1 use crate::check::regionck::OutlivesEnvironmentExt;
2 use crate::check::{FnCtxt, Inherited};
3 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
6 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
7 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorReported};
9 use rustc_hir::def_id::{DefId, LocalDefId};
10 use rustc_hir::intravisit as hir_visit;
11 use rustc_hir::intravisit::Visitor;
12 use rustc_hir::itemlikevisit::ParItemLikeVisitor;
13 use rustc_hir::lang_items::LangItem;
14 use rustc_hir::ItemKind;
15 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
16 use rustc_infer::infer::outlives::obligations::TypeOutlives;
17 use rustc_infer::infer::region_constraints::GenericKind;
18 use rustc_infer::infer::{self, RegionckMode};
19 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
20 use rustc_middle::hir::nested_filter;
21 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
22 use rustc_middle::ty::trait_def::TraitSpecializationKind;
23 use rustc_middle::ty::{
24 self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitor,
26 use rustc_session::parse::feature_err;
27 use rustc_span::symbol::{sym, Ident, Symbol};
28 use rustc_span::{Span, DUMMY_SP};
29 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
30 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode, WellFormedLoc};
32 use std::convert::TryInto;
34 use std::ops::ControlFlow;
36 /// Helper type of a temporary returned by `.for_item(...)`.
37 /// This is necessary because we can't write the following bound:
40 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
42 struct CheckWfFcxBuilder<'tcx> {
43 inherited: super::InheritedBuilder<'tcx>,
46 param_env: ty::ParamEnv<'tcx>,
49 impl<'tcx> CheckWfFcxBuilder<'tcx> {
50 fn with_fcx<F>(&mut self, f: F)
52 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>) -> FxHashSet<Ty<'tcx>>,
56 let param_env = self.param_env;
57 self.inherited.enter(|inh| {
58 let fcx = FnCtxt::new(&inh, param_env, id);
59 if !inh.tcx.features().trivial_bounds {
60 // As predicates are cached rather than obligations, this
61 // needs to be called first so that they are checked with an
63 check_false_global_bounds(&fcx, span, id);
66 fcx.select_all_obligations_or_error();
67 fcx.regionck_item(id, span, wf_tys);
72 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
73 /// well-formed, meaning that they do not require any constraints not declared in the struct
74 /// definition itself. For example, this definition would be illegal:
77 /// struct Ref<'a, T> { x: &'a T }
80 /// because the type did not declare that `T:'a`.
82 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
83 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
85 #[instrument(skip(tcx), level = "debug")]
86 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
87 let item = tcx.hir().expect_item(def_id);
91 item.name = ? tcx.def_path_str(def_id.to_def_id())
95 // Right now we check that every default trait implementation
96 // has an implementation of itself. Basically, a case like:
98 // impl Trait for T {}
100 // has a requirement of `T: Trait` which was required for default
101 // method implementations. Although this could be improved now that
102 // there's a better infrastructure in place for this, it's being left
103 // for a follow-up work.
105 // Since there's such a requirement, we need to check *just* positive
106 // implementations, otherwise things like:
108 // impl !Send for T {}
110 // won't be allowed unless there's an *explicit* implementation of `Send`
112 hir::ItemKind::Impl(ref impl_) => {
114 .impl_trait_ref(item.def_id)
115 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
116 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
117 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
119 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
120 err.span_labels(impl_.defaultness_span, "default because of this");
121 err.span_label(sp, "auto trait");
124 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
125 match (tcx.impl_polarity(def_id), impl_.polarity) {
126 (ty::ImplPolarity::Positive, _) => {
127 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait);
129 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
130 // FIXME(#27579): what amount of WF checking do we need for neg impls?
131 if let hir::Defaultness::Default { .. } = impl_.defaultness {
132 let mut spans = vec![span];
133 spans.extend(impl_.defaultness_span);
138 "negative impls cannot be default impls"
143 (ty::ImplPolarity::Reservation, _) => {
144 // FIXME: what amount of WF checking do we need for reservation impls?
149 hir::ItemKind::Fn(ref sig, ..) => {
150 check_item_fn(tcx, item.def_id, item.ident, item.span, sig.decl);
152 hir::ItemKind::Static(ty, ..) => {
153 check_item_type(tcx, item.def_id, ty.span, false);
155 hir::ItemKind::Const(ty, ..) => {
156 check_item_type(tcx, item.def_id, ty.span, false);
158 hir::ItemKind::ForeignMod { items, .. } => {
159 for it in items.iter() {
160 let it = tcx.hir().foreign_item(it.id);
162 hir::ForeignItemKind::Fn(decl, ..) => {
163 check_item_fn(tcx, it.def_id, it.ident, it.span, decl)
165 hir::ForeignItemKind::Static(ty, ..) => {
166 check_item_type(tcx, it.def_id, ty.span, true)
168 hir::ForeignItemKind::Type => (),
172 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
173 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
175 check_variances_for_type_defn(tcx, item, ast_generics);
177 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
178 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
180 check_variances_for_type_defn(tcx, item, ast_generics);
182 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
183 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
185 check_variances_for_type_defn(tcx, item, ast_generics);
187 hir::ItemKind::Trait(..) => {
188 check_trait(tcx, item);
190 hir::ItemKind::TraitAlias(..) => {
191 check_trait(tcx, item);
197 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
198 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
199 let trait_item = tcx.hir().expect_trait_item(def_id);
201 let (method_sig, span) = match trait_item.kind {
202 hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span),
203 hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span),
204 _ => (None, trait_item.span),
206 check_object_unsafe_self_trait_by_name(tcx, trait_item);
207 check_associated_item(tcx, trait_item.def_id, span, method_sig);
209 let encl_trait_def_id = tcx.hir().get_parent_item(hir_id);
210 let encl_trait = tcx.hir().expect_item(encl_trait_def_id);
211 let encl_trait_def_id = encl_trait.def_id.to_def_id();
212 let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() {
214 } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() {
220 if let (Some(fn_lang_item_name), "call") =
221 (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str())
223 // We are looking at the `call` function of the `fn` or `fn_mut` lang item.
224 // Do some rudimentary sanity checking to avoid an ICE later (issue #83471).
225 if let Some(hir::FnSig { decl, span, .. }) = method_sig {
226 if let [self_ty, _] = decl.inputs {
227 if !matches!(self_ty.kind, hir::TyKind::Rptr(_, _)) {
232 "first argument of `call` in `{}` lang item must be a reference",
243 "`call` function in `{}` lang item takes exactly two arguments",
254 "`call` trait item in `{}` lang item must be a function",
263 /// Require that the user writes where clauses on GATs for the implicit
264 /// outlives bounds involving trait parameters in trait functions and
265 /// lifetimes passed as GAT substs. See `self-outlives-lint` test.
267 /// We use the following trait as an example throughout this function:
268 /// ```rust,ignore (this code fails due to this lint)
270 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
272 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
275 fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
276 // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
277 let mut required_bounds_by_item = FxHashMap::default();
279 // Loop over all GATs together, because if this lint suggests adding a where-clause bound
280 // to one GAT, it might then require us to an additional bound on another GAT.
281 // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which
282 // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between
285 let mut should_continue = false;
286 for gat_item in associated_items {
287 let gat_def_id = gat_item.id.def_id;
288 let gat_item = tcx.associated_item(gat_def_id);
289 // If this item is not an assoc ty, or has no substs, then it's not a GAT
290 if gat_item.kind != ty::AssocKind::Type {
293 let gat_generics = tcx.generics_of(gat_def_id);
294 // FIXME(jackh726): we can also warn in the more general case
295 if gat_generics.params.is_empty() {
299 // Gather the bounds with which all other items inside of this trait constrain the GAT.
300 // This is calculated by taking the intersection of the bounds that each item
301 // constrains the GAT with individually.
302 let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
303 for item in associated_items {
304 let item_def_id = item.id.def_id;
305 // Skip our own GAT, since it does not constrain itself at all.
306 if item_def_id == gat_def_id {
310 let item_hir_id = item.id.hir_id();
311 let param_env = tcx.param_env(item_def_id);
313 let item_required_bounds = match item.kind {
314 // In our example, this corresponds to `into_iter` method
315 hir::AssocItemKind::Fn { .. } => {
316 // For methods, we check the function signature's return type for any GATs
317 // to constrain. In the `into_iter` case, we see that the return type
318 // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
319 let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions(
320 item_def_id.to_def_id(),
321 tcx.fn_sig(item_def_id),
328 // We also assume that all of the function signature's parameter types
330 &sig.inputs().iter().copied().collect(),
335 // In our example, this corresponds to the `Iter` and `Item` associated types
336 hir::AssocItemKind::Type => {
337 // If our associated item is a GAT with missing bounds, add them to
338 // the param-env here. This allows this GAT to propagate missing bounds
340 let param_env = augment_param_env(
343 required_bounds_by_item.get(&item_def_id),
349 tcx.explicit_item_bounds(item_def_id)
352 .collect::<Vec<_>>(),
353 &FxHashSet::default(),
358 hir::AssocItemKind::Const => None,
361 if let Some(item_required_bounds) = item_required_bounds {
362 // Take the intersection of the required bounds for this GAT, and
363 // the item_required_bounds which are the ones implied by just
365 // This is why we use an Option<_>, since we need to distinguish
366 // the empty set of bounds from the _uninitialized_ set of bounds.
367 if let Some(new_required_bounds) = &mut new_required_bounds {
368 new_required_bounds.retain(|b| item_required_bounds.contains(b));
370 new_required_bounds = Some(item_required_bounds);
375 if let Some(new_required_bounds) = new_required_bounds {
376 let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default();
377 if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) {
378 // Iterate until our required_bounds no longer change
379 // Since they changed here, we should continue the loop
380 should_continue = true;
384 // We know that this loop will eventually halt, since we only set `should_continue` if the
385 // `required_bounds` for this item grows. Since we are not creating any new region or type
386 // variables, the set of all region and type bounds that we could ever insert are limited
387 // by the number of unique types and regions we observe in a given item.
388 if !should_continue {
393 for (gat_def_id, required_bounds) in required_bounds_by_item {
394 let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id);
395 debug!(?required_bounds);
396 let param_env = tcx.param_env(gat_def_id);
397 let gat_hir = gat_item_hir.hir_id();
399 let mut unsatisfied_bounds: Vec<_> = required_bounds
401 .filter(|clause| match clause.kind().skip_binder() {
402 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
403 !region_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
405 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
406 !ty_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
408 _ => bug!("Unexpected PredicateKind"),
410 .map(|clause| clause.to_string())
413 // We sort so that order is predictable
414 unsatisfied_bounds.sort();
416 if !unsatisfied_bounds.is_empty() {
417 let plural = if unsatisfied_bounds.len() > 1 { "s" } else { "" };
418 let mut err = tcx.sess.struct_span_err(
420 &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
423 let suggestion = format!(
425 if !gat_item_hir.generics.where_clause.predicates.is_empty() {
430 unsatisfied_bounds.join(", "),
433 gat_item_hir.generics.where_clause.tail_span_for_suggestion(),
434 &format!("add the required where clause{}", plural),
436 Applicability::MachineApplicable,
440 if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
442 "{} currently required to ensure that impls have maximum flexibility",
446 "we are soliciting feedback, see issue #87479 \
447 <https://github.com/rust-lang/rust/issues/87479> \
448 for more information",
456 /// Add a new set of predicates to the caller_bounds of an existing param_env.
457 fn augment_param_env<'tcx>(
459 param_env: ty::ParamEnv<'tcx>,
460 new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
461 ) -> ty::ParamEnv<'tcx> {
462 let Some(new_predicates) = new_predicates else {
466 if new_predicates.is_empty() {
471 tcx.mk_predicates(param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()));
472 // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
473 // i.e. traits::normalize_param_env_or_error
474 ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness())
477 /// We use the following trait as an example throughout this function.
478 /// Specifically, let's assume that `to_check` here is the return type
479 /// of `into_iter`, and the GAT we are checking this for is `Iter`.
480 /// ```rust,ignore (this code fails due to this lint)
482 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
484 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
487 fn gather_gat_bounds<'tcx, T: TypeFoldable<'tcx>>(
489 param_env: ty::ParamEnv<'tcx>,
490 item_hir: hir::HirId,
492 wf_tys: &FxHashSet<Ty<'tcx>>,
493 gat_def_id: LocalDefId,
494 gat_generics: &'tcx ty::Generics,
495 ) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
496 // The bounds we that we would require from `to_check`
497 let mut bounds = FxHashSet::default();
499 let (regions, types) = GATSubstCollector::visit(tcx, gat_def_id.to_def_id(), to_check);
501 // If both regions and types are empty, then this GAT isn't in the
502 // set of types we are checking, and we shouldn't try to do clause analysis
503 // (particularly, doing so would end up with an empty set of clauses,
504 // since the current method would require none, and we take the
505 // intersection of requirements of all methods)
506 if types.is_empty() && regions.is_empty() {
510 for (region_a, region_a_idx) in ®ions {
511 // Ignore `'static` lifetimes for the purpose of this lint: it's
512 // because we know it outlives everything and so doesn't give meaninful
514 if let ty::ReStatic = **region_a {
517 // For each region argument (e.g., `'a` in our example), check for a
518 // relationship to the type arguments (e.g., `Self`). If there is an
519 // outlives relationship (`Self: 'a`), then we want to ensure that is
520 // reflected in a where clause on the GAT itself.
521 for (ty, ty_idx) in &types {
522 // In our example, requires that `Self: 'a`
523 if ty_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *ty, *region_a) {
524 debug!(?ty_idx, ?region_a_idx);
525 debug!("required clause: {} must outlive {}", ty, region_a);
526 // Translate into the generic parameters of the GAT. In
527 // our example, the type was `Self`, which will also be
528 // `Self` in the GAT.
529 let ty_param = gat_generics.param_at(*ty_idx, tcx);
531 .mk_ty(ty::Param(ty::ParamTy { index: ty_param.index, name: ty_param.name }));
532 // Same for the region. In our example, 'a corresponds
533 // to the 'me parameter.
534 let region_param = gat_generics.param_at(*region_a_idx, tcx);
536 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
537 def_id: region_param.def_id,
538 index: region_param.index,
539 name: region_param.name,
541 // The predicate we expect to see. (In our example,
544 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param));
545 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
546 bounds.insert(clause);
550 // For each region argument (e.g., `'a` in our example), also check for a
551 // relationship to the other region arguments. If there is an outlives
552 // relationship, then we want to ensure that is reflected in the where clause
553 // on the GAT itself.
554 for (region_b, region_b_idx) in ®ions {
555 // Again, skip `'static` because it outlives everything. Also, we trivially
556 // know that a region outlives itself.
557 if ty::ReStatic == **region_b || region_a == region_b {
560 if region_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *region_a, *region_b) {
561 debug!(?region_a_idx, ?region_b_idx);
562 debug!("required clause: {} must outlive {}", region_a, region_b);
563 // Translate into the generic parameters of the GAT.
564 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
566 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
567 def_id: region_a_param.def_id,
568 index: region_a_param.index,
569 name: region_a_param.name,
571 // Same for the region.
572 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
574 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
575 def_id: region_b_param.def_id,
576 index: region_b_param.index,
577 name: region_b_param.name,
579 // The predicate we expect to see.
580 let clause = ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(
584 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
585 bounds.insert(clause);
593 /// Given a known `param_env` and a set of well formed types, can we prove that
594 /// `ty` outlives `region`.
595 fn ty_known_to_outlive<'tcx>(
598 param_env: ty::ParamEnv<'tcx>,
599 wf_tys: &FxHashSet<Ty<'tcx>>,
601 region: ty::Region<'tcx>,
603 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| {
604 let origin = infer::RelateParamBound(DUMMY_SP, ty, None);
605 let outlives = &mut TypeOutlives::new(
609 Some(infcx.tcx.lifetimes.re_root_empty),
612 outlives.type_must_outlive(origin, ty, region);
616 /// Given a known `param_env` and a set of well formed types, can we prove that
617 /// `region_a` outlives `region_b`
618 fn region_known_to_outlive<'tcx>(
621 param_env: ty::ParamEnv<'tcx>,
622 wf_tys: &FxHashSet<Ty<'tcx>>,
623 region_a: ty::Region<'tcx>,
624 region_b: ty::Region<'tcx>,
626 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| {
627 use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
628 let origin = infer::RelateRegionParamBound(DUMMY_SP);
629 // `region_a: region_b` -> `region_b <= region_a`
630 infcx.push_sub_region_constraint(origin, region_b, region_a);
634 /// Given a known `param_env` and a set of well formed types, set up an
635 /// `InferCtxt`, call the passed function (to e.g. set up region constraints
636 /// to be tested), then resolve region and return errors
637 fn resolve_regions_with_wf_tys<'tcx>(
640 param_env: ty::ParamEnv<'tcx>,
641 wf_tys: &FxHashSet<Ty<'tcx>>,
642 add_constraints: impl for<'a> FnOnce(
643 &'a InferCtxt<'a, 'tcx>,
644 &'a Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>,
647 // Unfortunately, we have to use a new `InferCtxt` each call, because
648 // region constraints get added and solved there and we need to test each
649 // call individually.
650 tcx.infer_ctxt().enter(|infcx| {
651 let mut outlives_environment = OutlivesEnvironment::new(param_env);
652 outlives_environment.add_implied_bounds(&infcx, wf_tys.clone(), id, DUMMY_SP);
653 outlives_environment.save_implied_bounds(id);
654 let region_bound_pairs = outlives_environment.region_bound_pairs_map().get(&id).unwrap();
656 add_constraints(&infcx, region_bound_pairs);
658 let errors = infcx.resolve_regions(
659 id.expect_owner().to_def_id(),
660 &outlives_environment,
661 RegionckMode::default(),
664 debug!(?errors, "errors");
666 // If we were able to prove that the type outlives the region without
667 // an error, it must be because of the implied or explicit bounds...
672 /// TypeVisitor that looks for uses of GATs like
673 /// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into
674 /// the two vectors, `regions` and `types` (depending on their kind). For each
675 /// parameter `Pi` also track the index `i`.
676 struct GATSubstCollector<'tcx> {
679 // Which region appears and which parameter index its subsituted for
680 regions: FxHashSet<(ty::Region<'tcx>, usize)>,
681 // Which params appears and which parameter index its subsituted for
682 types: FxHashSet<(Ty<'tcx>, usize)>,
685 impl<'tcx> GATSubstCollector<'tcx> {
686 fn visit<T: TypeFoldable<'tcx>>(
690 ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) {
691 let mut visitor = GATSubstCollector {
694 regions: FxHashSet::default(),
695 types: FxHashSet::default(),
697 t.visit_with(&mut visitor);
698 (visitor.regions, visitor.types)
702 impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
705 fn visit_binder<T: TypeFoldable<'tcx>>(
707 t: &ty::Binder<'tcx, T>,
708 ) -> ControlFlow<Self::BreakTy> {
709 self.tcx.liberate_late_bound_regions(self.gat, t.clone()).visit_with(self)
712 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
714 ty::Projection(p) if p.item_def_id == self.gat => {
715 for (idx, subst) in p.substs.iter().enumerate() {
716 match subst.unpack() {
717 GenericArgKind::Lifetime(lt) => {
718 self.regions.insert((lt, idx));
720 GenericArgKind::Type(t) => {
721 self.types.insert((t, idx));
729 t.super_visit_with(self)
733 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
735 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
736 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
743 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
744 /// When this is done, suggest using `Self` instead.
745 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
746 let (trait_name, trait_def_id) =
747 match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id())) {
748 hir::Node::Item(item) => match item.kind {
749 hir::ItemKind::Trait(..) => (item.ident, item.def_id),
754 let mut trait_should_be_self = vec![];
756 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
757 if could_be_self(trait_def_id, ty) =>
759 trait_should_be_self.push(ty.span)
761 hir::TraitItemKind::Fn(sig, _) => {
762 for ty in sig.decl.inputs {
763 if could_be_self(trait_def_id, ty) {
764 trait_should_be_self.push(ty.span);
767 match sig.decl.output {
768 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
769 trait_should_be_self.push(ty.span);
776 if !trait_should_be_self.is_empty() {
777 if tcx.object_safety_violations(trait_def_id).is_empty() {
780 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
783 trait_should_be_self,
784 "associated item referring to unboxed trait object for its own trait",
786 .span_label(trait_name.span, "in this trait")
787 .multipart_suggestion(
788 "you might have meant to use `Self` to refer to the implementing type",
790 Applicability::MachineApplicable,
796 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
797 let impl_item = tcx.hir().expect_impl_item(def_id);
799 let (method_sig, span) = match impl_item.kind {
800 hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span),
801 // Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`.
802 hir::ImplItemKind::TyAlias(ty) if ty.span != DUMMY_SP => (None, ty.span),
803 _ => (None, impl_item.span),
806 check_associated_item(tcx, impl_item.def_id, span, method_sig);
809 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
811 // We currently only check wf of const params here.
812 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
814 // Const parameters are well formed if their type is structural match.
815 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
816 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
819 let mut is_ptr = true;
820 let err = if tcx.features().adt_const_params {
821 match ty.peel_refs().kind() {
822 ty::FnPtr(_) => Some("function pointers"),
823 ty::RawPtr(_) => Some("raw pointers"),
828 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
829 ty::FnPtr(_) => Some("function pointers"),
830 ty::RawPtr(_) => Some("raw pointers"),
833 err_ty_str = format!("`{}`", ty);
834 Some(err_ty_str.as_str())
838 if let Some(unsupported_type) = err {
843 "using {} as const generic parameters is forbidden",
848 let mut err = tcx.sess.struct_span_err(
851 "{} is forbidden as the type of a const generic parameter",
855 err.note("the only supported types are integers, `bool` and `char`");
856 if tcx.sess.is_nightly_build() {
858 "more complex types are supported with `#![feature(adt_const_params)]`",
865 if traits::search_for_structural_match_violation(param.span, tcx, ty).is_some() {
866 // We use the same error code in both branches, because this is really the same
867 // issue: we just special-case the message for type parameters to make it
869 if let ty::Param(_) = ty.peel_refs().kind() {
870 // Const parameters may not have type parameters as their types,
871 // because we cannot be sure that the type parameter derives `PartialEq`
872 // and `Eq` (just implementing them is not enough for `structural_match`).
877 "`{}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
878 used as the type of a const parameter",
883 format!("`{}` may not derive both `PartialEq` and `Eq`", ty),
886 "it is not currently possible to use a type parameter as the type of a \
895 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
896 the type of a const parameter",
901 format!("`{}` doesn't derive both `PartialEq` and `Eq`", ty),
910 #[tracing::instrument(level = "debug", skip(tcx, span, sig_if_method))]
911 fn check_associated_item(
915 sig_if_method: Option<&hir::FnSig<'_>>,
917 let code = ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(item_id)));
918 for_id(tcx, item_id, span).with_fcx(|fcx| {
919 let item = fcx.tcx.associated_item(item_id);
921 let (mut implied_bounds, self_ty) = match item.container {
922 ty::TraitContainer(_) => (FxHashSet::default(), fcx.tcx.types.self_param),
923 ty::ImplContainer(def_id) => {
924 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
929 ty::AssocKind::Const => {
930 let ty = fcx.tcx.type_of(item.def_id);
931 let ty = fcx.normalize_associated_types_in_wf(span, ty, WellFormedLoc::Ty(item_id));
932 fcx.register_wf_obligation(ty.into(), span, code.clone());
934 ty::AssocKind::Fn => {
935 let sig = fcx.tcx.fn_sig(item.def_id);
936 let hir_sig = sig_if_method.expect("bad signature for method");
939 item.ident(fcx.tcx).span,
945 check_method_receiver(fcx, hir_sig, item, self_ty);
947 ty::AssocKind::Type => {
948 if let ty::AssocItemContainer::TraitContainer(_) = item.container {
949 check_associated_type_bounds(fcx, item, span)
951 if item.defaultness.has_value() {
952 let ty = fcx.tcx.type_of(item.def_id);
954 fcx.normalize_associated_types_in_wf(span, ty, WellFormedLoc::Ty(item_id));
955 fcx.register_wf_obligation(ty.into(), span, code.clone());
964 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
965 for_id(tcx, item.def_id, item.span)
968 fn for_id(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) -> CheckWfFcxBuilder<'_> {
970 inherited: Inherited::build(tcx, def_id),
971 id: hir::HirId::make_owner(def_id),
973 param_env: tcx.param_env(def_id),
977 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
979 ItemKind::Struct(..) => Some(AdtKind::Struct),
980 ItemKind::Union(..) => Some(AdtKind::Union),
981 ItemKind::Enum(..) => Some(AdtKind::Enum),
986 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
987 fn check_type_defn<'tcx, F>(
989 item: &hir::Item<'tcx>,
991 mut lookup_fields: F,
993 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
995 for_item(tcx, item).with_fcx(|fcx| {
996 let variants = lookup_fields(fcx);
997 let packed = tcx.adt_def(item.def_id).repr.packed();
999 for variant in &variants {
1000 // For DST, or when drop needs to copy things around, all
1001 // intermediate types must be sized.
1002 let needs_drop_copy = || {
1004 let ty = variant.fields.last().unwrap().ty;
1005 let ty = tcx.erase_regions(ty);
1006 if ty.needs_infer() {
1008 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
1009 // Just treat unresolved type expression as if it needs drop.
1012 ty.needs_drop(tcx, tcx.param_env(item.def_id))
1016 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
1017 let unsized_len = if all_sized { 0 } else { 1 };
1019 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
1021 let last = idx == variant.fields.len() - 1;
1024 tcx.require_lang_item(LangItem::Sized, None),
1025 traits::ObligationCause::new(
1028 traits::FieldSized {
1029 adt_kind: match item_adt_kind(&item.kind) {
1040 // All field types must be well-formed.
1041 for field in &variant.fields {
1042 fcx.register_wf_obligation(
1045 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(field.def_id))),
1049 // Explicit `enum` discriminant values must const-evaluate successfully.
1050 if let Some(discr_def_id) = variant.explicit_discr {
1051 let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());
1053 let cause = traits::ObligationCause::new(
1054 tcx.def_span(discr_def_id),
1056 traits::MiscObligation,
1058 fcx.register_predicate(traits::Obligation::new(
1061 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ty::Unevaluated::new(
1062 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
1070 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
1072 // No implied bounds in a struct definition.
1073 FxHashSet::default()
1077 #[instrument(skip(tcx, item))]
1078 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
1079 debug!(?item.def_id);
1081 let trait_def = tcx.trait_def(item.def_id);
1082 if trait_def.is_marker
1083 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
1085 for associated_def_id in &*tcx.associated_item_def_ids(item.def_id) {
1088 tcx.def_span(*associated_def_id),
1090 "marker traits cannot have associated items",
1096 // FIXME: this shouldn't use an `FnCtxt` at all.
1097 for_item(tcx, item).with_fcx(|fcx| {
1098 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
1100 FxHashSet::default()
1103 // Only check traits, don't check trait aliases
1104 if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
1105 check_gat_where_clauses(tcx, items);
1109 /// Checks all associated type defaults of trait `trait_def_id`.
1111 /// Assuming the defaults are used, check that all predicates (bounds on the
1112 /// assoc type and where clauses on the trait) hold.
1113 fn check_associated_type_bounds(fcx: &FnCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
1116 let bounds = tcx.explicit_item_bounds(item.def_id);
1118 debug!("check_associated_type_bounds: bounds={:?}", bounds);
1119 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1120 let normalized_bound = fcx.normalize_associated_types_in(span, bound);
1121 traits::wf::predicate_obligations(
1130 for obligation in wf_obligations {
1131 debug!("next obligation cause: {:?}", obligation.cause);
1132 fcx.register_predicate(obligation);
1141 decl: &hir::FnDecl<'_>,
1143 for_id(tcx, def_id, span).with_fcx(|fcx| {
1144 let sig = tcx.fn_sig(def_id);
1145 let mut implied_bounds = FxHashSet::default();
1146 check_fn_or_method(fcx, ident.span, sig, decl, def_id.to_def_id(), &mut implied_bounds);
1151 fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) {
1152 debug!("check_item_type: {:?}", item_id);
1154 for_id(tcx, item_id, ty_span).with_fcx(|fcx| {
1155 let ty = tcx.type_of(item_id);
1156 let item_ty = fcx.normalize_associated_types_in_wf(ty_span, ty, WellFormedLoc::Ty(item_id));
1158 let mut forbid_unsized = true;
1159 if allow_foreign_ty {
1160 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
1161 if let ty::Foreign(_) = tail.kind() {
1162 forbid_unsized = false;
1166 fcx.register_wf_obligation(
1169 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(item_id))),
1174 tcx.require_lang_item(LangItem::Sized, None),
1175 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
1179 // Ensure that the end result is `Sync` in a non-thread local `static`.
1180 let should_check_for_sync = tcx.static_mutability(item_id.to_def_id())
1181 == Some(hir::Mutability::Not)
1182 && !tcx.is_foreign_item(item_id.to_def_id())
1183 && !tcx.is_thread_local_static(item_id.to_def_id());
1185 if should_check_for_sync {
1188 tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
1189 traits::ObligationCause::new(ty_span, fcx.body_id, traits::SharedStatic),
1193 // No implied bounds in a const, etc.
1194 FxHashSet::default()
1198 #[tracing::instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))]
1199 fn check_impl<'tcx>(
1201 item: &'tcx hir::Item<'tcx>,
1202 ast_self_ty: &hir::Ty<'_>,
1203 ast_trait_ref: &Option<hir::TraitRef<'_>>,
1205 for_item(tcx, item).with_fcx(|fcx| {
1206 match *ast_trait_ref {
1207 Some(ref ast_trait_ref) => {
1208 // `#[rustc_reservation_impl]` impls are not real impls and
1209 // therefore don't need to be WF (the trait's `Self: Trait` predicate
1211 let trait_ref = tcx.impl_trait_ref(item.def_id).unwrap();
1213 fcx.normalize_associated_types_in(ast_trait_ref.path.span, trait_ref);
1214 let obligations = traits::wf::trait_obligations(
1219 ast_trait_ref.path.span,
1222 debug!(?obligations);
1223 for obligation in obligations {
1224 fcx.register_predicate(obligation);
1228 let self_ty = tcx.type_of(item.def_id);
1229 let self_ty = fcx.normalize_associated_types_in(item.span, self_ty);
1230 fcx.register_wf_obligation(
1233 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(
1234 item.hir_id().expect_owner(),
1240 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
1242 fcx.impl_implied_bounds(item.def_id.to_def_id(), item.span)
1246 /// Checks where-clauses and inline bounds that are declared on `def_id`.
1247 #[instrument(skip(fcx), level = "debug")]
1248 fn check_where_clauses<'tcx, 'fcx>(
1249 fcx: &FnCtxt<'fcx, 'tcx>,
1252 return_ty: Option<(Ty<'tcx>, Span)>,
1256 let predicates = tcx.predicates_of(def_id);
1257 let generics = tcx.generics_of(def_id);
1259 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
1260 GenericParamDefKind::Type { has_default, .. }
1261 | GenericParamDefKind::Const { has_default } => {
1262 has_default && def.index >= generics.parent_count as u32
1264 GenericParamDefKind::Lifetime => unreachable!(),
1267 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
1268 // For example, this forbids the declaration:
1270 // struct Foo<T = Vec<[u32]>> { .. }
1272 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
1273 for param in &generics.params {
1275 GenericParamDefKind::Type { .. } => {
1276 if is_our_default(param) {
1277 let ty = tcx.type_of(param.def_id);
1278 // Ignore dependent defaults -- that is, where the default of one type
1279 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
1280 // be sure if it will error or not as user might always specify the other.
1281 if !ty.needs_subst() {
1282 fcx.register_wf_obligation(
1284 tcx.def_span(param.def_id),
1285 ObligationCauseCode::MiscObligation,
1290 GenericParamDefKind::Const { .. } => {
1291 if is_our_default(param) {
1292 // FIXME(const_generics_defaults): This
1293 // is incorrect when dealing with unused substs, for example
1294 // for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
1295 // we should eagerly error.
1296 let default_ct = tcx.const_param_default(param.def_id);
1297 if !default_ct.needs_subst() {
1298 fcx.register_wf_obligation(
1300 tcx.def_span(param.def_id),
1301 ObligationCauseCode::WellFormed(None),
1306 // Doesn't have defaults.
1307 GenericParamDefKind::Lifetime => {}
1311 // Check that trait predicates are WF when params are substituted by their defaults.
1312 // We don't want to overly constrain the predicates that may be written but we want to
1313 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
1314 // Therefore we check if a predicate which contains a single type param
1315 // with a concrete default is WF with that default substituted.
1316 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
1318 // First we build the defaulted substitution.
1319 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
1321 GenericParamDefKind::Lifetime => {
1322 // All regions are identity.
1323 tcx.mk_param_from_def(param)
1326 GenericParamDefKind::Type { .. } => {
1327 // If the param has a default, ...
1328 if is_our_default(param) {
1329 let default_ty = tcx.type_of(param.def_id);
1330 // ... and it's not a dependent default, ...
1331 if !default_ty.needs_subst() {
1332 // ... then substitute it with the default.
1333 return default_ty.into();
1337 tcx.mk_param_from_def(param)
1339 GenericParamDefKind::Const { .. } => {
1340 // If the param has a default, ...
1341 if is_our_default(param) {
1342 let default_ct = tcx.const_param_default(param.def_id);
1343 // ... and it's not a dependent default, ...
1344 if !default_ct.needs_subst() {
1345 // ... then substitute it with the default.
1346 return default_ct.into();
1350 tcx.mk_param_from_def(param)
1355 // Now we build the substituted predicates.
1356 let default_obligations = predicates
1359 .flat_map(|&(pred, sp)| {
1361 struct CountParams {
1362 params: FxHashSet<u32>,
1364 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
1367 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1368 if let ty::Param(param) = t.kind() {
1369 self.params.insert(param.index);
1371 t.super_visit_with(self)
1374 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1378 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1379 if let ty::ConstKind::Param(param) = c.val() {
1380 self.params.insert(param.index);
1382 c.super_visit_with(self)
1385 let mut param_count = CountParams::default();
1386 let has_region = pred.visit_with(&mut param_count).is_break();
1387 let substituted_pred = pred.subst(tcx, substs);
1388 // Don't check non-defaulted params, dependent defaults (including lifetimes)
1389 // or preds with multiple params.
1390 if substituted_pred.has_param_types_or_consts()
1391 || param_count.params.len() > 1
1395 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
1396 // Avoid duplication of predicates that contain no parameters, for example.
1399 Some((substituted_pred, sp))
1403 // Convert each of those into an obligation. So if you have
1404 // something like `struct Foo<T: Copy = String>`, we would
1405 // take that predicate `T: Copy`, substitute to `String: Copy`
1406 // (actually that happens in the previous `flat_map` call),
1407 // and then try to prove it (in this case, we'll fail).
1409 // Note the subtle difference from how we handle `predicates`
1410 // below: there, we are not trying to prove those predicates
1411 // to be *true* but merely *well-formed*.
1412 let pred = fcx.normalize_associated_types_in(sp, pred);
1414 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
1415 traits::Obligation::new(cause, fcx.param_env, pred)
1418 let predicates = predicates.instantiate_identity(tcx);
1420 if let Some((return_ty, _)) = return_ty {
1421 if return_ty.has_infer_types_or_consts() {
1422 fcx.select_obligations_where_possible(false, |_| {});
1426 let predicates = fcx.normalize_associated_types_in(span, predicates);
1428 debug!(?predicates.predicates);
1429 assert_eq!(predicates.predicates.len(), predicates.spans.len());
1430 let wf_obligations =
1431 iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| {
1432 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
1435 for obligation in wf_obligations.chain(default_obligations) {
1436 debug!("next obligation cause: {:?}", obligation.cause);
1437 fcx.register_predicate(obligation);
1441 #[tracing::instrument(level = "debug", skip(fcx, span, hir_decl))]
1442 fn check_fn_or_method<'fcx, 'tcx>(
1443 fcx: &FnCtxt<'fcx, 'tcx>,
1445 sig: ty::PolyFnSig<'tcx>,
1446 hir_decl: &hir::FnDecl<'_>,
1448 implied_bounds: &mut FxHashSet<Ty<'tcx>>,
1450 let sig = fcx.tcx.liberate_late_bound_regions(def_id, sig);
1452 // Normalize the input and output types one at a time, using a different
1453 // `WellFormedLoc` for each. We cannot call `normalize_associated_types`
1454 // on the entire `FnSig`, since this would use the same `WellFormedLoc`
1455 // for each type, preventing the HIR wf check from generating
1456 // a nice error message.
1457 let ty::FnSig { mut inputs_and_output, c_variadic, unsafety, abi } = sig;
1459 fcx.tcx.mk_type_list(inputs_and_output.iter().enumerate().map(|(i, ty)| {
1460 fcx.normalize_associated_types_in_wf(
1463 WellFormedLoc::Param {
1464 function: def_id.expect_local(),
1465 // Note that the `param_idx` of the output type is
1466 // one greater than the index of the last input type.
1467 param_idx: i.try_into().unwrap(),
1471 // Manually call `normalize_assocaited_types_in` on the other types
1472 // in `FnSig`. This ensures that if the types of these fields
1473 // ever change to include projections, we will start normalizing
1474 // them automatically.
1475 let sig = ty::FnSig {
1477 c_variadic: fcx.normalize_associated_types_in(span, c_variadic),
1478 unsafety: fcx.normalize_associated_types_in(span, unsafety),
1479 abi: fcx.normalize_associated_types_in(span, abi),
1482 for (i, (&input_ty, ty)) in iter::zip(sig.inputs(), hir_decl.inputs).enumerate() {
1483 fcx.register_wf_obligation(
1486 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Param {
1487 function: def_id.expect_local(),
1488 param_idx: i.try_into().unwrap(),
1493 implied_bounds.extend(sig.inputs());
1495 fcx.register_wf_obligation(
1496 sig.output().into(),
1497 hir_decl.output.span(),
1498 ObligationCauseCode::ReturnType,
1501 // FIXME(#27579) return types should not be implied bounds
1502 implied_bounds.insert(sig.output());
1504 debug!(?implied_bounds);
1506 check_where_clauses(fcx, span, def_id, Some((sig.output(), hir_decl.output.span())));
1509 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1510 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1511 of the previous types except `Self`)";
1513 #[tracing::instrument(level = "debug", skip(fcx))]
1514 fn check_method_receiver<'fcx, 'tcx>(
1515 fcx: &FnCtxt<'fcx, 'tcx>,
1516 fn_sig: &hir::FnSig<'_>,
1517 method: &ty::AssocItem,
1520 // Check that the method has a valid receiver type, given the type `Self`.
1521 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1523 if !method.fn_has_self_parameter {
1527 let span = fn_sig.decl.inputs[0].span;
1529 let sig = fcx.tcx.fn_sig(method.def_id);
1530 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, sig);
1531 let sig = fcx.normalize_associated_types_in(span, sig);
1533 debug!("check_method_receiver: sig={:?}", sig);
1535 let self_ty = fcx.normalize_associated_types_in(span, self_ty);
1537 let receiver_ty = sig.inputs()[0];
1538 let receiver_ty = fcx.normalize_associated_types_in(span, receiver_ty);
1540 if fcx.tcx.features().arbitrary_self_types {
1541 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1542 // Report error; `arbitrary_self_types` was enabled.
1543 e0307(fcx, span, receiver_ty);
1546 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1547 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1548 // Report error; would have worked with `arbitrary_self_types`.
1550 &fcx.tcx.sess.parse_sess,
1551 sym::arbitrary_self_types,
1554 "`{}` cannot be used as the type of `self` without \
1555 the `arbitrary_self_types` feature",
1559 .help(HELP_FOR_SELF_TYPE)
1562 // Report error; would not have worked with `arbitrary_self_types`.
1563 e0307(fcx, span, receiver_ty);
1569 fn e0307<'tcx>(fcx: &FnCtxt<'_, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1571 fcx.tcx.sess.diagnostic(),
1574 "invalid `self` parameter type: {}",
1577 .note("type of `self` must be `Self` or a type that dereferences to it")
1578 .help(HELP_FOR_SELF_TYPE)
1582 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1583 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1584 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1585 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1586 /// `Deref<Target = self_ty>`.
1588 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1589 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1590 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1591 fn receiver_is_valid<'fcx, 'tcx>(
1592 fcx: &FnCtxt<'fcx, 'tcx>,
1594 receiver_ty: Ty<'tcx>,
1596 arbitrary_self_types_enabled: bool,
1598 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1600 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1602 // `self: Self` is always valid.
1603 if can_eq_self(receiver_ty) {
1604 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1610 let mut autoderef = fcx.autoderef(span, receiver_ty);
1612 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1613 if arbitrary_self_types_enabled {
1614 autoderef = autoderef.include_raw_pointers();
1617 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1620 let receiver_trait_def_id = fcx.tcx.require_lang_item(LangItem::Receiver, None);
1622 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1624 if let Some((potential_self_ty, _)) = autoderef.next() {
1626 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1627 potential_self_ty, self_ty
1630 if can_eq_self(potential_self_ty) {
1631 fcx.register_predicates(autoderef.into_obligations());
1633 if let Some(mut err) =
1634 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1641 // Without `feature(arbitrary_self_types)`, we require that each step in the
1642 // deref chain implement `receiver`
1643 if !arbitrary_self_types_enabled
1644 && !receiver_is_implemented(
1646 receiver_trait_def_id,
1655 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1656 // If he receiver already has errors reported due to it, consider it valid to avoid
1657 // unnecessary errors (#58712).
1658 return receiver_ty.references_error();
1662 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1663 if !arbitrary_self_types_enabled
1664 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1672 fn receiver_is_implemented<'tcx>(
1673 fcx: &FnCtxt<'_, 'tcx>,
1674 receiver_trait_def_id: DefId,
1675 cause: ObligationCause<'tcx>,
1676 receiver_ty: Ty<'tcx>,
1678 let trait_ref = ty::Binder::dummy(ty::TraitRef {
1679 def_id: receiver_trait_def_id,
1680 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1683 let obligation = traits::Obligation::new(
1686 trait_ref.without_const().to_predicate(fcx.tcx),
1689 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1693 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1700 fn check_variances_for_type_defn<'tcx>(
1702 item: &hir::Item<'tcx>,
1703 hir_generics: &hir::Generics<'_>,
1705 let ty = tcx.type_of(item.def_id);
1706 if tcx.has_error_field(ty) {
1710 let ty_predicates = tcx.predicates_of(item.def_id);
1711 assert_eq!(ty_predicates.parent, None);
1712 let variances = tcx.variances_of(item.def_id);
1714 let mut constrained_parameters: FxHashSet<_> = variances
1717 .filter(|&(_, &variance)| variance != ty::Bivariant)
1718 .map(|(index, _)| Parameter(index as u32))
1721 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1723 for (index, _) in variances.iter().enumerate() {
1724 if constrained_parameters.contains(&Parameter(index as u32)) {
1728 let param = &hir_generics.params[index];
1731 hir::ParamName::Error => {}
1733 report_bivariance(tcx, param);
1739 fn report_bivariance(tcx: TyCtxt<'_>, param: &rustc_hir::GenericParam<'_>) -> ErrorReported {
1740 let span = param.span;
1741 let param_name = param.name.ident().name;
1742 let mut err = error_392(tcx, span, param_name);
1744 let suggested_marker_id = tcx.lang_items().phantom_data();
1745 // Help is available only in presence of lang items.
1746 let msg = if let Some(def_id) = suggested_marker_id {
1748 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1750 tcx.def_path_str(def_id),
1753 format!("consider removing `{}` or referring to it in a field", param_name)
1757 if matches!(param.kind, rustc_hir::GenericParamKind::Type { .. }) {
1759 "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
1766 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1768 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, mut span: Span, id: hir::HirId) {
1769 let empty_env = ty::ParamEnv::empty();
1771 let def_id = fcx.tcx.hir().local_def_id(id);
1772 let predicates_with_span =
1773 fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, span)| (*p, *span));
1774 // Check elaborated bounds.
1775 let implied_obligations = traits::elaborate_predicates_with_span(fcx.tcx, predicates_with_span);
1777 for obligation in implied_obligations {
1778 let pred = obligation.predicate;
1779 // Match the existing behavior.
1780 if pred.is_global() && !pred.has_late_bound_regions() {
1781 let pred = fcx.normalize_associated_types_in(span, pred);
1782 let hir_node = fcx.tcx.hir().find(id);
1784 // only use the span of the predicate clause (#90869)
1786 if let Some(hir::Generics { where_clause, .. }) =
1787 hir_node.and_then(|node| node.generics())
1789 let obligation_span = obligation.cause.span(fcx.tcx);
1794 // There seems to be no better way to find out which predicate we are in
1795 .find(|pred| pred.span().contains(obligation_span))
1796 .map(|pred| pred.span())
1797 .unwrap_or(obligation_span);
1800 let obligation = traits::Obligation::new(
1801 traits::ObligationCause::new(span, id, traits::TrivialBound),
1805 fcx.register_predicate(obligation);
1809 fcx.select_all_obligations_or_error();
1812 #[derive(Clone, Copy)]
1813 pub struct CheckTypeWellFormedVisitor<'tcx> {
1817 impl<'tcx> CheckTypeWellFormedVisitor<'tcx> {
1818 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1819 CheckTypeWellFormedVisitor { tcx }
1823 impl<'tcx> ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1824 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1825 Visitor::visit_item(&mut self.clone(), i);
1828 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1829 Visitor::visit_trait_item(&mut self.clone(), trait_item);
1832 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1833 Visitor::visit_impl_item(&mut self.clone(), impl_item);
1836 fn visit_foreign_item(&self, foreign_item: &'tcx hir::ForeignItem<'tcx>) {
1837 Visitor::visit_foreign_item(&mut self.clone(), foreign_item)
1841 impl<'tcx> Visitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1842 type NestedFilter = nested_filter::OnlyBodies;
1844 fn nested_visit_map(&mut self) -> Self::Map {
1848 #[instrument(skip(self, i), level = "debug")]
1849 fn visit_item(&mut self, i: &'tcx hir::Item<'tcx>) {
1851 self.tcx.ensure().check_item_well_formed(i.def_id);
1852 hir_visit::walk_item(self, i);
1855 #[instrument(skip(self, trait_item), level = "debug")]
1856 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1857 trace!(?trait_item);
1858 self.tcx.ensure().check_trait_item_well_formed(trait_item.def_id);
1859 hir_visit::walk_trait_item(self, trait_item);
1862 #[instrument(skip(self, impl_item), level = "debug")]
1863 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1865 self.tcx.ensure().check_impl_item_well_formed(impl_item.def_id);
1866 hir_visit::walk_impl_item(self, impl_item);
1869 fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
1870 check_param_wf(self.tcx, p);
1871 hir_visit::walk_generic_param(self, p);
1875 ///////////////////////////////////////////////////////////////////////////
1878 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1879 struct AdtVariant<'tcx> {
1880 /// Types of fields in the variant, that must be well-formed.
1881 fields: Vec<AdtField<'tcx>>,
1883 /// Explicit discriminant of this variant (e.g. `A = 123`),
1884 /// that must evaluate to a constant value.
1885 explicit_discr: Option<LocalDefId>,
1888 struct AdtField<'tcx> {
1894 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1895 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1896 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1897 let fields = struct_def
1901 let def_id = self.tcx.hir().local_def_id(field.hir_id);
1902 let field_ty = self.tcx.type_of(def_id);
1903 let field_ty = self.normalize_associated_types_in(field.ty.span, field_ty);
1904 let field_ty = self.resolve_vars_if_possible(field_ty);
1905 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1906 AdtField { ty: field_ty, span: field.ty.span, def_id }
1909 AdtVariant { fields, explicit_discr: None }
1912 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1916 .map(|variant| AdtVariant {
1917 fields: self.non_enum_variant(&variant.data).fields,
1918 explicit_discr: variant
1920 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1925 pub(super) fn impl_implied_bounds(
1929 ) -> FxHashSet<Ty<'tcx>> {
1930 match self.tcx.impl_trait_ref(impl_def_id) {
1931 Some(trait_ref) => {
1932 // Trait impl: take implied bounds from all types that
1933 // appear in the trait reference.
1934 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1935 trait_ref.substs.types().collect()
1939 // Inherent impl: take implied bounds from the `self` type.
1940 let self_ty = self.tcx.type_of(impl_def_id);
1941 let self_ty = self.normalize_associated_types_in(span, self_ty);
1942 FxHashSet::from_iter([self_ty])
1952 ) -> DiagnosticBuilder<'_, ErrorReported> {
1954 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1955 err.span_label(span, "unused parameter");