1 use crate::autoderef::Autoderef;
2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
6 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
7 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
9 use rustc_hir::def_id::{DefId, LocalDefId};
10 use rustc_hir::lang_items::LangItem;
11 use rustc_hir::ItemKind;
12 use rustc_infer::infer::outlives::env::{OutlivesEnvironment, RegionBoundPairs};
13 use rustc_infer::infer::outlives::obligations::TypeOutlives;
14 use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
15 use rustc_middle::mir::ConstraintCategory;
16 use rustc_middle::ty::query::Providers;
17 use rustc_middle::ty::trait_def::TraitSpecializationKind;
18 use rustc_middle::ty::{
19 self, AdtKind, DefIdTree, GenericParamDefKind, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
20 TypeVisitable, TypeVisitor,
22 use rustc_middle::ty::{GenericArgKind, InternalSubsts};
23 use rustc_session::parse::feature_err;
24 use rustc_span::symbol::{sym, Ident, Symbol};
25 use rustc_span::{Span, DUMMY_SP};
26 use rustc_target::spec::abi::Abi;
27 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
28 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
29 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
30 use rustc_trait_selection::traits::{
31 self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,
34 use std::cell::LazyCell;
35 use std::ops::{ControlFlow, Deref};
37 pub(super) struct WfCheckingCtxt<'a, 'tcx> {
38 pub(super) ocx: ObligationCtxt<'a, 'tcx>,
41 param_env: ty::ParamEnv<'tcx>,
43 impl<'a, 'tcx> Deref for WfCheckingCtxt<'a, 'tcx> {
44 type Target = ObligationCtxt<'a, 'tcx>;
45 fn deref(&self) -> &Self::Target {
50 impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
51 fn tcx(&self) -> TyCtxt<'tcx> {
55 // Convenience function to normalize during wfcheck. This performs
56 // `ObligationCtxt::normalize`, but provides a nice `ObligationCauseCode`.
57 fn normalize<T>(&self, span: Span, loc: Option<WellFormedLoc>, value: T) -> T
59 T: TypeFoldable<'tcx>,
62 &ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc)),
68 fn register_wf_obligation(
71 loc: Option<WellFormedLoc>,
72 arg: ty::GenericArg<'tcx>,
75 traits::ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc));
76 // for a type to be WF, we do not need to check if const trait predicates satisfy.
77 let param_env = self.param_env.without_const();
78 self.ocx.register_obligation(traits::Obligation::new(
82 ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)),
87 pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
90 body_def_id: LocalDefId,
93 F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>),
95 let param_env = tcx.param_env(body_def_id);
96 let body_id = tcx.hir().local_def_id_to_hir_id(body_def_id);
97 let infcx = &tcx.infer_ctxt().build();
98 let ocx = ObligationCtxt::new(infcx);
100 let mut wfcx = WfCheckingCtxt { ocx, span, body_id, param_env };
102 if !tcx.features().trivial_bounds {
103 wfcx.check_false_global_bounds()
107 let assumed_wf_types = wfcx.ocx.assumed_wf_types(param_env, span, body_def_id);
108 let implied_bounds = infcx.implied_bounds_tys(param_env, body_id, assumed_wf_types);
110 let errors = wfcx.select_all_or_error();
111 if !errors.is_empty() {
112 infcx.err_ctxt().report_fulfillment_errors(&errors, None);
116 let outlives_environment =
117 OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds);
121 .check_region_obligations_and_report_errors(body_def_id, &outlives_environment);
124 fn check_well_formed(tcx: TyCtxt<'_>, def_id: hir::OwnerId) {
125 let node = tcx.hir().owner(def_id);
127 hir::OwnerNode::Crate(_) => {}
128 hir::OwnerNode::Item(item) => check_item(tcx, item),
129 hir::OwnerNode::TraitItem(item) => check_trait_item(tcx, item),
130 hir::OwnerNode::ImplItem(item) => check_impl_item(tcx, item),
131 hir::OwnerNode::ForeignItem(item) => check_foreign_item(tcx, item),
134 if let Some(generics) = node.generics() {
135 for param in generics.params {
136 check_param_wf(tcx, param)
141 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
142 /// well-formed, meaning that they do not require any constraints not declared in the struct
143 /// definition itself. For example, this definition would be illegal:
146 /// struct Ref<'a, T> { x: &'a T }
149 /// because the type did not declare that `T:'a`.
151 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
152 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
154 #[instrument(skip(tcx), level = "debug")]
155 fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
156 let def_id = item.owner_id.def_id;
160 item.name = ? tcx.def_path_str(def_id.to_def_id())
164 // Right now we check that every default trait implementation
165 // has an implementation of itself. Basically, a case like:
167 // impl Trait for T {}
169 // has a requirement of `T: Trait` which was required for default
170 // method implementations. Although this could be improved now that
171 // there's a better infrastructure in place for this, it's being left
172 // for a follow-up work.
174 // Since there's such a requirement, we need to check *just* positive
175 // implementations, otherwise things like:
177 // impl !Send for T {}
179 // won't be allowed unless there's an *explicit* implementation of `Send`
181 hir::ItemKind::Impl(impl_) => {
183 .impl_trait_ref(def_id)
184 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.skip_binder().def_id));
185 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
186 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
188 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
189 err.span_labels(impl_.defaultness_span, "default because of this");
190 err.span_label(sp, "auto trait");
193 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
194 match (tcx.impl_polarity(def_id), impl_.polarity) {
195 (ty::ImplPolarity::Positive, _) => {
196 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait, impl_.constness);
198 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
199 // FIXME(#27579): what amount of WF checking do we need for neg impls?
200 if let hir::Defaultness::Default { .. } = impl_.defaultness {
201 let mut spans = vec![span];
202 spans.extend(impl_.defaultness_span);
207 "negative impls cannot be default impls"
212 (ty::ImplPolarity::Reservation, _) => {
213 // FIXME: what amount of WF checking do we need for reservation impls?
218 hir::ItemKind::Fn(ref sig, ..) => {
219 check_item_fn(tcx, def_id, item.ident, item.span, sig.decl);
221 hir::ItemKind::Static(ty, ..) => {
222 check_item_type(tcx, def_id, ty.span, false);
224 hir::ItemKind::Const(ty, ..) => {
225 check_item_type(tcx, def_id, ty.span, false);
227 hir::ItemKind::Struct(_, ast_generics) => {
228 check_type_defn(tcx, item, false);
229 check_variances_for_type_defn(tcx, item, ast_generics);
231 hir::ItemKind::Union(_, ast_generics) => {
232 check_type_defn(tcx, item, true);
233 check_variances_for_type_defn(tcx, item, ast_generics);
235 hir::ItemKind::Enum(_, ast_generics) => {
236 check_type_defn(tcx, item, true);
237 check_variances_for_type_defn(tcx, item, ast_generics);
239 hir::ItemKind::Trait(..) => {
240 check_trait(tcx, item);
242 hir::ItemKind::TraitAlias(..) => {
243 check_trait(tcx, item);
245 // `ForeignItem`s are handled separately.
246 hir::ItemKind::ForeignMod { .. } => {}
251 fn check_foreign_item(tcx: TyCtxt<'_>, item: &hir::ForeignItem<'_>) {
252 let def_id = item.owner_id.def_id;
256 item.name = ? tcx.def_path_str(def_id.to_def_id())
260 hir::ForeignItemKind::Fn(decl, ..) => {
261 check_item_fn(tcx, def_id, item.ident, item.span, decl)
263 hir::ForeignItemKind::Static(ty, ..) => check_item_type(tcx, def_id, ty.span, true),
264 hir::ForeignItemKind::Type => (),
268 fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) {
269 let def_id = trait_item.owner_id.def_id;
271 let (method_sig, span) = match trait_item.kind {
272 hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span),
273 hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span),
274 _ => (None, trait_item.span),
276 check_object_unsafe_self_trait_by_name(tcx, trait_item);
277 check_associated_item(tcx, def_id, span, method_sig);
279 let encl_trait_def_id = tcx.local_parent(def_id);
280 let encl_trait = tcx.hir().expect_item(encl_trait_def_id);
281 let encl_trait_def_id = encl_trait.owner_id.to_def_id();
282 let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() {
284 } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() {
290 if let (Some(fn_lang_item_name), "call") =
291 (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str())
293 // We are looking at the `call` function of the `fn` or `fn_mut` lang item.
294 // Do some rudimentary sanity checking to avoid an ICE later (issue #83471).
295 if let Some(hir::FnSig { decl, span, .. }) = method_sig {
296 if let [self_ty, _] = decl.inputs {
297 if !matches!(self_ty.kind, hir::TyKind::Ref(_, _)) {
302 "first argument of `call` in `{fn_lang_item_name}` lang item must be a reference",
312 "`call` function in `{fn_lang_item_name}` lang item takes exactly two arguments",
322 "`call` trait item in `{fn_lang_item_name}` lang item must be a function",
330 /// Require that the user writes where clauses on GATs for the implicit
331 /// outlives bounds involving trait parameters in trait functions and
332 /// lifetimes passed as GAT substs. See `self-outlives-lint` test.
334 /// We use the following trait as an example throughout this function:
335 /// ```rust,ignore (this code fails due to this lint)
337 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
339 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
342 fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
343 // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
344 let mut required_bounds_by_item = FxHashMap::default();
346 // Loop over all GATs together, because if this lint suggests adding a where-clause bound
347 // to one GAT, it might then require us to an additional bound on another GAT.
348 // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which
349 // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between
352 let mut should_continue = false;
353 for gat_item in associated_items {
354 let gat_def_id = gat_item.id.owner_id;
355 let gat_item = tcx.associated_item(gat_def_id);
356 // If this item is not an assoc ty, or has no substs, then it's not a GAT
357 if gat_item.kind != ty::AssocKind::Type {
360 let gat_generics = tcx.generics_of(gat_def_id);
361 // FIXME(jackh726): we can also warn in the more general case
362 if gat_generics.params.is_empty() {
366 // Gather the bounds with which all other items inside of this trait constrain the GAT.
367 // This is calculated by taking the intersection of the bounds that each item
368 // constrains the GAT with individually.
369 let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
370 for item in associated_items {
371 let item_def_id = item.id.owner_id;
372 // Skip our own GAT, since it does not constrain itself at all.
373 if item_def_id == gat_def_id {
377 let item_hir_id = item.id.hir_id();
378 let param_env = tcx.param_env(item_def_id);
380 let item_required_bounds = match item.kind {
381 // In our example, this corresponds to `into_iter` method
382 hir::AssocItemKind::Fn { .. } => {
383 // For methods, we check the function signature's return type for any GATs
384 // to constrain. In the `into_iter` case, we see that the return type
385 // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
386 let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions(
387 item_def_id.to_def_id(),
388 tcx.fn_sig(item_def_id),
394 sig.inputs_and_output,
395 // We also assume that all of the function signature's parameter types
397 &sig.inputs().iter().copied().collect(),
402 // In our example, this corresponds to the `Iter` and `Item` associated types
403 hir::AssocItemKind::Type => {
404 // If our associated item is a GAT with missing bounds, add them to
405 // the param-env here. This allows this GAT to propagate missing bounds
407 let param_env = augment_param_env(
410 required_bounds_by_item.get(&item_def_id),
416 tcx.explicit_item_bounds(item_def_id).to_vec(),
417 &FxIndexSet::default(),
422 hir::AssocItemKind::Const => None,
425 if let Some(item_required_bounds) = item_required_bounds {
426 // Take the intersection of the required bounds for this GAT, and
427 // the item_required_bounds which are the ones implied by just
429 // This is why we use an Option<_>, since we need to distinguish
430 // the empty set of bounds from the _uninitialized_ set of bounds.
431 if let Some(new_required_bounds) = &mut new_required_bounds {
432 new_required_bounds.retain(|b| item_required_bounds.contains(b));
434 new_required_bounds = Some(item_required_bounds);
439 if let Some(new_required_bounds) = new_required_bounds {
440 let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default();
441 if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) {
442 // Iterate until our required_bounds no longer change
443 // Since they changed here, we should continue the loop
444 should_continue = true;
448 // We know that this loop will eventually halt, since we only set `should_continue` if the
449 // `required_bounds` for this item grows. Since we are not creating any new region or type
450 // variables, the set of all region and type bounds that we could ever insert are limited
451 // by the number of unique types and regions we observe in a given item.
452 if !should_continue {
457 for (gat_def_id, required_bounds) in required_bounds_by_item {
458 let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id.def_id);
459 debug!(?required_bounds);
460 let param_env = tcx.param_env(gat_def_id);
461 let gat_hir = gat_item_hir.hir_id();
463 let mut unsatisfied_bounds: Vec<_> = required_bounds
465 .filter(|clause| match clause.kind().skip_binder() {
466 ty::PredicateKind::Clause(ty::Clause::RegionOutlives(ty::OutlivesPredicate(
470 !region_known_to_outlive(tcx, gat_hir, param_env, &FxIndexSet::default(), a, b)
472 ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
475 ))) => !ty_known_to_outlive(tcx, gat_hir, param_env, &FxIndexSet::default(), a, b),
476 _ => bug!("Unexpected PredicateKind"),
478 .map(|clause| clause.to_string())
481 // We sort so that order is predictable
482 unsatisfied_bounds.sort();
484 if !unsatisfied_bounds.is_empty() {
485 let plural = pluralize!(unsatisfied_bounds.len());
486 let mut err = tcx.sess.struct_span_err(
488 &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
491 let suggestion = format!(
493 gat_item_hir.generics.add_where_or_trailing_comma(),
494 unsatisfied_bounds.join(", "),
497 gat_item_hir.generics.tail_span_for_predicate_suggestion(),
498 &format!("add the required where clause{plural}"),
500 Applicability::MachineApplicable,
504 if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
506 "{} currently required to ensure that impls have maximum flexibility",
510 "we are soliciting feedback, see issue #87479 \
511 <https://github.com/rust-lang/rust/issues/87479> \
512 for more information",
520 /// Add a new set of predicates to the caller_bounds of an existing param_env.
521 fn augment_param_env<'tcx>(
523 param_env: ty::ParamEnv<'tcx>,
524 new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
525 ) -> ty::ParamEnv<'tcx> {
526 let Some(new_predicates) = new_predicates else {
530 if new_predicates.is_empty() {
535 tcx.mk_predicates(param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()));
536 // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
537 // i.e. traits::normalize_param_env_or_error
538 ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness())
541 /// We use the following trait as an example throughout this function.
542 /// Specifically, let's assume that `to_check` here is the return type
543 /// of `into_iter`, and the GAT we are checking this for is `Iter`.
544 /// ```rust,ignore (this code fails due to this lint)
546 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
548 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
551 fn gather_gat_bounds<'tcx, T: TypeFoldable<'tcx>>(
553 param_env: ty::ParamEnv<'tcx>,
554 item_hir: hir::HirId,
556 wf_tys: &FxIndexSet<Ty<'tcx>>,
557 gat_def_id: LocalDefId,
558 gat_generics: &'tcx ty::Generics,
559 ) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
560 // The bounds we that we would require from `to_check`
561 let mut bounds = FxHashSet::default();
563 let (regions, types) = GATSubstCollector::visit(gat_def_id.to_def_id(), to_check);
565 // If both regions and types are empty, then this GAT isn't in the
566 // set of types we are checking, and we shouldn't try to do clause analysis
567 // (particularly, doing so would end up with an empty set of clauses,
568 // since the current method would require none, and we take the
569 // intersection of requirements of all methods)
570 if types.is_empty() && regions.is_empty() {
574 for (region_a, region_a_idx) in ®ions {
575 // Ignore `'static` lifetimes for the purpose of this lint: it's
576 // because we know it outlives everything and so doesn't give meaningful
578 if let ty::ReStatic = **region_a {
581 // For each region argument (e.g., `'a` in our example), check for a
582 // relationship to the type arguments (e.g., `Self`). If there is an
583 // outlives relationship (`Self: 'a`), then we want to ensure that is
584 // reflected in a where clause on the GAT itself.
585 for (ty, ty_idx) in &types {
586 // In our example, requires that `Self: 'a`
587 if ty_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *ty, *region_a) {
588 debug!(?ty_idx, ?region_a_idx);
589 debug!("required clause: {ty} must outlive {region_a}");
590 // Translate into the generic parameters of the GAT. In
591 // our example, the type was `Self`, which will also be
592 // `Self` in the GAT.
593 let ty_param = gat_generics.param_at(*ty_idx, tcx);
595 .mk_ty(ty::Param(ty::ParamTy { index: ty_param.index, name: ty_param.name }));
596 // Same for the region. In our example, 'a corresponds
597 // to the 'me parameter.
598 let region_param = gat_generics.param_at(*region_a_idx, tcx);
600 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
601 def_id: region_param.def_id,
602 index: region_param.index,
603 name: region_param.name,
605 // The predicate we expect to see. (In our example,
607 let clause = ty::PredicateKind::Clause(ty::Clause::TypeOutlives(
608 ty::OutlivesPredicate(ty_param, region_param),
610 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
611 bounds.insert(clause);
615 // For each region argument (e.g., `'a` in our example), also check for a
616 // relationship to the other region arguments. If there is an outlives
617 // relationship, then we want to ensure that is reflected in the where clause
618 // on the GAT itself.
619 for (region_b, region_b_idx) in ®ions {
620 // Again, skip `'static` because it outlives everything. Also, we trivially
621 // know that a region outlives itself.
622 if ty::ReStatic == **region_b || region_a == region_b {
625 if region_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *region_a, *region_b) {
626 debug!(?region_a_idx, ?region_b_idx);
627 debug!("required clause: {region_a} must outlive {region_b}");
628 // Translate into the generic parameters of the GAT.
629 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
631 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
632 def_id: region_a_param.def_id,
633 index: region_a_param.index,
634 name: region_a_param.name,
636 // Same for the region.
637 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
639 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
640 def_id: region_b_param.def_id,
641 index: region_b_param.index,
642 name: region_b_param.name,
644 // The predicate we expect to see.
645 let clause = ty::PredicateKind::Clause(ty::Clause::RegionOutlives(
646 ty::OutlivesPredicate(region_a_param, region_b_param),
648 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
649 bounds.insert(clause);
657 /// Given a known `param_env` and a set of well formed types, can we prove that
658 /// `ty` outlives `region`.
659 fn ty_known_to_outlive<'tcx>(
662 param_env: ty::ParamEnv<'tcx>,
663 wf_tys: &FxIndexSet<Ty<'tcx>>,
665 region: ty::Region<'tcx>,
667 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| {
668 let origin = infer::RelateParamBound(DUMMY_SP, ty, None);
669 let outlives = &mut TypeOutlives::new(infcx, tcx, region_bound_pairs, None, param_env);
670 outlives.type_must_outlive(origin, ty, region, ConstraintCategory::BoringNoLocation);
674 /// Given a known `param_env` and a set of well formed types, can we prove that
675 /// `region_a` outlives `region_b`
676 fn region_known_to_outlive<'tcx>(
679 param_env: ty::ParamEnv<'tcx>,
680 wf_tys: &FxIndexSet<Ty<'tcx>>,
681 region_a: ty::Region<'tcx>,
682 region_b: ty::Region<'tcx>,
684 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| {
685 use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
686 let origin = infer::RelateRegionParamBound(DUMMY_SP);
687 // `region_a: region_b` -> `region_b <= region_a`
688 infcx.push_sub_region_constraint(
692 ConstraintCategory::BoringNoLocation,
697 /// Given a known `param_env` and a set of well formed types, set up an
698 /// `InferCtxt`, call the passed function (to e.g. set up region constraints
699 /// to be tested), then resolve region and return errors
700 fn resolve_regions_with_wf_tys<'tcx>(
703 param_env: ty::ParamEnv<'tcx>,
704 wf_tys: &FxIndexSet<Ty<'tcx>>,
705 add_constraints: impl for<'a> FnOnce(&'a InferCtxt<'tcx>, &'a RegionBoundPairs<'tcx>),
707 // Unfortunately, we have to use a new `InferCtxt` each call, because
708 // region constraints get added and solved there and we need to test each
709 // call individually.
710 let infcx = tcx.infer_ctxt().build();
711 let outlives_environment = OutlivesEnvironment::with_bounds(
714 infcx.implied_bounds_tys(param_env, id, wf_tys.clone()),
716 let region_bound_pairs = outlives_environment.region_bound_pairs();
718 add_constraints(&infcx, region_bound_pairs);
720 infcx.process_registered_region_obligations(
721 outlives_environment.region_bound_pairs(),
724 let errors = infcx.resolve_regions(&outlives_environment);
726 debug!(?errors, "errors");
728 // If we were able to prove that the type outlives the region without
729 // an error, it must be because of the implied or explicit bounds...
733 /// TypeVisitor that looks for uses of GATs like
734 /// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into
735 /// the two vectors, `regions` and `types` (depending on their kind). For each
736 /// parameter `Pi` also track the index `i`.
737 struct GATSubstCollector<'tcx> {
739 // Which region appears and which parameter index its substituted for
740 regions: FxHashSet<(ty::Region<'tcx>, usize)>,
741 // Which params appears and which parameter index its substituted for
742 types: FxHashSet<(Ty<'tcx>, usize)>,
745 impl<'tcx> GATSubstCollector<'tcx> {
746 fn visit<T: TypeFoldable<'tcx>>(
749 ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) {
751 GATSubstCollector { gat, regions: FxHashSet::default(), types: FxHashSet::default() };
752 t.visit_with(&mut visitor);
753 (visitor.regions, visitor.types)
757 impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
760 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
762 ty::Alias(ty::Projection, p) if p.def_id == self.gat => {
763 for (idx, subst) in p.substs.iter().enumerate() {
764 match subst.unpack() {
765 GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => {
766 self.regions.insert((lt, idx));
768 GenericArgKind::Type(t) => {
769 self.types.insert((t, idx));
777 t.super_visit_with(self)
781 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
783 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
784 [s] => s.res.opt_def_id() == Some(trait_def_id.to_def_id()),
791 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
792 /// When this is done, suggest using `Self` instead.
793 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
794 let (trait_name, trait_def_id) =
795 match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id()).def_id) {
796 hir::Node::Item(item) => match item.kind {
797 hir::ItemKind::Trait(..) => (item.ident, item.owner_id),
802 let mut trait_should_be_self = vec![];
804 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
805 if could_be_self(trait_def_id.def_id, ty) =>
807 trait_should_be_self.push(ty.span)
809 hir::TraitItemKind::Fn(sig, _) => {
810 for ty in sig.decl.inputs {
811 if could_be_self(trait_def_id.def_id, ty) {
812 trait_should_be_self.push(ty.span);
815 match sig.decl.output {
816 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id.def_id, ty) => {
817 trait_should_be_self.push(ty.span);
824 if !trait_should_be_self.is_empty() {
825 if tcx.object_safety_violations(trait_def_id).is_empty() {
828 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
831 trait_should_be_self,
832 "associated item referring to unboxed trait object for its own trait",
834 .span_label(trait_name.span, "in this trait")
835 .multipart_suggestion(
836 "you might have meant to use `Self` to refer to the implementing type",
838 Applicability::MachineApplicable,
844 fn check_impl_item(tcx: TyCtxt<'_>, impl_item: &hir::ImplItem<'_>) {
845 let (method_sig, span) = match impl_item.kind {
846 hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span),
847 // Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`.
848 hir::ImplItemKind::Type(ty) if ty.span != DUMMY_SP => (None, ty.span),
849 _ => (None, impl_item.span),
852 check_associated_item(tcx, impl_item.owner_id.def_id, span, method_sig);
855 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
857 // We currently only check wf of const params here.
858 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
860 // Const parameters are well formed if their type is structural match.
861 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
862 let ty = tcx.type_of(param.def_id);
864 if tcx.features().adt_const_params {
865 if let Some(non_structural_match_ty) =
866 traits::search_for_adt_const_param_violation(param.span, tcx, ty)
868 // We use the same error code in both branches, because this is really the same
869 // issue: we just special-case the message for type parameters to make it
871 match non_structural_match_ty.kind() {
873 // Const parameters may not have type parameters as their types,
874 // because we cannot be sure that the type parameter derives `PartialEq`
875 // and `Eq` (just implementing them is not enough for `structural_match`).
880 "`{ty}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
881 used as the type of a const parameter",
885 format!("`{ty}` may not derive both `PartialEq` and `Eq`"),
888 "it is not currently possible to use a type parameter as the type of a \
898 "`{ty}` is forbidden as the type of a const generic parameter",
900 .note("floats do not derive `Eq` or `Ord`, which are required for const parameters")
908 "using function pointers as const generic parameters is forbidden",
917 "using raw pointers as const generic parameters is forbidden",
922 let mut diag = struct_span_err!(
926 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
927 the type of a const parameter",
928 non_structural_match_ty,
931 if ty == non_structural_match_ty {
934 format!("`{ty}` doesn't derive both `PartialEq` and `Eq`"),
944 let mut is_ptr = true;
946 let err = match ty.kind() {
947 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
948 ty::FnPtr(_) => Some("function pointers"),
949 ty::RawPtr(_) => Some("raw pointers"),
952 err_ty_str = format!("`{ty}`");
953 Some(err_ty_str.as_str())
957 if let Some(unsupported_type) = err {
962 "using {unsupported_type} as const generic parameters is forbidden",
966 let mut err = tcx.sess.struct_span_err(
969 "{unsupported_type} is forbidden as the type of a const generic parameter",
972 err.note("the only supported types are integers, `bool` and `char`");
973 if tcx.sess.is_nightly_build() {
975 "more complex types are supported with `#![feature(adt_const_params)]`",
986 #[instrument(level = "debug", skip(tcx, span, sig_if_method))]
987 fn check_associated_item(
991 sig_if_method: Option<&hir::FnSig<'_>>,
993 let loc = Some(WellFormedLoc::Ty(item_id));
994 enter_wf_checking_ctxt(tcx, span, item_id, |wfcx| {
995 let item = tcx.associated_item(item_id);
997 let self_ty = match item.container {
998 ty::TraitContainer => tcx.types.self_param,
999 ty::ImplContainer => tcx.type_of(item.container_id(tcx)),
1003 ty::AssocKind::Const => {
1004 let ty = tcx.type_of(item.def_id);
1005 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
1006 wfcx.register_wf_obligation(span, loc, ty.into());
1008 ty::AssocKind::Fn => {
1009 let sig = tcx.fn_sig(item.def_id);
1010 let hir_sig = sig_if_method.expect("bad signature for method");
1013 item.ident(tcx).span,
1016 item.def_id.expect_local(),
1018 check_method_receiver(wfcx, hir_sig, item, self_ty);
1020 ty::AssocKind::Type => {
1021 if let ty::AssocItemContainer::TraitContainer = item.container {
1022 check_associated_type_bounds(wfcx, item, span)
1024 if item.defaultness(tcx).has_value() {
1025 let ty = tcx.type_of(item.def_id);
1026 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
1027 wfcx.register_wf_obligation(span, loc, ty.into());
1034 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
1036 ItemKind::Struct(..) => Some(AdtKind::Struct),
1037 ItemKind::Union(..) => Some(AdtKind::Union),
1038 ItemKind::Enum(..) => Some(AdtKind::Enum),
1043 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
1044 fn check_type_defn<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'tcx>, all_sized: bool) {
1045 let _ = tcx.representability(item.owner_id.def_id);
1046 let adt_def = tcx.adt_def(item.owner_id);
1048 enter_wf_checking_ctxt(tcx, item.span, item.owner_id.def_id, |wfcx| {
1049 let variants = adt_def.variants();
1050 let packed = adt_def.repr().packed();
1052 for variant in variants.iter() {
1053 // All field types must be well-formed.
1054 for field in &variant.fields {
1055 let field_id = field.did.expect_local();
1056 let hir::Node::Field(hir::FieldDef { ty: hir_ty, .. }) = tcx.hir().get_by_def_id(field_id)
1058 let ty = wfcx.normalize(hir_ty.span, None, tcx.type_of(field.did));
1059 wfcx.register_wf_obligation(
1061 Some(WellFormedLoc::Ty(field_id)),
1066 // For DST, or when drop needs to copy things around, all
1067 // intermediate types must be sized.
1068 let needs_drop_copy = || {
1070 let ty = tcx.type_of(variant.fields.last().unwrap().did);
1071 let ty = tcx.erase_regions(ty);
1072 if ty.needs_infer() {
1074 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
1075 // Just treat unresolved type expression as if it needs drop.
1078 ty.needs_drop(tcx, tcx.param_env(item.owner_id))
1082 // All fields (except for possibly the last) should be sized.
1083 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
1084 let unsized_len = if all_sized { 0 } else { 1 };
1086 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
1088 let last = idx == variant.fields.len() - 1;
1089 let field_id = field.did.expect_local();
1090 let hir::Node::Field(hir::FieldDef { ty: hir_ty, .. }) = tcx.hir().get_by_def_id(field_id)
1092 let ty = wfcx.normalize(hir_ty.span, None, tcx.type_of(field.did));
1093 wfcx.register_bound(
1094 traits::ObligationCause::new(
1097 traits::FieldSized {
1098 adt_kind: match item_adt_kind(&item.kind) {
1108 tcx.require_lang_item(LangItem::Sized, None),
1112 // Explicit `enum` discriminant values must const-evaluate successfully.
1113 if let ty::VariantDiscr::Explicit(discr_def_id) = variant.discr {
1114 let cause = traits::ObligationCause::new(
1115 tcx.def_span(discr_def_id),
1117 traits::MiscObligation,
1119 wfcx.register_obligation(traits::Obligation::new(
1123 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(
1124 ty::Const::from_anon_const(tcx, discr_def_id.expect_local()),
1130 check_where_clauses(wfcx, item.span, item.owner_id.def_id);
1134 #[instrument(skip(tcx, item))]
1135 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
1136 debug!(?item.owner_id);
1138 let def_id = item.owner_id.def_id;
1139 let trait_def = tcx.trait_def(def_id);
1140 if trait_def.is_marker
1141 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
1143 for associated_def_id in &*tcx.associated_item_def_ids(def_id) {
1146 tcx.def_span(*associated_def_id),
1148 "marker traits cannot have associated items",
1154 enter_wf_checking_ctxt(tcx, item.span, def_id, |wfcx| {
1155 check_where_clauses(wfcx, item.span, def_id)
1158 // Only check traits, don't check trait aliases
1159 if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
1160 check_gat_where_clauses(tcx, items);
1164 /// Checks all associated type defaults of trait `trait_def_id`.
1166 /// Assuming the defaults are used, check that all predicates (bounds on the
1167 /// assoc type and where clauses on the trait) hold.
1168 fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
1169 let bounds = wfcx.tcx().explicit_item_bounds(item.def_id);
1171 debug!("check_associated_type_bounds: bounds={:?}", bounds);
1172 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1173 let normalized_bound = wfcx.normalize(span, None, bound);
1174 traits::wf::predicate_obligations(
1183 wfcx.register_obligations(wf_obligations);
1191 decl: &hir::FnDecl<'_>,
1193 enter_wf_checking_ctxt(tcx, span, def_id, |wfcx| {
1194 let sig = tcx.fn_sig(def_id);
1195 check_fn_or_method(wfcx, ident.span, sig, decl, def_id);
1199 fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) {
1200 debug!("check_item_type: {:?}", item_id);
1202 enter_wf_checking_ctxt(tcx, ty_span, item_id, |wfcx| {
1203 let ty = tcx.type_of(item_id);
1204 let item_ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(item_id)), ty);
1206 let mut forbid_unsized = true;
1207 if allow_foreign_ty {
1208 let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env);
1209 if let ty::Foreign(_) = tail.kind() {
1210 forbid_unsized = false;
1214 wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(item_id)), item_ty.into());
1216 wfcx.register_bound(
1217 traits::ObligationCause::new(ty_span, wfcx.body_id, traits::WellFormed(None)),
1220 tcx.require_lang_item(LangItem::Sized, None),
1224 // Ensure that the end result is `Sync` in a non-thread local `static`.
1225 let should_check_for_sync = tcx.static_mutability(item_id.to_def_id())
1226 == Some(hir::Mutability::Not)
1227 && !tcx.is_foreign_item(item_id.to_def_id())
1228 && !tcx.is_thread_local_static(item_id.to_def_id());
1230 if should_check_for_sync {
1231 wfcx.register_bound(
1232 traits::ObligationCause::new(ty_span, wfcx.body_id, traits::SharedStatic),
1235 tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
1241 #[instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))]
1242 fn check_impl<'tcx>(
1244 item: &'tcx hir::Item<'tcx>,
1245 ast_self_ty: &hir::Ty<'_>,
1246 ast_trait_ref: &Option<hir::TraitRef<'_>>,
1247 constness: hir::Constness,
1249 enter_wf_checking_ctxt(tcx, item.span, item.owner_id.def_id, |wfcx| {
1250 match ast_trait_ref {
1251 Some(ast_trait_ref) => {
1252 // `#[rustc_reservation_impl]` impls are not real impls and
1253 // therefore don't need to be WF (the trait's `Self: Trait` predicate
1255 let trait_ref = tcx.impl_trait_ref(item.owner_id).unwrap().subst_identity();
1256 let trait_ref = wfcx.normalize(
1257 ast_trait_ref.path.span,
1258 Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
1261 let trait_pred = ty::TraitPredicate {
1263 constness: match constness {
1264 hir::Constness::Const => ty::BoundConstness::ConstIfConst,
1265 hir::Constness::NotConst => ty::BoundConstness::NotConst,
1267 polarity: ty::ImplPolarity::Positive,
1269 let mut obligations = traits::wf::trait_obligations(
1274 ast_trait_ref.path.span,
1277 for obligation in &mut obligations {
1278 if let Some(pred) = obligation.predicate.to_opt_poly_trait_pred()
1279 && pred.self_ty().skip_binder() == trait_ref.self_ty()
1281 obligation.cause.span = ast_self_ty.span;
1284 debug!(?obligations);
1285 wfcx.register_obligations(obligations);
1288 let self_ty = tcx.type_of(item.owner_id);
1289 let self_ty = wfcx.normalize(
1291 Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
1294 wfcx.register_wf_obligation(
1296 Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
1302 check_where_clauses(wfcx, item.span, item.owner_id.def_id);
1306 /// Checks where-clauses and inline bounds that are declared on `def_id`.
1307 #[instrument(level = "debug", skip(wfcx))]
1308 fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id: LocalDefId) {
1309 let infcx = wfcx.infcx;
1310 let tcx = wfcx.tcx();
1312 let predicates = tcx.predicates_of(def_id.to_def_id());
1313 let generics = tcx.generics_of(def_id);
1315 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
1316 GenericParamDefKind::Type { has_default, .. }
1317 | GenericParamDefKind::Const { has_default } => {
1318 has_default && def.index >= generics.parent_count as u32
1320 GenericParamDefKind::Lifetime => unreachable!(),
1323 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
1324 // For example, this forbids the declaration:
1326 // struct Foo<T = Vec<[u32]>> { .. }
1328 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
1329 for param in &generics.params {
1331 GenericParamDefKind::Type { .. } => {
1332 if is_our_default(param) {
1333 let ty = tcx.type_of(param.def_id);
1334 // Ignore dependent defaults -- that is, where the default of one type
1335 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
1336 // be sure if it will error or not as user might always specify the other.
1337 if !ty.needs_subst() {
1338 wfcx.register_wf_obligation(
1339 tcx.def_span(param.def_id),
1340 Some(WellFormedLoc::Ty(param.def_id.expect_local())),
1346 GenericParamDefKind::Const { .. } => {
1347 if is_our_default(param) {
1348 // FIXME(const_generics_defaults): This
1349 // is incorrect when dealing with unused substs, for example
1350 // for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
1351 // we should eagerly error.
1352 let default_ct = tcx.const_param_default(param.def_id).subst_identity();
1353 if !default_ct.needs_subst() {
1354 wfcx.register_wf_obligation(
1355 tcx.def_span(param.def_id),
1362 // Doesn't have defaults.
1363 GenericParamDefKind::Lifetime => {}
1367 // Check that trait predicates are WF when params are substituted by their defaults.
1368 // We don't want to overly constrain the predicates that may be written but we want to
1369 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
1370 // Therefore we check if a predicate which contains a single type param
1371 // with a concrete default is WF with that default substituted.
1372 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
1374 // First we build the defaulted substitution.
1375 let substs = InternalSubsts::for_item(tcx, def_id.to_def_id(), |param, _| {
1377 GenericParamDefKind::Lifetime => {
1378 // All regions are identity.
1379 tcx.mk_param_from_def(param)
1382 GenericParamDefKind::Type { .. } => {
1383 // If the param has a default, ...
1384 if is_our_default(param) {
1385 let default_ty = tcx.type_of(param.def_id);
1386 // ... and it's not a dependent default, ...
1387 if !default_ty.needs_subst() {
1388 // ... then substitute it with the default.
1389 return default_ty.into();
1393 tcx.mk_param_from_def(param)
1395 GenericParamDefKind::Const { .. } => {
1396 // If the param has a default, ...
1397 if is_our_default(param) {
1398 let default_ct = tcx.const_param_default(param.def_id).subst_identity();
1399 // ... and it's not a dependent default, ...
1400 if !default_ct.needs_subst() {
1401 // ... then substitute it with the default.
1402 return default_ct.into();
1406 tcx.mk_param_from_def(param)
1411 // Now we build the substituted predicates.
1412 let default_obligations = predicates
1415 .flat_map(|&(pred, sp)| {
1417 struct CountParams {
1418 params: FxHashSet<u32>,
1420 impl<'tcx> ty::visit::TypeVisitor<'tcx> for CountParams {
1423 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1424 if let ty::Param(param) = t.kind() {
1425 self.params.insert(param.index);
1427 t.super_visit_with(self)
1430 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1431 ControlFlow::Break(())
1434 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1435 if let ty::ConstKind::Param(param) = c.kind() {
1436 self.params.insert(param.index);
1438 c.super_visit_with(self)
1441 let mut param_count = CountParams::default();
1442 let has_region = pred.visit_with(&mut param_count).is_break();
1443 let substituted_pred = ty::EarlyBinder(pred).subst(tcx, substs);
1444 // Don't check non-defaulted params, dependent defaults (including lifetimes)
1445 // or preds with multiple params.
1446 if substituted_pred.has_non_region_param() || param_count.params.len() > 1 || has_region
1449 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
1450 // Avoid duplication of predicates that contain no parameters, for example.
1453 Some((substituted_pred, sp))
1457 // Convert each of those into an obligation. So if you have
1458 // something like `struct Foo<T: Copy = String>`, we would
1459 // take that predicate `T: Copy`, substitute to `String: Copy`
1460 // (actually that happens in the previous `flat_map` call),
1461 // and then try to prove it (in this case, we'll fail).
1463 // Note the subtle difference from how we handle `predicates`
1464 // below: there, we are not trying to prove those predicates
1465 // to be *true* but merely *well-formed*.
1466 let pred = wfcx.normalize(sp, None, pred);
1467 let cause = traits::ObligationCause::new(
1470 traits::ItemObligation(def_id.to_def_id()),
1472 traits::Obligation::new(tcx, cause, wfcx.param_env, pred)
1475 let predicates = predicates.instantiate_identity(tcx);
1477 let predicates = wfcx.normalize(span, None, predicates);
1479 debug!(?predicates.predicates);
1480 assert_eq!(predicates.predicates.len(), predicates.spans.len());
1481 let wf_obligations = predicates.into_iter().flat_map(|(p, sp)| {
1482 traits::wf::predicate_obligations(
1484 wfcx.param_env.without_const(),
1491 let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect();
1492 wfcx.register_obligations(obligations);
1495 #[instrument(level = "debug", skip(wfcx, span, hir_decl))]
1496 fn check_fn_or_method<'tcx>(
1497 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1499 sig: ty::PolyFnSig<'tcx>,
1500 hir_decl: &hir::FnDecl<'_>,
1503 let tcx = wfcx.tcx();
1504 let mut sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
1506 // Normalize the input and output types one at a time, using a different
1507 // `WellFormedLoc` for each. We cannot call `normalize_associated_types`
1508 // on the entire `FnSig`, since this would use the same `WellFormedLoc`
1509 // for each type, preventing the HIR wf check from generating
1510 // a nice error message.
1512 |idx| hir_decl.inputs.get(idx).map_or(hir_decl.output.span(), |arg: &hir::Ty<'_>| arg.span);
1514 sig.inputs_and_output =
1515 tcx.mk_type_list(sig.inputs_and_output.iter().enumerate().map(|(idx, ty)| {
1518 Some(WellFormedLoc::Param {
1520 // Note that the `param_idx` of the output type is
1521 // one greater than the index of the last input type.
1522 param_idx: idx.try_into().unwrap(),
1528 for (idx, ty) in sig.inputs_and_output.iter().enumerate() {
1529 wfcx.register_wf_obligation(
1531 Some(WellFormedLoc::Param { function: def_id, param_idx: idx.try_into().unwrap() }),
1536 check_where_clauses(wfcx, span, def_id);
1538 check_return_position_impl_trait_in_trait_bounds(
1542 hir_decl.output.span(),
1545 if sig.abi == Abi::RustCall {
1546 let span = tcx.def_span(def_id);
1547 let has_implicit_self = hir_decl.implicit_self != hir::ImplicitSelfKind::None;
1548 let mut inputs = sig.inputs().iter().skip(if has_implicit_self { 1 } else { 0 });
1549 // Check that the argument is a tuple
1550 if let Some(ty) = inputs.next() {
1551 wfcx.register_bound(
1552 ObligationCause::new(span, wfcx.body_id, ObligationCauseCode::RustCall),
1555 tcx.require_lang_item(hir::LangItem::Tuple, Some(span)),
1559 hir_decl.inputs.last().map_or(span, |input| input.span),
1560 "functions with the \"rust-call\" ABI must take a single non-self tuple argument",
1563 // No more inputs other than the `self` type and the tuple type
1564 if inputs.next().is_some() {
1566 hir_decl.inputs.last().map_or(span, |input| input.span),
1567 "functions with the \"rust-call\" ABI must take a single non-self tuple argument",
1573 /// Basically `check_associated_type_bounds`, but separated for now and should be
1574 /// deduplicated when RPITITs get lowered into real associated items.
1575 #[tracing::instrument(level = "trace", skip(wfcx))]
1576 fn check_return_position_impl_trait_in_trait_bounds<'tcx>(
1577 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1578 fn_def_id: LocalDefId,
1579 fn_output: Ty<'tcx>,
1582 let tcx = wfcx.tcx();
1583 if let Some(assoc_item) = tcx.opt_associated_item(fn_def_id.to_def_id())
1584 && assoc_item.container == ty::AssocItemContainer::TraitContainer
1586 for arg in fn_output.walk() {
1587 if let ty::GenericArgKind::Type(ty) = arg.unpack()
1588 && let ty::Alias(ty::Projection, proj) = ty.kind()
1589 && tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder
1590 && tcx.impl_trait_in_trait_parent(proj.def_id) == fn_def_id.to_def_id()
1592 let span = tcx.def_span(proj.def_id);
1593 let bounds = wfcx.tcx().explicit_item_bounds(proj.def_id);
1594 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1595 let bound = ty::EarlyBinder(bound).subst(tcx, proj.substs);
1596 let normalized_bound = wfcx.normalize(span, None, bound);
1597 traits::wf::predicate_obligations(
1605 wfcx.register_obligations(wf_obligations);
1611 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1612 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1613 of the previous types except `Self`)";
1615 #[instrument(level = "debug", skip(wfcx))]
1616 fn check_method_receiver<'tcx>(
1617 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1618 fn_sig: &hir::FnSig<'_>,
1619 method: &ty::AssocItem,
1622 let tcx = wfcx.tcx();
1624 if !method.fn_has_self_parameter {
1628 let span = fn_sig.decl.inputs[0].span;
1630 let sig = tcx.fn_sig(method.def_id);
1631 let sig = tcx.liberate_late_bound_regions(method.def_id, sig);
1632 let sig = wfcx.normalize(span, None, sig);
1634 debug!("check_method_receiver: sig={:?}", sig);
1636 let self_ty = wfcx.normalize(span, None, self_ty);
1638 let receiver_ty = sig.inputs()[0];
1639 let receiver_ty = wfcx.normalize(span, None, receiver_ty);
1641 if tcx.features().arbitrary_self_types {
1642 if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
1643 // Report error; `arbitrary_self_types` was enabled.
1644 e0307(tcx, span, receiver_ty);
1647 if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, false) {
1648 if receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
1649 // Report error; would have worked with `arbitrary_self_types`.
1651 &tcx.sess.parse_sess,
1652 sym::arbitrary_self_types,
1655 "`{receiver_ty}` cannot be used as the type of `self` without \
1656 the `arbitrary_self_types` feature",
1659 .help(HELP_FOR_SELF_TYPE)
1662 // Report error; would not have worked with `arbitrary_self_types`.
1663 e0307(tcx, span, receiver_ty);
1669 fn e0307(tcx: TyCtxt<'_>, span: Span, receiver_ty: Ty<'_>) {
1671 tcx.sess.diagnostic(),
1674 "invalid `self` parameter type: {receiver_ty}"
1676 .note("type of `self` must be `Self` or a type that dereferences to it")
1677 .help(HELP_FOR_SELF_TYPE)
1681 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1682 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1683 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1684 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1685 /// `Deref<Target = self_ty>`.
1687 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1688 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1689 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1690 fn receiver_is_valid<'tcx>(
1691 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1693 receiver_ty: Ty<'tcx>,
1695 arbitrary_self_types_enabled: bool,
1697 let infcx = wfcx.infcx;
1698 let tcx = wfcx.tcx();
1700 ObligationCause::new(span, wfcx.body_id, traits::ObligationCauseCode::MethodReceiver);
1702 let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty).is_ok();
1704 // `self: Self` is always valid.
1705 if can_eq_self(receiver_ty) {
1706 if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, receiver_ty) {
1707 infcx.err_ctxt().report_mismatched_types(&cause, self_ty, receiver_ty, err).emit();
1712 let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_id, span, receiver_ty);
1714 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1715 if arbitrary_self_types_enabled {
1716 autoderef = autoderef.include_raw_pointers();
1719 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1722 let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, Some(span));
1724 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1726 if let Some((potential_self_ty, _)) = autoderef.next() {
1728 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1729 potential_self_ty, self_ty
1732 if can_eq_self(potential_self_ty) {
1733 wfcx.register_obligations(autoderef.into_obligations());
1735 if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty) {
1738 .report_mismatched_types(&cause, self_ty, potential_self_ty, err)
1744 // Without `feature(arbitrary_self_types)`, we require that each step in the
1745 // deref chain implement `receiver`
1746 if !arbitrary_self_types_enabled
1747 && !receiver_is_implemented(
1749 receiver_trait_def_id,
1758 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1759 // If the receiver already has errors reported due to it, consider it valid to avoid
1760 // unnecessary errors (#58712).
1761 return receiver_ty.references_error();
1765 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1766 if !arbitrary_self_types_enabled
1767 && !receiver_is_implemented(wfcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1775 fn receiver_is_implemented<'tcx>(
1776 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1777 receiver_trait_def_id: DefId,
1778 cause: ObligationCause<'tcx>,
1779 receiver_ty: Ty<'tcx>,
1781 let tcx = wfcx.tcx();
1782 let trait_ref = ty::Binder::dummy(tcx.mk_trait_ref(receiver_trait_def_id, [receiver_ty]));
1784 let obligation = traits::Obligation::new(tcx, cause, wfcx.param_env, trait_ref);
1786 if wfcx.infcx.predicate_must_hold_modulo_regions(&obligation) {
1790 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1797 fn check_variances_for_type_defn<'tcx>(
1799 item: &hir::Item<'tcx>,
1800 hir_generics: &hir::Generics<'_>,
1802 let ty = tcx.type_of(item.owner_id);
1803 if tcx.has_error_field(ty) {
1807 let ty_predicates = tcx.predicates_of(item.owner_id);
1808 assert_eq!(ty_predicates.parent, None);
1809 let variances = tcx.variances_of(item.owner_id);
1811 let mut constrained_parameters: FxHashSet<_> = variances
1814 .filter(|&(_, &variance)| variance != ty::Bivariant)
1815 .map(|(index, _)| Parameter(index as u32))
1818 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1820 // Lazily calculated because it is only needed in case of an error.
1821 let explicitly_bounded_params = LazyCell::new(|| {
1822 let icx = crate::collect::ItemCtxt::new(tcx, item.owner_id.to_def_id());
1826 .filter_map(|predicate| match predicate {
1827 hir::WherePredicate::BoundPredicate(predicate) => {
1828 match icx.to_ty(predicate.bounded_ty).kind() {
1829 ty::Param(data) => Some(Parameter(data.index)),
1835 .collect::<FxHashSet<_>>()
1838 for (index, _) in variances.iter().enumerate() {
1839 let parameter = Parameter(index as u32);
1841 if constrained_parameters.contains(¶meter) {
1845 let param = &hir_generics.params[index];
1848 hir::ParamName::Error => {}
1850 let has_explicit_bounds = explicitly_bounded_params.contains(¶meter);
1851 report_bivariance(tcx, param, has_explicit_bounds);
1857 fn report_bivariance(
1859 param: &rustc_hir::GenericParam<'_>,
1860 has_explicit_bounds: bool,
1861 ) -> ErrorGuaranteed {
1862 let span = param.span;
1863 let param_name = param.name.ident().name;
1864 let mut err = error_392(tcx, span, param_name);
1866 let suggested_marker_id = tcx.lang_items().phantom_data();
1867 // Help is available only in presence of lang items.
1868 let msg = if let Some(def_id) = suggested_marker_id {
1870 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1872 tcx.def_path_str(def_id),
1875 format!("consider removing `{param_name}` or referring to it in a field")
1879 if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds {
1881 "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
1888 impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
1889 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1891 #[instrument(level = "debug", skip(self))]
1892 fn check_false_global_bounds(&mut self) {
1893 let tcx = self.ocx.infcx.tcx;
1894 let mut span = self.span;
1895 let empty_env = ty::ParamEnv::empty();
1897 let def_id = tcx.hir().local_def_id(self.body_id);
1898 let predicates_with_span = tcx.predicates_of(def_id).predicates.iter().copied();
1899 // Check elaborated bounds.
1900 let implied_obligations = traits::elaborate_predicates_with_span(tcx, predicates_with_span);
1902 for obligation in implied_obligations {
1903 // We lower empty bounds like `Vec<dyn Copy>:` as
1904 // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
1905 // regular WF checking
1906 if let ty::PredicateKind::WellFormed(..) = obligation.predicate.kind().skip_binder() {
1909 let pred = obligation.predicate;
1910 // Match the existing behavior.
1911 if pred.is_global() && !pred.has_late_bound_vars() {
1912 let pred = self.normalize(span, None, pred);
1913 let hir_node = tcx.hir().find(self.body_id);
1915 // only use the span of the predicate clause (#90869)
1917 if let Some(hir::Generics { predicates, .. }) =
1918 hir_node.and_then(|node| node.generics())
1920 let obligation_span = obligation.cause.span();
1924 // There seems to be no better way to find out which predicate we are in
1925 .find(|pred| pred.span().contains(obligation_span))
1926 .map(|pred| pred.span())
1927 .unwrap_or(obligation_span);
1930 let obligation = traits::Obligation::new(
1932 traits::ObligationCause::new(span, self.body_id, traits::TrivialBound),
1936 self.ocx.register_obligation(obligation);
1942 fn check_mod_type_wf(tcx: TyCtxt<'_>, module: LocalDefId) {
1943 let items = tcx.hir_module_items(module);
1944 items.par_items(|item| tcx.ensure().check_well_formed(item.owner_id));
1945 items.par_impl_items(|item| tcx.ensure().check_well_formed(item.owner_id));
1946 items.par_trait_items(|item| tcx.ensure().check_well_formed(item.owner_id));
1947 items.par_foreign_items(|item| tcx.ensure().check_well_formed(item.owner_id));
1954 ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
1955 let mut err = struct_span_err!(tcx.sess, span, E0392, "parameter `{param_name}` is never used");
1956 err.span_label(span, "unused parameter");
1960 pub fn provide(providers: &mut Providers) {
1961 *providers = Providers { check_mod_type_wf, check_well_formed, ..*providers };