1 use super::potentially_plural_count;
2 use crate::check::regionck::OutlivesEnvironmentExt;
3 use crate::check::wfcheck;
4 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
5 use rustc_data_structures::stable_set::FxHashSet;
6 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
8 use rustc_hir::def::{DefKind, Res};
9 use rustc_hir::intravisit;
10 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
11 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
12 use rustc_infer::infer::{self, TyCtxtInferExt};
13 use rustc_infer::traits::util;
14 use rustc_middle::ty::error::{ExpectedFound, TypeError};
15 use rustc_middle::ty::subst::{InternalSubsts, Subst};
16 use rustc_middle::ty::util::ExplicitSelf;
17 use rustc_middle::ty::{self, DefIdTree};
18 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
20 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
21 use rustc_trait_selection::traits::{
22 self, ObligationCause, ObligationCauseCode, ObligationCtxt, Reveal,
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
35 pub(crate) fn compare_impl_method<'tcx>(
37 impl_m: &ty::AssocItem,
38 trait_m: &ty::AssocItem,
39 impl_trait_ref: ty::TraitRef<'tcx>,
40 trait_item_span: Option<Span>,
42 debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
44 let impl_m_span = tcx.def_span(impl_m.def_id);
46 if let Err(_) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref) {
50 if let Err(_) = compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span) {
54 if let Err(_) = compare_generic_param_kinds(tcx, impl_m, trait_m) {
59 compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
64 if let Err(_) = compare_synthetic_generics(tcx, impl_m, trait_m) {
68 if let Err(_) = compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
74 fn compare_predicate_entailment<'tcx>(
76 impl_m: &ty::AssocItem,
78 trait_m: &ty::AssocItem,
79 impl_trait_ref: ty::TraitRef<'tcx>,
80 ) -> Result<(), ErrorGuaranteed> {
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`).
86 // FIXME(@lcnr): remove that after removing `cause.body_id` from
88 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
89 // We sometimes modify the span further down.
90 let mut cause = ObligationCause::new(
93 ObligationCauseCode::CompareImplMethodObligation {
94 impl_item_def_id: impl_m.def_id.expect_local(),
95 trait_item_def_id: trait_m.def_id,
99 // This code is best explained by example. Consider a trait:
101 // trait Trait<'t, T> {
102 // fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
107 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
108 // fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo;
111 // We wish to decide if those two method types are compatible.
113 // We start out with trait_to_impl_substs, that maps the trait
114 // type parameters to impl type parameters. This is taken from the
115 // impl trait reference:
117 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
119 // We create a mapping `dummy_substs` that maps from the impl type
120 // parameters to fresh types and regions. For type parameters,
121 // this is the identity transform, but we could as well use any
122 // placeholder types. For regions, we convert from bound to free
123 // regions (Note: but only early-bound regions, i.e., those
124 // declared on the impl or used in type parameter bounds).
126 // impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
128 // Now we can apply placeholder_substs to the type of the impl method
129 // to yield a new function type in terms of our fresh, placeholder
132 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
134 // We now want to extract and substitute the type of the *trait*
135 // method and compare it. To do so, we must create a compound
136 // substitution by combining trait_to_impl_substs and
137 // impl_to_placeholder_substs, and also adding a mapping for the method
138 // type parameters. We extend the mapping to also include
139 // the method parameters.
141 // trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
143 // Applying this to the trait method type yields:
145 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
147 // This type is also the same but the name of the bound region ('a
148 // vs 'b). However, the normal subtyping rules on fn types handle
149 // this kind of equivalency just fine.
151 // We now use these substitutions to ensure that all declared bounds are
152 // satisfied by the implementation's method.
154 // We do this by creating a parameter environment which contains a
155 // substitution corresponding to impl_to_placeholder_substs. We then build
156 // trait_to_placeholder_substs and use it to convert the predicates contained
157 // in the trait_m.generics to the placeholder form.
159 // Finally we register each of these predicates as an obligation in
160 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
162 // Create mapping from impl to placeholder.
163 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
165 // Create mapping from trait to placeholder.
166 let trait_to_placeholder_substs =
167 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
168 debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
170 let impl_m_generics = tcx.generics_of(impl_m.def_id);
171 let trait_m_generics = tcx.generics_of(trait_m.def_id);
172 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
173 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
175 // Check region bounds.
176 check_region_bounds_on_impl_item(tcx, impl_m, trait_m, &trait_m_generics, &impl_m_generics)?;
178 // Create obligations for each predicate declared by the impl
179 // definition in the context of the trait's parameter
180 // environment. We can't just use `impl_env.caller_bounds`,
181 // however, because we want to replace all late-bound regions with
183 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
184 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
186 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
188 // This is the only tricky bit of the new way we check implementation methods
189 // We need to build a set of predicates where only the method-level bounds
190 // are from the trait and we assume all other bounds from the implementation
191 // to be previously satisfied.
193 // We then register the obligations from the impl_m and check to see
194 // if all constraints hold.
197 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
199 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
200 // The key step here is to update the caller_bounds's predicates to be
201 // the new hybrid bounds we computed.
202 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
203 let param_env = ty::ParamEnv::new(
204 tcx.intern_predicates(&hybrid_preds.predicates),
206 hir::Constness::NotConst,
208 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
210 tcx.infer_ctxt().enter(|ref infcx| {
211 let ocx = ObligationCtxt::new(infcx);
213 debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
215 let mut selcx = traits::SelectionContext::new(&infcx);
216 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
217 for (predicate, span) in iter::zip(impl_m_own_bounds.predicates, impl_m_own_bounds.spans) {
218 let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id);
219 let traits::Normalized { value: predicate, obligations } =
220 traits::normalize(&mut selcx, param_env, normalize_cause, predicate);
222 ocx.register_obligations(obligations);
223 let cause = ObligationCause::new(
226 ObligationCauseCode::CompareImplMethodObligation {
227 impl_item_def_id: impl_m.def_id.expect_local(),
228 trait_item_def_id: trait_m.def_id,
231 ocx.register_obligation(traits::Obligation::new(cause, param_env, predicate));
234 // We now need to check that the signature of the impl method is
235 // compatible with that of the trait method. We do this by
236 // checking that `impl_fty <: trait_fty`.
238 // FIXME. Unfortunately, this doesn't quite work right now because
239 // associated type normalization is not integrated into subtype
240 // checks. For the comparison to be valid, we need to
241 // normalize the associated types in the impl/trait methods
242 // first. However, because function types bind regions, just
243 // calling `normalize_associated_types_in` would have no effect on
244 // any associated types appearing in the fn arguments or return
247 // Compute placeholder form of impl and trait method tys.
250 let mut wf_tys = FxHashSet::default();
252 let impl_sig = infcx.replace_bound_vars_with_fresh_vars(
254 infer::HigherRankedType,
255 tcx.fn_sig(impl_m.def_id),
258 let norm_cause = ObligationCause::misc(impl_m_span, impl_m_hir_id);
259 let impl_sig = ocx.normalize(norm_cause.clone(), param_env, impl_sig);
260 let impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig));
261 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
263 let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs);
264 let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig);
265 let trait_sig = ocx.normalize(norm_cause, param_env, trait_sig);
266 // Add the resulting inputs and output as well-formed.
267 wf_tys.extend(trait_sig.inputs_and_output.iter());
268 let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
270 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
272 // FIXME: We'd want to keep more accurate spans than "the method signature" when
273 // processing the comparison between the trait and impl fn, but we sadly lose them
274 // and point at the whole signature when a trait bound or specific input or output
275 // type would be more appropriate. In other places we have a `Vec<Span>`
276 // corresponding to their `Vec<Predicate>`, but we don't have that here.
277 // Fixing this would improve the output of test `issue-83765.rs`.
278 let sub_result = infcx
279 .at(&cause, param_env)
280 .sup(trait_fty, impl_fty)
281 .map(|infer_ok| ocx.register_infer_ok_obligations(infer_ok));
283 if let Err(terr) = sub_result {
284 debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
286 let (impl_err_span, trait_err_span) =
287 extract_spans_for_error_reporting(&infcx, &terr, &cause, impl_m, trait_m);
289 cause.span = impl_err_span;
291 let mut diag = struct_span_err!(
295 "method `{}` has an incompatible type for trait",
299 TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
300 if trait_m.fn_has_self_parameter =>
302 let ty = trait_sig.inputs()[0];
303 let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty())
305 ExplicitSelf::ByValue => "self".to_owned(),
306 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
307 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => {
308 "&mut self".to_owned()
310 _ => format!("self: {ty}"),
313 // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
314 // span points only at the type `Box<Self`>, but we want to cover the whole
315 // argument pattern and type.
316 let span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
317 ImplItemKind::Fn(ref sig, body) => tcx
319 .body_param_names(body)
320 .zip(sig.decl.inputs.iter())
321 .map(|(param, ty)| param.span.to(ty.span))
323 .unwrap_or(impl_err_span),
324 _ => bug!("{:?} is not a method", impl_m),
327 diag.span_suggestion(
329 "change the self-receiver type to match the trait",
331 Applicability::MachineApplicable,
334 TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
335 if trait_sig.inputs().len() == *i {
336 // Suggestion to change output type. We do not suggest in `async` functions
337 // to avoid complex logic or incorrect output.
338 match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
339 ImplItemKind::Fn(ref sig, _)
340 if sig.header.asyncness == hir::IsAsync::NotAsync =>
342 let msg = "change the output type to match the trait";
343 let ap = Applicability::MachineApplicable;
344 match sig.decl.output {
345 hir::FnRetTy::DefaultReturn(sp) => {
346 let sugg = format!("-> {} ", trait_sig.output());
347 diag.span_suggestion_verbose(sp, msg, sugg, ap);
349 hir::FnRetTy::Return(hir_ty) => {
350 let sugg = trait_sig.output();
351 diag.span_suggestion(hir_ty.span, msg, sugg, ap);
357 } else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
358 diag.span_suggestion(
360 "change the parameter type to match the trait",
362 Applicability::MachineApplicable,
372 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
373 Some(infer::ValuePairs::Terms(ExpectedFound {
374 expected: trait_fty.into(),
375 found: impl_fty.into(),
382 return Err(diag.emit());
385 // Check that all obligations are satisfied by the implementation's
387 let errors = ocx.select_all_or_error();
388 if !errors.is_empty() {
389 let reported = infcx.report_fulfillment_errors(&errors, None, false);
390 return Err(reported);
393 // Finally, resolve all regions. This catches wily misuses of
394 // lifetime parameters.
395 let mut outlives_environment = OutlivesEnvironment::new(param_env);
396 outlives_environment.add_implied_bounds(infcx, wf_tys, impl_m_hir_id);
397 infcx.check_region_obligations_and_report_errors(&outlives_environment);
403 fn check_region_bounds_on_impl_item<'tcx>(
405 impl_m: &ty::AssocItem,
406 trait_m: &ty::AssocItem,
407 trait_generics: &ty::Generics,
408 impl_generics: &ty::Generics,
409 ) -> Result<(), ErrorGuaranteed> {
410 let trait_params = trait_generics.own_counts().lifetimes;
411 let impl_params = impl_generics.own_counts().lifetimes;
414 "check_region_bounds_on_impl_item: \
415 trait_generics={:?} \
417 trait_generics, impl_generics
420 // Must have same number of early-bound lifetime parameters.
421 // Unfortunately, if the user screws up the bounds, then this
422 // will change classification between early and late. E.g.,
423 // if in trait we have `<'a,'b:'a>`, and in impl we just have
424 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
425 // in trait but 0 in the impl. But if we report "expected 2
426 // but found 0" it's confusing, because it looks like there
427 // are zero. Since I don't quite know how to phrase things at
428 // the moment, give a kind of vague error message.
429 if trait_params != impl_params {
432 .get_generics(impl_m.def_id.expect_local())
433 .expect("expected impl item to have generics or else we can't compare them")
435 let generics_span = if let Some(local_def_id) = trait_m.def_id.as_local() {
438 .get_generics(local_def_id)
439 .expect("expected trait item to have generics or else we can't compare them")
446 let reported = tcx.sess.emit_err(LifetimesOrBoundsMismatchOnTrait {
448 item_kind: assoc_item_kind_str(impl_m),
449 ident: impl_m.ident(tcx),
452 return Err(reported);
458 #[instrument(level = "debug", skip(infcx))]
459 fn extract_spans_for_error_reporting<'a, 'tcx>(
460 infcx: &infer::InferCtxt<'a, 'tcx>,
461 terr: &TypeError<'_>,
462 cause: &ObligationCause<'tcx>,
463 impl_m: &ty::AssocItem,
464 trait_m: &ty::AssocItem,
465 ) -> (Span, Option<Span>) {
467 let mut impl_args = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
468 ImplItemKind::Fn(ref sig, _) => {
469 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
471 _ => bug!("{:?} is not a method", impl_m),
474 trait_m.def_id.as_local().map(|def_id| match tcx.hir().expect_trait_item(def_id).kind {
475 TraitItemKind::Fn(ref sig, _) => {
476 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
478 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
482 TypeError::ArgumentMutability(i) => {
483 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
485 TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
486 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
488 _ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)),
492 fn compare_self_type<'tcx>(
494 impl_m: &ty::AssocItem,
496 trait_m: &ty::AssocItem,
497 impl_trait_ref: ty::TraitRef<'tcx>,
498 ) -> Result<(), ErrorGuaranteed> {
499 // Try to give more informative error messages about self typing
500 // mismatches. Note that any mismatch will also be detected
501 // below, where we construct a canonical function type that
502 // includes the self parameter as a normal parameter. It's just
503 // that the error messages you get out of this code are a bit more
504 // inscrutable, particularly for cases where one method has no
507 let self_string = |method: &ty::AssocItem| {
508 let untransformed_self_ty = match method.container {
509 ty::ImplContainer(_) => impl_trait_ref.self_ty(),
510 ty::TraitContainer(_) => tcx.types.self_param,
512 let self_arg_ty = tcx.fn_sig(method.def_id).input(0);
513 let param_env = ty::ParamEnv::reveal_all();
515 tcx.infer_ctxt().enter(|infcx| {
516 let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
517 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
518 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
519 ExplicitSelf::ByValue => "self".to_owned(),
520 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
521 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
522 _ => format!("self: {self_arg_ty}"),
527 match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
528 (false, false) | (true, true) => {}
531 let self_descr = self_string(impl_m);
532 let mut err = struct_span_err!(
536 "method `{}` has a `{}` declaration in the impl, but not in the trait",
540 err.span_label(impl_m_span, format!("`{self_descr}` used in impl"));
541 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
542 err.span_label(span, format!("trait method declared without `{self_descr}`"));
544 err.note_trait_signature(trait_m.name.to_string(), trait_m.signature(tcx));
546 let reported = err.emit();
547 return Err(reported);
551 let self_descr = self_string(trait_m);
552 let mut err = struct_span_err!(
556 "method `{}` has a `{}` declaration in the trait, but not in the impl",
560 err.span_label(impl_m_span, format!("expected `{self_descr}` in impl"));
561 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
562 err.span_label(span, format!("`{self_descr}` used in trait"));
564 err.note_trait_signature(trait_m.name.to_string(), trait_m.signature(tcx));
566 let reported = err.emit();
567 return Err(reported);
574 /// Checks that the number of generics on a given assoc item in a trait impl is the same
575 /// as the number of generics on the respective assoc item in the trait definition.
577 /// For example this code emits the errors in the following code:
584 /// impl Trait for () {
587 /// type Assoc = u32;
592 /// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
593 /// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
594 /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
595 fn compare_number_of_generics<'tcx>(
597 impl_: &ty::AssocItem,
599 trait_: &ty::AssocItem,
600 trait_span: Option<Span>,
601 ) -> Result<(), ErrorGuaranteed> {
602 let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
603 let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
605 // This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
606 // in `compare_generic_param_kinds` which will give a nicer error message than something like:
607 // "expected 1 type parameter, found 0 type parameters"
608 if (trait_own_counts.types + trait_own_counts.consts)
609 == (impl_own_counts.types + impl_own_counts.consts)
615 ("type", trait_own_counts.types, impl_own_counts.types),
616 ("const", trait_own_counts.consts, impl_own_counts.consts),
619 let item_kind = assoc_item_kind_str(impl_);
621 let mut err_occurred = None;
622 for (kind, trait_count, impl_count) in matchings {
623 if impl_count != trait_count {
624 let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| {
625 let mut spans = generics
628 .filter(|p| match p.kind {
629 hir::GenericParamKind::Lifetime {
630 kind: hir::LifetimeParamKind::Elided,
632 // A fn can have an arbitrary number of extra elided lifetimes for the
634 !matches!(kind, ty::AssocKind::Fn)
639 .collect::<Vec<Span>>();
640 if spans.is_empty() {
641 spans = vec![generics.span]
645 let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
646 let trait_item = tcx.hir().expect_trait_item(def_id);
647 let arg_spans: Vec<Span> = arg_spans(trait_.kind, trait_item.generics);
648 let impl_trait_spans: Vec<Span> = trait_item
652 .filter_map(|p| match p.kind {
653 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
657 (Some(arg_spans), impl_trait_spans)
659 (trait_span.map(|s| vec![s]), vec![])
662 let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local());
663 let impl_item_impl_trait_spans: Vec<Span> = impl_item
667 .filter_map(|p| match p.kind {
668 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
672 let spans = arg_spans(impl_.kind, impl_item.generics);
673 let span = spans.first().copied();
675 let mut err = tcx.sess.struct_span_err_with_code(
678 "{} `{}` has {} {kind} parameter{} but its trait \
679 declaration has {} {kind} parameter{}",
683 pluralize!(impl_count),
685 pluralize!(trait_count),
688 DiagnosticId::Error("E0049".into()),
691 let mut suffix = None;
693 if let Some(spans) = trait_spans {
694 let mut spans = spans.iter();
695 if let Some(span) = spans.next() {
699 "expected {} {} parameter{}",
702 pluralize!(trait_count),
707 err.span_label(*span, "");
710 suffix = Some(format!(", expected {trait_count}"));
713 if let Some(span) = span {
717 "found {} {} parameter{}{}",
720 pluralize!(impl_count),
721 suffix.unwrap_or_else(String::new),
726 for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
727 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
730 let reported = err.emit();
731 err_occurred = Some(reported);
735 if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) }
738 fn compare_number_of_method_arguments<'tcx>(
740 impl_m: &ty::AssocItem,
742 trait_m: &ty::AssocItem,
743 trait_item_span: Option<Span>,
744 ) -> Result<(), ErrorGuaranteed> {
745 let impl_m_fty = tcx.fn_sig(impl_m.def_id);
746 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
747 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
748 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
749 if trait_number_args != impl_number_args {
750 let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
751 match tcx.hir().expect_trait_item(def_id).kind {
752 TraitItemKind::Fn(ref trait_m_sig, _) => {
753 let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
754 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
758 arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
764 _ => bug!("{:?} is not a method", impl_m),
769 let impl_span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
770 ImplItemKind::Fn(ref impl_m_sig, _) => {
771 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
772 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
776 arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
782 _ => bug!("{:?} is not a method", impl_m),
784 let mut err = struct_span_err!(
788 "method `{}` has {} but the declaration in trait `{}` has {}",
790 potentially_plural_count(impl_number_args, "parameter"),
791 tcx.def_path_str(trait_m.def_id),
794 if let Some(trait_span) = trait_span {
799 potentially_plural_count(trait_number_args, "parameter")
803 err.note_trait_signature(trait_m.name.to_string(), trait_m.signature(tcx));
808 "expected {}, found {}",
809 potentially_plural_count(trait_number_args, "parameter"),
813 let reported = err.emit();
814 return Err(reported);
820 fn compare_synthetic_generics<'tcx>(
822 impl_m: &ty::AssocItem,
823 trait_m: &ty::AssocItem,
824 ) -> Result<(), ErrorGuaranteed> {
825 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
826 // 1. Better messages for the span labels
827 // 2. Explanation as to what is going on
828 // If we get here, we already have the same number of generics, so the zip will
830 let mut error_found = None;
831 let impl_m_generics = tcx.generics_of(impl_m.def_id);
832 let trait_m_generics = tcx.generics_of(trait_m.def_id);
833 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
834 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
835 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
837 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
838 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
839 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
841 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
842 iter::zip(impl_m_type_params, trait_m_type_params)
844 if impl_synthetic != trait_synthetic {
845 let impl_def_id = impl_def_id.expect_local();
846 let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_def_id);
847 let impl_span = tcx.hir().span(impl_hir_id);
848 let trait_span = tcx.def_span(trait_def_id);
849 let mut err = struct_span_err!(
853 "method `{}` has incompatible signature for trait",
856 err.span_label(trait_span, "declaration in trait here");
857 match (impl_synthetic, trait_synthetic) {
858 // The case where the impl method uses `impl Trait` but the trait method uses
861 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
863 // try taking the name from the trait impl
864 // FIXME: this is obviously suboptimal since the name can already be used
865 // as another generic argument
866 let new_name = tcx.sess.source_map().span_to_snippet(trait_span).ok()?;
867 let trait_m = trait_m.def_id.as_local()?;
868 let trait_m = tcx.hir().trait_item(hir::TraitItemId { def_id: trait_m });
870 let impl_m = impl_m.def_id.as_local()?;
871 let impl_m = tcx.hir().impl_item(hir::ImplItemId { def_id: impl_m });
873 // in case there are no generics, take the spot between the function name
874 // and the opening paren of the argument list
875 let new_generics_span =
876 tcx.sess.source_map().generate_fn_name_span(impl_span)?.shrink_to_hi();
877 // in case there are generics, just replace them
879 impl_m.generics.span.substitute_dummy(new_generics_span);
880 // replace with the generics from the trait
882 tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
884 err.multipart_suggestion(
885 "try changing the `impl Trait` argument to a generic parameter",
887 // replace `impl Trait` with `T`
888 (impl_span, new_name),
889 // replace impl method generics with trait method generics
890 // This isn't quite right, as users might have changed the names
891 // of the generics, but it works for the common case
892 (generics_span, new_generics),
894 Applicability::MaybeIncorrect,
899 // The case where the trait method uses `impl Trait`, but the impl method uses
900 // explicit generics.
902 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
904 let impl_m = impl_m.def_id.as_local()?;
905 let impl_m = tcx.hir().impl_item(hir::ImplItemId { def_id: impl_m });
906 let input_tys = match impl_m.kind {
907 hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
910 struct Visitor(Option<Span>, hir::def_id::LocalDefId);
911 impl<'v> intravisit::Visitor<'v> for Visitor {
912 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
913 intravisit::walk_ty(self, ty);
914 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
916 && let Res::Def(DefKind::TyParam, def_id) = path.res
917 && def_id == self.1.to_def_id()
919 self.0 = Some(ty.span);
923 let mut visitor = Visitor(None, impl_def_id);
924 for ty in input_tys {
925 intravisit::Visitor::visit_ty(&mut visitor, ty);
927 let span = visitor.0?;
929 let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds;
930 let bounds = bounds.first()?.span().to(bounds.last()?.span());
931 let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
933 err.multipart_suggestion(
934 "try removing the generic parameter and using `impl Trait` instead",
936 // delete generic parameters
937 (impl_m.generics.span, String::new()),
938 // replace param usage with `impl Trait`
939 (span, format!("impl {bounds}")),
941 Applicability::MaybeIncorrect,
948 let reported = err.emit();
949 error_found = Some(reported);
952 if let Some(reported) = error_found { Err(reported) } else { Ok(()) }
955 /// Checks that all parameters in the generics of a given assoc item in a trait impl have
956 /// the same kind as the respective generic parameter in the trait def.
958 /// For example all 4 errors in the following code are emitted here:
961 /// fn foo<const N: u8>();
962 /// type bar<const N: u8>;
963 /// fn baz<const N: u32>();
967 /// impl Foo for () {
968 /// fn foo<const N: u64>() {}
970 /// type bar<const N: u64> {}
974 /// type blah<const N: i64> = u32;
979 /// This function does not handle lifetime parameters
980 fn compare_generic_param_kinds<'tcx>(
982 impl_item: &ty::AssocItem,
983 trait_item: &ty::AssocItem,
984 ) -> Result<(), ErrorGuaranteed> {
985 assert_eq!(impl_item.kind, trait_item.kind);
987 let ty_const_params_of = |def_id| {
988 tcx.generics_of(def_id).params.iter().filter(|param| {
991 GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. }
996 for (param_impl, param_trait) in
997 iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id))
999 use GenericParamDefKind::*;
1000 if match (¶m_impl.kind, ¶m_trait.kind) {
1001 (Const { .. }, Const { .. })
1002 if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) =>
1006 (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true,
1007 // this is exhaustive so that anyone adding new generic param kinds knows
1008 // to make sure this error is reported for them.
1009 (Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false,
1010 (Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(),
1012 let param_impl_span = tcx.def_span(param_impl.def_id);
1013 let param_trait_span = tcx.def_span(param_trait.def_id);
1015 let mut err = struct_span_err!(
1019 "{} `{}` has an incompatible generic parameter for trait `{}`",
1020 assoc_item_kind_str(&impl_item),
1022 &tcx.def_path_str(tcx.parent(trait_item.def_id))
1025 let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind {
1027 format!("{} const parameter of type `{}`", prefix, tcx.type_of(param.def_id))
1029 Type { .. } => format!("{} type parameter", prefix),
1030 Lifetime { .. } => unreachable!(),
1033 let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap();
1034 err.span_label(trait_header_span, "");
1035 err.span_label(param_trait_span, make_param_message("expected", param_trait));
1037 let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id));
1038 err.span_label(impl_header_span, "");
1039 err.span_label(param_impl_span, make_param_message("found", param_impl));
1041 let reported = err.emit();
1042 return Err(reported);
1049 pub(crate) fn compare_const_impl<'tcx>(
1051 impl_c: &ty::AssocItem,
1053 trait_c: &ty::AssocItem,
1054 impl_trait_ref: ty::TraitRef<'tcx>,
1056 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
1058 tcx.infer_ctxt().enter(|infcx| {
1059 let param_env = tcx.param_env(impl_c.def_id);
1060 let ocx = ObligationCtxt::new(&infcx);
1062 // The below is for the most part highly similar to the procedure
1063 // for methods above. It is simpler in many respects, especially
1064 // because we shouldn't really have to deal with lifetimes or
1065 // predicates. In fact some of this should probably be put into
1066 // shared functions because of DRY violations...
1067 let trait_to_impl_substs = impl_trait_ref.substs;
1069 // Create a parameter environment that represents the implementation's
1071 let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_c.def_id.expect_local());
1073 // Compute placeholder form of impl and trait const tys.
1074 let impl_ty = tcx.type_of(impl_c.def_id);
1075 let trait_ty = tcx.bound_type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
1076 let mut cause = ObligationCause::new(
1079 ObligationCauseCode::CompareImplConstObligation,
1082 // There is no "body" here, so just pass dummy id.
1083 let impl_ty = ocx.normalize(cause.clone(), param_env, impl_ty);
1085 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
1087 let trait_ty = ocx.normalize(cause.clone(), param_env, trait_ty);
1089 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
1092 .at(&cause, param_env)
1093 .sup(trait_ty, impl_ty)
1094 .map(|ok| ocx.register_infer_ok_obligations(ok));
1096 if let Err(terr) = err {
1098 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
1102 // Locate the Span containing just the type of the offending impl
1103 match tcx.hir().expect_impl_item(impl_c.def_id.expect_local()).kind {
1104 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
1105 _ => bug!("{:?} is not a impl const", impl_c),
1108 let mut diag = struct_span_err!(
1112 "implemented const `{}` has an incompatible type for trait",
1116 let trait_c_span = trait_c.def_id.as_local().map(|trait_c_def_id| {
1117 // Add a label to the Span containing just the type of the const
1118 match tcx.hir().expect_trait_item(trait_c_def_id).kind {
1119 TraitItemKind::Const(ref ty, _) => ty.span,
1120 _ => bug!("{:?} is not a trait const", trait_c),
1124 infcx.note_type_err(
1127 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1128 Some(infer::ValuePairs::Terms(ExpectedFound {
1129 expected: trait_ty.into(),
1130 found: impl_ty.into(),
1139 // Check that all obligations are satisfied by the implementation's
1141 let errors = ocx.select_all_or_error();
1142 if !errors.is_empty() {
1143 infcx.report_fulfillment_errors(&errors, None, false);
1147 let outlives_environment = OutlivesEnvironment::new(param_env);
1148 infcx.resolve_regions_and_report_errors(&outlives_environment);
1152 pub(crate) fn compare_ty_impl<'tcx>(
1154 impl_ty: &ty::AssocItem,
1156 trait_ty: &ty::AssocItem,
1157 impl_trait_ref: ty::TraitRef<'tcx>,
1158 trait_item_span: Option<Span>,
1160 debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1162 let _: Result<(), ErrorGuaranteed> = (|| {
1163 compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1165 compare_generic_param_kinds(tcx, impl_ty, trait_ty)?;
1167 let sp = tcx.def_span(impl_ty.def_id);
1168 compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?;
1170 check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)
1174 /// The equivalent of [compare_predicate_entailment], but for associated types
1175 /// instead of associated functions.
1176 fn compare_type_predicate_entailment<'tcx>(
1178 impl_ty: &ty::AssocItem,
1180 trait_ty: &ty::AssocItem,
1181 impl_trait_ref: ty::TraitRef<'tcx>,
1182 ) -> Result<(), ErrorGuaranteed> {
1183 let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1184 let trait_to_impl_substs =
1185 impl_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1187 let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1188 let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1189 let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1190 let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1192 check_region_bounds_on_impl_item(
1200 let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1202 if impl_ty_own_bounds.is_empty() {
1203 // Nothing to check.
1207 // This `HirId` should be used for the `body_id` field on each
1208 // `ObligationCause` (and the `FnCtxt`). This is what
1209 // `regionck_item` expects.
1210 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1211 let cause = ObligationCause::new(
1214 ObligationCauseCode::CompareImplTypeObligation {
1215 impl_item_def_id: impl_ty.def_id.expect_local(),
1216 trait_item_def_id: trait_ty.def_id,
1220 debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1222 // The predicates declared by the impl definition, the trait and the
1223 // associated type in the trait are assumed.
1224 let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1225 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1228 .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1230 debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1232 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1233 let param_env = ty::ParamEnv::new(
1234 tcx.intern_predicates(&hybrid_preds.predicates),
1236 hir::Constness::NotConst,
1238 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause.clone());
1239 tcx.infer_ctxt().enter(|infcx| {
1240 let ocx = ObligationCtxt::new(&infcx);
1242 debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
1244 let mut selcx = traits::SelectionContext::new(&infcx);
1246 for predicate in impl_ty_own_bounds.predicates {
1247 let traits::Normalized { value: predicate, obligations } =
1248 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), predicate);
1250 ocx.register_obligations(obligations);
1251 ocx.register_obligation(traits::Obligation::new(cause.clone(), param_env, predicate));
1254 // Check that all obligations are satisfied by the implementation's
1256 let errors = ocx.select_all_or_error();
1257 if !errors.is_empty() {
1258 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1259 return Err(reported);
1262 // Finally, resolve all regions. This catches wily misuses of
1263 // lifetime parameters.
1264 let outlives_environment = OutlivesEnvironment::new(param_env);
1265 infcx.check_region_obligations_and_report_errors(&outlives_environment);
1271 /// Validate that `ProjectionCandidate`s created for this associated type will
1276 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1278 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1279 /// impl is well-formed we have to prove `S: Copy`.
1281 /// For default associated types the normalization is not possible (the value
1282 /// from the impl could be overridden). We also can't normalize generic
1283 /// associated types (yet) because they contain bound parameters.
1284 #[tracing::instrument(level = "debug", skip(tcx))]
1285 pub fn check_type_bounds<'tcx>(
1287 trait_ty: &ty::AssocItem,
1288 impl_ty: &ty::AssocItem,
1290 impl_trait_ref: ty::TraitRef<'tcx>,
1291 ) -> Result<(), ErrorGuaranteed> {
1294 // impl<A, B> Foo<u32> for (A, B) {
1298 // - `impl_trait_ref` would be `<(A, B) as Foo<u32>>
1299 // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
1300 // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
1301 // the *trait* with the generic associated type parameters (as bound vars).
1303 // A note regarding the use of bound vars here:
1304 // Imagine as an example
1307 // type Member<C: Eq>;
1310 // impl Family for VecFamily {
1311 // type Member<C: Eq> = i32;
1314 // Here, we would generate
1316 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
1318 // when we really would like to generate
1320 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
1322 // But, this is probably fine, because although the first clause can be used with types C that
1323 // do not implement Eq, for it to cause some kind of problem, there would have to be a
1324 // VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
1325 // Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
1326 // elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
1327 // the trait (notably, that X: Eq and T: Family).
1328 let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id);
1329 let mut substs = smallvec::SmallVec::with_capacity(defs.count());
1330 if let Some(def_id) = defs.parent {
1331 let parent_defs = tcx.generics_of(def_id);
1332 InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| {
1333 tcx.mk_param_from_def(param)
1336 let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
1337 smallvec::SmallVec::with_capacity(defs.count());
1338 InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind {
1339 GenericParamDefKind::Type { .. } => {
1340 let kind = ty::BoundTyKind::Param(param.name);
1341 let bound_var = ty::BoundVariableKind::Ty(kind);
1342 bound_vars.push(bound_var);
1343 tcx.mk_ty(ty::Bound(
1345 ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1349 GenericParamDefKind::Lifetime => {
1350 let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
1351 let bound_var = ty::BoundVariableKind::Region(kind);
1352 bound_vars.push(bound_var);
1353 tcx.mk_region(ty::ReLateBound(
1355 ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1359 GenericParamDefKind::Const { .. } => {
1360 let bound_var = ty::BoundVariableKind::Const;
1361 bound_vars.push(bound_var);
1362 tcx.mk_const(ty::ConstS {
1363 ty: tcx.type_of(param.def_id),
1364 kind: ty::ConstKind::Bound(
1366 ty::BoundVar::from_usize(bound_vars.len() - 1),
1372 let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter());
1373 let impl_ty_substs = tcx.intern_substs(&substs);
1375 let rebased_substs =
1376 impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1377 let impl_ty_value = tcx.type_of(impl_ty.def_id);
1379 let param_env = tcx.param_env(impl_ty.def_id);
1381 // When checking something like
1383 // trait X { type Y: PartialEq<<Self as X>::Y> }
1384 // impl X for T { default type Y = S; }
1386 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1387 // we want <T as X>::Y to normalize to S. This is valid because we are
1388 // checking the default value specifically here. Add this equality to the
1389 // ParamEnv for normalization specifically.
1390 let normalize_param_env = {
1391 let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
1392 match impl_ty_value.kind() {
1393 ty::Projection(proj)
1394 if proj.item_def_id == trait_ty.def_id && proj.substs == rebased_substs =>
1396 // Don't include this predicate if the projected type is
1397 // exactly the same as the projection. This can occur in
1398 // (somewhat dubious) code like this:
1400 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1402 _ => predicates.push(
1403 ty::Binder::bind_with_vars(
1404 ty::ProjectionPredicate {
1405 projection_ty: ty::ProjectionTy {
1406 item_def_id: trait_ty.def_id,
1407 substs: rebased_substs,
1409 term: impl_ty_value.into(),
1417 tcx.intern_predicates(&predicates),
1419 param_env.constness(),
1422 debug!(?normalize_param_env);
1424 let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1425 let rebased_substs =
1426 impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1428 tcx.infer_ctxt().enter(move |infcx| {
1429 let ocx = ObligationCtxt::new(&infcx);
1431 let mut selcx = traits::SelectionContext::new(&infcx);
1432 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1433 let normalize_cause = ObligationCause::new(
1436 ObligationCauseCode::CheckAssociatedTypeBounds {
1437 impl_item_def_id: impl_ty.def_id.expect_local(),
1438 trait_item_def_id: trait_ty.def_id,
1441 let mk_cause = |span: Span| {
1442 let code = if span.is_dummy() {
1443 traits::MiscObligation
1445 traits::BindingObligation(trait_ty.def_id, span)
1447 ObligationCause::new(impl_ty_span, impl_ty_hir_id, code)
1450 let obligations = tcx
1451 .bound_explicit_item_bounds(trait_ty.def_id)
1453 .map(|e| e.map_bound(|e| *e).transpose_tuple2())
1454 .map(|(bound, span)| {
1456 let concrete_ty_bound = bound.subst(tcx, rebased_substs);
1457 debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
1459 traits::Obligation::new(mk_cause(span.0), param_env, concrete_ty_bound)
1462 debug!("check_type_bounds: item_bounds={:?}", obligations);
1464 for mut obligation in util::elaborate_obligations(tcx, obligations) {
1465 let traits::Normalized { value: normalized_predicate, obligations } = traits::normalize(
1467 normalize_param_env,
1468 normalize_cause.clone(),
1469 obligation.predicate,
1471 debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
1472 obligation.predicate = normalized_predicate;
1474 ocx.register_obligations(obligations);
1475 ocx.register_obligation(obligation);
1478 // Check that all obligations are satisfied by the implementation's
1480 let errors = ocx.select_all_or_error();
1481 if !errors.is_empty() {
1482 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1483 return Err(reported);
1486 // Finally, resolve all regions. This catches wily misuses of
1487 // lifetime parameters.
1488 let implied_bounds = match impl_ty.container {
1489 ty::TraitContainer(_) => FxHashSet::default(),
1490 ty::ImplContainer(def_id) => {
1491 wfcheck::impl_implied_bounds(tcx, param_env, def_id.expect_local(), impl_ty_span)
1494 let mut outlives_environment = OutlivesEnvironment::new(param_env);
1495 outlives_environment.add_implied_bounds(&infcx, implied_bounds, impl_ty_hir_id);
1496 infcx.check_region_obligations_and_report_errors(&outlives_environment);
1502 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1503 match impl_item.kind {
1504 ty::AssocKind::Const => "const",
1505 ty::AssocKind::Fn => "method",
1506 ty::AssocKind::Type => "type",