1 use crate::check::regionck::OutlivesEnvironmentExt;
2 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
3 use rustc_data_structures::stable_set::FxHashSet;
4 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed};
6 use rustc_hir::def::{DefKind, Res};
7 use rustc_hir::intravisit;
8 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
9 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
10 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
11 use rustc_infer::traits::util;
12 use rustc_middle::ty::error::{ExpectedFound, TypeError};
13 use rustc_middle::ty::subst::{InternalSubsts, Subst};
14 use rustc_middle::ty::util::ExplicitSelf;
15 use rustc_middle::ty::{self, DefIdTree};
16 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
18 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
19 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
22 use super::{potentially_plural_count, FnCtxt, Inherited};
24 /// Checks that a method from an impl conforms to the signature of
25 /// the same method as declared in the trait.
29 /// - `impl_m`: type of the method we are checking
30 /// - `impl_m_span`: span to use for reporting errors
31 /// - `trait_m`: the method in the trait
32 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
33 pub(crate) fn compare_impl_method<'tcx>(
35 impl_m: &ty::AssocItem,
36 trait_m: &ty::AssocItem,
37 impl_trait_ref: ty::TraitRef<'tcx>,
38 trait_item_span: Option<Span>,
40 debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
42 let impl_m_span = tcx.def_span(impl_m.def_id);
44 if let Err(_) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref) {
48 if let Err(_) = compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span) {
52 if let Err(_) = compare_generic_param_kinds(tcx, impl_m, trait_m) {
57 compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
62 if let Err(_) = compare_synthetic_generics(tcx, impl_m, trait_m) {
66 if let Err(_) = compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
72 fn compare_predicate_entailment<'tcx>(
74 impl_m: &ty::AssocItem,
76 trait_m: &ty::AssocItem,
77 impl_trait_ref: ty::TraitRef<'tcx>,
78 ) -> Result<(), ErrorGuaranteed> {
79 let trait_to_impl_substs = impl_trait_ref.substs;
81 // This node-id should be used for the `body_id` field on each
82 // `ObligationCause` (and the `FnCtxt`).
84 // FIXME(@lcnr): remove that after removing `cause.body_id` from
86 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
87 // We sometimes modify the span further down.
88 let mut cause = ObligationCause::new(
91 ObligationCauseCode::CompareImplMethodObligation {
92 impl_item_def_id: impl_m.def_id.expect_local(),
93 trait_item_def_id: trait_m.def_id,
97 // This code is best explained by example. Consider a trait:
99 // trait Trait<'t, T> {
100 // fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
105 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
106 // fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo;
109 // We wish to decide if those two method types are compatible.
111 // We start out with trait_to_impl_substs, that maps the trait
112 // type parameters to impl type parameters. This is taken from the
113 // impl trait reference:
115 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
117 // We create a mapping `dummy_substs` that maps from the impl type
118 // parameters to fresh types and regions. For type parameters,
119 // this is the identity transform, but we could as well use any
120 // placeholder types. For regions, we convert from bound to free
121 // regions (Note: but only early-bound regions, i.e., those
122 // declared on the impl or used in type parameter bounds).
124 // impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
126 // Now we can apply placeholder_substs to the type of the impl method
127 // to yield a new function type in terms of our fresh, placeholder
130 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
132 // We now want to extract and substitute the type of the *trait*
133 // method and compare it. To do so, we must create a compound
134 // substitution by combining trait_to_impl_substs and
135 // impl_to_placeholder_substs, and also adding a mapping for the method
136 // type parameters. We extend the mapping to also include
137 // the method parameters.
139 // trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
141 // Applying this to the trait method type yields:
143 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
145 // This type is also the same but the name of the bound region ('a
146 // vs 'b). However, the normal subtyping rules on fn types handle
147 // this kind of equivalency just fine.
149 // We now use these substitutions to ensure that all declared bounds are
150 // satisfied by the implementation's method.
152 // We do this by creating a parameter environment which contains a
153 // substitution corresponding to impl_to_placeholder_substs. We then build
154 // trait_to_placeholder_substs and use it to convert the predicates contained
155 // in the trait_m.generics to the placeholder form.
157 // Finally we register each of these predicates as an obligation in
158 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
160 // Create mapping from impl to placeholder.
161 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
163 // Create mapping from trait to placeholder.
164 let trait_to_placeholder_substs =
165 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
166 debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
168 let impl_m_generics = tcx.generics_of(impl_m.def_id);
169 let trait_m_generics = tcx.generics_of(trait_m.def_id);
170 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
171 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
173 // Check region bounds.
174 check_region_bounds_on_impl_item(
183 // Create obligations for each predicate declared by the impl
184 // definition in the context of the trait's parameter
185 // environment. We can't just use `impl_env.caller_bounds`,
186 // however, because we want to replace all late-bound regions with
188 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
189 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
191 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
193 // This is the only tricky bit of the new way we check implementation methods
194 // We need to build a set of predicates where only the method-level bounds
195 // are from the trait and we assume all other bounds from the implementation
196 // to be previously satisfied.
198 // We then register the obligations from the impl_m and check to see
199 // if all constraints hold.
202 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
204 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
205 // The key step here is to update the caller_bounds's predicates to be
206 // the new hybrid bounds we computed.
207 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
208 let param_env = ty::ParamEnv::new(
209 tcx.intern_predicates(&hybrid_preds.predicates),
211 hir::Constness::NotConst,
213 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
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 for (predicate, span) in iter::zip(impl_m_own_bounds.predicates, impl_m_own_bounds.spans) {
225 let normalize_cause = traits::ObligationCause::misc(span, impl_m_hir_id);
226 let traits::Normalized { value: predicate, obligations } =
227 traits::normalize(&mut selcx, param_env, normalize_cause, predicate);
229 inh.register_predicates(obligations);
230 let cause = ObligationCause::new(
233 ObligationCauseCode::CompareImplMethodObligation {
234 impl_item_def_id: impl_m.def_id.expect_local(),
235 trait_item_def_id: trait_m.def_id,
238 inh.register_predicate(traits::Obligation::new(cause, param_env, predicate));
241 // We now need to check that the signature of the impl method is
242 // compatible with that of the trait method. We do this by
243 // checking that `impl_fty <: trait_fty`.
245 // FIXME. Unfortunately, this doesn't quite work right now because
246 // associated type normalization is not integrated into subtype
247 // checks. For the comparison to be valid, we need to
248 // normalize the associated types in the impl/trait methods
249 // first. However, because function types bind regions, just
250 // calling `normalize_associated_types_in` would have no effect on
251 // any associated types appearing in the fn arguments or return
254 // Compute placeholder form of impl and trait method tys.
257 let mut wf_tys = FxHashSet::default();
259 let impl_sig = infcx.replace_bound_vars_with_fresh_vars(
261 infer::HigherRankedType,
262 tcx.fn_sig(impl_m.def_id),
265 inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, impl_sig);
266 let impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig));
267 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
269 let trait_sig = tcx.bound_fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs);
270 let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig);
272 inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, trait_sig);
273 // Add the resulting inputs and output as well-formed.
274 wf_tys.extend(trait_sig.inputs_and_output.iter());
275 let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
277 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
279 let sub_result = infcx.at(&cause, param_env).sup(trait_fty, impl_fty).map(
280 |InferOk { obligations, .. }| {
281 // FIXME: We'd want to keep more accurate spans than "the method signature" when
282 // processing the comparison between the trait and impl fn, but we sadly lose them
283 // and point at the whole signature when a trait bound or specific input or output
284 // type would be more appropriate. In other places we have a `Vec<Span>`
285 // corresponding to their `Vec<Predicate>`, but we don't have that here.
286 // Fixing this would improve the output of test `issue-83765.rs`.
287 inh.register_predicates(obligations);
291 if let Err(terr) = sub_result {
292 debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
294 let (impl_err_span, trait_err_span) =
295 extract_spans_for_error_reporting(&infcx, &terr, &cause, impl_m, trait_m);
297 cause.span = impl_err_span;
299 let mut diag = struct_span_err!(
303 "method `{}` has an incompatible type for trait",
307 TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
308 if trait_m.fn_has_self_parameter =>
310 let ty = trait_sig.inputs()[0];
311 let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty())
313 ExplicitSelf::ByValue => "self".to_owned(),
314 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
315 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => {
316 "&mut self".to_owned()
318 _ => format!("self: {ty}"),
321 // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
322 // span points only at the type `Box<Self`>, but we want to cover the whole
323 // argument pattern and type.
324 let span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
325 ImplItemKind::Fn(ref sig, body) => tcx
327 .body_param_names(body)
328 .zip(sig.decl.inputs.iter())
329 .map(|(param, ty)| param.span.to(ty.span))
331 .unwrap_or(impl_err_span),
332 _ => bug!("{:?} is not a method", impl_m),
335 diag.span_suggestion(
337 "change the self-receiver type to match the trait",
339 Applicability::MachineApplicable,
342 TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
343 if trait_sig.inputs().len() == *i {
344 // Suggestion to change output type. We do not suggest in `async` functions
345 // to avoid complex logic or incorrect output.
346 match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
347 ImplItemKind::Fn(ref sig, _)
348 if sig.header.asyncness == hir::IsAsync::NotAsync =>
350 let msg = "change the output type to match the trait";
351 let ap = Applicability::MachineApplicable;
352 match sig.decl.output {
353 hir::FnRetTy::DefaultReturn(sp) => {
354 let sugg = format!("-> {} ", trait_sig.output());
355 diag.span_suggestion_verbose(sp, msg, sugg, ap);
357 hir::FnRetTy::Return(hir_ty) => {
358 let sugg = trait_sig.output();
359 diag.span_suggestion(hir_ty.span, msg, sugg, ap);
365 } else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
366 diag.span_suggestion(
368 "change the parameter type to match the trait",
370 Applicability::MachineApplicable,
380 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
381 Some(infer::ValuePairs::Terms(ExpectedFound {
382 expected: trait_fty.into(),
383 found: impl_fty.into(),
390 return Err(diag.emit());
393 // Check that all obligations are satisfied by the implementation's
395 let errors = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx);
396 if !errors.is_empty() {
397 let reported = infcx.report_fulfillment_errors(&errors, None, false);
398 return Err(reported);
401 // Finally, resolve all regions. This catches wily misuses of
402 // lifetime parameters.
403 let mut outlives_environment = OutlivesEnvironment::new(param_env);
404 outlives_environment.add_implied_bounds(infcx, wf_tys, impl_m_hir_id);
405 infcx.check_region_obligations_and_report_errors(&outlives_environment);
411 fn check_region_bounds_on_impl_item<'tcx>(
414 impl_m: &ty::AssocItem,
415 trait_m: &ty::AssocItem,
416 trait_generics: &ty::Generics,
417 impl_generics: &ty::Generics,
418 ) -> Result<(), ErrorGuaranteed> {
419 let trait_params = trait_generics.own_counts().lifetimes;
420 let impl_params = impl_generics.own_counts().lifetimes;
423 "check_region_bounds_on_impl_item: \
424 trait_generics={:?} \
426 trait_generics, impl_generics
429 // Must have same number of early-bound lifetime parameters.
430 // Unfortunately, if the user screws up the bounds, then this
431 // will change classification between early and late. E.g.,
432 // if in trait we have `<'a,'b:'a>`, and in impl we just have
433 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
434 // in trait but 0 in the impl. But if we report "expected 2
435 // but found 0" it's confusing, because it looks like there
436 // are zero. Since I don't quite know how to phrase things at
437 // the moment, give a kind of vague error message.
438 if trait_params != impl_params {
439 let item_kind = assoc_item_kind_str(impl_m);
440 let def_span = tcx.sess.source_map().guess_head_span(span);
444 .and_then(|did| tcx.hir().get_generics(did))
445 .map_or(def_span, |g| g.span);
446 let generics_span = trait_m.def_id.as_local().map(|did| {
447 let def_sp = tcx.def_span(did);
448 tcx.hir().get_generics(did).map_or(def_sp, |g| g.span)
451 let reported = tcx.sess.emit_err(LifetimesOrBoundsMismatchOnTrait {
454 ident: impl_m.ident(tcx),
457 return Err(reported);
463 #[instrument(level = "debug", skip(infcx))]
464 fn extract_spans_for_error_reporting<'a, 'tcx>(
465 infcx: &infer::InferCtxt<'a, 'tcx>,
466 terr: &TypeError<'_>,
467 cause: &ObligationCause<'tcx>,
468 impl_m: &ty::AssocItem,
469 trait_m: &ty::AssocItem,
470 ) -> (Span, Option<Span>) {
472 let mut impl_args = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
473 ImplItemKind::Fn(ref sig, _) => {
474 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
476 _ => bug!("{:?} is not a method", impl_m),
479 trait_m.def_id.as_local().map(|def_id| match tcx.hir().expect_trait_item(def_id).kind {
480 TraitItemKind::Fn(ref sig, _) => {
481 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
483 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
487 TypeError::ArgumentMutability(i) => {
488 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
490 TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
491 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
493 _ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
497 fn compare_self_type<'tcx>(
499 impl_m: &ty::AssocItem,
501 trait_m: &ty::AssocItem,
502 impl_trait_ref: ty::TraitRef<'tcx>,
503 ) -> Result<(), ErrorGuaranteed> {
504 // Try to give more informative error messages about self typing
505 // mismatches. Note that any mismatch will also be detected
506 // below, where we construct a canonical function type that
507 // includes the self parameter as a normal parameter. It's just
508 // that the error messages you get out of this code are a bit more
509 // inscrutable, particularly for cases where one method has no
512 let self_string = |method: &ty::AssocItem| {
513 let untransformed_self_ty = match method.container {
514 ty::ImplContainer(_) => impl_trait_ref.self_ty(),
515 ty::TraitContainer(_) => tcx.types.self_param,
517 let self_arg_ty = tcx.fn_sig(method.def_id).input(0);
518 let param_env = ty::ParamEnv::reveal_all();
520 tcx.infer_ctxt().enter(|infcx| {
521 let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
522 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
523 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
524 ExplicitSelf::ByValue => "self".to_owned(),
525 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
526 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
527 _ => format!("self: {self_arg_ty}"),
532 match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
533 (false, false) | (true, true) => {}
536 let self_descr = self_string(impl_m);
537 let mut err = struct_span_err!(
541 "method `{}` has a `{}` declaration in the impl, but not in the trait",
545 err.span_label(impl_m_span, format!("`{self_descr}` used in impl"));
546 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
547 err.span_label(span, format!("trait method declared without `{self_descr}`"));
549 err.note_trait_signature(trait_m.name.to_string(), trait_m.signature(tcx));
551 let reported = err.emit();
552 return Err(reported);
556 let self_descr = self_string(trait_m);
557 let mut err = struct_span_err!(
561 "method `{}` has a `{}` declaration in the trait, but not in the impl",
565 err.span_label(impl_m_span, format!("expected `{self_descr}` in impl"));
566 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
567 err.span_label(span, format!("`{self_descr}` used in trait"));
569 err.note_trait_signature(trait_m.name.to_string(), trait_m.signature(tcx));
571 let reported = err.emit();
572 return Err(reported);
579 /// Checks that the number of generics on a given assoc item in a trait impl is the same
580 /// as the number of generics on the respective assoc item in the trait definition.
582 /// For example this code emits the errors in the following code:
589 /// impl Trait for () {
592 /// type Assoc = u32;
597 /// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
598 /// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
599 /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
600 fn compare_number_of_generics<'tcx>(
602 impl_: &ty::AssocItem,
604 trait_: &ty::AssocItem,
605 trait_span: Option<Span>,
606 ) -> Result<(), ErrorGuaranteed> {
607 let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
608 let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
610 // This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
611 // in `compare_generic_param_kinds` which will give a nicer error message than something like:
612 // "expected 1 type parameter, found 0 type parameters"
613 if (trait_own_counts.types + trait_own_counts.consts)
614 == (impl_own_counts.types + impl_own_counts.consts)
620 ("type", trait_own_counts.types, impl_own_counts.types),
621 ("const", trait_own_counts.consts, impl_own_counts.consts),
624 let item_kind = assoc_item_kind_str(impl_);
626 let mut err_occurred = None;
627 for (kind, trait_count, impl_count) in matchings {
628 if impl_count != trait_count {
629 let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| {
630 let mut spans = generics
633 .filter(|p| match p.kind {
634 hir::GenericParamKind::Lifetime {
635 kind: hir::LifetimeParamKind::Elided,
637 // A fn can have an arbitrary number of extra elided lifetimes for the
639 !matches!(kind, ty::AssocKind::Fn)
644 .collect::<Vec<Span>>();
645 if spans.is_empty() {
646 spans = vec![generics.span]
650 let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
651 let trait_item = tcx.hir().expect_trait_item(def_id);
652 let arg_spans: Vec<Span> = arg_spans(trait_.kind, trait_item.generics);
653 let impl_trait_spans: Vec<Span> = trait_item
657 .filter_map(|p| match p.kind {
658 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
662 (Some(arg_spans), impl_trait_spans)
664 (trait_span.map(|s| vec![s]), vec![])
667 let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local());
668 let impl_item_impl_trait_spans: Vec<Span> = impl_item
672 .filter_map(|p| match p.kind {
673 GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
677 let spans = arg_spans(impl_.kind, impl_item.generics);
678 let span = spans.first().copied();
680 let mut err = tcx.sess.struct_span_err_with_code(
683 "{} `{}` has {} {kind} parameter{} but its trait \
684 declaration has {} {kind} parameter{}",
688 pluralize!(impl_count),
690 pluralize!(trait_count),
693 DiagnosticId::Error("E0049".into()),
696 let mut suffix = None;
698 if let Some(spans) = trait_spans {
699 let mut spans = spans.iter();
700 if let Some(span) = spans.next() {
704 "expected {} {} parameter{}",
707 pluralize!(trait_count),
712 err.span_label(*span, "");
715 suffix = Some(format!(", expected {trait_count}"));
718 if let Some(span) = span {
722 "found {} {} parameter{}{}",
725 pluralize!(impl_count),
726 suffix.unwrap_or_else(String::new),
731 for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
732 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
735 let reported = err.emit();
736 err_occurred = Some(reported);
740 if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) }
743 fn compare_number_of_method_arguments<'tcx>(
745 impl_m: &ty::AssocItem,
747 trait_m: &ty::AssocItem,
748 trait_item_span: Option<Span>,
749 ) -> Result<(), ErrorGuaranteed> {
750 let impl_m_fty = tcx.fn_sig(impl_m.def_id);
751 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
752 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
753 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
754 if trait_number_args != impl_number_args {
755 let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
756 match tcx.hir().expect_trait_item(def_id).kind {
757 TraitItemKind::Fn(ref trait_m_sig, _) => {
758 let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
759 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
763 arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
769 _ => bug!("{:?} is not a method", impl_m),
774 let impl_span = match tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind {
775 ImplItemKind::Fn(ref impl_m_sig, _) => {
776 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
777 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
781 arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
787 _ => bug!("{:?} is not a method", impl_m),
789 let mut err = struct_span_err!(
793 "method `{}` has {} but the declaration in trait `{}` has {}",
795 potentially_plural_count(impl_number_args, "parameter"),
796 tcx.def_path_str(trait_m.def_id),
799 if let Some(trait_span) = trait_span {
804 potentially_plural_count(trait_number_args, "parameter")
808 err.note_trait_signature(trait_m.name.to_string(), trait_m.signature(tcx));
813 "expected {}, found {}",
814 potentially_plural_count(trait_number_args, "parameter"),
818 let reported = err.emit();
819 return Err(reported);
825 fn compare_synthetic_generics<'tcx>(
827 impl_m: &ty::AssocItem,
828 trait_m: &ty::AssocItem,
829 ) -> Result<(), ErrorGuaranteed> {
830 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
831 // 1. Better messages for the span labels
832 // 2. Explanation as to what is going on
833 // If we get here, we already have the same number of generics, so the zip will
835 let mut error_found = None;
836 let impl_m_generics = tcx.generics_of(impl_m.def_id);
837 let trait_m_generics = tcx.generics_of(trait_m.def_id);
838 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
839 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
840 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
842 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
843 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
844 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
846 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
847 iter::zip(impl_m_type_params, trait_m_type_params)
849 if impl_synthetic != trait_synthetic {
850 let impl_def_id = impl_def_id.expect_local();
851 let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_def_id);
852 let impl_span = tcx.hir().span(impl_hir_id);
853 let trait_span = tcx.def_span(trait_def_id);
854 let mut err = struct_span_err!(
858 "method `{}` has incompatible signature for trait",
861 err.span_label(trait_span, "declaration in trait here");
862 match (impl_synthetic, trait_synthetic) {
863 // The case where the impl method uses `impl Trait` but the trait method uses
866 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
868 // try taking the name from the trait impl
869 // FIXME: this is obviously suboptimal since the name can already be used
870 // as another generic argument
871 let new_name = tcx.sess.source_map().span_to_snippet(trait_span).ok()?;
872 let trait_m = trait_m.def_id.as_local()?;
873 let trait_m = tcx.hir().trait_item(hir::TraitItemId { def_id: trait_m });
875 let impl_m = impl_m.def_id.as_local()?;
876 let impl_m = tcx.hir().impl_item(hir::ImplItemId { def_id: impl_m });
878 // in case there are no generics, take the spot between the function name
879 // and the opening paren of the argument list
880 let new_generics_span =
881 tcx.sess.source_map().generate_fn_name_span(impl_span)?.shrink_to_hi();
882 // in case there are generics, just replace them
884 impl_m.generics.span.substitute_dummy(new_generics_span);
885 // replace with the generics from the trait
887 tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
889 err.multipart_suggestion(
890 "try changing the `impl Trait` argument to a generic parameter",
892 // replace `impl Trait` with `T`
893 (impl_span, new_name),
894 // replace impl method generics with trait method generics
895 // This isn't quite right, as users might have changed the names
896 // of the generics, but it works for the common case
897 (generics_span, new_generics),
899 Applicability::MaybeIncorrect,
904 // The case where the trait method uses `impl Trait`, but the impl method uses
905 // explicit generics.
907 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
909 let impl_m = impl_m.def_id.as_local()?;
910 let impl_m = tcx.hir().impl_item(hir::ImplItemId { def_id: impl_m });
911 let input_tys = match impl_m.kind {
912 hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
915 struct Visitor(Option<Span>, hir::def_id::LocalDefId);
916 impl<'v> intravisit::Visitor<'v> for Visitor {
917 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
918 intravisit::walk_ty(self, ty);
919 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
921 && let Res::Def(DefKind::TyParam, def_id) = path.res
922 && def_id == self.1.to_def_id()
924 self.0 = Some(ty.span);
928 let mut visitor = Visitor(None, impl_def_id);
929 for ty in input_tys {
930 intravisit::Visitor::visit_ty(&mut visitor, ty);
932 let span = visitor.0?;
934 let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds;
935 let bounds = bounds.first()?.span().to(bounds.last()?.span());
936 let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
938 err.multipart_suggestion(
939 "try removing the generic parameter and using `impl Trait` instead",
941 // delete generic parameters
942 (impl_m.generics.span, String::new()),
943 // replace param usage with `impl Trait`
944 (span, format!("impl {bounds}")),
946 Applicability::MaybeIncorrect,
953 let reported = err.emit();
954 error_found = Some(reported);
957 if let Some(reported) = error_found { Err(reported) } else { Ok(()) }
960 /// Checks that all parameters in the generics of a given assoc item in a trait impl have
961 /// the same kind as the respective generic parameter in the trait def.
963 /// For example all 4 errors in the following code are emitted here:
966 /// fn foo<const N: u8>();
967 /// type bar<const N: u8>;
968 /// fn baz<const N: u32>();
972 /// impl Foo for () {
973 /// fn foo<const N: u64>() {}
975 /// type bar<const N: u64> {}
979 /// type blah<const N: i64> = u32;
984 /// This function does not handle lifetime parameters
985 fn compare_generic_param_kinds<'tcx>(
987 impl_item: &ty::AssocItem,
988 trait_item: &ty::AssocItem,
989 ) -> Result<(), ErrorGuaranteed> {
990 assert_eq!(impl_item.kind, trait_item.kind);
992 let ty_const_params_of = |def_id| {
993 tcx.generics_of(def_id).params.iter().filter(|param| {
996 GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. }
1001 for (param_impl, param_trait) in
1002 iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id))
1004 use GenericParamDefKind::*;
1005 if match (¶m_impl.kind, ¶m_trait.kind) {
1006 (Const { .. }, Const { .. })
1007 if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) =>
1011 (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true,
1012 // this is exhaustive so that anyone adding new generic param kinds knows
1013 // to make sure this error is reported for them.
1014 (Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false,
1015 (Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(),
1017 let param_impl_span = tcx.def_span(param_impl.def_id);
1018 let param_trait_span = tcx.def_span(param_trait.def_id);
1020 let mut err = struct_span_err!(
1024 "{} `{}` has an incompatible generic parameter for trait `{}`",
1025 assoc_item_kind_str(&impl_item),
1027 &tcx.def_path_str(tcx.parent(trait_item.def_id))
1030 let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind {
1032 format!("{} const parameter of type `{}`", prefix, tcx.type_of(param.def_id))
1034 Type { .. } => format!("{} type parameter", prefix),
1035 Lifetime { .. } => unreachable!(),
1038 let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap();
1039 err.span_label(trait_header_span, "");
1040 err.span_label(param_trait_span, make_param_message("expected", param_trait));
1042 let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id));
1043 err.span_label(impl_header_span, "");
1044 err.span_label(param_impl_span, make_param_message("found", param_impl));
1046 let reported = err.emit();
1047 return Err(reported);
1054 pub(crate) fn compare_const_impl<'tcx>(
1056 impl_c: &ty::AssocItem,
1058 trait_c: &ty::AssocItem,
1059 impl_trait_ref: ty::TraitRef<'tcx>,
1061 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
1063 tcx.infer_ctxt().enter(|infcx| {
1064 let param_env = tcx.param_env(impl_c.def_id);
1065 let inh = Inherited::new(infcx, impl_c.def_id.expect_local());
1066 let infcx = &inh.infcx;
1068 // The below is for the most part highly similar to the procedure
1069 // for methods above. It is simpler in many respects, especially
1070 // because we shouldn't really have to deal with lifetimes or
1071 // predicates. In fact some of this should probably be put into
1072 // shared functions because of DRY violations...
1073 let trait_to_impl_substs = impl_trait_ref.substs;
1075 // Create a parameter environment that represents the implementation's
1077 let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_c.def_id.expect_local());
1079 // Compute placeholder form of impl and trait const tys.
1080 let impl_ty = tcx.type_of(impl_c.def_id);
1081 let trait_ty = tcx.bound_type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
1082 let mut cause = ObligationCause::new(
1085 ObligationCauseCode::CompareImplConstObligation,
1088 // There is no "body" here, so just pass dummy id.
1090 inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, impl_ty);
1092 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
1095 inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, trait_ty);
1097 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
1100 .at(&cause, param_env)
1101 .sup(trait_ty, impl_ty)
1102 .map(|ok| inh.register_infer_ok_obligations(ok));
1104 if let Err(terr) = err {
1106 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
1110 // Locate the Span containing just the type of the offending impl
1111 match tcx.hir().expect_impl_item(impl_c.def_id.expect_local()).kind {
1112 ImplItemKind::Const(ref ty, _) => cause.span = ty.span,
1113 _ => bug!("{:?} is not a impl const", impl_c),
1116 let mut diag = struct_span_err!(
1120 "implemented const `{}` has an incompatible type for trait",
1124 let trait_c_span = trait_c.def_id.as_local().map(|trait_c_def_id| {
1125 // Add a label to the Span containing just the type of the const
1126 match tcx.hir().expect_trait_item(trait_c_def_id).kind {
1127 TraitItemKind::Const(ref ty, _) => ty.span,
1128 _ => bug!("{:?} is not a trait const", trait_c),
1132 infcx.note_type_err(
1135 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1136 Some(infer::ValuePairs::Terms(ExpectedFound {
1137 expected: trait_ty.into(),
1138 found: impl_ty.into(),
1147 // Check that all obligations are satisfied by the implementation's
1149 let errors = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx);
1150 if !errors.is_empty() {
1151 infcx.report_fulfillment_errors(&errors, None, false);
1155 let outlives_environment = OutlivesEnvironment::new(param_env);
1156 infcx.resolve_regions_and_report_errors(&outlives_environment);
1160 pub(crate) fn compare_ty_impl<'tcx>(
1162 impl_ty: &ty::AssocItem,
1164 trait_ty: &ty::AssocItem,
1165 impl_trait_ref: ty::TraitRef<'tcx>,
1166 trait_item_span: Option<Span>,
1168 debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1170 let _: Result<(), ErrorGuaranteed> = (|| {
1171 compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1173 compare_generic_param_kinds(tcx, impl_ty, trait_ty)?;
1175 let sp = tcx.def_span(impl_ty.def_id);
1176 compare_type_predicate_entailment(tcx, impl_ty, sp, trait_ty, impl_trait_ref)?;
1178 check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)
1182 /// The equivalent of [compare_predicate_entailment], but for associated types
1183 /// instead of associated functions.
1184 fn compare_type_predicate_entailment<'tcx>(
1186 impl_ty: &ty::AssocItem,
1188 trait_ty: &ty::AssocItem,
1189 impl_trait_ref: ty::TraitRef<'tcx>,
1190 ) -> Result<(), ErrorGuaranteed> {
1191 let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1192 let trait_to_impl_substs =
1193 impl_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1195 let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1196 let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1197 let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1198 let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1200 check_region_bounds_on_impl_item(
1209 let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1211 if impl_ty_own_bounds.is_empty() {
1212 // Nothing to check.
1216 // This `HirId` should be used for the `body_id` field on each
1217 // `ObligationCause` (and the `FnCtxt`). This is what
1218 // `regionck_item` expects.
1219 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1220 let cause = ObligationCause::new(
1223 ObligationCauseCode::CompareImplTypeObligation {
1224 impl_item_def_id: impl_ty.def_id.expect_local(),
1225 trait_item_def_id: trait_ty.def_id,
1229 debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1231 // The predicates declared by the impl definition, the trait and the
1232 // associated type in the trait are assumed.
1233 let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1234 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1237 .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1239 debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1241 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1242 let param_env = ty::ParamEnv::new(
1243 tcx.intern_predicates(&hybrid_preds.predicates),
1245 hir::Constness::NotConst,
1247 let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause.clone());
1248 tcx.infer_ctxt().enter(|infcx| {
1249 let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
1250 let infcx = &inh.infcx;
1252 debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
1254 let mut selcx = traits::SelectionContext::new(&infcx);
1256 for predicate in impl_ty_own_bounds.predicates {
1257 let traits::Normalized { value: predicate, obligations } =
1258 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), predicate);
1260 inh.register_predicates(obligations);
1261 inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
1264 // Check that all obligations are satisfied by the implementation's
1266 let errors = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx);
1267 if !errors.is_empty() {
1268 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1269 return Err(reported);
1272 // Finally, resolve all regions. This catches wily misuses of
1273 // lifetime parameters.
1274 let outlives_environment = OutlivesEnvironment::new(param_env);
1275 infcx.check_region_obligations_and_report_errors(&outlives_environment);
1281 /// Validate that `ProjectionCandidate`s created for this associated type will
1286 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1288 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1289 /// impl is well-formed we have to prove `S: Copy`.
1291 /// For default associated types the normalization is not possible (the value
1292 /// from the impl could be overridden). We also can't normalize generic
1293 /// associated types (yet) because they contain bound parameters.
1294 #[tracing::instrument(level = "debug", skip(tcx))]
1295 pub fn check_type_bounds<'tcx>(
1297 trait_ty: &ty::AssocItem,
1298 impl_ty: &ty::AssocItem,
1300 impl_trait_ref: ty::TraitRef<'tcx>,
1301 ) -> Result<(), ErrorGuaranteed> {
1304 // impl<A, B> Foo<u32> for (A, B) {
1308 // - `impl_trait_ref` would be `<(A, B) as Foo<u32>>
1309 // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
1310 // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
1311 // the *trait* with the generic associated type parameters (as bound vars).
1313 // A note regarding the use of bound vars here:
1314 // Imagine as an example
1317 // type Member<C: Eq>;
1320 // impl Family for VecFamily {
1321 // type Member<C: Eq> = i32;
1324 // Here, we would generate
1326 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
1328 // when we really would like to generate
1330 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
1332 // But, this is probably fine, because although the first clause can be used with types C that
1333 // do not implement Eq, for it to cause some kind of problem, there would have to be a
1334 // VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
1335 // Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
1336 // elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
1337 // the trait (notably, that X: Eq and T: Family).
1338 let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id);
1339 let mut substs = smallvec::SmallVec::with_capacity(defs.count());
1340 if let Some(def_id) = defs.parent {
1341 let parent_defs = tcx.generics_of(def_id);
1342 InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| {
1343 tcx.mk_param_from_def(param)
1346 let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
1347 smallvec::SmallVec::with_capacity(defs.count());
1348 InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind {
1349 GenericParamDefKind::Type { .. } => {
1350 let kind = ty::BoundTyKind::Param(param.name);
1351 let bound_var = ty::BoundVariableKind::Ty(kind);
1352 bound_vars.push(bound_var);
1353 tcx.mk_ty(ty::Bound(
1355 ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1359 GenericParamDefKind::Lifetime => {
1360 let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
1361 let bound_var = ty::BoundVariableKind::Region(kind);
1362 bound_vars.push(bound_var);
1363 tcx.mk_region(ty::ReLateBound(
1365 ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1369 GenericParamDefKind::Const { .. } => {
1370 let bound_var = ty::BoundVariableKind::Const;
1371 bound_vars.push(bound_var);
1372 tcx.mk_const(ty::ConstS {
1373 ty: tcx.type_of(param.def_id),
1374 kind: ty::ConstKind::Bound(
1376 ty::BoundVar::from_usize(bound_vars.len() - 1),
1382 let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter());
1383 let impl_ty_substs = tcx.intern_substs(&substs);
1385 let rebased_substs =
1386 impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1387 let impl_ty_value = tcx.type_of(impl_ty.def_id);
1389 let param_env = tcx.param_env(impl_ty.def_id);
1391 // When checking something like
1393 // trait X { type Y: PartialEq<<Self as X>::Y> }
1394 // impl X for T { default type Y = S; }
1396 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1397 // we want <T as X>::Y to normalize to S. This is valid because we are
1398 // checking the default value specifically here. Add this equality to the
1399 // ParamEnv for normalization specifically.
1400 let normalize_param_env = {
1401 let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
1402 match impl_ty_value.kind() {
1403 ty::Projection(proj)
1404 if proj.item_def_id == trait_ty.def_id && proj.substs == rebased_substs =>
1406 // Don't include this predicate if the projected type is
1407 // exactly the same as the projection. This can occur in
1408 // (somewhat dubious) code like this:
1410 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1412 _ => predicates.push(
1413 ty::Binder::bind_with_vars(
1414 ty::ProjectionPredicate {
1415 projection_ty: ty::ProjectionTy {
1416 item_def_id: trait_ty.def_id,
1417 substs: rebased_substs,
1419 term: impl_ty_value.into(),
1427 tcx.intern_predicates(&predicates),
1429 param_env.constness(),
1432 debug!(?normalize_param_env);
1434 let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1435 let rebased_substs =
1436 impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1438 tcx.infer_ctxt().enter(move |infcx| {
1439 let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
1440 let infcx = &inh.infcx;
1441 let mut selcx = traits::SelectionContext::new(&infcx);
1443 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1444 let normalize_cause = ObligationCause::new(
1447 ObligationCauseCode::CheckAssociatedTypeBounds {
1448 impl_item_def_id: impl_ty.def_id.expect_local(),
1449 trait_item_def_id: trait_ty.def_id,
1452 let mk_cause = |span: Span| {
1453 let code = if span.is_dummy() {
1454 traits::MiscObligation
1456 traits::BindingObligation(trait_ty.def_id, span)
1458 ObligationCause::new(impl_ty_span, impl_ty_hir_id, code)
1461 let obligations = tcx
1462 .bound_explicit_item_bounds(trait_ty.def_id)
1464 .map(|e| e.map_bound(|e| *e).transpose_tuple2())
1465 .map(|(bound, span)| {
1467 let concrete_ty_bound = bound.subst(tcx, rebased_substs);
1468 debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
1470 traits::Obligation::new(mk_cause(span.0), param_env, concrete_ty_bound)
1473 debug!("check_type_bounds: item_bounds={:?}", obligations);
1475 for mut obligation in util::elaborate_obligations(tcx, obligations) {
1476 let traits::Normalized { value: normalized_predicate, obligations } = traits::normalize(
1478 normalize_param_env,
1479 normalize_cause.clone(),
1480 obligation.predicate,
1482 debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
1483 obligation.predicate = normalized_predicate;
1485 inh.register_predicates(obligations);
1486 inh.register_predicate(obligation);
1489 // Check that all obligations are satisfied by the implementation's
1491 let errors = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx);
1492 if !errors.is_empty() {
1493 let reported = infcx.report_fulfillment_errors(&errors, None, false);
1494 return Err(reported);
1497 // Finally, resolve all regions. This catches wily misuses of
1498 // lifetime parameters.
1500 // FIXME: Remove that `FnCtxt`.
1501 let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1502 let implied_bounds = match impl_ty.container {
1503 ty::TraitContainer(_) => FxHashSet::default(),
1504 ty::ImplContainer(def_id) => fcx.impl_implied_bounds(def_id, impl_ty_span),
1506 let mut outlives_environment = OutlivesEnvironment::new(param_env);
1507 outlives_environment.add_implied_bounds(infcx, implied_bounds, impl_ty_hir_id);
1508 infcx.check_region_obligations_and_report_errors(&outlives_environment);
1514 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1515 match impl_item.kind {
1516 ty::AssocKind::Const => "const",
1517 ty::AssocKind::Fn => "method",
1518 ty::AssocKind::Type => "type",