1 use crate::infer::InferCtxt;
2 use crate::opaque_types::required_region_bounds;
3 use crate::traits::{self, AssocTypeBoundData};
5 use rustc_hir::def_id::DefId;
6 use rustc_hir::lang_items;
7 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
8 use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
9 use rustc_span::symbol::{kw, Ident};
12 /// Returns the set of obligations needed to make `ty` well-formed.
13 /// If `ty` contains unresolved inference variables, this may include
14 /// further WF obligations. However, if `ty` IS an unresolved
15 /// inference variable, returns `None`, because we are not able to
16 /// make any progress at all. This is to prevent "livelock" where we
17 /// say "$0 is WF if $0 is WF".
18 pub fn obligations<'a, 'tcx>(
19 infcx: &InferCtxt<'a, 'tcx>,
20 param_env: ty::ParamEnv<'tcx>,
24 ) -> Option<Vec<traits::PredicateObligation<'tcx>>> {
25 let mut wf = WfPredicates { infcx, param_env, body_id, span, out: vec![], item: None };
27 debug!("wf::obligations({:?}, body_id={:?}) = {:?}", ty, body_id, wf.out);
29 let result = wf.normalize();
30 debug!("wf::obligations({:?}, body_id={:?}) ~~> {:?}", ty, body_id, result);
33 None // no progress made, return None
37 /// Returns the obligations that make this trait reference
38 /// well-formed. For example, if there is a trait `Set` defined like
39 /// `trait Set<K:Eq>`, then the trait reference `Foo: Set<Bar>` is WF
41 pub fn trait_obligations<'a, 'tcx>(
42 infcx: &InferCtxt<'a, 'tcx>,
43 param_env: ty::ParamEnv<'tcx>,
45 trait_ref: &ty::TraitRef<'tcx>,
47 item: Option<&'tcx hir::Item<'tcx>>,
48 ) -> Vec<traits::PredicateObligation<'tcx>> {
49 let mut wf = WfPredicates { infcx, param_env, body_id, span, out: vec![], item };
50 wf.compute_trait_ref(trait_ref, Elaborate::All);
54 pub fn predicate_obligations<'a, 'tcx>(
55 infcx: &InferCtxt<'a, 'tcx>,
56 param_env: ty::ParamEnv<'tcx>,
58 predicate: &ty::Predicate<'tcx>,
60 ) -> Vec<traits::PredicateObligation<'tcx>> {
61 let mut wf = WfPredicates { infcx, param_env, body_id, span, out: vec![], item: None };
63 // (*) ok to skip binders, because wf code is prepared for it
65 ty::Predicate::Trait(ref t, _) => {
66 wf.compute_trait_ref(&t.skip_binder().trait_ref, Elaborate::None); // (*)
68 ty::Predicate::RegionOutlives(..) => {}
69 ty::Predicate::TypeOutlives(ref t) => {
70 wf.compute(t.skip_binder().0);
72 ty::Predicate::Projection(ref t) => {
73 let t = t.skip_binder(); // (*)
74 wf.compute_projection(t.projection_ty);
77 ty::Predicate::WellFormed(t) => {
80 ty::Predicate::ObjectSafe(_) => {}
81 ty::Predicate::ClosureKind(..) => {}
82 ty::Predicate::Subtype(ref data) => {
83 wf.compute(data.skip_binder().a); // (*)
84 wf.compute(data.skip_binder().b); // (*)
86 ty::Predicate::ConstEvaluatable(def_id, substs) => {
87 let obligations = wf.nominal_obligations(def_id, substs);
88 wf.out.extend(obligations);
90 for ty in substs.types() {
99 struct WfPredicates<'a, 'tcx> {
100 infcx: &'a InferCtxt<'a, 'tcx>,
101 param_env: ty::ParamEnv<'tcx>,
104 out: Vec<traits::PredicateObligation<'tcx>>,
105 item: Option<&'tcx hir::Item<'tcx>>,
108 /// Controls whether we "elaborate" supertraits and so forth on the WF
109 /// predicates. This is a kind of hack to address #43784. The
110 /// underlying problem in that issue was a trait structure like:
113 /// trait Foo: Copy { }
114 /// trait Bar: Foo { }
115 /// impl<T: Bar> Foo for T { }
116 /// impl<T> Bar for T { }
119 /// Here, in the `Foo` impl, we will check that `T: Copy` holds -- but
120 /// we decide that this is true because `T: Bar` is in the
121 /// where-clauses (and we can elaborate that to include `T:
122 /// Copy`). This wouldn't be a problem, except that when we check the
123 /// `Bar` impl, we decide that `T: Foo` must hold because of the `Foo`
124 /// impl. And so nowhere did we check that `T: Copy` holds!
126 /// To resolve this, we elaborate the WF requirements that must be
127 /// proven when checking impls. This means that (e.g.) the `impl Bar
128 /// for T` will be forced to prove not only that `T: Foo` but also `T:
129 /// Copy` (which it won't be able to do, because there is no `Copy`
131 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
137 fn extend_cause_with_original_assoc_item_obligation<'tcx>(
139 trait_ref: &ty::TraitRef<'tcx>,
140 item: Option<&hir::Item<'tcx>>,
141 cause: &mut traits::ObligationCause<'tcx>,
142 pred: &ty::Predicate<'_>,
143 mut trait_assoc_items: impl Iterator<Item = ty::AssocItem>,
146 tcx.hir().as_local_hir_id(trait_ref.def_id).and_then(|trait_id| tcx.hir().find(trait_id));
147 let (trait_name, trait_generics) = match trait_item {
148 Some(hir::Node::Item(hir::Item {
150 kind: hir::ItemKind::Trait(.., generics, _, _),
153 | Some(hir::Node::Item(hir::Item {
155 kind: hir::ItemKind::TraitAlias(generics, _),
157 })) => (Some(ident), Some(generics)),
161 let item_span = item.map(|i| tcx.sess.source_map().guess_head_span(i.span));
163 ty::Predicate::Projection(proj) => {
164 // The obligation comes not from the current `impl` nor the `trait` being
165 // implemented, but rather from a "second order" obligation, like in
166 // `src/test/ui/associated-types/point-at-type-on-obligation-failure.rs`:
168 // error[E0271]: type mismatch resolving `<Foo2 as Bar2>::Ok == ()`
169 // --> $DIR/point-at-type-on-obligation-failure.rs:13:5
172 // | -- associated type defined here
174 // LL | impl Bar for Foo {
175 // | ---------------- in this `impl` item
176 // LL | type Ok = ();
177 // | ^^^^^^^^^^^^^ expected `u32`, found `()`
179 // = note: expected type `u32`
182 // FIXME: we would want to point a span to all places that contributed to this
183 // obligation. In the case above, it should be closer to:
185 // error[E0271]: type mismatch resolving `<Foo2 as Bar2>::Ok == ()`
186 // --> $DIR/point-at-type-on-obligation-failure.rs:13:5
189 // | -- associated type defined here
190 // LL | type Sibling: Bar2<Ok=Self::Ok>;
191 // | -------------------------------- obligation set here
193 // LL | impl Bar for Foo {
194 // | ---------------- in this `impl` item
195 // LL | type Ok = ();
196 // | ^^^^^^^^^^^^^ expected `u32`, found `()`
198 // LL | impl Bar2 for Foo2 {
199 // | ---------------- in this `impl` item
200 // LL | type Ok = u32;
201 // | -------------- obligation set here
203 // = note: expected type `u32`
205 if let Some(hir::ItemKind::Impl { items, .. }) = item.map(|i| &i.kind) {
206 let trait_assoc_item = tcx.associated_item(proj.projection_def_id());
207 if let Some(impl_item) =
208 items.iter().find(|item| item.ident == trait_assoc_item.ident)
210 cause.span = impl_item.span;
211 cause.code = traits::AssocTypeBound(Box::new(AssocTypeBoundData {
212 impl_span: item_span,
213 original: trait_assoc_item.ident.span,
219 ty::Predicate::Trait(proj, _) => {
220 // An associated item obligation born out of the `trait` failed to be met.
221 // Point at the `impl` that failed the obligation, the associated item that
222 // needed to meet the obligation, and the definition of that associated item,
223 // which should hold the obligation in most cases. An example can be seen in
224 // `src/test/ui/associated-types/point-at-type-on-obligation-failure-2.rs`:
226 // error[E0277]: the trait bound `bool: Bar` is not satisfied
227 // --> $DIR/point-at-type-on-obligation-failure-2.rs:8:5
229 // LL | type Assoc: Bar;
230 // | ----- associated type defined here
232 // LL | impl Foo for () {
233 // | --------------- in this `impl` item
234 // LL | type Assoc = bool;
235 // | ^^^^^^^^^^^^^^^^^^ the trait `Bar` is not implemented for `bool`
237 // If the obligation comes from the where clause in the `trait`, we point at it:
239 // error[E0277]: the trait bound `bool: Bar` is not satisfied
240 // --> $DIR/point-at-type-on-obligation-failure-2.rs:8:5
242 // | trait Foo where <Self as Foo>>::Assoc: Bar {
243 // | -------------------------- restricted in this bound
245 // | ----- associated type defined here
247 // LL | impl Foo for () {
248 // | --------------- in this `impl` item
249 // LL | type Assoc = bool;
250 // | ^^^^^^^^^^^^^^^^^^ the trait `Bar` is not implemented for `bool`
252 ty::Projection(ty::ProjectionTy { item_def_id, .. }),
253 Some(hir::ItemKind::Impl { items, .. }),
254 ) = (&proj.skip_binder().self_ty().kind, item.map(|i| &i.kind))
256 if let Some((impl_item, trait_assoc_item)) = trait_assoc_items
257 .find(|i| i.def_id == *item_def_id)
258 .and_then(|trait_assoc_item| {
261 .find(|i| i.ident == trait_assoc_item.ident)
262 .map(|impl_item| (impl_item, trait_assoc_item))
265 let bounds = trait_generics
267 get_generic_bound_spans(&generics, trait_name, trait_assoc_item.ident)
269 .unwrap_or_else(Vec::new);
270 cause.span = impl_item.span;
271 cause.code = traits::AssocTypeBound(Box::new(AssocTypeBoundData {
272 impl_span: item_span,
273 original: trait_assoc_item.ident.span,
283 impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
284 fn cause(&mut self, code: traits::ObligationCauseCode<'tcx>) -> traits::ObligationCause<'tcx> {
285 traits::ObligationCause::new(self.span, self.body_id, code)
288 fn normalize(&mut self) -> Vec<traits::PredicateObligation<'tcx>> {
289 let cause = self.cause(traits::MiscObligation);
290 let infcx = &mut self.infcx;
291 let param_env = self.param_env;
292 let mut obligations = Vec::with_capacity(self.out.len());
293 for pred in &self.out {
294 assert!(!pred.has_escaping_bound_vars());
295 let mut selcx = traits::SelectionContext::new(infcx);
296 let i = obligations.len();
298 traits::normalize_to(&mut selcx, param_env, cause.clone(), pred, &mut obligations);
299 obligations.insert(i, value);
304 /// Pushes the obligations required for `trait_ref` to be WF into `self.out`.
305 fn compute_trait_ref(&mut self, trait_ref: &ty::TraitRef<'tcx>, elaborate: Elaborate) {
306 let tcx = self.infcx.tcx;
307 let obligations = self.nominal_obligations(trait_ref.def_id, trait_ref.substs);
309 let cause = self.cause(traits::MiscObligation);
310 let param_env = self.param_env;
312 let item = self.item;
314 if let Elaborate::All = elaborate {
315 let predicates = obligations.iter().map(|obligation| obligation.predicate).collect();
316 let implied_obligations = traits::elaborate_predicates(tcx, predicates);
317 let implied_obligations = implied_obligations.map(|pred| {
318 let mut cause = cause.clone();
319 extend_cause_with_original_assoc_item_obligation(
325 tcx.associated_items(trait_ref.def_id).in_definition_order().copied(),
327 traits::Obligation::new(cause, param_env, pred)
329 self.out.extend(implied_obligations);
332 self.out.extend(obligations);
334 self.out.extend(trait_ref.substs.types().filter(|ty| !ty.has_escaping_bound_vars()).map(
335 |ty| traits::Obligation::new(cause.clone(), param_env, ty::Predicate::WellFormed(ty)),
339 /// Pushes the obligations required for `trait_ref::Item` to be WF
341 fn compute_projection(&mut self, data: ty::ProjectionTy<'tcx>) {
342 // A projection is well-formed if (a) the trait ref itself is
343 // WF and (b) the trait-ref holds. (It may also be
344 // normalizable and be WF that way.)
345 let trait_ref = data.trait_ref(self.infcx.tcx);
346 self.compute_trait_ref(&trait_ref, Elaborate::None);
348 if !data.has_escaping_bound_vars() {
349 let predicate = trait_ref.without_const().to_predicate();
350 let cause = self.cause(traits::ProjectionWf(data));
351 self.out.push(traits::Obligation::new(cause, self.param_env, predicate));
355 /// Pushes the obligations required for an array length to be WF
357 fn compute_array_len(&mut self, constant: ty::Const<'tcx>) {
358 if let ty::ConstKind::Unevaluated(def_id, substs, promoted) = constant.val {
359 assert!(promoted.is_none());
361 let obligations = self.nominal_obligations(def_id, substs);
362 self.out.extend(obligations);
364 let predicate = ty::Predicate::ConstEvaluatable(def_id, substs);
365 let cause = self.cause(traits::MiscObligation);
366 self.out.push(traits::Obligation::new(cause, self.param_env, predicate));
370 fn require_sized(&mut self, subty: Ty<'tcx>, cause: traits::ObligationCauseCode<'tcx>) {
371 if !subty.has_escaping_bound_vars() {
372 let cause = self.cause(cause);
373 let trait_ref = ty::TraitRef {
374 def_id: self.infcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
375 substs: self.infcx.tcx.mk_substs_trait(subty, &[]),
377 self.out.push(traits::Obligation::new(
380 trait_ref.without_const().to_predicate(),
385 /// Pushes new obligations into `out`. Returns `true` if it was able
386 /// to generate all the predicates needed to validate that `ty0`
387 /// is WF. Returns false if `ty0` is an unresolved type variable,
388 /// in which case we are not able to simplify at all.
389 fn compute(&mut self, ty0: Ty<'tcx>) -> bool {
390 let mut walker = ty0.walk();
391 let param_env = self.param_env;
392 while let Some(arg) = walker.next() {
393 let ty = match arg.unpack() {
394 GenericArgKind::Type(ty) => ty,
396 // No WF constraints for lifetimes being present, any outlives
397 // obligations are handled by the parent (e.g. `ty::Ref`).
398 GenericArgKind::Lifetime(_) => continue,
400 // FIXME(eddyb) this is wrong and needs to be replaced
401 // (see https://github.com/rust-lang/rust/pull/70107).
402 GenericArgKind::Const(_) => continue,
413 | ty::GeneratorWitness(..)
417 | ty::Placeholder(..)
418 | ty::Foreign(..) => {
419 // WfScalar, WfParameter, etc
422 ty::Slice(subty) => {
423 self.require_sized(subty, traits::SliceOrArrayElem);
426 ty::Array(subty, len) => {
427 self.require_sized(subty, traits::SliceOrArrayElem);
428 // FIXME(eddyb) handle `GenericArgKind::Const` above instead.
429 self.compute_array_len(*len);
432 ty::Tuple(ref tys) => {
433 if let Some((_last, rest)) = tys.split_last() {
435 self.require_sized(elem.expect_ty(), traits::TupleElem);
441 // simple cases that are WF if their type args are WF
444 ty::Projection(data) => {
445 walker.skip_current_subtree(); // subtree handled by compute_projection
446 self.compute_projection(data);
449 ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
451 ty::Adt(def, substs) => {
453 let obligations = self.nominal_obligations(def.did, substs);
454 self.out.extend(obligations);
457 ty::FnDef(did, substs) => {
458 let obligations = self.nominal_obligations(did, substs);
459 self.out.extend(obligations);
462 ty::Ref(r, rty, _) => {
464 if !r.has_escaping_bound_vars() && !rty.has_escaping_bound_vars() {
465 let cause = self.cause(traits::ReferenceOutlivesReferent(ty));
466 self.out.push(traits::Obligation::new(
469 ty::Predicate::TypeOutlives(ty::Binder::dummy(ty::OutlivesPredicate(
476 ty::Generator(..) => {
477 // Walk ALL the types in the generator: this will
478 // include the upvar types as well as the yield
479 // type. Note that this is mildly distinct from
480 // the closure case, where we have to be careful
481 // about the signature of the closure. We don't
482 // have the problem of implied bounds here since
483 // generators don't take arguments.
486 ty::Closure(_, substs) => {
487 // Only check the upvar types for WF, not the rest
488 // of the types within. This is needed because we
489 // capture the signature and it may not be WF
490 // without the implied bounds. Consider a closure
491 // like `|x: &'a T|` -- it may be that `T: 'a` is
492 // not known to hold in the creator's context (and
493 // indeed the closure may not be invoked by its
494 // creator, but rather turned to someone who *can*
497 // The special treatment of closures here really
498 // ought not to be necessary either; the problem
499 // is related to #25860 -- there is no way for us
500 // to express a fn type complete with the implied
501 // bounds that it is assuming. I think in reality
502 // the WF rules around fn are a bit messed up, and
503 // that is the rot problem: `fn(&'a T)` should
504 // probably always be WF, because it should be
505 // shorthand for something like `where(T: 'a) {
506 // fn(&'a T) }`, as discussed in #25860.
508 // Note that we are also skipping the generic
509 // types. This is consistent with the `outlives`
510 // code, but anyway doesn't matter: within the fn
511 // body where they are created, the generics will
512 // always be WF, and outside of that fn body we
513 // are not directly inspecting closure types
514 // anyway, except via auto trait matching (which
515 // only inspects the upvar types).
516 walker.skip_current_subtree(); // subtree handled by compute_projection
517 for upvar_ty in substs.as_closure().upvar_tys() {
518 self.compute(upvar_ty);
523 // let the loop iterate into the argument/return
524 // types appearing in the fn signature
527 ty::Opaque(did, substs) => {
528 // all of the requirements on type parameters
529 // should've been checked by the instantiation
530 // of whatever returned this exact `impl Trait`.
532 // for named opaque `impl Trait` types we still need to check them
533 if ty::is_impl_trait_defn(self.infcx.tcx, did).is_none() {
534 let obligations = self.nominal_obligations(did, substs);
535 self.out.extend(obligations);
539 ty::Dynamic(data, r) => {
542 // Here, we defer WF checking due to higher-ranked
543 // regions. This is perhaps not ideal.
544 self.from_object_ty(ty, data, r);
546 // FIXME(#27579) RFC also considers adding trait
547 // obligations that don't refer to Self and
550 let defer_to_coercion = self.infcx.tcx.features().object_safe_for_dispatch;
552 if !defer_to_coercion {
553 let cause = self.cause(traits::MiscObligation);
554 let component_traits = data.auto_traits().chain(data.principal_def_id());
555 self.out.extend(component_traits.map(|did| {
556 traits::Obligation::new(
559 ty::Predicate::ObjectSafe(did),
565 // Inference variables are the complicated case, since we don't
566 // know what type they are. We do two things:
568 // 1. Check if they have been resolved, and if so proceed with
570 // 2. If not, check whether this is the type that we
571 // started with (ty0). In that case, we've made no
572 // progress at all, so return false. Otherwise,
573 // we've at least simplified things (i.e., we went
574 // from `Vec<$0>: WF` to `$0: WF`, so we can
575 // register a pending obligation and keep
576 // moving. (Goal is that an "inductive hypothesis"
577 // is satisfied to ensure termination.)
579 let ty = self.infcx.shallow_resolve(ty);
580 if let ty::Infer(_) = ty.kind {
581 // not yet resolved...
583 // ...this is the type we started from! no progress.
587 let cause = self.cause(traits::MiscObligation);
589 // ...not the type we started from, so we made progress.
590 traits::Obligation::new(
593 ty::Predicate::WellFormed(ty),
597 // Yes, resolved, proceed with the
598 // result. Should never return false because
599 // `ty` is not a Infer.
600 assert!(self.compute(ty));
606 // if we made it through that loop above, we made progress!
610 fn nominal_obligations(
613 substs: SubstsRef<'tcx>,
614 ) -> Vec<traits::PredicateObligation<'tcx>> {
615 let predicates = self.infcx.tcx.predicates_of(def_id).instantiate(self.infcx.tcx, substs);
616 let cause = self.cause(traits::ItemObligation(def_id));
620 .map(|pred| traits::Obligation::new(cause.clone(), self.param_env, pred))
621 .filter(|pred| !pred.has_escaping_bound_vars())
628 data: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
629 region: ty::Region<'tcx>,
631 // Imagine a type like this:
634 // trait Bar<'c> : 'c { }
636 // &'b (Foo+'c+Bar<'d>)
639 // In this case, the following relationships must hold:
644 // The first conditions is due to the normal region pointer
645 // rules, which say that a reference cannot outlive its
648 // The final condition may be a bit surprising. In particular,
649 // you may expect that it would have been `'c <= 'd`, since
650 // usually lifetimes of outer things are conservative
651 // approximations for inner things. However, it works somewhat
652 // differently with trait objects: here the idea is that if the
653 // user specifies a region bound (`'c`, in this case) it is the
654 // "master bound" that *implies* that bounds from other traits are
655 // all met. (Remember that *all bounds* in a type like
656 // `Foo+Bar+Zed` must be met, not just one, hence if we write
657 // `Foo<'x>+Bar<'y>`, we know that the type outlives *both* 'x and
660 // Note: in fact we only permit builtin traits, not `Bar<'d>`, I
661 // am looking forward to the future here.
662 if !data.has_escaping_bound_vars() && !region.has_escaping_bound_vars() {
663 let implicit_bounds = object_region_bounds(self.infcx.tcx, data);
665 let explicit_bound = region;
667 self.out.reserve(implicit_bounds.len());
668 for implicit_bound in implicit_bounds {
669 let cause = self.cause(traits::ObjectTypeBound(ty, explicit_bound));
671 ty::Binder::dummy(ty::OutlivesPredicate(explicit_bound, implicit_bound));
672 self.out.push(traits::Obligation::new(
675 outlives.to_predicate(),
682 /// Given an object type like `SomeTrait + Send`, computes the lifetime
683 /// bounds that must hold on the elided self type. These are derived
684 /// from the declarations of `SomeTrait`, `Send`, and friends -- if
685 /// they declare `trait SomeTrait : 'static`, for example, then
686 /// `'static` would appear in the list. The hard work is done by
687 /// `infer::required_region_bounds`, see that for more information.
688 pub fn object_region_bounds<'tcx>(
690 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
691 ) -> Vec<ty::Region<'tcx>> {
692 // Since we don't actually *know* the self type for an object,
693 // this "open(err)" serves as a kind of dummy standin -- basically
694 // a placeholder type.
695 let open_ty = tcx.mk_ty_infer(ty::FreshTy(0));
697 let predicates = existential_predicates
699 .filter_map(|predicate| {
700 if let ty::ExistentialPredicate::Projection(_) = *predicate.skip_binder() {
703 Some(predicate.with_self_ty(tcx, open_ty))
708 required_region_bounds(tcx, open_ty, predicates)
711 /// Find the span of a generic bound affecting an associated type.
712 fn get_generic_bound_spans(
713 generics: &hir::Generics<'_>,
714 trait_name: Option<&Ident>,
715 assoc_item_name: Ident,
717 let mut bounds = vec![];
718 for clause in generics.where_clause.predicates.iter() {
719 if let hir::WherePredicate::BoundPredicate(pred) = clause {
720 match &pred.bounded_ty.kind {
721 hir::TyKind::Path(hir::QPath::Resolved(Some(ty), path)) => {
722 let mut s = path.segments.iter();
723 if let (a, Some(b), None) = (s.next(), s.next(), s.next()) {
724 if a.map(|s| &s.ident) == trait_name
725 && b.ident == assoc_item_name
726 && is_self_path(&ty.kind)
728 // `<Self as Foo>::Bar`
729 bounds.push(pred.span);
733 hir::TyKind::Path(hir::QPath::TypeRelative(ty, segment)) => {
734 if segment.ident == assoc_item_name {
735 if is_self_path(&ty.kind) {
737 bounds.push(pred.span);
748 fn is_self_path(kind: &hir::TyKind<'_>) -> bool {
749 if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = kind {
750 let mut s = path.segments.iter();
751 if let (Some(segment), None) = (s.next(), s.next()) {
752 if segment.ident.name == kw::SelfUpper {