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fuchsia / third_party / rust / c38f75c21f016bffbf841ed5abce338f94201bde / . / compiler / rustc_hir_analysis / src / check / compare_impl_item.rs
blob: d2759087cb471a4399380cf9e58ec36f6f54559f [file] [log] [blame]
use super::potentially_plural_count;
use crate::errors::{LifetimesOrBoundsMismatchOnTrait, MethodShouldReturnFuture};
use core::ops::ControlFlow;
use hir::def_id::{DefId, DefIdMap, LocalDefId};
use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, ErrorGuaranteed};
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;
use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::{util, FulfillmentError};
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::fold::BottomUpFolder;
use rustc_middle::ty::util::ExplicitSelf;
use rustc_middle::ty::ToPredicate;
use rustc_middle::ty::{
self, GenericArgs, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
};
use rustc_middle::ty::{GenericParamDefKind, TyCtxt};
use rustc_span::Span;
use rustc_trait_selection::regions::InferCtxtRegionExt;
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::borrow::Cow;
use std::iter;
mod refine;
/// 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 {
check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, false)?;
compare_method_predicate_entailment(tcx, impl_m, trait_m, impl_trait_ref)?;
refine::check_refining_return_position_impl_trait_in_trait(
tcx,
impl_m,
trait_m,
impl_trait_ref,
);
};
}
/// Checks a bunch of different properties of the impl/trait methods for
/// compatibility, such as asyncness, number of argument, self receiver kind,
/// and number of early- and late-bound generics.
fn check_method_is_structurally_compatible<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
delay: bool,
) -> Result<(), ErrorGuaranteed> {
compare_self_type(tcx, impl_m, trait_m, impl_trait_ref, delay)?;
compare_number_of_generics(tcx, impl_m, trait_m, delay)?;
compare_generic_param_kinds(tcx, impl_m, trait_m, delay)?;
compare_number_of_method_arguments(tcx, impl_m, trait_m, delay)?;
compare_synthetic_generics(tcx, impl_m, trait_m, delay)?;
check_region_bounds_on_impl_item(tcx, impl_m, trait_m, delay)?;
Ok(())
}
/// This function is best explained by example. Consider a trait with its 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_args`, 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_args = {'t => 'j, T => &'i U, Self => Foo}
/// ```
///
/// We create a mapping `dummy_args` 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_args = {'i => 'i0, U => U0, N => N0 }
/// ```
///
/// Now we can apply `placeholder_args` 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 N0) -> Foo
/// ```
///
/// We now want to extract and instantiate the type of the *trait*
/// method and compare it. To do so, we must create a compound
/// instantiation by combining `trait_to_impl_args` and
/// `impl_to_placeholder_args`, 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_args = { 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 N0) -> 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 generic parameters to ensure that all declared bounds
/// are satisfied by the implementation's method.
///
/// We do this by creating a parameter environment which contains a
/// generic parameter corresponding to `impl_to_placeholder_args`. We then build
/// `trait_to_placeholder_args` 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>,
) -> Result<(), ErrorGuaranteed> {
let trait_to_impl_args = impl_trait_ref.args;
// 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_args = GenericArgs::identity_for_item(tcx, impl_m.def_id);
// Create mapping from trait to placeholder.
let trait_to_placeholder_args =
impl_to_placeholder_args.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_args);
debug!("compare_impl_method: trait_to_placeholder_args={:?}", trait_to_placeholder_args);
let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
// 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_args)
.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_clauses(&hybrid_preds.predicates), Reveal::UserFacing);
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_args);
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 `FnCtxt::normalize` 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 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).instantiate_identity(),
);
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).instantiate(tcx, trait_to_placeholder_args);
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 = Ty::new_fn_ptr(tcx, 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 !(impl_sig, trait_sig).references_error() {
// Select obligations to make progress on inference before processing
// the wf obligation below.
// FIXME(-Znext-solver): Not needed when the hack below is removed.
let errors = ocx.select_where_possible();
if !errors.is_empty() {
let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
return Err(reported);
}
// See #108544. Annoying, we can end up in cases where, because of winnowing,
// we pick param env candidates over a more general impl, leading to more
// stricter lifetime requirements than we would otherwise need. This can
// trigger the lint. Instead, let's only consider type outlives and
// region outlives obligations.
//
// FIXME(-Znext-solver): Try removing this hack again once the new
// solver is stable. We should just be able to register a WF pred for
// the fn sig.
let mut wf_args: smallvec::SmallVec<[_; 4]> =
unnormalized_impl_sig.inputs_and_output.iter().map(|ty| ty.into()).collect();
// Annoyingly, asking for the WF predicates of an array (with an unevaluated const (only?))
// will give back the well-formed predicate of the same array.
let mut wf_args_seen: FxHashSet<_> = wf_args.iter().copied().collect();
while let Some(arg) = wf_args.pop() {
let Some(obligations) = rustc_trait_selection::traits::wf::obligations(
infcx,
param_env,
impl_m_def_id,
0,
arg,
impl_m_span,
) else {
continue;
};
for obligation in obligations {
debug!(?obligation);
match obligation.predicate.kind().skip_binder() {
// We need to register Projection oblgiations too, because we may end up with
// an implied `X::Item: 'a`, which gets desugared into `X::Item = ?0`, `?0: 'a`.
// If we only register the region outlives obligation, this leads to an unconstrained var.
// See `implied_bounds_entailment_alias_var.rs` test.
ty::PredicateKind::Clause(
ty::ClauseKind::RegionOutlives(..)
| ty::ClauseKind::TypeOutlives(..)
| ty::ClauseKind::Projection(..),
) => ocx.register_obligation(obligation),
ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
if wf_args_seen.insert(arg) {
wf_args.push(arg)
}
}
_ => {}
}
}
}
}
// 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::with_bounds(
param_env,
infcx.implied_bounds_tys(param_env, impl_m_def_id, &wf_tys),
);
let errors = infcx.resolve_regions(&outlives_env);
if !errors.is_empty() {
return Err(infcx
.tainted_by_errors()
.unwrap_or_else(|| infcx.err_ctxt().report_region_errors(impl_m_def_id, &errors)));
}
Ok(())
}
struct RemapLateBound<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
mapping: &'a FxIndexMap<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::ReLateParam(fr) = *r {
ty::Region::new_late_param(
self.tcx,
fr.scope,
self.mapping.get(&fr.bound_region).copied().unwrap_or(fr.bound_region),
)
} else {
r
}
}
}
/// 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:
///
/// ```
/// 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 DefIdMap<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().instantiate_identity();
// First, check a few of the same things as `compare_impl_method`,
// just so we don't ICE during instantiation later.
check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, true)?;
let trait_to_impl_args = impl_trait_ref.args;
let impl_m_hir_id = tcx.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_args = GenericArgs::identity_for_item(tcx, impl_m.def_id);
// Create mapping from trait to placeholder.
let trait_to_placeholder_args =
impl_to_placeholder_args.rebase_onto(tcx, impl_m.container_id(tcx), trait_to_impl_args);
let hybrid_preds = tcx
.predicates_of(impl_m.container_id(tcx))
.instantiate_identity(tcx)
.into_iter()
.chain(tcx.predicates_of(trait_m.def_id).instantiate_own(tcx, trait_to_placeholder_args))
.map(|(clause, _)| clause);
let param_env = ty::ParamEnv::new(tcx.mk_clauses_from_iter(hybrid_preds), Reveal::UserFacing);
let param_env = traits::normalize_param_env_or_error(
tcx,
param_env,
ObligationCause::misc(tcx.def_span(impl_m_def_id), impl_m_def_id),
);
let infcx = &tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(infcx);
// Normalize the impl signature with fresh variables for lifetime inference.
let misc_cause = ObligationCause::misc(return_span, impl_m_def_id);
let impl_sig = ocx.normalize(
&misc_cause,
param_env,
tcx.liberate_late_bound_regions(
impl_m.def_id,
tcx.fn_sig(impl_m.def_id).instantiate_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 = infcx
.instantiate_binder_with_fresh_vars(
return_span,
infer::HigherRankedType,
tcx.fn_sig(trait_m.def_id).instantiate(tcx, trait_to_placeholder_args),
)
.fold_with(&mut collector);
let trait_sig = ocx.normalize(&misc_cause, param_env, unnormalized_trait_sig);
trait_sig.error_reported()?;
let trait_return_ty = trait_sig.output();
// RPITITs are allowed to use the implied predicates of the method that
// defines them. This is because we want code like:
// ```
// trait Foo {
// fn test<'a, T>(_: &'a T) -> impl Sized;
// }
// impl Foo for () {
// fn test<'a, T>(x: &'a T) -> &'a T { x }
// }
// ```
// .. to compile. However, since we use both the normalized and unnormalized
// inputs and outputs from the instantiated trait signature, we will end up
// seeing the hidden type of an RPIT in the signature itself. Naively, this
// means that we will use the hidden type to imply the hidden type's own
// well-formedness.
//
// To avoid this, we replace the infer vars used for hidden type inference
// with placeholders, which imply nothing about outlives bounds, and then
// prove below that the hidden types are well formed.
let universe = infcx.create_next_universe();
let mut idx = 0;
let mapping: FxIndexMap<_, _> = collector
.types
.iter()
.map(|(_, &(ty, _))| {
assert!(
infcx.resolve_vars_if_possible(ty) == ty && ty.is_ty_var(),
"{ty:?} should not have been constrained via normalization",
ty = infcx.resolve_vars_if_possible(ty)
);
idx += 1;
(
ty,
Ty::new_placeholder(
tcx,
ty::Placeholder {
universe,
bound: ty::BoundTy {
var: ty::BoundVar::from_usize(idx),
kind: ty::BoundTyKind::Anon,
},
},
),
)
})
.collect();
let mut type_mapper = BottomUpFolder {
tcx,
ty_op: |ty| *mapping.get(&ty).unwrap_or(&ty),
lt_op: |lt| lt,
ct_op: |ct| ct,
};
let wf_tys = FxIndexSet::from_iter(
unnormalized_trait_sig
.inputs_and_output
.iter()
.chain(trait_sig.inputs_and_output.iter())
.map(|ty| ty.fold_with(&mut type_mapper)),
);
match ocx.eq(&cause, param_env, trait_return_ty, impl_return_ty) {
Ok(()) => {}
Err(terr) => {
let mut diag = struct_span_code_err!(
tcx.dcx(),
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(), Cow::from("return type in trait"))),
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);
}
}
if !unnormalized_trait_sig.output().references_error() && collector.types.is_empty() {
tcx.dcx().delayed_bug(
"expect >0 RPITITs in call to `collect_return_position_impl_trait_in_trait_tys`",
);
}
// FIXME: This has the same issue as #108544, but since this isn't breaking
// existing code, I'm not particularly inclined to do the same hack as above
// where we process wf obligations manually. This can be fixed in a forward-
// compatible way later.
let collected_types = collector.types;
for (_, &(ty, _)) in &collected_types {
ocx.register_obligation(traits::Obligation::new(
tcx,
misc_cause.clone(),
param_env,
ty::ClauseKind::WellFormed(ty.into()),
));
}
// Check that all obligations are satisfied by the implementation's
// RPITs.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
if let Err(guar) = try_report_async_mismatch(tcx, infcx, &errors, trait_m, impl_m, impl_sig)
{
return Err(guar);
}
let guar = infcx.err_ctxt().report_fulfillment_errors(errors);
return Err(guar);
}
// 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 remapped_types = DefIdMap::default();
for (def_id, (ty, args)) in collected_types {
match infcx.fully_resolve((ty, args)) {
Ok((ty, args)) => {
// `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_args = GenericArgs::identity_for_item(tcx, def_id);
debug!(?id_args, ?args);
let map: FxIndexMap<_, _> = std::iter::zip(args, id_args)
.skip(tcx.generics_of(trait_m.def_id).count())
.filter_map(|(a, b)| Some((a.as_region()?, b.as_region()?)))
.collect();
debug!(?map);
// NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound
// region args that are synthesized during AST lowering. These are args
// that are appended to the parent args (trait and trait method). However,
// we're trying to infer the uninstantiated type value of the RPITIT inside
// the *impl*, so we can later use the impl's method args 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 args for the RPITIT in the impl.
// Since early region parameters are index-based, we can't just rebase these
// (trait method) early-bound region args onto the impl, and there's no
// guarantee that the indices from the trait args and impl args line up.
// So to fix this, we subtract the number of trait args and add the number of
// impl args to *renumber* these early-bound regions to their corresponding
// indices in the impl's generic parameters list.
//
// Also, we only need to account for a difference in trait and impl args,
// since we previously enforce that the trait method and impl method have the
// same generics.
let num_trait_args = trait_to_impl_args.len();
let num_impl_args = tcx.generics_of(impl_m.container_id(tcx)).params.len();
let ty = match ty.try_fold_with(&mut RemapHiddenTyRegions {
tcx,
map,
num_trait_args,
num_impl_args,
def_id,
impl_def_id: impl_m.container_id(tcx),
ty,
return_span,
}) {
Ok(ty) => ty,
Err(guar) => Ty::new_error(tcx, guar),
};
remapped_types.insert(def_id, ty::EarlyBinder::bind(ty));
}
Err(err) => {
// This code path is not reached in any tests, but may be
// reachable. If this is triggered, it should be converted to
// `span_delayed_bug` and the triggering case turned into a
// test.
tcx.dcx()
.span_bug(return_span, format!("could not fully resolve: {ty} => {err:?}"));
}
}
}
// We may not collect all RPITITs that we see in the HIR for a trait signature
// because an RPITIT was located within a missing item. Like if we have a sig
// returning `-> Missing<impl Sized>`, that gets converted to `-> {type error}`,
// and when walking through the signature we end up never collecting the def id
// of the `impl Sized`. Insert that here, so we don't ICE later.
for assoc_item in tcx.associated_types_for_impl_traits_in_associated_fn(trait_m.def_id) {
if !remapped_types.contains_key(assoc_item) {
remapped_types.insert(
*assoc_item,
ty::EarlyBinder::bind(Ty::new_error_with_message(
tcx,
return_span,
"missing synthetic item for RPITIT",
)),
);
}
}
Ok(&*tcx.arena.alloc(remapped_types))
}
struct ImplTraitInTraitCollector<'a, 'tcx> {
ocx: &'a ObligationCtxt<'a, 'tcx>,
types: FxIndexMap<DefId, (Ty<'tcx>, ty::GenericArgsRef<'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: FxIndexMap::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 args too
if proj.args.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, param_def_id: None });
self.types.insert(proj.def_id, (infer_ty, proj.args));
// Recurse into bounds
for (pred, pred_span) in self
.interner()
.explicit_item_bounds(proj.def_id)
.iter_instantiated_copied(self.interner(), proj.args)
{
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)
}
}
}
struct RemapHiddenTyRegions<'tcx> {
tcx: TyCtxt<'tcx>,
map: FxIndexMap<ty::Region<'tcx>, ty::Region<'tcx>>,
num_trait_args: usize,
num_impl_args: usize,
def_id: DefId,
impl_def_id: DefId,
ty: Ty<'tcx>,
return_span: Span,
}
impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
type Error = ErrorGuaranteed;
fn interner(&self) -> TyCtxt<'tcx> {
self.tcx
}
fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
if let ty::Alias(ty::Opaque, ty::AliasTy { args, def_id, .. }) = *t.kind() {
let mut mapped_args = Vec::with_capacity(args.len());
for (arg, v) in std::iter::zip(args, self.tcx.variances_of(def_id)) {
mapped_args.push(match (arg.unpack(), v) {
// Skip uncaptured opaque args
(ty::GenericArgKind::Lifetime(_), ty::Bivariant) => arg,
_ => arg.try_fold_with(self)?,
});
}
Ok(Ty::new_opaque(self.tcx, def_id, self.tcx.mk_args(&mapped_args)))
} else {
t.try_super_fold_with(self)
}
}
fn try_fold_region(
&mut self,
region: ty::Region<'tcx>,
) -> Result<ty::Region<'tcx>, Self::Error> {
match region.kind() {
// Remap late-bound regions from the function.
ty::ReLateParam(_) => {}
// Remap early-bound regions as long as they don't come from the `impl` itself,
// in which case we don't really need to renumber them.
ty::ReEarlyParam(ebr) if self.tcx.parent(ebr.def_id) != self.impl_def_id => {}
_ => return Ok(region),
}
let e = if let Some(id_region) = self.map.get(&region) {
if let ty::ReEarlyParam(e) = id_region.kind() {
e
} else {
bug!(
"expected to map region {region} to early-bound identity region, but got {id_region}"
);
}
} else {
let guar = match region.kind() {
ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. })
| ty::ReLateParam(ty::LateParamRegion {
bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
..
}) => {
let return_span = if let ty::Alias(ty::Opaque, opaque_ty) = self.ty.kind() {
self.tcx.def_span(opaque_ty.def_id)
} else {
self.return_span
};
self.tcx
.dcx()
.struct_span_err(
return_span,
"return type captures more lifetimes than trait definition",
)
.with_span_label(self.tcx.def_span(def_id), "this lifetime was captured")
.with_span_note(
self.tcx.def_span(self.def_id),
"hidden type must only reference lifetimes captured by this impl trait",
)
.with_note(format!("hidden type inferred to be `{}`", self.ty))
.emit()
}
_ => {
// This code path is not reached in any tests, but may be
// reachable. If this is triggered, it should be converted
// to `delayed_bug` and the triggering case turned into a
// test.
self.tcx.dcx().bug("should've been able to remap region");
}
};
return Err(guar);
};
Ok(ty::Region::new_early_param(
self.tcx,
ty::EarlyParamRegion {
def_id: e.def_id,
name: e.name,
index: (e.index as usize - self.num_trait_args + self.num_impl_args) as u32,
},
))
}
}
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_code_err!(
tcx.dcx(),
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| 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, Cow::from("type in trait"))),
Some(infer::ValuePairs::PolySigs(ExpectedFound {
expected: ty::Binder::dummy(trait_sig),
found: ty::Binder::dummy(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
.dcx()
.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>,
delay: bool,
) -> 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).instantiate_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_code_err!(
tcx.dcx(),
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_unless(delay));
}
(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_code_err!(
tcx.dcx(),
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_unless(delay));
}
}
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 trait_.is_impl_trait_in_trait() {
// FIXME: no tests trigger this. If you find example code that does
// trigger this, please add it to the test suite.
tcx.dcx()
.bug("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.dcx().struct_span_err(
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,
),
);
err.code(E0049);
let msg =
format!("expected {trait_count} {kind} parameter{}", pluralize!(trait_count),);
if let Some(spans) = trait_spans {
let mut spans = spans.iter();
if let Some(span) = spans.next() {
err.span_label(*span, msg);
}
for span in spans {
err.span_label(*span, "");
}
} else {
err.span_label(tcx.def_span(trait_.def_id), msg);
}
if let Some(span) = span {
err.span_label(
span,
format!("found {} {} parameter{}", impl_count, kind, pluralize!(impl_count),),
);
}
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,
delay: bool,
) -> 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_code_err!(
tcx.dcx(),
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_unless(delay));
}
Ok(())
}
fn compare_synthetic_generics<'tcx>(
tcx: TyCtxt<'tcx>,
impl_m: ty::AssocItem,
trait_m: ty::AssocItem,
delay: bool,
) -> 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_code_err!(
tcx.dcx(),
impl_span,
E0643,
"method `{}` has incompatible signature for trait",
trait_m.name
);
err.span_label(trait_span, "declaration in trait here");
if impl_synthetic {
// The case where the impl method uses `impl Trait` but the trait method uses
// explicit generics
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,
);
};
} else {
// The case where the trait method uses `impl Trait`, but the impl method uses
// explicit generics.
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(hir::def_id::LocalDefId);
impl<'v> intravisit::Visitor<'v> for Visitor {
type Result = ControlFlow<Span>;
fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) -> Self::Result {
if let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = ty.kind
&& let Res::Def(DefKind::TyParam, def_id) = path.res
&& def_id == self.0.to_def_id()
{
ControlFlow::Break(ty.span)
} else {
intravisit::walk_ty(self, ty)
}
}
}
let span = input_tys.iter().find_map(|ty| {
intravisit::Visitor::visit_ty(&mut Visitor(impl_def_id), ty).break_value()
})?;
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,
);
};
}
error_found = Some(err.emit_unless(delay));
}
}
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 { .. }) => {
bug!("lifetime params are expected to be filtered by `ty_const_params_of`")
}
} {
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_code_err!(
tcx.dcx(),
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).instantiate_identity()
)
}
Type { .. } => format!("{prefix} type parameter"),
Lifetime { .. } => span_bug!(
tcx.def_span(param.def_id),
"lifetime params are expected to be filtered by `ty_const_params_of`"
),
};
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().instantiate_identity();
debug!("compare_impl_const(impl_trait_ref={:?})", impl_trait_ref);
compare_number_of_generics(tcx, impl_const_item, trait_const_item, false)?;
compare_generic_param_kinds(tcx, impl_const_item, trait_const_item, false)?;
check_region_bounds_on_impl_item(tcx, impl_const_item, trait_const_item, false)?;
compare_const_predicate_entailment(tcx, impl_const_item, trait_const_item, impl_trait_ref)
}
/// The equivalent of [compare_method_predicate_entailment], but for associated constants
/// instead of associated functions.
// FIXME(generic_const_items): If possible extract the common parts of `compare_{type,const}_predicate_entailment`.
fn compare_const_predicate_entailment<'tcx>(
tcx: TyCtxt<'tcx>,
impl_ct: ty::AssocItem,
trait_ct: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let impl_ct_def_id = impl_ct.def_id.expect_local();
let impl_ct_span = tcx.def_span(impl_ct_def_id);
// 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 impl_args = GenericArgs::identity_for_item(tcx, impl_ct.def_id);
let trait_to_impl_args =
impl_args.rebase_onto(tcx, impl_ct.container_id(tcx), impl_trait_ref.args);
// 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_ct_def_id).instantiate_identity();
let trait_ty = tcx.type_of(trait_ct.def_id).instantiate(tcx, trait_to_impl_args);
let code = ObligationCauseCode::CompareImplItemObligation {
impl_item_def_id: impl_ct_def_id,
trait_item_def_id: trait_ct.def_id,
kind: impl_ct.kind,
};
let mut cause = ObligationCause::new(impl_ct_span, impl_ct_def_id, code.clone());
let impl_ct_predicates = tcx.predicates_of(impl_ct.def_id);
let trait_ct_predicates = tcx.predicates_of(trait_ct.def_id);
// The predicates declared by the impl definition, the trait and the
// associated const in the trait are assumed.
let impl_predicates = tcx.predicates_of(impl_ct_predicates.parent.unwrap());
let mut hybrid_preds = impl_predicates.instantiate_identity(tcx);
hybrid_preds.predicates.extend(
trait_ct_predicates
.instantiate_own(tcx, trait_to_impl_args)
.map(|(predicate, _)| predicate),
);
let param_env = ty::ParamEnv::new(tcx.mk_clauses(&hybrid_preds.predicates), Reveal::UserFacing);
let param_env = traits::normalize_param_env_or_error(
tcx,
param_env,
ObligationCause::misc(impl_ct_span, impl_ct_def_id),
);
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(&infcx);
let impl_ct_own_bounds = impl_ct_predicates.instantiate_own(tcx, impl_args);
for (predicate, span) in impl_ct_own_bounds {
let cause = ObligationCause::misc(span, impl_ct_def_id);
let predicate = ocx.normalize(&cause, param_env, predicate);
let cause = ObligationCause::new(span, impl_ct_def_id, code.clone());
ocx.register_obligation(traits::Obligation::new(tcx, cause, param_env, predicate));
}
// 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_ct_def_id).expect_const();
cause.span = ty.span;
let mut diag = struct_span_code_err!(
tcx.dcx(),
cause.span,
E0326,
"implemented const `{}` has an incompatible type for trait",
trait_ct.name
);
let trait_c_span = trait_ct.def_id.as_local().map(|trait_ct_def_id| {
// Add a label to the Span containing just the type of the const
let (ty, _) = tcx.hir().expect_trait_item(trait_ct_def_id).expect_const();
ty.span
});
infcx.err_ctxt().note_type_err(
&mut diag,
&cause,
trait_c_span.map(|span| (span, Cow::from("type in trait"))),
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_ct_def_id, &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)?;
check_region_bounds_on_impl_item(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_args = GenericArgs::identity_for_item(tcx, impl_ty.def_id);
let trait_to_impl_args =
impl_args.rebase_onto(tcx, impl_ty.container_id(tcx), impl_trait_ref.args);
let impl_ty_predicates = tcx.predicates_of(impl_ty.def_id);
let trait_ty_predicates = tcx.predicates_of(trait_ty.def_id);
let impl_ty_own_bounds = impl_ty_predicates.instantiate_own(tcx, impl_args);
if impl_ty_own_bounds.len() == 0 {
// Nothing to check.
return Ok(());
}
// This `DefId` 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_args={:?}", trait_to_impl_args);
// 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_args)
.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 = ObligationCause::misc(impl_ty_span, impl_ty_def_id);
let param_env = ty::ParamEnv::new(tcx.mk_clauses(&hybrid_preds.predicates), Reveal::UserFacing);
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>::Y` 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> {
// Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
// other `Foo` impls are incoherent.
tcx.ensure().coherent_trait(impl_trait_ref.def_id)?;
let param_env = tcx.param_env(impl_ty.def_id);
debug!(?param_env);
let container_id = impl_ty.container_id(tcx);
let impl_ty_def_id = impl_ty.def_id.expect_local();
let impl_ty_args = GenericArgs::identity_for_item(tcx, impl_ty.def_id);
let rebased_args = impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args);
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 impl_ty.is_impl_trait_in_trait() {
tcx.def_span(impl_ty_def_id)
} else {
match tcx.hir_node_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,
item => span_bug!(
tcx.def_span(impl_ty_def_id),
"cannot call `check_type_bounds` on item: {item:?}",
),
}
};
let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, 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)
.iter_instantiated_copied(tcx, rebased_args)
.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);
// Normalize predicates with the assumption that the GAT may always normalize
// to its definition type. This should be the param-env we use to *prove* the
// predicate too, but we don't do that because of performance issues.
// See <https://github.com/rust-lang/rust/pull/117542#issue-1976337685>.
let normalize_param_env = param_env_with_gat_bounds(tcx, impl_ty, impl_trait_ref);
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)
}
/// Install projection predicates that allow GATs to project to their own
/// definition types. This is not allowed in general in cases of default
/// associated types in trait definitions, or when specialization is involved,
/// but is needed when checking these definition types actually satisfy the
/// trait bounds of the GAT.
///
/// # How it works
///
/// ```ignore (example)
/// 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_args` 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_args` would be `[(A, B), u32, ^0.0]`, combining the args 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
/// ```ignore (pseudo-rust)
/// forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
/// ```
///
/// when we really would like to generate
/// ```ignore (pseudo-rust)
/// 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`).
fn param_env_with_gat_bounds<'tcx>(
tcx: TyCtxt<'tcx>,
impl_ty: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) -> ty::ParamEnv<'tcx> {
let param_env = tcx.param_env(impl_ty.def_id);
let container_id = impl_ty.container_id(tcx);
let mut predicates = param_env.caller_bounds().to_vec();
// for RPITITs, we should install predicates that allow us to project all
// of the RPITITs associated with the same body. This is because checking
// the item bounds of RPITITs often involves nested RPITITs having to prove
// bounds about themselves.
let impl_tys_to_install = match impl_ty.opt_rpitit_info {
None => vec![impl_ty],
Some(
ty::ImplTraitInTraitData::Impl { fn_def_id }
| ty::ImplTraitInTraitData::Trait { fn_def_id, .. },
) => tcx
.associated_types_for_impl_traits_in_associated_fn(fn_def_id)
.iter()
.map(|def_id| tcx.associated_item(*def_id))
.collect(),
};
for impl_ty in impl_tys_to_install {
let trait_ty = match impl_ty.container {
ty::AssocItemContainer::TraitContainer => impl_ty,
ty::AssocItemContainer::ImplContainer => {
tcx.associated_item(impl_ty.trait_item_def_id.unwrap())
}
};
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 args with late-bound GAT vars
let normalize_impl_ty_args = ty::GenericArgs::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);
Ty::new_bound(
tcx,
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);
ty::Region::new_bound(
tcx,
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);
ty::Const::new_bound(
tcx,
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).instantiate(tcx, normalize_impl_ty_args);
let rebased_args =
normalize_impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args);
let bound_vars = tcx.mk_bound_variable_kinds(&bound_vars);
match normalize_impl_ty.kind() {
ty::Alias(ty::Projection, proj)
if proj.def_id == trait_ty.def_id && proj.args == rebased_args =>
{
// 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: ty::AliasTy::new(tcx, trait_ty.def_id, rebased_args),
term: normalize_impl_ty.into(),
},
bound_vars,
)
.to_predicate(tcx),
),
};
}
ty::ParamEnv::new(tcx.mk_clauses(&predicates), Reveal::UserFacing)
}
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",
}
}
/// Manually check here that `async fn foo()` wasn't matched against `fn foo()`,
/// and extract a better error if so.
fn try_report_async_mismatch<'tcx>(
tcx: TyCtxt<'tcx>,
infcx: &InferCtxt<'tcx>,
errors: &[FulfillmentError<'tcx>],
trait_m: ty::AssocItem,
impl_m: ty::AssocItem,
impl_sig: ty::FnSig<'tcx>,
) -> Result<(), ErrorGuaranteed> {
if !tcx.asyncness(trait_m.def_id).is_async() {
return Ok(());
}
let ty::Alias(ty::Projection, ty::AliasTy { def_id: async_future_def_id, .. }) =
*tcx.fn_sig(trait_m.def_id).skip_binder().skip_binder().output().kind()
else {
bug!("expected `async fn` to return an RPITIT");
};
for error in errors {
if let traits::BindingObligation(def_id, _) = *error.root_obligation.cause.code()
&& def_id == async_future_def_id
&& let Some(proj) = error.root_obligation.predicate.to_opt_poly_projection_pred()
&& let Some(proj) = proj.no_bound_vars()
&& infcx.can_eq(
error.root_obligation.param_env,
proj.term.ty().unwrap(),
impl_sig.output(),
)
{
// FIXME: We should suggest making the fn `async`, but extracting
// the right span is a bit difficult.
return Err(tcx.sess.dcx().emit_err(MethodShouldReturnFuture {
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(())
}