1 // Copyright 2012-2014 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 rustc::hir::{self, ImplItemKind, TraitItemKind};
12 use rustc::infer::{self, InferOk};
13 use rustc::middle::free_region::FreeRegionMap;
14 use rustc::middle::region::RegionMaps;
15 use rustc::ty::{self, TyCtxt};
16 use rustc::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
17 use rustc::ty::error::{ExpectedFound, TypeError};
18 use rustc::ty::subst::{Subst, Substs};
19 use rustc::util::common::ErrorReported;
23 use super::{Inherited, FnCtxt};
24 use astconv::ExplicitSelf;
26 /// Checks that a method from an impl conforms to the signature of
27 /// the same method as declared in the trait.
31 /// - impl_m: type of the method we are checking
32 /// - impl_m_span: span to use for reporting errors
33 /// - trait_m: the method in the trait
34 /// - impl_trait_ref: the TraitRef corresponding to the trait implementation
36 pub fn compare_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
37 impl_m: &ty::AssociatedItem,
39 trait_m: &ty::AssociatedItem,
40 impl_trait_ref: ty::TraitRef<'tcx>,
41 trait_item_span: Option<Span>,
42 old_broken_mode: bool) {
43 debug!("compare_impl_method(impl_trait_ref={:?})",
46 if let Err(ErrorReported) = compare_self_type(tcx,
54 if let Err(ErrorReported) = compare_number_of_generics(tcx,
62 if let Err(ErrorReported) = compare_number_of_method_arguments(tcx,
70 if let Err(ErrorReported) = compare_predicate_entailment(tcx,
80 fn compare_predicate_entailment<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
81 impl_m: &ty::AssociatedItem,
83 trait_m: &ty::AssociatedItem,
84 impl_trait_ref: ty::TraitRef<'tcx>,
85 old_broken_mode: bool)
86 -> Result<(), ErrorReported> {
87 let trait_to_impl_substs = impl_trait_ref.substs;
89 // This node-id should be used for the `body_id` field on each
90 // `ObligationCause` (and the `FnCtxt`). This is what
91 // `regionck_item` expects.
92 let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
94 let cause = ObligationCause {
96 body_id: impl_m_node_id,
97 code: ObligationCauseCode::CompareImplMethodObligation {
98 item_name: impl_m.name,
99 impl_item_def_id: impl_m.def_id,
100 trait_item_def_id: trait_m.def_id,
101 lint_id: if !old_broken_mode { Some(impl_m_node_id) } else { None },
105 // This code is best explained by example. Consider a trait:
107 // trait Trait<'t,T> {
108 // fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
113 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
114 // fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
117 // We wish to decide if those two method types are compatible.
119 // We start out with trait_to_impl_substs, that maps the trait
120 // type parameters to impl type parameters. This is taken from the
121 // impl trait reference:
123 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
125 // We create a mapping `dummy_substs` that maps from the impl type
126 // parameters to fresh types and regions. For type parameters,
127 // this is the identity transform, but we could as well use any
128 // skolemized types. For regions, we convert from bound to free
129 // regions (Note: but only early-bound regions, i.e., those
130 // declared on the impl or used in type parameter bounds).
132 // impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
134 // Now we can apply skol_substs to the type of the impl method
135 // to yield a new function type in terms of our fresh, skolemized
138 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
140 // We now want to extract and substitute the type of the *trait*
141 // method and compare it. To do so, we must create a compound
142 // substitution by combining trait_to_impl_substs and
143 // impl_to_skol_substs, and also adding a mapping for the method
144 // type parameters. We extend the mapping to also include
145 // the method parameters.
147 // trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
149 // Applying this to the trait method type yields:
151 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
153 // This type is also the same but the name of the bound region ('a
154 // vs 'b). However, the normal subtyping rules on fn types handle
155 // this kind of equivalency just fine.
157 // We now use these substitutions to ensure that all declared bounds are
158 // satisfied by the implementation's method.
160 // We do this by creating a parameter environment which contains a
161 // substitution corresponding to impl_to_skol_substs. We then build
162 // trait_to_skol_substs and use it to convert the predicates contained
163 // in the trait_m.generics to the skolemized form.
165 // Finally we register each of these predicates as an obligation in
166 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
168 // Create a parameter environment that represents the implementation's
170 let impl_param_env = tcx.parameter_environment(impl_m.def_id);
172 // Create mapping from impl to skolemized.
173 let impl_to_skol_substs = Substs::identity_for_item(tcx, impl_m.def_id);
175 // Create mapping from trait to skolemized.
176 let trait_to_skol_substs = impl_to_skol_substs.rebase_onto(tcx,
177 impl_m.container.id(),
178 trait_to_impl_substs);
179 debug!("compare_impl_method: trait_to_skol_substs={:?}",
180 trait_to_skol_substs);
182 let impl_m_generics = tcx.generics_of(impl_m.def_id);
183 let trait_m_generics = tcx.generics_of(trait_m.def_id);
184 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
185 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
187 // Check region bounds.
188 check_region_bounds_on_impl_method(tcx,
193 trait_to_skol_substs)?;
195 // Create obligations for each predicate declared by the impl
196 // definition in the context of the trait's parameter
197 // environment. We can't just use `impl_env.caller_bounds`,
198 // however, because we want to replace all late-bound regions with
200 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
201 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
203 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
205 // This is the only tricky bit of the new way we check implementation methods
206 // We need to build a set of predicates where only the method-level bounds
207 // are from the trait and we assume all other bounds from the implementation
208 // to be previously satisfied.
210 // We then register the obligations from the impl_m and check to see
211 // if all constraints hold.
212 hybrid_preds.predicates
213 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
215 // Construct trait parameter environment and then shift it into the skolemized viewpoint.
216 // The key step here is to update the caller_bounds's predicates to be
217 // the new hybrid bounds we computed.
218 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_node_id);
219 let trait_param_env = impl_param_env.with_caller_bounds(
220 tcx.intern_predicates(&hybrid_preds.predicates));
221 let trait_param_env = traits::normalize_param_env_or_error(tcx,
224 normalize_cause.clone());
226 tcx.infer_ctxt(trait_param_env, Reveal::UserFacing).enter(|infcx| {
227 let inh = Inherited::new(infcx, impl_m.def_id);
228 let infcx = &inh.infcx;
230 debug!("compare_impl_method: caller_bounds={:?}",
231 infcx.parameter_environment.caller_bounds);
233 let mut selcx = traits::SelectionContext::new(&infcx);
235 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
236 let (impl_m_own_bounds, _) = infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
237 infer::HigherRankedType,
238 &ty::Binder(impl_m_own_bounds.predicates));
239 for predicate in impl_m_own_bounds {
240 let traits::Normalized { value: predicate, obligations } =
241 traits::normalize(&mut selcx, normalize_cause.clone(), &predicate);
243 inh.register_predicates(obligations);
244 inh.register_predicate(traits::Obligation::new(cause.clone(), predicate));
247 // We now need to check that the signature of the impl method is
248 // compatible with that of the trait method. We do this by
249 // checking that `impl_fty <: trait_fty`.
251 // FIXME. Unfortunately, this doesn't quite work right now because
252 // associated type normalization is not integrated into subtype
253 // checks. For the comparison to be valid, we need to
254 // normalize the associated types in the impl/trait methods
255 // first. However, because function types bind regions, just
256 // calling `normalize_associated_types_in` would have no effect on
257 // any associated types appearing in the fn arguments or return
260 // Compute skolemized form of impl and trait method tys.
263 let m_sig = |method: &ty::AssociatedItem| {
264 match tcx.type_of(method.def_id).sty {
265 ty::TyFnDef(_, _, f) => f,
271 infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
272 infer::HigherRankedType,
275 inh.normalize_associated_types_in(impl_m_span,
278 let impl_fty = tcx.mk_fn_ptr(ty::Binder(impl_sig));
279 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
281 let trait_sig = inh.liberate_late_bound_regions(
285 trait_sig.subst(tcx, trait_to_skol_substs);
287 inh.normalize_associated_types_in(impl_m_span,
290 let trait_fty = tcx.mk_fn_ptr(ty::Binder(trait_sig));
292 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
294 let sub_result = infcx.sub_types(false, &cause, impl_fty, trait_fty)
295 .map(|InferOk { obligations, .. }| {
296 inh.register_predicates(obligations);
299 if let Err(terr) = sub_result {
300 debug!("sub_types failed: impl ty {:?}, trait ty {:?}",
304 let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(&infcx,
312 let cause = ObligationCause {
317 let mut diag = struct_span_err!(tcx.sess,
320 "method `{}` has an incompatible type for trait",
323 infcx.note_type_err(&mut diag,
325 trait_err_span.map(|sp| (sp, format!("type in trait"))),
326 Some(infer::ValuePairs::Types(ExpectedFound {
332 return Err(ErrorReported);
335 // Check that all obligations are satisfied by the implementation's
337 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
338 infcx.report_fulfillment_errors(errors);
339 return Err(ErrorReported);
342 // Finally, resolve all regions. This catches wily misuses of
343 // lifetime parameters.
345 // FIXME(#18937) -- this is how the code used to
346 // work. This is buggy because the fulfillment cx creates
347 // region obligations that get overlooked. The right
348 // thing to do is the code below. But we keep this old
349 // pass around temporarily.
350 let region_maps = RegionMaps::new();
351 let mut free_regions = FreeRegionMap::new();
352 free_regions.relate_free_regions_from_predicates(
353 &infcx.parameter_environment.caller_bounds);
354 infcx.resolve_regions_and_report_errors(impl_m.def_id, ®ion_maps, &free_regions);
356 let fcx = FnCtxt::new(&inh, impl_m_node_id);
357 fcx.regionck_item(impl_m_node_id, impl_m_span, &[]);
364 fn check_region_bounds_on_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
366 impl_m: &ty::AssociatedItem,
367 trait_generics: &ty::Generics,
368 impl_generics: &ty::Generics,
369 trait_to_skol_substs: &Substs<'tcx>)
370 -> Result<(), ErrorReported> {
371 let trait_params = &trait_generics.regions[..];
372 let impl_params = &impl_generics.regions[..];
374 debug!("check_region_bounds_on_impl_method: \
375 trait_generics={:?} \
377 trait_to_skol_substs={:?}",
380 trait_to_skol_substs);
382 // Must have same number of early-bound lifetime parameters.
383 // Unfortunately, if the user screws up the bounds, then this
384 // will change classification between early and late. E.g.,
385 // if in trait we have `<'a,'b:'a>`, and in impl we just have
386 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
387 // in trait but 0 in the impl. But if we report "expected 2
388 // but found 0" it's confusing, because it looks like there
389 // are zero. Since I don't quite know how to phrase things at
390 // the moment, give a kind of vague error message.
391 if trait_params.len() != impl_params.len() {
392 struct_span_err!(tcx.sess,
395 "lifetime parameters or bounds on method `{}` do not match the \
398 .span_label(span, "lifetimes do not match trait")
400 return Err(ErrorReported);
406 fn extract_spans_for_error_reporting<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
408 cause: &ObligationCause<'tcx>,
409 impl_m: &ty::AssociatedItem,
410 impl_sig: ty::FnSig<'tcx>,
411 trait_m: &ty::AssociatedItem,
412 trait_sig: ty::FnSig<'tcx>)
413 -> (Span, Option<Span>) {
415 let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
416 let (impl_m_output, impl_m_iter) = match tcx.hir.expect_impl_item(impl_m_node_id).node {
417 ImplItemKind::Method(ref impl_m_sig, _) => {
418 (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
420 _ => bug!("{:?} is not a method", impl_m),
424 TypeError::Mutability => {
425 if let Some(trait_m_node_id) = tcx.hir.as_local_node_id(trait_m.def_id) {
426 let trait_m_iter = match tcx.hir.expect_trait_item(trait_m_node_id).node {
427 TraitItemKind::Method(ref trait_m_sig, _) => {
428 trait_m_sig.decl.inputs.iter()
430 _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
433 impl_m_iter.zip(trait_m_iter).find(|&(ref impl_arg, ref trait_arg)| {
434 match (&impl_arg.node, &trait_arg.node) {
435 (&hir::TyRptr(_, ref impl_mt), &hir::TyRptr(_, ref trait_mt)) |
436 (&hir::TyPtr(ref impl_mt), &hir::TyPtr(ref trait_mt)) => {
437 impl_mt.mutbl != trait_mt.mutbl
441 }).map(|(ref impl_arg, ref trait_arg)| {
442 (impl_arg.span, Some(trait_arg.span))
444 .unwrap_or_else(|| (cause.span, tcx.hir.span_if_local(trait_m.def_id)))
446 (cause.span, tcx.hir.span_if_local(trait_m.def_id))
449 TypeError::Sorts(ExpectedFound { .. }) => {
450 if let Some(trait_m_node_id) = tcx.hir.as_local_node_id(trait_m.def_id) {
451 let (trait_m_output, trait_m_iter) =
452 match tcx.hir.expect_trait_item(trait_m_node_id).node {
453 TraitItemKind::Method(ref trait_m_sig, _) => {
454 (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
456 _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
459 let impl_iter = impl_sig.inputs().iter();
460 let trait_iter = trait_sig.inputs().iter();
461 impl_iter.zip(trait_iter)
464 .filter_map(|(((impl_arg_ty, trait_arg_ty), impl_arg), trait_arg)| {
465 match infcx.sub_types(true, &cause, trait_arg_ty, impl_arg_ty) {
467 Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
472 if infcx.sub_types(false, &cause, impl_sig.output(),
475 (impl_m_output.span(), Some(trait_m_output.span()))
477 (cause.span, tcx.hir.span_if_local(trait_m.def_id))
481 (cause.span, tcx.hir.span_if_local(trait_m.def_id))
484 _ => (cause.span, tcx.hir.span_if_local(trait_m.def_id)),
488 fn compare_self_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
489 impl_m: &ty::AssociatedItem,
491 trait_m: &ty::AssociatedItem,
492 impl_trait_ref: ty::TraitRef<'tcx>)
493 -> Result<(), ErrorReported>
495 // Try to give more informative error messages about self typing
496 // mismatches. Note that any mismatch will also be detected
497 // below, where we construct a canonical function type that
498 // includes the self parameter as a normal parameter. It's just
499 // that the error messages you get out of this code are a bit more
500 // inscrutable, particularly for cases where one method has no
503 let self_string = |method: &ty::AssociatedItem| {
504 let untransformed_self_ty = match method.container {
505 ty::ImplContainer(_) => impl_trait_ref.self_ty(),
506 ty::TraitContainer(_) => tcx.mk_self_type()
508 let method_ty = tcx.type_of(method.def_id);
509 let self_arg_ty = *method_ty.fn_sig().input(0).skip_binder();
510 match ExplicitSelf::determine(untransformed_self_ty, self_arg_ty) {
511 ExplicitSelf::ByValue => "self".to_string(),
512 ExplicitSelf::ByReference(_, hir::MutImmutable) => "&self".to_string(),
513 ExplicitSelf::ByReference(_, hir::MutMutable) => "&mut self".to_string(),
514 _ => format!("self: {}", self_arg_ty)
518 match (trait_m.method_has_self_argument, impl_m.method_has_self_argument) {
519 (false, false) | (true, true) => {}
522 let self_descr = self_string(impl_m);
523 let mut err = struct_span_err!(tcx.sess,
526 "method `{}` has a `{}` declaration in the impl, but \
530 err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
531 if let Some(span) = tcx.hir.span_if_local(trait_m.def_id) {
532 err.span_label(span, format!("trait declared without `{}`", self_descr));
535 return Err(ErrorReported);
539 let self_descr = self_string(trait_m);
540 let mut err = struct_span_err!(tcx.sess,
543 "method `{}` has a `{}` declaration in the trait, but \
547 err.span_label(impl_m_span,
548 format!("expected `{}` in impl", self_descr));
549 if let Some(span) = tcx.hir.span_if_local(trait_m.def_id) {
550 err.span_label(span, format!("`{}` used in trait", self_descr));
553 return Err(ErrorReported);
560 fn compare_number_of_generics<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
561 impl_m: &ty::AssociatedItem,
563 trait_m: &ty::AssociatedItem,
564 trait_item_span: Option<Span>)
565 -> Result<(), ErrorReported> {
566 let impl_m_generics = tcx.generics_of(impl_m.def_id);
567 let trait_m_generics = tcx.generics_of(trait_m.def_id);
568 let num_impl_m_type_params = impl_m_generics.types.len();
569 let num_trait_m_type_params = trait_m_generics.types.len();
570 if num_impl_m_type_params != num_trait_m_type_params {
571 let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
572 let span = match tcx.hir.expect_impl_item(impl_m_node_id).node {
573 ImplItemKind::Method(ref impl_m_sig, _) => {
574 if impl_m_sig.generics.is_parameterized() {
575 impl_m_sig.generics.span
580 _ => bug!("{:?} is not a method", impl_m),
583 let mut err = struct_span_err!(tcx.sess,
586 "method `{}` has {} type parameter{} but its trait \
587 declaration has {} type parameter{}",
589 num_impl_m_type_params,
590 if num_impl_m_type_params == 1 { "" } else { "s" },
591 num_trait_m_type_params,
592 if num_trait_m_type_params == 1 {
598 let mut suffix = None;
600 if let Some(span) = trait_item_span {
602 format!("expected {}",
603 &if num_trait_m_type_params != 1 {
604 format!("{} type parameters", num_trait_m_type_params)
606 format!("{} type parameter", num_trait_m_type_params)
609 suffix = Some(format!(", expected {}", num_trait_m_type_params));
613 format!("found {}{}",
614 &if num_impl_m_type_params != 1 {
615 format!("{} type parameters", num_impl_m_type_params)
617 format!("1 type parameter")
619 suffix.as_ref().map(|s| &s[..]).unwrap_or("")));
623 return Err(ErrorReported);
629 fn compare_number_of_method_arguments<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
630 impl_m: &ty::AssociatedItem,
632 trait_m: &ty::AssociatedItem,
633 trait_item_span: Option<Span>)
634 -> Result<(), ErrorReported> {
635 let m_fty = |method: &ty::AssociatedItem| {
636 match tcx.type_of(method.def_id).sty {
637 ty::TyFnDef(_, _, f) => f,
641 let impl_m_fty = m_fty(impl_m);
642 let trait_m_fty = m_fty(trait_m);
643 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
644 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
645 if trait_number_args != impl_number_args {
646 let trait_m_node_id = tcx.hir.as_local_node_id(trait_m.def_id);
647 let trait_span = if let Some(trait_id) = trait_m_node_id {
648 match tcx.hir.expect_trait_item(trait_id).node {
649 TraitItemKind::Method(ref trait_m_sig, _) => {
650 if let Some(arg) = trait_m_sig.decl.inputs.get(if trait_number_args > 0 {
651 trait_number_args - 1
660 _ => bug!("{:?} is not a method", impl_m),
665 let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
666 let impl_span = match tcx.hir.expect_impl_item(impl_m_node_id).node {
667 ImplItemKind::Method(ref impl_m_sig, _) => {
668 if let Some(arg) = impl_m_sig.decl.inputs.get(if impl_number_args > 0 {
678 _ => bug!("{:?} is not a method", impl_m),
680 let mut err = struct_span_err!(tcx.sess,
683 "method `{}` has {} parameter{} but the declaration in \
687 if impl_number_args == 1 { "" } else { "s" },
688 tcx.item_path_str(trait_m.def_id),
690 if let Some(trait_span) = trait_span {
691 err.span_label(trait_span,
692 format!("trait requires {}",
693 &if trait_number_args != 1 {
694 format!("{} parameters", trait_number_args)
696 format!("{} parameter", trait_number_args)
699 err.span_label(impl_span,
700 format!("expected {}, found {}",
701 &if trait_number_args != 1 {
702 format!("{} parameters", trait_number_args)
704 format!("{} parameter", trait_number_args)
708 return Err(ErrorReported);
714 pub fn compare_const_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
715 impl_c: &ty::AssociatedItem,
717 trait_c: &ty::AssociatedItem,
718 impl_trait_ref: ty::TraitRef<'tcx>) {
719 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
721 tcx.infer_ctxt((), Reveal::UserFacing).enter(|infcx| {
722 let inh = Inherited::new(infcx, impl_c.def_id);
723 let infcx = &inh.infcx;
725 // The below is for the most part highly similar to the procedure
726 // for methods above. It is simpler in many respects, especially
727 // because we shouldn't really have to deal with lifetimes or
728 // predicates. In fact some of this should probably be put into
729 // shared functions because of DRY violations...
730 let trait_to_impl_substs = impl_trait_ref.substs;
732 // Create a parameter environment that represents the implementation's
734 let impl_c_node_id = tcx.hir.as_local_node_id(impl_c.def_id).unwrap();
736 // Compute skolemized form of impl and trait const tys.
737 let impl_ty = tcx.type_of(impl_c.def_id);
738 let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
739 let mut cause = ObligationCause::misc(impl_c_span, impl_c_node_id);
741 // There is no "body" here, so just pass dummy id.
742 let impl_ty = inh.normalize_associated_types_in(impl_c_span,
746 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
748 let trait_ty = inh.normalize_associated_types_in(impl_c_span,
752 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
754 let err = infcx.sub_types(false, &cause, impl_ty, trait_ty)
755 .map(|ok| inh.register_infer_ok_obligations(ok));
757 if let Err(terr) = err {
758 debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
762 // Locate the Span containing just the type of the offending impl
763 match tcx.hir.expect_impl_item(impl_c_node_id).node {
764 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
765 _ => bug!("{:?} is not a impl const", impl_c),
768 let mut diag = struct_span_err!(tcx.sess,
771 "implemented const `{}` has an incompatible type for \
775 let trait_c_node_id = tcx.hir.as_local_node_id(trait_c.def_id);
776 let trait_c_span = trait_c_node_id.map(|trait_c_node_id| {
777 // Add a label to the Span containing just the type of the const
778 match tcx.hir.expect_trait_item(trait_c_node_id).node {
779 TraitItemKind::Const(ref ty, _) => ty.span,
780 _ => bug!("{:?} is not a trait const", trait_c),
784 infcx.note_type_err(&mut diag,
786 trait_c_span.map(|span| (span, format!("type in trait"))),
787 Some(infer::ValuePairs::Types(ExpectedFound {
795 // FIXME(#41323) Check the obligations in the fulfillment context.