1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use dep_graph::DepGraph;
12 use infer::{InferCtxt, InferOk};
13 use ty::{self, Ty, TypeFoldable, ToPolyTraitRef, TyCtxt, ToPredicate};
14 use ty::error::ExpectedFound;
15 use rustc_data_structures::obligation_forest::{ObligationForest, Error};
16 use rustc_data_structures::obligation_forest::{ForestObligation, ObligationProcessor};
17 use std::marker::PhantomData;
19 use util::nodemap::{FxHashSet, NodeMap};
20 use hir::def_id::DefId;
22 use super::CodeAmbiguity;
23 use super::CodeProjectionError;
24 use super::CodeSelectionError;
25 use super::{FulfillmentError, FulfillmentErrorCode};
26 use super::{ObligationCause, PredicateObligation, Obligation};
28 use super::select::SelectionContext;
29 use super::Unimplemented;
31 impl<'tcx> ForestObligation for PendingPredicateObligation<'tcx> {
32 type Predicate = ty::Predicate<'tcx>;
34 fn as_predicate(&self) -> &Self::Predicate { &self.obligation.predicate }
37 pub struct GlobalFulfilledPredicates<'tcx> {
38 set: FxHashSet<ty::PolyTraitPredicate<'tcx>>,
42 /// The fulfillment context is used to drive trait resolution. It
43 /// consists of a list of obligations that must be (eventually)
44 /// satisfied. The job is to track which are satisfied, which yielded
45 /// errors, and which are still pending. At any point, users can call
46 /// `select_where_possible`, and the fulfilment context will try to do
47 /// selection, retaining only those obligations that remain
48 /// ambiguous. This may be helpful in pushing type inference
49 /// along. Once all type inference constraints have been generated, the
50 /// method `select_all_or_error` can be used to report any remaining
51 /// ambiguous cases as errors.
53 pub struct FulfillmentContext<'tcx> {
54 // A list of all obligations that have been registered with this
55 // fulfillment context.
56 predicates: ObligationForest<PendingPredicateObligation<'tcx>>,
58 // A set of constraints that regionck must validate. Each
59 // constraint has the form `T:'a`, meaning "some type `T` must
60 // outlive the lifetime 'a". These constraints derive from
61 // instantiated type parameters. So if you had a struct defined
64 // struct Foo<T:'static> { ... }
66 // then in some expression `let x = Foo { ... }` it will
67 // instantiate the type parameter `T` with a fresh type `$0`. At
68 // the same time, it will record a region obligation of
69 // `$0:'static`. This will get checked later by regionck. (We
70 // can't generally check these things right away because we have
71 // to wait until types are resolved.)
73 // These are stored in a map keyed to the id of the innermost
74 // enclosing fn body / static initializer expression. This is
75 // because the location where the obligation was incurred can be
76 // relevant with respect to which sublifetime assumptions are in
77 // place. The reason that we store under the fn-id, and not
78 // something more fine-grained, is so that it is easier for
79 // regionck to be sure that it has found *all* the region
80 // obligations (otherwise, it's easy to fail to walk to a
81 // particular node-id).
82 region_obligations: NodeMap<Vec<RegionObligation<'tcx>>>,
86 pub struct RegionObligation<'tcx> {
87 pub sub_region: &'tcx ty::Region,
88 pub sup_type: Ty<'tcx>,
89 pub cause: ObligationCause<'tcx>,
92 #[derive(Clone, Debug)]
93 pub struct PendingPredicateObligation<'tcx> {
94 pub obligation: PredicateObligation<'tcx>,
95 pub stalled_on: Vec<Ty<'tcx>>,
98 impl<'a, 'gcx, 'tcx> FulfillmentContext<'tcx> {
99 /// Creates a new fulfillment context.
100 pub fn new() -> FulfillmentContext<'tcx> {
102 predicates: ObligationForest::new(),
103 region_obligations: NodeMap(),
107 /// "Normalize" a projection type `<SomeType as SomeTrait>::X` by
108 /// creating a fresh type variable `$0` as well as a projection
109 /// predicate `<SomeType as SomeTrait>::X == $0`. When the
110 /// inference engine runs, it will attempt to find an impl of
111 /// `SomeTrait` or a where clause that lets us unify `$0` with
112 /// something concrete. If this fails, we'll unify `$0` with
113 /// `projection_ty` again.
114 pub fn normalize_projection_type(&mut self,
115 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
116 projection_ty: ty::ProjectionTy<'tcx>,
117 cause: ObligationCause<'tcx>)
120 debug!("normalize_projection_type(projection_ty={:?})",
123 assert!(!projection_ty.has_escaping_regions());
125 // FIXME(#20304) -- cache
127 let mut selcx = SelectionContext::new(infcx);
128 let normalized = project::normalize_projection_type(&mut selcx, projection_ty, cause, 0);
130 for obligation in normalized.obligations {
131 self.register_predicate_obligation(infcx, obligation);
134 debug!("normalize_projection_type: result={:?}", normalized.value);
139 pub fn register_bound(&mut self,
140 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
143 cause: ObligationCause<'tcx>)
145 let trait_ref = ty::TraitRef {
147 substs: infcx.tcx.mk_substs_trait(ty, &[]),
149 self.register_predicate_obligation(infcx, Obligation {
152 predicate: trait_ref.to_predicate()
156 pub fn register_region_obligation(&mut self,
158 r_b: &'tcx ty::Region,
159 cause: ObligationCause<'tcx>)
161 register_region_obligation(t_a, r_b, cause, &mut self.region_obligations);
164 pub fn register_predicate_obligation(&mut self,
165 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
166 obligation: PredicateObligation<'tcx>)
168 // this helps to reduce duplicate errors, as well as making
169 // debug output much nicer to read and so on.
170 let obligation = infcx.resolve_type_vars_if_possible(&obligation);
172 debug!("register_predicate_obligation(obligation={:?})", obligation);
174 assert!(!infcx.is_in_snapshot());
176 if infcx.tcx.fulfilled_predicates.borrow().check_duplicate(&obligation.predicate) {
177 debug!("register_predicate_obligation: duplicate");
181 self.predicates.register_obligation(PendingPredicateObligation {
182 obligation: obligation,
187 pub fn register_predicate_obligations(&mut self,
188 infcx: &InferCtxt<'a, 'gcx, 'tcx>,
189 obligations: Vec<PredicateObligation<'tcx>>)
191 for obligation in obligations {
192 self.register_predicate_obligation(infcx, obligation);
197 pub fn region_obligations(&self,
198 body_id: ast::NodeId)
199 -> &[RegionObligation<'tcx>]
201 match self.region_obligations.get(&body_id) {
202 None => Default::default(),
207 pub fn select_all_or_error(&mut self,
208 infcx: &InferCtxt<'a, 'gcx, 'tcx>)
209 -> Result<(),Vec<FulfillmentError<'tcx>>>
211 self.select_where_possible(infcx)?;
214 self.predicates.to_errors(CodeAmbiguity)
216 .map(|e| to_fulfillment_error(e))
218 if errors.is_empty() {
225 pub fn select_where_possible(&mut self,
226 infcx: &InferCtxt<'a, 'gcx, 'tcx>)
227 -> Result<(),Vec<FulfillmentError<'tcx>>>
229 let mut selcx = SelectionContext::new(infcx);
230 self.select(&mut selcx)
233 pub fn pending_obligations(&self) -> Vec<PendingPredicateObligation<'tcx>> {
234 self.predicates.pending_obligations()
237 /// Attempts to select obligations using `selcx`. If `only_new_obligations` is true, then it
238 /// only attempts to select obligations that haven't been seen before.
239 fn select(&mut self, selcx: &mut SelectionContext<'a, 'gcx, 'tcx>)
240 -> Result<(),Vec<FulfillmentError<'tcx>>> {
241 debug!("select(obligation-forest-size={})", self.predicates.len());
243 let mut errors = Vec::new();
246 debug!("select: starting another iteration");
248 // Process pending obligations.
249 let outcome = self.predicates.process_obligations(&mut FulfillProcessor {
251 region_obligations: &mut self.region_obligations,
253 debug!("select: outcome={:?}", outcome);
255 // these are obligations that were proven to be true.
256 for pending_obligation in outcome.completed {
257 let predicate = &pending_obligation.obligation.predicate;
258 selcx.tcx().fulfilled_predicates.borrow_mut()
259 .add_if_global(selcx.tcx(), predicate);
263 outcome.errors.into_iter()
264 .map(|e| to_fulfillment_error(e)));
266 // If nothing new was added, no need to keep looping.
272 debug!("select({} predicates remaining, {} errors) done",
273 self.predicates.len(), errors.len());
275 if errors.is_empty() {
283 struct FulfillProcessor<'a, 'b: 'a, 'gcx: 'tcx, 'tcx: 'b> {
284 selcx: &'a mut SelectionContext<'b, 'gcx, 'tcx>,
285 region_obligations: &'a mut NodeMap<Vec<RegionObligation<'tcx>>>,
288 impl<'a, 'b, 'gcx, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'b, 'gcx, 'tcx> {
289 type Obligation = PendingPredicateObligation<'tcx>;
290 type Error = FulfillmentErrorCode<'tcx>;
292 fn process_obligation(&mut self,
293 obligation: &mut Self::Obligation)
294 -> Result<Option<Vec<Self::Obligation>>, Self::Error>
296 process_predicate(self.selcx,
298 self.region_obligations)
299 .map(|os| os.map(|os| os.into_iter().map(|o| PendingPredicateObligation {
305 fn process_backedge<'c, I>(&mut self, cycle: I,
306 _marker: PhantomData<&'c PendingPredicateObligation<'tcx>>)
307 where I: Clone + Iterator<Item=&'c PendingPredicateObligation<'tcx>>,
309 if coinductive_match(self.selcx, cycle.clone()) {
310 debug!("process_child_obligations: coinductive match");
312 let cycle : Vec<_> = cycle.map(|c| c.obligation.clone()).collect();
313 self.selcx.infcx().report_overflow_error_cycle(&cycle);
318 /// Return the set of type variables contained in a trait ref
319 fn trait_ref_type_vars<'a, 'gcx, 'tcx>(selcx: &mut SelectionContext<'a, 'gcx, 'tcx>,
320 t: ty::PolyTraitRef<'tcx>) -> Vec<Ty<'tcx>>
322 t.skip_binder() // ok b/c this check doesn't care about regions
324 .map(|t| selcx.infcx().resolve_type_vars_if_possible(&t))
325 .filter(|t| t.has_infer_types())
326 .flat_map(|t| t.walk())
327 .filter(|t| match t.sty { ty::TyInfer(_) => true, _ => false })
331 /// Processes a predicate obligation and returns either:
332 /// - `Ok(Some(v))` if the predicate is true, presuming that `v` are also true
333 /// - `Ok(None)` if we don't have enough info to be sure
334 /// - `Err` if the predicate does not hold
335 fn process_predicate<'a, 'gcx, 'tcx>(
336 selcx: &mut SelectionContext<'a, 'gcx, 'tcx>,
337 pending_obligation: &mut PendingPredicateObligation<'tcx>,
338 region_obligations: &mut NodeMap<Vec<RegionObligation<'tcx>>>)
339 -> Result<Option<Vec<PredicateObligation<'tcx>>>,
340 FulfillmentErrorCode<'tcx>>
342 // if we were stalled on some unresolved variables, first check
343 // whether any of them have been resolved; if not, don't bother
344 // doing more work yet
345 if !pending_obligation.stalled_on.is_empty() {
346 if pending_obligation.stalled_on.iter().all(|&ty| {
347 let resolved_ty = selcx.infcx().shallow_resolve(&ty);
348 resolved_ty == ty // nothing changed here
350 debug!("process_predicate: pending obligation {:?} still stalled on {:?}",
351 selcx.infcx().resolve_type_vars_if_possible(&pending_obligation.obligation),
352 pending_obligation.stalled_on);
355 pending_obligation.stalled_on = vec![];
358 let obligation = &mut pending_obligation.obligation;
360 if obligation.predicate.has_infer_types() {
361 obligation.predicate = selcx.infcx().resolve_type_vars_if_possible(&obligation.predicate);
364 match obligation.predicate {
365 ty::Predicate::Trait(ref data) => {
366 if selcx.tcx().fulfilled_predicates.borrow().check_duplicate_trait(data) {
367 return Ok(Some(vec![]));
370 let trait_obligation = obligation.with(data.clone());
371 match selcx.select(&trait_obligation) {
372 Ok(Some(vtable)) => {
373 debug!("selecting trait `{:?}` at depth {} yielded Ok(Some)",
374 data, obligation.recursion_depth);
375 Ok(Some(vtable.nested_obligations()))
378 debug!("selecting trait `{:?}` at depth {} yielded Ok(None)",
379 data, obligation.recursion_depth);
381 // This is a bit subtle: for the most part, the
382 // only reason we can fail to make progress on
383 // trait selection is because we don't have enough
384 // information about the types in the trait. One
385 // exception is that we sometimes haven't decided
386 // what kind of closure a closure is. *But*, in
387 // that case, it turns out, the type of the
388 // closure will also change, because the closure
389 // also includes references to its upvars as part
390 // of its type, and those types are resolved at
393 // FIXME(#32286) logic seems false if no upvars
394 pending_obligation.stalled_on =
395 trait_ref_type_vars(selcx, data.to_poly_trait_ref());
397 debug!("process_predicate: pending obligation {:?} now stalled on {:?}",
398 selcx.infcx().resolve_type_vars_if_possible(obligation),
399 pending_obligation.stalled_on);
403 Err(selection_err) => {
404 info!("selecting trait `{:?}` at depth {} yielded Err",
405 data, obligation.recursion_depth);
407 Err(CodeSelectionError(selection_err))
412 ty::Predicate::Equate(ref binder) => {
413 match selcx.infcx().equality_predicate(&obligation.cause, binder) {
414 Ok(InferOk { obligations, value: () }) => {
415 Ok(Some(obligations))
417 Err(_) => Err(CodeSelectionError(Unimplemented)),
421 ty::Predicate::RegionOutlives(ref binder) => {
422 match selcx.infcx().region_outlives_predicate(&obligation.cause, binder) {
423 Ok(()) => Ok(Some(Vec::new())),
424 Err(_) => Err(CodeSelectionError(Unimplemented)),
428 ty::Predicate::TypeOutlives(ref binder) => {
429 // Check if there are higher-ranked regions.
430 match selcx.tcx().no_late_bound_regions(binder) {
431 // If there are, inspect the underlying type further.
433 // Convert from `Binder<OutlivesPredicate<Ty, Region>>` to `Binder<Ty>`.
434 let binder = binder.map_bound_ref(|pred| pred.0);
436 // Check if the type has any bound regions.
437 match selcx.tcx().no_late_bound_regions(&binder) {
438 // If so, this obligation is an error (for now). Eventually we should be
439 // able to support additional cases here, like `for<'a> &'a str: 'a`.
441 Err(CodeSelectionError(Unimplemented))
443 // Otherwise, we have something of the form
444 // `for<'a> T: 'a where 'a not in T`, which we can treat as `T: 'static`.
446 let r_static = selcx.tcx().mk_region(ty::ReStatic);
447 register_region_obligation(t_a, r_static,
448 obligation.cause.clone(),
454 // If there aren't, register the obligation.
455 Some(ty::OutlivesPredicate(t_a, r_b)) => {
456 register_region_obligation(t_a, r_b,
457 obligation.cause.clone(),
464 ty::Predicate::Projection(ref data) => {
465 let project_obligation = obligation.with(data.clone());
466 match project::poly_project_and_unify_type(selcx, &project_obligation) {
468 pending_obligation.stalled_on =
469 trait_ref_type_vars(selcx, data.to_poly_trait_ref());
473 Err(e) => Err(CodeProjectionError(e))
477 ty::Predicate::ObjectSafe(trait_def_id) => {
478 if !selcx.tcx().is_object_safe(trait_def_id) {
479 Err(CodeSelectionError(Unimplemented))
485 ty::Predicate::ClosureKind(closure_def_id, kind) => {
486 match selcx.infcx().closure_kind(closure_def_id) {
487 Some(closure_kind) => {
488 if closure_kind.extends(kind) {
491 Err(CodeSelectionError(Unimplemented))
500 ty::Predicate::WellFormed(ty) => {
501 match ty::wf::obligations(selcx.infcx(), obligation.cause.body_id,
502 ty, obligation.cause.span) {
504 pending_obligation.stalled_on = vec![ty];
511 ty::Predicate::Subtype(ref subtype) => {
512 match selcx.infcx().subtype_predicate(&obligation.cause, subtype) {
514 // none means that both are unresolved
515 pending_obligation.stalled_on = vec![subtype.skip_binder().a,
516 subtype.skip_binder().b];
520 Ok(Some(ok.obligations))
523 let expected_found = ExpectedFound::new(subtype.skip_binder().a_is_expected,
524 subtype.skip_binder().a,
525 subtype.skip_binder().b);
526 Err(FulfillmentErrorCode::CodeSubtypeError(expected_found, err))
533 /// For defaulted traits, we use a co-inductive strategy to solve, so
534 /// that recursion is ok. This routine returns true if the top of the
535 /// stack (`cycle[0]`):
536 /// - is a defaulted trait, and
537 /// - it also appears in the backtrace at some position `X`; and,
538 /// - all the predicates at positions `X..` between `X` an the top are
539 /// also defaulted traits.
540 fn coinductive_match<'a,'c,'gcx,'tcx,I>(selcx: &mut SelectionContext<'a,'gcx,'tcx>,
542 where I: Iterator<Item=&'c PendingPredicateObligation<'tcx>>,
545 let mut cycle = cycle;
547 .all(|bt_obligation| {
548 let result = coinductive_obligation(selcx, &bt_obligation.obligation);
549 debug!("coinductive_match: bt_obligation={:?} coinductive={}",
550 bt_obligation, result);
555 fn coinductive_obligation<'a,'gcx,'tcx>(selcx: &SelectionContext<'a,'gcx,'tcx>,
556 obligation: &PredicateObligation<'tcx>)
558 match obligation.predicate {
559 ty::Predicate::Trait(ref data) => {
560 selcx.tcx().trait_has_default_impl(data.def_id())
568 fn register_region_obligation<'tcx>(t_a: Ty<'tcx>,
569 r_b: &'tcx ty::Region,
570 cause: ObligationCause<'tcx>,
571 region_obligations: &mut NodeMap<Vec<RegionObligation<'tcx>>>)
573 let region_obligation = RegionObligation { sup_type: t_a,
577 debug!("register_region_obligation({:?}, cause={:?})",
578 region_obligation, region_obligation.cause);
580 region_obligations.entry(region_obligation.cause.body_id)
582 .push(region_obligation);
586 impl<'a, 'gcx, 'tcx> GlobalFulfilledPredicates<'gcx> {
587 pub fn new(dep_graph: DepGraph) -> GlobalFulfilledPredicates<'gcx> {
588 GlobalFulfilledPredicates {
590 dep_graph: dep_graph,
594 pub fn check_duplicate(&self, key: &ty::Predicate<'tcx>) -> bool {
595 if let ty::Predicate::Trait(ref data) = *key {
596 self.check_duplicate_trait(data)
602 pub fn check_duplicate_trait(&self, data: &ty::PolyTraitPredicate<'tcx>) -> bool {
603 // For the global predicate registry, when we find a match, it
604 // may have been computed by some other task, so we want to
605 // add a read from the node corresponding to the predicate
606 // processing to make sure we get the transitive dependencies.
607 if self.set.contains(data) {
608 debug_assert!(data.is_global());
609 self.dep_graph.read(data.dep_node());
610 debug!("check_duplicate: global predicate `{:?}` already proved elsewhere", data);
618 fn add_if_global(&mut self, tcx: TyCtxt<'a, 'gcx, 'tcx>, key: &ty::Predicate<'tcx>) {
619 if let ty::Predicate::Trait(ref data) = *key {
620 // We only add things to the global predicate registry
621 // after the current task has proved them, and hence
622 // already has the required read edges, so we don't need
623 // to add any more edges here.
624 if data.is_global() {
625 if let Some(data) = tcx.lift_to_global(data) {
626 if self.set.insert(data.clone()) {
627 debug!("add_if_global: global predicate `{:?}` added", data);
635 fn to_fulfillment_error<'tcx>(
636 error: Error<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>>)
637 -> FulfillmentError<'tcx>
639 let obligation = error.backtrace.into_iter().next().unwrap().obligation;
640 FulfillmentError::new(obligation, error.error)