94b46f34 XL |
213 | .collect(); |
214 | ||
48663c56 | 215 | infcx.process_registered_region_obligations(&body_id_map, None, full_env); |
94b46f34 XL |
216 | |
217 | let region_data = infcx | |
218 | .borrow_region_constraints() | |
219 | .region_constraint_data() | |
220 | .clone(); | |
221 | ||
222 | let vid_to_region = self.map_vid_to_region(®ion_data); | |
223 | ||
224 | let info = AutoTraitInfo { | |
225 | full_user_env, | |
226 | region_data, | |
94b46f34 XL |
227 | vid_to_region, |
228 | }; | |
229 | ||
230 | return AutoTraitResult::PositiveImpl(auto_trait_callback(&infcx, info)); | |
231 | }); | |
232 | } | |
233 | } | |
234 | ||
dc9dc135 | 235 | impl AutoTraitFinder<'tcx> { |
94b46f34 XL |
236 | // The core logic responsible for computing the bounds for our synthesized impl. |
237 | // | |
238 | // To calculate the bounds, we call SelectionContext.select in a loop. Like FulfillmentContext, | |
b7449926 | 239 | // we recursively select the nested obligations of predicates we encounter. However, whenever we |
94b46f34 XL |
240 | // encounter an UnimplementedError involving a type parameter, we add it to our ParamEnv. Since |
241 | // our goal is to determine when a particular type implements an auto trait, Unimplemented | |
242 | // errors tell us what conditions need to be met. | |
243 | // | |
b7449926 | 244 | // This method ends up working somewhat similarly to FulfillmentContext, but with a few key |
94b46f34 XL |
245 | // differences. FulfillmentContext works under the assumption that it's dealing with concrete |
246 | // user code. According, it considers all possible ways that a Predicate could be met - which | |
247 | // isn't always what we want for a synthesized impl. For example, given the predicate 'T: | |
248 | // Iterator', FulfillmentContext can end up reporting an Unimplemented error for T: | |
249 | // IntoIterator - since there's an implementation of Iteratpr where T: IntoIterator, | |
250 | // FulfillmentContext will drive SelectionContext to consider that impl before giving up. If we | |
251 | // were to rely on FulfillmentContext's decision, we might end up synthesizing an impl like | |
252 | // this: | |
253 | // 'impl<T> Send for Foo<T> where T: IntoIterator' | |
254 | // | |
255 | // While it might be technically true that Foo implements Send where T: IntoIterator, | |
256 | // the bound is overly restrictive - it's really only necessary that T: Iterator. | |
257 | // | |
258 | // For this reason, evaluate_predicates handles predicates with type variables specially. When | |
259 | // we encounter an Unimplemented error for a bound such as 'T: Iterator', we immediately add it | |
260 | // to our ParamEnv, and add it to our stack for recursive evaluation. When we later select it, | |
261 | // we'll pick up any nested bounds, without ever inferring that 'T: IntoIterator' needs to | |
262 | // hold. | |
263 | // | |
b7449926 | 264 | // One additional consideration is supertrait bounds. Normally, a ParamEnv is only ever |
0bf4aa26 | 265 | // constructed once for a given type. As part of the construction process, the ParamEnv will |
0731742a | 266 | // have any supertrait bounds normalized - e.g., if we have a type 'struct Foo<T: Copy>', the |
94b46f34 | 267 | // ParamEnv will contain 'T: Copy' and 'T: Clone', since 'Copy: Clone'. When we construct our |
b7449926 | 268 | // own ParamEnv, we need to do this ourselves, through traits::elaborate_predicates, or else |
94b46f34 XL |
269 | // SelectionContext will choke on the missing predicates. However, this should never show up in |
270 | // the final synthesized generics: we don't want our generated docs page to contain something | |
271 | // like 'T: Copy + Clone', as that's redundant. Therefore, we keep track of a separate | |
272 | // 'user_env', which only holds the predicates that will actually be displayed to the user. | |
dc9dc135 | 273 | fn evaluate_predicates( |
94b46f34 | 274 | &self, |
dc9dc135 | 275 | infcx: &InferCtxt<'_, 'tcx>, |
94b46f34 | 276 | trait_did: DefId, |
dc9dc135 XL |
277 | ty: Ty<'tcx>, |
278 | param_env: ty::ParamEnv<'tcx>, | |
279 | user_env: ty::ParamEnv<'tcx>, | |
280 | fresh_preds: &mut FxHashSet<ty::Predicate<'tcx>>, | |
94b46f34 | 281 | only_projections: bool, |
dc9dc135 | 282 | ) -> Option<(ty::ParamEnv<'tcx>, ty::ParamEnv<'tcx>)> { |
94b46f34 XL |
283 | let tcx = infcx.tcx; |
284 | ||
a1dfa0c6 | 285 | let mut select = SelectionContext::with_negative(&infcx, true); |
94b46f34 | 286 | |
0bf4aa26 | 287 | let mut already_visited = FxHashSet::default(); |
94b46f34 XL |
288 | let mut predicates = VecDeque::new(); |
289 | predicates.push_back(ty::Binder::bind(ty::TraitPredicate { | |
290 | trait_ref: ty::TraitRef { | |
291 | def_id: trait_did, | |
292 | substs: infcx.tcx.mk_substs_trait(ty, &[]), | |
293 | }, | |
294 | })); | |
295 | ||
296 | let mut computed_preds: FxHashSet<_> = param_env.caller_bounds.iter().cloned().collect(); | |
297 | let mut user_computed_preds: FxHashSet<_> = | |
298 | user_env.caller_bounds.iter().cloned().collect(); | |
299 | ||
48663c56 | 300 | let mut new_env = param_env; |
9fa01778 | 301 | let dummy_cause = ObligationCause::misc(DUMMY_SP, hir::DUMMY_HIR_ID); |
94b46f34 XL |
302 | |
303 | while let Some(pred) = predicates.pop_front() { | |
304 | infcx.clear_caches(); | |
305 | ||
48663c56 | 306 | if !already_visited.insert(pred) { |
94b46f34 XL |
307 | continue; |
308 | } | |
309 | ||
dc9dc135 | 310 | // Call infcx.resolve_vars_if_possible to see if we can |
69743fb6 | 311 | // get rid of any inference variables. |
dc9dc135 | 312 | let obligation = infcx.resolve_vars_if_possible( |
69743fb6 XL |
313 | &Obligation::new(dummy_cause.clone(), new_env, pred) |
314 | ); | |
315 | let result = select.select(&obligation); | |
94b46f34 XL |
316 | |
317 | match &result { | |
318 | &Ok(Some(ref vtable)) => { | |
0731742a | 319 | // If we see an explicit negative impl (e.g., 'impl !Send for MyStruct'), |
a1dfa0c6 XL |
320 | // we immediately bail out, since it's impossible for us to continue. |
321 | match vtable { | |
322 | Vtable::VtableImpl(VtableImplData { impl_def_id, .. }) => { | |
323 | // Blame tidy for the weird bracket placement | |
e74abb32 | 324 | if infcx.tcx.impl_polarity(*impl_def_id) == ty::ImplPolarity::Negative |
a1dfa0c6 XL |
325 | { |
326 | debug!("evaluate_nested_obligations: Found explicit negative impl\ | |
327 | {:?}, bailing out", impl_def_id); | |
328 | return None; | |
329 | } | |
330 | }, | |
331 | _ => {} | |
332 | } | |
333 | ||
94b46f34 XL |
334 | let obligations = vtable.clone().nested_obligations().into_iter(); |
335 | ||
336 | if !self.evaluate_nested_obligations( | |
337 | ty, | |
338 | obligations, | |
339 | &mut user_computed_preds, | |
340 | fresh_preds, | |
341 | &mut predicates, | |
342 | &mut select, | |
343 | only_projections, | |
344 | ) { | |
345 | return None; | |
346 | } | |
347 | } | |
348 | &Ok(None) => {} | |
349 | &Err(SelectionError::Unimplemented) => { | |
69743fb6 | 350 | if self.is_param_no_infer(pred.skip_binder().trait_ref.substs) { |
94b46f34 | 351 | already_visited.remove(&pred); |
0bf4aa26 XL |
352 | self.add_user_pred( |
353 | &mut user_computed_preds, | |
48663c56 | 354 | ty::Predicate::Trait(pred), |
0bf4aa26 | 355 | ); |
94b46f34 XL |
356 | predicates.push_back(pred); |
357 | } else { | |
358 | debug!( | |
359 | "evaluate_nested_obligations: Unimplemented found, bailing: \ | |
360 | {:?} {:?} {:?}", | |
361 | ty, | |
362 | pred, | |
363 | pred.skip_binder().trait_ref.substs | |
364 | ); | |
365 | return None; | |
366 | } | |
367 | } | |
368 | _ => panic!("Unexpected error for '{:?}': {:?}", ty, result), | |
369 | }; | |
370 | ||
371 | computed_preds.extend(user_computed_preds.iter().cloned()); | |
372 | let normalized_preds = | |
48663c56 | 373 | elaborate_predicates(tcx, computed_preds.iter().cloned().collect()); |
0731742a XL |
374 | new_env = ty::ParamEnv::new( |
375 | tcx.mk_predicates(normalized_preds), | |
376 | param_env.reveal, | |
377 | None | |
378 | ); | |
94b46f34 XL |
379 | } |
380 | ||
381 | let final_user_env = ty::ParamEnv::new( | |
382 | tcx.mk_predicates(user_computed_preds.into_iter()), | |
383 | user_env.reveal, | |
0731742a | 384 | None |
94b46f34 XL |
385 | ); |
386 | debug!( | |
48663c56 | 387 | "evaluate_nested_obligations(ty={:?}, trait_did={:?}): succeeded with '{:?}' \ |
94b46f34 | 388 | '{:?}'", |
48663c56 | 389 | ty, trait_did, new_env, final_user_env |
94b46f34 XL |
390 | ); |
391 | ||
392 | return Some((new_env, final_user_env)); | |
393 | } | |
394 | ||
b7449926 XL |
395 | // This method is designed to work around the following issue: |
396 | // When we compute auto trait bounds, we repeatedly call SelectionContext.select, | |
397 | // progressively building a ParamEnv based on the results we get. | |
398 | // However, our usage of SelectionContext differs from its normal use within the compiler, | |
399 | // in that we capture and re-reprocess predicates from Unimplemented errors. | |
400 | // | |
401 | // This can lead to a corner case when dealing with region parameters. | |
402 | // During our selection loop in evaluate_predicates, we might end up with | |
403 | // two trait predicates that differ only in their region parameters: | |
404 | // one containing a HRTB lifetime parameter, and one containing a 'normal' | |
405 | // lifetime parameter. For example: | |
406 | // | |
407 | // T as MyTrait<'a> | |
408 | // T as MyTrait<'static> | |
409 | // | |
410 | // If we put both of these predicates in our computed ParamEnv, we'll | |
411 | // confuse SelectionContext, since it will (correctly) view both as being applicable. | |
412 | // | |
0731742a | 413 | // To solve this, we pick the 'more strict' lifetime bound - i.e., the HRTB |
b7449926 XL |
414 | // Our end goal is to generate a user-visible description of the conditions |
415 | // under which a type implements an auto trait. A trait predicate involving | |
416 | // a HRTB means that the type needs to work with any choice of lifetime, | |
0731742a | 417 | // not just one specific lifetime (e.g., 'static). |
0bf4aa26 XL |
418 | fn add_user_pred<'c>( |
419 | &self, | |
420 | user_computed_preds: &mut FxHashSet<ty::Predicate<'c>>, | |
421 | new_pred: ty::Predicate<'c>, | |
422 | ) { | |
b7449926 XL |
423 | let mut should_add_new = true; |
424 | user_computed_preds.retain(|&old_pred| { | |
425 | match (&new_pred, old_pred) { | |
426 | (&ty::Predicate::Trait(new_trait), ty::Predicate::Trait(old_trait)) => { | |
427 | if new_trait.def_id() == old_trait.def_id() { | |
428 | let new_substs = new_trait.skip_binder().trait_ref.substs; | |
429 | let old_substs = old_trait.skip_binder().trait_ref.substs; | |
0bf4aa26 | 430 | |
b7449926 XL |
431 | if !new_substs.types().eq(old_substs.types()) { |
432 | // We can't compare lifetimes if the types are different, | |
433 | // so skip checking old_pred | |
0bf4aa26 | 434 | return true; |
b7449926 XL |
435 | } |
436 | ||
0bf4aa26 XL |
437 | for (new_region, old_region) in |
438 | new_substs.regions().zip(old_substs.regions()) | |
439 | { | |
b7449926 XL |
440 | match (new_region, old_region) { |
441 | // If both predicates have an 'ReLateBound' (a HRTB) in the | |
442 | // same spot, we do nothing | |
443 | ( | |
444 | ty::RegionKind::ReLateBound(_, _), | |
0bf4aa26 XL |
445 | ty::RegionKind::ReLateBound(_, _), |
446 | ) => {} | |
b7449926 | 447 | |
a1dfa0c6 XL |
448 | (ty::RegionKind::ReLateBound(_, _), _) | |
449 | (_, ty::RegionKind::ReVar(_)) => { | |
450 | // One of these is true: | |
b7449926 XL |
451 | // The new predicate has a HRTB in a spot where the old |
452 | // predicate does not (if they both had a HRTB, the previous | |
a1dfa0c6 XL |
453 | // match arm would have executed). A HRBT is a 'stricter' |
454 | // bound than anything else, so we want to keep the newer | |
455 | // predicate (with the HRBT) in place of the old predicate. | |
456 | // | |
457 | // OR | |
458 | // | |
459 | // The old predicate has a region variable where the new | |
460 | // predicate has some other kind of region. An region | |
461 | // variable isn't something we can actually display to a user, | |
462 | // so we choose ther new predicate (which doesn't have a region | |
463 | // varaible). | |
b7449926 | 464 | // |
a1dfa0c6 XL |
465 | // In both cases, we want to remove the old predicate, |
466 | // from user_computed_preds, and replace it with the new | |
467 | // one. Having both the old and the new | |
b7449926 | 468 | // predicate in a ParamEnv would confuse SelectionContext |
a1dfa0c6 | 469 | // |
b7449926 XL |
470 | // We're currently in the predicate passed to 'retain', |
471 | // so we return 'false' to remove the old predicate from | |
472 | // user_computed_preds | |
473 | return false; | |
0bf4aa26 | 474 | } |
a1dfa0c6 XL |
475 | (_, ty::RegionKind::ReLateBound(_, _)) | |
476 | (ty::RegionKind::ReVar(_), _) => { | |
477 | // This is the opposite situation as the previous arm. | |
478 | // One of these is true: | |
479 | // | |
480 | // The old predicate has a HRTB lifetime in a place where the | |
481 | // new predicate does not. | |
482 | // | |
483 | // OR | |
484 | // | |
485 | // The new predicate has a region variable where the old | |
486 | // predicate has some other type of region. | |
487 | // | |
488 | // We want to leave the old | |
b7449926 XL |
489 | // predicate in user_computed_preds, and skip adding |
490 | // new_pred to user_computed_params. | |
491 | should_add_new = false | |
a1dfa0c6 | 492 | }, |
b7449926 XL |
493 | _ => {} |
494 | } | |
495 | } | |
496 | } | |
0bf4aa26 | 497 | } |
b7449926 XL |
498 | _ => {} |
499 | } | |
0bf4aa26 | 500 | return true; |
b7449926 XL |
501 | }); |
502 | ||
503 | if should_add_new { | |
504 | user_computed_preds.insert(new_pred); | |
505 | } | |
506 | } | |
507 | ||
94b46f34 XL |
508 | // This is very similar to handle_lifetimes. However, instead of matching ty::Region's |
509 | // to each other, we match ty::RegionVid's to ty::Region's | |
48663c56 | 510 | fn map_vid_to_region<'cx>( |
94b46f34 XL |
511 | &self, |
512 | regions: &RegionConstraintData<'cx>, | |
513 | ) -> FxHashMap<ty::RegionVid, ty::Region<'cx>> { | |
0bf4aa26 XL |
514 | let mut vid_map: FxHashMap<RegionTarget<'cx>, RegionDeps<'cx>> = FxHashMap::default(); |
515 | let mut finished_map = FxHashMap::default(); | |
94b46f34 XL |
516 | |
517 | for constraint in regions.constraints.keys() { | |
518 | match constraint { | |
519 | &Constraint::VarSubVar(r1, r2) => { | |
520 | { | |
0bf4aa26 | 521 | let deps1 = vid_map.entry(RegionTarget::RegionVid(r1)).or_default(); |
94b46f34 XL |
522 | deps1.larger.insert(RegionTarget::RegionVid(r2)); |
523 | } | |
524 | ||
0bf4aa26 | 525 | let deps2 = vid_map.entry(RegionTarget::RegionVid(r2)).or_default(); |
94b46f34 XL |
526 | deps2.smaller.insert(RegionTarget::RegionVid(r1)); |
527 | } | |
528 | &Constraint::RegSubVar(region, vid) => { | |
529 | { | |
0bf4aa26 | 530 | let deps1 = vid_map.entry(RegionTarget::Region(region)).or_default(); |
94b46f34 XL |
531 | deps1.larger.insert(RegionTarget::RegionVid(vid)); |
532 | } | |
533 | ||
0bf4aa26 | 534 | let deps2 = vid_map.entry(RegionTarget::RegionVid(vid)).or_default(); |
94b46f34 XL |
535 | deps2.smaller.insert(RegionTarget::Region(region)); |
536 | } | |
537 | &Constraint::VarSubReg(vid, region) => { | |
538 | finished_map.insert(vid, region); | |
539 | } | |
540 | &Constraint::RegSubReg(r1, r2) => { | |
541 | { | |
0bf4aa26 | 542 | let deps1 = vid_map.entry(RegionTarget::Region(r1)).or_default(); |
94b46f34 XL |
543 | deps1.larger.insert(RegionTarget::Region(r2)); |
544 | } | |
545 | ||
0bf4aa26 | 546 | let deps2 = vid_map.entry(RegionTarget::Region(r2)).or_default(); |
94b46f34 XL |
547 | deps2.smaller.insert(RegionTarget::Region(r1)); |
548 | } | |
549 | } | |
550 | } | |
551 | ||
552 | while !vid_map.is_empty() { | |
553 | let target = vid_map.keys().next().expect("Keys somehow empty").clone(); | |
554 | let deps = vid_map.remove(&target).expect("Entry somehow missing"); | |
555 | ||
556 | for smaller in deps.smaller.iter() { | |
557 | for larger in deps.larger.iter() { | |
558 | match (smaller, larger) { | |
559 | (&RegionTarget::Region(_), &RegionTarget::Region(_)) => { | |
560 | if let Entry::Occupied(v) = vid_map.entry(*smaller) { | |
561 | let smaller_deps = v.into_mut(); | |
562 | smaller_deps.larger.insert(*larger); | |
563 | smaller_deps.larger.remove(&target); | |
564 | } | |
565 | ||
566 | if let Entry::Occupied(v) = vid_map.entry(*larger) { | |
567 | let larger_deps = v.into_mut(); | |
568 | larger_deps.smaller.insert(*smaller); | |
569 | larger_deps.smaller.remove(&target); | |
570 | } | |
571 | } | |
572 | (&RegionTarget::RegionVid(v1), &RegionTarget::Region(r1)) => { | |
573 | finished_map.insert(v1, r1); | |
574 | } | |
575 | (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => { | |
576 | // Do nothing - we don't care about regions that are smaller than vids | |
577 | } | |
578 | (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => { | |
579 | if let Entry::Occupied(v) = vid_map.entry(*smaller) { | |
580 | let smaller_deps = v.into_mut(); | |
581 | smaller_deps.larger.insert(*larger); | |
582 | smaller_deps.larger.remove(&target); | |
583 | } | |
584 | ||
585 | if let Entry::Occupied(v) = vid_map.entry(*larger) { | |
586 | let larger_deps = v.into_mut(); | |
587 | larger_deps.smaller.insert(*smaller); | |
588 | larger_deps.smaller.remove(&target); | |
589 | } | |
590 | } | |
591 | } | |
592 | } | |
593 | } | |
594 | } | |
595 | finished_map | |
596 | } | |
597 | ||
532ac7d7 | 598 | fn is_param_no_infer(&self, substs: SubstsRef<'_>) -> bool { |
69743fb6 XL |
599 | return self.is_of_param(substs.type_at(0)) && |
600 | !substs.types().any(|t| t.has_infer_types()); | |
601 | } | |
94b46f34 | 602 | |
69743fb6 | 603 | pub fn is_of_param(&self, ty: Ty<'_>) -> bool { |
e74abb32 | 604 | return match ty.kind { |
b7449926 | 605 | ty::Param(_) => true, |
69743fb6 | 606 | ty::Projection(p) => self.is_of_param(p.self_ty()), |
94b46f34 XL |
607 | _ => false, |
608 | }; | |
609 | } | |
610 | ||
69743fb6 | 611 | fn is_self_referential_projection(&self, p: ty::PolyProjectionPredicate<'_>) -> bool { |
e74abb32 | 612 | match p.ty().skip_binder().kind { |
69743fb6 XL |
613 | ty::Projection(proj) if proj == p.skip_binder().projection_ty => { |
614 | true | |
615 | }, | |
616 | _ => false | |
617 | } | |
618 | } | |
619 | ||
dc9dc135 | 620 | fn evaluate_nested_obligations( |
94b46f34 | 621 | &self, |
48663c56 | 622 | ty: Ty<'_>, |
dc9dc135 XL |
623 | nested: impl Iterator<Item = Obligation<'tcx, ty::Predicate<'tcx>>>, |
624 | computed_preds: &mut FxHashSet<ty::Predicate<'tcx>>, | |
625 | fresh_preds: &mut FxHashSet<ty::Predicate<'tcx>>, | |
626 | predicates: &mut VecDeque<ty::PolyTraitPredicate<'tcx>>, | |
627 | select: &mut SelectionContext<'_, 'tcx>, | |
94b46f34 XL |
628 | only_projections: bool, |
629 | ) -> bool { | |
9fa01778 | 630 | let dummy_cause = ObligationCause::misc(DUMMY_SP, hir::DUMMY_HIR_ID); |
94b46f34 | 631 | |
69743fb6 | 632 | for (obligation, mut predicate) in nested |
48663c56 | 633 | .map(|o| (o.clone(), o.predicate)) |
94b46f34 XL |
634 | { |
635 | let is_new_pred = | |
48663c56 | 636 | fresh_preds.insert(self.clean_pred(select.infcx(), predicate)); |
94b46f34 | 637 | |
69743fb6 | 638 | // Resolve any inference variables that we can, to help selection succeed |
dc9dc135 | 639 | predicate = select.infcx().resolve_vars_if_possible(&predicate); |
69743fb6 XL |
640 | |
641 | // We only add a predicate as a user-displayable bound if | |
642 | // it involves a generic parameter, and doesn't contain | |
643 | // any inference variables. | |
644 | // | |
645 | // Displaying a bound involving a concrete type (instead of a generic | |
646 | // parameter) would be pointless, since it's always true | |
647 | // (e.g. u8: Copy) | |
648 | // Displaying an inference variable is impossible, since they're | |
649 | // an internal compiler detail without a defined visual representation | |
650 | // | |
651 | // We check this by calling is_of_param on the relevant types | |
652 | // from the various possible predicates | |
94b46f34 | 653 | match &predicate { |
48663c56 | 654 | &ty::Predicate::Trait(p) => { |
69743fb6 XL |
655 | if self.is_param_no_infer(p.skip_binder().trait_ref.substs) |
656 | && !only_projections | |
657 | && is_new_pred { | |
94b46f34 | 658 | |
b7449926 | 659 | self.add_user_pred(computed_preds, predicate); |
94b46f34 | 660 | } |
48663c56 | 661 | predicates.push_back(p); |
94b46f34 XL |
662 | } |
663 | &ty::Predicate::Projection(p) => { | |
69743fb6 XL |
664 | debug!("evaluate_nested_obligations: examining projection predicate {:?}", |
665 | predicate); | |
666 | ||
667 | // As described above, we only want to display | |
668 | // bounds which include a generic parameter but don't include | |
669 | // an inference variable. | |
670 | // Additionally, we check if we've seen this predicate before, | |
671 | // to avoid rendering duplicate bounds to the user. | |
672 | if self.is_param_no_infer(p.skip_binder().projection_ty.substs) | |
48663c56 | 673 | && !p.ty().skip_binder().has_infer_types() |
69743fb6 XL |
674 | && is_new_pred { |
675 | debug!("evaluate_nested_obligations: adding projection predicate\ | |
676 | to computed_preds: {:?}", predicate); | |
677 | ||
678 | // Under unusual circumstances, we can end up with a self-refeential | |
679 | // projection predicate. For example: | |
680 | // <T as MyType>::Value == <T as MyType>::Value | |
681 | // Not only is displaying this to the user pointless, | |
682 | // having it in the ParamEnv will cause an issue if we try to call | |
683 | // poly_project_and_unify_type on the predicate, since this kind of | |
684 | // predicate will normally never end up in a ParamEnv. | |
685 | // | |
686 | // For these reasons, we ignore these weird predicates, | |
687 | // ensuring that we're able to properly synthesize an auto trait impl | |
688 | if self.is_self_referential_projection(p) { | |
689 | debug!("evaluate_nested_obligations: encountered a projection | |
690 | predicate equating a type with itself! Skipping"); | |
691 | ||
692 | } else { | |
693 | self.add_user_pred(computed_preds, predicate); | |
694 | } | |
695 | } | |
696 | ||
dc9dc135 XL |
697 | // There are three possible cases when we project a predicate: |
698 | // | |
699 | // 1. We encounter an error. This means that it's impossible for | |
700 | // our current type to implement the auto trait - there's bound | |
701 | // that we could add to our ParamEnv that would 'fix' this kind | |
702 | // of error, as it's not caused by an unimplemented type. | |
703 | // | |
704 | // 2. We succesfully project the predicate (Ok(Some(_))), generating | |
705 | // some subobligations. We then process these subobligations | |
706 | // like any other generated sub-obligations. | |
707 | // | |
708 | // 3. We receieve an 'ambiguous' result (Ok(None)) | |
709 | // If we were actually trying to compile a crate, | |
710 | // we would need to re-process this obligation later. | |
711 | // However, all we care about is finding out what bounds | |
712 | // are needed for our type to implement a particular auto trait. | |
713 | // We've already added this obligation to our computed ParamEnv | |
714 | // above (if it was necessary). Therefore, we don't need | |
715 | // to do any further processing of the obligation. | |
716 | // | |
717 | // Note that we *must* try to project *all* projection predicates | |
718 | // we encounter, even ones without inference variable. | |
719 | // This ensures that we detect any projection errors, | |
720 | // which indicate that our type can *never* implement the given | |
721 | // auto trait. In that case, we will generate an explicit negative | |
722 | // impl (e.g. 'impl !Send for MyType'). However, we don't | |
723 | // try to process any of the generated subobligations - | |
724 | // they contain no new information, since we already know | |
725 | // that our type implements the projected-through trait, | |
726 | // and can lead to weird region issues. | |
727 | // | |
728 | // Normally, we'll generate a negative impl as a result of encountering | |
729 | // a type with an explicit negative impl of an auto trait | |
730 | // (for example, raw pointers have !Send and !Sync impls) | |
731 | // However, through some **interesting** manipulations of the type | |
732 | // system, it's actually possible to write a type that never | |
733 | // implements an auto trait due to a projection error, not a normal | |
734 | // negative impl error. To properly handle this case, we need | |
735 | // to ensure that we catch any potential projection errors, | |
736 | // and turn them into an explicit negative impl for our type. | |
737 | debug!("Projecting and unifying projection predicate {:?}", | |
738 | predicate); | |
739 | ||
740 | match poly_project_and_unify_type(select, &obligation.with(p)) { | |
741 | Err(e) => { | |
742 | debug!( | |
743 | "evaluate_nested_obligations: Unable to unify predicate \ | |
744 | '{:?}' '{:?}', bailing out", | |
745 | ty, e | |
746 | ); | |
747 | return false; | |
748 | } | |
749 | Ok(Some(v)) => { | |
750 | // We only care about sub-obligations | |
751 | // when we started out trying to unify | |
752 | // some inference variables. See the comment above | |
753 | // for more infomration | |
754 | if p.ty().skip_binder().has_infer_types() { | |
94b46f34 XL |
755 | if !self.evaluate_nested_obligations( |
756 | ty, | |
757 | v.clone().iter().cloned(), | |
758 | computed_preds, | |
759 | fresh_preds, | |
760 | predicates, | |
761 | select, | |
762 | only_projections, | |
763 | ) { | |
764 | return false; | |
765 | } | |
766 | } | |
dc9dc135 XL |
767 | } |
768 | Ok(None) => { | |
769 | // It's ok not to make progress when hvave no inference variables - | |
770 | // in that case, we were only performing unifcation to check if an | |
771 | // error occured (which would indicate that it's impossible for our | |
772 | // type to implement the auto trait). | |
773 | // However, we should always make progress (either by generating | |
774 | // subobligations or getting an error) when we started off with | |
775 | // inference variables | |
776 | if p.ty().skip_binder().has_infer_types() { | |
94b46f34 XL |
777 | panic!("Unexpected result when selecting {:?} {:?}", ty, obligation) |
778 | } | |
779 | } | |
780 | } | |
781 | } | |
782 | &ty::Predicate::RegionOutlives(ref binder) => { | |
0bf4aa26 XL |
783 | if select |
784 | .infcx() | |
785 | .region_outlives_predicate(&dummy_cause, binder) | |
786 | .is_err() | |
787 | { | |
94b46f34 XL |
788 | return false; |
789 | } | |
790 | } | |
791 | &ty::Predicate::TypeOutlives(ref binder) => { | |
792 | match ( | |
a1dfa0c6 XL |
793 | binder.no_bound_vars(), |
794 | binder.map_bound_ref(|pred| pred.0).no_bound_vars(), | |
94b46f34 XL |
795 | ) { |
796 | (None, Some(t_a)) => { | |
0bf4aa26 XL |
797 | select.infcx().register_region_obligation_with_cause( |
798 | t_a, | |
48663c56 | 799 | select.infcx().tcx.lifetimes.re_static, |
0bf4aa26 | 800 | &dummy_cause, |
94b46f34 XL |
801 | ); |
802 | } | |
803 | (Some(ty::OutlivesPredicate(t_a, r_b)), _) => { | |
0bf4aa26 XL |
804 | select.infcx().register_region_obligation_with_cause( |
805 | t_a, | |
806 | r_b, | |
807 | &dummy_cause, | |
94b46f34 XL |
808 | ); |
809 | } | |
810 | _ => {} | |
811 | }; | |
812 | } | |
813 | _ => panic!("Unexpected predicate {:?} {:?}", ty, predicate), | |
814 | }; | |
815 | } | |
816 | return true; | |
817 | } | |
818 | ||
dc9dc135 | 819 | pub fn clean_pred( |
94b46f34 | 820 | &self, |
dc9dc135 XL |
821 | infcx: &InferCtxt<'_, 'tcx>, |
822 | p: ty::Predicate<'tcx>, | |
823 | ) -> ty::Predicate<'tcx> { | |
94b46f34 XL |
824 | infcx.freshen(p) |
825 | } | |
826 | } | |
827 | ||
828 | // Replaces all ReVars in a type with ty::Region's, using the provided map | |
dc9dc135 | 829 | pub struct RegionReplacer<'a, 'tcx> { |
94b46f34 | 830 | vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>, |
dc9dc135 | 831 | tcx: TyCtxt<'tcx>, |
94b46f34 XL |
832 | } |
833 | ||
dc9dc135 XL |
834 | impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx> { |
835 | fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { | |
94b46f34 XL |
836 | self.tcx |
837 | } | |
838 | ||
839 | fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { | |
840 | (match r { | |
841 | &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(), | |
842 | _ => None, | |
843 | }).unwrap_or_else(|| r.super_fold_with(self)) | |
844 | } | |
845 | } |