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fuchsia / third_party / rust / 03534ac8b70de1134ce7e91b172cd629048a6c8b / . / compiler / rustc_hir_analysis / src / check / compare_impl_item.rs
blob: 283a9ed3388eb9518022465cf2f882cd77fc12b7 [file] [log] [blame]
use super::potentially_plural_count;
use crate::errors::LifetimesOrBoundsMismatchOnTrait;
use hir::def_id::{DefId, LocalDefId};
use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
use rustc_errors::{
pluralize, struct_span_err, Applicability, DiagnosticId, ErrorGuaranteed, MultiSpan,
};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit;
use rustc_hir::{GenericParamKind, ImplItemKind};
use rustc_infer::infer::outlives::env::OutlivesEnvironment;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::util;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::util::ExplicitSelf;
use rustc_middle::ty::{
self, InternalSubsts, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
};
use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
use rustc_span::Span;
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
use rustc_trait_selection::traits::{
self, ObligationCause, ObligationCauseCode, ObligationCtxt, Reveal,
};
use std::iter;
/// Checks that a method from an impl conforms to the signature of
/// the same method as declared in the trait.
///
/// # Parameters
///
/// - `impl_m`: type of the method we are checking
/// - `trait_m`: the method in the trait
/// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
pub(super) fn compare_impl_method<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) {
debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
let _: Result<_, ErrorGuaranteed> = try {
compare_self_type(tcx, impl_m, trait_m, impl_trait_ref)?;
compare_number_of_generics(tcx, impl_m, trait_m, false)?;
compare_generic_param_kinds(tcx, impl_m, trait_m, false)?;
compare_number_of_method_arguments(tcx, impl_m, trait_m)?;
compare_synthetic_generics(tcx, impl_m, trait_m)?;
compare_asyncness(tcx, impl_m, trait_m)?;
compare_method_predicate_entailment(
tcx,
impl_m,
trait_m,
impl_trait_ref,
CheckImpliedWfMode::Check,
)?;
};
}
/// This function is best explained by example. Consider a trait with it's implementation:
///
/// ```rust
/// trait Trait<'t, T> {
/// // `trait_m`
/// fn method<'a, M>(t: &'t T, m: &'a M) -> Self;
/// }
///
/// struct Foo;
///
/// impl<'i, 'j, U> Trait<'j, &'i U> for Foo {
/// // `impl_m`
/// fn method<'b, N>(t: &'j &'i U, m: &'b N) -> Foo { Foo }
/// }
/// ```
///
/// We wish to decide if those two method types are compatible.
/// For this we have to show that, assuming the bounds of the impl hold, the
/// bounds of `trait_m` imply the bounds of `impl_m`.
///
/// We start out with `trait_to_impl_substs`, that maps the trait
/// type parameters to impl type parameters. This is taken from the
/// impl trait reference:
///
/// ```rust,ignore (pseudo-Rust)
/// trait_to_impl_substs = {'t => 'j, T => &'i U, Self => Foo}
/// ```
///
/// We create a mapping `dummy_substs` that maps from the impl type
/// parameters to fresh types and regions. For type parameters,
/// this is the identity transform, but we could as well use any
/// placeholder types. For regions, we convert from bound to free
/// regions (Note: but only early-bound regions, i.e., those
/// declared on the impl or used in type parameter bounds).
///
/// ```rust,ignore (pseudo-Rust)
/// impl_to_placeholder_substs = {'i => 'i0, U => U0, N => N0 }
/// ```
///
/// Now we can apply `placeholder_substs` to the type of the impl method
/// to yield a new function type in terms of our fresh, placeholder
/// types:
///
/// ```rust,ignore (pseudo-Rust)
/// <'b> fn(t: &'i0 U0, m: &'b) -> Foo
/// ```
///
/// We now want to extract and substitute the type of the *trait*
/// method and compare it. To do so, we must create a compound
/// substitution by combining `trait_to_impl_substs` and
/// `impl_to_placeholder_substs`, and also adding a mapping for the method
/// type parameters. We extend the mapping to also include
/// the method parameters.
///
/// ```rust,ignore (pseudo-Rust)
/// trait_to_placeholder_substs = { T => &'i0 U0, Self => Foo, M => N0 }
/// ```
///
/// Applying this to the trait method type yields:
///
/// ```rust,ignore (pseudo-Rust)
/// <'a> fn(t: &'i0 U0, m: &'a) -> Foo
/// ```
///
/// This type is also the same but the name of the bound region (`'a`
/// vs `'b`). However, the normal subtyping rules on fn types handle
/// this kind of equivalency just fine.
///
/// We now use these substitutions to ensure that all declared bounds are
/// satisfied by the implementation's method.
///
/// We do this by creating a parameter environment which contains a
/// substitution corresponding to `impl_to_placeholder_substs`. We then build
/// `trait_to_placeholder_substs` and use it to convert the predicates contained
/// in the `trait_m` generics to the placeholder form.
///
/// Finally we register each of these predicates as an obligation and check that
/// they hold.
#[instrument(level = "debug", skip(tcx, impl_trait_ref))]
fn compare_method_predicate_entailment<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
check_implied_wf: CheckImpliedWfMode,
) -> Result<(), ErrorGuaranteed> {
let trait_to_impl_substs = impl_trait_ref.substs;
// This node-id should be used for the `body_id` field on each
// `ObligationCause` (and the `FnCtxt`).
//
// FIXME(@lcnr): remove that after removing `cause.body_id` from
// obligations.
let impl_m_def_id = impl_m.def_id.expect_local();
let impl_m_span = tcx.def_span(impl_m_def_id);
let cause = ObligationCause::new(
impl_m_span,
impl_m_def_id,
ObligationCauseCode::CompareImplItemObligation {
impl_item_def_id: impl_m_def_id,
trait_item_def_id: trait_m.def_id,
kind: impl_m.kind,
},
);
// Create mapping from impl to placeholder.
let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
// Create mapping from trait to placeholder.
let trait_to_placeholder_substs =
impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs);
debug!("compare_impl_method: trait_to_placeholder_substs={:?}", trait_to_placeholder_substs);
let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
// Check region bounds.
check_region_bounds_on_impl_item(tcx, impl_m, trait_m, false)?;
// Create obligations for each predicate declared by the impl
// definition in the context of the trait's parameter
// environment. We can't just use `impl_env.caller_bounds`,
// however, because we want to replace all late-bound regions with
// region variables.
let impl_predicates = tcx.predicates_of(impl_m_predicates.parent.unwrap());
let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
// This is the only tricky bit of the new way we check implementation methods
// We need to build a set of predicates where only the method-level bounds
// are from the trait and we assume all other bounds from the implementation
// to be previously satisfied.
//
// We then register the obligations from the impl_m and check to see
// if all constraints hold.
hybrid_preds.predicates.extend(
trait_m_predicates
.instantiate_own(tcx, trait_to_placeholder_substs)
.map(|(predicate, _)| predicate),
);
// Construct trait parameter environment and then shift it into the placeholder viewpoint.
// The key step here is to update the caller_bounds's predicates to be
// the new hybrid bounds we computed.
let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_def_id);
let param_env = ty::ParamEnv::new(
tcx.mk_predicates(&hybrid_preds.predicates),
Reveal::UserFacing,
hir::Constness::NotConst,
);
let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
let infcx = &tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(infcx);
debug!("compare_impl_method: caller_bounds={:?}", param_env.caller_bounds());
let impl_m_own_bounds = impl_m_predicates.instantiate_own(tcx, impl_to_placeholder_substs);
for (predicate, span) in impl_m_own_bounds {
let normalize_cause = traits::ObligationCause::misc(span, impl_m_def_id);
let predicate = ocx.normalize(&normalize_cause, param_env, predicate);
let cause = ObligationCause::new(
span,
impl_m_def_id,
ObligationCauseCode::CompareImplItemObligation {
impl_item_def_id: impl_m_def_id,
trait_item_def_id: trait_m.def_id,
kind: impl_m.kind,
},
);
ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate));
}
// We now need to check that the signature of the impl method is
// compatible with that of the trait method. We do this by
// checking that `impl_fty <: trait_fty`.
//
// FIXME. Unfortunately, this doesn't quite work right now because
// associated type normalization is not integrated into subtype
// checks. For the comparison to be valid, we need to
// normalize the associated types in the impl/trait methods
// first. However, because function types bind regions, just
// calling `normalize_associated_types_in` would have no effect on
// any associated types appearing in the fn arguments or return
// type.
// Compute placeholder form of impl and trait method tys.
let tcx = infcx.tcx;
let mut wf_tys = FxIndexSet::default();
let unnormalized_impl_sig = infcx.instantiate_binder_with_fresh_vars(
impl_m_span,
infer::HigherRankedType,
tcx.fn_sig(impl_m.def_id).subst_identity(),
);
let unnormalized_impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(unnormalized_impl_sig));
let norm_cause = ObligationCause::misc(impl_m_span, impl_m_def_id);
let impl_sig = ocx.normalize(&norm_cause, param_env, unnormalized_impl_sig);
debug!("compare_impl_method: impl_fty={:?}", impl_sig);
let trait_sig = tcx.fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs);
let trait_sig = tcx.liberate_late_bound_regions(impl_m.def_id, trait_sig);
// Next, add all inputs and output as well-formed tys. Importantly,
// we have to do this before normalization, since the normalized ty may
// not contain the input parameters. See issue #87748.
wf_tys.extend(trait_sig.inputs_and_output.iter());
let trait_sig = ocx.normalize(&norm_cause, param_env, trait_sig);
// We also have to add the normalized trait signature
// as we don't normalize during implied bounds computation.
wf_tys.extend(trait_sig.inputs_and_output.iter());
let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
debug!("compare_impl_method: trait_fty={:?}", trait_fty);
// FIXME: We'd want to keep more accurate spans than "the method signature" when
// processing the comparison between the trait and impl fn, but we sadly lose them
// and point at the whole signature when a trait bound or specific input or output
// type would be more appropriate. In other places we have a `Vec<Span>`
// corresponding to their `Vec<Predicate>`, but we don't have that here.
// Fixing this would improve the output of test `issue-83765.rs`.
let result = ocx.sup(&cause, param_env, trait_sig, impl_sig);
if let Err(terr) = result {
debug!(?impl_sig, ?trait_sig, ?terr, "sub_types failed");
let emitted = report_trait_method_mismatch(
&infcx,
cause,
terr,
(trait_m, trait_sig),
(impl_m, impl_sig),
impl_trait_ref,
);
return Err(emitted);
}
if check_implied_wf == CheckImpliedWfMode::Check {
// We need to check that the impl's args are well-formed given
// the hybrid param-env (impl + trait method where-clauses).
ocx.register_obligation(traits::Obligation::new(
infcx.tcx,
ObligationCause::dummy(),
param_env,
ty::Binder::dummy(ty::PredicateKind::WellFormed(unnormalized_impl_fty.into())),
));
}
// Check that all obligations are satisfied by the implementation's
// version.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
match check_implied_wf {
CheckImpliedWfMode::Check => {
let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m_def_id);
return compare_method_predicate_entailment(
tcx,
impl_m,
trait_m,
impl_trait_ref,
CheckImpliedWfMode::Skip,
)
.map(|()| {
// If the skip-mode was successful, emit a lint.
emit_implied_wf_lint(infcx.tcx, impl_m, impl_m_hir_id, vec![]);
});
}
CheckImpliedWfMode::Skip => {
let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
return Err(reported);
}
}
}
// Finally, resolve all regions. This catches wily misuses of
// lifetime parameters.
let outlives_env = OutlivesEnvironment::with_bounds(
param_env,
infcx.implied_bounds_tys(param_env, impl_m_def_id, wf_tys.clone()),
);
let errors = infcx.resolve_regions(&outlives_env);
if !errors.is_empty() {
// FIXME(compiler-errors): This can be simplified when IMPLIED_BOUNDS_ENTAILMENT
// becomes a hard error (i.e. ideally we'd just call `resolve_regions_and_report_errors`
let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m_def_id);
match check_implied_wf {
CheckImpliedWfMode::Check => {
return compare_method_predicate_entailment(
tcx,
impl_m,
trait_m,
impl_trait_ref,
CheckImpliedWfMode::Skip,
)
.map(|()| {
let bad_args = extract_bad_args_for_implies_lint(
tcx,
&errors,
(trait_m, trait_sig),
// Unnormalized impl sig corresponds to the HIR types written
(impl_m, unnormalized_impl_sig),
impl_m_hir_id,
);
// If the skip-mode was successful, emit a lint.
emit_implied_wf_lint(tcx, impl_m, impl_m_hir_id, bad_args);
});
}
CheckImpliedWfMode::Skip => {
if infcx.tainted_by_errors().is_none() {
infcx.err_ctxt().report_region_errors(impl_m_def_id, &errors);
}
return Err(tcx
.sess
.delay_span_bug(rustc_span::DUMMY_SP, "error should have been emitted"));
}
}
}
Ok(())
}
fn extract_bad_args_for_implies_lint<'tcx>(
tcx: TyCtxt<'tcx>,
errors: &[infer::RegionResolutionError<'tcx>],
(trait_m, trait_sig): (ty::AssocItem, ty::FnSig<'tcx>),
(impl_m, impl_sig): (ty::AssocItem, ty::FnSig<'tcx>),
hir_id: hir::HirId,
) -> Vec<(Span, Option<String>)> {
let mut blame_generics = vec![];
for error in errors {
// Look for the subregion origin that contains an input/output type
let origin = match error {
infer::RegionResolutionError::ConcreteFailure(o, ..) => o,
infer::RegionResolutionError::GenericBoundFailure(o, ..) => o,
infer::RegionResolutionError::SubSupConflict(_, _, o, ..) => o,
infer::RegionResolutionError::UpperBoundUniverseConflict(.., o, _) => o,
};
// Extract (possible) input/output types from origin
match origin {
infer::SubregionOrigin::Subtype(trace) => {
if let Some((a, b)) = trace.values.ty() {
blame_generics.extend([a, b]);
}
}
infer::SubregionOrigin::RelateParamBound(_, ty, _) => blame_generics.push(*ty),
infer::SubregionOrigin::ReferenceOutlivesReferent(ty, _) => blame_generics.push(*ty),
_ => {}
}
}
let fn_decl = tcx.hir().fn_decl_by_hir_id(hir_id).unwrap();
let opt_ret_ty = match fn_decl.output {
hir::FnRetTy::DefaultReturn(_) => None,
hir::FnRetTy::Return(ty) => Some(ty),
};
// Map late-bound regions from trait to impl, so the names are right.
let mapping = std::iter::zip(
tcx.fn_sig(trait_m.def_id).skip_binder().bound_vars(),
tcx.fn_sig(impl_m.def_id).skip_binder().bound_vars(),
)
.filter_map(|(impl_bv, trait_bv)| {
if let ty::BoundVariableKind::Region(impl_bv) = impl_bv
&& let ty::BoundVariableKind::Region(trait_bv) = trait_bv
{
Some((impl_bv, trait_bv))
} else {
None
}
})
.collect();
// For each arg, see if it was in the "blame" of any of the region errors.
// If so, then try to produce a suggestion to replace the argument type with
// one from the trait.
let mut bad_args = vec![];
for (idx, (ty, hir_ty)) in
std::iter::zip(impl_sig.inputs_and_output, fn_decl.inputs.iter().chain(opt_ret_ty))
.enumerate()
{
let expected_ty = trait_sig.inputs_and_output[idx]
.fold_with(&mut RemapLateBound { tcx, mapping: &mapping });
if blame_generics.iter().any(|blame| ty.contains(*blame)) {
let expected_ty_sugg = expected_ty.to_string();
bad_args.push((
hir_ty.span,
// Only suggest something if it actually changed.
(expected_ty_sugg != ty.to_string()).then_some(expected_ty_sugg),
));
}
}
bad_args
}
struct RemapLateBound<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
mapping: &'a FxHashMap<ty::BoundRegionKind, ty::BoundRegionKind>,
}
impl<'tcx> TypeFolder<TyCtxt<'tcx>> for RemapLateBound<'_, 'tcx> {
fn interner(&self) -> TyCtxt<'tcx> {
self.tcx
}
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
if let ty::ReFree(fr) = *r {
self.tcx.mk_re_free(
fr.scope,
self.mapping.get(&fr.bound_region).copied().unwrap_or(fr.bound_region),
)
} else {
r
}
}
}
fn emit_implied_wf_lint<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
hir_id: hir::HirId,
bad_args: Vec<(Span, Option<String>)>,
) {
let span: MultiSpan = if bad_args.is_empty() {
tcx.def_span(impl_m.def_id).into()
} else {
bad_args.iter().map(|(span, _)| *span).collect::<Vec<_>>().into()
};
tcx.struct_span_lint_hir(
rustc_session::lint::builtin::IMPLIED_BOUNDS_ENTAILMENT,
hir_id,
span,
"impl method assumes more implied bounds than the corresponding trait method",
|lint| {
let bad_args: Vec<_> =
bad_args.into_iter().filter_map(|(span, sugg)| Some((span, sugg?))).collect();
if !bad_args.is_empty() {
lint.multipart_suggestion(
format!(
"replace {} type{} to make the impl signature compatible",
pluralize!("this", bad_args.len()),
pluralize!(bad_args.len())
),
bad_args,
Applicability::MaybeIncorrect,
);
}
lint
},
);
}
#[derive(Debug, PartialEq, Eq)]
enum CheckImpliedWfMode {
/// Checks implied well-formedness of the impl method. If it fails, we will
/// re-check with `Skip`, and emit a lint if it succeeds.
Check,
/// Skips checking implied well-formedness of the impl method, but will emit
/// a lint if the `compare_method_predicate_entailment` succeeded. This means that
/// the reason that we had failed earlier during `Check` was due to the impl
/// having stronger requirements than the trait.
Skip,
}
fn compare_asyncness<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
) -> Result<(), ErrorGuaranteed> {
if tcx.asyncness(trait_m.def_id) == hir::IsAsync::Async {
match tcx.fn_sig(impl_m.def_id).skip_binder().skip_binder().output().kind() {
ty::Alias(ty::Opaque, ..) => {
// allow both `async fn foo()` and `fn foo() -> impl Future`
}
ty::Error(_) => {
// We don't know if it's ok, but at least it's already an error.
}
_ => {
return Err(tcx.sess.emit_err(crate::errors::AsyncTraitImplShouldBeAsync {
span: tcx.def_span(impl_m.def_id),
method_name: trait_m.name,
trait_item_span: tcx.hir().span_if_local(trait_m.def_id),
}));
}
};
}
Ok(())
}
/// Given a method def-id in an impl, compare the method signature of the impl
/// against the trait that it's implementing. In doing so, infer the hidden types
/// that this method's signature provides to satisfy each return-position `impl Trait`
/// in the trait signature.
///
/// The method is also responsible for making sure that the hidden types for each
/// RPITIT actually satisfy the bounds of the `impl Trait`, i.e. that if we infer
/// `impl Trait = Foo`, that `Foo: Trait` holds.
///
/// For example, given the sample code:
///
/// ```
/// #![feature(return_position_impl_trait_in_trait)]
///
/// use std::ops::Deref;
///
/// trait Foo {
/// fn bar() -> impl Deref<Target = impl Sized>;
/// // ^- RPITIT #1 ^- RPITIT #2
/// }
///
/// impl Foo for () {
/// fn bar() -> Box<String> { Box::new(String::new()) }
/// }
/// ```
///
/// The hidden types for the RPITITs in `bar` would be inferred to:
/// * `impl Deref` (RPITIT #1) = `Box<String>`
/// * `impl Sized` (RPITIT #2) = `String`
///
/// The relationship between these two types is straightforward in this case, but
/// may be more tenuously connected via other `impl`s and normalization rules for
/// cases of more complicated nested RPITITs.
#[instrument(skip(tcx), level = "debug", ret)]
pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m_def_id: LocalDefId,
) -> Result<&'tcx FxHashMap<DefId, ty::EarlyBinder<Ty<'tcx>>>, ErrorGuaranteed> {
let impl_m = tcx.opt_associated_item(impl_m_def_id.to_def_id()).unwrap();
let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
let impl_trait_ref =
tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap().subst_identity();
let param_env = tcx.param_env(impl_m_def_id);
// First, check a few of the same things as `compare_impl_method`,
// just so we don't ICE during substitution later.
compare_number_of_generics(tcx, impl_m, trait_m, true)?;
compare_generic_param_kinds(tcx, impl_m, trait_m, true)?;
check_region_bounds_on_impl_item(tcx, impl_m, trait_m, true)?;
let trait_to_impl_substs = impl_trait_ref.substs;
let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m_def_id);
let return_span = tcx.hir().fn_decl_by_hir_id(impl_m_hir_id).unwrap().output.span();
let cause = ObligationCause::new(
return_span,
impl_m_def_id,
ObligationCauseCode::CompareImplItemObligation {
impl_item_def_id: impl_m_def_id,
trait_item_def_id: trait_m.def_id,
kind: impl_m.kind,
},
);
// Create mapping from impl to placeholder.
let impl_to_placeholder_substs = InternalSubsts::identity_for_item(tcx, impl_m.def_id);
// Create mapping from trait to placeholder.
let trait_to_placeholder_substs =
impl_to_placeholder_substs.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_substs);
let infcx = &tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(infcx);
// Normalize the impl signature with fresh variables for lifetime inference.
let norm_cause = ObligationCause::misc(return_span, impl_m_def_id);
let impl_sig = ocx.normalize(
&norm_cause,
param_env,
infcx.instantiate_binder_with_fresh_vars(
return_span,
infer::HigherRankedType,
tcx.fn_sig(impl_m.def_id).subst_identity(),
),
);
impl_sig.error_reported()?;
let impl_return_ty = impl_sig.output();
// Normalize the trait signature with liberated bound vars, passing it through
// the ImplTraitInTraitCollector, which gathers all of the RPITITs and replaces
// them with inference variables.
// We will use these inference variables to collect the hidden types of RPITITs.
let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_def_id);
let unnormalized_trait_sig = tcx
.liberate_late_bound_regions(
impl_m.def_id,
tcx.fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs),
)
.fold_with(&mut collector);
debug_assert_ne!(
collector.types.len(),
0,
"expect >1 RPITITs in call to `collect_return_position_impl_trait_in_trait_tys`"
);
let trait_sig = ocx.normalize(&norm_cause, param_env, unnormalized_trait_sig);
trait_sig.error_reported()?;
let trait_return_ty = trait_sig.output();
let wf_tys = FxIndexSet::from_iter(
unnormalized_trait_sig.inputs_and_output.iter().chain(trait_sig.inputs_and_output.iter()),
);
match ocx.eq(&cause, param_env, trait_return_ty, impl_return_ty) {
Ok(()) => {}
Err(terr) => {
let mut diag = struct_span_err!(
tcx.sess,
cause.span(),
E0053,
"method `{}` has an incompatible return type for trait",
trait_m.name
);
let hir = tcx.hir();
infcx.err_ctxt().note_type_err(
&mut diag,
&cause,
hir.get_if_local(impl_m.def_id)
.and_then(|node| node.fn_decl())
.map(|decl| (decl.output.span(), "return type in trait".to_owned())),
Some(infer::ValuePairs::Terms(ExpectedFound {
expected: trait_return_ty.into(),
found: impl_return_ty.into(),
})),
terr,
false,
false,
);
return Err(diag.emit());
}
}
debug!(?trait_sig, ?impl_sig, "equating function signatures");
// Unify the whole function signature. We need to do this to fully infer
// the lifetimes of the return type, but do this after unifying just the
// return types, since we want to avoid duplicating errors from
// `compare_method_predicate_entailment`.
match ocx.eq(&cause, param_env, trait_sig, impl_sig) {
Ok(()) => {}
Err(terr) => {
// This function gets called during `compare_method_predicate_entailment` when normalizing a
// signature that contains RPITIT. When the method signatures don't match, we have to
// emit an error now because `compare_method_predicate_entailment` will not report the error
// when normalization fails.
let emitted = report_trait_method_mismatch(
infcx,
cause,
terr,
(trait_m, trait_sig),
(impl_m, impl_sig),
impl_trait_ref,
);
return Err(emitted);
}
}
// Check that all obligations are satisfied by the implementation's
// RPITs.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
return Err(reported);
}
let collected_types = collector.types;
// Finally, resolve all regions. This catches wily misuses of
// lifetime parameters.
let outlives_env = OutlivesEnvironment::with_bounds(
param_env,
infcx.implied_bounds_tys(param_env, impl_m_def_id, wf_tys),
);
ocx.resolve_regions_and_report_errors(impl_m_def_id, &outlives_env)?;
let mut collected_tys = FxHashMap::default();
for (def_id, (ty, substs)) in collected_types {
match infcx.fully_resolve(ty) {
Ok(ty) => {
// `ty` contains free regions that we created earlier while liberating the
// trait fn signature. However, projection normalization expects `ty` to
// contains `def_id`'s early-bound regions.
let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
debug!(?id_substs, ?substs);
let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> =
std::iter::zip(substs, id_substs).collect();
debug!(?map);
// NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound
// region substs that are synthesized during AST lowering. These are substs
// that are appended to the parent substs (trait and trait method). However,
// we're trying to infer the unsubstituted type value of the RPITIT inside
// the *impl*, so we can later use the impl's method substs to normalize
// an RPITIT to a concrete type (`confirm_impl_trait_in_trait_candidate`).
//
// Due to the design of RPITITs, during AST lowering, we have no idea that
// an impl method corresponds to a trait method with RPITITs in it. Therefore,
// we don't have a list of early-bound region substs for the RPITIT in the impl.
// Since early region parameters are index-based, we can't just rebase these
// (trait method) early-bound region substs onto the impl, and there's no
// guarantee that the indices from the trait substs and impl substs line up.
// So to fix this, we subtract the number of trait substs and add the number of
// impl substs to *renumber* these early-bound regions to their corresponding
// indices in the impl's substitutions list.
//
// Also, we only need to account for a difference in trait and impl substs,
// since we previously enforce that the trait method and impl method have the
// same generics.
let num_trait_substs = trait_to_impl_substs.len();
let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len();
let ty = tcx.fold_regions(ty, |region, _| {
match region.kind() {
// Remap all free regions, which correspond to late-bound regions in the function.
ty::ReFree(_) => {}
// Remap early-bound regions as long as they don't come from the `impl` itself.
ty::ReEarlyBound(ebr) if tcx.parent(ebr.def_id) != impl_m.container_id(tcx) => {}
_ => return region,
}
let Some(ty::ReEarlyBound(e)) = map.get(&region.into()).map(|r| r.expect_region().kind())
else {
return tcx.mk_re_error_with_message(return_span, "expected ReFree to map to ReEarlyBound")
};
tcx.mk_re_early_bound(ty::EarlyBoundRegion {
def_id: e.def_id,
name: e.name,
index: (e.index as usize - num_trait_substs + num_impl_substs) as u32,
})
});
debug!(%ty);
collected_tys.insert(def_id, ty::EarlyBinder::new(ty));
}
Err(err) => {
let reported = tcx.sess.delay_span_bug(
return_span,
format!("could not fully resolve: {ty} => {err:?}"),
);
collected_tys.insert(def_id, ty::EarlyBinder::new(tcx.ty_error(reported)));
}
}
}
Ok(&*tcx.arena.alloc(collected_tys))
}
struct ImplTraitInTraitCollector<'a, 'tcx> {
ocx: &'a ObligationCtxt<'a, 'tcx>,
types: FxHashMap<DefId, (Ty<'tcx>, ty::SubstsRef<'tcx>)>,
span: Span,
param_env: ty::ParamEnv<'tcx>,
body_id: LocalDefId,
}
impl<'a, 'tcx> ImplTraitInTraitCollector<'a, 'tcx> {
fn new(
ocx: &'a ObligationCtxt<'a, 'tcx>,
span: Span,
param_env: ty::ParamEnv<'tcx>,
body_id: LocalDefId,
) -> Self {
ImplTraitInTraitCollector { ocx, types: FxHashMap::default(), span, param_env, body_id }
}
}
impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ImplTraitInTraitCollector<'_, 'tcx> {
fn interner(&self) -> TyCtxt<'tcx> {
self.ocx.infcx.tcx
}
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
if let ty::Alias(ty::Projection, proj) = ty.kind()
&& self.interner().is_impl_trait_in_trait(proj.def_id)
{
if let Some((ty, _)) = self.types.get(&proj.def_id) {
return *ty;
}
//FIXME(RPITIT): Deny nested RPITIT in substs too
if proj.substs.has_escaping_bound_vars() {
bug!("FIXME(RPITIT): error here");
}
// Replace with infer var
let infer_ty = self.ocx.infcx.next_ty_var(TypeVariableOrigin {
span: self.span,
kind: TypeVariableOriginKind::MiscVariable,
});
self.types.insert(proj.def_id, (infer_ty, proj.substs));
// Recurse into bounds
for (pred, pred_span) in self.interner().explicit_item_bounds(proj.def_id).subst_iter_copied(self.interner(), proj.substs) {
let pred = pred.fold_with(self);
let pred = self.ocx.normalize(
&ObligationCause::misc(self.span, self.body_id),
self.param_env,
pred,
);
self.ocx.register_obligation(traits::Obligation::new(
self.interner(),
ObligationCause::new(
self.span,
self.body_id,
ObligationCauseCode::BindingObligation(proj.def_id, pred_span),
),
self.param_env,
pred,
));
}
infer_ty
} else {
ty.super_fold_with(self)
}
}
}
fn report_trait_method_mismatch<'tcx>(
infcx: &InferCtxt<'tcx>,
mut cause: ObligationCause<'tcx>,
terr: TypeError<'tcx>,
(trait_m, trait_sig): (ty::AssocItem, ty::FnSig<'tcx>),
(impl_m, impl_sig): (ty::AssocItem, ty::FnSig<'tcx>),
impl_trait_ref: ty::TraitRef<'tcx>,
) -> ErrorGuaranteed {
let tcx = infcx.tcx;
let (impl_err_span, trait_err_span) =
extract_spans_for_error_reporting(&infcx, terr, &cause, impl_m, trait_m);
let mut diag = struct_span_err!(
tcx.sess,
impl_err_span,
E0053,
"method `{}` has an incompatible type for trait",
trait_m.name
);
match &terr {
TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
if trait_m.fn_has_self_parameter =>
{
let ty = trait_sig.inputs()[0];
let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty()) {
ExplicitSelf::ByValue => "self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
_ => format!("self: {ty}"),
};
// When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
// span points only at the type `Box<Self`>, but we want to cover the whole
// argument pattern and type.
let (sig, body) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
let span = tcx
.hir()
.body_param_names(body)
.zip(sig.decl.inputs.iter())
.map(|(param, ty)| param.span.to(ty.span))
.next()
.unwrap_or(impl_err_span);
diag.span_suggestion(
span,
"change the self-receiver type to match the trait",
sugg,
Applicability::MachineApplicable,
);
}
TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
if trait_sig.inputs().len() == *i {
// Suggestion to change output type. We do not suggest in `async` functions
// to avoid complex logic or incorrect output.
if let ImplItemKind::Fn(sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).kind
&& !sig.header.asyncness.is_async()
{
let msg = "change the output type to match the trait";
let ap = Applicability::MachineApplicable;
match sig.decl.output {
hir::FnRetTy::DefaultReturn(sp) => {
let sugg = format!("-> {} ", trait_sig.output());
diag.span_suggestion_verbose(sp, msg, sugg, ap);
}
hir::FnRetTy::Return(hir_ty) => {
let sugg = trait_sig.output();
diag.span_suggestion(hir_ty.span, msg, sugg, ap);
}
};
};
} else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
diag.span_suggestion(
impl_err_span,
"change the parameter type to match the trait",
trait_ty,
Applicability::MachineApplicable,
);
}
}
_ => {}
}
cause.span = impl_err_span;
infcx.err_ctxt().note_type_err(
&mut diag,
&cause,
trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
Some(infer::ValuePairs::Sigs(ExpectedFound { expected: trait_sig, found: impl_sig })),
terr,
false,
false,
);
return diag.emit();
}
fn check_region_bounds_on_impl_item<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
delay: bool,
) -> Result<(), ErrorGuaranteed> {
let impl_generics = tcx.generics_of(impl_m.def_id);
let impl_params = impl_generics.own_counts().lifetimes;
let trait_generics = tcx.generics_of(trait_m.def_id);
let trait_params = trait_generics.own_counts().lifetimes;
debug!(
"check_region_bounds_on_impl_item: \
trait_generics={:?} \
impl_generics={:?}",
trait_generics, impl_generics
);
// Must have same number of early-bound lifetime parameters.
// Unfortunately, if the user screws up the bounds, then this
// will change classification between early and late. E.g.,
// if in trait we have `<'a,'b:'a>`, and in impl we just have
// `<'a,'b>`, then we have 2 early-bound lifetime parameters
// in trait but 0 in the impl. But if we report "expected 2
// but found 0" it's confusing, because it looks like there
// are zero. Since I don't quite know how to phrase things at
// the moment, give a kind of vague error message.
if trait_params != impl_params {
let span = tcx
.hir()
.get_generics(impl_m.def_id.expect_local())
.expect("expected impl item to have generics or else we can't compare them")
.span;
let mut generics_span = None;
let mut bounds_span = vec![];
let mut where_span = None;
if let Some(trait_node) = tcx.hir().get_if_local(trait_m.def_id)
&& let Some(trait_generics) = trait_node.generics()
{
generics_span = Some(trait_generics.span);
// FIXME: we could potentially look at the impl's bounds to not point at bounds that
// *are* present in the impl.
for p in trait_generics.predicates {
if let hir::WherePredicate::BoundPredicate(pred) = p {
for b in pred.bounds {
if let hir::GenericBound::Outlives(lt) = b {
bounds_span.push(lt.ident.span);
}
}
}
}
if let Some(impl_node) = tcx.hir().get_if_local(impl_m.def_id)
&& let Some(impl_generics) = impl_node.generics()
{
let mut impl_bounds = 0;
for p in impl_generics.predicates {
if let hir::WherePredicate::BoundPredicate(pred) = p {
for b in pred.bounds {
if let hir::GenericBound::Outlives(_) = b {
impl_bounds += 1;
}
}
}
}
if impl_bounds == bounds_span.len() {
bounds_span = vec![];
} else if impl_generics.has_where_clause_predicates {
where_span = Some(impl_generics.where_clause_span);
}
}
}
let reported = tcx
.sess
.create_err(LifetimesOrBoundsMismatchOnTrait {
span,
item_kind: assoc_item_kind_str(&impl_m),
ident: impl_m.ident(tcx),
generics_span,
bounds_span,
where_span,
})
.emit_unless(delay);
return Err(reported);
}
Ok(())
}
#[instrument(level = "debug", skip(infcx))]
fn extract_spans_for_error_reporting<'tcx>(
infcx: &infer::InferCtxt<'tcx>,
terr: TypeError<'_>,
cause: &ObligationCause<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
) -> (Span, Option<Span>) {
let tcx = infcx.tcx;
let mut impl_args = {
let (sig, _) = tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
};
let trait_args = trait_m.def_id.as_local().map(|def_id| {
let (sig, _) = tcx.hir().expect_trait_item(def_id).expect_fn();
sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
});
match terr {
TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
(impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
}
_ => (cause.span(), tcx.hir().span_if_local(trait_m.def_id)),
}
}
fn compare_self_type<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) -> Result<(), ErrorGuaranteed> {
// Try to give more informative error messages about self typing
// mismatches. Note that any mismatch will also be detected
// below, where we construct a canonical function type that
// includes the self parameter as a normal parameter. It's just
// that the error messages you get out of this code are a bit more
// inscrutable, particularly for cases where one method has no
// self.
let self_string = |method: ty::AssocItem| {
let untransformed_self_ty = match method.container {
ty::ImplContainer => impl_trait_ref.self_ty(),
ty::TraitContainer => tcx.types.self_param,
};
let self_arg_ty = tcx.fn_sig(method.def_id).subst_identity().input(0);
let param_env = ty::ParamEnv::reveal_all();
let infcx = tcx.infer_ctxt().build();
let self_arg_ty = tcx.liberate_late_bound_regions(method.def_id, self_arg_ty);
let can_eq_self = |ty| infcx.can_eq(param_env, untransformed_self_ty, ty);
match ExplicitSelf::determine(self_arg_ty, can_eq_self) {
ExplicitSelf::ByValue => "self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
_ => format!("self: {self_arg_ty}"),
}
};
match (trait_m.fn_has_self_parameter, impl_m.fn_has_self_parameter) {
(false, false) | (true, true) => {}
(false, true) => {
let self_descr = self_string(impl_m);
let impl_m_span = tcx.def_span(impl_m.def_id);
let mut err = struct_span_err!(
tcx.sess,
impl_m_span,
E0185,
"method `{}` has a `{}` declaration in the impl, but not in the trait",
trait_m.name,
self_descr
);
err.span_label(impl_m_span, format!("`{self_descr}` used in impl"));
if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
err.span_label(span, format!("trait method declared without `{self_descr}`"));
} else {
err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
}
return Err(err.emit());
}
(true, false) => {
let self_descr = self_string(trait_m);
let impl_m_span = tcx.def_span(impl_m.def_id);
let mut err = struct_span_err!(
tcx.sess,
impl_m_span,
E0186,
"method `{}` has a `{}` declaration in the trait, but not in the impl",
trait_m.name,
self_descr
);
err.span_label(impl_m_span, format!("expected `{self_descr}` in impl"));
if let Some(span) = tcx.hir().span_if_local(trait_m.def_id) {
err.span_label(span, format!("`{self_descr}` used in trait"));
} else {
err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
}
return Err(err.emit());
}
}
Ok(())
}
/// Checks that the number of generics on a given assoc item in a trait impl is the same
/// as the number of generics on the respective assoc item in the trait definition.
///
/// For example this code emits the errors in the following code:
/// ```rust,compile_fail
/// trait Trait {
/// fn foo();
/// type Assoc<T>;
/// }
///
/// impl Trait for () {
/// fn foo<T>() {}
/// //~^ error
/// type Assoc = u32;
/// //~^ error
/// }
/// ```
///
/// Notably this does not error on `foo<T>` implemented as `foo<const N: u8>` or
/// `foo<const N: u8>` implemented as `foo<const N: u32>`. This is handled in
/// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
fn compare_number_of_generics<'tcx>(
tcx: TyCtxt<'tcx>,
impl_: ty::AssocItem,
trait_: ty::AssocItem,
delay: bool,
) -> Result<(), ErrorGuaranteed> {
let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
let impl_own_counts = tcx.generics_of(impl_.def_id).own_counts();
// This avoids us erroring on `foo<T>` implemented as `foo<const N: u8>` as this is implemented
// in `compare_generic_param_kinds` which will give a nicer error message than something like:
// "expected 1 type parameter, found 0 type parameters"
if (trait_own_counts.types + trait_own_counts.consts)
== (impl_own_counts.types + impl_own_counts.consts)
{
return Ok(());
}
// We never need to emit a separate error for RPITITs, since if an RPITIT
// has mismatched type or const generic arguments, then the method that it's
// inheriting the generics from will also have mismatched arguments, and
// we'll report an error for that instead. Delay a bug for safety, though.
if tcx.opt_rpitit_info(trait_.def_id).is_some() {
return Err(tcx.sess.delay_span_bug(
rustc_span::DUMMY_SP,
"errors comparing numbers of generics of trait/impl functions were not emitted",
));
}
let matchings = [
("type", trait_own_counts.types, impl_own_counts.types),
("const", trait_own_counts.consts, impl_own_counts.consts),
];
let item_kind = assoc_item_kind_str(&impl_);
let mut err_occurred = None;
for (kind, trait_count, impl_count) in matchings {
if impl_count != trait_count {
let arg_spans = |kind: ty::AssocKind, generics: &hir::Generics<'_>| {
let mut spans = generics
.params
.iter()
.filter(|p| match p.kind {
hir::GenericParamKind::Lifetime {
kind: hir::LifetimeParamKind::Elided,
} => {
// A fn can have an arbitrary number of extra elided lifetimes for the
// same signature.
!matches!(kind, ty::AssocKind::Fn)
}
_ => true,
})
.map(|p| p.span)
.collect::<Vec<Span>>();
if spans.is_empty() {
spans = vec![generics.span]
}
spans
};
let (trait_spans, impl_trait_spans) = if let Some(def_id) = trait_.def_id.as_local() {
let trait_item = tcx.hir().expect_trait_item(def_id);
let arg_spans: Vec<Span> = arg_spans(trait_.kind, trait_item.generics);
let impl_trait_spans: Vec<Span> = trait_item
.generics
.params
.iter()
.filter_map(|p| match p.kind {
GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
_ => None,
})
.collect();
(Some(arg_spans), impl_trait_spans)
} else {
let trait_span = tcx.hir().span_if_local(trait_.def_id);
(trait_span.map(|s| vec![s]), vec![])
};
let impl_item = tcx.hir().expect_impl_item(impl_.def_id.expect_local());
let impl_item_impl_trait_spans: Vec<Span> = impl_item
.generics
.params
.iter()
.filter_map(|p| match p.kind {
GenericParamKind::Type { synthetic: true, .. } => Some(p.span),
_ => None,
})
.collect();
let spans = arg_spans(impl_.kind, impl_item.generics);
let span = spans.first().copied();
let mut err = tcx.sess.struct_span_err_with_code(
spans,
format!(
"{} `{}` has {} {kind} parameter{} but its trait \
declaration has {} {kind} parameter{}",
item_kind,
trait_.name,
impl_count,
pluralize!(impl_count),
trait_count,
pluralize!(trait_count),
kind = kind,
),
DiagnosticId::Error("E0049".into()),
);
let mut suffix = None;
if let Some(spans) = trait_spans {
let mut spans = spans.iter();
if let Some(span) = spans.next() {
err.span_label(
*span,
format!(
"expected {} {} parameter{}",
trait_count,
kind,
pluralize!(trait_count),
),
);
}
for span in spans {
err.span_label(*span, "");
}
} else {
suffix = Some(format!(", expected {trait_count}"));
}
if let Some(span) = span {
err.span_label(
span,
format!(
"found {} {} parameter{}{}",
impl_count,
kind,
pluralize!(impl_count),
suffix.unwrap_or_default(),
),
);
}
for span in impl_trait_spans.iter().chain(impl_item_impl_trait_spans.iter()) {
err.span_label(*span, "`impl Trait` introduces an implicit type parameter");
}
let reported = err.emit_unless(delay);
err_occurred = Some(reported);
}
}
if let Some(reported) = err_occurred { Err(reported) } else { Ok(()) }
}
fn compare_number_of_method_arguments<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
) -> Result<(), ErrorGuaranteed> {
let impl_m_fty = tcx.fn_sig(impl_m.def_id);
let trait_m_fty = tcx.fn_sig(trait_m.def_id);
let trait_number_args = trait_m_fty.skip_binder().inputs().skip_binder().len();
let impl_number_args = impl_m_fty.skip_binder().inputs().skip_binder().len();
if trait_number_args != impl_number_args {
let trait_span = trait_m
.def_id
.as_local()
.and_then(|def_id| {
let (trait_m_sig, _) = &tcx.hir().expect_trait_item(def_id).expect_fn();
let pos = trait_number_args.saturating_sub(1);
trait_m_sig.decl.inputs.get(pos).map(|arg| {
if pos == 0 {
arg.span
} else {
arg.span.with_lo(trait_m_sig.decl.inputs[0].span.lo())
}
})
})
.or_else(|| tcx.hir().span_if_local(trait_m.def_id));
let (impl_m_sig, _) = &tcx.hir().expect_impl_item(impl_m.def_id.expect_local()).expect_fn();
let pos = impl_number_args.saturating_sub(1);
let impl_span = impl_m_sig
.decl
.inputs
.get(pos)
.map(|arg| {
if pos == 0 {
arg.span
} else {
arg.span.with_lo(impl_m_sig.decl.inputs[0].span.lo())
}
})
.unwrap_or_else(|| tcx.def_span(impl_m.def_id));
let mut err = struct_span_err!(
tcx.sess,
impl_span,
E0050,
"method `{}` has {} but the declaration in trait `{}` has {}",
trait_m.name,
potentially_plural_count(impl_number_args, "parameter"),
tcx.def_path_str(trait_m.def_id),
trait_number_args
);
if let Some(trait_span) = trait_span {
err.span_label(
trait_span,
format!(
"trait requires {}",
potentially_plural_count(trait_number_args, "parameter")
),
);
} else {
err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
}
err.span_label(
impl_span,
format!(
"expected {}, found {}",
potentially_plural_count(trait_number_args, "parameter"),
impl_number_args
),
);
return Err(err.emit());
}
Ok(())
}
fn compare_synthetic_generics<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
) -> Result<(), ErrorGuaranteed> {
// FIXME(chrisvittal) Clean up this function, list of FIXME items:
// 1. Better messages for the span labels
// 2. Explanation as to what is going on
// If we get here, we already have the same number of generics, so the zip will
// be okay.
let mut error_found = None;
let impl_m_generics = tcx.generics_of(impl_m.def_id);
let trait_m_generics = tcx.generics_of(trait_m.def_id);
let impl_m_type_params = impl_m_generics.params.iter().filter_map(|param| match param.kind {
GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
});
let trait_m_type_params = trait_m_generics.params.iter().filter_map(|param| match param.kind {
GenericParamDefKind::Type { synthetic, .. } => Some((param.def_id, synthetic)),
GenericParamDefKind::Lifetime | GenericParamDefKind::Const { .. } => None,
});
for ((impl_def_id, impl_synthetic), (trait_def_id, trait_synthetic)) in
iter::zip(impl_m_type_params, trait_m_type_params)
{
if impl_synthetic != trait_synthetic {
let impl_def_id = impl_def_id.expect_local();
let impl_span = tcx.def_span(impl_def_id);
let trait_span = tcx.def_span(trait_def_id);
let mut err = struct_span_err!(
tcx.sess,
impl_span,
E0643,
"method `{}` has incompatible signature for trait",
trait_m.name
);
err.span_label(trait_span, "declaration in trait here");
match (impl_synthetic, trait_synthetic) {
// The case where the impl method uses `impl Trait` but the trait method uses
// explicit generics
(true, false) => {
err.span_label(impl_span, "expected generic parameter, found `impl Trait`");
let _: Option<_> = try {
// try taking the name from the trait impl
// FIXME: this is obviously suboptimal since the name can already be used
// as another generic argument
let new_name = tcx.opt_item_name(trait_def_id)?;
let trait_m = trait_m.def_id.as_local()?;
let trait_m = tcx.hir().expect_trait_item(trait_m);
let impl_m = impl_m.def_id.as_local()?;
let impl_m = tcx.hir().expect_impl_item(impl_m);
// in case there are no generics, take the spot between the function name
// and the opening paren of the argument list
let new_generics_span = tcx.def_ident_span(impl_def_id)?.shrink_to_hi();
// in case there are generics, just replace them
let generics_span =
impl_m.generics.span.substitute_dummy(new_generics_span);
// replace with the generics from the trait
let new_generics =
tcx.sess.source_map().span_to_snippet(trait_m.generics.span).ok()?;
err.multipart_suggestion(
"try changing the `impl Trait` argument to a generic parameter",
vec![
// replace `impl Trait` with `T`
(impl_span, new_name.to_string()),
// replace impl method generics with trait method generics
// This isn't quite right, as users might have changed the names
// of the generics, but it works for the common case
(generics_span, new_generics),
],
Applicability::MaybeIncorrect,
);
};
}
// The case where the trait method uses `impl Trait`, but the impl method uses
// explicit generics.
(false, true) => {
err.span_label(impl_span, "expected `impl Trait`, found generic parameter");
let _: Option<_> = try {
let impl_m = impl_m.def_id.as_local()?;
let impl_m = tcx.hir().expect_impl_item(impl_m);
let (sig, _) = impl_m.expect_fn();
let input_tys = sig.decl.inputs;
struct Visitor(Option<Span>, hir::def_id::LocalDefId);
impl<'v> intravisit::Visitor<'v> for Visitor {
fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
intravisit::walk_ty(self, ty);
if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = ty.kind
&& let Res::Def(DefKind::TyParam, def_id) = path.res
&& def_id == self.1.to_def_id()
{
self.0 = Some(ty.span);
}
}
}
let mut visitor = Visitor(None, impl_def_id);
for ty in input_tys {
intravisit::Visitor::visit_ty(&mut visitor, ty);
}
let span = visitor.0?;
let bounds = impl_m.generics.bounds_for_param(impl_def_id).next()?.bounds;
let bounds = bounds.first()?.span().to(bounds.last()?.span());
let bounds = tcx.sess.source_map().span_to_snippet(bounds).ok()?;
err.multipart_suggestion(
"try removing the generic parameter and using `impl Trait` instead",
vec![
// delete generic parameters
(impl_m.generics.span, String::new()),
// replace param usage with `impl Trait`
(span, format!("impl {bounds}")),
],
Applicability::MaybeIncorrect,
);
};
}
_ => unreachable!(),
}
error_found = Some(err.emit());
}
}
if let Some(reported) = error_found { Err(reported) } else { Ok(()) }
}
/// Checks that all parameters in the generics of a given assoc item in a trait impl have
/// the same kind as the respective generic parameter in the trait def.
///
/// For example all 4 errors in the following code are emitted here:
/// ```rust,ignore (pseudo-Rust)
/// trait Foo {
/// fn foo<const N: u8>();
/// type bar<const N: u8>;
/// fn baz<const N: u32>();
/// type blah<T>;
/// }
///
/// impl Foo for () {
/// fn foo<const N: u64>() {}
/// //~^ error
/// type bar<const N: u64> {}
/// //~^ error
/// fn baz<T>() {}
/// //~^ error
/// type blah<const N: i64> = u32;
/// //~^ error
/// }
/// ```
///
/// This function does not handle lifetime parameters
fn compare_generic_param_kinds<'tcx>(
tcx: TyCtxt<'tcx>,
impl_item: ty::AssocItem,
trait_item: ty::AssocItem,
delay: bool,
) -> Result<(), ErrorGuaranteed> {
assert_eq!(impl_item.kind, trait_item.kind);
let ty_const_params_of = |def_id| {
tcx.generics_of(def_id).params.iter().filter(|param| {
matches!(
param.kind,
GenericParamDefKind::Const { .. } | GenericParamDefKind::Type { .. }
)
})
};
for (param_impl, param_trait) in
iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id))
{
use GenericParamDefKind::*;
if match (&param_impl.kind, &param_trait.kind) {
(Const { .. }, Const { .. })
if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) =>
{
true
}
(Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true,
// this is exhaustive so that anyone adding new generic param kinds knows
// to make sure this error is reported for them.
(Const { .. }, Const { .. }) | (Type { .. }, Type { .. }) => false,
(Lifetime { .. }, _) | (_, Lifetime { .. }) => unreachable!(),
} {
let param_impl_span = tcx.def_span(param_impl.def_id);
let param_trait_span = tcx.def_span(param_trait.def_id);
let mut err = struct_span_err!(
tcx.sess,
param_impl_span,
E0053,
"{} `{}` has an incompatible generic parameter for trait `{}`",
assoc_item_kind_str(&impl_item),
trait_item.name,
&tcx.def_path_str(tcx.parent(trait_item.def_id))
);
let make_param_message = |prefix: &str, param: &ty::GenericParamDef| match param.kind {
Const { .. } => {
format!(
"{} const parameter of type `{}`",
prefix,
tcx.type_of(param.def_id).subst_identity()
)
}
Type { .. } => format!("{} type parameter", prefix),
Lifetime { .. } => unreachable!(),
};
let trait_header_span = tcx.def_ident_span(tcx.parent(trait_item.def_id)).unwrap();
err.span_label(trait_header_span, "");
err.span_label(param_trait_span, make_param_message("expected", param_trait));
let impl_header_span = tcx.def_span(tcx.parent(impl_item.def_id));
err.span_label(impl_header_span, "");
err.span_label(param_impl_span, make_param_message("found", param_impl));
let reported = err.emit_unless(delay);
return Err(reported);
}
}
Ok(())
}
/// Use `tcx.compare_impl_const` instead
pub(super) fn compare_impl_const_raw(
tcx: TyCtxt<'_>,
(impl_const_item_def, trait_const_item_def): (LocalDefId, DefId),
) -> Result<(), ErrorGuaranteed> {
let impl_const_item = tcx.associated_item(impl_const_item_def);
let trait_const_item = tcx.associated_item(trait_const_item_def);
let impl_trait_ref =
tcx.impl_trait_ref(impl_const_item.container_id(tcx)).unwrap().subst_identity();
debug!("compare_const_impl(impl_trait_ref={:?})", impl_trait_ref);
let impl_c_span = tcx.def_span(impl_const_item_def.to_def_id());
let infcx = tcx.infer_ctxt().build();
let param_env = tcx.param_env(impl_const_item_def.to_def_id());
let ocx = ObligationCtxt::new(&infcx);
// The below is for the most part highly similar to the procedure
// for methods above. It is simpler in many respects, especially
// because we shouldn't really have to deal with lifetimes or
// predicates. In fact some of this should probably be put into
// shared functions because of DRY violations...
let trait_to_impl_substs = impl_trait_ref.substs;
// Create a parameter environment that represents the implementation's
// method.
// Compute placeholder form of impl and trait const tys.
let impl_ty = tcx.type_of(impl_const_item_def.to_def_id()).subst_identity();
let trait_ty = tcx.type_of(trait_const_item_def).subst(tcx, trait_to_impl_substs);
let mut cause = ObligationCause::new(
impl_c_span,
impl_const_item_def,
ObligationCauseCode::CompareImplItemObligation {
impl_item_def_id: impl_const_item_def,
trait_item_def_id: trait_const_item_def,
kind: impl_const_item.kind,
},
);
// There is no "body" here, so just pass dummy id.
let impl_ty = ocx.normalize(&cause, param_env, impl_ty);
debug!("compare_const_impl: impl_ty={:?}", impl_ty);
let trait_ty = ocx.normalize(&cause, param_env, trait_ty);
debug!("compare_const_impl: trait_ty={:?}", trait_ty);
let err = ocx.sup(&cause, param_env, trait_ty, impl_ty);
if let Err(terr) = err {
debug!(
"checking associated const for compatibility: impl ty {:?}, trait ty {:?}",
impl_ty, trait_ty
);
// Locate the Span containing just the type of the offending impl
let (ty, _) = tcx.hir().expect_impl_item(impl_const_item_def).expect_const();
cause.span = ty.span;
let mut diag = struct_span_err!(
tcx.sess,
cause.span,
E0326,
"implemented const `{}` has an incompatible type for trait",
trait_const_item.name
);
let trait_c_span = trait_const_item_def.as_local().map(|trait_c_def_id| {
// Add a label to the Span containing just the type of the const
let (ty, _) = tcx.hir().expect_trait_item(trait_c_def_id).expect_const();
ty.span
});
infcx.err_ctxt().note_type_err(
&mut diag,
&cause,
trait_c_span.map(|span| (span, "type in trait".to_owned())),
Some(infer::ValuePairs::Terms(ExpectedFound {
expected: trait_ty.into(),
found: impl_ty.into(),
})),
terr,
false,
false,
);
return Err(diag.emit());
};
// Check that all obligations are satisfied by the implementation's
// version.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
return Err(infcx.err_ctxt().report_fulfillment_errors(&errors));
}
let outlives_env = OutlivesEnvironment::new(param_env);
ocx.resolve_regions_and_report_errors(impl_const_item_def, &outlives_env)
}
pub(super) fn compare_impl_ty<'tcx>(
tcx: TyCtxt<'tcx>,
impl_ty: ty::AssocItem,
trait_ty: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) {
debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
let _: Result<(), ErrorGuaranteed> = try {
compare_number_of_generics(tcx, impl_ty, trait_ty, false)?;
compare_generic_param_kinds(tcx, impl_ty, trait_ty, false)?;
compare_type_predicate_entailment(tcx, impl_ty, trait_ty, impl_trait_ref)?;
check_type_bounds(tcx, trait_ty, impl_ty, impl_trait_ref)?;
};
}
/// The equivalent of [compare_method_predicate_entailment], but for associated types
/// instead of associated functions.
fn compare_type_predicate_entailment<'tcx>(
tcx: TyCtxt<'tcx>,
impl_ty: ty::AssocItem,
trait_ty: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
let trait_to_impl_substs =
impl_substs.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.substs);
let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
check_region_bounds_on_impl_item(tcx, impl_ty, trait_ty, false)?;
let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_substs);
if impl_ty_own_bounds.len() == 0 {
// Nothing to check.
return Ok(());
}
// This `HirId` should be used for the `body_id` field on each
// `ObligationCause` (and the `FnCtxt`). This is what
// `regionck_item` expects.
let impl_ty_def_id = impl_ty.def_id.expect_local();
debug!("compare_type_predicate_entailment: trait_to_impl_substs={:?}", trait_to_impl_substs);
// The predicates declared by the impl definition, the trait and the
// associated type in the trait are assumed.
let impl_predicates = tcx.predicates_of(impl_ty_predicates.parent.unwrap());
let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
hybrid_preds.predicates.extend(
trait_ty_predicates
.instantiate_own(tcx, trait_to_impl_substs)
.map(|(predicate, _)| predicate),
);
debug!("compare_type_predicate_entailment: bounds={:?}", hybrid_preds);
let impl_ty_span = tcx.def_span(impl_ty_def_id);
let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_def_id);
let param_env = ty::ParamEnv::new(
tcx.mk_predicates(&hybrid_preds.predicates),
Reveal::UserFacing,
hir::Constness::NotConst,
);
let param_env = traits::normalize_param_env_or_error(tcx, param_env, normalize_cause);
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(&infcx);
debug!("compare_type_predicate_entailment: caller_bounds={:?}", param_env.caller_bounds());
for (predicate, span) in impl_ty_own_bounds {
let cause = ObligationCause::misc(span, impl_ty_def_id);
let predicate = ocx.normalize(&cause, param_env, predicate);
let cause = ObligationCause::new(
span,
impl_ty_def_id,
ObligationCauseCode::CompareImplItemObligation {
impl_item_def_id: impl_ty.def_id.expect_local(),
trait_item_def_id: trait_ty.def_id,
kind: impl_ty.kind,
},
);
ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate));
}
// Check that all obligations are satisfied by the implementation's
// version.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
return Err(reported);
}
// Finally, resolve all regions. This catches wily misuses of
// lifetime parameters.
let outlives_env = OutlivesEnvironment::new(param_env);
ocx.resolve_regions_and_report_errors(impl_ty_def_id, &outlives_env)
}
/// Validate that `ProjectionCandidate`s created for this associated type will
/// be valid.
///
/// Usually given
///
/// trait X { type Y: Copy } impl X for T { type Y = S; }
///
/// We are able to normalize `<T as X>::U` to `S`, and so when we check the
/// impl is well-formed we have to prove `S: Copy`.
///
/// For default associated types the normalization is not possible (the value
/// from the impl could be overridden). We also can't normalize generic
/// associated types (yet) because they contain bound parameters.
#[instrument(level = "debug", skip(tcx))]
pub(super) fn check_type_bounds<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ty: ty::AssocItem,
impl_ty: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let param_env = tcx.param_env(impl_ty.def_id);
let container_id = impl_ty.container_id(tcx);
// Given
//
// impl<A, B> Foo<u32> for (A, B) {
// type Bar<C> = Wrapper<A, B, C>
// }
//
// - `impl_trait_ref` would be `<(A, B) as Foo<u32>>`
// - `normalize_impl_ty_substs` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
// - `normalize_impl_ty` would be `Wrapper<A, B, ^0.0>`
// - `rebased_substs` would be `[(A, B), u32, ^0.0]`, combining the substs from
// the *trait* with the generic associated type parameters (as bound vars).
//
// A note regarding the use of bound vars here:
// Imagine as an example
// ```
// trait Family {
// type Member<C: Eq>;
// }
//
// impl Family for VecFamily {
// type Member<C: Eq> = i32;
// }
// ```
// Here, we would generate
// ```notrust
// forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
// ```
// when we really would like to generate
// ```notrust
// forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
// ```
// But, this is probably fine, because although the first clause can be used with types C that
// do not implement Eq, for it to cause some kind of problem, there would have to be a
// VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
// Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
// elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
// the trait (notably, that X: Eq and T: Family).
let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
smallvec::SmallVec::with_capacity(tcx.generics_of(impl_ty.def_id).params.len());
// Extend the impl's identity substs with late-bound GAT vars
let normalize_impl_ty_substs = ty::InternalSubsts::identity_for_item(tcx, container_id)
.extend_to(tcx, impl_ty.def_id, |param, _| match param.kind {
GenericParamDefKind::Type { .. } => {
let kind = ty::BoundTyKind::Param(param.def_id, param.name);
let bound_var = ty::BoundVariableKind::Ty(kind);
bound_vars.push(bound_var);
tcx.mk_bound(
ty::INNERMOST,
ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
)
.into()
}
GenericParamDefKind::Lifetime => {
let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
let bound_var = ty::BoundVariableKind::Region(kind);
bound_vars.push(bound_var);
tcx.mk_re_late_bound(
ty::INNERMOST,
ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
)
.into()
}
GenericParamDefKind::Const { .. } => {
let bound_var = ty::BoundVariableKind::Const;
bound_vars.push(bound_var);
tcx.mk_const(
ty::ConstKind::Bound(
ty::INNERMOST,
ty::BoundVar::from_usize(bound_vars.len() - 1),
),
tcx.type_of(param.def_id)
.no_bound_vars()
.expect("const parameter types cannot be generic"),
)
.into()
}
});
// When checking something like
//
// trait X { type Y: PartialEq<<Self as X>::Y> }
// impl X for T { default type Y = S; }
//
// We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
// we want <T as X>::Y to normalize to S. This is valid because we are
// checking the default value specifically here. Add this equality to the
// ParamEnv for normalization specifically.
let normalize_impl_ty = tcx.type_of(impl_ty.def_id).subst(tcx, normalize_impl_ty_substs);
let rebased_substs =
normalize_impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
let bound_vars = tcx.mk_bound_variable_kinds(&bound_vars);
let normalize_param_env = {
let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
match normalize_impl_ty.kind() {
ty::Alias(ty::Projection, proj)
if proj.def_id == trait_ty.def_id && proj.substs == rebased_substs =>
{
// Don't include this predicate if the projected type is
// exactly the same as the projection. This can occur in
// (somewhat dubious) code like this:
//
// impl<T> X for T where T: X { type Y = <T as X>::Y; }
}
_ => predicates.push(
ty::Binder::bind_with_vars(
ty::ProjectionPredicate {
projection_ty: tcx.mk_alias_ty(trait_ty.def_id, rebased_substs),
term: normalize_impl_ty.into(),
},
bound_vars,
)
.to_predicate(tcx),
),
};
ty::ParamEnv::new(tcx.mk_predicates(&predicates), Reveal::UserFacing, param_env.constness())
};
debug!(?normalize_param_env);
let impl_ty_def_id = impl_ty.def_id.expect_local();
let impl_ty_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
let rebased_substs = impl_ty_substs.rebase_onto(tcx, container_id, impl_trait_ref.substs);
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(&infcx);
// A synthetic impl Trait for RPITIT desugaring has no HIR, which we currently use to get the
// span for an impl's associated type. Instead, for these, use the def_span for the synthesized
// associated type.
let impl_ty_span = if tcx.opt_rpitit_info(impl_ty.def_id).is_some() {
tcx.def_span(impl_ty_def_id)
} else {
match tcx.hir().get_by_def_id(impl_ty_def_id) {
hir::Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Type(_, Some(ty)),
..
}) => ty.span,
hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Type(ty), .. }) => ty.span,
_ => bug!(),
}
};
let assumed_wf_types = ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty_def_id);
let normalize_cause = ObligationCause::new(
impl_ty_span,
impl_ty_def_id,
ObligationCauseCode::CheckAssociatedTypeBounds {
impl_item_def_id: impl_ty.def_id.expect_local(),
trait_item_def_id: trait_ty.def_id,
},
);
let mk_cause = |span: Span| {
let code = if span.is_dummy() {
traits::ItemObligation(trait_ty.def_id)
} else {
traits::BindingObligation(trait_ty.def_id, span)
};
ObligationCause::new(impl_ty_span, impl_ty_def_id, code)
};
let obligations: Vec<_> = tcx
.explicit_item_bounds(trait_ty.def_id)
.subst_iter_copied(tcx, rebased_substs)
.map(|(concrete_ty_bound, span)| {
debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
traits::Obligation::new(tcx, mk_cause(span), param_env, concrete_ty_bound)
})
.collect();
debug!("check_type_bounds: item_bounds={:?}", obligations);
for mut obligation in util::elaborate(tcx, obligations) {
let normalized_predicate =
ocx.normalize(&normalize_cause, normalize_param_env, obligation.predicate);
debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
obligation.predicate = normalized_predicate;
ocx.register_obligation(obligation);
}
// Check that all obligations are satisfied by the implementation's
// version.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
let reported = infcx.err_ctxt().report_fulfillment_errors(&errors);
return Err(reported);
}
// Finally, resolve all regions. This catches wily misuses of
// lifetime parameters.
let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_def_id, assumed_wf_types);
let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
ocx.resolve_regions_and_report_errors(impl_ty_def_id, &outlives_env)
}
fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {
match impl_item.kind {
ty::AssocKind::Const => "const",
ty::AssocKind::Fn => "method",
ty::AssocKind::Type => "type",
}
}