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 rustc_data_structures
::obligation_forest
::{ObligationForest, Error}
;
15 use rustc_data_structures
::obligation_forest
::{ForestObligation, ObligationProcessor}
;
16 use std
::marker
::PhantomData
;
18 use util
::nodemap
::{FxHashSet, NodeMap}
;
19 use hir
::def_id
::DefId
;
21 use super::CodeAmbiguity
;
22 use super::CodeProjectionError
;
23 use super::CodeSelectionError
;
24 use super::{FulfillmentError, FulfillmentErrorCode}
;
25 use super::{ObligationCause, PredicateObligation, Obligation}
;
27 use super::select
::SelectionContext
;
28 use super::Unimplemented
;
30 impl<'tcx
> ForestObligation
for PendingPredicateObligation
<'tcx
> {
31 type Predicate
= ty
::Predicate
<'tcx
>;
33 fn as_predicate(&self) -> &Self::Predicate { &self.obligation.predicate }
36 pub struct GlobalFulfilledPredicates
<'tcx
> {
37 set
: FxHashSet
<ty
::PolyTraitPredicate
<'tcx
>>,
41 /// The fulfillment context is used to drive trait resolution. It
42 /// consists of a list of obligations that must be (eventually)
43 /// satisfied. The job is to track which are satisfied, which yielded
44 /// errors, and which are still pending. At any point, users can call
45 /// `select_where_possible`, and the fulfilment context will try to do
46 /// selection, retaining only those obligations that remain
47 /// ambiguous. This may be helpful in pushing type inference
48 /// along. Once all type inference constraints have been generated, the
49 /// method `select_all_or_error` can be used to report any remaining
50 /// ambiguous cases as errors.
52 pub struct FulfillmentContext
<'tcx
> {
53 // A list of all obligations that have been registered with this
54 // fulfillment context.
55 predicates
: ObligationForest
<PendingPredicateObligation
<'tcx
>>,
57 // A set of constraints that regionck must validate. Each
58 // constraint has the form `T:'a`, meaning "some type `T` must
59 // outlive the lifetime 'a". These constraints derive from
60 // instantiated type parameters. So if you had a struct defined
63 // struct Foo<T:'static> { ... }
65 // then in some expression `let x = Foo { ... }` it will
66 // instantiate the type parameter `T` with a fresh type `$0`. At
67 // the same time, it will record a region obligation of
68 // `$0:'static`. This will get checked later by regionck. (We
69 // can't generally check these things right away because we have
70 // to wait until types are resolved.)
72 // These are stored in a map keyed to the id of the innermost
73 // enclosing fn body / static initializer expression. This is
74 // because the location where the obligation was incurred can be
75 // relevant with respect to which sublifetime assumptions are in
76 // place. The reason that we store under the fn-id, and not
77 // something more fine-grained, is so that it is easier for
78 // regionck to be sure that it has found *all* the region
79 // obligations (otherwise, it's easy to fail to walk to a
80 // particular node-id).
81 region_obligations
: NodeMap
<Vec
<RegionObligation
<'tcx
>>>,
85 pub struct RegionObligation
<'tcx
> {
86 pub sub_region
: &'tcx ty
::Region
,
87 pub sup_type
: Ty
<'tcx
>,
88 pub cause
: ObligationCause
<'tcx
>,
91 #[derive(Clone, Debug)]
92 pub struct PendingPredicateObligation
<'tcx
> {
93 pub obligation
: PredicateObligation
<'tcx
>,
94 pub stalled_on
: Vec
<Ty
<'tcx
>>,
97 impl<'a
, 'gcx
, 'tcx
> FulfillmentContext
<'tcx
> {
98 /// Creates a new fulfillment context.
99 pub fn new() -> FulfillmentContext
<'tcx
> {
101 predicates
: ObligationForest
::new(),
102 region_obligations
: NodeMap(),
106 /// "Normalize" a projection type `<SomeType as SomeTrait>::X` by
107 /// creating a fresh type variable `$0` as well as a projection
108 /// predicate `<SomeType as SomeTrait>::X == $0`. When the
109 /// inference engine runs, it will attempt to find an impl of
110 /// `SomeTrait` or a where clause that lets us unify `$0` with
111 /// something concrete. If this fails, we'll unify `$0` with
112 /// `projection_ty` again.
113 pub fn normalize_projection_type(&mut self,
114 infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>,
115 projection_ty
: ty
::ProjectionTy
<'tcx
>,
116 cause
: ObligationCause
<'tcx
>)
119 debug
!("normalize_projection_type(projection_ty={:?})",
122 assert
!(!projection_ty
.has_escaping_regions());
124 // FIXME(#20304) -- cache
126 let mut selcx
= SelectionContext
::new(infcx
);
127 let normalized
= project
::normalize_projection_type(&mut selcx
, projection_ty
, cause
, 0);
129 for obligation
in normalized
.obligations
{
130 self.register_predicate_obligation(infcx
, obligation
);
133 debug
!("normalize_projection_type: result={:?}", normalized
.value
);
138 pub fn register_bound(&mut self,
139 infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>,
142 cause
: ObligationCause
<'tcx
>)
144 let trait_ref
= ty
::TraitRef
{
146 substs
: infcx
.tcx
.mk_substs_trait(ty
, &[]),
148 self.register_predicate_obligation(infcx
, Obligation
{
151 predicate
: trait_ref
.to_predicate()
155 pub fn register_region_obligation(&mut self,
157 r_b
: &'tcx ty
::Region
,
158 cause
: ObligationCause
<'tcx
>)
160 register_region_obligation(t_a
, r_b
, cause
, &mut self.region_obligations
);
163 pub fn register_predicate_obligation(&mut self,
164 infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>,
165 obligation
: PredicateObligation
<'tcx
>)
167 // this helps to reduce duplicate errors, as well as making
168 // debug output much nicer to read and so on.
169 let obligation
= infcx
.resolve_type_vars_if_possible(&obligation
);
171 debug
!("register_predicate_obligation(obligation={:?})", obligation
);
173 infcx
.obligations_in_snapshot
.set(true);
175 if infcx
.tcx
.fulfilled_predicates
.borrow().check_duplicate(&obligation
.predicate
) {
176 debug
!("register_predicate_obligation: duplicate");
180 self.predicates
.register_obligation(PendingPredicateObligation
{
181 obligation
: obligation
,
186 pub fn region_obligations(&self,
187 body_id
: ast
::NodeId
)
188 -> &[RegionObligation
<'tcx
>]
190 match self.region_obligations
.get(&body_id
) {
191 None
=> Default
::default(),
196 pub fn select_all_or_error(&mut self,
197 infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>)
198 -> Result
<(),Vec
<FulfillmentError
<'tcx
>>>
200 self.select_where_possible(infcx
)?
;
203 self.predicates
.to_errors(CodeAmbiguity
)
205 .map(|e
| to_fulfillment_error(e
))
207 if errors
.is_empty() {
214 pub fn select_where_possible(&mut self,
215 infcx
: &InferCtxt
<'a
, 'gcx
, 'tcx
>)
216 -> Result
<(),Vec
<FulfillmentError
<'tcx
>>>
218 let mut selcx
= SelectionContext
::new(infcx
);
219 self.select(&mut selcx
)
222 pub fn pending_obligations(&self) -> Vec
<PendingPredicateObligation
<'tcx
>> {
223 self.predicates
.pending_obligations()
226 /// Attempts to select obligations using `selcx`. If `only_new_obligations` is true, then it
227 /// only attempts to select obligations that haven't been seen before.
228 fn select(&mut self, selcx
: &mut SelectionContext
<'a
, 'gcx
, 'tcx
>)
229 -> Result
<(),Vec
<FulfillmentError
<'tcx
>>> {
230 debug
!("select(obligation-forest-size={})", self.predicates
.len());
232 let mut errors
= Vec
::new();
235 debug
!("select: starting another iteration");
237 // Process pending obligations.
238 let outcome
= self.predicates
.process_obligations(&mut FulfillProcessor
{
240 region_obligations
: &mut self.region_obligations
,
242 debug
!("select: outcome={:?}", outcome
);
244 // these are obligations that were proven to be true.
245 for pending_obligation
in outcome
.completed
{
246 let predicate
= &pending_obligation
.obligation
.predicate
;
247 selcx
.tcx().fulfilled_predicates
.borrow_mut()
248 .add_if_global(selcx
.tcx(), predicate
);
252 outcome
.errors
.into_iter()
253 .map(|e
| to_fulfillment_error(e
)));
255 // If nothing new was added, no need to keep looping.
261 debug
!("select({} predicates remaining, {} errors) done",
262 self.predicates
.len(), errors
.len());
264 if errors
.is_empty() {
272 struct FulfillProcessor
<'a
, 'b
: 'a
, 'gcx
: 'tcx
, 'tcx
: 'b
> {
273 selcx
: &'a
mut SelectionContext
<'b
, 'gcx
, 'tcx
>,
274 region_obligations
: &'a
mut NodeMap
<Vec
<RegionObligation
<'tcx
>>>,
277 impl<'a
, 'b
, 'gcx
, 'tcx
> ObligationProcessor
for FulfillProcessor
<'a
, 'b
, 'gcx
, 'tcx
> {
278 type Obligation
= PendingPredicateObligation
<'tcx
>;
279 type Error
= FulfillmentErrorCode
<'tcx
>;
281 fn process_obligation(&mut self,
282 obligation
: &mut Self::Obligation
)
283 -> Result
<Option
<Vec
<Self::Obligation
>>, Self::Error
>
285 process_predicate(self.selcx
,
287 self.region_obligations
)
288 .map(|os
| os
.map(|os
| os
.into_iter().map(|o
| PendingPredicateObligation
{
294 fn process_backedge
<'c
, I
>(&mut self, cycle
: I
,
295 _marker
: PhantomData
<&'c PendingPredicateObligation
<'tcx
>>)
296 where I
: Clone
+ Iterator
<Item
=&'c PendingPredicateObligation
<'tcx
>>,
298 if coinductive_match(self.selcx
, cycle
.clone()) {
299 debug
!("process_child_obligations: coinductive match");
301 let cycle
: Vec
<_
> = cycle
.map(|c
| c
.obligation
.clone()).collect();
302 self.selcx
.infcx().report_overflow_error_cycle(&cycle
);
307 /// Return the set of type variables contained in a trait ref
308 fn trait_ref_type_vars
<'a
, 'gcx
, 'tcx
>(selcx
: &mut SelectionContext
<'a
, 'gcx
, 'tcx
>,
309 t
: ty
::PolyTraitRef
<'tcx
>) -> Vec
<Ty
<'tcx
>>
311 t
.skip_binder() // ok b/c this check doesn't care about regions
313 .map(|t
| selcx
.infcx().resolve_type_vars_if_possible(&t
))
314 .filter(|t
| t
.has_infer_types())
315 .flat_map(|t
| t
.walk())
316 .filter(|t
| match t
.sty { ty::TyInfer(_) => true, _ => false }
)
320 /// Processes a predicate obligation and returns either:
321 /// - `Ok(Some(v))` if the predicate is true, presuming that `v` are also true
322 /// - `Ok(None)` if we don't have enough info to be sure
323 /// - `Err` if the predicate does not hold
324 fn process_predicate
<'a
, 'gcx
, 'tcx
>(
325 selcx
: &mut SelectionContext
<'a
, 'gcx
, 'tcx
>,
326 pending_obligation
: &mut PendingPredicateObligation
<'tcx
>,
327 region_obligations
: &mut NodeMap
<Vec
<RegionObligation
<'tcx
>>>)
328 -> Result
<Option
<Vec
<PredicateObligation
<'tcx
>>>,
329 FulfillmentErrorCode
<'tcx
>>
331 // if we were stalled on some unresolved variables, first check
332 // whether any of them have been resolved; if not, don't bother
333 // doing more work yet
334 if !pending_obligation
.stalled_on
.is_empty() {
335 if pending_obligation
.stalled_on
.iter().all(|&ty
| {
336 let resolved_ty
= selcx
.infcx().shallow_resolve(&ty
);
337 resolved_ty
== ty
// nothing changed here
339 debug
!("process_predicate: pending obligation {:?} still stalled on {:?}",
340 selcx
.infcx().resolve_type_vars_if_possible(&pending_obligation
.obligation
),
341 pending_obligation
.stalled_on
);
344 pending_obligation
.stalled_on
= vec
![];
347 let obligation
= &mut pending_obligation
.obligation
;
349 if obligation
.predicate
.has_infer_types() {
350 obligation
.predicate
= selcx
.infcx().resolve_type_vars_if_possible(&obligation
.predicate
);
353 match obligation
.predicate
{
354 ty
::Predicate
::Trait(ref data
) => {
355 if selcx
.tcx().fulfilled_predicates
.borrow().check_duplicate_trait(data
) {
356 return Ok(Some(vec
![]));
359 let trait_obligation
= obligation
.with(data
.clone());
360 match selcx
.select(&trait_obligation
) {
361 Ok(Some(vtable
)) => {
362 debug
!("selecting trait `{:?}` at depth {} yielded Ok(Some)",
363 data
, obligation
.recursion_depth
);
364 Ok(Some(vtable
.nested_obligations()))
367 debug
!("selecting trait `{:?}` at depth {} yielded Ok(None)",
368 data
, obligation
.recursion_depth
);
370 // This is a bit subtle: for the most part, the
371 // only reason we can fail to make progress on
372 // trait selection is because we don't have enough
373 // information about the types in the trait. One
374 // exception is that we sometimes haven't decided
375 // what kind of closure a closure is. *But*, in
376 // that case, it turns out, the type of the
377 // closure will also change, because the closure
378 // also includes references to its upvars as part
379 // of its type, and those types are resolved at
382 // FIXME(#32286) logic seems false if no upvars
383 pending_obligation
.stalled_on
=
384 trait_ref_type_vars(selcx
, data
.to_poly_trait_ref());
386 debug
!("process_predicate: pending obligation {:?} now stalled on {:?}",
387 selcx
.infcx().resolve_type_vars_if_possible(obligation
),
388 pending_obligation
.stalled_on
);
392 Err(selection_err
) => {
393 info
!("selecting trait `{:?}` at depth {} yielded Err",
394 data
, obligation
.recursion_depth
);
396 Err(CodeSelectionError(selection_err
))
401 ty
::Predicate
::Equate(ref binder
) => {
402 match selcx
.infcx().equality_predicate(&obligation
.cause
, binder
) {
403 Ok(InferOk { obligations, value: () }
) => {
404 Ok(Some(obligations
))
406 Err(_
) => Err(CodeSelectionError(Unimplemented
)),
410 ty
::Predicate
::RegionOutlives(ref binder
) => {
411 match selcx
.infcx().region_outlives_predicate(&obligation
.cause
, binder
) {
412 Ok(()) => Ok(Some(Vec
::new())),
413 Err(_
) => Err(CodeSelectionError(Unimplemented
)),
417 ty
::Predicate
::TypeOutlives(ref binder
) => {
418 // Check if there are higher-ranked regions.
419 match selcx
.tcx().no_late_bound_regions(binder
) {
420 // If there are, inspect the underlying type further.
422 // Convert from `Binder<OutlivesPredicate<Ty, Region>>` to `Binder<Ty>`.
423 let binder
= binder
.map_bound_ref(|pred
| pred
.0);
425 // Check if the type has any bound regions.
426 match selcx
.tcx().no_late_bound_regions(&binder
) {
427 // If so, this obligation is an error (for now). Eventually we should be
428 // able to support additional cases here, like `for<'a> &'a str: 'a`.
430 Err(CodeSelectionError(Unimplemented
))
432 // Otherwise, we have something of the form
433 // `for<'a> T: 'a where 'a not in T`, which we can treat as `T: 'static`.
435 let r_static
= selcx
.tcx().mk_region(ty
::ReStatic
);
436 register_region_obligation(t_a
, r_static
,
437 obligation
.cause
.clone(),
443 // If there aren't, register the obligation.
444 Some(ty
::OutlivesPredicate(t_a
, r_b
)) => {
445 register_region_obligation(t_a
, r_b
,
446 obligation
.cause
.clone(),
453 ty
::Predicate
::Projection(ref data
) => {
454 let project_obligation
= obligation
.with(data
.clone());
455 match project
::poly_project_and_unify_type(selcx
, &project_obligation
) {
457 pending_obligation
.stalled_on
=
458 trait_ref_type_vars(selcx
, data
.to_poly_trait_ref());
462 Err(e
) => Err(CodeProjectionError(e
))
466 ty
::Predicate
::ObjectSafe(trait_def_id
) => {
467 if !selcx
.tcx().is_object_safe(trait_def_id
) {
468 Err(CodeSelectionError(Unimplemented
))
474 ty
::Predicate
::ClosureKind(closure_def_id
, kind
) => {
475 match selcx
.infcx().closure_kind(closure_def_id
) {
476 Some(closure_kind
) => {
477 if closure_kind
.extends(kind
) {
480 Err(CodeSelectionError(Unimplemented
))
489 ty
::Predicate
::WellFormed(ty
) => {
490 match ty
::wf
::obligations(selcx
.infcx(), obligation
.cause
.body_id
,
491 ty
, obligation
.cause
.span
) {
493 pending_obligation
.stalled_on
= vec
![ty
];
502 /// For defaulted traits, we use a co-inductive strategy to solve, so
503 /// that recursion is ok. This routine returns true if the top of the
504 /// stack (`cycle[0]`):
505 /// - is a defaulted trait, and
506 /// - it also appears in the backtrace at some position `X`; and,
507 /// - all the predicates at positions `X..` between `X` an the top are
508 /// also defaulted traits.
509 fn coinductive_match
<'a
,'c
,'gcx
,'tcx
,I
>(selcx
: &mut SelectionContext
<'a
,'gcx
,'tcx
>,
511 where I
: Iterator
<Item
=&'c PendingPredicateObligation
<'tcx
>>,
514 let mut cycle
= cycle
;
516 .all(|bt_obligation
| {
517 let result
= coinductive_obligation(selcx
, &bt_obligation
.obligation
);
518 debug
!("coinductive_match: bt_obligation={:?} coinductive={}",
519 bt_obligation
, result
);
524 fn coinductive_obligation
<'a
,'gcx
,'tcx
>(selcx
: &SelectionContext
<'a
,'gcx
,'tcx
>,
525 obligation
: &PredicateObligation
<'tcx
>)
527 match obligation
.predicate
{
528 ty
::Predicate
::Trait(ref data
) => {
529 selcx
.tcx().trait_has_default_impl(data
.def_id())
537 fn register_region_obligation
<'tcx
>(t_a
: Ty
<'tcx
>,
538 r_b
: &'tcx ty
::Region
,
539 cause
: ObligationCause
<'tcx
>,
540 region_obligations
: &mut NodeMap
<Vec
<RegionObligation
<'tcx
>>>)
542 let region_obligation
= RegionObligation
{ sup_type
: t_a
,
546 debug
!("register_region_obligation({:?}, cause={:?})",
547 region_obligation
, region_obligation
.cause
);
549 region_obligations
.entry(region_obligation
.cause
.body_id
)
551 .push(region_obligation
);
555 impl<'a
, 'gcx
, 'tcx
> GlobalFulfilledPredicates
<'gcx
> {
556 pub fn new(dep_graph
: DepGraph
) -> GlobalFulfilledPredicates
<'gcx
> {
557 GlobalFulfilledPredicates
{
559 dep_graph
: dep_graph
,
563 pub fn check_duplicate(&self, key
: &ty
::Predicate
<'tcx
>) -> bool
{
564 if let ty
::Predicate
::Trait(ref data
) = *key
{
565 self.check_duplicate_trait(data
)
571 pub fn check_duplicate_trait(&self, data
: &ty
::PolyTraitPredicate
<'tcx
>) -> bool
{
572 // For the global predicate registry, when we find a match, it
573 // may have been computed by some other task, so we want to
574 // add a read from the node corresponding to the predicate
575 // processing to make sure we get the transitive dependencies.
576 if self.set
.contains(data
) {
577 debug_assert
!(data
.is_global());
578 self.dep_graph
.read(data
.dep_node());
579 debug
!("check_duplicate: global predicate `{:?}` already proved elsewhere", data
);
587 fn add_if_global(&mut self, tcx
: TyCtxt
<'a
, 'gcx
, 'tcx
>, key
: &ty
::Predicate
<'tcx
>) {
588 if let ty
::Predicate
::Trait(ref data
) = *key
{
589 // We only add things to the global predicate registry
590 // after the current task has proved them, and hence
591 // already has the required read edges, so we don't need
592 // to add any more edges here.
593 if data
.is_global() {
594 if let Some(data
) = tcx
.lift_to_global(data
) {
595 if self.set
.insert(data
.clone()) {
596 debug
!("add_if_global: global predicate `{:?}` added", data
);
604 fn to_fulfillment_error
<'tcx
>(
605 error
: Error
<PendingPredicateObligation
<'tcx
>, FulfillmentErrorCode
<'tcx
>>)
606 -> FulfillmentError
<'tcx
>
608 let obligation
= error
.backtrace
.into_iter().next().unwrap().obligation
;
609 FulfillmentError
::new(obligation
, error
.error
)