1 use crate::errors
::LifetimesOrBoundsMismatchOnTrait
;
2 use rustc_data_structures
::stable_set
::FxHashSet
;
3 use rustc_errors
::{pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed}
;
5 use rustc_hir
::def
::{DefKind, Res}
;
6 use rustc_hir
::intravisit
;
7 use rustc_hir
::{GenericParamKind, ImplItemKind, TraitItemKind}
;
8 use rustc_infer
::infer
::{self, InferOk, TyCtxtInferExt}
;
9 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
::{self, DefIdTree}
;
14 use rustc_middle
::ty
::{GenericParamDefKind, ToPredicate, TyCtxt}
;
16 use rustc_trait_selection
::traits
::error_reporting
::InferCtxtExt
;
17 use rustc_trait_selection
::traits
::{self, ObligationCause, ObligationCauseCode, Reveal}
;
20 use super::{potentially_plural_count, FnCtxt, Inherited}
;
22 /// Checks that a method from an impl conforms to the signature of
23 /// the same method as declared in the trait.
27 /// - `impl_m`: type of the method we are checking
28 /// - `impl_m_span`: span to use for reporting errors
29 /// - `trait_m`: the method in the trait
30 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
31 pub(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(_
) = compare_self_type(tcx
, impl_m
, impl_m_span
, trait_m
, impl_trait_ref
) {
47 if let Err(_
) = compare_number_of_generics(tcx
, impl_m
, impl_m_span
, trait_m
, trait_item_span
) {
51 if let Err(_
) = compare_generic_param_kinds(tcx
, impl_m
, trait_m
) {
56 compare_number_of_method_arguments(tcx
, impl_m
, impl_m_span
, trait_m
, trait_item_span
)
61 if let Err(_
) = compare_synthetic_generics(tcx
, impl_m
, trait_m
) {
65 if let Err(_
) = compare_predicate_entailment(tcx
, impl_m
, impl_m_span
, trait_m
, impl_trait_ref
)
71 fn compare_predicate_entailment
<'tcx
>(
73 impl_m
: &ty
::AssocItem
,
75 trait_m
: &ty
::AssocItem
,
76 impl_trait_ref
: ty
::TraitRef
<'tcx
>,
77 ) -> Result
<(), ErrorGuaranteed
> {
78 let trait_to_impl_substs
= impl_trait_ref
.substs
;
80 // This node-id should be used for the `body_id` field on each
81 // `ObligationCause` (and the `FnCtxt`). This is what
82 // `regionck_item` expects.
83 let impl_m_hir_id
= tcx
.hir().local_def_id_to_hir_id(impl_m
.def_id
.expect_local());
85 // We sometimes modify the span further down.
86 let mut cause
= ObligationCause
::new(
89 ObligationCauseCode
::CompareImplMethodObligation
{
90 impl_item_def_id
: impl_m
.def_id
.expect_local(),
91 trait_item_def_id
: trait_m
.def_id
,
95 // This code is best explained by example. Consider a trait:
97 // trait Trait<'t, T> {
98 // fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
103 // impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
104 // fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo;
107 // We wish to decide if those two method types are compatible.
109 // We start out with trait_to_impl_substs, that maps the trait
110 // type parameters to impl type parameters. This is taken from the
111 // impl trait reference:
113 // trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
115 // We create a mapping `dummy_substs` that maps from the impl type
116 // parameters to fresh types and regions. For type parameters,
117 // this is the identity transform, but we could as well use any
118 // placeholder types. For regions, we convert from bound to free
119 // regions (Note: but only early-bound regions, i.e., those
120 // declared on the impl or used in type parameter bounds).
122 // impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
124 // Now we can apply placeholder_substs to the type of the impl method
125 // to yield a new function type in terms of our fresh, placeholder
128 // <'b> fn(t: &'i0 U0, m: &'b) -> Foo
130 // We now want to extract and substitute the type of the *trait*
131 // method and compare it. To do so, we must create a compound
132 // substitution by combining trait_to_impl_substs and
133 // impl_to_placeholder_substs, and also adding a mapping for the method
134 // type parameters. We extend the mapping to also include
135 // the method parameters.
137 // trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
139 // Applying this to the trait method type yields:
141 // <'a> fn(t: &'i0 U0, m: &'a) -> Foo
143 // This type is also the same but the name of the bound region ('a
144 // vs 'b). However, the normal subtyping rules on fn types handle
145 // this kind of equivalency just fine.
147 // We now use these substitutions to ensure that all declared bounds are
148 // satisfied by the implementation's method.
150 // We do this by creating a parameter environment which contains a
151 // substitution corresponding to impl_to_placeholder_substs. We then build
152 // trait_to_placeholder_substs and use it to convert the predicates contained
153 // in the trait_m.generics to the placeholder form.
155 // Finally we register each of these predicates as an obligation in
156 // a fresh FulfillmentCtxt, and invoke select_all_or_error.
158 // Create mapping from impl to placeholder.
159 let impl_to_placeholder_substs
= InternalSubsts
::identity_for_item(tcx
, impl_m
.def_id
);
161 // Create mapping from trait to placeholder.
162 let trait_to_placeholder_substs
=
163 impl_to_placeholder_substs
.rebase_onto(tcx
, impl_m
.container
.id(), trait_to_impl_substs
);
164 debug
!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs
);
166 let impl_m_generics
= tcx
.generics_of(impl_m
.def_id
);
167 let trait_m_generics
= tcx
.generics_of(trait_m
.def_id
);
168 let impl_m_predicates
= tcx
.predicates_of(impl_m
.def_id
);
169 let trait_m_predicates
= tcx
.predicates_of(trait_m
.def_id
);
171 // Check region bounds.
172 check_region_bounds_on_impl_item(
181 // Create obligations for each predicate declared by the impl
182 // definition in the context of the trait's parameter
183 // environment. We can't just use `impl_env.caller_bounds`,
184 // however, because we want to replace all late-bound regions with
186 let impl_predicates
= tcx
.predicates_of(impl_m_predicates
.parent
.unwrap());
187 let mut hybrid_preds
= impl_predicates
.instantiate_identity(tcx
);
189 debug
!("compare_impl_method: impl_bounds={:?}", hybrid_preds
);
191 // This is the only tricky bit of the new way we check implementation methods
192 // We need to build a set of predicates where only the method-level bounds
193 // are from the trait and we assume all other bounds from the implementation
194 // to be previously satisfied.
196 // We then register the obligations from the impl_m and check to see
197 // if all constraints hold.
200 .extend(trait_m_predicates
.instantiate_own(tcx
, trait_to_placeholder_substs
).predicates
);
202 // Construct trait parameter environment and then shift it into the placeholder viewpoint.
203 // The key step here is to update the caller_bounds's predicates to be
204 // the new hybrid bounds we computed.
205 let normalize_cause
= traits
::ObligationCause
::misc(impl_m_span
, impl_m_hir_id
);
206 let param_env
= ty
::ParamEnv
::new(
207 tcx
.intern_predicates(&hybrid_preds
.predicates
),
209 hir
::Constness
::NotConst
,
212 traits
::normalize_param_env_or_error(tcx
, impl_m
.def_id
, param_env
, normalize_cause
);
214 tcx
.infer_ctxt().enter(|infcx
| {
215 let inh
= Inherited
::new(infcx
, impl_m
.def_id
.expect_local());
216 let infcx
= &inh
.infcx
;
218 debug
!("compare_impl_method: caller_bounds={:?}", param_env
.caller_bounds());
220 let mut selcx
= traits
::SelectionContext
::new(&infcx
);
222 let impl_m_own_bounds
= impl_m_predicates
.instantiate_own(tcx
, impl_to_placeholder_substs
);
223 for (predicate
, span
) in iter
::zip(impl_m_own_bounds
.predicates
, impl_m_own_bounds
.spans
) {
224 let normalize_cause
= traits
::ObligationCause
::misc(span
, impl_m_hir_id
);
225 let traits
::Normalized { value: predicate, obligations }
=
226 traits
::normalize(&mut selcx
, param_env
, normalize_cause
, predicate
);
228 inh
.register_predicates(obligations
);
229 let cause
= ObligationCause
::new(
232 ObligationCauseCode
::CompareImplMethodObligation
{
233 impl_item_def_id
: impl_m
.def_id
.expect_local(),
234 trait_item_def_id
: trait_m
.def_id
,
237 inh
.register_predicate(traits
::Obligation
::new(cause
, param_env
, predicate
));
240 // We now need to check that the signature of the impl method is
241 // compatible with that of the trait method. We do this by
242 // checking that `impl_fty <: trait_fty`.
244 // FIXME. Unfortunately, this doesn't quite work right now because
245 // associated type normalization is not integrated into subtype
246 // checks. For the comparison to be valid, we need to
247 // normalize the associated types in the impl/trait methods
248 // first. However, because function types bind regions, just
249 // calling `normalize_associated_types_in` would have no effect on
250 // any associated types appearing in the fn arguments or return
253 // Compute placeholder form of impl and trait method tys.
256 let mut wf_tys
= FxHashSet
::default();
258 let impl_sig
= infcx
.replace_bound_vars_with_fresh_vars(
260 infer
::HigherRankedType
,
261 tcx
.fn_sig(impl_m
.def_id
),
264 inh
.normalize_associated_types_in(impl_m_span
, impl_m_hir_id
, param_env
, impl_sig
);
265 let impl_fty
= tcx
.mk_fn_ptr(ty
::Binder
::dummy(impl_sig
));
266 debug
!("compare_impl_method: impl_fty={:?}", impl_fty
);
268 let trait_sig
= tcx
.bound_fn_sig(trait_m
.def_id
).subst(tcx
, trait_to_placeholder_substs
);
269 let trait_sig
= tcx
.liberate_late_bound_regions(impl_m
.def_id
, trait_sig
);
271 inh
.normalize_associated_types_in(impl_m_span
, impl_m_hir_id
, param_env
, trait_sig
);
272 // Add the resulting inputs and output as well-formed.
273 wf_tys
.extend(trait_sig
.inputs_and_output
.iter());
274 let trait_fty
= tcx
.mk_fn_ptr(ty
::Binder
::dummy(trait_sig
));
276 debug
!("compare_impl_method: trait_fty={:?}", trait_fty
);
278 let sub_result
= infcx
.at(&cause
, param_env
).sup(trait_fty
, impl_fty
).map(
279 |InferOk { obligations, .. }
| {
280 // FIXME: We'd want to keep more accurate spans than "the method signature" when
281 // processing the comparison between the trait and impl fn, but we sadly lose them
282 // and point at the whole signature when a trait bound or specific input or output
283 // type would be more appropriate. In other places we have a `Vec<Span>`
284 // corresponding to their `Vec<Predicate>`, but we don't have that here.
285 // Fixing this would improve the output of test `issue-83765.rs`.
286 inh
.register_predicates(obligations
);
290 if let Err(terr
) = sub_result
{
291 debug
!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty
, trait_fty
);
293 let (impl_err_span
, trait_err_span
) =
294 extract_spans_for_error_reporting(&infcx
, &terr
, &cause
, impl_m
, trait_m
);
296 cause
.span
= impl_err_span
;
298 let mut diag
= struct_span_err
!(
302 "method `{}` has an incompatible type for trait",
306 TypeError
::ArgumentMutability(0) | TypeError
::ArgumentSorts(_
, 0)
307 if trait_m
.fn_has_self_parameter
=>
309 let ty
= trait_sig
.inputs()[0];
310 let sugg
= match ExplicitSelf
::determine(ty
, |_
| ty
== impl_trait_ref
.self_ty())
312 ExplicitSelf
::ByValue
=> "self".to_owned(),
313 ExplicitSelf
::ByReference(_
, hir
::Mutability
::Not
) => "&self".to_owned(),
314 ExplicitSelf
::ByReference(_
, hir
::Mutability
::Mut
) => {
315 "&mut self".to_owned()
317 _
=> format
!("self: {ty}"),
320 // When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
321 // span points only at the type `Box<Self`>, but we want to cover the whole
322 // argument pattern and type.
323 let span
= match tcx
.hir().expect_impl_item(impl_m
.def_id
.expect_local()).kind
{
324 ImplItemKind
::Fn(ref sig
, body
) => tcx
326 .body_param_names(body
)
327 .zip(sig
.decl
.inputs
.iter())
328 .map(|(param
, ty
)| param
.span
.to(ty
.span
))
330 .unwrap_or(impl_err_span
),
331 _
=> bug
!("{:?} is not a method", impl_m
),
334 diag
.span_suggestion(
336 "change the self-receiver type to match the trait",
338 Applicability
::MachineApplicable
,
341 TypeError
::ArgumentMutability(i
) | TypeError
::ArgumentSorts(_
, i
) => {
342 if trait_sig
.inputs().len() == *i
{
343 // Suggestion to change output type. We do not suggest in `async` functions
344 // to avoid complex logic or incorrect output.
345 match tcx
.hir().expect_impl_item(impl_m
.def_id
.expect_local()).kind
{
346 ImplItemKind
::Fn(ref sig
, _
)
347 if sig
.header
.asyncness
== hir
::IsAsync
::NotAsync
=>
349 let msg
= "change the output type to match the trait";
350 let ap
= Applicability
::MachineApplicable
;
351 match sig
.decl
.output
{
352 hir
::FnRetTy
::DefaultReturn(sp
) => {
353 let sugg
= format
!("-> {} ", trait_sig
.output());
354 diag
.span_suggestion_verbose(sp
, msg
, sugg
, ap
);
356 hir
::FnRetTy
::Return(hir_ty
) => {
357 let sugg
= trait_sig
.output();
358 diag
.span_suggestion(hir_ty
.span
, msg
, sugg
, ap
);
364 } else if let Some(trait_ty
) = trait_sig
.inputs().get(*i
) {
365 diag
.span_suggestion(
367 "change the parameter type to match the trait",
369 Applicability
::MachineApplicable
,
379 trait_err_span
.map(|sp
| (sp
, "type in trait".to_owned())),
380 Some(infer
::ValuePairs
::Terms(ExpectedFound
{
381 expected
: trait_fty
.into(),
382 found
: impl_fty
.into(),
389 return Err(diag
.emit());
392 // Check that all obligations are satisfied by the implementation's
394 let errors
= inh
.fulfillment_cx
.borrow_mut().select_all_or_error(&infcx
);
395 if !errors
.is_empty() {
396 let reported
= infcx
.report_fulfillment_errors(&errors
, None
, false);
397 return Err(reported
);
400 // Finally, resolve all regions. This catches wily misuses of
401 // lifetime parameters.
402 let fcx
= FnCtxt
::new(&inh
, param_env
, impl_m_hir_id
);
403 fcx
.regionck_item(impl_m_hir_id
, impl_m_span
, wf_tys
);
409 fn check_region_bounds_on_impl_item
<'tcx
>(
412 impl_m
: &ty
::AssocItem
,
413 trait_m
: &ty
::AssocItem
,
414 trait_generics
: &ty
::Generics
,
415 impl_generics
: &ty
::Generics
,
416 ) -> Result
<(), ErrorGuaranteed
> {
417 let trait_params
= trait_generics
.own_counts().lifetimes
;
418 let impl_params
= impl_generics
.own_counts().lifetimes
;
421 "check_region_bounds_on_impl_item: \
422 trait_generics={:?} \
424 trait_generics
, impl_generics
427 // Must have same number of early-bound lifetime parameters.
428 // Unfortunately, if the user screws up the bounds, then this
429 // will change classification between early and late. E.g.,
430 // if in trait we have `<'a,'b:'a>`, and in impl we just have
431 // `<'a,'b>`, then we have 2 early-bound lifetime parameters
432 // in trait but 0 in the impl. But if we report "expected 2
433 // but found 0" it's confusing, because it looks like there
434 // are zero. Since I don't quite know how to phrase things at
435 // the moment, give a kind of vague error message.
436 if trait_params
!= impl_params
{
437 let item_kind
= assoc_item_kind_str(impl_m
);
438 let def_span
= tcx
.sess
.source_map().guess_head_span(span
);
442 .and_then(|did
| tcx
.hir().get_generics(did
))
443 .map_or(def_span
, |g
| g
.span
);
444 let generics_span
= tcx
.hir().span_if_local(trait_m
.def_id
).map(|sp
| {
445 let def_sp
= tcx
.sess
.source_map().guess_head_span(sp
);
449 .and_then(|did
| tcx
.hir().get_generics(did
))
450 .map_or(def_sp
, |g
| g
.span
)
453 let reported
= tcx
.sess
.emit_err(LifetimesOrBoundsMismatchOnTrait
{
456 ident
: impl_m
.ident(tcx
),
459 return Err(reported
);
465 #[instrument(level = "debug", skip(infcx))]
466 fn extract_spans_for_error_reporting
<'a
, 'tcx
>(
467 infcx
: &infer
::InferCtxt
<'a
, 'tcx
>,
468 terr
: &TypeError
<'_
>,
469 cause
: &ObligationCause
<'tcx
>,
470 impl_m
: &ty
::AssocItem
,
471 trait_m
: &ty
::AssocItem
,
472 ) -> (Span
, Option
<Span
>) {
474 let mut impl_args
= match tcx
.hir().expect_impl_item(impl_m
.def_id
.expect_local()).kind
{
475 ImplItemKind
::Fn(ref sig
, _
) => {
476 sig
.decl
.inputs
.iter().map(|t
| t
.span
).chain(iter
::once(sig
.decl
.output
.span()))
478 _
=> bug
!("{:?} is not a method", impl_m
),
481 trait_m
.def_id
.as_local().map(|def_id
| match tcx
.hir().expect_trait_item(def_id
).kind
{
482 TraitItemKind
::Fn(ref sig
, _
) => {
483 sig
.decl
.inputs
.iter().map(|t
| t
.span
).chain(iter
::once(sig
.decl
.output
.span()))
485 _
=> bug
!("{:?} is not a TraitItemKind::Fn", trait_m
),
489 TypeError
::ArgumentMutability(i
) => {
490 (impl_args
.nth(i
).unwrap(), trait_args
.and_then(|mut args
| args
.nth(i
)))
492 TypeError
::ArgumentSorts(ExpectedFound { .. }
, i
) => {
493 (impl_args
.nth(i
).unwrap(), trait_args
.and_then(|mut args
| args
.nth(i
)))
495 _
=> (cause
.span(tcx
), tcx
.hir().span_if_local(trait_m
.def_id
)),
499 fn compare_self_type
<'tcx
>(
501 impl_m
: &ty
::AssocItem
,
503 trait_m
: &ty
::AssocItem
,
504 impl_trait_ref
: ty
::TraitRef
<'tcx
>,
505 ) -> Result
<(), ErrorGuaranteed
> {
506 // Try to give more informative error messages about self typing
507 // mismatches. Note that any mismatch will also be detected
508 // below, where we construct a canonical function type that
509 // includes the self parameter as a normal parameter. It's just
510 // that the error messages you get out of this code are a bit more
511 // inscrutable, particularly for cases where one method has no
514 let self_string
= |method
: &ty
::AssocItem
| {
515 let untransformed_self_ty
= match method
.container
{
516 ty
::ImplContainer(_
) => impl_trait_ref
.self_ty(),
517 ty
::TraitContainer(_
) => tcx
.types
.self_param
,
519 let self_arg_ty
= tcx
.fn_sig(method
.def_id
).input(0);
520 let param_env
= ty
::ParamEnv
::reveal_all();
522 tcx
.infer_ctxt().enter(|infcx
| {
523 let self_arg_ty
= tcx
.liberate_late_bound_regions(method
.def_id
, self_arg_ty
);
524 let can_eq_self
= |ty
| infcx
.can_eq(param_env
, untransformed_self_ty
, ty
).is_ok();
525 match ExplicitSelf
::determine(self_arg_ty
, can_eq_self
) {
526 ExplicitSelf
::ByValue
=> "self".to_owned(),
527 ExplicitSelf
::ByReference(_
, hir
::Mutability
::Not
) => "&self".to_owned(),
528 ExplicitSelf
::ByReference(_
, hir
::Mutability
::Mut
) => "&mut self".to_owned(),
529 _
=> format
!("self: {self_arg_ty}"),
534 match (trait_m
.fn_has_self_parameter
, impl_m
.fn_has_self_parameter
) {
535 (false, false) | (true, true) => {}
538 let self_descr
= self_string(impl_m
);
539 let mut err
= struct_span_err
!(
543 "method `{}` has a `{}` declaration in the impl, but not in the trait",
547 err
.span_label(impl_m_span
, format
!("`{self_descr}` used in impl"));
548 if let Some(span
) = tcx
.hir().span_if_local(trait_m
.def_id
) {
549 err
.span_label(span
, format
!("trait method declared without `{self_descr}`"));
551 err
.note_trait_signature(trait_m
.name
.to_string(), trait_m
.signature(tcx
));
553 let reported
= err
.emit();
554 return Err(reported
);
558 let self_descr
= self_string(trait_m
);
559 let mut err
= struct_span_err
!(
563 "method `{}` has a `{}` declaration in the trait, but not in the impl",
567 err
.span_label(impl_m_span
, format
!("expected `{self_descr}` in impl"));
568 if let Some(span
) = tcx
.hir().span_if_local(trait_m
.def_id
) {
569 err
.span_label(span
, format
!("`{self_descr}` used in trait"));
571 err
.note_trait_signature(trait_m
.name
.to_string(), trait_m
.signature(tcx
));
573 let reported
= err
.emit();
574 return Err(reported
);
581 /// Checks that the number of generics on a given assoc item in a trait impl is the same
582 /// as the number of generics on the respective assoc item in the trait definition.
584 /// For example this code emits the errors in the following code:
591 /// impl Trait for () {
594 /// type Assoc = u32;
599 /// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
600 /// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
601 /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
602 fn compare_number_of_generics
<'tcx
>(
604 impl_
: &ty
::AssocItem
,
606 trait_
: &ty
::AssocItem
,
607 trait_span
: Option
<Span
>,
608 ) -> Result
<(), ErrorGuaranteed
> {
609 let trait_own_counts
= tcx
.generics_of(trait_
.def_id
).own_counts();
610 let impl_own_counts
= tcx
.generics_of(impl_
.def_id
).own_counts();
612 // This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
613 // in `compare_generic_param_kinds` which will give a nicer error message than something like:
614 // "expected 1 type parameter, found 0 type parameters"
615 if (trait_own_counts
.types
+ trait_own_counts
.consts
)
616 == (impl_own_counts
.types
+ impl_own_counts
.consts
)
622 ("type", trait_own_counts
.types
, impl_own_counts
.types
),
623 ("const", trait_own_counts
.consts
, impl_own_counts
.consts
),
626 let item_kind
= assoc_item_kind_str(impl_
);
628 let mut err_occurred
= None
;
629 for (kind
, trait_count
, impl_count
) in matchings
{
630 if impl_count
!= trait_count
{
631 let arg_spans
= |kind
: ty
::AssocKind
, generics
: &hir
::Generics
<'_
>| {
632 let mut spans
= generics
635 .filter(|p
| match p
.kind
{
636 hir
::GenericParamKind
::Lifetime
{
637 kind
: hir
::LifetimeParamKind
::Elided
,
639 // A fn can have an arbitrary number of extra elided lifetimes for the
641 !matches
!(kind
, ty
::AssocKind
::Fn
)
646 .collect
::<Vec
<Span
>>();
647 if spans
.is_empty() {
648 spans
= vec
![generics
.span
]
652 let (trait_spans
, impl_trait_spans
) = if let Some(def_id
) = trait_
.def_id
.as_local() {
653 let trait_item
= tcx
.hir().expect_trait_item(def_id
);
654 let arg_spans
: Vec
<Span
> = arg_spans(trait_
.kind
, trait_item
.generics
);
655 let impl_trait_spans
: Vec
<Span
> = trait_item
659 .filter_map(|p
| match p
.kind
{
660 GenericParamKind
::Type { synthetic: true, .. }
=> Some(p
.span
),
664 (Some(arg_spans
), impl_trait_spans
)
666 (trait_span
.map(|s
| vec
![s
]), vec
![])
669 let impl_item
= tcx
.hir().expect_impl_item(impl_
.def_id
.expect_local());
670 let impl_item_impl_trait_spans
: Vec
<Span
> = impl_item
674 .filter_map(|p
| match p
.kind
{
675 GenericParamKind
::Type { synthetic: true, .. }
=> Some(p
.span
),
679 let spans
= arg_spans(impl_
.kind
, impl_item
.generics
);
680 let span
= spans
.first().copied();
682 let mut err
= tcx
.sess
.struct_span_err_with_code(
685 "{} `{}` has {} {kind} parameter{} but its trait \
686 declaration has {} {kind} parameter{}",
690 pluralize
!(impl_count
),
692 pluralize
!(trait_count
),
695 DiagnosticId
::Error("E0049".into()),
698 let mut suffix
= None
;
700 if let Some(spans
) = trait_spans
{
701 let mut spans
= spans
.iter();
702 if let Some(span
) = spans
.next() {
706 "expected {} {} parameter{}",
709 pluralize
!(trait_count
),
714 err
.span_label(*span
, "");
717 suffix
= Some(format
!(", expected {trait_count}"));
720 if let Some(span
) = span
{
724 "found {} {} parameter{}{}",
727 pluralize
!(impl_count
),
728 suffix
.unwrap_or_else(String
::new
),
733 for span
in impl_trait_spans
.iter().chain(impl_item_impl_trait_spans
.iter()) {
734 err
.span_label(*span
, "`impl Trait` introduces an implicit type parameter");
737 let reported
= err
.emit();
738 err_occurred
= Some(reported
);
742 if let Some(reported
) = err_occurred { Err(reported) }
else { Ok(()) }
745 fn compare_number_of_method_arguments
<'tcx
>(
747 impl_m
: &ty
::AssocItem
,
749 trait_m
: &ty
::AssocItem
,
750 trait_item_span
: Option
<Span
>,
751 ) -> Result
<(), ErrorGuaranteed
> {
752 let impl_m_fty
= tcx
.fn_sig(impl_m
.def_id
);
753 let trait_m_fty
= tcx
.fn_sig(trait_m
.def_id
);
754 let trait_number_args
= trait_m_fty
.inputs().skip_binder().len();
755 let impl_number_args
= impl_m_fty
.inputs().skip_binder().len();
756 if trait_number_args
!= impl_number_args
{
757 let trait_span
= if let Some(def_id
) = trait_m
.def_id
.as_local() {
758 match tcx
.hir().expect_trait_item(def_id
).kind
{
759 TraitItemKind
::Fn(ref trait_m_sig
, _
) => {
760 let pos
= if trait_number_args
> 0 { trait_number_args - 1 }
else { 0 }
;
761 if let Some(arg
) = trait_m_sig
.decl
.inputs
.get(pos
) {
765 arg
.span
.with_lo(trait_m_sig
.decl
.inputs
[0].span
.lo())
771 _
=> bug
!("{:?} is not a method", impl_m
),
776 let impl_span
= match tcx
.hir().expect_impl_item(impl_m
.def_id
.expect_local()).kind
{
777 ImplItemKind
::Fn(ref impl_m_sig
, _
) => {
778 let pos
= if impl_number_args
> 0 { impl_number_args - 1 }
else { 0 }
;
779 if let Some(arg
) = impl_m_sig
.decl
.inputs
.get(pos
) {
783 arg
.span
.with_lo(impl_m_sig
.decl
.inputs
[0].span
.lo())
789 _
=> bug
!("{:?} is not a method", impl_m
),
791 let mut err
= struct_span_err
!(
795 "method `{}` has {} but the declaration in trait `{}` has {}",
797 potentially_plural_count(impl_number_args
, "parameter"),
798 tcx
.def_path_str(trait_m
.def_id
),
801 if let Some(trait_span
) = trait_span
{
806 potentially_plural_count(trait_number_args
, "parameter")
810 err
.note_trait_signature(trait_m
.name
.to_string(), trait_m
.signature(tcx
));
815 "expected {}, found {}",
816 potentially_plural_count(trait_number_args
, "parameter"),
820 let reported
= err
.emit();
821 return Err(reported
);
827 fn compare_synthetic_generics
<'tcx
>(
829 impl_m
: &ty
::AssocItem
,
830 trait_m
: &ty
::AssocItem
,
831 ) -> Result
<(), ErrorGuaranteed
> {
832 // FIXME(chrisvittal) Clean up this function, list of FIXME items:
833 // 1. Better messages for the span labels
834 // 2. Explanation as to what is going on
835 // If we get here, we already have the same number of generics, so the zip will
837 let mut error_found
= None
;
838 let impl_m_generics
= tcx
.generics_of(impl_m
.def_id
);
839 let trait_m_generics
= tcx
.generics_of(trait_m
.def_id
);
840 let impl_m_type_params
= impl_m_generics
.params
.iter().filter_map(|param
| match param
.kind
{
841 GenericParamDefKind
::Type { synthetic, .. }
=> Some((param
.def_id
, synthetic
)),
842 GenericParamDefKind
::Lifetime
| GenericParamDefKind
::Const { .. }
=> None
,
844 let trait_m_type_params
= trait_m_generics
.params
.iter().filter_map(|param
| match param
.kind
{
845 GenericParamDefKind
::Type { synthetic, .. }
=> Some((param
.def_id
, synthetic
)),
846 GenericParamDefKind
::Lifetime
| GenericParamDefKind
::Const { .. }
=> None
,
848 for ((impl_def_id
, impl_synthetic
), (trait_def_id
, trait_synthetic
)) in
849 iter
::zip(impl_m_type_params
, trait_m_type_params
)
851 if impl_synthetic
!= trait_synthetic
{
852 let impl_def_id
= impl_def_id
.expect_local();
853 let impl_hir_id
= tcx
.hir().local_def_id_to_hir_id(impl_def_id
);
854 let impl_span
= tcx
.hir().span(impl_hir_id
);
855 let trait_span
= tcx
.def_span(trait_def_id
);
856 let mut err
= struct_span_err
!(
860 "method `{}` has incompatible signature for trait",
863 err
.span_label(trait_span
, "declaration in trait here");
864 match (impl_synthetic
, trait_synthetic
) {
865 // The case where the impl method uses `impl Trait` but the trait method uses
868 err
.span_label(impl_span
, "expected generic parameter, found `impl Trait`");
870 // try taking the name from the trait impl
871 // FIXME: this is obviously suboptimal since the name can already be used
872 // as another generic argument
873 let new_name
= tcx
.sess
.source_map().span_to_snippet(trait_span
).ok()?
;
874 let trait_m
= trait_m
.def_id
.as_local()?
;
875 let trait_m
= tcx
.hir().trait_item(hir
::TraitItemId { def_id: trait_m }
);
877 let impl_m
= impl_m
.def_id
.as_local()?
;
878 let impl_m
= tcx
.hir().impl_item(hir
::ImplItemId { def_id: impl_m }
);
880 // in case there are no generics, take the spot between the function name
881 // and the opening paren of the argument list
882 let new_generics_span
=
883 tcx
.sess
.source_map().generate_fn_name_span(impl_span
)?
.shrink_to_hi();
884 // in case there are generics, just replace them
886 impl_m
.generics
.span
.substitute_dummy(new_generics_span
);
887 // replace with the generics from the trait
889 tcx
.sess
.source_map().span_to_snippet(trait_m
.generics
.span
).ok()?
;
891 err
.multipart_suggestion(
892 "try changing the `impl Trait` argument to a generic parameter",
894 // replace `impl Trait` with `T`
895 (impl_span
, new_name
),
896 // replace impl method generics with trait method generics
897 // This isn't quite right, as users might have changed the names
898 // of the generics, but it works for the common case
899 (generics_span
, new_generics
),
901 Applicability
::MaybeIncorrect
,
906 // The case where the trait method uses `impl Trait`, but the impl method uses
907 // explicit generics.
909 err
.span_label(impl_span
, "expected `impl Trait`, found generic parameter");
911 let impl_m
= impl_m
.def_id
.as_local()?
;
912 let impl_m
= tcx
.hir().impl_item(hir
::ImplItemId { def_id: impl_m }
);
913 let input_tys
= match impl_m
.kind
{
914 hir
::ImplItemKind
::Fn(ref sig
, _
) => sig
.decl
.inputs
,
917 struct Visitor(Option
<Span
>, hir
::def_id
::LocalDefId
);
918 impl<'v
> intravisit
::Visitor
<'v
> for Visitor
{
919 fn visit_ty(&mut self, ty
: &'v hir
::Ty
<'v
>) {
920 intravisit
::walk_ty(self, ty
);
921 if let hir
::TyKind
::Path(hir
::QPath
::Resolved(None
, ref path
)) =
923 && let Res
::Def(DefKind
::TyParam
, def_id
) = path
.res
924 && def_id
== self.1.to_def_id()
926 self.0 = Some(ty
.span
);
930 let mut visitor
= Visitor(None
, impl_def_id
);
931 for ty
in input_tys
{
932 intravisit
::Visitor
::visit_ty(&mut visitor
, ty
);
934 let span
= visitor
.0?
;
936 let bounds
= impl_m
.generics
.bounds_for_param(impl_def_id
).next()?
.bounds
;
937 let bounds
= bounds
.first()?
.span().to(bounds
.last()?
.span());
938 let bounds
= tcx
.sess
.source_map().span_to_snippet(bounds
).ok()?
;
940 err
.multipart_suggestion(
941 "try removing the generic parameter and using `impl Trait` instead",
943 // delete generic parameters
944 (impl_m
.generics
.span
, String
::new()),
945 // replace param usage with `impl Trait`
946 (span
, format
!("impl {bounds}")),
948 Applicability
::MaybeIncorrect
,
955 let reported
= err
.emit();
956 error_found
= Some(reported
);
959 if let Some(reported
) = error_found { Err(reported) }
else { Ok(()) }
962 /// Checks that all parameters in the generics of a given assoc item in a trait impl have
963 /// the same kind as the respective generic parameter in the trait def.
965 /// For example all 4 errors in the following code are emitted here:
968 /// fn foo<const N: u8>();
969 /// type bar<const N: u8>;
970 /// fn baz<const N: u32>();
974 /// impl Foo for () {
975 /// fn foo<const N: u64>() {}
977 /// type bar<const N: u64> {}
981 /// type blah<const N: i64> = u32;
986 /// This function does not handle lifetime parameters
987 fn compare_generic_param_kinds
<'tcx
>(
989 impl_item
: &ty
::AssocItem
,
990 trait_item
: &ty
::AssocItem
,
991 ) -> Result
<(), ErrorGuaranteed
> {
992 assert_eq
!(impl_item
.kind
, trait_item
.kind
);
994 let ty_const_params_of
= |def_id
| {
995 tcx
.generics_of(def_id
).params
.iter().filter(|param
| {
998 GenericParamDefKind
::Const { .. }
| GenericParamDefKind
::Type { .. }
1003 for (param_impl
, param_trait
) in
1004 iter
::zip(ty_const_params_of(impl_item
.def_id
), ty_const_params_of(trait_item
.def_id
))
1006 use GenericParamDefKind
::*;
1007 if match (¶m_impl
.kind
, ¶m_trait
.kind
) {
1008 (Const { .. }
, Const { .. }
)
1009 if tcx
.type_of(param_impl
.def_id
) != tcx
.type_of(param_trait
.def_id
) =>
1013 (Const { .. }
, Type { .. }
) | (Type { .. }
, Const { .. }
) => true,
1014 // this is exhaustive so that anyone adding new generic param kinds knows
1015 // to make sure this error is reported for them.
1016 (Const { .. }
, Const { .. }
) | (Type { .. }
, Type { .. }
) => false,
1017 (Lifetime { .. }
, _
) | (_
, Lifetime { .. }
) => unreachable
!(),
1019 let param_impl_span
= tcx
.def_span(param_impl
.def_id
);
1020 let param_trait_span
= tcx
.def_span(param_trait
.def_id
);
1022 let mut err
= struct_span_err
!(
1026 "{} `{}` has an incompatible generic parameter for trait `{}`",
1027 assoc_item_kind_str(&impl_item
),
1029 &tcx
.def_path_str(tcx
.parent(trait_item
.def_id
))
1032 let make_param_message
= |prefix
: &str, param
: &ty
::GenericParamDef
| match param
.kind
{
1034 format
!("{} const parameter of type `{}`", prefix
, tcx
.type_of(param
.def_id
))
1036 Type { .. }
=> format
!("{} type parameter", prefix
),
1037 Lifetime { .. }
=> unreachable
!(),
1040 let trait_header_span
= tcx
.def_ident_span(tcx
.parent(trait_item
.def_id
)).unwrap();
1041 err
.span_label(trait_header_span
, "");
1042 err
.span_label(param_trait_span
, make_param_message("expected", param_trait
));
1044 let impl_header_span
=
1045 tcx
.sess
.source_map().guess_head_span(tcx
.def_span(tcx
.parent(impl_item
.def_id
)));
1046 err
.span_label(impl_header_span
, "");
1047 err
.span_label(param_impl_span
, make_param_message("found", param_impl
));
1049 let reported
= err
.emit();
1050 return Err(reported
);
1057 pub(crate) fn compare_const_impl
<'tcx
>(
1059 impl_c
: &ty
::AssocItem
,
1061 trait_c
: &ty
::AssocItem
,
1062 impl_trait_ref
: ty
::TraitRef
<'tcx
>,
1064 debug
!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref
);
1066 tcx
.infer_ctxt().enter(|infcx
| {
1067 let param_env
= tcx
.param_env(impl_c
.def_id
);
1068 let inh
= Inherited
::new(infcx
, impl_c
.def_id
.expect_local());
1069 let infcx
= &inh
.infcx
;
1071 // The below is for the most part highly similar to the procedure
1072 // for methods above. It is simpler in many respects, especially
1073 // because we shouldn't really have to deal with lifetimes or
1074 // predicates. In fact some of this should probably be put into
1075 // shared functions because of DRY violations...
1076 let trait_to_impl_substs
= impl_trait_ref
.substs
;
1078 // Create a parameter environment that represents the implementation's
1080 let impl_c_hir_id
= tcx
.hir().local_def_id_to_hir_id(impl_c
.def_id
.expect_local());
1082 // Compute placeholder form of impl and trait const tys.
1083 let impl_ty
= tcx
.type_of(impl_c
.def_id
);
1084 let trait_ty
= tcx
.bound_type_of(trait_c
.def_id
).subst(tcx
, trait_to_impl_substs
);
1085 let mut cause
= ObligationCause
::new(
1088 ObligationCauseCode
::CompareImplConstObligation
,
1091 // There is no "body" here, so just pass dummy id.
1093 inh
.normalize_associated_types_in(impl_c_span
, impl_c_hir_id
, param_env
, impl_ty
);
1095 debug
!("compare_const_impl: impl_ty={:?}", impl_ty
);
1098 inh
.normalize_associated_types_in(impl_c_span
, impl_c_hir_id
, param_env
, trait_ty
);
1100 debug
!("compare_const_impl: trait_ty={:?}", trait_ty
);
1103 .at(&cause
, param_env
)
1104 .sup(trait_ty
, impl_ty
)
1105 .map(|ok
| inh
.register_infer_ok_obligations(ok
));
1107 if let Err(terr
) = err
{
1109 "checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
1113 // Locate the Span containing just the type of the offending impl
1114 match tcx
.hir().expect_impl_item(impl_c
.def_id
.expect_local()).kind
{
1115 ImplItemKind
::Const(ref ty
, _
) => cause
.span
= ty
.span
,
1116 _
=> bug
!("{:?} is not a impl const", impl_c
),
1119 let mut diag
= struct_span_err
!(
1123 "implemented const `{}` has an incompatible type for trait",
1127 let trait_c_span
= trait_c
.def_id
.as_local().map(|trait_c_def_id
| {
1128 // Add a label to the Span containing just the type of the const
1129 match tcx
.hir().expect_trait_item(trait_c_def_id
).kind
{
1130 TraitItemKind
::Const(ref ty
, _
) => ty
.span
,
1131 _
=> bug
!("{:?} is not a trait const", trait_c
),
1135 infcx
.note_type_err(
1138 trait_c_span
.map(|span
| (span
, "type in trait".to_owned())),
1139 Some(infer
::ValuePairs
::Terms(ExpectedFound
{
1140 expected
: trait_ty
.into(),
1141 found
: impl_ty
.into(),
1150 // Check that all obligations are satisfied by the implementation's
1152 let errors
= inh
.fulfillment_cx
.borrow_mut().select_all_or_error(&infcx
);
1153 if !errors
.is_empty() {
1154 infcx
.report_fulfillment_errors(&errors
, None
, false);
1158 let fcx
= FnCtxt
::new(&inh
, param_env
, impl_c_hir_id
);
1159 fcx
.regionck_item(impl_c_hir_id
, impl_c_span
, FxHashSet
::default());
1163 pub(crate) fn compare_ty_impl
<'tcx
>(
1165 impl_ty
: &ty
::AssocItem
,
1167 trait_ty
: &ty
::AssocItem
,
1168 impl_trait_ref
: ty
::TraitRef
<'tcx
>,
1169 trait_item_span
: Option
<Span
>,
1171 debug
!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref
);
1173 let _
: Result
<(), ErrorGuaranteed
> = (|| {
1174 compare_number_of_generics(tcx
, impl_ty
, impl_ty_span
, trait_ty
, trait_item_span
)?
;
1176 compare_generic_param_kinds(tcx
, impl_ty
, trait_ty
)?
;
1178 let sp
= tcx
.def_span(impl_ty
.def_id
);
1179 compare_type_predicate_entailment(tcx
, impl_ty
, sp
, trait_ty
, impl_trait_ref
)?
;
1181 check_type_bounds(tcx
, trait_ty
, impl_ty
, impl_ty_span
, impl_trait_ref
)
1185 /// The equivalent of [compare_predicate_entailment], but for associated types
1186 /// instead of associated functions.
1187 fn compare_type_predicate_entailment
<'tcx
>(
1189 impl_ty
: &ty
::AssocItem
,
1191 trait_ty
: &ty
::AssocItem
,
1192 impl_trait_ref
: ty
::TraitRef
<'tcx
>,
1193 ) -> Result
<(), ErrorGuaranteed
> {
1194 let impl_substs
= InternalSubsts
::identity_for_item(tcx
, impl_ty
.def_id
);
1195 let trait_to_impl_substs
=
1196 impl_substs
.rebase_onto(tcx
, impl_ty
.container
.id(), impl_trait_ref
.substs
);
1198 let impl_ty_generics
= tcx
.generics_of(impl_ty
.def_id
);
1199 let trait_ty_generics
= tcx
.generics_of(trait_ty
.def_id
);
1200 let impl_ty_predicates
= tcx
.predicates_of(impl_ty
.def_id
);
1201 let trait_ty_predicates
= tcx
.predicates_of(trait_ty
.def_id
);
1203 check_region_bounds_on_impl_item(
1212 let impl_ty_own_bounds
= impl_ty_predicates
.instantiate_own(tcx
, impl_substs
);
1214 if impl_ty_own_bounds
.is_empty() {
1215 // Nothing to check.
1219 // This `HirId` should be used for the `body_id` field on each
1220 // `ObligationCause` (and the `FnCtxt`). This is what
1221 // `regionck_item` expects.
1222 let impl_ty_hir_id
= tcx
.hir().local_def_id_to_hir_id(impl_ty
.def_id
.expect_local());
1223 let cause
= ObligationCause
::new(
1226 ObligationCauseCode
::CompareImplTypeObligation
{
1227 impl_item_def_id
: impl_ty
.def_id
.expect_local(),
1228 trait_item_def_id
: trait_ty
.def_id
,
1232 debug
!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs
);
1234 // The predicates declared by the impl definition, the trait and the
1235 // associated type in the trait are assumed.
1236 let impl_predicates
= tcx
.predicates_of(impl_ty_predicates
.parent
.unwrap());
1237 let mut hybrid_preds
= impl_predicates
.instantiate_identity(tcx
);
1240 .extend(trait_ty_predicates
.instantiate_own(tcx
, trait_to_impl_substs
).predicates
);
1242 debug
!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds
);
1244 let normalize_cause
= traits
::ObligationCause
::misc(impl_ty_span
, impl_ty_hir_id
);
1245 let param_env
= ty
::ParamEnv
::new(
1246 tcx
.intern_predicates(&hybrid_preds
.predicates
),
1248 hir
::Constness
::NotConst
,
1250 let param_env
= traits
::normalize_param_env_or_error(
1254 normalize_cause
.clone(),
1256 tcx
.infer_ctxt().enter(|infcx
| {
1257 let inh
= Inherited
::new(infcx
, impl_ty
.def_id
.expect_local());
1258 let infcx
= &inh
.infcx
;
1260 debug
!("compare_type_predicate_entailment: caller_bounds={:?}", param_env
.caller_bounds());
1262 let mut selcx
= traits
::SelectionContext
::new(&infcx
);
1264 for predicate
in impl_ty_own_bounds
.predicates
{
1265 let traits
::Normalized { value: predicate, obligations }
=
1266 traits
::normalize(&mut selcx
, param_env
, normalize_cause
.clone(), predicate
);
1268 inh
.register_predicates(obligations
);
1269 inh
.register_predicate(traits
::Obligation
::new(cause
.clone(), param_env
, predicate
));
1272 // Check that all obligations are satisfied by the implementation's
1274 let errors
= inh
.fulfillment_cx
.borrow_mut().select_all_or_error(&infcx
);
1275 if !errors
.is_empty() {
1276 let reported
= infcx
.report_fulfillment_errors(&errors
, None
, false);
1277 return Err(reported
);
1280 // Finally, resolve all regions. This catches wily misuses of
1281 // lifetime parameters.
1282 let fcx
= FnCtxt
::new(&inh
, param_env
, impl_ty_hir_id
);
1283 fcx
.regionck_item(impl_ty_hir_id
, impl_ty_span
, FxHashSet
::default());
1289 /// Validate that `ProjectionCandidate`s created for this associated type will
1294 /// trait X { type Y: Copy } impl X for T { type Y = S; }
1296 /// We are able to normalize `<T as X>::U` to `S`, and so when we check the
1297 /// impl is well-formed we have to prove `S: Copy`.
1299 /// For default associated types the normalization is not possible (the value
1300 /// from the impl could be overridden). We also can't normalize generic
1301 /// associated types (yet) because they contain bound parameters.
1302 #[tracing::instrument(level = "debug", skip(tcx))]
1303 pub fn check_type_bounds
<'tcx
>(
1305 trait_ty
: &ty
::AssocItem
,
1306 impl_ty
: &ty
::AssocItem
,
1308 impl_trait_ref
: ty
::TraitRef
<'tcx
>,
1309 ) -> Result
<(), ErrorGuaranteed
> {
1312 // impl<A, B> Foo<u32> for (A, B) {
1316 // - `impl_trait_ref` would be `<(A, B) as Foo<u32>>
1317 // - `impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
1318 // - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
1319 // the *trait* with the generic associated type parameters (as bound vars).
1321 // A note regarding the use of bound vars here:
1322 // Imagine as an example
1325 // type Member<C: Eq>;
1328 // impl Family for VecFamily {
1329 // type Member<C: Eq> = i32;
1332 // Here, we would generate
1334 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
1336 // when we really would like to generate
1338 // forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
1340 // But, this is probably fine, because although the first clause can be used with types C that
1341 // do not implement Eq, for it to cause some kind of problem, there would have to be a
1342 // VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
1343 // Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
1344 // elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
1345 // the trait (notably, that X: Eq and T: Family).
1346 let defs
: &ty
::Generics
= tcx
.generics_of(impl_ty
.def_id
);
1347 let mut substs
= smallvec
::SmallVec
::with_capacity(defs
.count());
1348 if let Some(def_id
) = defs
.parent
{
1349 let parent_defs
= tcx
.generics_of(def_id
);
1350 InternalSubsts
::fill_item(&mut substs
, tcx
, parent_defs
, &mut |param
, _
| {
1351 tcx
.mk_param_from_def(param
)
1354 let mut bound_vars
: smallvec
::SmallVec
<[ty
::BoundVariableKind
; 8]> =
1355 smallvec
::SmallVec
::with_capacity(defs
.count());
1356 InternalSubsts
::fill_single(&mut substs
, defs
, &mut |param
, _
| match param
.kind
{
1357 GenericParamDefKind
::Type { .. }
=> {
1358 let kind
= ty
::BoundTyKind
::Param(param
.name
);
1359 let bound_var
= ty
::BoundVariableKind
::Ty(kind
);
1360 bound_vars
.push(bound_var
);
1361 tcx
.mk_ty(ty
::Bound(
1363 ty
::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind }
,
1367 GenericParamDefKind
::Lifetime
=> {
1368 let kind
= ty
::BoundRegionKind
::BrNamed(param
.def_id
, param
.name
);
1369 let bound_var
= ty
::BoundVariableKind
::Region(kind
);
1370 bound_vars
.push(bound_var
);
1371 tcx
.mk_region(ty
::ReLateBound(
1373 ty
::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind }
,
1377 GenericParamDefKind
::Const { .. }
=> {
1378 let bound_var
= ty
::BoundVariableKind
::Const
;
1379 bound_vars
.push(bound_var
);
1380 tcx
.mk_const(ty
::ConstS
{
1381 ty
: tcx
.type_of(param
.def_id
),
1382 kind
: ty
::ConstKind
::Bound(
1384 ty
::BoundVar
::from_usize(bound_vars
.len() - 1),
1390 let bound_vars
= tcx
.mk_bound_variable_kinds(bound_vars
.into_iter());
1391 let impl_ty_substs
= tcx
.intern_substs(&substs
);
1393 let rebased_substs
=
1394 impl_ty_substs
.rebase_onto(tcx
, impl_ty
.container
.id(), impl_trait_ref
.substs
);
1395 let impl_ty_value
= tcx
.type_of(impl_ty
.def_id
);
1397 let param_env
= tcx
.param_env(impl_ty
.def_id
);
1399 // When checking something like
1401 // trait X { type Y: PartialEq<<Self as X>::Y> }
1402 // impl X for T { default type Y = S; }
1404 // We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
1405 // we want <T as X>::Y to normalize to S. This is valid because we are
1406 // checking the default value specifically here. Add this equality to the
1407 // ParamEnv for normalization specifically.
1408 let normalize_param_env
= {
1409 let mut predicates
= param_env
.caller_bounds().iter().collect
::<Vec
<_
>>();
1410 match impl_ty_value
.kind() {
1411 ty
::Projection(proj
)
1412 if proj
.item_def_id
== trait_ty
.def_id
&& proj
.substs
== rebased_substs
=>
1414 // Don't include this predicate if the projected type is
1415 // exactly the same as the projection. This can occur in
1416 // (somewhat dubious) code like this:
1418 // impl<T> X for T where T: X { type Y = <T as X>::Y; }
1420 _
=> predicates
.push(
1421 ty
::Binder
::bind_with_vars(
1422 ty
::ProjectionPredicate
{
1423 projection_ty
: ty
::ProjectionTy
{
1424 item_def_id
: trait_ty
.def_id
,
1425 substs
: rebased_substs
,
1427 term
: impl_ty_value
.into(),
1435 tcx
.intern_predicates(&predicates
),
1437 param_env
.constness(),
1440 debug
!(?normalize_param_env
);
1442 let impl_ty_substs
= InternalSubsts
::identity_for_item(tcx
, impl_ty
.def_id
);
1443 let rebased_substs
=
1444 impl_ty_substs
.rebase_onto(tcx
, impl_ty
.container
.id(), impl_trait_ref
.substs
);
1446 tcx
.infer_ctxt().enter(move |infcx
| {
1447 let inh
= Inherited
::new(infcx
, impl_ty
.def_id
.expect_local());
1448 let infcx
= &inh
.infcx
;
1449 let mut selcx
= traits
::SelectionContext
::new(&infcx
);
1451 let impl_ty_hir_id
= tcx
.hir().local_def_id_to_hir_id(impl_ty
.def_id
.expect_local());
1452 let normalize_cause
= ObligationCause
::new(
1455 ObligationCauseCode
::CheckAssociatedTypeBounds
{
1456 impl_item_def_id
: impl_ty
.def_id
.expect_local(),
1457 trait_item_def_id
: trait_ty
.def_id
,
1460 let mk_cause
= |span
: Span
| {
1461 let code
= if span
.is_dummy() {
1462 traits
::MiscObligation
1464 traits
::BindingObligation(trait_ty
.def_id
, span
)
1466 ObligationCause
::new(impl_ty_span
, impl_ty_hir_id
, code
)
1469 let obligations
= tcx
1470 .bound_explicit_item_bounds(trait_ty
.def_id
)
1472 .map(|e
| e
.map_bound(|e
| *e
).transpose_tuple2())
1473 .map(|(bound
, span
)| {
1475 let concrete_ty_bound
= bound
.subst(tcx
, rebased_substs
);
1476 debug
!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound
);
1478 traits
::Obligation
::new(mk_cause(span
.0), param_env
, concrete_ty_bound
)
1481 debug
!("check_type_bounds: item_bounds={:?}", obligations
);
1483 for mut obligation
in util
::elaborate_obligations(tcx
, obligations
) {
1484 let traits
::Normalized { value: normalized_predicate, obligations }
= traits
::normalize(
1486 normalize_param_env
,
1487 normalize_cause
.clone(),
1488 obligation
.predicate
,
1490 debug
!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate
);
1491 obligation
.predicate
= normalized_predicate
;
1493 inh
.register_predicates(obligations
);
1494 inh
.register_predicate(obligation
);
1497 // Check that all obligations are satisfied by the implementation's
1499 let errors
= inh
.fulfillment_cx
.borrow_mut().select_all_or_error(&infcx
);
1500 if !errors
.is_empty() {
1501 let reported
= infcx
.report_fulfillment_errors(&errors
, None
, false);
1502 return Err(reported
);
1505 // Finally, resolve all regions. This catches wily misuses of
1506 // lifetime parameters.
1507 let fcx
= FnCtxt
::new(&inh
, param_env
, impl_ty_hir_id
);
1508 let implied_bounds
= match impl_ty
.container
{
1509 ty
::TraitContainer(_
) => FxHashSet
::default(),
1510 ty
::ImplContainer(def_id
) => fcx
.impl_implied_bounds(def_id
, impl_ty_span
),
1512 fcx
.regionck_item(impl_ty_hir_id
, impl_ty_span
, implied_bounds
);
1518 fn assoc_item_kind_str(impl_item
: &ty
::AssocItem
) -> &'
static str {
1519 match impl_item
.kind
{
1520 ty
::AssocKind
::Const
=> "const",
1521 ty
::AssocKind
::Fn
=> "method",
1522 ty
::AssocKind
::Type
=> "type",