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fuchsia / third_party / rust / 6e1d94708a0a4a35ca7e46c6cac98adf62fe800e / . / compiler / rustc_hir_analysis / src / check / wfcheck.rs
blob: 0578317f9145909ec70cb900fb62d6f9e46f0fef [file] [log] [blame]
use crate::autoderef::Autoderef;
use crate::collect::CollectItemTypesVisitor;
use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
use crate::errors;
use crate::fluent_generated as fluent;
use hir::intravisit::Visitor;
use rustc_ast as ast;
use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, ErrorGuaranteed};
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId};
use rustc_hir::lang_items::LangItem;
use rustc_hir::ItemKind;
use rustc_infer::infer::outlives::env::OutlivesEnvironment;
use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
use rustc_macros::LintDiagnostic;
use rustc_middle::query::Providers;
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::trait_def::TraitSpecializationKind;
use rustc_middle::ty::{
self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
TypeVisitable, TypeVisitableExt, TypeVisitor,
};
use rustc_middle::ty::{GenericArgKind, GenericArgs};
use rustc_session::parse::feature_err;
use rustc_span::symbol::{sym, Ident};
use rustc_span::{Span, DUMMY_SP};
use rustc_target::spec::abi::Abi;
use rustc_trait_selection::regions::InferCtxtRegionExt;
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
use rustc_trait_selection::traits::misc::{
type_allowed_to_implement_const_param_ty, ConstParamTyImplementationError,
};
use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
use rustc_trait_selection::traits::{
self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,
};
use rustc_type_ir::TypeFlags;
use std::cell::LazyCell;
use std::ops::{ControlFlow, Deref};
pub(super) struct WfCheckingCtxt<'a, 'tcx> {
pub(super) ocx: ObligationCtxt<'a, 'tcx>,
span: Span,
body_def_id: LocalDefId,
param_env: ty::ParamEnv<'tcx>,
}
impl<'a, 'tcx> Deref for WfCheckingCtxt<'a, 'tcx> {
type Target = ObligationCtxt<'a, 'tcx>;
fn deref(&self) -> &Self::Target {
&self.ocx
}
}
impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
fn tcx(&self) -> TyCtxt<'tcx> {
self.ocx.infcx.tcx
}
// Convenience function to normalize during wfcheck. This performs
// `ObligationCtxt::normalize`, but provides a nice `ObligationCauseCode`.
fn normalize<T>(&self, span: Span, loc: Option<WellFormedLoc>, value: T) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
self.ocx.normalize(
&ObligationCause::new(span, self.body_def_id, ObligationCauseCode::WellFormed(loc)),
self.param_env,
value,
)
}
fn register_wf_obligation(
&self,
span: Span,
loc: Option<WellFormedLoc>,
arg: ty::GenericArg<'tcx>,
) {
let cause = traits::ObligationCause::new(
span,
self.body_def_id,
ObligationCauseCode::WellFormed(loc),
);
self.ocx.register_obligation(traits::Obligation::new(
self.tcx(),
cause,
self.param_env,
ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg))),
));
}
}
pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
tcx: TyCtxt<'tcx>,
span: Span,
body_def_id: LocalDefId,
f: F,
) -> Result<(), ErrorGuaranteed>
where
F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>) -> Result<(), ErrorGuaranteed>,
{
let param_env = tcx.param_env(body_def_id);
let infcx = &tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(infcx);
let mut wfcx = WfCheckingCtxt { ocx, span, body_def_id, param_env };
if !tcx.features().trivial_bounds {
wfcx.check_false_global_bounds()
}
f(&mut wfcx)?;
let assumed_wf_types = wfcx.ocx.assumed_wf_types_and_report_errors(param_env, body_def_id)?;
let errors = wfcx.select_all_or_error();
if !errors.is_empty() {
let err = infcx.err_ctxt().report_fulfillment_errors(errors);
if tcx.dcx().has_errors().is_some() {
return Err(err);
} else {
// HACK(oli-obk): tests/ui/specialization/min_specialization/specialize_on_type_error.rs
// causes an delayed bug during normalization, without reporting an error, so we need
// to act as if no error happened, in order to let our callers continue and report an
// error later in check_impl_items_against_trait.
return Ok(());
}
}
debug!(?assumed_wf_types);
let infcx_compat = infcx.fork();
// We specifically want to call the non-compat version of `implied_bounds_tys`; we do this always.
let implied_bounds =
infcx.implied_bounds_tys_compat(param_env, body_def_id, &assumed_wf_types, false);
let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
lint_redundant_lifetimes(tcx, body_def_id, &outlives_env);
let errors = infcx.resolve_regions(&outlives_env);
if errors.is_empty() {
return Ok(());
}
let is_bevy = 'is_bevy: {
// We don't want to emit this for dependents of Bevy, for now.
// See #119956
let is_bevy_paramset = |def: ty::AdtDef<'_>| {
let adt_did = with_no_trimmed_paths!(infcx.tcx.def_path_str(def.0.did));
adt_did.contains("ParamSet")
};
for ty in assumed_wf_types.iter() {
match ty.kind() {
ty::Adt(def, _) => {
if is_bevy_paramset(*def) {
break 'is_bevy true;
}
}
ty::Ref(_, ty, _) => match ty.kind() {
ty::Adt(def, _) => {
if is_bevy_paramset(*def) {
break 'is_bevy true;
}
}
_ => {}
},
_ => {}
}
}
false
};
// If we have set `no_implied_bounds_compat`, then do not attempt compatibility.
// We could also just always enter if `is_bevy`, and call `implied_bounds_tys`,
// but that does result in slightly more work when this option is set and
// just obscures what we mean here anyways. Let's just be explicit.
if is_bevy && !infcx.tcx.sess.opts.unstable_opts.no_implied_bounds_compat {
let implied_bounds =
infcx_compat.implied_bounds_tys_compat(param_env, body_def_id, &assumed_wf_types, true);
let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
let errors_compat = infcx_compat.resolve_regions(&outlives_env);
if errors_compat.is_empty() {
Ok(())
} else {
Err(infcx_compat.err_ctxt().report_region_errors(body_def_id, &errors_compat))
}
} else {
Err(infcx.err_ctxt().report_region_errors(body_def_id, &errors))
}
}
fn check_well_formed(tcx: TyCtxt<'_>, def_id: hir::OwnerId) -> Result<(), ErrorGuaranteed> {
let node = tcx.hir_owner_node(def_id);
let mut res = match node {
hir::OwnerNode::Crate(_) => bug!("check_well_formed cannot be applied to the crate root"),
hir::OwnerNode::Item(item) => check_item(tcx, item),
hir::OwnerNode::TraitItem(item) => check_trait_item(tcx, item),
hir::OwnerNode::ImplItem(item) => check_impl_item(tcx, item),
hir::OwnerNode::ForeignItem(item) => check_foreign_item(tcx, item),
hir::OwnerNode::Synthetic => unreachable!(),
};
if let Some(generics) = node.generics() {
for param in generics.params {
res = res.and(check_param_wf(tcx, param));
}
}
res
}
/// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
/// well-formed, meaning that they do not require any constraints not declared in the struct
/// definition itself. For example, this definition would be illegal:
///
/// ```rust
/// struct Ref<'a, T> { x: &'a T }
/// ```
///
/// because the type did not declare that `T:'a`.
///
/// We do this check as a pre-pass before checking fn bodies because if these constraints are
/// not included it frequently leads to confusing errors in fn bodies. So it's better to check
/// the types first.
#[instrument(skip(tcx), level = "debug")]
fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) -> Result<(), ErrorGuaranteed> {
let def_id = item.owner_id.def_id;
debug!(
?item.owner_id,
item.name = ? tcx.def_path_str(def_id)
);
CollectItemTypesVisitor { tcx }.visit_item(item);
let res = match item.kind {
// Right now we check that every default trait implementation
// has an implementation of itself. Basically, a case like:
//
// impl Trait for T {}
//
// has a requirement of `T: Trait` which was required for default
// method implementations. Although this could be improved now that
// there's a better infrastructure in place for this, it's being left
// for a follow-up work.
//
// Since there's such a requirement, we need to check *just* positive
// implementations, otherwise things like:
//
// impl !Send for T {}
//
// won't be allowed unless there's an *explicit* implementation of `Send`
// for `T`
hir::ItemKind::Impl(impl_) => {
let header = tcx.impl_trait_header(def_id);
let is_auto = header
.is_some_and(|header| tcx.trait_is_auto(header.trait_ref.skip_binder().def_id));
crate::impl_wf_check::check_impl_wf(tcx, def_id)?;
let mut res = Ok(());
if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
res = Err(tcx
.dcx()
.struct_span_err(sp, "impls of auto traits cannot be default")
.with_span_labels(impl_.defaultness_span, "default because of this")
.with_span_label(sp, "auto trait")
.emit());
}
// We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
match header.map(|h| h.polarity) {
// `None` means this is an inherent impl
Some(ty::ImplPolarity::Positive) | None => {
res = res.and(check_impl(tcx, item, impl_.self_ty, &impl_.of_trait));
}
Some(ty::ImplPolarity::Negative) => {
let ast::ImplPolarity::Negative(span) = impl_.polarity else {
bug!("impl_polarity query disagrees with impl's polarity in HIR");
};
// FIXME(#27579): what amount of WF checking do we need for neg impls?
if let hir::Defaultness::Default { .. } = impl_.defaultness {
let mut spans = vec![span];
spans.extend(impl_.defaultness_span);
res = Err(struct_span_code_err!(
tcx.dcx(),
spans,
E0750,
"negative impls cannot be default impls"
)
.emit());
}
}
Some(ty::ImplPolarity::Reservation) => {
// FIXME: what amount of WF checking do we need for reservation impls?
}
}
res
}
hir::ItemKind::Fn(ref sig, ..) => {
check_item_fn(tcx, def_id, item.ident, item.span, sig.decl)
}
hir::ItemKind::Static(ty, ..) => {
check_item_type(tcx, def_id, ty.span, UnsizedHandling::Forbid)
}
hir::ItemKind::Const(ty, ..) => {
check_item_type(tcx, def_id, ty.span, UnsizedHandling::Forbid)
}
hir::ItemKind::Struct(_, hir_generics) => {
let res = check_type_defn(tcx, item, false);
check_variances_for_type_defn(tcx, item, hir_generics);
res
}
hir::ItemKind::Union(_, hir_generics) => {
let res = check_type_defn(tcx, item, true);
check_variances_for_type_defn(tcx, item, hir_generics);
res
}
hir::ItemKind::Enum(_, hir_generics) => {
let res = check_type_defn(tcx, item, true);
check_variances_for_type_defn(tcx, item, hir_generics);
res
}
hir::ItemKind::Trait(..) => check_trait(tcx, item),
hir::ItemKind::TraitAlias(..) => check_trait(tcx, item),
// `ForeignItem`s are handled separately.
hir::ItemKind::ForeignMod { .. } => Ok(()),
hir::ItemKind::TyAlias(hir_ty, hir_generics) => {
if tcx.type_alias_is_lazy(item.owner_id) {
// Bounds of lazy type aliases and of eager ones that contain opaque types are respected.
// E.g: `type X = impl Trait;`, `type X = (impl Trait, Y);`.
let res = check_item_type(tcx, def_id, hir_ty.span, UnsizedHandling::Allow);
check_variances_for_type_defn(tcx, item, hir_generics);
res
} else {
Ok(())
}
}
_ => Ok(()),
};
crate::check::check::check_item_type(tcx, def_id);
res
}
fn check_foreign_item<'tcx>(
tcx: TyCtxt<'tcx>,
item: &'tcx hir::ForeignItem<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let def_id = item.owner_id.def_id;
CollectItemTypesVisitor { tcx }.visit_foreign_item(item);
debug!(
?item.owner_id,
item.name = ? tcx.def_path_str(def_id)
);
match item.kind {
hir::ForeignItemKind::Fn(decl, ..) => {
check_item_fn(tcx, def_id, item.ident, item.span, decl)
}
hir::ForeignItemKind::Static(ty, ..) => {
check_item_type(tcx, def_id, ty.span, UnsizedHandling::AllowIfForeignTail)
}
hir::ForeignItemKind::Type => Ok(()),
}
}
fn check_trait_item<'tcx>(
tcx: TyCtxt<'tcx>,
trait_item: &'tcx hir::TraitItem<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let def_id = trait_item.owner_id.def_id;
CollectItemTypesVisitor { tcx }.visit_trait_item(trait_item);
let (method_sig, span) = match trait_item.kind {
hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span),
hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span),
_ => (None, trait_item.span),
};
check_object_unsafe_self_trait_by_name(tcx, trait_item);
let mut res = check_associated_item(tcx, def_id, span, method_sig);
if matches!(trait_item.kind, hir::TraitItemKind::Fn(..)) {
for &assoc_ty_def_id in tcx.associated_types_for_impl_traits_in_associated_fn(def_id) {
res = res.and(check_associated_item(
tcx,
assoc_ty_def_id.expect_local(),
tcx.def_span(assoc_ty_def_id),
None,
));
}
}
res
}
/// Require that the user writes where clauses on GATs for the implicit
/// outlives bounds involving trait parameters in trait functions and
/// lifetimes passed as GAT args. See `self-outlives-lint` test.
///
/// We use the following trait as an example throughout this function:
/// ```rust,ignore (this code fails due to this lint)
/// trait IntoIter {
/// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
/// type Item<'a>;
/// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
/// }
/// ```
fn check_gat_where_clauses(tcx: TyCtxt<'_>, trait_def_id: LocalDefId) {
// Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
let mut required_bounds_by_item = FxHashMap::default();
let associated_items = tcx.associated_items(trait_def_id);
// Loop over all GATs together, because if this lint suggests adding a where-clause bound
// to one GAT, it might then require us to an additional bound on another GAT.
// In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which
// then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between
// those GATs.
loop {
let mut should_continue = false;
for gat_item in associated_items.in_definition_order() {
let gat_def_id = gat_item.def_id.expect_local();
let gat_item = tcx.associated_item(gat_def_id);
// If this item is not an assoc ty, or has no args, then it's not a GAT
if gat_item.kind != ty::AssocKind::Type {
continue;
}
let gat_generics = tcx.generics_of(gat_def_id);
// FIXME(jackh726): we can also warn in the more general case
if gat_generics.own_params.is_empty() {
continue;
}
// Gather the bounds with which all other items inside of this trait constrain the GAT.
// This is calculated by taking the intersection of the bounds that each item
// constrains the GAT with individually.
let mut new_required_bounds: Option<FxHashSet<ty::Clause<'_>>> = None;
for item in associated_items.in_definition_order() {
let item_def_id = item.def_id.expect_local();
// Skip our own GAT, since it does not constrain itself at all.
if item_def_id == gat_def_id {
continue;
}
let param_env = tcx.param_env(item_def_id);
let item_required_bounds = match tcx.associated_item(item_def_id).kind {
// In our example, this corresponds to `into_iter` method
ty::AssocKind::Fn => {
// For methods, we check the function signature's return type for any GATs
// to constrain. In the `into_iter` case, we see that the return type
// `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions(
item_def_id.to_def_id(),
tcx.fn_sig(item_def_id).instantiate_identity(),
);
gather_gat_bounds(
tcx,
param_env,
item_def_id,
sig.inputs_and_output,
// We also assume that all of the function signature's parameter types
// are well formed.
&sig.inputs().iter().copied().collect(),
gat_def_id,
gat_generics,
)
}
// In our example, this corresponds to the `Iter` and `Item` associated types
ty::AssocKind::Type => {
// If our associated item is a GAT with missing bounds, add them to
// the param-env here. This allows this GAT to propagate missing bounds
// to other GATs.
let param_env = augment_param_env(
tcx,
param_env,
required_bounds_by_item.get(&item_def_id),
);
gather_gat_bounds(
tcx,
param_env,
item_def_id,
tcx.explicit_item_bounds(item_def_id)
.instantiate_identity_iter_copied()
.collect::<Vec<_>>(),
&FxIndexSet::default(),
gat_def_id,
gat_generics,
)
}
ty::AssocKind::Const => None,
};
if let Some(item_required_bounds) = item_required_bounds {
// Take the intersection of the required bounds for this GAT, and
// the item_required_bounds which are the ones implied by just
// this item alone.
// This is why we use an Option<_>, since we need to distinguish
// the empty set of bounds from the _uninitialized_ set of bounds.
if let Some(new_required_bounds) = &mut new_required_bounds {
new_required_bounds.retain(|b| item_required_bounds.contains(b));
} else {
new_required_bounds = Some(item_required_bounds);
}
}
}
if let Some(new_required_bounds) = new_required_bounds {
let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default();
if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) {
// Iterate until our required_bounds no longer change
// Since they changed here, we should continue the loop
should_continue = true;
}
}
}
// We know that this loop will eventually halt, since we only set `should_continue` if the
// `required_bounds` for this item grows. Since we are not creating any new region or type
// variables, the set of all region and type bounds that we could ever insert are limited
// by the number of unique types and regions we observe in a given item.
if !should_continue {
break;
}
}
for (gat_def_id, required_bounds) in required_bounds_by_item {
// Don't suggest adding `Self: 'a` to a GAT that can't be named
if tcx.is_impl_trait_in_trait(gat_def_id.to_def_id()) {
continue;
}
let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id);
debug!(?required_bounds);
let param_env = tcx.param_env(gat_def_id);
let mut unsatisfied_bounds: Vec<_> = required_bounds
.into_iter()
.filter(|clause| match clause.kind().skip_binder() {
ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
!region_known_to_outlive(
tcx,
gat_def_id,
param_env,
&FxIndexSet::default(),
a,
b,
)
}
ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
!ty_known_to_outlive(tcx, gat_def_id, param_env, &FxIndexSet::default(), a, b)
}
_ => bug!("Unexpected ClauseKind"),
})
.map(|clause| clause.to_string())
.collect();
// We sort so that order is predictable
unsatisfied_bounds.sort();
if !unsatisfied_bounds.is_empty() {
let plural = pluralize!(unsatisfied_bounds.len());
let suggestion = format!(
"{} {}",
gat_item_hir.generics.add_where_or_trailing_comma(),
unsatisfied_bounds.join(", "),
);
let bound =
if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
tcx.dcx()
.struct_span_err(
gat_item_hir.span,
format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
)
.with_span_suggestion(
gat_item_hir.generics.tail_span_for_predicate_suggestion(),
format!("add the required where clause{plural}"),
suggestion,
Applicability::MachineApplicable,
)
.with_note(format!(
"{bound} currently required to ensure that impls have maximum flexibility"
))
.with_note(
"we are soliciting feedback, see issue #87479 \
<https://github.com/rust-lang/rust/issues/87479> for more information",
)
.emit();
}
}
}
/// Add a new set of predicates to the caller_bounds of an existing param_env.
fn augment_param_env<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
new_predicates: Option<&FxHashSet<ty::Clause<'tcx>>>,
) -> ty::ParamEnv<'tcx> {
let Some(new_predicates) = new_predicates else {
return param_env;
};
if new_predicates.is_empty() {
return param_env;
}
let bounds = tcx.mk_clauses_from_iter(
param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()),
);
// FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
// i.e. traits::normalize_param_env_or_error
ty::ParamEnv::new(bounds, param_env.reveal())
}
/// We use the following trait as an example throughout this function.
/// Specifically, let's assume that `to_check` here is the return type
/// of `into_iter`, and the GAT we are checking this for is `Iter`.
/// ```rust,ignore (this code fails due to this lint)
/// trait IntoIter {
/// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
/// type Item<'a>;
/// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
/// }
/// ```
fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
item_def_id: LocalDefId,
to_check: T,
wf_tys: &FxIndexSet<Ty<'tcx>>,
gat_def_id: LocalDefId,
gat_generics: &'tcx ty::Generics,
) -> Option<FxHashSet<ty::Clause<'tcx>>> {
// The bounds we that we would require from `to_check`
let mut bounds = FxHashSet::default();
let (regions, types) = GATArgsCollector::visit(gat_def_id.to_def_id(), to_check);
// If both regions and types are empty, then this GAT isn't in the
// set of types we are checking, and we shouldn't try to do clause analysis
// (particularly, doing so would end up with an empty set of clauses,
// since the current method would require none, and we take the
// intersection of requirements of all methods)
if types.is_empty() && regions.is_empty() {
return None;
}
for (region_a, region_a_idx) in &regions {
// Ignore `'static` lifetimes for the purpose of this lint: it's
// because we know it outlives everything and so doesn't give meaningful
// clues. Also ignore `ReError`, to avoid knock-down errors.
if let ty::ReStatic | ty::ReError(_) = **region_a {
continue;
}
// For each region argument (e.g., `'a` in our example), check for a
// relationship to the type arguments (e.g., `Self`). If there is an
// outlives relationship (`Self: 'a`), then we want to ensure that is
// reflected in a where clause on the GAT itself.
for (ty, ty_idx) in &types {
// In our example, requires that `Self: 'a`
if ty_known_to_outlive(tcx, item_def_id, param_env, wf_tys, *ty, *region_a) {
debug!(?ty_idx, ?region_a_idx);
debug!("required clause: {ty} must outlive {region_a}");
// Translate into the generic parameters of the GAT. In
// our example, the type was `Self`, which will also be
// `Self` in the GAT.
let ty_param = gat_generics.param_at(*ty_idx, tcx);
let ty_param = Ty::new_param(tcx, ty_param.index, ty_param.name);
// Same for the region. In our example, 'a corresponds
// to the 'me parameter.
let region_param = gat_generics.param_at(*region_a_idx, tcx);
let region_param = ty::Region::new_early_param(
tcx,
ty::EarlyParamRegion {
def_id: region_param.def_id,
index: region_param.index,
name: region_param.name,
},
);
// The predicate we expect to see. (In our example,
// `Self: 'me`.)
bounds.insert(
ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param))
.to_predicate(tcx),
);
}
}
// For each region argument (e.g., `'a` in our example), also check for a
// relationship to the other region arguments. If there is an outlives
// relationship, then we want to ensure that is reflected in the where clause
// on the GAT itself.
for (region_b, region_b_idx) in &regions {
// Again, skip `'static` because it outlives everything. Also, we trivially
// know that a region outlives itself. Also ignore `ReError`, to avoid
// knock-down errors.
if matches!(**region_b, ty::ReStatic | ty::ReError(_)) || region_a == region_b {
continue;
}
if region_known_to_outlive(tcx, item_def_id, param_env, wf_tys, *region_a, *region_b) {
debug!(?region_a_idx, ?region_b_idx);
debug!("required clause: {region_a} must outlive {region_b}");
// Translate into the generic parameters of the GAT.
let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
let region_a_param = ty::Region::new_early_param(
tcx,
ty::EarlyParamRegion {
def_id: region_a_param.def_id,
index: region_a_param.index,
name: region_a_param.name,
},
);
// Same for the region.
let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
let region_b_param = ty::Region::new_early_param(
tcx,
ty::EarlyParamRegion {
def_id: region_b_param.def_id,
index: region_b_param.index,
name: region_b_param.name,
},
);
// The predicate we expect to see.
bounds.insert(
ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
region_a_param,
region_b_param,
))
.to_predicate(tcx),
);
}
}
}
Some(bounds)
}
/// Given a known `param_env` and a set of well formed types, can we prove that
/// `ty` outlives `region`.
fn ty_known_to_outlive<'tcx>(
tcx: TyCtxt<'tcx>,
id: LocalDefId,
param_env: ty::ParamEnv<'tcx>,
wf_tys: &FxIndexSet<Ty<'tcx>>,
ty: Ty<'tcx>,
region: ty::Region<'tcx>,
) -> bool {
test_region_obligations(tcx, id, param_env, wf_tys, |infcx| {
infcx.register_region_obligation(infer::RegionObligation {
sub_region: region,
sup_type: ty,
origin: infer::RelateParamBound(DUMMY_SP, ty, None),
});
})
}
/// Given a known `param_env` and a set of well formed types, can we prove that
/// `region_a` outlives `region_b`
fn region_known_to_outlive<'tcx>(
tcx: TyCtxt<'tcx>,
id: LocalDefId,
param_env: ty::ParamEnv<'tcx>,
wf_tys: &FxIndexSet<Ty<'tcx>>,
region_a: ty::Region<'tcx>,
region_b: ty::Region<'tcx>,
) -> bool {
test_region_obligations(tcx, id, param_env, wf_tys, |infcx| {
infcx.sub_regions(infer::RelateRegionParamBound(DUMMY_SP), region_b, region_a);
})
}
/// Given a known `param_env` and a set of well formed types, set up an
/// `InferCtxt`, call the passed function (to e.g. set up region constraints
/// to be tested), then resolve region and return errors
fn test_region_obligations<'tcx>(
tcx: TyCtxt<'tcx>,
id: LocalDefId,
param_env: ty::ParamEnv<'tcx>,
wf_tys: &FxIndexSet<Ty<'tcx>>,
add_constraints: impl FnOnce(&InferCtxt<'tcx>),
) -> bool {
// Unfortunately, we have to use a new `InferCtxt` each call, because
// region constraints get added and solved there and we need to test each
// call individually.
let infcx = tcx.infer_ctxt().build();
add_constraints(&infcx);
let outlives_environment = OutlivesEnvironment::with_bounds(
param_env,
infcx.implied_bounds_tys(param_env, id, wf_tys),
);
let errors = infcx.resolve_regions(&outlives_environment);
debug!(?errors, "errors");
// If we were able to prove that the type outlives the region without
// an error, it must be because of the implied or explicit bounds...
errors.is_empty()
}
/// TypeVisitor that looks for uses of GATs like
/// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into
/// the two vectors, `regions` and `types` (depending on their kind). For each
/// parameter `Pi` also track the index `i`.
struct GATArgsCollector<'tcx> {
gat: DefId,
// Which region appears and which parameter index its instantiated with
regions: FxHashSet<(ty::Region<'tcx>, usize)>,
// Which params appears and which parameter index its instantiated with
types: FxHashSet<(Ty<'tcx>, usize)>,
}
impl<'tcx> GATArgsCollector<'tcx> {
fn visit<T: TypeFoldable<TyCtxt<'tcx>>>(
gat: DefId,
t: T,
) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) {
let mut visitor =
GATArgsCollector { gat, regions: FxHashSet::default(), types: FxHashSet::default() };
t.visit_with(&mut visitor);
(visitor.regions, visitor.types)
}
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GATArgsCollector<'tcx> {
fn visit_ty(&mut self, t: Ty<'tcx>) {
match t.kind() {
ty::Alias(ty::Projection, p) if p.def_id == self.gat => {
for (idx, arg) in p.args.iter().enumerate() {
match arg.unpack() {
GenericArgKind::Lifetime(lt) if !lt.is_bound() => {
self.regions.insert((lt, idx));
}
GenericArgKind::Type(t) => {
self.types.insert((t, idx));
}
_ => {}
}
}
}
_ => {}
}
t.super_visit_with(self)
}
}
fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
match ty.kind {
hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
[s] => s.res.opt_def_id() == Some(trait_def_id.to_def_id()),
_ => false,
},
_ => false,
}
}
/// Detect when an object unsafe trait is referring to itself in one of its associated items.
/// When this is done, suggest using `Self` instead.
fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
let (trait_name, trait_def_id) =
match tcx.hir_node_by_def_id(tcx.hir().get_parent_item(item.hir_id()).def_id) {
hir::Node::Item(item) => match item.kind {
hir::ItemKind::Trait(..) => (item.ident, item.owner_id),
_ => return,
},
_ => return,
};
let mut trait_should_be_self = vec![];
match &item.kind {
hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
if could_be_self(trait_def_id.def_id, ty) =>
{
trait_should_be_self.push(ty.span)
}
hir::TraitItemKind::Fn(sig, _) => {
for ty in sig.decl.inputs {
if could_be_self(trait_def_id.def_id, ty) {
trait_should_be_self.push(ty.span);
}
}
match sig.decl.output {
hir::FnRetTy::Return(ty) if could_be_self(trait_def_id.def_id, ty) => {
trait_should_be_self.push(ty.span);
}
_ => {}
}
}
_ => {}
}
if !trait_should_be_self.is_empty() {
if tcx.check_is_object_safe(trait_def_id) {
return;
}
let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
tcx.dcx()
.struct_span_err(
trait_should_be_self,
"associated item referring to unboxed trait object for its own trait",
)
.with_span_label(trait_name.span, "in this trait")
.with_multipart_suggestion(
"you might have meant to use `Self` to refer to the implementing type",
sugg,
Applicability::MachineApplicable,
)
.emit();
}
}
fn check_impl_item<'tcx>(
tcx: TyCtxt<'tcx>,
impl_item: &'tcx hir::ImplItem<'tcx>,
) -> Result<(), ErrorGuaranteed> {
CollectItemTypesVisitor { tcx }.visit_impl_item(impl_item);
let (method_sig, span) = match impl_item.kind {
hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span),
// Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`.
hir::ImplItemKind::Type(ty) if ty.span != DUMMY_SP => (None, ty.span),
_ => (None, impl_item.span),
};
check_associated_item(tcx, impl_item.owner_id.def_id, span, method_sig)
}
fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(), ErrorGuaranteed> {
match param.kind {
// We currently only check wf of const params here.
hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => Ok(()),
// Const parameters are well formed if their type is structural match.
hir::GenericParamKind::Const { ty: hir_ty, default: _, is_host_effect: _ } => {
let ty = tcx.type_of(param.def_id).instantiate_identity();
if tcx.features().adt_const_params {
enter_wf_checking_ctxt(tcx, hir_ty.span, param.def_id, |wfcx| {
let trait_def_id =
tcx.require_lang_item(LangItem::ConstParamTy, Some(hir_ty.span));
wfcx.register_bound(
ObligationCause::new(
hir_ty.span,
param.def_id,
ObligationCauseCode::ConstParam(ty),
),
wfcx.param_env,
ty,
trait_def_id,
);
Ok(())
})
} else {
let mut diag = match ty.kind() {
ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => return Ok(()),
ty::FnPtr(_) => tcx.dcx().struct_span_err(
hir_ty.span,
"using function pointers as const generic parameters is forbidden",
),
ty::RawPtr(_, _) => tcx.dcx().struct_span_err(
hir_ty.span,
"using raw pointers as const generic parameters is forbidden",
),
_ => tcx.dcx().struct_span_err(
hir_ty.span,
format!("`{}` is forbidden as the type of a const generic parameter", ty),
),
};
diag.note("the only supported types are integers, `bool` and `char`");
let cause = ObligationCause::misc(hir_ty.span, param.def_id);
let may_suggest_feature = match type_allowed_to_implement_const_param_ty(
tcx,
tcx.param_env(param.def_id),
ty,
cause,
) {
// Can never implement `ConstParamTy`, don't suggest anything.
Err(ConstParamTyImplementationError::NotAnAdtOrBuiltinAllowed) => false,
// May be able to implement `ConstParamTy`. Only emit the feature help
// if the type is local, since the user may be able to fix the local type.
Err(ConstParamTyImplementationError::InfrigingFields(..)) => {
fn ty_is_local(ty: Ty<'_>) -> bool {
match ty.kind() {
ty::Adt(adt_def, ..) => adt_def.did().is_local(),
// Arrays and slices use the inner type's `ConstParamTy`.
ty::Array(ty, ..) => ty_is_local(*ty),
ty::Slice(ty) => ty_is_local(*ty),
// `&` references use the inner type's `ConstParamTy`.
// `&mut` are not supported.
ty::Ref(_, ty, ast::Mutability::Not) => ty_is_local(*ty),
// Say that a tuple is local if any of its components are local.
// This is not strictly correct, but it's likely that the user can fix the local component.
ty::Tuple(tys) => tys.iter().any(|ty| ty_is_local(ty)),
_ => false,
}
}
ty_is_local(ty)
}
// Implments `ConstParamTy`, suggest adding the feature to enable.
Ok(..) => true,
};
if may_suggest_feature {
tcx.disabled_nightly_features(
&mut diag,
Some(param.hir_id),
[(
" more complex and user defined types".to_string(),
sym::adt_const_params,
)],
);
}
Err(diag.emit())
}
}
}
}
#[instrument(level = "debug", skip(tcx, span, sig_if_method))]
fn check_associated_item(
tcx: TyCtxt<'_>,
item_id: LocalDefId,
span: Span,
sig_if_method: Option<&hir::FnSig<'_>>,
) -> Result<(), ErrorGuaranteed> {
let loc = Some(WellFormedLoc::Ty(item_id));
enter_wf_checking_ctxt(tcx, span, item_id, |wfcx| {
let item = tcx.associated_item(item_id);
// Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
// other `Foo` impls are incoherent.
tcx.ensure()
.coherent_trait(tcx.parent(item.trait_item_def_id.unwrap_or(item_id.into())))?;
let self_ty = match item.container {
ty::TraitContainer => tcx.types.self_param,
ty::ImplContainer => tcx.type_of(item.container_id(tcx)).instantiate_identity(),
};
match item.kind {
ty::AssocKind::Const => {
let ty = tcx.type_of(item.def_id).instantiate_identity();
let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
wfcx.register_wf_obligation(span, loc, ty.into());
Ok(())
}
ty::AssocKind::Fn => {
let sig = tcx.fn_sig(item.def_id).instantiate_identity();
let hir_sig = sig_if_method.expect("bad signature for method");
check_fn_or_method(
wfcx,
item.ident(tcx).span,
sig,
hir_sig.decl,
item.def_id.expect_local(),
);
check_method_receiver(wfcx, hir_sig, item, self_ty)
}
ty::AssocKind::Type => {
if let ty::AssocItemContainer::TraitContainer = item.container {
check_associated_type_bounds(wfcx, item, span)
}
if item.defaultness(tcx).has_value() {
let ty = tcx.type_of(item.def_id).instantiate_identity();
let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
wfcx.register_wf_obligation(span, loc, ty.into());
}
Ok(())
}
}
})
}
/// In a type definition, we check that to ensure that the types of the fields are well-formed.
fn check_type_defn<'tcx>(
tcx: TyCtxt<'tcx>,
item: &hir::Item<'tcx>,
all_sized: bool,
) -> Result<(), ErrorGuaranteed> {
let _ = tcx.representability(item.owner_id.def_id);
let adt_def = tcx.adt_def(item.owner_id);
enter_wf_checking_ctxt(tcx, item.span, item.owner_id.def_id, |wfcx| {
let variants = adt_def.variants();
let packed = adt_def.repr().packed();
for variant in variants.iter() {
// All field types must be well-formed.
for field in &variant.fields {
let field_id = field.did.expect_local();
let hir::FieldDef { ty: hir_ty, .. } =
tcx.hir_node_by_def_id(field_id).expect_field();
let ty = wfcx.normalize(
hir_ty.span,
None,
tcx.type_of(field.did).instantiate_identity(),
);
wfcx.register_wf_obligation(
hir_ty.span,
Some(WellFormedLoc::Ty(field_id)),
ty.into(),
)
}
// For DST, or when drop needs to copy things around, all
// intermediate types must be sized.
let needs_drop_copy = || {
packed && {
let ty = tcx.type_of(variant.tail().did).instantiate_identity();
let ty = tcx.erase_regions(ty);
assert!(!ty.has_infer());
ty.needs_drop(tcx, tcx.param_env(item.owner_id))
}
};
// All fields (except for possibly the last) should be sized.
let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
let unsized_len = if all_sized { 0 } else { 1 };
for (idx, field) in
variant.fields.raw[..variant.fields.len() - unsized_len].iter().enumerate()
{
let last = idx == variant.fields.len() - 1;
let field_id = field.did.expect_local();
let hir::FieldDef { ty: hir_ty, .. } =
tcx.hir_node_by_def_id(field_id).expect_field();
let ty = wfcx.normalize(
hir_ty.span,
None,
tcx.type_of(field.did).instantiate_identity(),
);
wfcx.register_bound(
traits::ObligationCause::new(
hir_ty.span,
wfcx.body_def_id,
ObligationCauseCode::FieldSized {
adt_kind: match &item.kind {
ItemKind::Struct(..) => AdtKind::Struct,
ItemKind::Union(..) => AdtKind::Union,
ItemKind::Enum(..) => AdtKind::Enum,
kind => span_bug!(
item.span,
"should be wfchecking an ADT, got {kind:?}"
),
},
span: hir_ty.span,
last,
},
),
wfcx.param_env,
ty,
tcx.require_lang_item(LangItem::Sized, None),
);
}
// Explicit `enum` discriminant values must const-evaluate successfully.
if let ty::VariantDiscr::Explicit(discr_def_id) = variant.discr {
let cause = traits::ObligationCause::new(
tcx.def_span(discr_def_id),
wfcx.body_def_id,
ObligationCauseCode::Misc,
);
wfcx.register_obligation(traits::Obligation::new(
tcx,
cause,
wfcx.param_env,
ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(
ty::Const::from_anon_const(tcx, discr_def_id.expect_local()),
))),
));
}
}
check_where_clauses(wfcx, item.span, item.owner_id.def_id);
Ok(())
})
}
#[instrument(skip(tcx, item))]
fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) -> Result<(), ErrorGuaranteed> {
debug!(?item.owner_id);
let def_id = item.owner_id.def_id;
let trait_def = tcx.trait_def(def_id);
if trait_def.is_marker
|| matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
{
for associated_def_id in &*tcx.associated_item_def_ids(def_id) {
struct_span_code_err!(
tcx.dcx(),
tcx.def_span(*associated_def_id),
E0714,
"marker traits cannot have associated items",
)
.emit();
}
}
let res = enter_wf_checking_ctxt(tcx, item.span, def_id, |wfcx| {
check_where_clauses(wfcx, item.span, def_id);
Ok(())
});
// Only check traits, don't check trait aliases
if let hir::ItemKind::Trait(..) = item.kind {
check_gat_where_clauses(tcx, item.owner_id.def_id);
}
res
}
/// Checks all associated type defaults of trait `trait_def_id`.
///
/// Assuming the defaults are used, check that all predicates (bounds on the
/// assoc type and where clauses on the trait) hold.
fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: ty::AssocItem, span: Span) {
let bounds = wfcx.tcx().explicit_item_bounds(item.def_id);
debug!("check_associated_type_bounds: bounds={:?}", bounds);
let wf_obligations =
bounds.instantiate_identity_iter_copied().flat_map(|(bound, bound_span)| {
let normalized_bound = wfcx.normalize(span, None, bound);
traits::wf::clause_obligations(
wfcx.infcx,
wfcx.param_env,
wfcx.body_def_id,
normalized_bound,
bound_span,
)
});
wfcx.register_obligations(wf_obligations);
}
fn check_item_fn(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
ident: Ident,
span: Span,
decl: &hir::FnDecl<'_>,
) -> Result<(), ErrorGuaranteed> {
enter_wf_checking_ctxt(tcx, span, def_id, |wfcx| {
let sig = tcx.fn_sig(def_id).instantiate_identity();
check_fn_or_method(wfcx, ident.span, sig, decl, def_id);
Ok(())
})
}
enum UnsizedHandling {
Forbid,
Allow,
AllowIfForeignTail,
}
fn check_item_type(
tcx: TyCtxt<'_>,
item_id: LocalDefId,
ty_span: Span,
unsized_handling: UnsizedHandling,
) -> Result<(), ErrorGuaranteed> {
debug!("check_item_type: {:?}", item_id);
enter_wf_checking_ctxt(tcx, ty_span, item_id, |wfcx| {
let ty = tcx.type_of(item_id).instantiate_identity();
let item_ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(item_id)), ty);
let forbid_unsized = match unsized_handling {
UnsizedHandling::Forbid => true,
UnsizedHandling::Allow => false,
UnsizedHandling::AllowIfForeignTail => {
let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env);
!matches!(tail.kind(), ty::Foreign(_))
}
};
wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(item_id)), item_ty.into());
if forbid_unsized {
wfcx.register_bound(
traits::ObligationCause::new(
ty_span,
wfcx.body_def_id,
ObligationCauseCode::WellFormed(None),
),
wfcx.param_env,
item_ty,
tcx.require_lang_item(LangItem::Sized, None),
);
}
// Ensure that the end result is `Sync` in a non-thread local `static`.
let should_check_for_sync = tcx.static_mutability(item_id.to_def_id())
== Some(hir::Mutability::Not)
&& !tcx.is_foreign_item(item_id.to_def_id())
&& !tcx.is_thread_local_static(item_id.to_def_id());
if should_check_for_sync {
wfcx.register_bound(
traits::ObligationCause::new(
ty_span,
wfcx.body_def_id,
ObligationCauseCode::SharedStatic,
),
wfcx.param_env,
item_ty,
tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
);
}
Ok(())
})
}
#[instrument(level = "debug", skip(tcx, hir_self_ty, hir_trait_ref))]
fn check_impl<'tcx>(
tcx: TyCtxt<'tcx>,
item: &'tcx hir::Item<'tcx>,
hir_self_ty: &hir::Ty<'_>,
hir_trait_ref: &Option<hir::TraitRef<'_>>,
) -> Result<(), ErrorGuaranteed> {
enter_wf_checking_ctxt(tcx, item.span, item.owner_id.def_id, |wfcx| {
match hir_trait_ref {
Some(hir_trait_ref) => {
// `#[rustc_reservation_impl]` impls are not real impls and
// therefore don't need to be WF (the trait's `Self: Trait` predicate
// won't hold).
let trait_ref = tcx.impl_trait_ref(item.owner_id).unwrap().instantiate_identity();
// Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
// other `Foo` impls are incoherent.
tcx.ensure().coherent_trait(trait_ref.def_id)?;
let trait_span = hir_trait_ref.path.span;
let trait_ref = wfcx.normalize(
trait_span,
Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
trait_ref,
);
let trait_pred =
ty::TraitPredicate { trait_ref, polarity: ty::PredicatePolarity::Positive };
let mut obligations = traits::wf::trait_obligations(
wfcx.infcx,
wfcx.param_env,
wfcx.body_def_id,
trait_pred,
trait_span,
item,
);
for obligation in &mut obligations {
if obligation.cause.span != trait_span {
// We already have a better span.
continue;
}
if let Some(pred) = obligation.predicate.to_opt_poly_trait_pred()
&& pred.skip_binder().self_ty() == trait_ref.self_ty()
{
obligation.cause.span = hir_self_ty.span;
}
if let Some(pred) = obligation.predicate.to_opt_poly_projection_pred()
&& pred.skip_binder().self_ty() == trait_ref.self_ty()
{
obligation.cause.span = hir_self_ty.span;
}
}
debug!(?obligations);
wfcx.register_obligations(obligations);
}
None => {
let self_ty = tcx.type_of(item.owner_id).instantiate_identity();
let self_ty = wfcx.normalize(
item.span,
Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
self_ty,
);
wfcx.register_wf_obligation(
hir_self_ty.span,
Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
self_ty.into(),
);
}
}
check_where_clauses(wfcx, item.span, item.owner_id.def_id);
Ok(())
})
}
/// Checks where-clauses and inline bounds that are declared on `def_id`.
#[instrument(level = "debug", skip(wfcx))]
fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id: LocalDefId) {
let infcx = wfcx.infcx;
let tcx = wfcx.tcx();
let predicates = tcx.predicates_of(def_id.to_def_id());
let generics = tcx.generics_of(def_id);
let is_our_default = |def: &ty::GenericParamDef| match def.kind {
GenericParamDefKind::Type { has_default, .. }
| GenericParamDefKind::Const { has_default, .. } => {
has_default && def.index >= generics.parent_count as u32
}
GenericParamDefKind::Lifetime => {
span_bug!(tcx.def_span(def.def_id), "lifetime params can have no default")
}
};
// Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
// For example, this forbids the declaration:
//
// struct Foo<T = Vec<[u32]>> { .. }
//
// Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
for param in &generics.own_params {
match param.kind {
GenericParamDefKind::Type { .. } => {
if is_our_default(param) {
let ty = tcx.type_of(param.def_id).instantiate_identity();
// Ignore dependent defaults -- that is, where the default of one type
// parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
// be sure if it will error or not as user might always specify the other.
if !ty.has_param() {
wfcx.register_wf_obligation(
tcx.def_span(param.def_id),
Some(WellFormedLoc::Ty(param.def_id.expect_local())),
ty.into(),
);
}
}
}
GenericParamDefKind::Const { .. } => {
if is_our_default(param) {
// FIXME(const_generics_defaults): This
// is incorrect when dealing with unused args, for example
// for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
// we should eagerly error.
let default_ct = tcx.const_param_default(param.def_id).instantiate_identity();
if !default_ct.has_param() {
wfcx.register_wf_obligation(
tcx.def_span(param.def_id),
None,
default_ct.into(),
);
}
}
}
// Doesn't have defaults.
GenericParamDefKind::Lifetime => {}
}
}
// Check that trait predicates are WF when params are instantiated with their defaults.
// We don't want to overly constrain the predicates that may be written but we want to
// catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
// Therefore we check if a predicate which contains a single type param
// with a concrete default is WF with that default instantiated.
// For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
//
// First we build the defaulted generic parameters.
let args = GenericArgs::for_item(tcx, def_id.to_def_id(), |param, _| {
match param.kind {
GenericParamDefKind::Lifetime => {
// All regions are identity.
tcx.mk_param_from_def(param)
}
GenericParamDefKind::Type { .. } => {
// If the param has a default, ...
if is_our_default(param) {
let default_ty = tcx.type_of(param.def_id).instantiate_identity();
// ... and it's not a dependent default, ...
if !default_ty.has_param() {
// ... then instantiate it with the default.
return default_ty.into();
}
}
tcx.mk_param_from_def(param)
}
GenericParamDefKind::Const { .. } => {
// If the param has a default, ...
if is_our_default(param) {
let default_ct = tcx.const_param_default(param.def_id).instantiate_identity();
// ... and it's not a dependent default, ...
if !default_ct.has_param() {
// ... then instantiate it with the default.
return default_ct.into();
}
}
tcx.mk_param_from_def(param)
}
}
});
// Now we build the instantiated predicates.
let default_obligations = predicates
.predicates
.iter()
.flat_map(|&(pred, sp)| {
#[derive(Default)]
struct CountParams {
params: FxHashSet<u32>,
}
impl<'tcx> ty::visit::TypeVisitor<TyCtxt<'tcx>> for CountParams {
type Result = ControlFlow<()>;
fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
if let ty::Param(param) = t.kind() {
self.params.insert(param.index);
}
t.super_visit_with(self)
}
fn visit_region(&mut self, _: ty::Region<'tcx>) -> Self::Result {
ControlFlow::Break(())
}
fn visit_const(&mut self, c: ty::Const<'tcx>) -> Self::Result {
if let ty::ConstKind::Param(param) = c.kind() {
self.params.insert(param.index);
}
c.super_visit_with(self)
}
}
let mut param_count = CountParams::default();
let has_region = pred.visit_with(&mut param_count).is_break();
let instantiated_pred = ty::EarlyBinder::bind(pred).instantiate(tcx, args);
// Don't check non-defaulted params, dependent defaults (including lifetimes)
// or preds with multiple params.
if instantiated_pred.has_non_region_param()
|| param_count.params.len() > 1
|| has_region
{
None
} else if predicates.predicates.iter().any(|&(p, _)| p == instantiated_pred) {
// Avoid duplication of predicates that contain no parameters, for example.
None
} else {
Some((instantiated_pred, sp))
}
})
.map(|(pred, sp)| {
// Convert each of those into an obligation. So if you have
// something like `struct Foo<T: Copy = String>`, we would
// take that predicate `T: Copy`, instantiated with `String: Copy`
// (actually that happens in the previous `flat_map` call),
// and then try to prove it (in this case, we'll fail).
//
// Note the subtle difference from how we handle `predicates`
// below: there, we are not trying to prove those predicates
// to be *true* but merely *well-formed*.
let pred = wfcx.normalize(sp, None, pred);
let cause = traits::ObligationCause::new(
sp,
wfcx.body_def_id,
ObligationCauseCode::WhereClause(def_id.to_def_id()),
);
traits::Obligation::new(tcx, cause, wfcx.param_env, pred)
});
let predicates = predicates.instantiate_identity(tcx);
let predicates = wfcx.normalize(span, None, predicates);
debug!(?predicates.predicates);
assert_eq!(predicates.predicates.len(), predicates.spans.len());
let wf_obligations = predicates.into_iter().flat_map(|(p, sp)| {
traits::wf::clause_obligations(infcx, wfcx.param_env, wfcx.body_def_id, p, sp)
});
let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect();
wfcx.register_obligations(obligations);
}
#[instrument(level = "debug", skip(wfcx, span, hir_decl))]
fn check_fn_or_method<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
span: Span,
sig: ty::PolyFnSig<'tcx>,
hir_decl: &hir::FnDecl<'_>,
def_id: LocalDefId,
) {
let tcx = wfcx.tcx();
let mut sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
// Normalize the input and output types one at a time, using a different
// `WellFormedLoc` for each. We cannot call `normalize_associated_types`
// on the entire `FnSig`, since this would use the same `WellFormedLoc`
// for each type, preventing the HIR wf check from generating
// a nice error message.
let arg_span =
|idx| hir_decl.inputs.get(idx).map_or(hir_decl.output.span(), |arg: &hir::Ty<'_>| arg.span);
sig.inputs_and_output =
tcx.mk_type_list_from_iter(sig.inputs_and_output.iter().enumerate().map(|(idx, ty)| {
wfcx.normalize(
arg_span(idx),
Some(WellFormedLoc::Param {
function: def_id,
// Note that the `param_idx` of the output type is
// one greater than the index of the last input type.
param_idx: idx.try_into().unwrap(),
}),
ty,
)
}));
for (idx, ty) in sig.inputs_and_output.iter().enumerate() {
wfcx.register_wf_obligation(
arg_span(idx),
Some(WellFormedLoc::Param { function: def_id, param_idx: idx.try_into().unwrap() }),
ty.into(),
);
}
check_where_clauses(wfcx, span, def_id);
if sig.abi == Abi::RustCall {
let span = tcx.def_span(def_id);
let has_implicit_self = hir_decl.implicit_self != hir::ImplicitSelfKind::None;
let mut inputs = sig.inputs().iter().skip(if has_implicit_self { 1 } else { 0 });
// Check that the argument is a tuple and is sized
if let Some(ty) = inputs.next() {
wfcx.register_bound(
ObligationCause::new(span, wfcx.body_def_id, ObligationCauseCode::RustCall),
wfcx.param_env,
*ty,
tcx.require_lang_item(hir::LangItem::Tuple, Some(span)),
);
wfcx.register_bound(
ObligationCause::new(span, wfcx.body_def_id, ObligationCauseCode::RustCall),
wfcx.param_env,
*ty,
tcx.require_lang_item(hir::LangItem::Sized, Some(span)),
);
} else {
tcx.dcx().span_err(
hir_decl.inputs.last().map_or(span, |input| input.span),
"functions with the \"rust-call\" ABI must take a single non-self tuple argument",
);
}
// No more inputs other than the `self` type and the tuple type
if inputs.next().is_some() {
tcx.dcx().span_err(
hir_decl.inputs.last().map_or(span, |input| input.span),
"functions with the \"rust-call\" ABI must take a single non-self tuple argument",
);
}
}
}
#[instrument(level = "debug", skip(wfcx))]
fn check_method_receiver<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
fn_sig: &hir::FnSig<'_>,
method: ty::AssocItem,
self_ty: Ty<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let tcx = wfcx.tcx();
if !method.fn_has_self_parameter {
return Ok(());
}
let span = fn_sig.decl.inputs[0].span;
let sig = tcx.fn_sig(method.def_id).instantiate_identity();
let sig = tcx.liberate_late_bound_regions(method.def_id, sig);
let sig = wfcx.normalize(span, None, sig);
debug!("check_method_receiver: sig={:?}", sig);
let self_ty = wfcx.normalize(span, None, self_ty);
let receiver_ty = sig.inputs()[0];
let receiver_ty = wfcx.normalize(span, None, receiver_ty);
// If the receiver already has errors reported, consider it valid to avoid
// unnecessary errors (#58712).
if receiver_ty.references_error() {
return Ok(());
}
if tcx.features().arbitrary_self_types {
if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
// Report error; `arbitrary_self_types` was enabled.
return Err(tcx.dcx().emit_err(errors::InvalidReceiverTy { span, receiver_ty }));
}
} else {
if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, false) {
return Err(if receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
// Report error; would have worked with `arbitrary_self_types`.
feature_err(
&tcx.sess,
sym::arbitrary_self_types,
span,
format!(
"`{receiver_ty}` cannot be used as the type of `self` without \
the `arbitrary_self_types` feature",
),
)
.with_help(fluent::hir_analysis_invalid_receiver_ty_help)
.emit()
} else {
// Report error; would not have worked with `arbitrary_self_types`.
tcx.dcx().emit_err(errors::InvalidReceiverTy { span, receiver_ty })
});
}
}
Ok(())
}
/// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
/// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
/// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
/// strict: `receiver_ty` must implement `Receiver` and directly implement
/// `Deref<Target = self_ty>`.
///
/// N.B., there are cases this function returns `true` but causes an error to be emitted,
/// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
/// wrong lifetime. Be careful of this if you are calling this function speculatively.
fn receiver_is_valid<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
span: Span,
receiver_ty: Ty<'tcx>,
self_ty: Ty<'tcx>,
arbitrary_self_types_enabled: bool,
) -> bool {
let infcx = wfcx.infcx;
let tcx = wfcx.tcx();
let cause =
ObligationCause::new(span, wfcx.body_def_id, traits::ObligationCauseCode::MethodReceiver);
let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty);
// `self: Self` is always valid.
if can_eq_self(receiver_ty) {
if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, receiver_ty) {
infcx.err_ctxt().report_mismatched_types(&cause, self_ty, receiver_ty, err).emit();
}
return true;
}
let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_def_id, span, receiver_ty);
// The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
if arbitrary_self_types_enabled {
autoderef = autoderef.include_raw_pointers();
}
// The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
autoderef.next();
let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, Some(span));
// Keep dereferencing `receiver_ty` until we get to `self_ty`.
loop {
if let Some((potential_self_ty, _)) = autoderef.next() {
debug!(
"receiver_is_valid: potential self type `{:?}` to match `{:?}`",
potential_self_ty, self_ty
);
if can_eq_self(potential_self_ty) {
wfcx.register_obligations(autoderef.into_obligations());
if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty) {
infcx
.err_ctxt()
.report_mismatched_types(&cause, self_ty, potential_self_ty, err)
.emit();
}
break;
} else {
// Without `feature(arbitrary_self_types)`, we require that each step in the
// deref chain implement `receiver`
if !arbitrary_self_types_enabled
&& !receiver_is_implemented(
wfcx,
receiver_trait_def_id,
cause.clone(),
potential_self_ty,
)
{
return false;
}
}
} else {
debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
return false;
}
}
// Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
if !arbitrary_self_types_enabled
&& !receiver_is_implemented(wfcx, receiver_trait_def_id, cause.clone(), receiver_ty)
{
return false;
}
true
}
fn receiver_is_implemented<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
receiver_trait_def_id: DefId,
cause: ObligationCause<'tcx>,
receiver_ty: Ty<'tcx>,
) -> bool {
let tcx = wfcx.tcx();
let trait_ref = ty::TraitRef::new(tcx, receiver_trait_def_id, [receiver_ty]);
let obligation = traits::Obligation::new(tcx, cause, wfcx.param_env, trait_ref);
if wfcx.infcx.predicate_must_hold_modulo_regions(&obligation) {
true
} else {
debug!(
"receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
receiver_ty
);
false
}
}
fn check_variances_for_type_defn<'tcx>(
tcx: TyCtxt<'tcx>,
item: &hir::Item<'tcx>,
hir_generics: &hir::Generics<'tcx>,
) {
let identity_args = ty::GenericArgs::identity_for_item(tcx, item.owner_id);
match item.kind {
ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
for field in tcx.adt_def(item.owner_id).all_fields() {
if field.ty(tcx, identity_args).references_error() {
return;
}
}
}
ItemKind::TyAlias(..) => {
assert!(
tcx.type_alias_is_lazy(item.owner_id),
"should not be computing variance of non-weak type alias"
);
if tcx.type_of(item.owner_id).skip_binder().references_error() {
return;
}
}
kind => span_bug!(item.span, "cannot compute the variances of {kind:?}"),
}
let ty_predicates = tcx.predicates_of(item.owner_id);
assert_eq!(ty_predicates.parent, None);
let variances = tcx.variances_of(item.owner_id);
let mut constrained_parameters: FxHashSet<_> = variances
.iter()
.enumerate()
.filter(|&(_, &variance)| variance != ty::Bivariant)
.map(|(index, _)| Parameter(index as u32))
.collect();
identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
// Lazily calculated because it is only needed in case of an error.
let explicitly_bounded_params = LazyCell::new(|| {
let icx = crate::collect::ItemCtxt::new(tcx, item.owner_id.def_id);
hir_generics
.predicates
.iter()
.filter_map(|predicate| match predicate {
hir::WherePredicate::BoundPredicate(predicate) => {
match icx.lower_ty(predicate.bounded_ty).kind() {
ty::Param(data) => Some(Parameter(data.index)),
_ => None,
}
}
_ => None,
})
.collect::<FxHashSet<_>>()
});
let ty_generics = tcx.generics_of(item.owner_id);
for (index, _) in variances.iter().enumerate() {
let parameter = Parameter(index as u32);
if constrained_parameters.contains(&parameter) {
continue;
}
let ty_param = &ty_generics.own_params[index];
let hir_param = &hir_generics.params[index];
if ty_param.def_id != hir_param.def_id.into() {
// Valid programs always have lifetimes before types in the generic parameter list.
// ty_generics are normalized to be in this required order, and variances are built
// from ty generics, not from hir generics. but we need hir generics to get
// a span out.
//
// If they aren't in the same order, then the user has written invalid code, and already
// got an error about it (or I'm wrong about this).
tcx.dcx().span_delayed_bug(
hir_param.span,
"hir generics and ty generics in different order",
);
continue;
}
match hir_param.name {
hir::ParamName::Error => {}
_ => {
let has_explicit_bounds = explicitly_bounded_params.contains(&parameter);
report_bivariance(tcx, hir_param, has_explicit_bounds, item.kind);
}
}
}
}
fn report_bivariance(
tcx: TyCtxt<'_>,
param: &rustc_hir::GenericParam<'_>,
has_explicit_bounds: bool,
item_kind: ItemKind<'_>,
) -> ErrorGuaranteed {
let param_name = param.name.ident();
let help = match item_kind {
ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
if let Some(def_id) = tcx.lang_items().phantom_data() {
errors::UnusedGenericParameterHelp::Adt {
param_name,
phantom_data: tcx.def_path_str(def_id),
}
} else {
errors::UnusedGenericParameterHelp::AdtNoPhantomData { param_name }
}
}
ItemKind::TyAlias(..) => errors::UnusedGenericParameterHelp::TyAlias { param_name },
item_kind => bug!("report_bivariance: unexpected item kind: {item_kind:?}"),
};
let const_param_help =
matches!(param.kind, hir::GenericParamKind::Type { .. } if !has_explicit_bounds)
.then_some(());
let mut diag = tcx.dcx().create_err(errors::UnusedGenericParameter {
span: param.span,
param_name,
param_def_kind: tcx.def_descr(param.def_id.to_def_id()),
help,
const_param_help,
});
diag.code(E0392);
diag.emit()
}
impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
/// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
/// aren't true.
#[instrument(level = "debug", skip(self))]
fn check_false_global_bounds(&mut self) {
let tcx = self.ocx.infcx.tcx;
let mut span = self.span;
let empty_env = ty::ParamEnv::empty();
let predicates_with_span = tcx.predicates_of(self.body_def_id).predicates.iter().copied();
// Check elaborated bounds.
let implied_obligations = traits::elaborate(tcx, predicates_with_span);
for (pred, obligation_span) in implied_obligations {
// We lower empty bounds like `Vec<dyn Copy>:` as
// `WellFormed(Vec<dyn Copy>)`, which will later get checked by
// regular WF checking
if let ty::ClauseKind::WellFormed(..) = pred.kind().skip_binder() {
continue;
}
// Match the existing behavior.
if pred.is_global() && !pred.has_type_flags(TypeFlags::HAS_BINDER_VARS) {
let pred = self.normalize(span, None, pred);
// only use the span of the predicate clause (#90869)
let hir_node = tcx.hir_node_by_def_id(self.body_def_id);
if let Some(hir::Generics { predicates, .. }) = hir_node.generics() {
span = predicates
.iter()
// There seems to be no better way to find out which predicate we are in
.find(|pred| pred.span().contains(obligation_span))
.map(|pred| pred.span())
.unwrap_or(obligation_span);
}
let obligation = traits::Obligation::new(
tcx,
traits::ObligationCause::new(
span,
self.body_def_id,
ObligationCauseCode::TrivialBound,
),
empty_env,
pred,
);
self.ocx.register_obligation(obligation);
}
}
}
}
fn check_mod_type_wf(tcx: TyCtxt<'_>, module: LocalModDefId) -> Result<(), ErrorGuaranteed> {
let items = tcx.hir_module_items(module);
let mut res = items.par_items(|item| tcx.ensure().check_well_formed(item.owner_id));
res = res.and(items.par_impl_items(|item| tcx.ensure().check_well_formed(item.owner_id)));
res = res.and(items.par_trait_items(|item| tcx.ensure().check_well_formed(item.owner_id)));
res = res.and(items.par_foreign_items(|item| tcx.ensure().check_well_formed(item.owner_id)));
if module == LocalModDefId::CRATE_DEF_ID {
super::entry::check_for_entry_fn(tcx);
}
res
}
fn lint_redundant_lifetimes<'tcx>(
tcx: TyCtxt<'tcx>,
owner_id: LocalDefId,
outlives_env: &OutlivesEnvironment<'tcx>,
) {
let def_kind = tcx.def_kind(owner_id);
match def_kind {
DefKind::Struct
| DefKind::Union
| DefKind::Enum
| DefKind::Trait
| DefKind::TraitAlias
| DefKind::Fn
| DefKind::Const
| DefKind::Impl { of_trait: _ } => {
// Proceed
}
DefKind::AssocFn | DefKind::AssocTy | DefKind::AssocConst => {
let parent_def_id = tcx.local_parent(owner_id);
if matches!(tcx.def_kind(parent_def_id), DefKind::Impl { of_trait: true }) {
// Don't check for redundant lifetimes for associated items of trait
// implementations, since the signature is required to be compatible
// with the trait, even if the implementation implies some lifetimes
// are redundant.
return;
}
}
DefKind::Mod
| DefKind::Variant
| DefKind::TyAlias
| DefKind::ForeignTy
| DefKind::TyParam
| DefKind::ConstParam
| DefKind::Static { .. }
| DefKind::Ctor(_, _)
| DefKind::Macro(_)
| DefKind::ExternCrate
| DefKind::Use
| DefKind::ForeignMod
| DefKind::AnonConst
| DefKind::InlineConst
| DefKind::OpaqueTy
| DefKind::Field
| DefKind::LifetimeParam
| DefKind::GlobalAsm
| DefKind::Closure => return,
}
// The ordering of this lifetime map is a bit subtle.
//
// Specifically, we want to find a "candidate" lifetime that precedes a "victim" lifetime,
// where we can prove that `'candidate = 'victim`.
//
// `'static` must come first in this list because we can never replace `'static` with
// something else, but if we find some lifetime `'a` where `'a = 'static`, we want to
// suggest replacing `'a` with `'static`.
let mut lifetimes = vec![tcx.lifetimes.re_static];
lifetimes.extend(
ty::GenericArgs::identity_for_item(tcx, owner_id).iter().filter_map(|arg| arg.as_region()),
);
// If we are in a function, add its late-bound lifetimes too.
if matches!(def_kind, DefKind::Fn | DefKind::AssocFn) {
for var in tcx.fn_sig(owner_id).instantiate_identity().bound_vars() {
let ty::BoundVariableKind::Region(kind) = var else { continue };
lifetimes.push(ty::Region::new_late_param(tcx, owner_id.to_def_id(), kind));
}
}
lifetimes.retain(|candidate| candidate.has_name());
// Keep track of lifetimes which have already been replaced with other lifetimes.
// This makes sure that if `'a = 'b = 'c`, we don't say `'c` should be replaced by
// both `'a` and `'b`.
let mut shadowed = FxHashSet::default();
for (idx, &candidate) in lifetimes.iter().enumerate() {
// Don't suggest removing a lifetime twice. We only need to check this
// here and not up in the `victim` loop because equality is transitive,
// so if A = C and B = C, then A must = B, so it'll be shadowed too in
// A's victim loop.
if shadowed.contains(&candidate) {
continue;
}
for &victim in &lifetimes[(idx + 1)..] {
// We should only have late-bound lifetimes of the `BrNamed` variety,
// since we get these signatures straight from `hir_lowering`. And any
// other regions (ReError/ReStatic/etc.) shouldn't matter, since we
// can't really suggest to remove them.
let (ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. })
| ty::ReLateParam(ty::LateParamRegion {
bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
..
})) = victim.kind()
else {
continue;
};
// Do not rename lifetimes not local to this item since they'll overlap
// with the lint running on the parent. We still want to consider parent
// lifetimes which make child lifetimes redundant, otherwise we would
// have truncated the `identity_for_item` args above.
if tcx.parent(def_id) != owner_id.to_def_id() {
continue;
}
// If `candidate <: victim` and `victim <: candidate`, then they're equal.
if outlives_env.free_region_map().sub_free_regions(tcx, candidate, victim)
&& outlives_env.free_region_map().sub_free_regions(tcx, victim, candidate)
{
shadowed.insert(victim);
tcx.emit_node_span_lint(
rustc_lint_defs::builtin::REDUNDANT_LIFETIMES,
tcx.local_def_id_to_hir_id(def_id.expect_local()),
tcx.def_span(def_id),
RedundantLifetimeArgsLint { candidate, victim },
);
}
}
}
}
#[derive(LintDiagnostic)]
#[diag(hir_analysis_redundant_lifetime_args)]
#[note]
struct RedundantLifetimeArgsLint<'tcx> {
/// The lifetime we have found to be redundant.
victim: ty::Region<'tcx>,
// The lifetime we can replace the victim with.
candidate: ty::Region<'tcx>,
}
pub fn provide(providers: &mut Providers) {
*providers = Providers { check_mod_type_wf, check_well_formed, ..*providers };
}