1 use rustc::hir::{self, GenericParamKind, ImplItemKind, TraitItemKind};
2 use rustc::infer::{self, InferOk};
3 use rustc::ty::{self, TyCtxt, GenericParamDefKind};
4 use rustc::ty::util::ExplicitSelf;
5 use rustc::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
6 use rustc::ty::error::{ExpectedFound, TypeError};
7 use rustc::ty::subst::{Subst, Substs};
8 use rustc::util::common::ErrorReported;
9 use errors::Applicability;
13 use super::{Inherited, FnCtxt, potentially_plural_count};
15 /// Checks that a method from an impl conforms to the signature of
16 /// the same method as declared in the trait.
20 /// - impl_m: type of the method we are checking
21 /// - impl_m_span: span to use for reporting errors
22 /// - trait_m: the method in the trait
23 /// - impl_trait_ref: the TraitRef corresponding to the trait implementation
25 pub fn compare_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
26 impl_m: &ty::AssociatedItem,
28 trait_m: &ty::AssociatedItem,
29 impl_trait_ref: ty::TraitRef<'tcx>,
30 trait_item_span: Option<Span>) {
31 debug!("compare_impl_method(impl_trait_ref={:?})",
34 let impl_m_span = tcx.sess.source_map().def_span(impl_m_span);
36 if let Err(ErrorReported) = compare_self_type(tcx,
44 if let Err(ErrorReported) = compare_number_of_generics(tcx,
52 if let Err(ErrorReported) = compare_number_of_method_arguments(tcx,
60 if let Err(ErrorReported) = compare_synthetic_generics(tcx,
66 if let Err(ErrorReported) = compare_predicate_entailment(tcx,
75 fn compare_predicate_entailment<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
76 impl_m: &ty::AssociatedItem,
78 trait_m: &ty::AssociatedItem,
79 impl_trait_ref: ty::TraitRef<'tcx>)
80 -> Result<(), ErrorReported> {
81 let trait_to_impl_substs = impl_trait_ref.substs;
83 // This node-id should be used for the `body_id` field on each
84 // `ObligationCause` (and the `FnCtxt`). This is what
85 // `regionck_item` expects.
86 let impl_m_node_id = tcx.hir().as_local_node_id(impl_m.def_id).unwrap();
88 let cause = ObligationCause {
90 body_id: impl_m_node_id,
91 code: ObligationCauseCode::CompareImplMethodObligation {
92 item_name: impl_m.ident.name,
93 impl_item_def_id: impl_m.def_id,
94 trait_item_def_id: trait_m.def_id,
98 // This code is best explained by example. Consider a trait:
100 // trait Trait<'t,T> {
101 // fn method<'a,M>(t: &'t T, m: &'a M) -> Self;
106 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
107 // fn method<'b,N>(t: &'j &'i U, m: &'b N) -> Foo;
110 // We wish to decide if those two method types are compatible.
112 // We start out with trait_to_impl_substs, that maps the trait
113 // type parameters to impl type parameters. This is taken from the
114 // impl trait reference:
116 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
118 // We create a mapping `dummy_substs` that maps from the impl type
119 // parameters to fresh types and regions. For type parameters,
120 // this is the identity transform, but we could as well use any
121 // placeholder types. For regions, we convert from bound to free
122 // regions (Note: but only early-bound regions, i.e., those
123 // declared on the impl or used in type parameter bounds).
125 // impl_to_skol_substs = {'i => 'i0, U => U0, N => N0 }
127 // Now we can apply skol_substs to the type of the impl method
128 // to yield a new function type in terms of our fresh, placeholder
131 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
133 // We now want to extract and substitute the type of the *trait*
134 // method and compare it. To do so, we must create a compound
135 // substitution by combining trait_to_impl_substs and
136 // impl_to_skol_substs, and also adding a mapping for the method
137 // type parameters. We extend the mapping to also include
138 // the method parameters.
140 // trait_to_skol_substs = { T => &'i0 U0, Self => Foo, M => N0 }
142 // Applying this to the trait method type yields:
144 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
146 // This type is also the same but the name of the bound region ('a
147 // vs 'b). However, the normal subtyping rules on fn types handle
148 // this kind of equivalency just fine.
150 // We now use these substitutions to ensure that all declared bounds are
151 // satisfied by the implementation's method.
153 // We do this by creating a parameter environment which contains a
154 // substitution corresponding to impl_to_skol_substs. We then build
155 // trait_to_skol_substs and use it to convert the predicates contained
156 // in the trait_m.generics to the placeholder form.
158 // Finally we register each of these predicates as an obligation in
159 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
161 // Create mapping from impl to placeholder.
162 let impl_to_skol_substs = Substs::identity_for_item(tcx, impl_m.def_id);
164 // Create mapping from trait to placeholder.
165 let trait_to_skol_substs = impl_to_skol_substs.rebase_onto(tcx,
166 impl_m.container.id(),
167 trait_to_impl_substs);
168 debug!("compare_impl_method: trait_to_skol_substs={:?}",
169 trait_to_skol_substs);
171 let impl_m_generics = tcx.generics_of(impl_m.def_id);
172 let trait_m_generics = tcx.generics_of(trait_m.def_id);
173 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
174 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
176 // Check region bounds.
177 check_region_bounds_on_impl_method(tcx,
183 trait_to_skol_substs)?;
185 // Create obligations for each predicate declared by the impl
186 // definition in the context of the trait's parameter
187 // environment. We can't just use `impl_env.caller_bounds`,
188 // however, because we want to replace all late-bound regions with
190 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
191 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
193 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
195 // This is the only tricky bit of the new way we check implementation methods
196 // We need to build a set of predicates where only the method-level bounds
197 // are from the trait and we assume all other bounds from the implementation
198 // to be previously satisfied.
200 // We then register the obligations from the impl_m and check to see
201 // if all constraints hold.
202 hybrid_preds.predicates.extend(
203 trait_m_predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
205 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
206 // The key step here is to update the caller_bounds's predicates to be
207 // the new hybrid bounds we computed.
208 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_node_id);
209 let param_env = ty::ParamEnv::new(
210 tcx.intern_predicates(&hybrid_preds.predicates),
214 let param_env = traits::normalize_param_env_or_error(tcx,
217 normalize_cause.clone());
219 tcx.infer_ctxt().enter(|infcx| {
220 let inh = Inherited::new(infcx, impl_m.def_id);
221 let infcx = &inh.infcx;
223 debug!("compare_impl_method: caller_bounds={:?}",
224 param_env.caller_bounds);
226 let mut selcx = traits::SelectionContext::new(&infcx);
228 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_skol_substs);
229 let (impl_m_own_bounds, _) = infcx.replace_bound_vars_with_fresh_vars(
231 infer::HigherRankedType,
232 &ty::Binder::bind(impl_m_own_bounds.predicates)
234 for predicate in impl_m_own_bounds {
235 let traits::Normalized { value: predicate, obligations } =
236 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), &predicate);
238 inh.register_predicates(obligations);
239 inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
242 // We now need to check that the signature of the impl method is
243 // compatible with that of the trait method. We do this by
244 // checking that `impl_fty <: trait_fty`.
246 // FIXME. Unfortunately, this doesn't quite work right now because
247 // associated type normalization is not integrated into subtype
248 // checks. For the comparison to be valid, we need to
249 // normalize the associated types in the impl/trait methods
250 // first. However, because function types bind regions, just
251 // calling `normalize_associated_types_in` would have no effect on
252 // any associated types appearing in the fn arguments or return
255 // Compute placeholder form of impl and trait method tys.
258 let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
260 infer::HigherRankedType,
261 &tcx.fn_sig(impl_m.def_id)
264 inh.normalize_associated_types_in(impl_m_span,
268 let impl_fty = tcx.mk_fn_ptr(ty::Binder::bind(impl_sig));
269 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
271 let trait_sig = tcx.liberate_late_bound_regions(
273 &tcx.fn_sig(trait_m.def_id));
275 trait_sig.subst(tcx, trait_to_skol_substs);
277 inh.normalize_associated_types_in(impl_m_span,
281 let trait_fty = tcx.mk_fn_ptr(ty::Binder::bind(trait_sig));
283 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
285 let sub_result = infcx.at(&cause, param_env)
286 .sup(trait_fty, impl_fty)
287 .map(|InferOk { obligations, .. }| {
288 inh.register_predicates(obligations);
291 if let Err(terr) = sub_result {
292 debug!("sub_types failed: impl ty {:?}, trait ty {:?}",
296 let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(&infcx,
305 let cause = ObligationCause {
310 let mut diag = struct_span_err!(tcx.sess,
313 "method `{}` has an incompatible type for trait",
315 if let TypeError::Mutability = terr {
316 if let Some(trait_err_span) = trait_err_span {
317 if let Ok(trait_err_str) = tcx.sess.source_map()
318 .span_to_snippet(trait_err_span) {
319 diag.span_suggestion_with_applicability(
321 "consider change the type to match the mutability in trait",
323 Applicability::MachineApplicable,
329 infcx.note_type_err(&mut diag,
331 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
332 Some(infer::ValuePairs::Types(ExpectedFound {
338 return Err(ErrorReported);
341 // Check that all obligations are satisfied by the implementation's
343 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
344 infcx.report_fulfillment_errors(errors, None, false);
345 return Err(ErrorReported);
348 // Finally, resolve all regions. This catches wily misuses of
349 // lifetime parameters.
350 let fcx = FnCtxt::new(&inh, param_env, impl_m_node_id);
351 fcx.regionck_item(impl_m_node_id, impl_m_span, &[]);
357 fn check_region_bounds_on_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
359 impl_m: &ty::AssociatedItem,
360 trait_m: &ty::AssociatedItem,
361 trait_generics: &ty::Generics,
362 impl_generics: &ty::Generics,
363 trait_to_skol_substs: &Substs<'tcx>)
364 -> Result<(), ErrorReported> {
365 let trait_params = trait_generics.own_counts().lifetimes;
366 let impl_params = impl_generics.own_counts().lifetimes;
368 debug!("check_region_bounds_on_impl_method: \
369 trait_generics={:?} \
371 trait_to_skol_substs={:?}",
374 trait_to_skol_substs);
376 // Must have same number of early-bound lifetime parameters.
377 // Unfortunately, if the user screws up the bounds, then this
378 // will change classification between early and late. E.g.,
379 // if in trait we have `<'a,'b:'a>`, and in impl we just have
380 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
381 // in trait but 0 in the impl. But if we report "expected 2
382 // but found 0" it's confusing, because it looks like there
383 // are zero. Since I don't quite know how to phrase things at
384 // the moment, give a kind of vague error message.
385 if trait_params != impl_params {
386 let def_span = tcx.sess.source_map().def_span(span);
387 let span = tcx.hir().get_generics_span(impl_m.def_id).unwrap_or(def_span);
388 let mut err = struct_span_err!(
392 "lifetime parameters or bounds on method `{}` do not match the trait declaration",
395 err.span_label(span, "lifetimes do not match method in trait");
396 if let Some(sp) = tcx.hir().span_if_local(trait_m.def_id) {
397 let def_sp = tcx.sess.source_map().def_span(sp);
398 let sp = tcx.hir().get_generics_span(trait_m.def_id).unwrap_or(def_sp);
399 err.span_label(sp, "lifetimes in impl do not match this method in trait");
402 return Err(ErrorReported);
408 fn extract_spans_for_error_reporting<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a, 'gcx, 'tcx>,
409 param_env: ty::ParamEnv<'tcx>,
411 cause: &ObligationCause<'tcx>,
412 impl_m: &ty::AssociatedItem,
413 impl_sig: ty::FnSig<'tcx>,
414 trait_m: &ty::AssociatedItem,
415 trait_sig: ty::FnSig<'tcx>)
416 -> (Span, Option<Span>) {
418 let impl_m_node_id = tcx.hir().as_local_node_id(impl_m.def_id).unwrap();
419 let (impl_m_output, impl_m_iter) = match tcx.hir().expect_impl_item(impl_m_node_id).node {
420 ImplItemKind::Method(ref impl_m_sig, _) => {
421 (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
423 _ => bug!("{:?} is not a method", impl_m),
427 TypeError::Mutability => {
428 if let Some(trait_m_node_id) = tcx.hir().as_local_node_id(trait_m.def_id) {
429 let trait_m_iter = match tcx.hir().expect_trait_item(trait_m_node_id).node {
430 TraitItemKind::Method(ref trait_m_sig, _) => {
431 trait_m_sig.decl.inputs.iter()
433 _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
436 impl_m_iter.zip(trait_m_iter).find(|&(ref impl_arg, ref trait_arg)| {
437 match (&impl_arg.node, &trait_arg.node) {
438 (&hir::TyKind::Rptr(_, ref impl_mt), &hir::TyKind::Rptr(_, ref trait_mt)) |
439 (&hir::TyKind::Ptr(ref impl_mt), &hir::TyKind::Ptr(ref trait_mt)) => {
440 impl_mt.mutbl != trait_mt.mutbl
444 }).map(|(ref impl_arg, ref trait_arg)| {
445 (impl_arg.span, Some(trait_arg.span))
447 .unwrap_or_else(|| (cause.span(&tcx), tcx.hir().span_if_local(trait_m.def_id)))
449 (cause.span(&tcx), tcx.hir().span_if_local(trait_m.def_id))
452 TypeError::Sorts(ExpectedFound { .. }) => {
453 if let Some(trait_m_node_id) = tcx.hir().as_local_node_id(trait_m.def_id) {
454 let (trait_m_output, trait_m_iter) =
455 match tcx.hir().expect_trait_item(trait_m_node_id).node {
456 TraitItemKind::Method(ref trait_m_sig, _) => {
457 (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
459 _ => bug!("{:?} is not a TraitItemKind::Method", trait_m),
462 let impl_iter = impl_sig.inputs().iter();
463 let trait_iter = trait_sig.inputs().iter();
464 impl_iter.zip(trait_iter)
467 .filter_map(|(((&impl_arg_ty, &trait_arg_ty), impl_arg), trait_arg)|
468 match infcx.at(&cause, param_env).sub(trait_arg_ty, impl_arg_ty) {
470 Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
476 infcx.at(&cause, param_env)
477 .sup(trait_sig.output(), impl_sig.output())
480 (impl_m_output.span(), Some(trait_m_output.span()))
482 (cause.span(&tcx), tcx.hir().span_if_local(trait_m.def_id))
486 (cause.span(&tcx), tcx.hir().span_if_local(trait_m.def_id))
489 _ => (cause.span(&tcx), tcx.hir().span_if_local(trait_m.def_id)),
493 fn compare_self_type<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
494 impl_m: &ty::AssociatedItem,
496 trait_m: &ty::AssociatedItem,
497 impl_trait_ref: ty::TraitRef<'tcx>)
498 -> Result<(), ErrorReported>
500 // Try to give more informative error messages about self typing
501 // mismatches. Note that any mismatch will also be detected
502 // below, where we construct a canonical function type that
503 // includes the self parameter as a normal parameter. It's just
504 // that the error messages you get out of this code are a bit more
505 // inscrutable, particularly for cases where one method has no
508 let self_string = |method: &ty::AssociatedItem| {
509 let untransformed_self_ty = match method.container {
510 ty::ImplContainer(_) => impl_trait_ref.self_ty(),
511 ty::TraitContainer(_) => tcx.mk_self_type()
513 let self_arg_ty = *tcx.fn_sig(method.def_id).input(0).skip_binder();
514 let param_env = ty::ParamEnv::reveal_all();
516 tcx.infer_ctxt().enter(|infcx| {
517 let self_arg_ty = tcx.liberate_late_bound_regions(
519 &ty::Binder::bind(self_arg_ty)
521 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
522 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
523 ExplicitSelf::ByValue => "self".to_owned(),
524 ExplicitSelf::ByReference(_, hir::MutImmutable) => "&self".to_owned(),
525 ExplicitSelf::ByReference(_, hir::MutMutable) => "&mut self".to_owned(),
526 _ => format!("self: {}", self_arg_ty)
531 match (trait_m.method_has_self_argument, impl_m.method_has_self_argument) {
532 (false, false) | (true, true) => {}
535 let self_descr = self_string(impl_m);
536 let mut err = struct_span_err!(tcx.sess,
539 "method `{}` has a `{}` declaration in the impl, but \
543 err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
544 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
545 err.span_label(span, format!("trait method declared without `{}`", self_descr));
547 err.note_trait_signature(trait_m.ident.to_string(),
548 trait_m.signature(&tcx));
551 return Err(ErrorReported);
555 let self_descr = self_string(trait_m);
556 let mut err = struct_span_err!(tcx.sess,
559 "method `{}` has a `{}` declaration in the trait, but \
563 err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
564 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
565 err.span_label(span, format!("`{}` used in trait", self_descr));
567 err.note_trait_signature(trait_m.ident.to_string(),
568 trait_m.signature(&tcx));
571 return Err(ErrorReported);
578 fn compare_number_of_generics<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
579 impl_m: &ty::AssociatedItem,
581 trait_m: &ty::AssociatedItem,
582 trait_item_span: Option<Span>)
583 -> Result<(), ErrorReported> {
584 let impl_m_generics = tcx.generics_of(impl_m.def_id);
585 let trait_m_generics = tcx.generics_of(trait_m.def_id);
586 let num_impl_m_type_params = impl_m_generics.own_counts().types;
587 let num_trait_m_type_params = trait_m_generics.own_counts().types;
589 if num_impl_m_type_params != num_trait_m_type_params {
590 let impl_m_node_id = tcx.hir().as_local_node_id(impl_m.def_id).unwrap();
591 let impl_m_item = tcx.hir().expect_impl_item(impl_m_node_id);
592 let span = if impl_m_item.generics.params.is_empty()
593 || impl_m_item.generics.span.is_dummy() // impl Trait in argument position (#55374)
597 impl_m_item.generics.span
600 let mut err = struct_span_err!(tcx.sess, span, E0049,
601 "method `{}` has {} but its trait declaration has {}",
603 potentially_plural_count(num_impl_m_type_params, "type parameter"),
604 potentially_plural_count(num_trait_m_type_params, "type parameter")
607 let mut suffix = None;
609 if let Some(span) = trait_item_span {
610 err.span_label(span, format!("expected {}",
611 potentially_plural_count(num_trait_m_type_params, "type parameter")));
613 suffix = Some(format!(", expected {}", num_trait_m_type_params));
617 format!("found {}{}",
618 potentially_plural_count(num_impl_m_type_params, "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 impl_m_fty = tcx.fn_sig(impl_m.def_id);
636 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
637 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
638 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
639 if trait_number_args != impl_number_args {
640 let trait_m_node_id = tcx.hir().as_local_node_id(trait_m.def_id);
641 let trait_span = if let Some(trait_id) = trait_m_node_id {
642 match tcx.hir().expect_trait_item(trait_id).node {
643 TraitItemKind::Method(ref trait_m_sig, _) => {
644 let pos = if trait_number_args > 0 {
645 trait_number_args - 1
649 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
653 Span::new(trait_m_sig.decl.inputs[0].span.lo(),
661 _ => bug!("{:?} is not a method", impl_m),
666 let impl_m_node_id = tcx.hir().as_local_node_id(impl_m.def_id).unwrap();
667 let impl_span = match tcx.hir().expect_impl_item(impl_m_node_id).node {
668 ImplItemKind::Method(ref impl_m_sig, _) => {
669 let pos = if impl_number_args > 0 {
674 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
678 Span::new(impl_m_sig.decl.inputs[0].span.lo(),
686 _ => bug!("{:?} is not a method", impl_m),
688 let mut err = struct_span_err!(tcx.sess,
691 "method `{}` has {} but the declaration in \
694 potentially_plural_count(impl_number_args, "parameter"),
695 tcx.item_path_str(trait_m.def_id),
697 if let Some(trait_span) = trait_span {
698 err.span_label(trait_span, format!("trait requires {}",
699 potentially_plural_count(trait_number_args, "parameter")));
701 err.note_trait_signature(trait_m.ident.to_string(),
702 trait_m.signature(&tcx));
704 err.span_label(impl_span, format!("expected {}, found {}",
705 potentially_plural_count(trait_number_args, "parameter"), impl_number_args));
707 return Err(ErrorReported);
713 fn compare_synthetic_generics<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
714 impl_m: &ty::AssociatedItem,
715 trait_m: &ty::AssociatedItem)
716 -> Result<(), ErrorReported> {
717 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
718 // 1. Better messages for the span labels
719 // 2. Explanation as to what is going on
720 // If we get here, we already have the same number of generics, so the zip will
722 let mut error_found = false;
723 let impl_m_generics = tcx.generics_of(impl_m.def_id);
724 let trait_m_generics = tcx.generics_of(trait_m.def_id);
725 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
726 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
727 GenericParamDefKind::Lifetime => None,
729 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| {
731 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
732 GenericParamDefKind::Lifetime => None,
735 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic))
736 in impl_m_type_params.zip(trait_m_type_params)
738 if impl_synthetic != trait_synthetic {
739 let impl_node_id = tcx.hir().as_local_node_id(impl_def_id).unwrap();
740 let impl_span = tcx.hir().span(impl_node_id);
741 let trait_span = tcx.def_span(trait_def_id);
742 let mut err = struct_span_err!(tcx.sess,
745 "method `{}` has incompatible signature for trait",
747 err.span_label(trait_span, "declaration in trait here");
748 match (impl_synthetic, trait_synthetic) {
749 // The case where the impl method uses `impl Trait` but the trait method uses
751 (Some(hir::SyntheticTyParamKind::ImplTrait), None) => {
752 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
754 // try taking the name from the trait impl
755 // FIXME: this is obviously suboptimal since the name can already be used
756 // as another generic argument
760 .span_to_snippet(trait_span)
762 let trait_m = tcx.hir().as_local_node_id(trait_m.def_id)?;
763 let trait_m = tcx.hir().trait_item(hir::TraitItemId { node_id: trait_m });
765 let impl_m = tcx.hir().as_local_node_id(impl_m.def_id)?;
766 let impl_m = tcx.hir().impl_item(hir::ImplItemId { node_id: impl_m });
768 // in case there are no generics, take the spot between the function name
769 // and the opening paren of the argument list
770 let new_generics_span = tcx
773 .generate_fn_name_span(impl_span)?
775 // in case there are generics, just replace them
776 let generics_span = impl_m
779 .substitute_dummy(new_generics_span);
780 // replace with the generics from the trait
781 let new_generics = tcx
784 .span_to_snippet(trait_m.generics.span)
787 err.multipart_suggestion_with_applicability(
788 "try changing the `impl Trait` argument to a generic parameter",
790 // replace `impl Trait` with `T`
791 (impl_span, new_name),
792 // replace impl method generics with trait method generics
793 // This isn't quite right, as users might have changed the names
794 // of the generics, but it works for the common case
795 (generics_span, new_generics),
797 Applicability::MaybeIncorrect,
802 // The case where the trait method uses `impl Trait`, but the impl method uses
803 // explicit generics.
804 (None, Some(hir::SyntheticTyParamKind::ImplTrait)) => {
805 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
807 let impl_m = tcx.hir().as_local_node_id(impl_m.def_id)?;
808 let impl_m = tcx.hir().impl_item(hir::ImplItemId { node_id: impl_m });
809 let input_tys = match impl_m.node {
810 hir::ImplItemKind::Method(ref sig, _) => &sig.decl.inputs,
813 struct Visitor(Option<Span>, hir::def_id::DefId);
814 impl<'v> hir::intravisit::Visitor<'v> for Visitor {
815 fn visit_ty(&mut self, ty: &'v hir::Ty) {
816 hir::intravisit::walk_ty(self, ty);
817 if let hir::TyKind::Path(
818 hir::QPath::Resolved(None, ref path)) = ty.node
820 if let hir::def::Def::TyParam(def_id) = path.def {
821 if def_id == self.1 {
822 self.0 = Some(ty.span);
827 fn nested_visit_map<'this>(
829 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
830 hir::intravisit::NestedVisitorMap::None
833 let mut visitor = Visitor(None, impl_def_id);
834 for ty in input_tys {
835 hir::intravisit::Visitor::visit_ty(&mut visitor, ty);
837 let span = visitor.0?;
839 let bounds = impl_m.generics.params.iter().find_map(|param| {
841 GenericParamKind::Lifetime { .. } => None,
842 GenericParamKind::Type { .. } => {
843 if param.id == impl_node_id {
851 let bounds = bounds.first()?.span().to(bounds.last()?.span());
855 .span_to_snippet(bounds)
858 err.multipart_suggestion_with_applicability(
859 "try removing the generic parameter and using `impl Trait` instead",
861 // delete generic parameters
862 (impl_m.generics.span, String::new()),
863 // replace param usage with `impl Trait`
864 (span, format!("impl {}", bounds)),
866 Applicability::MaybeIncorrect,
884 pub fn compare_const_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
885 impl_c: &ty::AssociatedItem,
887 trait_c: &ty::AssociatedItem,
888 impl_trait_ref: ty::TraitRef<'tcx>) {
889 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
891 tcx.infer_ctxt().enter(|infcx| {
892 let param_env = ty::ParamEnv::empty();
893 let inh = Inherited::new(infcx, impl_c.def_id);
894 let infcx = &inh.infcx;
896 // The below is for the most part highly similar to the procedure
897 // for methods above. It is simpler in many respects, especially
898 // because we shouldn't really have to deal with lifetimes or
899 // predicates. In fact some of this should probably be put into
900 // shared functions because of DRY violations...
901 let trait_to_impl_substs = impl_trait_ref.substs;
903 // Create a parameter environment that represents the implementation's
905 let impl_c_node_id = tcx.hir().as_local_node_id(impl_c.def_id).unwrap();
907 // Compute placeholder form of impl and trait const tys.
908 let impl_ty = tcx.type_of(impl_c.def_id);
909 let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
910 let mut cause = ObligationCause::misc(impl_c_span, impl_c_node_id);
912 // There is no "body" here, so just pass dummy id.
913 let impl_ty = inh.normalize_associated_types_in(impl_c_span,
918 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
920 let trait_ty = inh.normalize_associated_types_in(impl_c_span,
925 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
927 let err = infcx.at(&cause, param_env)
928 .sup(trait_ty, impl_ty)
929 .map(|ok| inh.register_infer_ok_obligations(ok));
931 if let Err(terr) = err {
932 debug!("checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
936 // Locate the Span containing just the type of the offending impl
937 match tcx.hir().expect_impl_item(impl_c_node_id).node {
938 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
939 _ => bug!("{:?} is not a impl const", impl_c),
942 let mut diag = struct_span_err!(tcx.sess,
945 "implemented const `{}` has an incompatible type for \
949 let trait_c_node_id = tcx.hir().as_local_node_id(trait_c.def_id);
950 let trait_c_span = trait_c_node_id.map(|trait_c_node_id| {
951 // Add a label to the Span containing just the type of the const
952 match tcx.hir().expect_trait_item(trait_c_node_id).node {
953 TraitItemKind::Const(ref ty, _) => ty.span,
954 _ => bug!("{:?} is not a trait const", trait_c),
958 infcx.note_type_err(&mut diag,
960 trait_c_span.map(|span| (span, "type in trait".to_owned())),
961 Some(infer::ValuePairs::Types(ExpectedFound {
969 // Check that all obligations are satisfied by the implementation's
971 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
972 infcx.report_fulfillment_errors(errors, None, false);
976 let fcx = FnCtxt::new(&inh, param_env, impl_c_node_id);
977 fcx.regionck_item(impl_c_node_id, impl_c_span, &[]);