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::mir::ConstraintCategory;
14 use rustc_middle::ty::query::Providers;
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_middle::ty::{GenericArgKind, InternalSubsts};
21 use rustc_session::parse::feature_err;
22 use rustc_span::symbol::{sym, Ident, Symbol};
23 use rustc_span::{Span, DUMMY_SP};
24 use rustc_trait_selection::autoderef::Autoderef;
25 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
26 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
27 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
28 use rustc_trait_selection::traits::{
29 self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc,
32 use std::cell::LazyCell;
33 use std::convert::TryInto;
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 fn normalize<T>(&self, span: Span, loc: Option<WellFormedLoc>, value: T) -> T
57 T: TypeFoldable<'tcx>,
60 ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc)),
66 fn register_wf_obligation(
69 loc: Option<WellFormedLoc>,
70 arg: ty::GenericArg<'tcx>,
73 traits::ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc));
74 // for a type to be WF, we do not need to check if const trait predicates satisfy.
75 let param_env = self.param_env.without_const();
76 self.ocx.register_obligation(traits::Obligation::new(
79 ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)).to_predicate(self.tcx()),
84 pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
87 body_def_id: LocalDefId,
90 F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>),
92 let param_env = tcx.param_env(body_def_id);
93 let body_id = tcx.hir().local_def_id_to_hir_id(body_def_id);
94 tcx.infer_ctxt().enter(|ref infcx| {
95 let ocx = ObligationCtxt::new(infcx);
97 let assumed_wf_types = ocx.assumed_wf_types(param_env, span, body_def_id);
99 let mut wfcx = WfCheckingCtxt { ocx, span, body_id, param_env };
101 if !tcx.features().trivial_bounds {
102 wfcx.check_false_global_bounds()
105 let errors = wfcx.select_all_or_error();
106 if !errors.is_empty() {
107 infcx.report_fulfillment_errors(&errors, None, false);
111 let implied_bounds = infcx.implied_bounds_tys(param_env, body_id, assumed_wf_types);
112 let outlives_environment =
113 OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds);
115 infcx.check_region_obligations_and_report_errors(body_def_id, &outlives_environment);
119 fn check_well_formed(tcx: TyCtxt<'_>, def_id: hir::OwnerId) {
120 let node = tcx.hir().expect_owner(def_id);
122 hir::OwnerNode::Crate(_) => {}
123 hir::OwnerNode::Item(item) => check_item(tcx, item),
124 hir::OwnerNode::TraitItem(item) => check_trait_item(tcx, item),
125 hir::OwnerNode::ImplItem(item) => check_impl_item(tcx, item),
126 hir::OwnerNode::ForeignItem(item) => check_foreign_item(tcx, item),
129 if let Some(generics) = node.generics() {
130 for param in generics.params {
131 check_param_wf(tcx, param)
136 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
137 /// well-formed, meaning that they do not require any constraints not declared in the struct
138 /// definition itself. For example, this definition would be illegal:
141 /// struct Ref<'a, T> { x: &'a T }
144 /// because the type did not declare that `T:'a`.
146 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
147 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
149 #[instrument(skip(tcx), level = "debug")]
150 fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
151 let def_id = item.def_id.def_id;
155 item.name = ? tcx.def_path_str(def_id.to_def_id())
159 // Right now we check that every default trait implementation
160 // has an implementation of itself. Basically, a case like:
162 // impl Trait for T {}
164 // has a requirement of `T: Trait` which was required for default
165 // method implementations. Although this could be improved now that
166 // there's a better infrastructure in place for this, it's being left
167 // for a follow-up work.
169 // Since there's such a requirement, we need to check *just* positive
170 // implementations, otherwise things like:
172 // impl !Send for T {}
174 // won't be allowed unless there's an *explicit* implementation of `Send`
176 hir::ItemKind::Impl(ref impl_) => {
178 .impl_trait_ref(def_id)
179 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
180 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
181 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
183 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
184 err.span_labels(impl_.defaultness_span, "default because of this");
185 err.span_label(sp, "auto trait");
188 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
189 match (tcx.impl_polarity(def_id), impl_.polarity) {
190 (ty::ImplPolarity::Positive, _) => {
191 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait, impl_.constness);
193 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
194 // FIXME(#27579): what amount of WF checking do we need for neg impls?
195 if let hir::Defaultness::Default { .. } = impl_.defaultness {
196 let mut spans = vec![span];
197 spans.extend(impl_.defaultness_span);
202 "negative impls cannot be default impls"
207 (ty::ImplPolarity::Reservation, _) => {
208 // FIXME: what amount of WF checking do we need for reservation impls?
213 hir::ItemKind::Fn(ref sig, ..) => {
214 check_item_fn(tcx, def_id, item.ident, item.span, sig.decl);
216 hir::ItemKind::Static(ty, ..) => {
217 check_item_type(tcx, def_id, ty.span, false);
219 hir::ItemKind::Const(ty, ..) => {
220 check_item_type(tcx, def_id, ty.span, false);
222 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
223 check_type_defn(tcx, item, false, |wfcx| vec![wfcx.non_enum_variant(struct_def)]);
225 check_variances_for_type_defn(tcx, item, ast_generics);
227 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
228 check_type_defn(tcx, item, true, |wfcx| vec![wfcx.non_enum_variant(struct_def)]);
230 check_variances_for_type_defn(tcx, item, ast_generics);
232 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
233 check_type_defn(tcx, item, true, |wfcx| wfcx.enum_variants(enum_def));
235 check_variances_for_type_defn(tcx, item, ast_generics);
237 hir::ItemKind::Trait(..) => {
238 check_trait(tcx, item);
240 hir::ItemKind::TraitAlias(..) => {
241 check_trait(tcx, item);
243 // `ForeignItem`s are handled separately.
244 hir::ItemKind::ForeignMod { .. } => {}
249 fn check_foreign_item(tcx: TyCtxt<'_>, item: &hir::ForeignItem<'_>) {
250 let def_id = item.def_id.def_id;
254 item.name = ? tcx.def_path_str(def_id.to_def_id())
258 hir::ForeignItemKind::Fn(decl, ..) => {
259 check_item_fn(tcx, def_id, item.ident, item.span, decl)
261 hir::ForeignItemKind::Static(ty, ..) => check_item_type(tcx, def_id, ty.span, true),
262 hir::ForeignItemKind::Type => (),
266 fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) {
267 let def_id = trait_item.def_id.def_id;
269 let (method_sig, span) = match trait_item.kind {
270 hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span),
271 hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span),
272 _ => (None, trait_item.span),
274 check_object_unsafe_self_trait_by_name(tcx, trait_item);
275 check_associated_item(tcx, def_id, span, method_sig);
277 let encl_trait_def_id = tcx.local_parent(def_id);
278 let encl_trait = tcx.hir().expect_item(encl_trait_def_id);
279 let encl_trait_def_id = encl_trait.def_id.to_def_id();
280 let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() {
282 } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() {
288 if let (Some(fn_lang_item_name), "call") =
289 (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str())
291 // We are looking at the `call` function of the `fn` or `fn_mut` lang item.
292 // Do some rudimentary sanity checking to avoid an ICE later (issue #83471).
293 if let Some(hir::FnSig { decl, span, .. }) = method_sig {
294 if let [self_ty, _] = decl.inputs {
295 if !matches!(self_ty.kind, hir::TyKind::Rptr(_, _)) {
300 "first argument of `call` in `{fn_lang_item_name}` lang item must be a reference",
310 "`call` function in `{fn_lang_item_name}` lang item takes exactly two arguments",
320 "`call` trait item in `{fn_lang_item_name}` lang item must be a function",
328 /// Require that the user writes where clauses on GATs for the implicit
329 /// outlives bounds involving trait parameters in trait functions and
330 /// lifetimes passed as GAT substs. See `self-outlives-lint` test.
332 /// We use the following trait as an example throughout this function:
333 /// ```rust,ignore (this code fails due to this lint)
335 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
337 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
340 fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
341 // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
342 let mut required_bounds_by_item = FxHashMap::default();
344 // Loop over all GATs together, because if this lint suggests adding a where-clause bound
345 // to one GAT, it might then require us to an additional bound on another GAT.
346 // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which
347 // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between
350 let mut should_continue = false;
351 for gat_item in associated_items {
352 let gat_def_id = gat_item.id.def_id;
353 let gat_item = tcx.associated_item(gat_def_id);
354 // If this item is not an assoc ty, or has no substs, then it's not a GAT
355 if gat_item.kind != ty::AssocKind::Type {
358 let gat_generics = tcx.generics_of(gat_def_id);
359 // FIXME(jackh726): we can also warn in the more general case
360 if gat_generics.params.is_empty() {
364 // Gather the bounds with which all other items inside of this trait constrain the GAT.
365 // This is calculated by taking the intersection of the bounds that each item
366 // constrains the GAT with individually.
367 let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
368 for item in associated_items {
369 let item_def_id = item.id.def_id;
370 // Skip our own GAT, since it does not constrain itself at all.
371 if item_def_id == gat_def_id {
375 let item_hir_id = item.id.hir_id();
376 let param_env = tcx.param_env(item_def_id);
378 let item_required_bounds = match item.kind {
379 // In our example, this corresponds to `into_iter` method
380 hir::AssocItemKind::Fn { .. } => {
381 // For methods, we check the function signature's return type for any GATs
382 // to constrain. In the `into_iter` case, we see that the return type
383 // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
384 let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions(
385 item_def_id.to_def_id(),
386 tcx.fn_sig(item_def_id),
392 sig.inputs_and_output,
393 // We also assume that all of the function signature's parameter types
395 &sig.inputs().iter().copied().collect(),
400 // In our example, this corresponds to the `Iter` and `Item` associated types
401 hir::AssocItemKind::Type => {
402 // If our associated item is a GAT with missing bounds, add them to
403 // the param-env here. This allows this GAT to propagate missing bounds
405 let param_env = augment_param_env(
408 required_bounds_by_item.get(&item_def_id),
414 tcx.explicit_item_bounds(item_def_id)
417 .collect::<Vec<_>>(),
418 &FxHashSet::default(),
423 hir::AssocItemKind::Const => None,
426 if let Some(item_required_bounds) = item_required_bounds {
427 // Take the intersection of the required bounds for this GAT, and
428 // the item_required_bounds which are the ones implied by just
430 // This is why we use an Option<_>, since we need to distinguish
431 // the empty set of bounds from the _uninitialized_ set of bounds.
432 if let Some(new_required_bounds) = &mut new_required_bounds {
433 new_required_bounds.retain(|b| item_required_bounds.contains(b));
435 new_required_bounds = Some(item_required_bounds);
440 if let Some(new_required_bounds) = new_required_bounds {
441 let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default();
442 if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) {
443 // Iterate until our required_bounds no longer change
444 // Since they changed here, we should continue the loop
445 should_continue = true;
449 // We know that this loop will eventually halt, since we only set `should_continue` if the
450 // `required_bounds` for this item grows. Since we are not creating any new region or type
451 // variables, the set of all region and type bounds that we could ever insert are limited
452 // by the number of unique types and regions we observe in a given item.
453 if !should_continue {
458 for (gat_def_id, required_bounds) in required_bounds_by_item {
459 let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id.def_id);
460 debug!(?required_bounds);
461 let param_env = tcx.param_env(gat_def_id);
462 let gat_hir = gat_item_hir.hir_id();
464 let mut unsatisfied_bounds: Vec<_> = required_bounds
466 .filter(|clause| match clause.kind().skip_binder() {
467 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
468 !region_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
470 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
471 !ty_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
473 _ => bug!("Unexpected PredicateKind"),
475 .map(|clause| clause.to_string())
478 // We sort so that order is predictable
479 unsatisfied_bounds.sort();
481 if !unsatisfied_bounds.is_empty() {
482 let plural = pluralize!(unsatisfied_bounds.len());
483 let mut err = tcx.sess.struct_span_err(
485 &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
488 let suggestion = format!(
490 gat_item_hir.generics.add_where_or_trailing_comma(),
491 unsatisfied_bounds.join(", "),
494 gat_item_hir.generics.tail_span_for_predicate_suggestion(),
495 &format!("add the required where clause{plural}"),
497 Applicability::MachineApplicable,
501 if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
503 "{} currently required to ensure that impls have maximum flexibility",
507 "we are soliciting feedback, see issue #87479 \
508 <https://github.com/rust-lang/rust/issues/87479> \
509 for more information",
517 /// Add a new set of predicates to the caller_bounds of an existing param_env.
518 fn augment_param_env<'tcx>(
520 param_env: ty::ParamEnv<'tcx>,
521 new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
522 ) -> ty::ParamEnv<'tcx> {
523 let Some(new_predicates) = new_predicates else {
527 if new_predicates.is_empty() {
532 tcx.mk_predicates(param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()));
533 // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
534 // i.e. traits::normalize_param_env_or_error
535 ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness())
538 /// We use the following trait as an example throughout this function.
539 /// Specifically, let's assume that `to_check` here is the return type
540 /// of `into_iter`, and the GAT we are checking this for is `Iter`.
541 /// ```rust,ignore (this code fails due to this lint)
543 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
545 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
548 fn gather_gat_bounds<'tcx, T: TypeFoldable<'tcx>>(
550 param_env: ty::ParamEnv<'tcx>,
551 item_hir: hir::HirId,
553 wf_tys: &FxHashSet<Ty<'tcx>>,
554 gat_def_id: LocalDefId,
555 gat_generics: &'tcx ty::Generics,
556 ) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
557 // The bounds we that we would require from `to_check`
558 let mut bounds = FxHashSet::default();
560 let (regions, types) = GATSubstCollector::visit(gat_def_id.to_def_id(), to_check);
562 // If both regions and types are empty, then this GAT isn't in the
563 // set of types we are checking, and we shouldn't try to do clause analysis
564 // (particularly, doing so would end up with an empty set of clauses,
565 // since the current method would require none, and we take the
566 // intersection of requirements of all methods)
567 if types.is_empty() && regions.is_empty() {
571 for (region_a, region_a_idx) in ®ions {
572 // Ignore `'static` lifetimes for the purpose of this lint: it's
573 // because we know it outlives everything and so doesn't give meaningful
575 if let ty::ReStatic = **region_a {
578 // For each region argument (e.g., `'a` in our example), check for a
579 // relationship to the type arguments (e.g., `Self`). If there is an
580 // outlives relationship (`Self: 'a`), then we want to ensure that is
581 // reflected in a where clause on the GAT itself.
582 for (ty, ty_idx) in &types {
583 // In our example, requires that `Self: 'a`
584 if ty_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *ty, *region_a) {
585 debug!(?ty_idx, ?region_a_idx);
586 debug!("required clause: {ty} must outlive {region_a}");
587 // Translate into the generic parameters of the GAT. In
588 // our example, the type was `Self`, which will also be
589 // `Self` in the GAT.
590 let ty_param = gat_generics.param_at(*ty_idx, tcx);
592 .mk_ty(ty::Param(ty::ParamTy { index: ty_param.index, name: ty_param.name }));
593 // Same for the region. In our example, 'a corresponds
594 // to the 'me parameter.
595 let region_param = gat_generics.param_at(*region_a_idx, tcx);
597 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
598 def_id: region_param.def_id,
599 index: region_param.index,
600 name: region_param.name,
602 // The predicate we expect to see. (In our example,
605 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param));
606 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
607 bounds.insert(clause);
611 // For each region argument (e.g., `'a` in our example), also check for a
612 // relationship to the other region arguments. If there is an outlives
613 // relationship, then we want to ensure that is reflected in the where clause
614 // on the GAT itself.
615 for (region_b, region_b_idx) in ®ions {
616 // Again, skip `'static` because it outlives everything. Also, we trivially
617 // know that a region outlives itself.
618 if ty::ReStatic == **region_b || region_a == region_b {
621 if region_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *region_a, *region_b) {
622 debug!(?region_a_idx, ?region_b_idx);
623 debug!("required clause: {region_a} must outlive {region_b}");
624 // Translate into the generic parameters of the GAT.
625 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
627 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
628 def_id: region_a_param.def_id,
629 index: region_a_param.index,
630 name: region_a_param.name,
632 // Same for the region.
633 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
635 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
636 def_id: region_b_param.def_id,
637 index: region_b_param.index,
638 name: region_b_param.name,
640 // The predicate we expect to see.
641 let clause = ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(
645 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
646 bounds.insert(clause);
654 /// Given a known `param_env` and a set of well formed types, can we prove that
655 /// `ty` outlives `region`.
656 fn ty_known_to_outlive<'tcx>(
659 param_env: ty::ParamEnv<'tcx>,
660 wf_tys: &FxHashSet<Ty<'tcx>>,
662 region: ty::Region<'tcx>,
664 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| {
665 let origin = infer::RelateParamBound(DUMMY_SP, ty, None);
666 let outlives = &mut TypeOutlives::new(infcx, tcx, region_bound_pairs, None, param_env);
667 outlives.type_must_outlive(origin, ty, region, ConstraintCategory::BoringNoLocation);
671 /// Given a known `param_env` and a set of well formed types, can we prove that
672 /// `region_a` outlives `region_b`
673 fn region_known_to_outlive<'tcx>(
676 param_env: ty::ParamEnv<'tcx>,
677 wf_tys: &FxHashSet<Ty<'tcx>>,
678 region_a: ty::Region<'tcx>,
679 region_b: ty::Region<'tcx>,
681 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| {
682 use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
683 let origin = infer::RelateRegionParamBound(DUMMY_SP);
684 // `region_a: region_b` -> `region_b <= region_a`
685 infcx.push_sub_region_constraint(
689 ConstraintCategory::BoringNoLocation,
694 /// Given a known `param_env` and a set of well formed types, set up an
695 /// `InferCtxt`, call the passed function (to e.g. set up region constraints
696 /// to be tested), then resolve region and return errors
697 fn resolve_regions_with_wf_tys<'tcx>(
700 param_env: ty::ParamEnv<'tcx>,
701 wf_tys: &FxHashSet<Ty<'tcx>>,
702 add_constraints: impl for<'a> FnOnce(&'a InferCtxt<'a, 'tcx>, &'a RegionBoundPairs<'tcx>),
704 // Unfortunately, we have to use a new `InferCtxt` each call, because
705 // region constraints get added and solved there and we need to test each
706 // call individually.
707 tcx.infer_ctxt().enter(|infcx| {
708 let outlives_environment = OutlivesEnvironment::with_bounds(
711 infcx.implied_bounds_tys(param_env, id, wf_tys.clone()),
713 let region_bound_pairs = outlives_environment.region_bound_pairs();
715 add_constraints(&infcx, region_bound_pairs);
717 let errors = infcx.resolve_regions(&outlives_environment);
719 debug!(?errors, "errors");
721 // If we were able to prove that the type outlives the region without
722 // an error, it must be because of the implied or explicit bounds...
727 /// TypeVisitor that looks for uses of GATs like
728 /// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into
729 /// the two vectors, `regions` and `types` (depending on their kind). For each
730 /// parameter `Pi` also track the index `i`.
731 struct GATSubstCollector<'tcx> {
733 // Which region appears and which parameter index its substituted for
734 regions: FxHashSet<(ty::Region<'tcx>, usize)>,
735 // Which params appears and which parameter index its substituted for
736 types: FxHashSet<(Ty<'tcx>, usize)>,
739 impl<'tcx> GATSubstCollector<'tcx> {
740 fn visit<T: TypeFoldable<'tcx>>(
743 ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) {
745 GATSubstCollector { gat, regions: FxHashSet::default(), types: FxHashSet::default() };
746 t.visit_with(&mut visitor);
747 (visitor.regions, visitor.types)
751 impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
754 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
756 ty::Projection(p) if p.item_def_id == self.gat => {
757 for (idx, subst) in p.substs.iter().enumerate() {
758 match subst.unpack() {
759 GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => {
760 self.regions.insert((lt, idx));
762 GenericArgKind::Type(t) => {
763 self.types.insert((t, idx));
771 t.super_visit_with(self)
775 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
777 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
778 [s] => s.res.opt_def_id() == Some(trait_def_id.to_def_id()),
785 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
786 /// When this is done, suggest using `Self` instead.
787 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
788 let (trait_name, trait_def_id) =
789 match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id()).def_id) {
790 hir::Node::Item(item) => match item.kind {
791 hir::ItemKind::Trait(..) => (item.ident, item.def_id),
796 let mut trait_should_be_self = vec![];
798 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
799 if could_be_self(trait_def_id.def_id, ty) =>
801 trait_should_be_self.push(ty.span)
803 hir::TraitItemKind::Fn(sig, _) => {
804 for ty in sig.decl.inputs {
805 if could_be_self(trait_def_id.def_id, ty) {
806 trait_should_be_self.push(ty.span);
809 match sig.decl.output {
810 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id.def_id, ty) => {
811 trait_should_be_self.push(ty.span);
818 if !trait_should_be_self.is_empty() {
819 if tcx.object_safety_violations(trait_def_id).is_empty() {
822 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
825 trait_should_be_self,
826 "associated item referring to unboxed trait object for its own trait",
828 .span_label(trait_name.span, "in this trait")
829 .multipart_suggestion(
830 "you might have meant to use `Self` to refer to the implementing type",
832 Applicability::MachineApplicable,
838 fn check_impl_item(tcx: TyCtxt<'_>, impl_item: &hir::ImplItem<'_>) {
839 let (method_sig, span) = match impl_item.kind {
840 hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span),
841 // Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`.
842 hir::ImplItemKind::TyAlias(ty) if ty.span != DUMMY_SP => (None, ty.span),
843 _ => (None, impl_item.span),
846 check_associated_item(tcx, impl_item.def_id.def_id, span, method_sig);
849 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
851 // We currently only check wf of const params here.
852 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
854 // Const parameters are well formed if their type is structural match.
855 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
856 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
858 if tcx.features().adt_const_params {
859 if let Some(non_structural_match_ty) =
860 traits::search_for_adt_const_param_violation(param.span, tcx, ty)
862 // We use the same error code in both branches, because this is really the same
863 // issue: we just special-case the message for type parameters to make it
865 match non_structural_match_ty.kind() {
867 // Const parameters may not have type parameters as their types,
868 // because we cannot be sure that the type parameter derives `PartialEq`
869 // and `Eq` (just implementing them is not enough for `structural_match`).
874 "`{ty}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
875 used as the type of a const parameter",
879 format!("`{ty}` may not derive both `PartialEq` and `Eq`"),
882 "it is not currently possible to use a type parameter as the type of a \
892 "`{ty}` is forbidden as the type of a const generic parameter",
894 .note("floats do not derive `Eq` or `Ord`, which are required for const parameters")
902 "using function pointers as const generic parameters is forbidden",
911 "using raw pointers as const generic parameters is forbidden",
916 let mut diag = struct_span_err!(
920 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
921 the type of a const parameter",
922 non_structural_match_ty,
925 if ty == non_structural_match_ty {
928 format!("`{ty}` doesn't derive both `PartialEq` and `Eq`"),
938 let mut is_ptr = true;
940 let err = match ty.kind() {
941 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
942 ty::FnPtr(_) => Some("function pointers"),
943 ty::RawPtr(_) => Some("raw pointers"),
946 err_ty_str = format!("`{ty}`");
947 Some(err_ty_str.as_str())
951 if let Some(unsupported_type) = err {
956 "using {unsupported_type} as const generic parameters is forbidden",
960 let mut err = tcx.sess.struct_span_err(
963 "{unsupported_type} is forbidden as the type of a const generic parameter",
966 err.note("the only supported types are integers, `bool` and `char`");
967 if tcx.sess.is_nightly_build() {
969 "more complex types are supported with `#![feature(adt_const_params)]`",
980 #[instrument(level = "debug", skip(tcx, span, sig_if_method))]
981 fn check_associated_item(
985 sig_if_method: Option<&hir::FnSig<'_>>,
987 let loc = Some(WellFormedLoc::Ty(item_id));
988 enter_wf_checking_ctxt(tcx, span, item_id, |wfcx| {
989 let item = tcx.associated_item(item_id);
991 let self_ty = match item.container {
992 ty::TraitContainer => tcx.types.self_param,
993 ty::ImplContainer => tcx.type_of(item.container_id(tcx)),
997 ty::AssocKind::Const => {
998 let ty = tcx.type_of(item.def_id);
999 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
1000 wfcx.register_wf_obligation(span, loc, ty.into());
1002 ty::AssocKind::Fn => {
1003 let sig = tcx.fn_sig(item.def_id);
1004 let hir_sig = sig_if_method.expect("bad signature for method");
1007 item.ident(tcx).span,
1010 item.def_id.expect_local(),
1012 check_method_receiver(wfcx, hir_sig, item, self_ty);
1014 ty::AssocKind::Type => {
1015 if let ty::AssocItemContainer::TraitContainer = item.container {
1016 check_associated_type_bounds(wfcx, item, span)
1018 if item.defaultness(tcx).has_value() {
1019 let ty = tcx.type_of(item.def_id);
1020 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
1021 wfcx.register_wf_obligation(span, loc, ty.into());
1028 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
1030 ItemKind::Struct(..) => Some(AdtKind::Struct),
1031 ItemKind::Union(..) => Some(AdtKind::Union),
1032 ItemKind::Enum(..) => Some(AdtKind::Enum),
1037 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
1038 fn check_type_defn<'tcx, F>(
1040 item: &hir::Item<'tcx>,
1042 mut lookup_fields: F,
1044 F: FnMut(&WfCheckingCtxt<'_, 'tcx>) -> Vec<AdtVariant<'tcx>>,
1046 enter_wf_checking_ctxt(tcx, item.span, item.def_id.def_id, |wfcx| {
1047 let variants = lookup_fields(wfcx);
1048 let packed = tcx.adt_def(item.def_id).repr().packed();
1050 for variant in &variants {
1051 // All field types must be well-formed.
1052 for field in &variant.fields {
1053 wfcx.register_wf_obligation(
1055 Some(WellFormedLoc::Ty(field.def_id)),
1060 // For DST, or when drop needs to copy things around, all
1061 // intermediate types must be sized.
1062 let needs_drop_copy = || {
1064 let ty = variant.fields.last().unwrap().ty;
1065 let ty = tcx.erase_regions(ty);
1066 if ty.needs_infer() {
1068 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
1069 // Just treat unresolved type expression as if it needs drop.
1072 ty.needs_drop(tcx, tcx.param_env(item.def_id))
1076 // All fields (except for possibly the last) should be sized.
1077 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
1078 let unsized_len = if all_sized { 0 } else { 1 };
1080 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
1082 let last = idx == variant.fields.len() - 1;
1083 wfcx.register_bound(
1084 traits::ObligationCause::new(
1087 traits::FieldSized {
1088 adt_kind: match item_adt_kind(&item.kind) {
1098 tcx.require_lang_item(LangItem::Sized, None),
1102 // Explicit `enum` discriminant values must const-evaluate successfully.
1103 if let Some(discr_def_id) = variant.explicit_discr {
1104 let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());
1106 let cause = traits::ObligationCause::new(
1107 tcx.def_span(discr_def_id),
1109 traits::MiscObligation,
1111 wfcx.register_obligation(traits::Obligation::new(
1114 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(
1115 ty::UnevaluatedConst::new(
1116 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
1125 check_where_clauses(wfcx, item.span, item.def_id.def_id);
1129 #[instrument(skip(tcx, item))]
1130 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
1131 debug!(?item.def_id);
1133 let def_id = item.def_id.def_id;
1134 let trait_def = tcx.trait_def(def_id);
1135 if trait_def.is_marker
1136 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
1138 for associated_def_id in &*tcx.associated_item_def_ids(def_id) {
1141 tcx.def_span(*associated_def_id),
1143 "marker traits cannot have associated items",
1149 enter_wf_checking_ctxt(tcx, item.span, def_id, |wfcx| {
1150 check_where_clauses(wfcx, item.span, def_id)
1153 // Only check traits, don't check trait aliases
1154 if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
1155 check_gat_where_clauses(tcx, items);
1159 /// Checks all associated type defaults of trait `trait_def_id`.
1161 /// Assuming the defaults are used, check that all predicates (bounds on the
1162 /// assoc type and where clauses on the trait) hold.
1163 fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
1164 let bounds = wfcx.tcx().explicit_item_bounds(item.def_id);
1166 debug!("check_associated_type_bounds: bounds={:?}", bounds);
1167 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1168 let normalized_bound = wfcx.normalize(span, None, bound);
1169 traits::wf::predicate_obligations(
1178 wfcx.register_obligations(wf_obligations);
1186 decl: &hir::FnDecl<'_>,
1188 enter_wf_checking_ctxt(tcx, span, def_id, |wfcx| {
1189 let sig = tcx.fn_sig(def_id);
1190 check_fn_or_method(wfcx, ident.span, sig, decl, def_id);
1194 fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) {
1195 debug!("check_item_type: {:?}", item_id);
1197 enter_wf_checking_ctxt(tcx, ty_span, item_id, |wfcx| {
1198 let ty = tcx.type_of(item_id);
1199 let item_ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(item_id)), ty);
1201 let mut forbid_unsized = true;
1202 if allow_foreign_ty {
1203 let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env);
1204 if let ty::Foreign(_) = tail.kind() {
1205 forbid_unsized = false;
1209 wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(item_id)), item_ty.into());
1211 wfcx.register_bound(
1212 traits::ObligationCause::new(ty_span, wfcx.body_id, traits::WellFormed(None)),
1215 tcx.require_lang_item(LangItem::Sized, None),
1219 // Ensure that the end result is `Sync` in a non-thread local `static`.
1220 let should_check_for_sync = tcx.static_mutability(item_id.to_def_id())
1221 == Some(hir::Mutability::Not)
1222 && !tcx.is_foreign_item(item_id.to_def_id())
1223 && !tcx.is_thread_local_static(item_id.to_def_id());
1225 if should_check_for_sync {
1226 wfcx.register_bound(
1227 traits::ObligationCause::new(ty_span, wfcx.body_id, traits::SharedStatic),
1230 tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
1236 #[instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))]
1237 fn check_impl<'tcx>(
1239 item: &'tcx hir::Item<'tcx>,
1240 ast_self_ty: &hir::Ty<'_>,
1241 ast_trait_ref: &Option<hir::TraitRef<'_>>,
1242 constness: hir::Constness,
1244 enter_wf_checking_ctxt(tcx, item.span, item.def_id.def_id, |wfcx| {
1245 match *ast_trait_ref {
1246 Some(ref ast_trait_ref) => {
1247 // `#[rustc_reservation_impl]` impls are not real impls and
1248 // therefore don't need to be WF (the trait's `Self: Trait` predicate
1250 let trait_ref = tcx.impl_trait_ref(item.def_id).unwrap();
1251 let trait_ref = wfcx.normalize(ast_trait_ref.path.span, None, trait_ref);
1252 let trait_pred = ty::TraitPredicate {
1254 constness: match constness {
1255 hir::Constness::Const => ty::BoundConstness::ConstIfConst,
1256 hir::Constness::NotConst => ty::BoundConstness::NotConst,
1258 polarity: ty::ImplPolarity::Positive,
1260 let obligations = traits::wf::trait_obligations(
1265 ast_trait_ref.path.span,
1268 debug!(?obligations);
1269 wfcx.register_obligations(obligations);
1272 let self_ty = tcx.type_of(item.def_id);
1273 let self_ty = wfcx.normalize(
1275 Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
1278 wfcx.register_wf_obligation(
1280 Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
1286 check_where_clauses(wfcx, item.span, item.def_id.def_id);
1290 /// Checks where-clauses and inline bounds that are declared on `def_id`.
1291 #[instrument(level = "debug", skip(wfcx))]
1292 fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id: LocalDefId) {
1293 let infcx = wfcx.infcx;
1294 let tcx = wfcx.tcx();
1296 let predicates = tcx.bound_predicates_of(def_id.to_def_id());
1297 let generics = tcx.generics_of(def_id);
1299 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
1300 GenericParamDefKind::Type { has_default, .. }
1301 | GenericParamDefKind::Const { has_default } => {
1302 has_default && def.index >= generics.parent_count as u32
1304 GenericParamDefKind::Lifetime => unreachable!(),
1307 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
1308 // For example, this forbids the declaration:
1310 // struct Foo<T = Vec<[u32]>> { .. }
1312 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
1313 for param in &generics.params {
1315 GenericParamDefKind::Type { .. } => {
1316 if is_our_default(param) {
1317 let ty = tcx.type_of(param.def_id);
1318 // Ignore dependent defaults -- that is, where the default of one type
1319 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
1320 // be sure if it will error or not as user might always specify the other.
1321 if !ty.needs_subst() {
1322 wfcx.register_wf_obligation(
1323 tcx.def_span(param.def_id),
1324 Some(WellFormedLoc::Ty(param.def_id.expect_local())),
1330 GenericParamDefKind::Const { .. } => {
1331 if is_our_default(param) {
1332 // FIXME(const_generics_defaults): This
1333 // is incorrect when dealing with unused substs, for example
1334 // for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
1335 // we should eagerly error.
1336 let default_ct = tcx.const_param_default(param.def_id);
1337 if !default_ct.needs_subst() {
1338 wfcx.register_wf_obligation(
1339 tcx.def_span(param.def_id),
1346 // Doesn't have defaults.
1347 GenericParamDefKind::Lifetime => {}
1351 // Check that trait predicates are WF when params are substituted by their defaults.
1352 // We don't want to overly constrain the predicates that may be written but we want to
1353 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
1354 // Therefore we check if a predicate which contains a single type param
1355 // with a concrete default is WF with that default substituted.
1356 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
1358 // First we build the defaulted substitution.
1359 let substs = InternalSubsts::for_item(tcx, def_id.to_def_id(), |param, _| {
1361 GenericParamDefKind::Lifetime => {
1362 // All regions are identity.
1363 tcx.mk_param_from_def(param)
1366 GenericParamDefKind::Type { .. } => {
1367 // If the param has a default, ...
1368 if is_our_default(param) {
1369 let default_ty = tcx.type_of(param.def_id);
1370 // ... and it's not a dependent default, ...
1371 if !default_ty.needs_subst() {
1372 // ... then substitute it with the default.
1373 return default_ty.into();
1377 tcx.mk_param_from_def(param)
1379 GenericParamDefKind::Const { .. } => {
1380 // If the param has a default, ...
1381 if is_our_default(param) {
1382 let default_ct = tcx.const_param_default(param.def_id);
1383 // ... and it's not a dependent default, ...
1384 if !default_ct.needs_subst() {
1385 // ... then substitute it with the default.
1386 return default_ct.into();
1390 tcx.mk_param_from_def(param)
1395 // Now we build the substituted predicates.
1396 let default_obligations = predicates
1400 .flat_map(|&(pred, sp)| {
1402 struct CountParams {
1403 params: FxHashSet<u32>,
1405 impl<'tcx> ty::visit::TypeVisitor<'tcx> for CountParams {
1408 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1409 if let ty::Param(param) = t.kind() {
1410 self.params.insert(param.index);
1412 t.super_visit_with(self)
1415 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1419 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1420 if let ty::ConstKind::Param(param) = c.kind() {
1421 self.params.insert(param.index);
1423 c.super_visit_with(self)
1426 let mut param_count = CountParams::default();
1427 let has_region = pred.visit_with(&mut param_count).is_break();
1428 let substituted_pred = predicates.rebind(pred).subst(tcx, substs);
1429 // Don't check non-defaulted params, dependent defaults (including lifetimes)
1430 // or preds with multiple params.
1431 if substituted_pred.has_param_types_or_consts()
1432 || param_count.params.len() > 1
1436 } else if predicates.0.predicates.iter().any(|&(p, _)| p == substituted_pred) {
1437 // Avoid duplication of predicates that contain no parameters, for example.
1440 Some((substituted_pred, sp))
1444 // Convert each of those into an obligation. So if you have
1445 // something like `struct Foo<T: Copy = String>`, we would
1446 // take that predicate `T: Copy`, substitute to `String: Copy`
1447 // (actually that happens in the previous `flat_map` call),
1448 // and then try to prove it (in this case, we'll fail).
1450 // Note the subtle difference from how we handle `predicates`
1451 // below: there, we are not trying to prove those predicates
1452 // to be *true* but merely *well-formed*.
1453 let pred = wfcx.normalize(sp, None, pred);
1454 let cause = traits::ObligationCause::new(
1457 traits::ItemObligation(def_id.to_def_id()),
1459 traits::Obligation::new(cause, wfcx.param_env, pred)
1462 let predicates = predicates.0.instantiate_identity(tcx);
1464 let predicates = wfcx.normalize(span, None, predicates);
1466 debug!(?predicates.predicates);
1467 assert_eq!(predicates.predicates.len(), predicates.spans.len());
1468 let wf_obligations =
1469 iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| {
1470 traits::wf::predicate_obligations(
1472 wfcx.param_env.without_const(),
1479 let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect();
1480 wfcx.register_obligations(obligations);
1483 #[instrument(level = "debug", skip(wfcx, span, hir_decl))]
1484 fn check_fn_or_method<'tcx>(
1485 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1487 sig: ty::PolyFnSig<'tcx>,
1488 hir_decl: &hir::FnDecl<'_>,
1491 let tcx = wfcx.tcx();
1492 let sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
1494 // Normalize the input and output types one at a time, using a different
1495 // `WellFormedLoc` for each. We cannot call `normalize_associated_types`
1496 // on the entire `FnSig`, since this would use the same `WellFormedLoc`
1497 // for each type, preventing the HIR wf check from generating
1498 // a nice error message.
1499 let ty::FnSig { mut inputs_and_output, c_variadic, unsafety, abi } = sig;
1500 inputs_and_output = tcx.mk_type_list(inputs_and_output.iter().enumerate().map(|(i, ty)| {
1503 Some(WellFormedLoc::Param {
1505 // Note that the `param_idx` of the output type is
1506 // one greater than the index of the last input type.
1507 param_idx: i.try_into().unwrap(),
1512 // Manually call `normalize_associated_types_in` on the other types
1513 // in `FnSig`. This ensures that if the types of these fields
1514 // ever change to include projections, we will start normalizing
1515 // them automatically.
1516 let sig = ty::FnSig {
1518 c_variadic: wfcx.normalize(span, None, c_variadic),
1519 unsafety: wfcx.normalize(span, None, unsafety),
1520 abi: wfcx.normalize(span, None, abi),
1523 for (i, (&input_ty, ty)) in iter::zip(sig.inputs(), hir_decl.inputs).enumerate() {
1524 wfcx.register_wf_obligation(
1526 Some(WellFormedLoc::Param { function: def_id, param_idx: i.try_into().unwrap() }),
1531 wfcx.register_wf_obligation(
1532 hir_decl.output.span(),
1533 Some(WellFormedLoc::Param {
1535 param_idx: sig.inputs().len().try_into().unwrap(),
1537 sig.output().into(),
1540 check_where_clauses(wfcx, span, def_id);
1542 check_return_position_impl_trait_in_trait_bounds(
1547 hir_decl.output.span(),
1551 /// Basically `check_associated_type_bounds`, but separated for now and should be
1552 /// deduplicated when RPITITs get lowered into real associated items.
1553 fn check_return_position_impl_trait_in_trait_bounds<'tcx>(
1555 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1556 fn_def_id: LocalDefId,
1557 fn_output: Ty<'tcx>,
1560 if let Some(assoc_item) = tcx.opt_associated_item(fn_def_id.to_def_id())
1561 && assoc_item.container == ty::AssocItemContainer::TraitContainer
1563 for arg in fn_output.walk() {
1564 if let ty::GenericArgKind::Type(ty) = arg.unpack()
1565 && let ty::Projection(proj) = ty.kind()
1566 && tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
1567 && tcx.impl_trait_in_trait_parent(proj.item_def_id) == fn_def_id.to_def_id()
1569 let bounds = wfcx.tcx().explicit_item_bounds(proj.item_def_id);
1570 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1571 let normalized_bound = wfcx.normalize(span, None, bound);
1572 traits::wf::predicate_obligations(
1580 wfcx.register_obligations(wf_obligations);
1586 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1587 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1588 of the previous types except `Self`)";
1590 #[instrument(level = "debug", skip(wfcx))]
1591 fn check_method_receiver<'tcx>(
1592 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1593 fn_sig: &hir::FnSig<'_>,
1594 method: &ty::AssocItem,
1597 let tcx = wfcx.tcx();
1599 if !method.fn_has_self_parameter {
1603 let span = fn_sig.decl.inputs[0].span;
1605 let sig = tcx.fn_sig(method.def_id);
1606 let sig = tcx.liberate_late_bound_regions(method.def_id, sig);
1607 let sig = wfcx.normalize(span, None, sig);
1609 debug!("check_method_receiver: sig={:?}", sig);
1611 let self_ty = wfcx.normalize(span, None, self_ty);
1613 let receiver_ty = sig.inputs()[0];
1614 let receiver_ty = wfcx.normalize(span, None, receiver_ty);
1616 if tcx.features().arbitrary_self_types {
1617 if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
1618 // Report error; `arbitrary_self_types` was enabled.
1619 e0307(tcx, span, receiver_ty);
1622 if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, false) {
1623 if receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) {
1624 // Report error; would have worked with `arbitrary_self_types`.
1626 &tcx.sess.parse_sess,
1627 sym::arbitrary_self_types,
1630 "`{receiver_ty}` cannot be used as the type of `self` without \
1631 the `arbitrary_self_types` feature",
1634 .help(HELP_FOR_SELF_TYPE)
1637 // Report error; would not have worked with `arbitrary_self_types`.
1638 e0307(tcx, span, receiver_ty);
1644 fn e0307<'tcx>(tcx: TyCtxt<'tcx>, span: Span, receiver_ty: Ty<'_>) {
1646 tcx.sess.diagnostic(),
1649 "invalid `self` parameter type: {receiver_ty}"
1651 .note("type of `self` must be `Self` or a type that dereferences to it")
1652 .help(HELP_FOR_SELF_TYPE)
1656 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1657 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1658 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1659 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1660 /// `Deref<Target = self_ty>`.
1662 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1663 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1664 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1665 fn receiver_is_valid<'tcx>(
1666 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1668 receiver_ty: Ty<'tcx>,
1670 arbitrary_self_types_enabled: bool,
1672 let infcx = wfcx.infcx;
1673 let tcx = wfcx.tcx();
1675 ObligationCause::new(span, wfcx.body_id, traits::ObligationCauseCode::MethodReceiver);
1677 let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty).is_ok();
1679 // `self: Self` is always valid.
1680 if can_eq_self(receiver_ty) {
1681 if let Err(err) = wfcx.equate_types(&cause, wfcx.param_env, self_ty, receiver_ty) {
1682 infcx.report_mismatched_types(&cause, self_ty, receiver_ty, err).emit();
1688 Autoderef::new(infcx, wfcx.param_env, wfcx.body_id, span, receiver_ty, span);
1690 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1691 if arbitrary_self_types_enabled {
1692 autoderef = autoderef.include_raw_pointers();
1695 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1698 let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, None);
1700 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1702 if let Some((potential_self_ty, _)) = autoderef.next() {
1704 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1705 potential_self_ty, self_ty
1708 if can_eq_self(potential_self_ty) {
1709 wfcx.register_obligations(autoderef.into_obligations());
1712 wfcx.equate_types(&cause, wfcx.param_env, self_ty, potential_self_ty)
1714 infcx.report_mismatched_types(&cause, self_ty, potential_self_ty, err).emit();
1719 // Without `feature(arbitrary_self_types)`, we require that each step in the
1720 // deref chain implement `receiver`
1721 if !arbitrary_self_types_enabled
1722 && !receiver_is_implemented(
1724 receiver_trait_def_id,
1733 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1734 // If the receiver already has errors reported due to it, consider it valid to avoid
1735 // unnecessary errors (#58712).
1736 return receiver_ty.references_error();
1740 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1741 if !arbitrary_self_types_enabled
1742 && !receiver_is_implemented(wfcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1750 fn receiver_is_implemented<'tcx>(
1751 wfcx: &WfCheckingCtxt<'_, 'tcx>,
1752 receiver_trait_def_id: DefId,
1753 cause: ObligationCause<'tcx>,
1754 receiver_ty: Ty<'tcx>,
1756 let tcx = wfcx.tcx();
1757 let trait_ref = ty::Binder::dummy(ty::TraitRef {
1758 def_id: receiver_trait_def_id,
1759 substs: tcx.mk_substs_trait(receiver_ty, &[]),
1763 traits::Obligation::new(cause, wfcx.param_env, trait_ref.without_const().to_predicate(tcx));
1765 if wfcx.infcx.predicate_must_hold_modulo_regions(&obligation) {
1769 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1776 fn check_variances_for_type_defn<'tcx>(
1778 item: &hir::Item<'tcx>,
1779 hir_generics: &hir::Generics<'_>,
1781 let ty = tcx.type_of(item.def_id);
1782 if tcx.has_error_field(ty) {
1786 let ty_predicates = tcx.predicates_of(item.def_id);
1787 assert_eq!(ty_predicates.parent, None);
1788 let variances = tcx.variances_of(item.def_id);
1790 let mut constrained_parameters: FxHashSet<_> = variances
1793 .filter(|&(_, &variance)| variance != ty::Bivariant)
1794 .map(|(index, _)| Parameter(index as u32))
1797 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1799 // Lazily calculated because it is only needed in case of an error.
1800 let explicitly_bounded_params = LazyCell::new(|| {
1801 let icx = crate::collect::ItemCtxt::new(tcx, item.def_id.to_def_id());
1805 .filter_map(|predicate| match predicate {
1806 hir::WherePredicate::BoundPredicate(predicate) => {
1807 match icx.to_ty(predicate.bounded_ty).kind() {
1808 ty::Param(data) => Some(Parameter(data.index)),
1814 .collect::<FxHashSet<_>>()
1817 for (index, _) in variances.iter().enumerate() {
1818 let parameter = Parameter(index as u32);
1820 if constrained_parameters.contains(¶meter) {
1824 let param = &hir_generics.params[index];
1827 hir::ParamName::Error => {}
1829 let has_explicit_bounds = explicitly_bounded_params.contains(¶meter);
1830 report_bivariance(tcx, param, has_explicit_bounds);
1836 fn report_bivariance(
1838 param: &rustc_hir::GenericParam<'_>,
1839 has_explicit_bounds: bool,
1840 ) -> ErrorGuaranteed {
1841 let span = param.span;
1842 let param_name = param.name.ident().name;
1843 let mut err = error_392(tcx, span, param_name);
1845 let suggested_marker_id = tcx.lang_items().phantom_data();
1846 // Help is available only in presence of lang items.
1847 let msg = if let Some(def_id) = suggested_marker_id {
1849 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1851 tcx.def_path_str(def_id),
1854 format!("consider removing `{param_name}` or referring to it in a field")
1858 if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds {
1860 "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
1867 impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
1868 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1870 #[instrument(level = "debug", skip(self))]
1871 fn check_false_global_bounds(&mut self) {
1872 let tcx = self.ocx.infcx.tcx;
1873 let mut span = self.span;
1874 let empty_env = ty::ParamEnv::empty();
1876 let def_id = tcx.hir().local_def_id(self.body_id);
1877 let predicates_with_span = tcx.predicates_of(def_id).predicates.iter().copied();
1878 // Check elaborated bounds.
1879 let implied_obligations = traits::elaborate_predicates_with_span(tcx, predicates_with_span);
1881 for obligation in implied_obligations {
1882 // We lower empty bounds like `Vec<dyn Copy>:` as
1883 // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
1884 // regular WF checking
1885 if let ty::PredicateKind::WellFormed(..) = obligation.predicate.kind().skip_binder() {
1888 let pred = obligation.predicate;
1889 // Match the existing behavior.
1890 if pred.is_global() && !pred.has_late_bound_regions() {
1891 let pred = self.normalize(span, None, pred);
1892 let hir_node = tcx.hir().find(self.body_id);
1894 // only use the span of the predicate clause (#90869)
1896 if let Some(hir::Generics { predicates, .. }) =
1897 hir_node.and_then(|node| node.generics())
1899 let obligation_span = obligation.cause.span();
1903 // There seems to be no better way to find out which predicate we are in
1904 .find(|pred| pred.span().contains(obligation_span))
1905 .map(|pred| pred.span())
1906 .unwrap_or(obligation_span);
1909 let obligation = traits::Obligation::new(
1910 traits::ObligationCause::new(span, self.body_id, traits::TrivialBound),
1914 self.ocx.register_obligation(obligation);
1920 fn check_mod_type_wf(tcx: TyCtxt<'_>, module: LocalDefId) {
1921 let items = tcx.hir_module_items(module);
1922 items.par_items(|item| tcx.ensure().check_well_formed(item.def_id));
1923 items.par_impl_items(|item| tcx.ensure().check_well_formed(item.def_id));
1924 items.par_trait_items(|item| tcx.ensure().check_well_formed(item.def_id));
1925 items.par_foreign_items(|item| tcx.ensure().check_well_formed(item.def_id));
1928 ///////////////////////////////////////////////////////////////////////////
1931 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1932 struct AdtVariant<'tcx> {
1933 /// Types of fields in the variant, that must be well-formed.
1934 fields: Vec<AdtField<'tcx>>,
1936 /// Explicit discriminant of this variant (e.g. `A = 123`),
1937 /// that must evaluate to a constant value.
1938 explicit_discr: Option<LocalDefId>,
1941 struct AdtField<'tcx> {
1947 impl<'a, 'tcx> WfCheckingCtxt<'a, 'tcx> {
1948 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1949 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1950 let fields = struct_def
1954 let def_id = self.tcx().hir().local_def_id(field.hir_id);
1955 let field_ty = self.tcx().type_of(def_id);
1956 let field_ty = self.normalize(field.ty.span, None, field_ty);
1957 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1958 AdtField { ty: field_ty, span: field.ty.span, def_id }
1961 AdtVariant { fields, explicit_discr: None }
1964 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1968 .map(|variant| AdtVariant {
1969 fields: self.non_enum_variant(&variant.data).fields,
1970 explicit_discr: variant
1972 .map(|explicit_discr| self.tcx().hir().local_def_id(explicit_discr.hir_id)),
1982 ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
1983 let mut err = struct_span_err!(tcx.sess, span, E0392, "parameter `{param_name}` is never used");
1984 err.span_label(span, "unused parameter");
1988 pub fn provide(providers: &mut Providers) {
1989 *providers = Providers { check_mod_type_wf, check_well_formed, ..*providers };