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 = ty::ParameterEnvironment::for_item(tcx, impl_m_node_id);
172 // Create mapping from impl to skolemized.
173 let impl_to_skol_substs = &impl_param_env.free_substs;
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.subst(tcx,
179 impl_to_skol_substs));
180 debug!("compare_impl_method: trait_to_skol_substs={:?}",
181 trait_to_skol_substs);
183 let impl_m_generics = tcx.generics_of(impl_m.def_id);
184 let trait_m_generics = tcx.generics_of(trait_m.def_id);
185 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
186 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
188 // Check region bounds.
189 check_region_bounds_on_impl_method(tcx,
194 trait_to_skol_substs,
195 impl_to_skol_substs)?;
197 // Create obligations for each predicate declared by the impl
198 // definition in the context of the trait's parameter
199 // environment. We can't just use `impl_env.caller_bounds`,
200 // however, because we want to replace all late-bound regions with
202 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
203 let mut hybrid_preds = impl_predicates.instantiate(tcx, impl_to_skol_substs);
205 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
207 // This is the only tricky bit of the new way we check implementation methods
208 // We need to build a set of predicates where only the method-level bounds
209 // are from the trait and we assume all other bounds from the implementation
210 // to be previously satisfied.
212 // We then register the obligations from the impl_m and check to see
213 // if all constraints hold.
214 hybrid_preds.predicates
215 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
217 // Construct trait parameter environment and then shift it into the skolemized viewpoint.
218 // The key step here is to update the caller_bounds's predicates to be
219 // the new hybrid bounds we computed.
220 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_node_id);
221 let trait_param_env = impl_param_env.with_caller_bounds(
222 tcx.intern_predicates(&hybrid_preds.predicates));
223 let trait_param_env = traits::normalize_param_env_or_error(tcx,
226 normalize_cause.clone());
228 tcx.infer_ctxt(trait_param_env, Reveal::UserFacing).enter(|infcx| {
229 let inh = Inherited::new(infcx);
230 let infcx = &inh.infcx;
232 debug!("compare_impl_method: caller_bounds={:?}",
233 infcx.parameter_environment.caller_bounds);
235 let mut selcx = traits::SelectionContext::new(&infcx);
237 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
238 let (impl_m_own_bounds, _) = infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
239 infer::HigherRankedType,
240 &ty::Binder(impl_m_own_bounds.predicates));
241 for predicate in impl_m_own_bounds {
242 let traits::Normalized { value: predicate, obligations } =
243 traits::normalize(&mut selcx, normalize_cause.clone(), &predicate);
245 inh.register_predicates(obligations);
246 inh.register_predicate(traits::Obligation::new(cause.clone(), predicate));
249 // We now need to check that the signature of the impl method is
250 // compatible with that of the trait method. We do this by
251 // checking that `impl_fty <: trait_fty`.
253 // FIXME. Unfortunately, this doesn't quite work right now because
254 // associated type normalization is not integrated into subtype
255 // checks. For the comparison to be valid, we need to
256 // normalize the associated types in the impl/trait methods
257 // first. However, because function types bind regions, just
258 // calling `normalize_associated_types_in` would have no effect on
259 // any associated types appearing in the fn arguments or return
262 // Compute skolemized form of impl and trait method tys.
265 let m_sig = |method: &ty::AssociatedItem| {
266 match tcx.type_of(method.def_id).sty {
267 ty::TyFnDef(_, _, f) => f,
273 infcx.replace_late_bound_regions_with_fresh_var(impl_m_span,
274 infer::HigherRankedType,
277 impl_sig.subst(tcx, impl_to_skol_substs);
279 inh.normalize_associated_types_in(impl_m_span,
282 let impl_fty = tcx.mk_fn_ptr(ty::Binder(impl_sig));
283 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
285 let trait_sig = tcx.liberate_late_bound_regions(
286 infcx.parameter_environment.free_id_outlive,
289 trait_sig.subst(tcx, trait_to_skol_substs);
291 inh.normalize_associated_types_in(impl_m_span,
294 let trait_fty = tcx.mk_fn_ptr(ty::Binder(trait_sig));
296 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
298 let sub_result = infcx.sub_types(false, &cause, impl_fty, trait_fty)
299 .map(|InferOk { obligations, .. }| {
300 inh.register_predicates(obligations);
303 if let Err(terr) = sub_result {
304 debug!("sub_types failed: impl ty {:?}, trait ty {:?}",
308 let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(&infcx,
316 let cause = ObligationCause {
321 let mut diag = struct_span_err!(tcx.sess,
324 "method `{}` has an incompatible type for trait",
327 infcx.note_type_err(&mut diag,
329 trait_err_span.map(|sp| (sp, format!("type in trait"))),
330 Some(infer::ValuePairs::Types(ExpectedFound {
336 return Err(ErrorReported);
339 // Check that all obligations are satisfied by the implementation's
341 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
342 infcx.report_fulfillment_errors(errors);
343 return Err(ErrorReported);
346 // Finally, resolve all regions. This catches wily misuses of
347 // lifetime parameters.
349 // FIXME(#18937) -- this is how the code used to
350 // work. This is buggy because the fulfillment cx creates
351 // region obligations that get overlooked. The right
352 // thing to do is the code below. But we keep this old
353 // pass around temporarily.
354 let region_maps = RegionMaps::new();
355 let mut free_regions = FreeRegionMap::new();
356 free_regions.relate_free_regions_from_predicates(
357 &infcx.parameter_environment.caller_bounds);
358 infcx.resolve_regions_and_report_errors(impl_m.def_id, ®ion_maps, &free_regions);
360 let fcx = FnCtxt::new(&inh, impl_m_node_id);
361 fcx.regionck_item(impl_m_node_id, impl_m_span, &[]);
368 fn check_region_bounds_on_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
370 impl_m: &ty::AssociatedItem,
371 trait_generics: &ty::Generics,
372 impl_generics: &ty::Generics,
373 trait_to_skol_substs: &Substs<'tcx>,
374 impl_to_skol_substs: &Substs<'tcx>)
375 -> Result<(), ErrorReported> {
376 let trait_params = &trait_generics.regions[..];
377 let impl_params = &impl_generics.regions[..];
379 debug!("check_region_bounds_on_impl_method: \
380 trait_generics={:?} \
382 trait_to_skol_substs={:?} \
383 impl_to_skol_substs={:?}",
386 trait_to_skol_substs,
387 impl_to_skol_substs);
389 // Must have same number of early-bound lifetime parameters.
390 // Unfortunately, if the user screws up the bounds, then this
391 // will change classification between early and late. E.g.,
392 // if in trait we have `<'a,'b:'a>`, and in impl we just have
393 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
394 // in trait but 0 in the impl. But if we report "expected 2
395 // but found 0" it's confusing, because it looks like there
396 // are zero. Since I don't quite know how to phrase things at
397 // the moment, give a kind of vague error message.
398 if trait_params.len() != impl_params.len() {
399 struct_span_err!(tcx.sess,
402 "lifetime parameters or bounds on method `{}` do not match the \
405 .span_label(span, "lifetimes do not match trait")
407 return Err(ErrorReported);
413 fn extract_spans_for_error_reporting<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
415 cause: &ObligationCause<'tcx>,
416 impl_m: &ty::AssociatedItem,
417 impl_sig: ty::FnSig<'tcx>,
418 trait_m: &ty::AssociatedItem,
419 trait_sig: ty::FnSig<'tcx>)
420 -> (Span, Option<Span>) {
422 let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
423 let (impl_m_output, impl_m_iter) = match tcx.hir.expect_impl_item(impl_m_node_id).node {
424 ImplItemKind::Method(ref impl_m_sig, _) => {
425 (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
427 _ => bug!("{:?} is not a method", impl_m),
431 TypeError::Mutability => {
432 if let Some(trait_m_node_id) = tcx.hir.as_local_node_id(trait_m.def_id) {
433 let trait_m_iter = match tcx.hir.expect_trait_item(trait_m_node_id).node {
434 TraitItemKind::Method(ref trait_m_sig, _) => {
435 trait_m_sig.decl.inputs.iter()
437 _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
440 impl_m_iter.zip(trait_m_iter).find(|&(ref impl_arg, ref trait_arg)| {
441 match (&impl_arg.node, &trait_arg.node) {
442 (&hir::TyRptr(_, ref impl_mt), &hir::TyRptr(_, ref trait_mt)) |
443 (&hir::TyPtr(ref impl_mt), &hir::TyPtr(ref trait_mt)) => {
444 impl_mt.mutbl != trait_mt.mutbl
448 }).map(|(ref impl_arg, ref trait_arg)| {
449 (impl_arg.span, Some(trait_arg.span))
451 .unwrap_or_else(|| (cause.span, tcx.hir.span_if_local(trait_m.def_id)))
453 (cause.span, tcx.hir.span_if_local(trait_m.def_id))
456 TypeError::Sorts(ExpectedFound { .. }) => {
457 if let Some(trait_m_node_id) = tcx.hir.as_local_node_id(trait_m.def_id) {
458 let (trait_m_output, trait_m_iter) =
459 match tcx.hir.expect_trait_item(trait_m_node_id).node {
460 TraitItemKind::Method(ref trait_m_sig, _) => {
461 (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
463 _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
466 let impl_iter = impl_sig.inputs().iter();
467 let trait_iter = trait_sig.inputs().iter();
468 impl_iter.zip(trait_iter)
471 .filter_map(|(((impl_arg_ty, trait_arg_ty), impl_arg), trait_arg)| {
472 match infcx.sub_types(true, &cause, trait_arg_ty, impl_arg_ty) {
474 Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
479 if infcx.sub_types(false, &cause, impl_sig.output(),
482 (impl_m_output.span(), Some(trait_m_output.span()))
484 (cause.span, tcx.hir.span_if_local(trait_m.def_id))
488 (cause.span, tcx.hir.span_if_local(trait_m.def_id))
491 _ => (cause.span, tcx.hir.span_if_local(trait_m.def_id)),
495 fn compare_self_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
496 impl_m: &ty::AssociatedItem,
498 trait_m: &ty::AssociatedItem,
499 impl_trait_ref: ty::TraitRef<'tcx>)
500 -> Result<(), ErrorReported>
502 // Try to give more informative error messages about self typing
503 // mismatches. Note that any mismatch will also be detected
504 // below, where we construct a canonical function type that
505 // includes the self parameter as a normal parameter. It's just
506 // that the error messages you get out of this code are a bit more
507 // inscrutable, particularly for cases where one method has no
510 let self_string = |method: &ty::AssociatedItem| {
511 let untransformed_self_ty = match method.container {
512 ty::ImplContainer(_) => impl_trait_ref.self_ty(),
513 ty::TraitContainer(_) => tcx.mk_self_type()
515 let method_ty = tcx.type_of(method.def_id);
516 let self_arg_ty = *method_ty.fn_sig().input(0).skip_binder();
517 match ExplicitSelf::determine(untransformed_self_ty, self_arg_ty) {
518 ExplicitSelf::ByValue => "self".to_string(),
519 ExplicitSelf::ByReference(_, hir::MutImmutable) => "&self".to_string(),
520 ExplicitSelf::ByReference(_, hir::MutMutable) => "&mut self".to_string(),
521 _ => format!("self: {}", self_arg_ty)
525 match (trait_m.method_has_self_argument, impl_m.method_has_self_argument) {
526 (false, false) | (true, true) => {}
529 let self_descr = self_string(impl_m);
530 let mut err = struct_span_err!(tcx.sess,
533 "method `{}` has a `{}` declaration in the impl, but \
537 err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
538 if let Some(span) = tcx.hir.span_if_local(trait_m.def_id) {
539 err.span_label(span, format!("trait declared without `{}`", self_descr));
542 return Err(ErrorReported);
546 let self_descr = self_string(trait_m);
547 let mut err = struct_span_err!(tcx.sess,
550 "method `{}` has a `{}` declaration in the trait, but \
554 err.span_label(impl_m_span,
555 format!("expected `{}` in impl", self_descr));
556 if let Some(span) = tcx.hir.span_if_local(trait_m.def_id) {
557 err.span_label(span, format!("`{}` used in trait", self_descr));
560 return Err(ErrorReported);
567 fn compare_number_of_generics<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
568 impl_m: &ty::AssociatedItem,
570 trait_m: &ty::AssociatedItem,
571 trait_item_span: Option<Span>)
572 -> Result<(), ErrorReported> {
573 let impl_m_generics = tcx.generics_of(impl_m.def_id);
574 let trait_m_generics = tcx.generics_of(trait_m.def_id);
575 let num_impl_m_type_params = impl_m_generics.types.len();
576 let num_trait_m_type_params = trait_m_generics.types.len();
577 if num_impl_m_type_params != num_trait_m_type_params {
578 let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
579 let span = match tcx.hir.expect_impl_item(impl_m_node_id).node {
580 ImplItemKind::Method(ref impl_m_sig, _) => {
581 if impl_m_sig.generics.is_parameterized() {
582 impl_m_sig.generics.span
587 _ => bug!("{:?} is not a method", impl_m),
590 let mut err = struct_span_err!(tcx.sess,
593 "method `{}` has {} type parameter{} but its trait \
594 declaration has {} type parameter{}",
596 num_impl_m_type_params,
597 if num_impl_m_type_params == 1 { "" } else { "s" },
598 num_trait_m_type_params,
599 if num_trait_m_type_params == 1 {
605 let mut suffix = None;
607 if let Some(span) = trait_item_span {
609 format!("expected {}",
610 &if num_trait_m_type_params != 1 {
611 format!("{} type parameters", num_trait_m_type_params)
613 format!("{} type parameter", num_trait_m_type_params)
616 suffix = Some(format!(", expected {}", num_trait_m_type_params));
620 format!("found {}{}",
621 &if num_impl_m_type_params != 1 {
622 format!("{} type parameters", num_impl_m_type_params)
624 format!("1 type parameter")
626 suffix.as_ref().map(|s| &s[..]).unwrap_or("")));
630 return Err(ErrorReported);
636 fn compare_number_of_method_arguments<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
637 impl_m: &ty::AssociatedItem,
639 trait_m: &ty::AssociatedItem,
640 trait_item_span: Option<Span>)
641 -> Result<(), ErrorReported> {
642 let m_fty = |method: &ty::AssociatedItem| {
643 match tcx.type_of(method.def_id).sty {
644 ty::TyFnDef(_, _, f) => f,
648 let impl_m_fty = m_fty(impl_m);
649 let trait_m_fty = m_fty(trait_m);
650 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
651 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
652 if trait_number_args != impl_number_args {
653 let trait_m_node_id = tcx.hir.as_local_node_id(trait_m.def_id);
654 let trait_span = if let Some(trait_id) = trait_m_node_id {
655 match tcx.hir.expect_trait_item(trait_id).node {
656 TraitItemKind::Method(ref trait_m_sig, _) => {
657 if let Some(arg) = trait_m_sig.decl.inputs.get(if trait_number_args > 0 {
658 trait_number_args - 1
667 _ => bug!("{:?} is not a method", impl_m),
672 let impl_m_node_id = tcx.hir.as_local_node_id(impl_m.def_id).unwrap();
673 let impl_span = match tcx.hir.expect_impl_item(impl_m_node_id).node {
674 ImplItemKind::Method(ref impl_m_sig, _) => {
675 if let Some(arg) = impl_m_sig.decl.inputs.get(if impl_number_args > 0 {
685 _ => bug!("{:?} is not a method", impl_m),
687 let mut err = struct_span_err!(tcx.sess,
690 "method `{}` has {} parameter{} but the declaration in \
694 if impl_number_args == 1 { "" } else { "s" },
695 tcx.item_path_str(trait_m.def_id),
697 if let Some(trait_span) = trait_span {
698 err.span_label(trait_span,
699 format!("trait requires {}",
700 &if trait_number_args != 1 {
701 format!("{} parameters", trait_number_args)
703 format!("{} parameter", trait_number_args)
706 err.span_label(impl_span,
707 format!("expected {}, found {}",
708 &if trait_number_args != 1 {
709 format!("{} parameters", trait_number_args)
711 format!("{} parameter", trait_number_args)
715 return Err(ErrorReported);
721 pub fn compare_const_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
722 impl_c: &ty::AssociatedItem,
724 trait_c: &ty::AssociatedItem,
725 impl_trait_ref: ty::TraitRef<'tcx>) {
726 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
728 tcx.infer_ctxt((), Reveal::UserFacing).enter(|infcx| {
729 let inh = Inherited::new(infcx);
730 let infcx = &inh.infcx;
732 // The below is for the most part highly similar to the procedure
733 // for methods above. It is simpler in many respects, especially
734 // because we shouldn't really have to deal with lifetimes or
735 // predicates. In fact some of this should probably be put into
736 // shared functions because of DRY violations...
737 let trait_to_impl_substs = impl_trait_ref.substs;
739 // Create a parameter environment that represents the implementation's
741 let impl_c_node_id = tcx.hir.as_local_node_id(impl_c.def_id).unwrap();
742 let impl_param_env = ty::ParameterEnvironment::for_item(tcx, impl_c_node_id);
744 // Create mapping from impl to skolemized.
745 let impl_to_skol_substs = &impl_param_env.free_substs;
747 // Create mapping from trait to skolemized.
748 let trait_to_skol_substs = impl_to_skol_substs.rebase_onto(tcx,
749 impl_c.container.id(),
750 trait_to_impl_substs.subst(tcx,
751 impl_to_skol_substs));
752 debug!("compare_const_impl: trait_to_skol_substs={:?}",
753 trait_to_skol_substs);
755 // Compute skolemized form of impl and trait const tys.
756 let impl_ty = tcx.type_of(impl_c.def_id).subst(tcx, impl_to_skol_substs);
757 let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_skol_substs);
758 let mut cause = ObligationCause::misc(impl_c_span, impl_c_node_id);
760 // There is no "body" here, so just pass dummy id.
761 let impl_ty = inh.normalize_associated_types_in(impl_c_span,
765 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
767 let trait_ty = inh.normalize_associated_types_in(impl_c_span,
771 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
773 let err = infcx.sub_types(false, &cause, impl_ty, trait_ty)
774 .map(|ok| inh.register_infer_ok_obligations(ok));
776 if let Err(terr) = err {
777 debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
781 // Locate the Span containing just the type of the offending impl
782 match tcx.hir.expect_impl_item(impl_c_node_id).node {
783 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
784 _ => bug!("{:?} is not a impl const", impl_c),
787 let mut diag = struct_span_err!(tcx.sess,
790 "implemented const `{}` has an incompatible type for \
794 let trait_c_node_id = tcx.hir.as_local_node_id(trait_c.def_id);
795 let trait_c_span = trait_c_node_id.map(|trait_c_node_id| {
796 // Add a label to the Span containing just the type of the const
797 match tcx.hir.expect_trait_item(trait_c_node_id).node {
798 TraitItemKind::Const(ref ty, _) => ty.span,
799 _ => bug!("{:?} is not a trait const", trait_c),
803 infcx.note_type_err(&mut diag,
805 trait_c_span.map(|span| (span, format!("type in trait"))),
806 Some(infer::ValuePairs::Types(ExpectedFound {
814 // FIXME(#41323) Check the obligations in the fulfillment context.