1 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
4 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
5 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
7 use rustc_hir::def_id::{DefId, LocalDefId};
8 use rustc_hir::lang_items::LangItem;
9 use rustc_hir::ItemKind;
10 use rustc_infer::infer::outlives::env::{OutlivesEnvironment, RegionBoundPairs};
11 use rustc_infer::infer::outlives::obligations::TypeOutlives;
12 use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
13 use rustc_middle::ty::query::Providers;
14 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
15 use rustc_middle::ty::trait_def::TraitSpecializationKind;
16 use rustc_middle::ty::{
17 self, AdtKind, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable,
18 TypeSuperVisitable, TypeVisitable, TypeVisitor,
20 use rustc_session::parse::feature_err;
21 use rustc_span::symbol::{sym, Ident, Symbol};
22 use rustc_span::{Span, DUMMY_SP};
23 use rustc_trait_selection::autoderef::Autoderef;
24 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
25 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
26 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
27 use rustc_trait_selection::traits::{
28 self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,
31 use std::cell::LazyCell;
32 use std::convert::TryInto;
34 use std::ops::{ControlFlow, Deref};
36 pub(super) struct WfCheckingCtxt<'a, 'tcx> {
37 pub(super) ocx: ObligationCtxt<'a, 'tcx>,
40 param_env: ty::ParamEnv<'tcx>,
42 impl<'a, 'tcx> Deref for WfCheckingCtxt<'a, 'tcx> {
43 type Target = ObligationCtxt<'a, 'tcx>;
44 fn deref(&self) -> &Self::Target {
49 impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
50 fn tcx(&self) -> TyCtxt<'tcx> {
54 fn normalize<T>(&self, span: Span, loc: Option<WellFormedLoc>, value: T) -> T
56 T: TypeFoldable<'tcx>,
59 ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc)),
65 fn register_wf_obligation(
68 loc: Option<WellFormedLoc>,
69 arg: ty::GenericArg<'tcx>,
72 traits::ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc));
73 // for a type to be WF, we do not need to check if const trait predicates satisfy.
74 let param_env = self.param_env.without_const();
75 self.ocx.register_obligation(traits::Obligation::new(
78 ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)).to_predicate(self.tcx()),
83 pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
86 body_def_id: LocalDefId,
89 F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>),
91 let param_env = tcx.param_env(body_def_id);
92 let body_id = tcx.hir().local_def_id_to_hir_id(body_def_id);
93 tcx.infer_ctxt().enter(|ref infcx| {
94 let ocx = ObligationCtxt::new(infcx);
96 let assumed_wf_types = ocx.assumed_wf_types(param_env, span, body_def_id);
98 let mut wfcx = WfCheckingCtxt { ocx, span, body_id, param_env };
100 if !tcx.features().trivial_bounds {
101 wfcx.check_false_global_bounds()
104 let errors = wfcx.select_all_or_error();
105 if !errors.is_empty() {
106 infcx.report_fulfillment_errors(&errors, None, false);
110 let implied_bounds = infcx.implied_bounds_tys(param_env, body_id, assumed_wf_types);
111 let outlives_environment =
112 OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds);
114 infcx.check_region_obligations_and_report_errors(body_def_id, &outlives_environment);
118 fn check_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
119 let node = tcx.hir().expect_owner(def_id);
121 hir::OwnerNode::Crate(_) => {}
122 hir::OwnerNode::Item(item) => check_item(tcx, item),
123 hir::OwnerNode::TraitItem(item) => check_trait_item(tcx, item),
124 hir::OwnerNode::ImplItem(item) => check_impl_item(tcx, item),
125 hir::OwnerNode::ForeignItem(item) => check_foreign_item(tcx, item),
128 if let Some(generics) = node.generics() {
129 for param in generics.params {
130 check_param_wf(tcx, param)
135 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
136 /// well-formed, meaning that they do not require any constraints not declared in the struct
137 /// definition itself. For example, this definition would be illegal:
140 /// struct Ref<'a, T> { x: &'a T }
143 /// because the type did not declare that `T:'a`.
145 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
146 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
148 #[instrument(skip(tcx), level = "debug")]
149 fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
150 let def_id = item.def_id;
154 item.name = ? tcx.def_path_str(def_id.to_def_id())
158 // Right now we check that every default trait implementation
159 // has an implementation of itself. Basically, a case like:
161 // impl Trait for T {}
163 // has a requirement of `T: Trait` which was required for default
164 // method implementations. Although this could be improved now that
165 // there's a better infrastructure in place for this, it's being left
166 // for a follow-up work.
168 // Since there's such a requirement, we need to check *just* positive
169 // implementations, otherwise things like:
171 // impl !Send for T {}
173 // won't be allowed unless there's an *explicit* implementation of `Send`
175 hir::ItemKind::Impl(ref impl_) => {
177 .impl_trait_ref(item.def_id)
178 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
179 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
180 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
182 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
183 err.span_labels(impl_.defaultness_span, "default because of this");
184 err.span_label(sp, "auto trait");
187 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
188 match (tcx.impl_polarity(def_id), impl_.polarity) {
189 (ty::ImplPolarity::Positive, _) => {
190 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait, impl_.constness);
192 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
193 // FIXME(#27579): what amount of WF checking do we need for neg impls?
194 if let hir::Defaultness::Default { .. } = impl_.defaultness {
195 let mut spans = vec![span];
196 spans.extend(impl_.defaultness_span);
201 "negative impls cannot be default impls"
206 (ty::ImplPolarity::Reservation, _) => {
207 // FIXME: what amount of WF checking do we need for reservation impls?
212 hir::ItemKind::Fn(ref sig, ..) => {
213 check_item_fn(tcx, item.def_id, item.ident, item.span, sig.decl);
215 hir::ItemKind::Static(ty, ..) => {
216 check_item_type(tcx, item.def_id, ty.span, false);
218 hir::ItemKind::Const(ty, ..) => {
219 check_item_type(tcx, item.def_id, ty.span, false);
221 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
222 check_type_defn(tcx, item, false, |wfcx| vec![wfcx.non_enum_variant(struct_def)]);
224 check_variances_for_type_defn(tcx, item, ast_generics);
226 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
227 check_type_defn(tcx, item, true, |wfcx| vec![wfcx.non_enum_variant(struct_def)]);
229 check_variances_for_type_defn(tcx, item, ast_generics);
231 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
232 check_type_defn(tcx, item, true, |wfcx| wfcx.enum_variants(enum_def));
234 check_variances_for_type_defn(tcx, item, ast_generics);
236 hir::ItemKind::Trait(..) => {
237 check_trait(tcx, item);
239 hir::ItemKind::TraitAlias(..) => {
240 check_trait(tcx, item);
242 // `ForeignItem`s are handled separately.
243 hir::ItemKind::ForeignMod { .. } => {}
248 fn check_foreign_item(tcx: TyCtxt<'_>, item: &hir::ForeignItem<'_>) {
249 let def_id = item.def_id;
253 item.name = ? tcx.def_path_str(def_id.to_def_id())
257 hir::ForeignItemKind::Fn(decl, ..) => {
258 check_item_fn(tcx, item.def_id, item.ident, item.span, decl)
260 hir::ForeignItemKind::Static(ty, ..) => check_item_type(tcx, item.def_id, ty.span, true),
261 hir::ForeignItemKind::Type => (),
265 fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) {
266 let def_id = trait_item.def_id;
268 let (method_sig, span) = match trait_item.kind {
269 hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span),
270 hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span),
271 _ => (None, trait_item.span),
273 check_object_unsafe_self_trait_by_name(tcx, trait_item);
274 check_associated_item(tcx, trait_item.def_id, span, method_sig);
276 let encl_trait_def_id = tcx.local_parent(def_id);
277 let encl_trait = tcx.hir().expect_item(encl_trait_def_id);
278 let encl_trait_def_id = encl_trait.def_id.to_def_id();
279 let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() {
281 } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() {
287 if let (Some(fn_lang_item_name), "call") =
288 (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str())
290 // We are looking at the `call` function of the `fn` or `fn_mut` lang item.
291 // Do some rudimentary sanity checking to avoid an ICE later (issue #83471).
292 if let Some(hir::FnSig { decl, span, .. }) = method_sig {
293 if let [self_ty, _] = decl.inputs {
294 if !matches!(self_ty.kind, hir::TyKind::Rptr(_, _)) {
299 "first argument of `call` in `{fn_lang_item_name}` lang item must be a reference",
309 "`call` function in `{fn_lang_item_name}` lang item takes exactly two arguments",
319 "`call` trait item in `{fn_lang_item_name}` lang item must be a function",
327 /// Require that the user writes where clauses on GATs for the implicit
328 /// outlives bounds involving trait parameters in trait functions and
329 /// lifetimes passed as GAT substs. See `self-outlives-lint` test.
331 /// We use the following trait as an example throughout this function:
332 /// ```rust,ignore (this code fails due to this lint)
334 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
336 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
339 fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
340 // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
341 let mut required_bounds_by_item = FxHashMap::default();
343 // Loop over all GATs together, because if this lint suggests adding a where-clause bound
344 // to one GAT, it might then require us to an additional bound on another GAT.
345 // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which
346 // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between
349 let mut should_continue = false;
350 for gat_item in associated_items {
351 let gat_def_id = gat_item.id.def_id;
352 let gat_item = tcx.associated_item(gat_def_id);
353 // If this item is not an assoc ty, or has no substs, then it's not a GAT
354 if gat_item.kind != ty::AssocKind::Type {
357 let gat_generics = tcx.generics_of(gat_def_id);
358 // FIXME(jackh726): we can also warn in the more general case
359 if gat_generics.params.is_empty() {
363 // Gather the bounds with which all other items inside of this trait constrain the GAT.
364 // This is calculated by taking the intersection of the bounds that each item
365 // constrains the GAT with individually.
366 let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
367 for item in associated_items {
368 let item_def_id = item.id.def_id;
369 // Skip our own GAT, since it does not constrain itself at all.
370 if item_def_id == gat_def_id {
374 let item_hir_id = item.id.hir_id();
375 let param_env = tcx.param_env(item_def_id);
377 let item_required_bounds = match item.kind {
378 // In our example, this corresponds to `into_iter` method
379 hir::AssocItemKind::Fn { .. } => {
380 // For methods, we check the function signature's return type for any GATs
381 // to constrain. In the `into_iter` case, we see that the return type
382 // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
383 let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions(
384 item_def_id.to_def_id(),
385 tcx.fn_sig(item_def_id),
391 sig.inputs_and_output,
392 // We also assume that all of the function signature's parameter types
394 &sig.inputs().iter().copied().collect(),
399 // In our example, this corresponds to the `Iter` and `Item` associated types
400 hir::AssocItemKind::Type => {
401 // If our associated item is a GAT with missing bounds, add them to
402 // the param-env here. This allows this GAT to propagate missing bounds
404 let param_env = augment_param_env(
407 required_bounds_by_item.get(&item_def_id),
413 tcx.explicit_item_bounds(item_def_id)
416 .collect::<Vec<_>>(),
417 &FxHashSet::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);
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::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
467 !region_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
469 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
470 !ty_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
472 _ => bug!("Unexpected PredicateKind"),
474 .map(|clause| clause.to_string())
477 // We sort so that order is predictable
478 unsatisfied_bounds.sort();
480 if !unsatisfied_bounds.is_empty() {
481 let plural = pluralize!(unsatisfied_bounds.len());
482 let mut err = tcx.sess.struct_span_err(
484 &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
487 let suggestion = format!(
489 gat_item_hir.generics.add_where_or_trailing_comma(),
490 unsatisfied_bounds.join(", "),
493 gat_item_hir.generics.tail_span_for_predicate_suggestion(),
494 &format!("add the required where clause{plural}"),
496 Applicability::MachineApplicable,
500 if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
502 "{} currently required to ensure that impls have maximum flexibility",
506 "we are soliciting feedback, see issue #87479 \
507 <https://github.com/rust-lang/rust/issues/87479> \
508 for more information",
516 /// Add a new set of predicates to the caller_bounds of an existing param_env.
517 fn augment_param_env<'tcx>(
519 param_env: ty::ParamEnv<'tcx>,
520 new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
521 ) -> ty::ParamEnv<'tcx> {
522 let Some(new_predicates) = new_predicates else {
526 if new_predicates.is_empty() {
531 tcx.mk_predicates(param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()));
532 // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
533 // i.e. traits::normalize_param_env_or_error
534 ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness())
537 /// We use the following trait as an example throughout this function.
538 /// Specifically, let's assume that `to_check` here is the return type
539 /// of `into_iter`, and the GAT we are checking this for is `Iter`.
540 /// ```rust,ignore (this code fails due to this lint)
542 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
544 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
547 fn gather_gat_bounds<'tcx, T: TypeFoldable<'tcx>>(
549 param_env: ty::ParamEnv<'tcx>,
550 item_hir: hir::HirId,
552 wf_tys: &FxHashSet<Ty<'tcx>>,
553 gat_def_id: LocalDefId,
554 gat_generics: &'tcx ty::Generics,
555 ) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
556 // The bounds we that we would require from `to_check`
557 let mut bounds = FxHashSet::default();
559 let (regions, types) = GATSubstCollector::visit(gat_def_id.to_def_id(), to_check);
561 // If both regions and types are empty, then this GAT isn't in the
562 // set of types we are checking, and we shouldn't try to do clause analysis
563 // (particularly, doing so would end up with an empty set of clauses,
564 // since the current method would require none, and we take the
565 // intersection of requirements of all methods)
566 if types.is_empty() && regions.is_empty() {
570 for (region_a, region_a_idx) in ®ions {
571 // Ignore `'static` lifetimes for the purpose of this lint: it's
572 // because we know it outlives everything and so doesn't give meaningful
574 if let ty::ReStatic = **region_a {
577 // For each region argument (e.g., `'a` in our example), check for a
578 // relationship to the type arguments (e.g., `Self`). If there is an
579 // outlives relationship (`Self: 'a`), then we want to ensure that is
580 // reflected in a where clause on the GAT itself.
581 for (ty, ty_idx) in &types {
582 // In our example, requires that `Self: 'a`
583 if ty_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *ty, *region_a) {
584 debug!(?ty_idx, ?region_a_idx);
585 debug!("required clause: {ty} must outlive {region_a}");
586 // Translate into the generic parameters of the GAT. In
587 // our example, the type was `Self`, which will also be
588 // `Self` in the GAT.
589 let ty_param = gat_generics.param_at(*ty_idx, tcx);
591 .mk_ty(ty::Param(ty::ParamTy { index: ty_param.index, name: ty_param.name }));
592 // Same for the region. In our example, 'a corresponds
593 // to the 'me parameter.
594 let region_param = gat_generics.param_at(*region_a_idx, tcx);
596 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
597 def_id: region_param.def_id,
598 index: region_param.index,
599 name: region_param.name,
601 // The predicate we expect to see. (In our example,
604 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param));
605 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
606 bounds.insert(clause);
610 // For each region argument (e.g., `'a` in our example), also check for a
611 // relationship to the other region arguments. If there is an outlives
612 // relationship, then we want to ensure that is reflected in the where clause
613 // on the GAT itself.
614 for (region_b, region_b_idx) in ®ions {
615 // Again, skip `'static` because it outlives everything. Also, we trivially
616 // know that a region outlives itself.
617 if ty::ReStatic == **region_b || region_a == region_b {
620 if region_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *region_a, *region_b) {
621 debug!(?region_a_idx, ?region_b_idx);
622 debug!("required clause: {region_a} must outlive {region_b}");
623 // Translate into the generic parameters of the GAT.
624 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
626 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
627 def_id: region_a_param.def_id,
628 index: region_a_param.index,
629 name: region_a_param.name,
631 // Same for the region.
632 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
634 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
635 def_id: region_b_param.def_id,
636 index: region_b_param.index,
637 name: region_b_param.name,
639 // The predicate we expect to see.
640 let clause = ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(
644 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
645 bounds.insert(clause);
653 /// Given a known `param_env` and a set of well formed types, can we prove that
654 /// `ty` outlives `region`.
655 fn ty_known_to_outlive<'tcx>(
658 param_env: ty::ParamEnv<'tcx>,
659 wf_tys: &FxHashSet<Ty<'tcx>>,
661 region: ty::Region<'tcx>,
663 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| {
664 let origin = infer::RelateParamBound(DUMMY_SP, ty, None);
665 let outlives = &mut TypeOutlives::new(infcx, tcx, region_bound_pairs, None, param_env);
666 outlives.type_must_outlive(origin, ty, region);
670 /// Given a known `param_env` and a set of well formed types, can we prove that
671 /// `region_a` outlives `region_b`
672 fn region_known_to_outlive<'tcx>(
675 param_env: ty::ParamEnv<'tcx>,
676 wf_tys: &FxHashSet<Ty<'tcx>>,
677 region_a: ty::Region<'tcx>,
678 region_b: ty::Region<'tcx>,
680 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| {
681 use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
682 let origin = infer::RelateRegionParamBound(DUMMY_SP);
683 // `region_a: region_b` -> `region_b <= region_a`
684 infcx.push_sub_region_constraint(origin, region_b, region_a);
688 /// Given a known `param_env` and a set of well formed types, set up an
689 /// `InferCtxt`, call the passed function (to e.g. set up region constraints
690 /// to be tested), then resolve region and return errors
691 fn resolve_regions_with_wf_tys<'tcx>(
694 param_env: ty::ParamEnv<'tcx>,
695 wf_tys: &FxHashSet<Ty<'tcx>>,
696 add_constraints: impl for<'a> FnOnce(&'a InferCtxt<'a, 'tcx>, &'a RegionBoundPairs<'tcx>),
698 // Unfortunately, we have to use a new `InferCtxt` each call, because
699 // region constraints get added and solved there and we need to test each
700 // call individually.
701 tcx.infer_ctxt().enter(|infcx| {
702 let outlives_environment = OutlivesEnvironment::with_bounds(
705 infcx.implied_bounds_tys(param_env, id, wf_tys.clone()),
707 let region_bound_pairs = outlives_environment.region_bound_pairs();
709 add_constraints(&infcx, region_bound_pairs);
711 let errors = infcx.resolve_regions(&outlives_environment);
713 debug!(?errors, "errors");
715 // If we were able to prove that the type outlives the region without
716 // an error, it must be because of the implied or explicit bounds...
721 /// TypeVisitor that looks for uses of GATs like
722 /// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into
723 /// the two vectors, `regions` and `types` (depending on their kind). For each
724 /// parameter `Pi` also track the index `i`.
725 struct GATSubstCollector<'tcx> {
727 // Which region appears and which parameter index its substituted for
728 regions: FxHashSet<(ty::Region<'tcx>, usize)>,
729 // Which params appears and which parameter index its substituted for
730 types: FxHashSet<(Ty<'tcx>, usize)>,
733 impl<'tcx> GATSubstCollector<'tcx> {
734 fn visit<T: TypeFoldable<'tcx>>(
737 ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) {
739 GATSubstCollector { gat, regions: FxHashSet::default(), types: FxHashSet::default() };
740 t.visit_with(&mut visitor);
741 (visitor.regions, visitor.types)
745 impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
748 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
750 ty::Projection(p) if p.item_def_id == self.gat => {
751 for (idx, subst) in p.substs.iter().enumerate() {
752 match subst.unpack() {
753 GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => {
754 self.regions.insert((lt, idx));
756 GenericArgKind::Type(t) => {
757 self.types.insert((t, idx));
765 t.super_visit_with(self)
769 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
771 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
772 [s] => s.res.opt_def_id() == Some(trait_def_id.to_def_id()),
779 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
780 /// When this is done, suggest using `Self` instead.
781 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
782 let (trait_name, trait_def_id) =
783 match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id())) {
784 hir::Node::Item(item) => match item.kind {
785 hir::ItemKind::Trait(..) => (item.ident, item.def_id),
790 let mut trait_should_be_self = vec![];
792 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
793 if could_be_self(trait_def_id, ty) =>
795 trait_should_be_self.push(ty.span)
797 hir::TraitItemKind::Fn(sig, _) => {
798 for ty in sig.decl.inputs {
799 if could_be_self(trait_def_id, ty) {
800 trait_should_be_self.push(ty.span);
803 match sig.decl.output {
804 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
805 trait_should_be_self.push(ty.span);
812 if !trait_should_be_self.is_empty() {
813 if tcx.object_safety_violations(trait_def_id).is_empty() {
816 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
819 trait_should_be_self,
820 "associated item referring to unboxed trait object for its own trait",
822 .span_label(trait_name.span, "in this trait")
823 .multipart_suggestion(
824 "you might have meant to use `Self` to refer to the implementing type",
826 Applicability::MachineApplicable,
832 fn check_impl_item(tcx: TyCtxt<'_>, impl_item: &hir::ImplItem<'_>) {
833 let def_id = impl_item.def_id;
835 let (method_sig, span) = match impl_item.kind {
836 hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span),
837 // Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`.
838 hir::ImplItemKind::TyAlias(ty) if ty.span != DUMMY_SP => (None, ty.span),
839 _ => (None, impl_item.span),
842 check_associated_item(tcx, def_id, span, method_sig);
845 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
847 // We currently only check wf of const params here.
848 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
850 // Const parameters are well formed if their type is structural match.
851 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
852 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
854 if tcx.features().adt_const_params {
855 if let Some(non_structural_match_ty) =
856 traits::search_for_adt_const_param_violation(param.span, tcx, ty)
858 // We use the same error code in both branches, because this is really the same
859 // issue: we just special-case the message for type parameters to make it
861 match non_structural_match_ty.kind() {
863 // Const parameters may not have type parameters as their types,
864 // because we cannot be sure that the type parameter derives `PartialEq`
865 // and `Eq` (just implementing them is not enough for `structural_match`).
870 "`{ty}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
871 used as the type of a const parameter",
875 format!("`{ty}` may not derive both `PartialEq` and `Eq`"),
878 "it is not currently possible to use a type parameter as the type of a \
888 "`{ty}` is forbidden as the type of a const generic parameter",
890 .note("floats do not derive `Eq` or `Ord`, which are required for const parameters")
898 "using function pointers as const generic parameters is forbidden",
907 "using raw pointers as const generic parameters is forbidden",
912 let mut diag = struct_span_err!(
916 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
917 the type of a const parameter",
918 non_structural_match_ty,
921 if ty == non_structural_match_ty {
924 format!("`{ty}` doesn't derive both `PartialEq` and `Eq`"),
934 let mut is_ptr = true;
936 let err = match ty.kind() {
937 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
938 ty::FnPtr(_) => Some("function pointers"),
939 ty::RawPtr(_) => Some("raw pointers"),
942 err_ty_str = format!("`{ty}`");
943 Some(err_ty_str.as_str())
947 if let Some(unsupported_type) = err {
952 "using {unsupported_type} as const generic parameters is forbidden",
956 let mut err = tcx.sess.struct_span_err(
959 "{unsupported_type} is forbidden as the type of a const generic parameter",
962 err.note("the only supported types are integers, `bool` and `char`");
963 if tcx.sess.is_nightly_build() {
965 "more complex types are supported with `#![feature(adt_const_params)]`",
976 #[instrument(level = "debug", skip(tcx, span, sig_if_method))]
977 fn check_associated_item(
981 sig_if_method: Option<&hir::FnSig<'_>>,
983 let loc = Some(WellFormedLoc::Ty(item_id));
984 enter_wf_checking_ctxt(tcx, span, item_id, |wfcx| {
985 let item = tcx.associated_item(item_id);
987 let self_ty = match item.container {
988 ty::TraitContainer => tcx.types.self_param,
989 ty::ImplContainer => tcx.type_of(item.container_id(tcx)),
993 ty::AssocKind::Const => {
994 let ty = tcx.type_of(item.def_id);
995 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
996 wfcx.register_wf_obligation(span, loc, ty.into());
998 ty::AssocKind::Fn => {
999 let sig = tcx.fn_sig(item.def_id);
1000 let hir_sig = sig_if_method.expect("bad signature for method");
1003 item.ident(tcx).span,
1006 item.def_id.expect_local(),
1008 check_method_receiver(wfcx, hir_sig, item, self_ty);
1010 ty::AssocKind::Type => {
1011 if let ty::AssocItemContainer::TraitContainer = item.container {
1012 check_associated_type_bounds(wfcx, item, span)
1014 if item.defaultness(tcx).has_value() {
1015 let ty = tcx.type_of(item.def_id);
1016 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
1017 wfcx.register_wf_obligation(span, loc, ty.into());
1024 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
1026 ItemKind::Struct(..) => Some(AdtKind::Struct),
1027 ItemKind::Union(..) => Some(AdtKind::Union),
1028 ItemKind::Enum(..) => Some(AdtKind::Enum),
1033 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
1034 fn check_type_defn<'tcx, F>(
1036 item: &hir::Item<'tcx>,
1038 mut lookup_fields: F,
1040 F: FnMut(&WfCheckingCtxt<'_, 'tcx>) -> Vec<AdtVariant<'tcx>>,
1042 enter_wf_checking_ctxt(tcx, item.span, item.def_id, |wfcx| {
1043 let variants = lookup_fields(wfcx);
1044 let packed = tcx.adt_def(item.def_id).repr().packed();
1046 for variant in &variants {
1047 // All field types must be well-formed.
1048 for field in &variant.fields {
1049 wfcx.register_wf_obligation(
1051 Some(WellFormedLoc::Ty(field.def_id)),
1056 // For DST, or when drop needs to copy things around, all
1057 // intermediate types must be sized.
1058 let needs_drop_copy = || {
1060 let ty = variant.fields.last().unwrap().ty;
1061 let ty = tcx.erase_regions(ty);
1062 if ty.needs_infer() {
1064 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
1065 // Just treat unresolved type expression as if it needs drop.
1068 ty.needs_drop(tcx, tcx.param_env(item.def_id))
1072 // All fields (except for possibly the last) should be sized.
1073 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
1074 let unsized_len = if all_sized { 0 } else { 1 };
1076 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
1078 let last = idx == variant.fields.len() - 1;
1079 wfcx.register_bound(
1080 traits::ObligationCause::new(
1083 traits::FieldSized {
1084 adt_kind: match item_adt_kind(&item.kind) {
1094 tcx.require_lang_item(LangItem::Sized, None),
1098 // Explicit `enum` discriminant values must const-evaluate successfully.
1099 if let Some(discr_def_id) = variant.explicit_discr {
1100 let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());
1102 let cause = traits::ObligationCause::new(
1103 tcx.def_span(discr_def_id),
1105 traits::MiscObligation,
1107 wfcx.register_obligation(traits::Obligation::new(
1110 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ty::Unevaluated::new(
1111 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
1119 check_where_clauses(wfcx, item.span, item.def_id);
1123 #[instrument(skip(tcx, item))]
1124 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
1125 debug!(?item.def_id);
1127 let trait_def = tcx.trait_def(item.def_id);
1128 if trait_def.is_marker
1129 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
1131 for associated_def_id in &*tcx.associated_item_def_ids(item.def_id) {
1134 tcx.def_span(*associated_def_id),
1136 "marker traits cannot have associated items",
1142 enter_wf_checking_ctxt(tcx, item.span, item.def_id, |wfcx| {
1143 check_where_clauses(wfcx, item.span, item.def_id)
1146 // Only check traits, don't check trait aliases
1147 if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
1148 check_gat_where_clauses(tcx, items);
1152 /// Checks all associated type defaults of trait `trait_def_id`.
1154 /// Assuming the defaults are used, check that all predicates (bounds on the
1155 /// assoc type and where clauses on the trait) hold.
1156 fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
1157 let bounds = wfcx.tcx().explicit_item_bounds(item.def_id);
1159 debug!("check_associated_type_bounds: bounds={:?}", bounds);
1160 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1161 let normalized_bound = wfcx.normalize(span, None, bound);
1162 traits::wf::predicate_obligations(
1171 wfcx.register_obligations(wf_obligations);
1179 decl: &hir::FnDecl<'_>,
1181 enter_wf_checking_ctxt(tcx, span, def_id, |wfcx| {
1182 let sig = tcx.fn_sig(def_id);
1183 check_fn_or_method(wfcx, ident.span, sig, decl, def_id);
1187 fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) {
1188 debug!("check_item_type: {:?}", item_id);
1190 enter_wf_checking_ctxt(tcx, ty_span, item_id, |wfcx| {
1191 let ty = tcx.type_of(item_id);
1192 let item_ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(item_id)), ty);
1194 let mut forbid_unsized = true;
1195 if allow_foreign_ty {
1196 let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env);
1197 if let ty::Foreign(_) = tail.kind() {
1198 forbid_unsized = false;
1202 wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(item_id)), item_ty.into());
1204 wfcx.register_bound(
1205 traits::ObligationCause::new(ty_span, wfcx.body_id, traits::WellFormed(None)),
1208 tcx.require_lang_item(LangItem::Sized, None),
1212 // Ensure that the end result is `Sync` in a non-thread local `static`.
1213 let should_check_for_sync = tcx.static_mutability(item_id.to_def_id())
1214 == Some(hir::Mutability::Not)
1215 && !tcx.is_foreign_item(item_id.to_def_id())
1216 && !tcx.is_thread_local_static(item_id.to_def_id());
1218 if should_check_for_sync {
1219 wfcx.register_bound(
1220 traits::ObligationCause::new(ty_span, wfcx.body_id, traits::SharedStatic),
1223 tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
1229 #[instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))]
1230 fn check_impl<'tcx>(
1232 item: &'tcx hir::Item<'tcx>,
1233 ast_self_ty: &hir::Ty<'_>,
1234 ast_trait_ref: &Option<hir::TraitRef<'_>>,
1235 constness: hir::Constness,
1237 enter_wf_checking_ctxt(tcx, item.span, item.def_id, |wfcx| {
1238 match *ast_trait_ref {
1239 Some(ref ast_trait_ref) => {
1240 // `#[rustc_reservation_impl]` impls are not real impls and
1241 // therefore don't need to be WF (the trait's `Self: Trait` predicate
1243 let trait_ref = tcx.impl_trait_ref(item.def_id).unwrap();
1244 let trait_ref = wfcx.normalize(ast_trait_ref.path.span, None, trait_ref);
1245 let trait_pred = ty::TraitPredicate {
1247 constness: match constness {
1248 hir::Constness::Const => ty::BoundConstness::ConstIfConst,
1249 hir::Constness::NotConst => ty::BoundConstness::NotConst,
1251 polarity: ty::ImplPolarity::Positive,
1253 let obligations = traits::wf::trait_obligations(
1258 ast_trait_ref.path.span,
1261 debug!(?obligations);
1262 wfcx.register_obligations(obligations);
1265 let self_ty = tcx.type_of(item.def_id);
1266 let self_ty = wfcx.normalize(
1268 Some(WellFormedLoc::Ty(item.hir_id().expect_owner())),
1271 wfcx.register_wf_obligation(
1273 Some(WellFormedLoc::Ty(item.hir_id().expect_owner())),
1279 check_where_clauses(wfcx, item.span, item.def_id);
1283 /// Checks where-clauses and inline bounds that are declared on `def_id`.
1284 #[instrument(level = "debug", skip(wfcx))]
1285 fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id: LocalDefId) {
1286 let infcx = wfcx.infcx;
1287 let tcx = wfcx.tcx();
1289 let predicates = tcx.bound_predicates_of(def_id.to_def_id());
1290 let generics = tcx.generics_of(def_id);
1292 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
1293 GenericParamDefKind::Type { has_default, .. }
1294 | GenericParamDefKind::Const { has_default } => {
1295 has_default && def.index >= generics.parent_count as u32
1297 GenericParamDefKind::Lifetime => unreachable!(),
1300 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
1301 // For example, this forbids the declaration:
1303 // struct Foo<T = Vec<[u32]>> { .. }
1305 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
1306 for param in &generics.params {
1308 GenericParamDefKind::Type { .. } => {
1309 if is_our_default(param) {
1310 let ty = tcx.type_of(param.def_id);
1311 // Ignore dependent defaults -- that is, where the default of one type
1312 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
1313 // be sure if it will error or not as user might always specify the other.
1314 if !ty.needs_subst() {
1315 wfcx.register_wf_obligation(
1316 tcx.def_span(param.def_id),
1317 Some(WellFormedLoc::Ty(param.def_id.expect_local())),
1323 GenericParamDefKind::Const { .. } => {
1324 if is_our_default(param) {
1325 // FIXME(const_generics_defaults): This
1326 // is incorrect when dealing with unused substs, for example
1327 // for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
1328 // we should eagerly error.
1329 let default_ct = tcx.const_param_default(param.def_id);
1330 if !default_ct.needs_subst() {
1331 wfcx.register_wf_obligation(
1332 tcx.def_span(param.def_id),
1339 // Doesn't have defaults.
1340 GenericParamDefKind::Lifetime => {}
1344 // Check that trait predicates are WF when params are substituted by their defaults.
1345 // We don't want to overly constrain the predicates that may be written but we want to
1346 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
1347 // Therefore we check if a predicate which contains a single type param
1348 // with a concrete default is WF with that default substituted.
1349 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
1351 // First we build the defaulted substitution.
1352 let substs = InternalSubsts::for_item(tcx, def_id.to_def_id(), |param, _| {
1354 GenericParamDefKind::Lifetime => {
1355 // All regions are identity.
1356 tcx.mk_param_from_def(param)
1359 GenericParamDefKind::Type { .. } => {
1360 // If the param has a default, ...
1361 if is_our_default(param) {
1362 let default_ty = tcx.type_of(param.def_id);
1363 // ... and it's not a dependent default, ...
1364 if !default_ty.needs_subst() {
1365 // ... then substitute it with the default.
1366 return default_ty.into();
1370 tcx.mk_param_from_def(param)
1372 GenericParamDefKind::Const { .. } => {
1373 // If the param has a default, ...
1374 if is_our_default(param) {
1375 let default_ct = tcx.const_param_default(param.def_id);
1376 // ... and it's not a dependent default, ...
1377 if !default_ct.needs_subst() {
1378 // ... then substitute it with the default.
1379 return default_ct.into();
1383 tcx.mk_param_from_def(param)
1388 // Now we build the substituted predicates.
1389 let default_obligations = predicates
1393 .flat_map(|&(pred, sp)| {
1395 struct CountParams {
1396 params: FxHashSet<u32>,
1398 impl<'tcx> ty::visit::TypeVisitor<'tcx> for CountParams {
1401 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1402 if let ty::Param(param) = t.kind() {
1403 self.params.insert(param.index);
1405 t.super_visit_with(self)
1408 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1412 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1413 if let ty::ConstKind::Param(param) = c.kind() {
1414 self.params.insert(param.index);
1416 c.super_visit_with(self)
1419 let mut param_count = CountParams::default();
1420 let has_region = pred.visit_with(&mut param_count).is_break();
1421 let substituted_pred = predicates.rebind(pred).subst(tcx, substs);
1422 // Don't check non-defaulted params, dependent defaults (including lifetimes)
1423 // or preds with multiple params.
1424 if substituted_pred.has_param_types_or_consts()
1425 || param_count.params.len() > 1
1429 } else if predicates.0.predicates.iter().any(|&(p, _)| p == substituted_pred) {
1430 // Avoid duplication of predicates that contain no parameters, for example.
1433 Some((substituted_pred, sp))
1437 // Convert each of those into an obligation. So if you have
1438 // something like `struct Foo<T: Copy = String>`, we would
1439 // take that predicate `T: Copy`, substitute to `String: Copy`
1440 // (actually that happens in the previous `flat_map` call),
1441 // and then try to prove it (in this case, we'll fail).
1443 // Note the subtle difference from how we handle `predicates`
1444 // below: there, we are not trying to prove those predicates
1445 // to be *true* but merely *well-formed*.
1446 let pred = wfcx.normalize(sp, None, pred);
1447 let cause = traits::ObligationCause::new(
1450 traits::ItemObligation(def_id.to_def_id()),
1452 traits::Obligation::new(cause, wfcx.param_env, pred)
1455 let predicates = predicates.0.instantiate_identity(tcx);
1457 let predicates = wfcx.normalize(span, None, predicates);
1459 debug!(?predicates.predicates);
1460 assert_eq!(predicates.predicates.len(), predicates.spans.len());
1461 let wf_obligations =
1462 iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| {
1463 traits::wf::predicate_obligations(
1465 wfcx.param_env.without_const(),
1472 let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect();
1473 wfcx.register_obligations(obligations);
1476 #[instrument(level = "debug", skip(wfcx, span, hir_decl))]
1477 fn check_fn_or_method<'tcx>(
1478 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1480 sig: ty::PolyFnSig<'tcx>,
1481 hir_decl: &hir::FnDecl<'_>,
1484 let tcx = wfcx.tcx();
1485 let sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
1487 // Normalize the input and output types one at a time, using a different
1488 // `WellFormedLoc` for each. We cannot call `normalize_associated_types`
1489 // on the entire `FnSig`, since this would use the same `WellFormedLoc`
1490 // for each type, preventing the HIR wf check from generating
1491 // a nice error message.
1492 let ty::FnSig { mut inputs_and_output, c_variadic, unsafety, abi } = sig;
1493 inputs_and_output = tcx.mk_type_list(inputs_and_output.iter().enumerate().map(|(i, ty)| {
1496 Some(WellFormedLoc::Param {
1498 // Note that the `param_idx` of the output type is
1499 // one greater than the index of the last input type.
1500 param_idx: i.try_into().unwrap(),
1505 // Manually call `normalize_associated_types_in` on the other types
1506 // in `FnSig`. This ensures that if the types of these fields
1507 // ever change to include projections, we will start normalizing
1508 // them automatically.
1509 let sig = ty::FnSig {
1511 c_variadic: wfcx.normalize(span, None, c_variadic),
1512 unsafety: wfcx.normalize(span, None, unsafety),
1513 abi: wfcx.normalize(span, None, abi),
1516 for (i, (&input_ty, ty)) in iter::zip(sig.inputs(), hir_decl.inputs).enumerate() {
1517 wfcx.register_wf_obligation(
1519 Some(WellFormedLoc::Param { function: def_id, param_idx: i.try_into().unwrap() }),
1524 wfcx.register_wf_obligation(
1525 hir_decl.output.span(),
1526 Some(WellFormedLoc::Param {
1528 param_idx: sig.inputs().len().try_into().unwrap(),
1530 sig.output().into(),
1533 check_where_clauses(wfcx, span, def_id);
1535 check_return_position_impl_trait_in_trait_bounds(
1540 hir_decl.output.span(),
1544 /// Basically `check_associated_type_bounds`, but separated for now and should be
1545 /// deduplicated when RPITITs get lowered into real associated items.
1546 fn check_return_position_impl_trait_in_trait_bounds<'tcx>(
1548 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1549 fn_def_id: LocalDefId,
1550 fn_output: Ty<'tcx>,
1553 if let Some(assoc_item) = tcx.opt_associated_item(fn_def_id.to_def_id())
1554 && assoc_item.container == ty::AssocItemContainer::TraitContainer
1556 for arg in fn_output.walk() {
1557 if let ty::GenericArgKind::Type(ty) = arg.unpack()
1558 && let ty::Projection(proj) = ty.kind()
1559 && tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
1560 && tcx.impl_trait_in_trait_parent(proj.item_def_id) == fn_def_id.to_def_id()
1562 let bounds = wfcx.tcx().explicit_item_bounds(proj.item_def_id);
1563 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1564 let normalized_bound = wfcx.normalize(span, None, bound);
1565 traits::wf::predicate_obligations(
1573 wfcx.register_obligations(wf_obligations);
1579 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1580 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1581 of the previous types except `Self`)";
1583 #[instrument(level = "debug", skip(wfcx))]
1584 fn check_method_receiver<'tcx>(
1585 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1586 fn_sig: &hir::FnSig<'_>,
1587 method: &ty::AssocItem,
1590 let tcx = wfcx.tcx();
1592 if !method.fn_has_self_parameter {
1596 let span = fn_sig.decl.inputs[0].span;
1598 let sig = tcx.fn_sig(method.def_id);
1599 let sig = tcx.liberate_late_bound_regions(method.def_id, sig);
1600 let sig = wfcx.normalize(span, None, sig);
1602 debug!("check_method_receiver: sig={:?}", sig);
1604 let self_ty = wfcx.normalize(span, None, self_ty);
1606 let receiver_ty = sig.inputs()[0];
1607 let receiver_ty = wfcx.normalize(span, None, receiver_ty);
1609 if tcx.features().arbitrary_self_types {
1610 if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
1611 // Report error; `arbitrary_self_types` was enabled.
1612 e0307(tcx, span, receiver_ty);
1615 if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, false) {
1616 if receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
1617 // Report error; would have worked with `arbitrary_self_types`.
1619 &tcx.sess.parse_sess,
1620 sym::arbitrary_self_types,
1623 "`{receiver_ty}` cannot be used as the type of `self` without \
1624 the `arbitrary_self_types` feature",
1627 .help(HELP_FOR_SELF_TYPE)
1630 // Report error; would not have worked with `arbitrary_self_types`.
1631 e0307(tcx, span, receiver_ty);
1637 fn e0307<'tcx>(tcx: TyCtxt<'tcx>, span: Span, receiver_ty: Ty<'_>) {
1639 tcx.sess.diagnostic(),
1642 "invalid `self` parameter type: {receiver_ty}"
1644 .note("type of `self` must be `Self` or a type that dereferences to it")
1645 .help(HELP_FOR_SELF_TYPE)
1649 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1650 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1651 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1652 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1653 /// `Deref<Target = self_ty>`.
1655 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1656 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1657 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1658 fn receiver_is_valid<'tcx>(
1659 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1661 receiver_ty: Ty<'tcx>,
1663 arbitrary_self_types_enabled: bool,
1665 let infcx = wfcx.infcx;
1666 let tcx = wfcx.tcx();
1668 ObligationCause::new(span, wfcx.body_id, traits::ObligationCauseCode::MethodReceiver);
1670 let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty).is_ok();
1672 // `self: Self` is always valid.
1673 if can_eq_self(receiver_ty) {
1674 if let Err(err) = wfcx.equate_types(&cause, wfcx.param_env, self_ty, receiver_ty) {
1675 infcx.report_mismatched_types(&cause, self_ty, receiver_ty, err).emit();
1681 Autoderef::new(infcx, wfcx.param_env, wfcx.body_id, span, receiver_ty, span);
1683 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1684 if arbitrary_self_types_enabled {
1685 autoderef = autoderef.include_raw_pointers();
1688 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1691 let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, None);
1693 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1695 if let Some((potential_self_ty, _)) = autoderef.next() {
1697 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1698 potential_self_ty, self_ty
1701 if can_eq_self(potential_self_ty) {
1702 wfcx.register_obligations(autoderef.into_obligations());
1705 wfcx.equate_types(&cause, wfcx.param_env, self_ty, potential_self_ty)
1707 infcx.report_mismatched_types(&cause, self_ty, potential_self_ty, err).emit();
1712 // Without `feature(arbitrary_self_types)`, we require that each step in the
1713 // deref chain implement `receiver`
1714 if !arbitrary_self_types_enabled
1715 && !receiver_is_implemented(
1717 receiver_trait_def_id,
1726 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1727 // If the receiver already has errors reported due to it, consider it valid to avoid
1728 // unnecessary errors (#58712).
1729 return receiver_ty.references_error();
1733 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1734 if !arbitrary_self_types_enabled
1735 && !receiver_is_implemented(wfcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1743 fn receiver_is_implemented<'tcx>(
1744 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1745 receiver_trait_def_id: DefId,
1746 cause: ObligationCause<'tcx>,
1747 receiver_ty: Ty<'tcx>,
1749 let tcx = wfcx.tcx();
1750 let trait_ref = ty::Binder::dummy(ty::TraitRef {
1751 def_id: receiver_trait_def_id,
1752 substs: tcx.mk_substs_trait(receiver_ty, &[]),
1756 traits::Obligation::new(cause, wfcx.param_env, trait_ref.without_const().to_predicate(tcx));
1758 if wfcx.infcx.predicate_must_hold_modulo_regions(&obligation) {
1762 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1769 fn check_variances_for_type_defn<'tcx>(
1771 item: &hir::Item<'tcx>,
1772 hir_generics: &hir::Generics<'_>,
1774 let ty = tcx.type_of(item.def_id);
1775 if tcx.has_error_field(ty) {
1779 let ty_predicates = tcx.predicates_of(item.def_id);
1780 assert_eq!(ty_predicates.parent, None);
1781 let variances = tcx.variances_of(item.def_id);
1783 let mut constrained_parameters: FxHashSet<_> = variances
1786 .filter(|&(_, &variance)| variance != ty::Bivariant)
1787 .map(|(index, _)| Parameter(index as u32))
1790 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1792 // Lazily calculated because it is only needed in case of an error.
1793 let explicitly_bounded_params = LazyCell::new(|| {
1794 let icx = crate::collect::ItemCtxt::new(tcx, item.def_id.to_def_id());
1798 .filter_map(|predicate| match predicate {
1799 hir::WherePredicate::BoundPredicate(predicate) => {
1800 match icx.to_ty(predicate.bounded_ty).kind() {
1801 ty::Param(data) => Some(Parameter(data.index)),
1807 .collect::<FxHashSet<_>>()
1810 for (index, _) in variances.iter().enumerate() {
1811 let parameter = Parameter(index as u32);
1813 if constrained_parameters.contains(¶meter) {
1817 let param = &hir_generics.params[index];
1820 hir::ParamName::Error => {}
1822 let has_explicit_bounds = explicitly_bounded_params.contains(¶meter);
1823 report_bivariance(tcx, param, has_explicit_bounds);
1829 fn report_bivariance(
1831 param: &rustc_hir::GenericParam<'_>,
1832 has_explicit_bounds: bool,
1833 ) -> ErrorGuaranteed {
1834 let span = param.span;
1835 let param_name = param.name.ident().name;
1836 let mut err = error_392(tcx, span, param_name);
1838 let suggested_marker_id = tcx.lang_items().phantom_data();
1839 // Help is available only in presence of lang items.
1840 let msg = if let Some(def_id) = suggested_marker_id {
1842 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1844 tcx.def_path_str(def_id),
1847 format!("consider removing `{param_name}` or referring to it in a field")
1851 if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds {
1853 "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
1860 impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
1861 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1863 #[instrument(level = "debug", skip(self))]
1864 fn check_false_global_bounds(&mut self) {
1865 let tcx = self.ocx.infcx.tcx;
1866 let mut span = self.span;
1867 let empty_env = ty::ParamEnv::empty();
1869 let def_id = tcx.hir().local_def_id(self.body_id);
1870 let predicates_with_span = tcx.predicates_of(def_id).predicates.iter().copied();
1871 // Check elaborated bounds.
1872 let implied_obligations = traits::elaborate_predicates_with_span(tcx, predicates_with_span);
1874 for obligation in implied_obligations {
1875 // We lower empty bounds like `Vec<dyn Copy>:` as
1876 // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
1877 // regular WF checking
1878 if let ty::PredicateKind::WellFormed(..) = obligation.predicate.kind().skip_binder() {
1881 let pred = obligation.predicate;
1882 // Match the existing behavior.
1883 if pred.is_global() && !pred.has_late_bound_regions() {
1884 let pred = self.normalize(span, None, pred);
1885 let hir_node = tcx.hir().find(self.body_id);
1887 // only use the span of the predicate clause (#90869)
1889 if let Some(hir::Generics { predicates, .. }) =
1890 hir_node.and_then(|node| node.generics())
1892 let obligation_span = obligation.cause.span();
1896 // There seems to be no better way to find out which predicate we are in
1897 .find(|pred| pred.span().contains(obligation_span))
1898 .map(|pred| pred.span())
1899 .unwrap_or(obligation_span);
1902 let obligation = traits::Obligation::new(
1903 traits::ObligationCause::new(span, self.body_id, traits::TrivialBound),
1907 self.ocx.register_obligation(obligation);
1913 fn check_mod_type_wf(tcx: TyCtxt<'_>, module: LocalDefId) {
1914 let items = tcx.hir_module_items(module);
1915 items.par_items(|item| tcx.ensure().check_well_formed(item.def_id));
1916 items.par_impl_items(|item| tcx.ensure().check_well_formed(item.def_id));
1917 items.par_trait_items(|item| tcx.ensure().check_well_formed(item.def_id));
1918 items.par_foreign_items(|item| tcx.ensure().check_well_formed(item.def_id));
1921 ///////////////////////////////////////////////////////////////////////////
1924 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1925 struct AdtVariant<'tcx> {
1926 /// Types of fields in the variant, that must be well-formed.
1927 fields: Vec<AdtField<'tcx>>,
1929 /// Explicit discriminant of this variant (e.g. `A = 123`),
1930 /// that must evaluate to a constant value.
1931 explicit_discr: Option<LocalDefId>,
1934 struct AdtField<'tcx> {
1940 impl<'a, 'tcx> WfCheckingCtxt<'a, 'tcx> {
1941 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1942 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1943 let fields = struct_def
1947 let def_id = self.tcx().hir().local_def_id(field.hir_id);
1948 let field_ty = self.tcx().type_of(def_id);
1949 let field_ty = self.normalize(field.ty.span, None, field_ty);
1950 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1951 AdtField { ty: field_ty, span: field.ty.span, def_id }
1954 AdtVariant { fields, explicit_discr: None }
1957 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1961 .map(|variant| AdtVariant {
1962 fields: self.non_enum_variant(&variant.data).fields,
1963 explicit_discr: variant
1965 .map(|explicit_discr| self.tcx().hir().local_def_id(explicit_discr.hir_id)),
1975 ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
1976 let mut err = struct_span_err!(tcx.sess, span, E0392, "parameter `{param_name}` is never used");
1977 err.span_label(span, "unused parameter");
1981 pub fn provide(providers: &mut Providers) {
1982 *providers = Providers { check_mod_type_wf, check_well_formed, ..*providers };