1 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
2 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorReported};
4 use rustc_hir::def::{DefKind, Res};
5 use rustc_hir::intravisit;
6 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
7 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
8 use rustc_infer::traits::util;
10 use rustc_middle::ty::error::{ExpectedFound, TypeError};
11 use rustc_middle::ty::subst::{InternalSubsts, Subst};
12 use rustc_middle::ty::util::ExplicitSelf;
13 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
15 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
16 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
18 use super::{potentially_plural_count, FnCtxt, Inherited};
20 /// Checks that a method from an impl conforms to the signature of
21 /// the same method as declared in the trait.
25 /// - `impl_m`: type of the method we are checking
26 /// - `impl_m_span`: span to use for reporting errors
27 /// - `trait_m`: the method in the trait
28 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
30 crate fn compare_impl_method<'tcx>(
32 impl_m: &ty::AssocItem,
34 trait_m: &ty::AssocItem,
35 impl_trait_ref: ty::TraitRef<'tcx>,
36 trait_item_span: Option<Span>,
38 debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
40 let impl_m_span = tcx.sess.source_map().guess_head_span(impl_m_span);
42 if let Err(ErrorReported) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
47 if let Err(ErrorReported) =
48 compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
53 if let Err(ErrorReported) =
54 compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
59 if let Err(ErrorReported) = compare_synthetic_generics(tcx, impl_m, trait_m) {
63 if let Err(ErrorReported) =
64 compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
70 fn compare_predicate_entailment<'tcx>(
72 impl_m: &ty::AssocItem,
74 trait_m: &ty::AssocItem,
75 impl_trait_ref: ty::TraitRef<'tcx>,
76 ) -> Result<(), ErrorReported> {
77 let trait_to_impl_substs = impl_trait_ref.substs;
79 // This node-id should be used for the `body_id` field on each
80 // `ObligationCause` (and the `FnCtxt`). This is what
81 // `regionck_item` expects.
82 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
84 // We sometimes modify the span further down.
85 let mut cause = ObligationCause::new(
88 ObligationCauseCode::CompareImplMethodObligation {
89 item_name: impl_m.ident.name,
90 impl_item_def_id: impl_m.def_id,
91 trait_item_def_id: trait_m.def_id,
95 // This code is best explained by example. Consider a trait:
97 // trait Trait<'t, T> {
98 // fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
103 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
104 // fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo;
107 // We wish to decide if those two method types are compatible.
109 // We start out with trait_to_impl_substs, that maps the trait
110 // type parameters to impl type parameters. This is taken from the
111 // impl trait reference:
113 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
115 // We create a mapping `dummy_substs` that maps from the impl type
116 // parameters to fresh types and regions. For type parameters,
117 // this is the identity transform, but we could as well use any
118 // placeholder types. For regions, we convert from bound to free
119 // regions (Note: but only early-bound regions, i.e., those
120 // declared on the impl or used in type parameter bounds).
122 // impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
124 // Now we can apply placeholder_substs to the type of the impl method
125 // to yield a new function type in terms of our fresh, placeholder
128 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
130 // We now want to extract and substitute the type of the *trait*
131 // method and compare it. To do so, we must create a compound
132 // substitution by combining trait_to_impl_substs and
133 // impl_to_placeholder_substs, and also adding a mapping for the method
134 // type parameters. We extend the mapping to also include
135 // the method parameters.
137 // trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
139 // Applying this to the trait method type yields:
141 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
143 // This type is also the same but the name of the bound region ('a
144 // vs 'b). However, the normal subtyping rules on fn types handle
145 // this kind of equivalency just fine.
147 // We now use these substitutions to ensure that all declared bounds are
148 // satisfied by the implementation's method.
150 // We do this by creating a parameter environment which contains a
151 // substitution corresponding to impl_to_placeholder_substs. We then build
152 // trait_to_placeholder_substs and use it to convert the predicates contained
153 // in the trait_m.generics to the placeholder form.
155 // Finally we register each of these predicates as an obligation in
156 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
158 // Create mapping from impl to placeholder.
159 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
161 // Create mapping from trait to placeholder.
162 let trait_to_placeholder_substs =
163 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
164 debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
166 let impl_m_generics = tcx.generics_of(impl_m.def_id);
167 let trait_m_generics = tcx.generics_of(trait_m.def_id);
168 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
169 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
171 // Check region bounds.
172 check_region_bounds_on_impl_item(
181 // Create obligations for each predicate declared by the impl
182 // definition in the context of the trait's parameter
183 // environment. We can't just use `impl_env.caller_bounds`,
184 // however, because we want to replace all late-bound regions with
186 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
187 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
189 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
191 // This is the only tricky bit of the new way we check implementation methods
192 // We need to build a set of predicates where only the method-level bounds
193 // are from the trait and we assume all other bounds from the implementation
194 // to be previously satisfied.
196 // We then register the obligations from the impl_m and check to see
197 // if all constraints hold.
200 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
202 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
203 // The key step here is to update the caller_bounds's predicates to be
204 // the new hybrid bounds we computed.
205 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
207 ty::ParamEnv::new(tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing);
208 let param_env = traits::normalize_param_env_or_error(
212 normalize_cause.clone(),
215 tcx.infer_ctxt().enter(|infcx| {
216 let inh = Inherited::new(infcx, impl_m.def_id.expect_local());
217 let infcx = &inh.infcx;
219 debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
221 let mut selcx = traits::SelectionContext::new(&infcx);
223 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
224 let (impl_m_own_bounds, _) = infcx.replace_bound_vars_with_fresh_vars(
226 infer::HigherRankedType,
227 ty::Binder::bind(impl_m_own_bounds.predicates),
229 for predicate in impl_m_own_bounds {
230 let traits::Normalized { value: predicate, obligations } =
231 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), predicate);
233 inh.register_predicates(obligations);
234 inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
237 // We now need to check that the signature of the impl method is
238 // compatible with that of the trait method. We do this by
239 // checking that `impl_fty <: trait_fty`.
241 // FIXME. Unfortunately, this doesn't quite work right now because
242 // associated type normalization is not integrated into subtype
243 // checks. For the comparison to be valid, we need to
244 // normalize the associated types in the impl/trait methods
245 // first. However, because function types bind regions, just
246 // calling `normalize_associated_types_in` would have no effect on
247 // any associated types appearing in the fn arguments or return
250 // Compute placeholder form of impl and trait method tys.
253 let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
255 infer::HigherRankedType,
256 tcx.fn_sig(impl_m.def_id),
259 inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, impl_sig);
260 let impl_fty = tcx.mk_fn_ptr(ty::Binder::bind(impl_sig));
261 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
263 let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, tcx.fn_sig(trait_m.def_id));
264 let trait_sig = trait_sig.subst(tcx, trait_to_placeholder_substs);
266 inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, trait_sig);
267 let trait_fty = tcx.mk_fn_ptr(ty::Binder::bind(trait_sig));
269 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
271 let sub_result = infcx.at(&cause, param_env).sup(trait_fty, impl_fty).map(
272 |InferOk { obligations, .. }| {
273 inh.register_predicates(obligations);
277 if let Err(terr) = sub_result {
278 debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
280 let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(
281 &infcx, param_env, &terr, &cause, impl_m, impl_sig, trait_m, trait_sig,
284 cause.make_mut().span = impl_err_span;
286 let mut diag = struct_span_err!(
290 "method `{}` has an incompatible type for trait",
293 if let TypeError::Mutability = terr {
294 if let Some(trait_err_span) = trait_err_span {
295 if let Ok(trait_err_str) = tcx.sess.source_map().span_to_snippet(trait_err_span)
297 diag.span_suggestion(
299 "consider changing the mutability to match the trait",
301 Applicability::MachineApplicable,
310 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
311 Some(infer::ValuePairs::Types(ExpectedFound {
318 return Err(ErrorReported);
321 // Check that all obligations are satisfied by the implementation's
323 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
324 infcx.report_fulfillment_errors(errors, None, false);
325 return Err(ErrorReported);
328 // Finally, resolve all regions. This catches wily misuses of
329 // lifetime parameters.
330 let fcx = FnCtxt::new(&inh, param_env, impl_m_hir_id);
331 fcx.regionck_item(impl_m_hir_id, impl_m_span, trait_sig.inputs_and_output);
337 fn check_region_bounds_on_impl_item<'tcx>(
340 impl_m: &ty::AssocItem,
341 trait_m: &ty::AssocItem,
342 trait_generics: &ty::Generics,
343 impl_generics: &ty::Generics,
344 ) -> Result<(), ErrorReported> {
345 let trait_params = trait_generics.own_counts().lifetimes;
346 let impl_params = impl_generics.own_counts().lifetimes;
349 "check_region_bounds_on_impl_item: \
350 trait_generics={:?} \
352 trait_generics, impl_generics
355 // Must have same number of early-bound lifetime parameters.
356 // Unfortunately, if the user screws up the bounds, then this
357 // will change classification between early and late. E.g.,
358 // if in trait we have `<'a,'b:'a>`, and in impl we just have
359 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
360 // in trait but 0 in the impl. But if we report "expected 2
361 // but found 0" it's confusing, because it looks like there
362 // are zero. Since I don't quite know how to phrase things at
363 // the moment, give a kind of vague error message.
364 if trait_params != impl_params {
365 let item_kind = assoc_item_kind_str(impl_m);
366 let def_span = tcx.sess.source_map().guess_head_span(span);
367 let span = tcx.hir().get_generics(impl_m.def_id).map(|g| g.span).unwrap_or(def_span);
368 let generics_span = if let Some(sp) = tcx.hir().span_if_local(trait_m.def_id) {
369 let def_sp = tcx.sess.source_map().guess_head_span(sp);
370 Some(tcx.hir().get_generics(trait_m.def_id).map(|g| g.span).unwrap_or(def_sp))
374 tcx.sess.emit_err(LifetimesOrBoundsMismatchOnTrait {
380 return Err(ErrorReported);
386 fn extract_spans_for_error_reporting<'a, 'tcx>(
387 infcx: &infer::InferCtxt<'a, 'tcx>,
388 param_env: ty::ParamEnv<'tcx>,
389 terr: &TypeError<'_>,
390 cause: &ObligationCause<'tcx>,
391 impl_m: &ty::AssocItem,
392 impl_sig: ty::FnSig<'tcx>,
393 trait_m: &ty::AssocItem,
394 trait_sig: ty::FnSig<'tcx>,
395 ) -> (Span, Option<Span>) {
397 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
398 let (impl_m_output, impl_m_iter) = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
399 ImplItemKind::Fn(ref impl_m_sig, _) => {
400 (&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
402 _ => bug!("{:?} is not a method", impl_m),
406 TypeError::Mutability => {
407 if let Some(def_id) = trait_m.def_id.as_local() {
408 let trait_m_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
409 let trait_m_iter = match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
410 TraitItemKind::Fn(ref trait_m_sig, _) => trait_m_sig.decl.inputs.iter(),
411 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
416 .find(|&(ref impl_arg, ref trait_arg)| {
417 match (&impl_arg.kind, &trait_arg.kind) {
419 &hir::TyKind::Rptr(_, ref impl_mt),
420 &hir::TyKind::Rptr(_, ref trait_mt),
422 | (&hir::TyKind::Ptr(ref impl_mt), &hir::TyKind::Ptr(ref trait_mt)) => {
423 impl_mt.mutbl != trait_mt.mutbl
428 .map(|(ref impl_arg, ref trait_arg)| (impl_arg.span, Some(trait_arg.span)))
429 .unwrap_or_else(|| (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)))
431 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
434 TypeError::Sorts(ExpectedFound { .. }) => {
435 if let Some(def_id) = trait_m.def_id.as_local() {
436 let trait_m_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
437 let (trait_m_output, trait_m_iter) =
438 match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
439 TraitItemKind::Fn(ref trait_m_sig, _) => {
440 (&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
442 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
445 let impl_iter = impl_sig.inputs().iter();
446 let trait_iter = trait_sig.inputs().iter();
451 .find_map(|(((&impl_arg_ty, &trait_arg_ty), impl_arg), trait_arg)| match infcx
452 .at(&cause, param_env)
453 .sub(trait_arg_ty, impl_arg_ty)
456 Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
460 .at(&cause, param_env)
461 .sup(trait_sig.output(), impl_sig.output())
464 (impl_m_output.span(), Some(trait_m_output.span()))
466 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
470 (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
473 _ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
477 fn compare_self_type<'tcx>(
479 impl_m: &ty::AssocItem,
481 trait_m: &ty::AssocItem,
482 impl_trait_ref: ty::TraitRef<'tcx>,
483 ) -> Result<(), ErrorReported> {
484 // Try to give more informative error messages about self typing
485 // mismatches. Note that any mismatch will also be detected
486 // below, where we construct a canonical function type that
487 // includes the self parameter as a normal parameter. It's just
488 // that the error messages you get out of this code are a bit more
489 // inscrutable, particularly for cases where one method has no
492 let self_string = |method: &ty::AssocItem| {
493 let untransformed_self_ty = match method.container {
494 ty::ImplContainer(_) => impl_trait_ref.self_ty(),
495 ty::TraitContainer(_) => tcx.types.self_param,
497 let self_arg_ty = tcx.fn_sig(method.def_id).input(0);
498 let param_env = ty::ParamEnv::reveal_all();
500 tcx.infer_ctxt().enter(|infcx| {
501 let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
502 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
503 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
504 ExplicitSelf::ByValue => "self".to_owned(),
505 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
506 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
507 _ => format!("self: {}", self_arg_ty),
512 match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
513 (false, false) | (true, true) => {}
516 let self_descr = self_string(impl_m);
517 let mut err = struct_span_err!(
521 "method `{}` has a `{}` declaration in the impl, but \
526 err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
527 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
528 err.span_label(span, format!("trait method declared without `{}`", self_descr));
530 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
533 return Err(ErrorReported);
537 let self_descr = self_string(trait_m);
538 let mut err = struct_span_err!(
542 "method `{}` has a `{}` declaration in the trait, but \
547 err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
548 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
549 err.span_label(span, format!("`{}` used in trait", self_descr));
551 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
554 return Err(ErrorReported);
561 fn compare_number_of_generics<'tcx>(
563 impl_: &ty::AssocItem,
565 trait_: &ty::AssocItem,
566 trait_span: Option<Span>,
567 ) -> Result<(), ErrorReported> {
568 let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
569 let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
572 ("type", trait_own_counts.types, impl_own_counts.types),
573 ("const", trait_own_counts.consts, impl_own_counts.consts),
576 let item_kind = assoc_item_kind_str(impl_);
578 let mut err_occurred = false;
579 for &(kind, trait_count, impl_count) in &matchings {
580 if impl_count != trait_count {
583 let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
584 let trait_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
585 let trait_item = tcx.hir().expect_trait_item(trait_hir_id);
586 if trait_item.generics.params.is_empty() {
587 (Some(vec![trait_item.generics.span]), vec![])
589 let arg_spans: Vec<Span> =
590 trait_item.generics.params.iter().map(|p| p.span).collect();
591 let impl_trait_spans: Vec<Span> = trait_item
595 .filter_map(|p| match p.kind {
596 GenericParamKind::Type {
597 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
603 (Some(arg_spans), impl_trait_spans)
606 (trait_span.map(|s| vec![s]), vec![])
609 let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_.def_id.expect_local());
610 let impl_item = tcx.hir().expect_impl_item(impl_hir_id);
611 let impl_item_impl_trait_spans: Vec<Span> = impl_item
615 .filter_map(|p| match p.kind {
616 GenericParamKind::Type {
617 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
623 let spans = impl_item.generics.spans();
624 let span = spans.primary_span();
626 let mut err = tcx.sess.struct_span_err_with_code(
629 "{} `{}` has {} {kind} parameter{} but its trait \
630 declaration has {} {kind} parameter{}",
634 pluralize!(impl_count),
636 pluralize!(trait_count),
639 DiagnosticId::Error("E0049".into()),
642 let mut suffix = None;
644 if let Some(spans) = trait_spans {
645 let mut spans = spans.iter();
646 if let Some(span) = spans.next() {
650 "expected {} {} parameter{}",
653 pluralize!(trait_count),
658 err.span_label(*span, "");
661 suffix = Some(format!(", expected {}", trait_count));
664 if let Some(span) = span {
668 "found {} {} parameter{}{}",
671 pluralize!(impl_count),
672 suffix.unwrap_or_else(String::new),
677 for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
678 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
685 if err_occurred { Err(ErrorReported) } else { Ok(()) }
688 fn compare_number_of_method_arguments<'tcx>(
690 impl_m: &ty::AssocItem,
692 trait_m: &ty::AssocItem,
693 trait_item_span: Option<Span>,
694 ) -> Result<(), ErrorReported> {
695 let impl_m_fty = tcx.fn_sig(impl_m.def_id);
696 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
697 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
698 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
699 if trait_number_args != impl_number_args {
700 let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
701 let trait_id = tcx.hir().local_def_id_to_hir_id(def_id);
702 match tcx.hir().expect_trait_item(trait_id).kind {
703 TraitItemKind::Fn(ref trait_m_sig, _) => {
704 let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
705 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
710 trait_m_sig.decl.inputs[0].span.lo(),
719 _ => bug!("{:?} is not a method", impl_m),
724 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
725 let impl_span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
726 ImplItemKind::Fn(ref impl_m_sig, _) => {
727 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
728 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
733 impl_m_sig.decl.inputs[0].span.lo(),
742 _ => bug!("{:?} is not a method", impl_m),
744 let mut err = struct_span_err!(
748 "method `{}` has {} but the declaration in \
751 potentially_plural_count(impl_number_args, "parameter"),
752 tcx.def_path_str(trait_m.def_id),
755 if let Some(trait_span) = trait_span {
760 potentially_plural_count(trait_number_args, "parameter")
764 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
769 "expected {}, found {}",
770 potentially_plural_count(trait_number_args, "parameter"),
775 return Err(ErrorReported);
781 fn compare_synthetic_generics<'tcx>(
783 impl_m: &ty::AssocItem,
784 trait_m: &ty::AssocItem,
785 ) -> Result<(), ErrorReported> {
786 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
787 // 1. Better messages for the span labels
788 // 2. Explanation as to what is going on
789 // If we get here, we already have the same number of generics, so the zip will
791 let mut error_found = false;
792 let impl_m_generics = tcx.generics_of(impl_m.def_id);
793 let trait_m_generics = tcx.generics_of(trait_m.def_id);
794 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
795 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
796 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
798 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
799 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
800 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
802 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
803 impl_m_type_params.zip(trait_m_type_params)
805 if impl_synthetic != trait_synthetic {
806 let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_def_id.expect_local());
807 let impl_span = tcx.hir().span(impl_hir_id);
808 let trait_span = tcx.def_span(trait_def_id);
809 let mut err = struct_span_err!(
813 "method `{}` has incompatible signature for trait",
816 err.span_label(trait_span, "declaration in trait here");
817 match (impl_synthetic, trait_synthetic) {
818 // The case where the impl method uses `impl Trait` but the trait method uses
820 (Some(hir::SyntheticTyParamKind::ImplTrait), None) => {
821 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
823 // try taking the name from the trait impl
824 // FIXME: this is obviously suboptimal since the name can already be used
825 // as another generic argument
826 let new_name = tcx.sess.source_map().span_to_snippet(trait_span).ok()?;
827 let trait_m = tcx.hir().local_def_id_to_hir_id(trait_m.def_id.as_local()?);
828 let trait_m = tcx.hir().trait_item(hir::TraitItemId { hir_id: trait_m });
830 let impl_m = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.as_local()?);
831 let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
833 // in case there are no generics, take the spot between the function name
834 // and the opening paren of the argument list
835 let new_generics_span =
836 tcx.sess.source_map().generate_fn_name_span(impl_span)?.shrink_to_hi();
837 // in case there are generics, just replace them
839 impl_m.generics.span.substitute_dummy(new_generics_span);
840 // replace with the generics from the trait
842 tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
844 err.multipart_suggestion(
845 "try changing the `impl Trait` argument to a generic parameter",
847 // replace `impl Trait` with `T`
848 (impl_span, new_name),
849 // replace impl method generics with trait method generics
850 // This isn't quite right, as users might have changed the names
851 // of the generics, but it works for the common case
852 (generics_span, new_generics),
854 Applicability::MaybeIncorrect,
859 // The case where the trait method uses `impl Trait`, but the impl method uses
860 // explicit generics.
861 (None, Some(hir::SyntheticTyParamKind::ImplTrait)) => {
862 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
864 let impl_m = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.as_local()?);
865 let impl_m = tcx.hir().impl_item(hir::ImplItemId { hir_id: impl_m });
866 let input_tys = match impl_m.kind {
867 hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
870 struct Visitor(Option<Span>, hir::def_id::DefId);
871 impl<'v> intravisit::Visitor<'v> for Visitor {
872 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
873 intravisit::walk_ty(self, ty);
874 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
877 if let Res::Def(DefKind::TyParam, def_id) = path.res {
878 if def_id == self.1 {
879 self.0 = Some(ty.span);
884 type Map = intravisit::ErasedMap<'v>;
887 ) -> intravisit::NestedVisitorMap<Self::Map>
889 intravisit::NestedVisitorMap::None
892 let mut visitor = Visitor(None, impl_def_id);
893 for ty in input_tys {
894 intravisit::Visitor::visit_ty(&mut visitor, ty);
896 let span = visitor.0?;
899 impl_m.generics.params.iter().find_map(|param| match param.kind {
900 GenericParamKind::Lifetime { .. } => None,
901 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
902 if param.hir_id == impl_hir_id {
909 let bounds = bounds.first()?.span().to(bounds.last()?.span());
910 let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
912 err.multipart_suggestion(
913 "try removing the generic parameter and using `impl Trait` instead",
915 // delete generic parameters
916 (impl_m.generics.span, String::new()),
917 // replace param usage with `impl Trait`
918 (span, format!("impl {}", bounds)),
920 Applicability::MaybeIncorrect,
931 if error_found { Err(ErrorReported) } else { Ok(()) }
934 crate fn compare_const_impl<'tcx>(
936 impl_c: &ty::AssocItem,
938 trait_c: &ty::AssocItem,
939 impl_trait_ref: ty::TraitRef<'tcx>,
941 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
943 tcx.infer_ctxt().enter(|infcx| {
944 let param_env = tcx.param_env(impl_c.def_id);
945 let inh = Inherited::new(infcx, impl_c.def_id.expect_local());
946 let infcx = &inh.infcx;
948 // The below is for the most part highly similar to the procedure
949 // for methods above. It is simpler in many respects, especially
950 // because we shouldn't really have to deal with lifetimes or
951 // predicates. In fact some of this should probably be put into
952 // shared functions because of DRY violations...
953 let trait_to_impl_substs = impl_trait_ref.substs;
955 // Create a parameter environment that represents the implementation's
957 let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_c.def_id.expect_local());
959 // Compute placeholder form of impl and trait const tys.
960 let impl_ty = tcx.type_of(impl_c.def_id);
961 let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
962 let mut cause = ObligationCause::new(
965 ObligationCauseCode::CompareImplConstObligation,
968 // There is no "body" here, so just pass dummy id.
970 inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, impl_ty);
972 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
975 inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, trait_ty);
977 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
980 .at(&cause, param_env)
981 .sup(trait_ty, impl_ty)
982 .map(|ok| inh.register_infer_ok_obligations(ok));
984 if let Err(terr) = err {
986 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
990 // Locate the Span containing just the type of the offending impl
991 match tcx.hir().expect_impl_item(impl_c_hir_id).kind {
992 ImplItemKind::Const(ref ty, _) => cause.make_mut().span = ty.span,
993 _ => bug!("{:?} is not a impl const", impl_c),
996 let mut diag = struct_span_err!(
1000 "implemented const `{}` has an incompatible type for \
1005 let trait_c_hir_id =
1006 trait_c.def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
1007 let trait_c_span = trait_c_hir_id.map(|trait_c_hir_id| {
1008 // Add a label to the Span containing just the type of the const
1009 match tcx.hir().expect_trait_item(trait_c_hir_id).kind {
1010 TraitItemKind::Const(ref ty, _) => ty.span,
1011 _ => bug!("{:?} is not a trait const", trait_c),
1015 infcx.note_type_err(
1018 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1019 Some(infer::ValuePairs::Types(ExpectedFound {
1028 // Check that all obligations are satisfied by the implementation's
1030 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1031 infcx.report_fulfillment_errors(errors, None, false);
1035 let fcx = FnCtxt::new(&inh, param_env, impl_c_hir_id);
1036 fcx.regionck_item(impl_c_hir_id, impl_c_span, &[]);
1040 crate fn compare_ty_impl<'tcx>(
1042 impl_ty: &ty::AssocItem,
1044 trait_ty: &ty::AssocItem,
1045 impl_trait_ref: ty::TraitRef<'tcx>,
1046 trait_item_span: Option<Span>,
1048 debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1050 let _: Result<(), ErrorReported> = (|| {
1051 compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1053 compare_type_predicate_entailment(tcx, impl_ty, impl_ty_span, trait_ty, impl_trait_ref)?;
1055 check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)
1059 /// The equivalent of [compare_predicate_entailment], but for associated types
1060 /// instead of associated functions.
1061 fn compare_type_predicate_entailment<'tcx>(
1063 impl_ty: &ty::AssocItem,
1065 trait_ty: &ty::AssocItem,
1066 impl_trait_ref: ty::TraitRef<'tcx>,
1067 ) -> Result<(), ErrorReported> {
1068 let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1069 let trait_to_impl_substs =
1070 impl_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1072 let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1073 let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1074 let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1075 let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1077 check_region_bounds_on_impl_item(
1086 let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1088 if impl_ty_own_bounds.is_empty() {
1089 // Nothing to check.
1093 // This `HirId` should be used for the `body_id` field on each
1094 // `ObligationCause` (and the `FnCtxt`). This is what
1095 // `regionck_item` expects.
1096 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1097 let cause = ObligationCause::new(
1100 ObligationCauseCode::CompareImplTypeObligation {
1101 item_name: impl_ty.ident.name,
1102 impl_item_def_id: impl_ty.def_id,
1103 trait_item_def_id: trait_ty.def_id,
1107 debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1109 // The predicates declared by the impl definition, the trait and the
1110 // associated type in the trait are assumed.
1111 let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1112 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1115 .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1117 debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1119 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1121 ty::ParamEnv::new(tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing);
1122 let param_env = traits::normalize_param_env_or_error(
1126 normalize_cause.clone(),
1128 tcx.infer_ctxt().enter(|infcx| {
1129 let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
1130 let infcx = &inh.infcx;
1132 debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
1134 let mut selcx = traits::SelectionContext::new(&infcx);
1136 for predicate in impl_ty_own_bounds.predicates {
1137 let traits::Normalized { value: predicate, obligations } =
1138 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), predicate);
1140 inh.register_predicates(obligations);
1141 inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
1144 // Check that all obligations are satisfied by the implementation's
1146 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1147 infcx.report_fulfillment_errors(errors, None, false);
1148 return Err(ErrorReported);
1151 // Finally, resolve all regions. This catches wily misuses of
1152 // lifetime parameters.
1153 let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1154 fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &[]);
1160 /// Validate that `ProjectionCandidate`s created for this associated type will
1165 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1167 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1168 /// impl is well-formed we have to prove `S: Copy`.
1170 /// For default associated types the normalization is not possible (the value
1171 /// from the impl could be overridden). We also can't normalize generic
1172 /// associated types (yet) because they contain bound parameters.
1173 pub fn check_type_bounds<'tcx>(
1175 trait_ty: &ty::AssocItem,
1176 impl_ty: &ty::AssocItem,
1178 impl_trait_ref: ty::TraitRef<'tcx>,
1179 ) -> Result<(), ErrorReported> {
1182 // impl<A, B> Foo<u32> for (A, B) {
1186 // - `impl_substs` would be `[A, B, C]`
1187 // - `rebased_substs` would be `[(A, B), u32, C]`, combining the substs from
1188 // the *trait* with the generic associated type parameters.
1189 let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1190 let rebased_substs =
1191 impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1192 let impl_ty_value = tcx.type_of(impl_ty.def_id);
1194 let param_env = tcx.param_env(impl_ty.def_id);
1196 // When checking something like
1198 // trait X { type Y: PartialEq<<Self as X>::Y> }
1199 // impl X for T { default type Y = S; }
1201 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1202 // we want <T as X>::Y to normalize to S. This is valid because we are
1203 // checking the default value specifically here. Add this equality to the
1204 // ParamEnv for normalization specifically.
1205 let normalize_param_env = {
1206 let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
1207 match impl_ty_value.kind() {
1208 ty::Projection(proj)
1209 if proj.item_def_id == trait_ty.def_id && proj.substs == rebased_substs =>
1211 // Don't include this predicate if the projected type is
1212 // exactly the same as the projection. This can occur in
1213 // (somewhat dubious) code like this:
1215 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1217 _ => predicates.push(
1218 ty::Binder::dummy(ty::ProjectionPredicate {
1219 projection_ty: ty::ProjectionTy {
1220 item_def_id: trait_ty.def_id,
1221 substs: rebased_substs,
1228 ty::ParamEnv::new(tcx.intern_predicates(&predicates), Reveal::UserFacing)
1231 tcx.infer_ctxt().enter(move |infcx| {
1232 let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
1233 let infcx = &inh.infcx;
1234 let mut selcx = traits::SelectionContext::new(&infcx);
1236 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1237 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1238 let mk_cause = |span| {
1239 ObligationCause::new(
1242 ObligationCauseCode::BindingObligation(trait_ty.def_id, span),
1246 let obligations = tcx
1247 .explicit_item_bounds(trait_ty.def_id)
1249 .map(|&(bound, span)| {
1250 let concrete_ty_bound = bound.subst(tcx, rebased_substs);
1251 debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
1253 traits::Obligation::new(mk_cause(span), param_env, concrete_ty_bound)
1256 debug!("check_type_bounds: item_bounds={:?}", obligations);
1258 for mut obligation in util::elaborate_obligations(tcx, obligations) {
1259 let traits::Normalized { value: normalized_predicate, obligations } = traits::normalize(
1261 normalize_param_env,
1262 normalize_cause.clone(),
1263 obligation.predicate,
1265 debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
1266 obligation.predicate = normalized_predicate;
1268 inh.register_predicates(obligations);
1269 inh.register_predicate(obligation);
1272 // Check that all obligations are satisfied by the implementation's
1274 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1275 infcx.report_fulfillment_errors(errors, None, false);
1276 return Err(ErrorReported);
1279 // Finally, resolve all regions. This catches wily misuses of
1280 // lifetime parameters.
1281 let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1282 let implied_bounds = match impl_ty.container {
1283 ty::TraitContainer(_) => vec![],
1284 ty::ImplContainer(def_id) => fcx.impl_implied_bounds(def_id, impl_ty_span),
1286 fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &implied_bounds);
1292 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1293 match impl_item.kind {
1294 ty::AssocKind::Const => "const",
1295 ty::AssocKind::Fn => "method",
1296 ty::AssocKind::Type => "type",