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rust/rust/573bd7d4ada3677648942e644f0894de7d22ac14/./compiler/rustc_hir_analysis/src/check/wfcheck.rs
blob: 1d17621be217f46b6b1a73e93497774fcd1b9156 [file]
use std::cell::LazyCell;
use std::ops::{ControlFlow, Deref};
use hir::intravisit::{self, Visitor};
use rustc_abi::{ExternAbi, ScalableElt};
use rustc_ast as ast;
use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
use rustc_errors::codes::*;
use rustc_errors::{Applicability, ErrorGuaranteed, msg, pluralize, struct_span_code_err};
use rustc_hir as hir;
use rustc_hir::attrs::{EiiDecl, EiiImpl, EiiImplResolution};
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::lang_items::LangItem;
use rustc_hir::{AmbigArg, ItemKind, find_attr};
use rustc_infer::infer::outlives::env::OutlivesEnvironment;
use rustc_infer::infer::{self, InferCtxt, SubregionOrigin, TyCtxtInferExt};
use rustc_infer::traits::PredicateObligations;
use rustc_lint_defs::builtin::SHADOWING_SUPERTRAIT_ITEMS;
use rustc_macros::Diagnostic;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::traits::solve::NoSolution;
use rustc_middle::ty::trait_def::TraitSpecializationKind;
use rustc_middle::ty::{
self, GenericArgKind, GenericArgs, GenericParamDefKind, Ty, TyCtxt, TypeFlags, TypeFoldable,
TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, TypingMode, Unnormalized,
Upcast,
};
use rustc_middle::{bug, span_bug};
use rustc_session::errors::feature_err;
use rustc_span::{DUMMY_SP, Span, sym};
use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
use rustc_trait_selection::regions::{InferCtxtRegionExt, OutlivesEnvironmentBuildExt};
use rustc_trait_selection::traits::misc::{
ConstParamTyImplementationError, type_allowed_to_implement_const_param_ty,
};
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
use rustc_trait_selection::traits::{
self, FulfillmentError, Obligation, ObligationCause, ObligationCauseCode, ObligationCtxt,
WellFormedLoc,
};
use tracing::{debug, instrument};
use super::compare_eii::{compare_eii_function_types, compare_eii_statics};
use crate::autoderef::Autoderef;
use crate::constrained_generic_params::{Parameter, identify_constrained_generic_params};
use crate::diagnostics;
use crate::diagnostics::InvalidReceiverTyHint;
pub(super) struct WfCheckingCtxt<'a, 'tcx> {
pub(super) ocx: ObligationCtxt<'a, 'tcx, FulfillmentError<'tcx>>,
body_def_id: LocalDefId,
param_env: ty::ParamEnv<'tcx>,
}
impl<'a, 'tcx> Deref for WfCheckingCtxt<'a, 'tcx> {
type Target = ObligationCtxt<'a, 'tcx, FulfillmentError<'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: Unnormalized<'tcx, T>,
) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
self.ocx.normalize(
&ObligationCause::new(span, self.body_def_id, ObligationCauseCode::WellFormed(loc)),
self.param_env,
value,
)
}
/// Convenience function to *deeply* normalize during wfcheck. In the old solver,
/// this just dispatches to [`WfCheckingCtxt::normalize`], but in the new solver
/// this calls `deeply_normalize` and reports errors if they are encountered.
///
/// This function should be called in favor of `normalize` in cases where we will
/// then check the well-formedness of the type, since we only use the normalized
/// signature types for implied bounds when checking regions.
// FIXME(-Znext-solver): This should be removed when we compute implied outlives
// bounds using the unnormalized signature of the function we're checking.
pub(super) fn deeply_normalize<T>(
&self,
span: Span,
loc: Option<WellFormedLoc>,
value: Unnormalized<'tcx, T>,
) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
if self.infcx.next_trait_solver() {
match self.ocx.deeply_normalize(
&ObligationCause::new(span, self.body_def_id, ObligationCauseCode::WellFormed(loc)),
self.param_env,
value.clone(),
) {
Ok(value) => value,
Err(errors) => {
self.infcx.err_ctxt().report_fulfillment_errors(errors);
value.skip_norm_wip()
}
}
} else {
self.normalize(span, loc, value)
}
}
pub(super) fn register_wf_obligation(
&self,
span: Span,
loc: Option<WellFormedLoc>,
term: ty::Term<'tcx>,
) {
let cause = traits::ObligationCause::new(
span,
self.body_def_id,
ObligationCauseCode::WellFormed(loc),
);
self.ocx.register_obligation(Obligation::new(
self.tcx(),
cause,
self.param_env,
ty::ClauseKind::WellFormed(term),
));
}
pub(super) fn unnormalized_obligations(
&self,
span: Span,
ty: Ty<'tcx>,
) -> Option<PredicateObligations<'tcx>> {
traits::wf::unnormalized_obligations(
self.ocx.infcx,
self.param_env,
ty.into(),
span,
self.body_def_id,
)
}
}
pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
tcx: TyCtxt<'tcx>,
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(TypingMode::non_body_analysis());
let ocx = ObligationCtxt::new_with_diagnostics(infcx);
let mut wfcx = WfCheckingCtxt { ocx, body_def_id, param_env };
// As of now, bounds are only checked on lazy type aliases, they're ignored for most type
// aliases. So, only check for false global bounds if we're not ignoring bounds altogether.
let ignore_bounds =
tcx.def_kind(body_def_id) == DefKind::TyAlias && !tcx.type_alias_is_lazy(body_def_id);
if !ignore_bounds && !tcx.features().trivial_bounds() {
wfcx.check_false_global_bounds()
}
f(&mut wfcx)?;
let errors = wfcx.evaluate_obligations_error_on_ambiguity();
if !errors.is_empty() {
return Err(infcx.err_ctxt().report_fulfillment_errors(errors));
}
let assumed_wf_types = wfcx.ocx.assumed_wf_types_and_report_errors(param_env, body_def_id)?;
debug!(?assumed_wf_types);
let infcx_compat = infcx.fork();
// We specifically want to *disable* the implied bounds hack, first,
// so we can detect when failures are due to bevy's implied bounds.
let outlives_env = OutlivesEnvironment::new_with_implied_bounds_compat(
&infcx,
body_def_id,
param_env,
assumed_wf_types.iter().copied(),
true,
);
lint_redundant_lifetimes(tcx, body_def_id, &outlives_env);
let errors = infcx.resolve_regions_with_outlives_env(&outlives_env, tcx.def_span(body_def_id));
if errors.is_empty() {
return Ok(());
}
let outlives_env = OutlivesEnvironment::new_with_implied_bounds_compat(
&infcx_compat,
body_def_id,
param_env,
assumed_wf_types,
// Don't *disable* the implied bounds hack; though this will only apply
// the implied bounds hack if this contains `bevy_ecs`'s `ParamSet` type.
false,
);
let errors_compat =
infcx_compat.resolve_regions_with_outlives_env(&outlives_env, tcx.def_span(body_def_id));
if errors_compat.is_empty() {
// FIXME: Once we fix bevy, this would be the place to insert a warning
// to upgrade bevy.
Ok(())
} else {
Err(infcx_compat.err_ctxt().report_region_errors(body_def_id, &errors_compat))
}
}
pub(super) fn check_well_formed(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
) -> Result<(), ErrorGuaranteed> {
let mut res = crate::check::check::check_item_type(tcx, def_id);
for param in &tcx.generics_of(def_id).own_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 StaticRef<T> { x: &'static T }
/// ```
///
/// because the type did not declare that `T: 'static`.
///
/// 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")]
pub(super) 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)
);
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(ref impl_) => {
crate::impl_wf_check::check_impl_wf(tcx, def_id, impl_.of_trait.is_some())?;
let mut res = Ok(());
if let Some(of_trait) = impl_.of_trait {
let header = tcx.impl_trait_header(def_id);
let is_auto = tcx.trait_is_auto(header.trait_ref.skip_binder().def_id);
if let (hir::Defaultness::Default { .. }, true) = (of_trait.defaultness, is_auto) {
let sp = of_trait.trait_ref.path.span;
res = Err(tcx
.dcx()
.struct_span_err(sp, "impls of auto traits cannot be default")
.with_span_labels(of_trait.defaultness_span, "default because of this")
.with_span_label(sp, "auto trait")
.emit());
}
match header.polarity {
ty::ImplPolarity::Positive => {
res = res.and(check_impl(tcx, item, impl_));
}
ty::ImplPolarity::Negative => {
let ast::ImplPolarity::Negative(span) = of_trait.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 { .. } = of_trait.defaultness {
let mut spans = vec![span];
spans.extend(of_trait.defaultness_span);
res = Err(struct_span_code_err!(
tcx.dcx(),
spans,
E0750,
"negative impls cannot be default impls"
)
.emit());
}
}
ty::ImplPolarity::Reservation => {
// FIXME: what amount of WF checking do we need for reservation impls?
}
}
} else {
res = res.and(check_impl(tcx, item, impl_));
}
res
}
hir::ItemKind::Fn { sig, .. } => check_item_fn(tcx, def_id, sig.decl),
// Note: do not add new entries to this match. Instead add all new logic in `check_item_type`
_ => span_bug!(item.span, "should have been handled by the type based wf check: {item:?}"),
}
}
pub(super) fn check_foreign_item<'tcx>(
tcx: TyCtxt<'tcx>,
item: &'tcx hir::ForeignItem<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let def_id = item.owner_id.def_id;
debug!(
?item.owner_id,
item.name = ? tcx.def_path_str(def_id)
);
match item.kind {
hir::ForeignItemKind::Fn(sig, ..) => check_item_fn(tcx, def_id, sig.decl),
hir::ForeignItemKind::Static(..) | hir::ForeignItemKind::Type => Ok(()),
}
}
pub(crate) fn check_trait_item<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: LocalDefId,
) -> Result<(), ErrorGuaranteed> {
// Check that an item definition in a subtrait is shadowing a supertrait item.
lint_item_shadowing_supertrait_item(tcx, def_id);
let mut res = Ok(());
if tcx.def_kind(def_id) == DefKind::AssocFn {
for &assoc_ty_def_id in
tcx.associated_types_for_impl_traits_in_associated_fn(def_id.to_def_id())
{
res = res.and(check_associated_item(tcx, assoc_ty_def_id.expect_local()));
}
}
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>;
/// }
/// ```
pub(crate) 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 = FxIndexMap::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.is_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.is_own_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<FxIndexSet<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().skip_norm_wip(),
);
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)
.iter_identity_copied()
.map(Unnormalized::skip_norm_wip)
.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 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();
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<&FxIndexSet<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)
}
/// 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<FxIndexSet<ty::Clause<'tcx>>> {
// The bounds we that we would require from `to_check`
let mut bounds = FxIndexSet::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.kind() {
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 { 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))
.upcast(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.kind(), 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 { 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 { 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,
))
.upcast(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_type_outlives_constraint_inner(infer::TypeOutlivesConstraint {
sub_region: region,
sup_type: ty,
origin: SubregionOrigin::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(
SubregionOrigin::RelateRegionParamBound(DUMMY_SP, None),
region_b,
region_a,
ty::VisibleForLeakCheck::Unreachable,
);
})
}
/// 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(TypingMode::non_body_analysis());
add_constraints(&infcx);
let errors = infcx.resolve_regions(id, param_env, wf_tys.iter().copied());
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: FxIndexSet<(ty::Region<'tcx>, usize)>,
// Which params appears and which parameter index its instantiated with
types: FxIndexSet<(Ty<'tcx>, usize)>,
}
impl<'tcx> GATArgsCollector<'tcx> {
fn visit<T: TypeFoldable<TyCtxt<'tcx>>>(
gat: DefId,
t: T,
) -> (FxIndexSet<(ty::Region<'tcx>, usize)>, FxIndexSet<(Ty<'tcx>, usize)>) {
let mut visitor =
GATArgsCollector { gat, regions: FxIndexSet::default(), types: FxIndexSet::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::AliasTy { kind: ty::Projection { def_id }, args, .. })
if def_id == self.gat =>
{
for (idx, arg) in args.iter().enumerate() {
match arg.kind() {
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 lint_item_shadowing_supertrait_item<'tcx>(tcx: TyCtxt<'tcx>, trait_item_def_id: LocalDefId) {
let item_name = tcx.item_name(trait_item_def_id.to_def_id());
let trait_def_id = tcx.local_parent(trait_item_def_id);
let shadowed: Vec<_> = traits::supertrait_def_ids(tcx, trait_def_id.to_def_id())
.skip(1)
.flat_map(|supertrait_def_id| {
tcx.associated_items(supertrait_def_id).filter_by_name_unhygienic(item_name)
})
.collect();
if !shadowed.is_empty() {
let shadowee = if let [shadowed] = shadowed[..] {
diagnostics::SupertraitItemShadowee::Labeled {
span: tcx.def_span(shadowed.def_id),
supertrait: tcx.item_name(shadowed.trait_container(tcx).unwrap()),
}
} else {
let (traits, spans): (Vec<_>, Vec<_>) = shadowed
.iter()
.map(|item| {
(tcx.item_name(item.trait_container(tcx).unwrap()), tcx.def_span(item.def_id))
})
.unzip();
diagnostics::SupertraitItemShadowee::Several {
traits: traits.into(),
spans: spans.into(),
}
};
tcx.emit_node_span_lint(
SHADOWING_SUPERTRAIT_ITEMS,
tcx.local_def_id_to_hir_id(trait_item_def_id),
tcx.def_span(trait_item_def_id),
diagnostics::SupertraitItemShadowing {
item: item_name,
subtrait: tcx.item_name(trait_def_id.to_def_id()),
shadowee,
},
);
}
}
fn check_param_wf(tcx: TyCtxt<'_>, param: &ty::GenericParamDef) -> Result<(), ErrorGuaranteed> {
match param.kind {
// We currently only check wf of const params here.
ty::GenericParamDefKind::Lifetime | ty::GenericParamDefKind::Type { .. } => Ok(()),
// Const parameters are well formed if their type is structural match.
ty::GenericParamDefKind::Const { .. } => {
let ty = tcx.type_of(param.def_id).instantiate_identity().skip_norm_wip();
let span = tcx.def_span(param.def_id);
let def_id = param.def_id.expect_local();
if tcx.features().const_param_ty_unchecked() {
enter_wf_checking_ctxt(tcx, tcx.local_parent(def_id), |wfcx| {
wfcx.register_wf_obligation(span, None, ty.into());
Ok(())
})
} else if tcx.features().adt_const_params() || tcx.features().min_adt_const_params() {
enter_wf_checking_ctxt(tcx, tcx.local_parent(def_id), |wfcx| {
wfcx.register_bound(
ObligationCause::new(span, def_id, ObligationCauseCode::ConstParam(ty)),
wfcx.param_env,
ty,
tcx.require_lang_item(LangItem::ConstParamTy, span),
);
Ok(())
})
} else {
let span = || {
let hir::GenericParamKind::Const { ty: &hir::Ty { span, .. }, .. } =
tcx.hir_node_by_def_id(def_id).expect_generic_param().kind
else {
bug!()
};
span
};
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(
span(),
"using function pointers as const generic parameters is forbidden",
),
ty::RawPtr(_, _) => tcx.dcx().struct_span_err(
span(),
"using raw pointers as const generic parameters is forbidden",
),
_ => {
// Avoid showing "{type error}" to users. See #118179.
ty.error_reported()?;
tcx.dcx().struct_span_err(
span(),
format!(
"`{ty}` is forbidden as the type of a const generic parameter",
),
)
}
};
diag.note("the only supported types are integers, `bool`, and `char`");
let cause = ObligationCause::misc(span(), def_id);
let adt_const_params_feature_string =
" more complex and user defined types".to_string();
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
| ConstParamTyImplementationError::NonExhaustive(..)
| ConstParamTyImplementationError::InvalidInnerTyOfBuiltinTy(..),
) => None,
Err(ConstParamTyImplementationError::UnsizedConstParamsFeatureRequired) => {
Some(vec![
(adt_const_params_feature_string, sym::min_adt_const_params),
(
" references to implement the `ConstParamTy` trait".into(),
sym::unsized_const_params,
),
])
}
// 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::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).then_some(vec![(
adt_const_params_feature_string,
sym::min_adt_const_params,
)])
}
// Implements `ConstParamTy`, suggest adding the feature to enable.
Ok(..) => {
Some(vec![(adt_const_params_feature_string, sym::min_adt_const_params)])
}
};
if let Some(features) = may_suggest_feature {
tcx.disabled_nightly_features(&mut diag, features);
}
Err(diag.emit())
}
}
}
}
#[instrument(level = "debug", skip(tcx))]
pub(crate) fn check_associated_item(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
) -> Result<(), ErrorGuaranteed> {
let loc = Some(WellFormedLoc::Ty(def_id));
enter_wf_checking_ctxt(tcx, def_id, |wfcx| {
let item = tcx.associated_item(def_id);
// Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
// other `Foo` impls are incoherent.
tcx.ensure_result().coherent_trait(tcx.parent(item.trait_item_or_self()?))?;
let self_ty = match item.container {
ty::AssocContainer::Trait => tcx.types.self_param,
ty::AssocContainer::InherentImpl | ty::AssocContainer::TraitImpl(_) => {
tcx.type_of(item.container_id(tcx)).instantiate_identity().skip_norm_wip()
}
};
let span = tcx.def_span(def_id);
match item.kind {
ty::AssocKind::Const { .. } => {
let ty = tcx.type_of(def_id).instantiate_identity();
let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_id)), ty);
wfcx.register_wf_obligation(span, loc, ty.into());
let has_value = item.defaultness(tcx).has_value();
if tcx.is_type_const(def_id) {
check_type_const(wfcx, def_id, ty, has_value)?;
}
if has_value {
let code = ObligationCauseCode::SizedConstOrStatic;
wfcx.register_bound(
ObligationCause::new(span, def_id, code),
wfcx.param_env,
ty,
tcx.require_lang_item(LangItem::Sized, span),
);
}
Ok(())
}
ty::AssocKind::Fn { .. } => {
let sig = tcx.fn_sig(def_id).instantiate_identity().skip_norm_wip();
let hir_sig =
tcx.hir_node_by_def_id(def_id).fn_sig().expect("bad signature for method");
check_fn_or_method(wfcx, sig, hir_sig.decl, def_id);
check_method_receiver(wfcx, hir_sig, item, self_ty)
}
ty::AssocKind::Type { .. } => {
if let ty::AssocContainer::Trait = item.container {
check_associated_type_bounds(wfcx, item, span)
}
if item.defaultness(tcx).has_value() {
let ty = tcx.type_of(def_id).instantiate_identity();
let ty = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_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.
pub(crate) fn check_type_defn<'tcx>(
tcx: TyCtxt<'tcx>,
item: LocalDefId,
all_sized: bool,
) -> Result<(), ErrorGuaranteed> {
tcx.ensure_ok().check_representability(item);
let adt_def = tcx.adt_def(item);
enter_wf_checking_ctxt(tcx, item, |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 {
if let Some(def_id) = field.value
&& let Some(_ty) = tcx.type_of(def_id).no_bound_vars()
{
// FIXME(generic_const_exprs, default_field_values): this is a hack and needs to
// be refactored to check the instantiate-ability of the code better.
if let Some(def_id) = def_id.as_local()
&& let DefKind::AnonConst = tcx.def_kind(def_id)
&& let hir::Node::AnonConst(anon) = tcx.hir_node_by_def_id(def_id)
&& let expr = &tcx.hir_body(anon.body).value
&& let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
&& let Res::Def(DefKind::ConstParam, _def_id) = path.res
{
// Do not evaluate bare `const` params, as those would ICE and are only
// usable if `#![feature(generic_const_exprs)]` is enabled.
} else {
// Evaluate the constant proactively, to emit an error if the constant has
// an unconditional error. We only do so if the const has no type params.
let _ = tcx.const_eval_poly(def_id);
}
}
let field_id = field.did.expect_local();
let span = tcx.ty_span(field_id);
let ty = wfcx.deeply_normalize(
span,
None,
tcx.type_of(field.did).instantiate_identity(),
);
wfcx.register_wf_obligation(span, Some(WellFormedLoc::Ty(field_id)), ty.into());
if matches!(ty.kind(), ty::Adt(def, _) if def.repr().scalable())
&& !matches!(adt_def.repr().scalable, Some(ScalableElt::Container))
{
// Scalable vectors can only be fields of structs if the type has a
// `rustc_scalable_vector` attribute w/out specifying an element count
tcx.dcx().span_err(
span,
format!(
"scalable vectors cannot be fields of a {}",
adt_def.variant_descr()
),
);
}
}
// 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().skip_norm_wip();
let ty = tcx.erase_and_anonymize_regions(ty);
assert!(!ty.has_infer());
ty.needs_drop(tcx, wfcx.infcx.typing_env(wfcx.param_env))
}
};
// 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 span = tcx.ty_span(field.did.expect_local());
let ty = wfcx.normalize(span, None, tcx.type_of(field.did).instantiate_identity());
wfcx.register_bound(
traits::ObligationCause::new(
span,
wfcx.body_def_id,
ObligationCauseCode::FieldSized {
adt_kind: adt_def.adt_kind(),
span,
last,
},
),
wfcx.param_env,
ty,
tcx.require_lang_item(LangItem::Sized, span),
);
}
// Explicit `enum` discriminant values must const-evaluate successfully.
if let ty::VariantDiscr::Explicit(discr_def_id) = variant.discr {
match tcx.const_eval_poly(discr_def_id) {
Ok(_) => {}
Err(ErrorHandled::Reported(..)) => {}
Err(ErrorHandled::TooGeneric(sp)) => {
span_bug!(sp, "enum variant discr was too generic to eval")
}
}
}
}
check_where_clauses(wfcx, item);
Ok(())
})
}
#[instrument(skip(tcx))]
pub(crate) fn check_trait(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(), ErrorGuaranteed> {
if tcx.is_lang_item(def_id.into(), LangItem::PointeeSized) {
// `PointeeSized` is removed during lowering.
return Ok(());
}
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, def_id, |wfcx| {
check_where_clauses(wfcx, def_id);
Ok(())
});
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.iter_identity_copied().map(Unnormalized::skip_norm_wip).flat_map(
|(bound, bound_span)| {
traits::wf::clause_obligations(
wfcx.infcx,
wfcx.param_env,
wfcx.body_def_id,
bound,
bound_span,
)
},
);
wfcx.register_obligations(wf_obligations);
}
fn check_item_fn(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
decl: &hir::FnDecl<'_>,
) -> Result<(), ErrorGuaranteed> {
enter_wf_checking_ctxt(tcx, def_id, |wfcx| {
check_eiis_fn(tcx, def_id);
let sig = tcx.fn_sig(def_id).instantiate_identity().skip_norm_wip();
check_fn_or_method(wfcx, sig, decl, def_id);
Ok(())
})
}
fn check_eiis_fn(tcx: TyCtxt<'_>, def_id: LocalDefId) {
// does the function have an EiiImpl attribute? that contains the defid of a *macro*
// that was used to mark the implementation. This is a two step process.
for EiiImpl { resolution, span, .. } in
find_attr!(tcx, def_id, EiiImpls(impls) => impls).into_iter().flatten()
{
let (foreign_item, name) = match resolution {
EiiImplResolution::Macro(def_id) => {
// we expect this macro to have the `EiiMacroFor` attribute, that points to a function
// signature that we'd like to compare the function we're currently checking with
if let Some(foreign_item) =
find_attr!(tcx, *def_id, EiiDeclaration(EiiDecl {foreign_item: t, ..}) => *t)
{
(foreign_item, tcx.item_name(*def_id))
} else {
tcx.dcx().span_delayed_bug(*span, "resolved to something that's not an EII");
continue;
}
}
EiiImplResolution::Known(decl) => (decl.foreign_item, decl.name.name),
EiiImplResolution::Error(_eg) => continue,
};
let _ = compare_eii_function_types(tcx, def_id, foreign_item, name, *span);
}
}
fn check_eiis_static<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId, ty: Ty<'tcx>) {
// does the function have an EiiImpl attribute? that contains the defid of a *macro*
// that was used to mark the implementation. This is a two step process.
for EiiImpl { resolution, span, .. } in
find_attr!(tcx, def_id, EiiImpls(impls) => impls).into_iter().flatten()
{
let (foreign_item, name) = match resolution {
EiiImplResolution::Macro(def_id) => {
// we expect this macro to have the `EiiMacroFor` attribute, that points to a function
// signature that we'd like to compare the function we're currently checking with
if let Some(foreign_item) =
find_attr!(tcx, *def_id, EiiDeclaration(EiiDecl {foreign_item: t, ..}) => *t)
{
(foreign_item, tcx.item_name(*def_id))
} else {
tcx.dcx().span_delayed_bug(*span, "resolved to something that's not an EII");
continue;
}
}
EiiImplResolution::Known(decl) => (decl.foreign_item, decl.name.name),
EiiImplResolution::Error(_eg) => continue,
};
let _ = compare_eii_statics(tcx, def_id, ty, foreign_item, name, *span);
}
}
#[instrument(level = "debug", skip(tcx))]
pub(crate) fn check_static_item<'tcx>(
tcx: TyCtxt<'tcx>,
item_id: LocalDefId,
ty: Ty<'tcx>,
should_check_for_sync: bool,
) -> Result<(), ErrorGuaranteed> {
enter_wf_checking_ctxt(tcx, item_id, |wfcx| {
if should_check_for_sync {
check_eiis_static(tcx, item_id, ty);
}
let span = tcx.ty_span(item_id);
let loc = Some(WellFormedLoc::Ty(item_id));
let item_ty = wfcx.deeply_normalize(span, loc, Unnormalized::new_wip(ty));
let is_foreign_item = tcx.is_foreign_item(item_id);
let is_structurally_foreign_item = || {
let tail = tcx.struct_tail_raw(
item_ty,
&ObligationCause::dummy(),
|ty| wfcx.deeply_normalize(span, loc, ty),
|| {},
);
matches!(tail.kind(), ty::Foreign(_))
};
let forbid_unsized = !(is_foreign_item && is_structurally_foreign_item());
wfcx.register_wf_obligation(span, Some(WellFormedLoc::Ty(item_id)), item_ty.into());
if forbid_unsized {
let span = tcx.def_span(item_id);
wfcx.register_bound(
traits::ObligationCause::new(
span,
wfcx.body_def_id,
ObligationCauseCode::SizedConstOrStatic,
),
wfcx.param_env,
item_ty,
tcx.require_lang_item(LangItem::Sized, span),
);
}
// Ensure that the end result is `Sync` in a non-thread local `static`.
let should_check_for_sync = should_check_for_sync
&& !is_foreign_item
&& tcx.static_mutability(item_id.to_def_id()) == Some(hir::Mutability::Not)
&& !tcx.is_thread_local_static(item_id.to_def_id());
if should_check_for_sync {
wfcx.register_bound(
traits::ObligationCause::new(
span,
wfcx.body_def_id,
ObligationCauseCode::SharedStatic,
),
wfcx.param_env,
item_ty,
tcx.require_lang_item(LangItem::Sync, span),
);
}
Ok(())
})
}
#[instrument(level = "debug", skip(wfcx))]
pub(super) fn check_type_const<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
def_id: LocalDefId,
item_ty: Ty<'tcx>,
has_value: bool,
) -> Result<(), ErrorGuaranteed> {
let tcx = wfcx.tcx();
let span = tcx.def_span(def_id);
if !tcx.features().const_param_ty_unchecked() {
wfcx.register_bound(
ObligationCause::new(span, def_id, ObligationCauseCode::ConstParam(item_ty)),
wfcx.param_env,
item_ty,
tcx.require_lang_item(LangItem::ConstParamTy, span),
);
}
if has_value {
let raw_ct = tcx.const_of_item(def_id).instantiate_identity();
let norm_ct = wfcx.deeply_normalize(span, Some(WellFormedLoc::Ty(def_id)), raw_ct);
wfcx.register_wf_obligation(span, Some(WellFormedLoc::Ty(def_id)), norm_ct.into());
wfcx.register_obligation(Obligation::new(
tcx,
ObligationCause::new(span, def_id, ObligationCauseCode::WellFormed(None)),
wfcx.param_env,
ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(norm_ct, item_ty)),
));
}
Ok(())
}
#[instrument(level = "debug", skip(tcx, impl_))]
fn check_impl<'tcx>(
tcx: TyCtxt<'tcx>,
item: &'tcx hir::Item<'tcx>,
impl_: &hir::Impl<'_>,
) -> Result<(), ErrorGuaranteed> {
enter_wf_checking_ctxt(tcx, item.owner_id.def_id, |wfcx| {
match impl_.of_trait {
Some(of_trait) => {
// `#[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).instantiate_identity();
// Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in
// case other `Foo` impls are incoherent.
tcx.ensure_result().coherent_trait(trait_ref.skip_normalization().def_id)?;
let trait_span = of_trait.trait_ref.path.span;
let trait_ref = wfcx.deeply_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.as_trait_clause()
&& pred.skip_binder().self_ty() == trait_ref.self_ty()
{
obligation.cause.span = impl_.self_ty.span;
}
if let Some(pred) = obligation.predicate.as_projection_clause()
&& pred.skip_binder().self_ty() == trait_ref.self_ty()
{
obligation.cause.span = impl_.self_ty.span;
}
}
// Ensure that the `[const]` where clauses of the trait hold for the impl.
if tcx.is_conditionally_const(item.owner_id.def_id) {
for (bound, _) in
tcx.const_conditions(trait_ref.def_id).instantiate(tcx, trait_ref.args)
{
let bound = wfcx.normalize(
item.span,
Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
bound,
);
wfcx.register_obligation(Obligation::new(
tcx,
ObligationCause::new(
impl_.self_ty.span,
wfcx.body_def_id,
ObligationCauseCode::WellFormed(None),
),
wfcx.param_env,
bound.to_host_effect_clause(tcx, ty::BoundConstness::Maybe),
))
}
}
debug!(?obligations);
wfcx.register_obligations(obligations);
}
None => {
let self_ty = tcx.type_of(item.owner_id).instantiate_identity().skip_norm_wip();
let self_ty = wfcx.deeply_normalize(
item.span,
Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
Unnormalized::new_wip(self_ty),
);
wfcx.register_wf_obligation(
impl_.self_ty.span,
Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
self_ty.into(),
);
}
}
check_where_clauses(wfcx, item.owner_id.def_id);
Ok(())
})
}
/// Checks where-clauses and inline bounds that are declared on `def_id`.
#[instrument(level = "debug", skip(wfcx))]
pub(super) fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, 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);
// 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 {
if let Some(default) = param
.default_value(tcx)
.map(ty::EarlyBinder::instantiate_identity)
.map(Unnormalized::skip_norm_wip)
{
// 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.
// FIXME(generic_const_exprs): This is incorrect when dealing with unused const params.
// E.g: `struct Foo<const N: usize, const M: usize = { 1 - 2 }>;`. Here, we should
// eagerly error but we don't as we have `ConstKind::Alias(.., [N, M])`.
if !default.has_param() {
wfcx.register_wf_obligation(
tcx.def_span(param.def_id),
matches!(param.kind, GenericParamDefKind::Type { .. })
.then(|| WellFormedLoc::Ty(param.def_id.expect_local())),
default.as_term().unwrap(),
);
} else {
// If we've got a generic const parameter we still want to check its
// type is correct in case both it and the param type are fully concrete.
let GenericArgKind::Const(ct) = default.kind() else {
continue;
};
let ct_ty = match ct.kind() {
ty::ConstKind::Infer(_)
| ty::ConstKind::Placeholder(_)
| ty::ConstKind::Bound(_, _) => unreachable!(),
ty::ConstKind::Error(_) | ty::ConstKind::Expr(_) => continue,
ty::ConstKind::Value(cv) => cv.ty,
ty::ConstKind::Alias(_, alias_const) => {
alias_const.type_of(infcx.tcx).skip_norm_wip()
}
ty::ConstKind::Param(param_ct) => {
param_ct.find_const_ty_from_env(wfcx.param_env)
}
};
let param_ty = tcx.type_of(param.def_id).instantiate_identity().skip_norm_wip();
if !ct_ty.has_param() && !param_ty.has_param() {
let cause = traits::ObligationCause::new(
tcx.def_span(param.def_id),
wfcx.body_def_id,
ObligationCauseCode::WellFormed(None),
);
wfcx.register_obligation(Obligation::new(
tcx,
cause,
wfcx.param_env,
ty::ClauseKind::ConstArgHasType(ct, param_ty),
));
}
}
}
}
// 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, _| {
if param.index >= generics.parent_count as u32
// If the param has a default, ...
&& let Some(default) = param.default_value(tcx).map(ty::EarlyBinder::instantiate_identity).map(Unnormalized::skip_norm_wip)
// ... and it's not a dependent default, ...
&& !default.has_param()
{
// ... then instantiate it with the default.
return default;
}
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::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(tcx, pred).instantiate(tcx, args);
// Don't check non-defaulted params, dependent defaults (including lifetimes)
// or preds with multiple params.
if instantiated_pred.skip_normalization().has_non_region_param()
|| param_count.params.len() > 1
|| has_region
{
None
} else if predicates
.predicates
.iter()
.any(|&(p, _)| Unnormalized::new_wip(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(), sp),
);
Obligation::new(tcx, cause, wfcx.param_env, pred)
});
let predicates = predicates.instantiate_identity(tcx);
let assoc_const_obligations: Vec<_> = predicates
.predicates
.iter()
.copied()
.zip(predicates.spans.iter().copied())
.filter_map(|(clause, sp)| {
let clause = clause.skip_norm_wip();
let proj = clause.as_projection_clause()?;
let pred_binder = proj
.map_bound(|pred| {
pred.term.as_const().map(|ct| {
let assoc_const_ty =
pred.projection_term.expect_ct().type_of(tcx).skip_norm_wip();
ty::ClauseKind::ConstArgHasType(ct, assoc_const_ty)
})
})
.transpose();
pred_binder.map(|pred_binder| {
let cause = traits::ObligationCause::new(
sp,
wfcx.body_def_id,
ObligationCauseCode::WhereClause(def_id.to_def_id(), sp),
);
Obligation::new(tcx, cause, wfcx.param_env, pred_binder)
})
})
.collect();
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.skip_norm_wip(),
sp,
)
});
let obligations: Vec<_> =
wf_obligations.chain(default_obligations).chain(assoc_const_obligations).collect();
wfcx.register_obligations(obligations);
}
#[instrument(level = "debug", skip(wfcx, hir_decl))]
fn check_fn_or_method<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
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.deeply_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,
}),
Unnormalized::new_wip(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 }),
ty.into(),
);
}
check_where_clauses(wfcx, def_id);
if sig.abi() == ExternAbi::RustCall {
let span = tcx.def_span(def_id);
let has_implicit_self = hir_decl.implicit_self().has_implicit_self();
let mut inputs = sig.inputs().iter().skip(if has_implicit_self { 1 } else { 0 });
// FIXME(splat): support the rest of closure splatting, or replace this code with an error
if let Some(mut splatted_arg_index) = sig.splatted() {
let mut inputs_count = sig.inputs().len();
if has_implicit_self {
splatted_arg_index = splatted_arg_index.strict_sub(1);
inputs_count = inputs_count.strict_sub(1);
}
debug!(?splatted_arg_index, ?inputs_count, ?has_implicit_self, ?sig);
sig = sig.set_splatted(Some(splatted_arg_index), inputs_count).unwrap();
}
// 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, span),
);
wfcx.register_bound(
ObligationCause::new(span, wfcx.body_def_id, ObligationCauseCode::RustCall),
wfcx.param_env,
*ty,
tcx.require_lang_item(hir::LangItem::Sized, 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",
);
}
}
// If the function has a body, additionally require that the return type is sized.
if let Some(body) = tcx.hir_maybe_body_owned_by(def_id) {
let span = match hir_decl.output {
hir::FnRetTy::Return(ty) => ty.span,
hir::FnRetTy::DefaultReturn(_) => body.value.span,
};
wfcx.register_bound(
ObligationCause::new(span, def_id, ObligationCauseCode::SizedReturnType),
wfcx.param_env,
sig.output(),
tcx.require_lang_item(LangItem::Sized, span),
);
}
}
/// The `arbitrary_self_types_pointers` feature implies `arbitrary_self_types`.
#[derive(Clone, Copy, PartialEq)]
enum ArbitrarySelfTypesLevel {
Basic, // just arbitrary_self_types
WithPointers, // both arbitrary_self_types and arbitrary_self_types_pointers
}
#[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.is_method() {
return Ok(());
}
let span = fn_sig.decl.inputs[0].span;
let loc = Some(WellFormedLoc::Param { function: method.def_id.expect_local(), param_idx: 0 });
let sig = tcx.fn_sig(method.def_id).instantiate_identity().skip_norm_wip();
let sig = tcx.liberate_late_bound_regions(method.def_id, sig);
let sig = wfcx.normalize(DUMMY_SP, loc, Unnormalized::new_wip(sig));
debug!("check_method_receiver: sig={:?}", sig);
let self_ty = wfcx.normalize(DUMMY_SP, loc, Unnormalized::new_wip(self_ty));
let receiver_ty = sig.inputs()[0];
let receiver_ty = wfcx.normalize(DUMMY_SP, loc, Unnormalized::new_wip(receiver_ty));
// If the receiver already has errors reported, consider it valid to avoid
// unnecessary errors (#58712).
receiver_ty.error_reported()?;
let arbitrary_self_types_level = if tcx.features().arbitrary_self_types_pointers() {
Some(ArbitrarySelfTypesLevel::WithPointers)
} else if tcx.features().arbitrary_self_types() {
Some(ArbitrarySelfTypesLevel::Basic)
} else {
None
};
let generics = tcx.generics_of(method.def_id);
let receiver_validity =
receiver_is_valid(wfcx, span, receiver_ty, self_ty, arbitrary_self_types_level, generics);
if let Err(receiver_validity_err) = receiver_validity {
return Err(match arbitrary_self_types_level {
// Wherever possible, emit a message advising folks that the features
// `arbitrary_self_types` or `arbitrary_self_types_pointers` might
// have helped.
None if receiver_is_valid(
wfcx,
span,
receiver_ty,
self_ty,
Some(ArbitrarySelfTypesLevel::Basic),
generics,
)
.is_ok() =>
{
// 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(msg!("consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`"))
.emit()
}
None | Some(ArbitrarySelfTypesLevel::Basic)
if receiver_is_valid(
wfcx,
span,
receiver_ty,
self_ty,
Some(ArbitrarySelfTypesLevel::WithPointers),
generics,
)
.is_ok() =>
{
// Report error; would have worked with `arbitrary_self_types_pointers`.
feature_err(
&tcx.sess,
sym::arbitrary_self_types_pointers,
span,
format!(
"`{receiver_ty}` cannot be used as the type of `self` without \
the `arbitrary_self_types_pointers` feature",
),
)
.with_help(msg!("consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`"))
.emit()
}
_ =>
// Report error; would not have worked with `arbitrary_self_types[_pointers]`.
{
match receiver_validity_err {
ReceiverValidityError::DoesNotDeref if arbitrary_self_types_level.is_some() => {
let hint = match receiver_ty
.builtin_deref(false)
.unwrap_or(receiver_ty)
.ty_adt_def()
.and_then(|adt_def| tcx.get_diagnostic_name(adt_def.did()))
{
Some(sym::RcWeak | sym::ArcWeak) => Some(InvalidReceiverTyHint::Weak),
Some(sym::NonNull) => Some(InvalidReceiverTyHint::NonNull),
_ => None,
};
tcx.dcx().emit_err(diagnostics::InvalidReceiverTy {
span,
receiver_ty,
hint,
})
}
ReceiverValidityError::DoesNotDeref => {
tcx.dcx().emit_err(diagnostics::InvalidReceiverTyNoArbitrarySelfTypes {
span,
receiver_ty,
})
}
ReceiverValidityError::MethodGenericParamUsed => tcx
.dcx()
.emit_err(diagnostics::InvalidGenericReceiverTy { span, receiver_ty }),
}
}
});
}
Ok(())
}
/// Error cases which may be returned from `receiver_is_valid`. These error
/// cases are generated in this function as they may be unearthed as we explore
/// the `autoderef` chain, but they're converted to diagnostics in the caller.
enum ReceiverValidityError {
/// The self type does not get to the receiver type by following the
/// autoderef chain.
DoesNotDeref,
/// A type was found which is a method type parameter, and that's not allowed.
MethodGenericParamUsed,
}
/// Confirms that a type is not a type parameter referring to one of the
/// method's type params.
fn confirm_type_is_not_a_method_generic_param(
ty: Ty<'_>,
method_generics: &ty::Generics,
) -> Result<(), ReceiverValidityError> {
if let ty::Param(param) = ty.kind() {
if (param.index as usize) >= method_generics.parent_count {
return Err(ReceiverValidityError::MethodGenericParamUsed);
}
}
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 `arbitrary_self_types_pointers` is also enabled.
/// If neither feature is 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: Option<ArbitrarySelfTypesLevel>,
method_generics: &ty::Generics,
) -> Result<(), ReceiverValidityError> {
let infcx = wfcx.infcx;
let tcx = wfcx.tcx();
let cause =
ObligationCause::new(span, wfcx.body_def_id, traits::ObligationCauseCode::MethodReceiver);
// Special case `receiver == self_ty`, which doesn't necessarily require the `Receiver` lang item.
if let Ok(()) = wfcx.infcx.commit_if_ok(|_| {
let ocx = ObligationCtxt::new(wfcx.infcx);
ocx.eq(&cause, wfcx.param_env, self_ty, receiver_ty)?;
if ocx.evaluate_obligations_error_on_ambiguity().is_empty() {
Ok(())
} else {
Err(NoSolution)
}
}) {
return Ok(());
}
confirm_type_is_not_a_method_generic_param(receiver_ty, method_generics)?;
let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_def_id, span, receiver_ty);
// The `arbitrary_self_types` feature allows custom smart pointer
// types to be method receivers, as identified by following the Receiver<Target=T>
// chain.
if arbitrary_self_types_enabled.is_some() {
autoderef = autoderef.use_receiver_trait();
}
// The `arbitrary_self_types_pointers` feature allows raw pointer receivers like `self: *const Self`.
if arbitrary_self_types_enabled == Some(ArbitrarySelfTypesLevel::WithPointers) {
autoderef = autoderef.include_raw_pointers();
}
// Keep dereferencing `receiver_ty` until we get to `self_ty`.
while let Some((potential_self_ty, _)) = autoderef.next() {
debug!(
"receiver_is_valid: potential self type `{:?}` to match `{:?}`",
potential_self_ty, self_ty
);
confirm_type_is_not_a_method_generic_param(potential_self_ty, method_generics)?;
// Check if the self type unifies. If it does, then commit the result
// since it may have region side-effects.
if let Ok(()) = wfcx.infcx.commit_if_ok(|_| {
let ocx = ObligationCtxt::new(wfcx.infcx);
ocx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty)?;
if ocx.evaluate_obligations_error_on_ambiguity().is_empty() {
Ok(())
} else {
Err(NoSolution)
}
}) {
wfcx.register_obligations(autoderef.into_obligations());
return Ok(());
}
// Without `feature(arbitrary_self_types)`, we require that each step in the
// deref chain implement `LegacyReceiver`.
if arbitrary_self_types_enabled.is_none() {
let legacy_receiver_trait_def_id =
tcx.require_lang_item(LangItem::LegacyReceiver, span);
if !legacy_receiver_is_implemented(
wfcx,
legacy_receiver_trait_def_id,
cause.clone(),
potential_self_ty,
) {
// We cannot proceed.
break;
}
// Register the bound, in case it has any region side-effects.
wfcx.register_bound(
cause.clone(),
wfcx.param_env,
potential_self_ty,
legacy_receiver_trait_def_id,
);
}
}
debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
Err(ReceiverValidityError::DoesNotDeref)
}
fn legacy_receiver_is_implemented<'tcx>(
wfcx: &WfCheckingCtxt<'_, 'tcx>,
legacy_receiver_trait_def_id: DefId,
cause: ObligationCause<'tcx>,
receiver_ty: Ty<'tcx>,
) -> bool {
let tcx = wfcx.tcx();
let trait_ref = ty::TraitRef::new(tcx, legacy_receiver_trait_def_id, [receiver_ty]);
let obligation = 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 `LegacyReceiver` trait",
receiver_ty
);
false
}
}
pub(super) fn check_variances_for_type_defn<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) {
match tcx.def_kind(def_id) {
DefKind::Enum | DefKind::Struct | DefKind::Union => {
// Ok
}
kind => span_bug!(tcx.def_span(def_id), "cannot compute the variances of {kind:?}"),
}
let ty_predicates = tcx.predicates_of(def_id);
assert_eq!(ty_predicates.parent, None);
let variances = tcx.variances_of(def_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, def_id);
tcx.hir_node_by_def_id(def_id)
.generics()
.unwrap()
.predicates
.iter()
.filter_map(|predicate| match predicate.kind {
hir::WherePredicateKind::BoundPredicate(predicate) => {
match icx.lower_ty(predicate.bounded_ty).kind() {
ty::Param(data) => Some(Parameter(data.index)),
_ => None,
}
}
_ => None,
})
.collect::<FxHashSet<_>>()
});
for (index, _) in variances.iter().enumerate() {
let parameter = Parameter(index as u32);
if constrained_parameters.contains(&parameter) {
continue;
}
let node = tcx.hir_node_by_def_id(def_id);
let item = node.expect_item();
let hir_generics = node.generics().unwrap();
let hir_param = &hir_generics.params[index];
let ty_param = &tcx.generics_of(item.owner_id).own_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;
}
// Look for `ErrorGuaranteed` deeply within this type.
if let ControlFlow::Break(ErrorGuaranteed { .. }) = tcx
.type_of(def_id)
.instantiate_identity()
.skip_norm_wip()
.visit_with(&mut HasErrorDeep { tcx, seen: Default::default() })
{
continue;
}
match hir_param.name {
hir::ParamName::Error(_) => {
// Don't report a bivariance error for a lifetime that isn't
// even valid to name.
}
_ => {
let has_explicit_bounds = explicitly_bounded_params.contains(&parameter);
report_bivariance(tcx, hir_param, has_explicit_bounds, item);
}
}
}
}
/// Look for `ErrorGuaranteed` deeply within structs' (unsubstituted) fields.
struct HasErrorDeep<'tcx> {
tcx: TyCtxt<'tcx>,
seen: FxHashSet<DefId>,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for HasErrorDeep<'tcx> {
type Result = ControlFlow<ErrorGuaranteed>;
fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
match *ty.kind() {
ty::Adt(def, _) => {
if self.seen.insert(def.did()) {
for field in def.all_fields() {
self.tcx
.type_of(field.did)
.instantiate_identity()
.skip_norm_wip()
.visit_with(self)?;
}
}
}
ty::Error(guar) => return ControlFlow::Break(guar),
_ => {}
}
ty.super_visit_with(self)
}
fn visit_region(&mut self, r: ty::Region<'tcx>) -> Self::Result {
if let Err(guar) = r.error_reported() {
ControlFlow::Break(guar)
} else {
ControlFlow::Continue(())
}
}
fn visit_const(&mut self, c: ty::Const<'tcx>) -> Self::Result {
if let Err(guar) = c.error_reported() {
ControlFlow::Break(guar)
} else {
ControlFlow::Continue(())
}
}
}
fn report_bivariance<'tcx>(
tcx: TyCtxt<'tcx>,
param: &'tcx hir::GenericParam<'tcx>,
has_explicit_bounds: bool,
item: &'tcx hir::Item<'tcx>,
) -> 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() {
diagnostics::UnusedGenericParameterHelp::Adt {
param_name,
phantom_data: tcx.def_path_str(def_id),
}
} else {
diagnostics::UnusedGenericParameterHelp::AdtNoPhantomData { param_name }
}
}
item_kind => bug!("report_bivariance: unexpected item kind: {item_kind:?}"),
};
let mut usage_spans = vec![];
intravisit::walk_item(
&mut CollectUsageSpans { spans: &mut usage_spans, param_def_id: param.def_id.to_def_id() },
item,
);
if !usage_spans.is_empty() {
// First, check if the ADT/LTA is (probably) cyclical. We say probably here, since we're
// not actually looking into substitutions, just walking through fields / the "RHS".
// We don't recurse into the hidden types of opaques or anything else fancy.
let item_def_id = item.owner_id.to_def_id();
let is_probably_cyclical =
IsProbablyCyclical { tcx, item_def_id, seen: Default::default() }
.visit_def(item_def_id)
.is_break();
// If the ADT/LTA is cyclical, then if at least one usage of the type parameter or
// the `Self` alias is present in the, then it's probably a cyclical struct/ type
// alias, and we should call those parameter usages recursive rather than just saying
// they're unused...
//
// We currently report *all* of the parameter usages, since computing the exact
// subset is very involved, and the fact we're mentioning recursion at all is
// likely to guide the user in the right direction.
if is_probably_cyclical {
return tcx.dcx().emit_err(diagnostics::RecursiveGenericParameter {
spans: usage_spans,
param_span: param.span,
param_name,
param_def_kind: tcx.def_descr(param.def_id.to_def_id()),
help,
note: (),
});
}
}
let const_param_help =
matches!(param.kind, hir::GenericParamKind::Type { .. } if !has_explicit_bounds);
let mut diag = tcx.dcx().create_err(diagnostics::UnusedGenericParameter {
span: param.span,
param_name,
param_def_kind: tcx.def_descr(param.def_id.to_def_id()),
usage_spans,
help,
const_param_help,
});
diag.code(E0392);
if item.kind.recovered() {
// Silence potentially redundant error, as the item had a parse error.
diag.delay_as_bug()
} else {
diag.emit()
}
}
/// Detects cases where an ADT/LTA is trivially cyclical -- we want to detect this so
/// we only mention that its parameters are used cyclically if the ADT/LTA is truly
/// cyclical.
///
/// Notably, we don't consider substitutions here, so this may have false positives.
struct IsProbablyCyclical<'tcx> {
tcx: TyCtxt<'tcx>,
item_def_id: DefId,
seen: FxHashSet<DefId>,
}
impl<'tcx> IsProbablyCyclical<'tcx> {
fn visit_def(&mut self, def_id: DefId) -> ControlFlow<(), ()> {
match self.tcx.def_kind(def_id) {
DefKind::Struct | DefKind::Enum | DefKind::Union => {
self.tcx.adt_def(def_id).all_fields().try_for_each(|field| {
self.tcx
.type_of(field.did)
.instantiate_identity()
.skip_norm_wip()
.visit_with(self)
})
}
_ => ControlFlow::Continue(()),
}
}
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for IsProbablyCyclical<'tcx> {
type Result = ControlFlow<(), ()>;
fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<(), ()> {
if let Some(adt_def) = ty.ty_adt_def() {
if adt_def.did() == self.item_def_id {
return ControlFlow::Break(());
}
if self.seen.insert(adt_def.did()) {
self.visit_def(adt_def.did())?;
}
}
ty.super_visit_with(self)
}
}
/// Collect usages of the `param_def_id` and `Res::SelfTyAlias` in the HIR.
///
/// This is used to report places where the user has used parameters in a
/// non-variance-constraining way for better bivariance errors.
struct CollectUsageSpans<'a> {
spans: &'a mut Vec<Span>,
param_def_id: DefId,
}
impl<'tcx> Visitor<'tcx> for CollectUsageSpans<'_> {
type Result = ();
fn visit_generics(&mut self, _g: &'tcx rustc_hir::Generics<'tcx>) -> Self::Result {
// Skip the generics. We only care about fields, not where clause/param bounds.
}
fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx, AmbigArg>) -> Self::Result {
if let hir::TyKind::Path(hir::QPath::Resolved(None, qpath)) = t.kind {
if let Res::Def(DefKind::TyParam, def_id) = qpath.res
&& def_id == self.param_def_id
{
self.spans.push(t.span);
return;
} else if let Res::SelfTyAlias { .. } = qpath.res {
self.spans.push(t.span);
return;
}
}
intravisit::walk_ty(self, t);
}
}
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 = tcx.def_span(self.body_def_id);
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 {
match pred.kind().skip_binder() {
// We lower empty bounds like `Vec<dyn Copy>:` as
// `WellFormed(Vec<dyn Copy>)`, which will later get checked by
// regular WF checking
ty::ClauseKind::WellFormed(..)
// Unstable feature goals cannot be proven in an empty environment so skip them
| ty::ClauseKind::UnstableFeature(..) => continue,
_ => {}
}
// Match the existing behavior.
if pred.is_global() && !pred.has_type_flags(TypeFlags::HAS_BINDER_VARS) {
let pred = self.normalize(span, None, Unnormalized::new_wip(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 = Obligation::new(
tcx,
traits::ObligationCause::new(
span,
self.body_def_id,
ObligationCauseCode::TrivialBound,
),
empty_env,
pred,
);
self.ocx.register_obligation(obligation);
}
}
}
}
pub(super) fn check_type_wf(tcx: TyCtxt<'_>, (): ()) -> Result<(), ErrorGuaranteed> {
let items = tcx.hir_crate_items(());
let res =
items
.par_items(|item| tcx.ensure_result().check_well_formed(item.owner_id.def_id))
.and(
items.par_impl_items(|item| {
tcx.ensure_result().check_well_formed(item.owner_id.def_id)
}),
)
.and(items.par_trait_items(|item| {
tcx.ensure_result().check_well_formed(item.owner_id.def_id)
}))
.and(items.par_foreign_items(|item| {
tcx.ensure_result().check_well_formed(item.owner_id.def_id)
}))
.and(items.par_nested_bodies(|item| tcx.ensure_result().check_well_formed(item)))
.and(items.par_opaques(|item| tcx.ensure_result().check_well_formed(item)));
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 { .. } => {
if tcx.trait_impl_of_assoc(owner_id.to_def_id()).is_some() {
// 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
| DefKind::SyntheticCoroutineBody => 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 (idx, var) in tcx
.fn_sig(owner_id)
.instantiate_identity()
.skip_norm_wip()
.bound_vars()
.iter()
.enumerate()
{
let ty::BoundVariableKind::Region(kind) = var else { continue };
let kind = ty::LateParamRegionKind::from_bound(ty::BoundVar::from_usize(idx), kind);
lifetimes.push(ty::Region::new_late_param(tcx, owner_id.to_def_id(), kind));
}
}
lifetimes.retain(|candidate| candidate.is_named(tcx));
// 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)..] {
// All region parameters should have a `DefId` available as:
// - Late-bound parameters should be of the`BrNamed` variety,
// since we get these signatures straight from `hir_lowering`.
// - Early-bound parameters unconditionally have a `DefId` available.
//
// Any other regions (ReError/ReStatic/etc.) shouldn't matter, since we
// can't really suggest to remove them.
let Some(def_id) = victim.opt_param_def_id(tcx, owner_id.to_def_id()) 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(Diagnostic)]
#[diag("unnecessary lifetime parameter `{$victim}`")]
#[note("you can use the `{$candidate}` lifetime directly, in place of `{$victim}`")]
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>,
}