1 use crate::errors::LifetimesOrBoundsMismatchOnTrait;
2 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorReported};
4 use rustc_hir::def::{DefKind, Res};
5 use rustc_hir::intravisit;
6 use rustc_hir::{GenericParamKind, ImplItemKind, TraitItemKind};
7 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
8 use rustc_infer::traits::util;
10 use rustc_middle::ty::error::{ExpectedFound, TypeError};
11 use rustc_middle::ty::subst::{InternalSubsts, Subst};
12 use rustc_middle::ty::util::ExplicitSelf;
13 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
15 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
16 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode, Reveal};
19 use super::{potentially_plural_count, FnCtxt, Inherited};
21 /// Checks that a method from an impl conforms to the signature of
22 /// the same method as declared in the trait.
26 /// - `impl_m`: type of the method we are checking
27 /// - `impl_m_span`: span to use for reporting errors
28 /// - `trait_m`: the method in the trait
29 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
31 crate fn compare_impl_method<'tcx>(
33 impl_m: &ty::AssocItem,
35 trait_m: &ty::AssocItem,
36 impl_trait_ref: ty::TraitRef<'tcx>,
37 trait_item_span: Option<Span>,
39 debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
41 let impl_m_span = tcx.sess.source_map().guess_head_span(impl_m_span);
43 if let Err(ErrorReported) = compare_self_type(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
48 if let Err(ErrorReported) =
49 compare_number_of_generics(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
54 if let Err(ErrorReported) =
55 compare_number_of_method_arguments(tcx, impl_m, impl_m_span, trait_m, trait_item_span)
60 if let Err(ErrorReported) = compare_synthetic_generics(tcx, impl_m, trait_m) {
64 if let Err(ErrorReported) =
65 compare_predicate_entailment(tcx, impl_m, impl_m_span, trait_m, impl_trait_ref)
70 if let Err(ErrorReported) = compare_const_param_types(tcx, impl_m, trait_m, trait_item_span) {
75 fn compare_predicate_entailment<'tcx>(
77 impl_m: &ty::AssocItem,
79 trait_m: &ty::AssocItem,
80 impl_trait_ref: ty::TraitRef<'tcx>,
81 ) -> Result<(), ErrorReported> {
82 let trait_to_impl_substs = impl_trait_ref.substs;
84 // This node-id should be used for the `body_id` field on each
85 // `ObligationCause` (and the `FnCtxt`). This is what
86 // `regionck_item` expects.
87 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 item_name: impl_m.ident.name,
95 impl_item_def_id: impl_m.def_id,
96 trait_item_def_id: trait_m.def_id,
100 // This code is best explained by example. Consider a trait:
102 // trait Trait<'t, T> {
103 // fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
108 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
109 // fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo;
112 // We wish to decide if those two method types are compatible.
114 // We start out with trait_to_impl_substs, that maps the trait
115 // type parameters to impl type parameters. This is taken from the
116 // impl trait reference:
118 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
120 // We create a mapping `dummy_substs` that maps from the impl type
121 // parameters to fresh types and regions. For type parameters,
122 // this is the identity transform, but we could as well use any
123 // placeholder types. For regions, we convert from bound to free
124 // regions (Note: but only early-bound regions, i.e., those
125 // declared on the impl or used in type parameter bounds).
127 // impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
129 // Now we can apply placeholder_substs to the type of the impl method
130 // to yield a new function type in terms of our fresh, placeholder
133 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
135 // We now want to extract and substitute the type of the *trait*
136 // method and compare it. To do so, we must create a compound
137 // substitution by combining trait_to_impl_substs and
138 // impl_to_placeholder_substs, and also adding a mapping for the method
139 // type parameters. We extend the mapping to also include
140 // the method parameters.
142 // trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
144 // Applying this to the trait method type yields:
146 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
148 // This type is also the same but the name of the bound region ('a
149 // vs 'b). However, the normal subtyping rules on fn types handle
150 // this kind of equivalency just fine.
152 // We now use these substitutions to ensure that all declared bounds are
153 // satisfied by the implementation's method.
155 // We do this by creating a parameter environment which contains a
156 // substitution corresponding to impl_to_placeholder_substs. We then build
157 // trait_to_placeholder_substs and use it to convert the predicates contained
158 // in the trait_m.generics to the placeholder form.
160 // Finally we register each of these predicates as an obligation in
161 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
163 // Create mapping from impl to placeholder.
164 let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
166 // Create mapping from trait to placeholder.
167 let trait_to_placeholder_substs =
168 impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container.id(), trait_to_impl_substs);
169 debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
171 let impl_m_generics = tcx.generics_of(impl_m.def_id);
172 let trait_m_generics = tcx.generics_of(trait_m.def_id);
173 let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
174 let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
176 // Check region bounds.
177 check_region_bounds_on_impl_item(
186 // Create obligations for each predicate declared by the impl
187 // definition in the context of the trait's parameter
188 // environment. We can't just use `impl_env.caller_bounds`,
189 // however, because we want to replace all late-bound regions with
191 let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
192 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
194 debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
196 // This is the only tricky bit of the new way we check implementation methods
197 // We need to build a set of predicates where only the method-level bounds
198 // are from the trait and we assume all other bounds from the implementation
199 // to be previously satisfied.
201 // We then register the obligations from the impl_m and check to see
202 // if all constraints hold.
205 .extend(trait_m_predicates.instantiate_own(tcx, trait_to_placeholder_substs).predicates);
207 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
208 // The key step here is to update the caller_bounds's predicates to be
209 // the new hybrid bounds we computed.
210 let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_hir_id);
212 ty::ParamEnv::new(tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing);
213 let param_env = traits::normalize_param_env_or_error(
217 normalize_cause.clone(),
220 tcx.infer_ctxt().enter(|infcx| {
221 let inh = Inherited::new(infcx, impl_m.def_id.expect_local());
222 let infcx = &inh.infcx;
224 debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
226 let mut selcx = traits::SelectionContext::new(&infcx);
228 let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
229 for predicate in impl_m_own_bounds.predicates {
230 let traits::Normalized { value: predicate, obligations } =
231 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), predicate);
233 inh.register_predicates(obligations);
234 inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
237 // We now need to check that the signature of the impl method is
238 // compatible with that of the trait method. We do this by
239 // checking that `impl_fty <: trait_fty`.
241 // FIXME. Unfortunately, this doesn't quite work right now because
242 // associated type normalization is not integrated into subtype
243 // checks. For the comparison to be valid, we need to
244 // normalize the associated types in the impl/trait methods
245 // first. However, because function types bind regions, just
246 // calling `normalize_associated_types_in` would have no effect on
247 // any associated types appearing in the fn arguments or return
250 // Compute placeholder form of impl and trait method tys.
253 let (impl_sig, _) = infcx.replace_bound_vars_with_fresh_vars(
255 infer::HigherRankedType,
256 tcx.fn_sig(impl_m.def_id),
259 inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, impl_sig);
260 let impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(impl_sig));
261 debug!("compare_impl_method: impl_fty={:?}", impl_fty);
263 let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, tcx.fn_sig(trait_m.def_id));
264 let trait_sig = trait_sig.subst(tcx, trait_to_placeholder_substs);
266 inh.normalize_associated_types_in(impl_m_span, impl_m_hir_id, param_env, trait_sig);
267 let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
269 debug!("compare_impl_method: trait_fty={:?}", trait_fty);
271 let sub_result = infcx.at(&cause, param_env).sup(trait_fty, impl_fty).map(
272 |InferOk { obligations, .. }| {
273 inh.register_predicates(obligations);
277 if let Err(terr) = sub_result {
278 debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);
280 let (impl_err_span, trait_err_span) =
281 extract_spans_for_error_reporting(&infcx, &terr, &cause, impl_m, trait_m);
283 cause.make_mut().span = impl_err_span;
285 let mut diag = struct_span_err!(
289 "method `{}` has an incompatible type for trait",
293 TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
294 if trait_m.fn_has_self_parameter =>
296 let ty = trait_sig.inputs()[0];
297 let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty())
299 ExplicitSelf::ByValue => "self".to_owned(),
300 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
301 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => {
302 "&mut self".to_owned()
304 _ => format!("self: {}", ty),
307 // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
308 // span points only at the type `Box<Self`>, but we want to cover the whole
309 // argument pattern and type.
311 tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
312 let span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
313 ImplItemKind::Fn(ref sig, body) => tcx
315 .body_param_names(body)
316 .zip(sig.decl.inputs.iter())
317 .map(|(param, ty)| param.span.to(ty.span))
319 .unwrap_or(impl_err_span),
320 _ => bug!("{:?} is not a method", impl_m),
323 diag.span_suggestion(
325 "change the self-receiver type to match the trait",
327 Applicability::MachineApplicable,
330 TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
331 if trait_sig.inputs().len() == *i {
332 // Suggestion to change output type. We do not suggest in `async` functions
333 // to avoid complex logic or incorrect output.
335 tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
336 match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
337 ImplItemKind::Fn(ref sig, _)
338 if sig.header.asyncness == hir::IsAsync::NotAsync =>
340 let msg = "change the output type to match the trait";
341 let ap = Applicability::MachineApplicable;
342 match sig.decl.output {
343 hir::FnRetTy::DefaultReturn(sp) => {
344 let sugg = format!("-> {} ", trait_sig.output());
345 diag.span_suggestion_verbose(sp, msg, sugg, ap);
347 hir::FnRetTy::Return(hir_ty) => {
348 let sugg = trait_sig.output().to_string();
349 diag.span_suggestion(hir_ty.span, msg, sugg, ap);
355 } else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
356 diag.span_suggestion(
358 "change the parameter type to match the trait",
359 trait_ty.to_string(),
360 Applicability::MachineApplicable,
370 trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
371 Some(infer::ValuePairs::Types(ExpectedFound {
378 return Err(ErrorReported);
381 // Check that all obligations are satisfied by the implementation's
383 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
384 infcx.report_fulfillment_errors(errors, None, false);
385 return Err(ErrorReported);
388 // Finally, resolve all regions. This catches wily misuses of
389 // lifetime parameters.
390 let fcx = FnCtxt::new(&inh, param_env, impl_m_hir_id);
391 fcx.regionck_item(impl_m_hir_id, impl_m_span, trait_sig.inputs_and_output);
397 fn check_region_bounds_on_impl_item<'tcx>(
400 impl_m: &ty::AssocItem,
401 trait_m: &ty::AssocItem,
402 trait_generics: &ty::Generics,
403 impl_generics: &ty::Generics,
404 ) -> Result<(), ErrorReported> {
405 let trait_params = trait_generics.own_counts().lifetimes;
406 let impl_params = impl_generics.own_counts().lifetimes;
409 "check_region_bounds_on_impl_item: \
410 trait_generics={:?} \
412 trait_generics, impl_generics
415 // Must have same number of early-bound lifetime parameters.
416 // Unfortunately, if the user screws up the bounds, then this
417 // will change classification between early and late. E.g.,
418 // if in trait we have `<'a,'b:'a>`, and in impl we just have
419 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
420 // in trait but 0 in the impl. But if we report "expected 2
421 // but found 0" it's confusing, because it looks like there
422 // are zero. Since I don't quite know how to phrase things at
423 // the moment, give a kind of vague error message.
424 if trait_params != impl_params {
425 let item_kind = assoc_item_kind_str(impl_m);
426 let def_span = tcx.sess.source_map().guess_head_span(span);
427 let span = tcx.hir().get_generics(impl_m.def_id).map_or(def_span, |g| g.span);
428 let generics_span = tcx.hir().span_if_local(trait_m.def_id).map(|sp| {
429 let def_sp = tcx.sess.source_map().guess_head_span(sp);
430 tcx.hir().get_generics(trait_m.def_id).map_or(def_sp, |g| g.span)
433 tcx.sess.emit_err(LifetimesOrBoundsMismatchOnTrait {
439 return Err(ErrorReported);
445 fn extract_spans_for_error_reporting<'a, 'tcx>(
446 infcx: &infer::InferCtxt<'a, 'tcx>,
447 terr: &TypeError<'_>,
448 cause: &ObligationCause<'tcx>,
449 impl_m: &ty::AssocItem,
450 trait_m: &ty::AssocItem,
451 ) -> (Span, Option<Span>) {
453 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
454 let mut impl_args = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
455 ImplItemKind::Fn(ref sig, _) => {
456 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
458 _ => bug!("{:?} is not a method", impl_m),
460 let trait_args = trait_m.def_id.as_local().map(|def_id| {
461 let trait_m_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
462 match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
463 TraitItemKind::Fn(ref sig, _) => {
464 sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
466 _ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
471 TypeError::ArgumentMutability(i) => {
472 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
474 TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
475 (impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
477 _ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
481 fn compare_self_type<'tcx>(
483 impl_m: &ty::AssocItem,
485 trait_m: &ty::AssocItem,
486 impl_trait_ref: ty::TraitRef<'tcx>,
487 ) -> Result<(), ErrorReported> {
488 // Try to give more informative error messages about self typing
489 // mismatches. Note that any mismatch will also be detected
490 // below, where we construct a canonical function type that
491 // includes the self parameter as a normal parameter. It's just
492 // that the error messages you get out of this code are a bit more
493 // inscrutable, particularly for cases where one method has no
496 let self_string = |method: &ty::AssocItem| {
497 let untransformed_self_ty = match method.container {
498 ty::ImplContainer(_) => impl_trait_ref.self_ty(),
499 ty::TraitContainer(_) => tcx.types.self_param,
501 let self_arg_ty = tcx.fn_sig(method.def_id).input(0);
502 let param_env = ty::ParamEnv::reveal_all();
504 tcx.infer_ctxt().enter(|infcx| {
505 let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
506 let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty).is_ok();
507 match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
508 ExplicitSelf::ByValue => "self".to_owned(),
509 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
510 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
511 _ => format!("self: {}", self_arg_ty),
516 match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
517 (false, false) | (true, true) => {}
520 let self_descr = self_string(impl_m);
521 let mut err = struct_span_err!(
525 "method `{}` has a `{}` declaration in the impl, but not in the trait",
529 err.span_label(impl_m_span, format!("`{}` used in impl", self_descr));
530 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
531 err.span_label(span, format!("trait method declared without `{}`", self_descr));
533 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
536 return Err(ErrorReported);
540 let self_descr = self_string(trait_m);
541 let mut err = struct_span_err!(
545 "method `{}` has a `{}` declaration in the trait, but not in the impl",
549 err.span_label(impl_m_span, format!("expected `{}` in impl", self_descr));
550 if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
551 err.span_label(span, format!("`{}` used in trait", self_descr));
553 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
556 return Err(ErrorReported);
563 fn compare_number_of_generics<'tcx>(
565 impl_: &ty::AssocItem,
567 trait_: &ty::AssocItem,
568 trait_span: Option<Span>,
569 ) -> Result<(), ErrorReported> {
570 let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
571 let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
574 ("type", trait_own_counts.types, impl_own_counts.types),
575 ("const", trait_own_counts.consts, impl_own_counts.consts),
578 let item_kind = assoc_item_kind_str(impl_);
580 let mut err_occurred = false;
581 for (kind, trait_count, impl_count) in matchings {
582 if impl_count != trait_count {
585 let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
586 let trait_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
587 let trait_item = tcx.hir().expect_trait_item(trait_hir_id);
588 if trait_item.generics.params.is_empty() {
589 (Some(vec![trait_item.generics.span]), vec![])
591 let arg_spans: Vec<Span> =
592 trait_item.generics.params.iter().map(|p| p.span).collect();
593 let impl_trait_spans: Vec<Span> = trait_item
597 .filter_map(|p| match p.kind {
598 GenericParamKind::Type {
599 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
605 (Some(arg_spans), impl_trait_spans)
608 (trait_span.map(|s| vec![s]), vec![])
611 let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_.def_id.expect_local());
612 let impl_item = tcx.hir().expect_impl_item(impl_hir_id);
613 let impl_item_impl_trait_spans: Vec<Span> = impl_item
617 .filter_map(|p| match p.kind {
618 GenericParamKind::Type {
619 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
625 let spans = impl_item.generics.spans();
626 let span = spans.primary_span();
628 let mut err = tcx.sess.struct_span_err_with_code(
631 "{} `{}` has {} {kind} parameter{} but its trait \
632 declaration has {} {kind} parameter{}",
636 pluralize!(impl_count),
638 pluralize!(trait_count),
641 DiagnosticId::Error("E0049".into()),
644 let mut suffix = None;
646 if let Some(spans) = trait_spans {
647 let mut spans = spans.iter();
648 if let Some(span) = spans.next() {
652 "expected {} {} parameter{}",
655 pluralize!(trait_count),
660 err.span_label(*span, "");
663 suffix = Some(format!(", expected {}", trait_count));
666 if let Some(span) = span {
670 "found {} {} parameter{}{}",
673 pluralize!(impl_count),
674 suffix.unwrap_or_else(String::new),
679 for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
680 err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
687 if err_occurred { Err(ErrorReported) } else { Ok(()) }
690 fn compare_number_of_method_arguments<'tcx>(
692 impl_m: &ty::AssocItem,
694 trait_m: &ty::AssocItem,
695 trait_item_span: Option<Span>,
696 ) -> Result<(), ErrorReported> {
697 let impl_m_fty = tcx.fn_sig(impl_m.def_id);
698 let trait_m_fty = tcx.fn_sig(trait_m.def_id);
699 let trait_number_args = trait_m_fty.inputs().skip_binder().len();
700 let impl_number_args = impl_m_fty.inputs().skip_binder().len();
701 if trait_number_args != impl_number_args {
702 let trait_span = if let Some(def_id) = trait_m.def_id.as_local() {
703 let trait_id = tcx.hir().local_def_id_to_hir_id(def_id);
704 match tcx.hir().expect_trait_item(trait_id).kind {
705 TraitItemKind::Fn(ref trait_m_sig, _) => {
706 let pos = if trait_number_args > 0 { trait_number_args - 1 } else { 0 };
707 if let Some(arg) = trait_m_sig.decl.inputs.get(pos) {
711 arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
717 _ => bug!("{:?} is not a method", impl_m),
722 let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
723 let impl_span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
724 ImplItemKind::Fn(ref impl_m_sig, _) => {
725 let pos = if impl_number_args > 0 { impl_number_args - 1 } else { 0 };
726 if let Some(arg) = impl_m_sig.decl.inputs.get(pos) {
730 arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
736 _ => bug!("{:?} is not a method", impl_m),
738 let mut err = struct_span_err!(
742 "method `{}` has {} but the declaration in \
745 potentially_plural_count(impl_number_args, "parameter"),
746 tcx.def_path_str(trait_m.def_id),
749 if let Some(trait_span) = trait_span {
754 potentially_plural_count(trait_number_args, "parameter")
758 err.note_trait_signature(trait_m.ident.to_string(), trait_m.signature(tcx));
763 "expected {}, found {}",
764 potentially_plural_count(trait_number_args, "parameter"),
769 return Err(ErrorReported);
775 fn compare_synthetic_generics<'tcx>(
777 impl_m: &ty::AssocItem,
778 trait_m: &ty::AssocItem,
779 ) -> Result<(), ErrorReported> {
780 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
781 // 1. Better messages for the span labels
782 // 2. Explanation as to what is going on
783 // If we get here, we already have the same number of generics, so the zip will
785 let mut error_found = false;
786 let impl_m_generics = tcx.generics_of(impl_m.def_id);
787 let trait_m_generics = tcx.generics_of(trait_m.def_id);
788 let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
789 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
790 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
792 let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
793 GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
794 GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
796 for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
797 iter::zip(impl_m_type_params, trait_m_type_params)
799 if impl_synthetic != trait_synthetic {
800 let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_def_id.expect_local());
801 let impl_span = tcx.hir().span(impl_hir_id);
802 let trait_span = tcx.def_span(trait_def_id);
803 let mut err = struct_span_err!(
807 "method `{}` has incompatible signature for trait",
810 err.span_label(trait_span, "declaration in trait here");
811 match (impl_synthetic, trait_synthetic) {
812 // The case where the impl method uses `impl Trait` but the trait method uses
814 (Some(hir::SyntheticTyParamKind::ImplTrait), None) => {
815 err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
817 // try taking the name from the trait impl
818 // FIXME: this is obviously suboptimal since the name can already be used
819 // as another generic argument
820 let new_name = tcx.sess.source_map().span_to_snippet(trait_span).ok()?;
821 let trait_m = trait_m.def_id.as_local()?;
822 let trait_m = tcx.hir().trait_item(hir::TraitItemId { def_id: trait_m });
824 let impl_m = impl_m.def_id.as_local()?;
825 let impl_m = tcx.hir().impl_item(hir::ImplItemId { def_id: impl_m });
827 // in case there are no generics, take the spot between the function name
828 // and the opening paren of the argument list
829 let new_generics_span =
830 tcx.sess.source_map().generate_fn_name_span(impl_span)?.shrink_to_hi();
831 // in case there are generics, just replace them
833 impl_m.generics.span.substitute_dummy(new_generics_span);
834 // replace with the generics from the trait
836 tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
838 err.multipart_suggestion(
839 "try changing the `impl Trait` argument to a generic parameter",
841 // replace `impl Trait` with `T`
842 (impl_span, new_name),
843 // replace impl method generics with trait method generics
844 // This isn't quite right, as users might have changed the names
845 // of the generics, but it works for the common case
846 (generics_span, new_generics),
848 Applicability::MaybeIncorrect,
853 // The case where the trait method uses `impl Trait`, but the impl method uses
854 // explicit generics.
855 (None, Some(hir::SyntheticTyParamKind::ImplTrait)) => {
856 err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
858 let impl_m = impl_m.def_id.as_local()?;
859 let impl_m = tcx.hir().impl_item(hir::ImplItemId { def_id: impl_m });
860 let input_tys = match impl_m.kind {
861 hir::ImplItemKind::Fn(ref sig, _) => sig.decl.inputs,
864 struct Visitor(Option<Span>, hir::def_id::DefId);
865 impl<'v> intravisit::Visitor<'v> for Visitor {
866 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
867 intravisit::walk_ty(self, ty);
868 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) =
871 if let Res::Def(DefKind::TyParam, def_id) = path.res {
872 if def_id == self.1 {
873 self.0 = Some(ty.span);
878 type Map = intravisit::ErasedMap<'v>;
881 ) -> intravisit::NestedVisitorMap<Self::Map>
883 intravisit::NestedVisitorMap::None
886 let mut visitor = Visitor(None, impl_def_id);
887 for ty in input_tys {
888 intravisit::Visitor::visit_ty(&mut visitor, ty);
890 let span = visitor.0?;
893 impl_m.generics.params.iter().find_map(|param| match param.kind {
894 GenericParamKind::Lifetime { .. } => None,
895 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
896 if param.hir_id == impl_hir_id {
903 let bounds = bounds.first()?.span().to(bounds.last()?.span());
904 let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
906 err.multipart_suggestion(
907 "try removing the generic parameter and using `impl Trait` instead",
909 // delete generic parameters
910 (impl_m.generics.span, String::new()),
911 // replace param usage with `impl Trait`
912 (span, format!("impl {}", bounds)),
914 Applicability::MaybeIncorrect,
925 if error_found { Err(ErrorReported) } else { Ok(()) }
928 fn compare_const_param_types<'tcx>(
930 impl_m: &ty::AssocItem,
931 trait_m: &ty::AssocItem,
932 trait_item_span: Option<Span>,
933 ) -> Result<(), ErrorReported> {
934 let const_params_of = |def_id| {
935 tcx.generics_of(def_id).params.iter().filter_map(|param| match param.kind {
936 GenericParamDefKind::Const { .. } => Some(param.def_id),
940 let const_params_impl = const_params_of(impl_m.def_id);
941 let const_params_trait = const_params_of(trait_m.def_id);
943 for (const_param_impl, const_param_trait) in iter::zip(const_params_impl, const_params_trait) {
944 let impl_ty = tcx.type_of(const_param_impl);
945 let trait_ty = tcx.type_of(const_param_trait);
946 if impl_ty != trait_ty {
947 let (impl_span, impl_ident) = match tcx.hir().get_if_local(const_param_impl) {
948 Some(hir::Node::GenericParam(hir::GenericParam { span, name, .. })) => (
951 hir::ParamName::Plain(ident) => Some(ident),
956 "expected GenericParam, found {:?}",
957 other.map_or_else(|| "nothing".to_string(), |n| format!("{:?}", n))
960 let trait_span = match tcx.hir().get_if_local(const_param_trait) {
961 Some(hir::Node::GenericParam(hir::GenericParam { span, .. })) => Some(span),
964 let mut err = struct_span_err!(
968 "method `{}` has an incompatible const parameter type for trait",
972 trait_span.map_or_else(|| trait_item_span.unwrap_or(*impl_span), |span| *span),
974 "the const parameter{} has type `{}`, but the declaration \
975 in trait `{}` has type `{}`",
976 &impl_ident.map_or_else(|| "".to_string(), |ident| format!(" `{}`", ident)),
978 tcx.def_path_str(trait_m.def_id),
983 return Err(ErrorReported);
990 crate fn compare_const_impl<'tcx>(
992 impl_c: &ty::AssocItem,
994 trait_c: &ty::AssocItem,
995 impl_trait_ref: ty::TraitRef<'tcx>,
997 debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
999 tcx.infer_ctxt().enter(|infcx| {
1000 let param_env = tcx.param_env(impl_c.def_id);
1001 let inh = Inherited::new(infcx, impl_c.def_id.expect_local());
1002 let infcx = &inh.infcx;
1004 // The below is for the most part highly similar to the procedure
1005 // for methods above. It is simpler in many respects, especially
1006 // because we shouldn't really have to deal with lifetimes or
1007 // predicates. In fact some of this should probably be put into
1008 // shared functions because of DRY violations...
1009 let trait_to_impl_substs = impl_trait_ref.substs;
1011 // Create a parameter environment that represents the implementation's
1013 let impl_c_hir_id = tcx.hir().local_def_id_to_hir_id(impl_c.def_id.expect_local());
1015 // Compute placeholder form of impl and trait const tys.
1016 let impl_ty = tcx.type_of(impl_c.def_id);
1017 let trait_ty = tcx.type_of(trait_c.def_id).subst(tcx, trait_to_impl_substs);
1018 let mut cause = ObligationCause::new(
1021 ObligationCauseCode::CompareImplConstObligation,
1024 // There is no "body" here, so just pass dummy id.
1026 inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, impl_ty);
1028 debug!("compare_const_impl: impl_ty={:?}", impl_ty);
1031 inh.normalize_associated_types_in(impl_c_span, impl_c_hir_id, param_env, trait_ty);
1033 debug!("compare_const_impl: trait_ty={:?}", trait_ty);
1036 .at(&cause, param_env)
1037 .sup(trait_ty, impl_ty)
1038 .map(|ok| inh.register_infer_ok_obligations(ok));
1040 if let Err(terr) = err {
1042 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
1046 // Locate the Span containing just the type of the offending impl
1047 match tcx.hir().expect_impl_item(impl_c_hir_id).kind {
1048 ImplItemKind::Const(ref ty, _) => cause.make_mut().span = ty.span,
1049 _ => bug!("{:?} is not a impl const", impl_c),
1052 let mut diag = struct_span_err!(
1056 "implemented const `{}` has an incompatible type for trait",
1060 let trait_c_hir_id =
1061 trait_c.def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
1062 let trait_c_span = trait_c_hir_id.map(|trait_c_hir_id| {
1063 // Add a label to the Span containing just the type of the const
1064 match tcx.hir().expect_trait_item(trait_c_hir_id).kind {
1065 TraitItemKind::Const(ref ty, _) => ty.span,
1066 _ => bug!("{:?} is not a trait const", trait_c),
1070 infcx.note_type_err(
1073 trait_c_span.map(|span| (span, "type in trait".to_owned())),
1074 Some(infer::ValuePairs::Types(ExpectedFound {
1083 // Check that all obligations are satisfied by the implementation's
1085 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1086 infcx.report_fulfillment_errors(errors, None, false);
1090 let fcx = FnCtxt::new(&inh, param_env, impl_c_hir_id);
1091 fcx.regionck_item(impl_c_hir_id, impl_c_span, &[]);
1095 crate fn compare_ty_impl<'tcx>(
1097 impl_ty: &ty::AssocItem,
1099 trait_ty: &ty::AssocItem,
1100 impl_trait_ref: ty::TraitRef<'tcx>,
1101 trait_item_span: Option<Span>,
1103 debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
1105 let _: Result<(), ErrorReported> = (|| {
1106 compare_number_of_generics(tcx, impl_ty, impl_ty_span, trait_ty, trait_item_span)?;
1108 compare_type_predicate_entailment(tcx, impl_ty, impl_ty_span, trait_ty, impl_trait_ref)?;
1110 check_type_bounds(tcx, trait_ty, impl_ty, impl_ty_span, impl_trait_ref)
1114 /// The equivalent of [compare_predicate_entailment], but for associated types
1115 /// instead of associated functions.
1116 fn compare_type_predicate_entailment<'tcx>(
1118 impl_ty: &ty::AssocItem,
1120 trait_ty: &ty::AssocItem,
1121 impl_trait_ref: ty::TraitRef<'tcx>,
1122 ) -> Result<(), ErrorReported> {
1123 let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1124 let trait_to_impl_substs =
1125 impl_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1127 let impl_ty_generics = tcx.generics_of(impl_ty.def_id);
1128 let trait_ty_generics = tcx.generics_of(trait_ty.def_id);
1129 let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
1130 let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
1132 check_region_bounds_on_impl_item(
1141 let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
1143 if impl_ty_own_bounds.is_empty() {
1144 // Nothing to check.
1148 // This `HirId` should be used for the `body_id` field on each
1149 // `ObligationCause` (and the `FnCtxt`). This is what
1150 // `regionck_item` expects.
1151 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1152 let cause = ObligationCause::new(
1155 ObligationCauseCode::CompareImplTypeObligation {
1156 item_name: impl_ty.ident.name,
1157 impl_item_def_id: impl_ty.def_id,
1158 trait_item_def_id: trait_ty.def_id,
1162 debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
1164 // The predicates declared by the impl definition, the trait and the
1165 // associated type in the trait are assumed.
1166 let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
1167 let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
1170 .extend(trait_ty_predicates.instantiate_own(tcx, trait_to_impl_substs).predicates);
1172 debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
1174 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1176 ty::ParamEnv::new(tcx.intern_predicates(&hybrid_preds.predicates), Reveal::UserFacing);
1177 let param_env = traits::normalize_param_env_or_error(
1181 normalize_cause.clone(),
1183 tcx.infer_ctxt().enter(|infcx| {
1184 let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
1185 let infcx = &inh.infcx;
1187 debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
1189 let mut selcx = traits::SelectionContext::new(&infcx);
1191 for predicate in impl_ty_own_bounds.predicates {
1192 let traits::Normalized { value: predicate, obligations } =
1193 traits::normalize(&mut selcx, param_env, normalize_cause.clone(), predicate);
1195 inh.register_predicates(obligations);
1196 inh.register_predicate(traits::Obligation::new(cause.clone(), param_env, predicate));
1199 // Check that all obligations are satisfied by the implementation's
1201 if let Err(ref errors) = inh.fulfillment_cx.borrow_mut().select_all_or_error(&infcx) {
1202 infcx.report_fulfillment_errors(errors, None, false);
1203 return Err(ErrorReported);
1206 // Finally, resolve all regions. This catches wily misuses of
1207 // lifetime parameters.
1208 let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1209 fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &[]);
1215 /// Validate that `ProjectionCandidate`s created for this associated type will
1220 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1222 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1223 /// impl is well-formed we have to prove `S: Copy`.
1225 /// For default associated types the normalization is not possible (the value
1226 /// from the impl could be overridden). We also can't normalize generic
1227 /// associated types (yet) because they contain bound parameters.
1228 #[tracing::instrument(level = "debug", skip(tcx))]
1229 pub fn check_type_bounds<'tcx>(
1231 trait_ty: &ty::AssocItem,
1232 impl_ty: &ty::AssocItem,
1234 impl_trait_ref: ty::TraitRef<'tcx>,
1235 ) -> Result<(), ErrorReported> {
1238 // impl<A, B> Foo<u32> for (A, B) {
1242 // - `impl_trait_ref` would be `<(A, B) as Foo<u32>>
1243 // - `impl_ty_substs` would be `[A, B, ^0.0]`
1244 // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
1245 // the *trait* with the generic associated type parameters (as bound vars).
1246 let defs: &ty::Generics = tcx.generics_of(impl_ty.def_id);
1247 let mut substs = smallvec::SmallVec::with_capacity(defs.count());
1248 if let Some(def_id) = defs.parent {
1249 let parent_defs = tcx.generics_of(def_id);
1250 InternalSubsts::fill_item(&mut substs, tcx, parent_defs, &mut |param, _| {
1251 tcx.mk_param_from_def(param)
1254 let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
1255 smallvec::SmallVec::with_capacity(defs.count());
1256 InternalSubsts::fill_single(&mut substs, defs, &mut |param, _| match param.kind {
1257 GenericParamDefKind::Type { .. } => {
1258 let kind = ty::BoundTyKind::Param(param.name);
1259 let bound_var = ty::BoundVariableKind::Ty(kind);
1260 bound_vars.push(bound_var);
1261 tcx.mk_ty(ty::Bound(
1263 ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1267 GenericParamDefKind::Lifetime => {
1268 let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
1269 let bound_var = ty::BoundVariableKind::Region(kind);
1270 bound_vars.push(bound_var);
1271 tcx.mk_region(ty::ReLateBound(
1273 ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
1277 GenericParamDefKind::Const { .. } => {
1278 let bound_var = ty::BoundVariableKind::Const;
1279 bound_vars.push(bound_var);
1280 tcx.mk_const(ty::Const {
1281 ty: tcx.type_of(param.def_id),
1282 val: ty::ConstKind::Bound(
1284 ty::BoundVar::from_usize(bound_vars.len() - 1),
1290 let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter());
1291 let impl_ty_substs = tcx.intern_substs(&substs);
1293 let rebased_substs =
1294 impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1295 let impl_ty_value = tcx.type_of(impl_ty.def_id);
1297 let param_env = tcx.param_env(impl_ty.def_id);
1299 // When checking something like
1301 // trait X { type Y: PartialEq<<Self as X>::Y> }
1302 // impl X for T { default type Y = S; }
1304 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1305 // we want <T as X>::Y to normalize to S. This is valid because we are
1306 // checking the default value specifically here. Add this equality to the
1307 // ParamEnv for normalization specifically.
1308 let normalize_param_env = {
1309 let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
1310 match impl_ty_value.kind() {
1311 ty::Projection(proj)
1312 if proj.item_def_id == trait_ty.def_id && proj.substs == rebased_substs =>
1314 // Don't include this predicate if the projected type is
1315 // exactly the same as the projection. This can occur in
1316 // (somewhat dubious) code like this:
1318 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1320 _ => predicates.push(
1321 ty::Binder::bind_with_vars(
1322 ty::ProjectionPredicate {
1323 projection_ty: ty::ProjectionTy {
1324 item_def_id: trait_ty.def_id,
1325 substs: rebased_substs,
1334 ty::ParamEnv::new(tcx.intern_predicates(&predicates), Reveal::UserFacing)
1336 debug!(?normalize_param_env);
1338 let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
1339 let rebased_substs =
1340 impl_ty_substs.rebase_onto(tcx, impl_ty.container.id(), impl_trait_ref.substs);
1342 tcx.infer_ctxt().enter(move |infcx| {
1343 let constness = impl_ty
1346 .map(|did| tcx.impl_constness(did))
1347 .unwrap_or(hir::Constness::NotConst);
1349 let inh = Inherited::with_constness(infcx, impl_ty.def_id.expect_local(), constness);
1350 let infcx = &inh.infcx;
1351 let mut selcx = traits::SelectionContext::new(&infcx);
1353 let impl_ty_hir_id = tcx.hir().local_def_id_to_hir_id(impl_ty.def_id.expect_local());
1354 let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_hir_id);
1355 let mk_cause = |span| {
1356 ObligationCause::new(
1359 ObligationCauseCode::BindingObligation(trait_ty.def_id, span),
1363 let obligations = tcx
1364 .explicit_item_bounds(trait_ty.def_id)
1366 .map(|&(bound, span)| {
1368 let concrete_ty_bound = bound.subst(tcx, rebased_substs);
1369 debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
1371 traits::Obligation::new(mk_cause(span), param_env, concrete_ty_bound)
1374 debug!("check_type_bounds: item_bounds={:?}", obligations);
1376 for mut obligation in util::elaborate_obligations(tcx, obligations) {
1377 let traits::Normalized { value: normalized_predicate, obligations } = traits::normalize(
1379 normalize_param_env,
1380 normalize_cause.clone(),
1381 obligation.predicate,
1383 debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
1384 obligation.predicate = normalized_predicate;
1386 inh.register_predicates(obligations);
1387 inh.register_predicate(obligation);
1390 // Check that all obligations are satisfied by the implementation's
1392 if let Err(ref errors) =
1393 inh.fulfillment_cx.borrow_mut().select_all_with_constness_or_error(&infcx, constness)
1395 infcx.report_fulfillment_errors(errors, None, false);
1396 return Err(ErrorReported);
1399 // Finally, resolve all regions. This catches wily misuses of
1400 // lifetime parameters.
1401 let fcx = FnCtxt::new(&inh, param_env, impl_ty_hir_id);
1402 let implied_bounds = match impl_ty.container {
1403 ty::TraitContainer(_) => vec![],
1404 ty::ImplContainer(def_id) => fcx.impl_implied_bounds(def_id, impl_ty_span),
1406 fcx.regionck_item(impl_ty_hir_id, impl_ty_span, &implied_bounds);
1412 fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
1413 match impl_item.kind {
1414 ty::AssocKind::Const => "const",
1415 ty::AssocKind::Fn => "method",
1416 ty::AssocKind::Type => "type",