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, ErrorGuaranteed};
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;
35 use std::ops::ControlFlow;
37 /// Helper type of a temporary returned by `.for_item(...)`.
38 /// This is necessary because we can't write the following bound:
41 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
43 struct CheckWfFcxBuilder<'tcx> {
44 inherited: super::InheritedBuilder<'tcx>,
47 param_env: ty::ParamEnv<'tcx>,
50 impl<'tcx> CheckWfFcxBuilder<'tcx> {
51 fn with_fcx<F>(&mut self, f: F)
53 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>) -> FxHashSet<Ty<'tcx>>,
57 let param_env = self.param_env;
58 self.inherited.enter(|inh| {
59 let fcx = FnCtxt::new(&inh, param_env, id);
60 if !inh.tcx.features().trivial_bounds {
61 // As predicates are cached rather than obligations, this
62 // needs to be called first so that they are checked with an
64 check_false_global_bounds(&fcx, span, id);
67 fcx.select_all_obligations_or_error();
68 fcx.regionck_item(id, span, wf_tys);
73 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
74 /// well-formed, meaning that they do not require any constraints not declared in the struct
75 /// definition itself. For example, this definition would be illegal:
78 /// struct Ref<'a, T> { x: &'a T }
81 /// because the type did not declare that `T:'a`.
83 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
84 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
86 #[instrument(skip(tcx), level = "debug")]
87 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
88 let item = tcx.hir().expect_item(def_id);
92 item.name = ? tcx.def_path_str(def_id.to_def_id())
96 // Right now we check that every default trait implementation
97 // has an implementation of itself. Basically, a case like:
99 // impl Trait for T {}
101 // has a requirement of `T: Trait` which was required for default
102 // method implementations. Although this could be improved now that
103 // there's a better infrastructure in place for this, it's being left
104 // for a follow-up work.
106 // Since there's such a requirement, we need to check *just* positive
107 // implementations, otherwise things like:
109 // impl !Send for T {}
111 // won't be allowed unless there's an *explicit* implementation of `Send`
113 hir::ItemKind::Impl(ref impl_) => {
115 .impl_trait_ref(item.def_id)
116 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
117 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
118 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
120 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
121 err.span_labels(impl_.defaultness_span, "default because of this");
122 err.span_label(sp, "auto trait");
125 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
126 match (tcx.impl_polarity(def_id), impl_.polarity) {
127 (ty::ImplPolarity::Positive, _) => {
128 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait);
130 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
131 // FIXME(#27579): what amount of WF checking do we need for neg impls?
132 if let hir::Defaultness::Default { .. } = impl_.defaultness {
133 let mut spans = vec![span];
134 spans.extend(impl_.defaultness_span);
139 "negative impls cannot be default impls"
144 (ty::ImplPolarity::Reservation, _) => {
145 // FIXME: what amount of WF checking do we need for reservation impls?
150 hir::ItemKind::Fn(ref sig, ..) => {
151 check_item_fn(tcx, item.def_id, item.ident, item.span, sig.decl);
153 hir::ItemKind::Static(ty, ..) => {
154 check_item_type(tcx, item.def_id, ty.span, false);
156 hir::ItemKind::Const(ty, ..) => {
157 check_item_type(tcx, item.def_id, ty.span, false);
159 hir::ItemKind::ForeignMod { items, .. } => {
160 for it in items.iter() {
161 let it = tcx.hir().foreign_item(it.id);
163 hir::ForeignItemKind::Fn(decl, ..) => {
164 check_item_fn(tcx, it.def_id, it.ident, it.span, decl)
166 hir::ForeignItemKind::Static(ty, ..) => {
167 check_item_type(tcx, it.def_id, ty.span, true)
169 hir::ForeignItemKind::Type => (),
173 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
174 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
176 check_variances_for_type_defn(tcx, item, ast_generics);
178 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
179 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
181 check_variances_for_type_defn(tcx, item, ast_generics);
183 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
184 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
186 check_variances_for_type_defn(tcx, item, ast_generics);
188 hir::ItemKind::Trait(..) => {
189 check_trait(tcx, item);
191 hir::ItemKind::TraitAlias(..) => {
192 check_trait(tcx, item);
198 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
199 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
200 let trait_item = tcx.hir().expect_trait_item(def_id);
202 let (method_sig, span) = match trait_item.kind {
203 hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span),
204 hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span),
205 _ => (None, trait_item.span),
207 check_object_unsafe_self_trait_by_name(tcx, trait_item);
208 check_associated_item(tcx, trait_item.def_id, span, method_sig);
210 let encl_trait_def_id = tcx.hir().get_parent_item(hir_id);
211 let encl_trait = tcx.hir().expect_item(encl_trait_def_id);
212 let encl_trait_def_id = encl_trait.def_id.to_def_id();
213 let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() {
215 } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() {
221 if let (Some(fn_lang_item_name), "call") =
222 (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str())
224 // We are looking at the `call` function of the `fn` or `fn_mut` lang item.
225 // Do some rudimentary sanity checking to avoid an ICE later (issue #83471).
226 if let Some(hir::FnSig { decl, span, .. }) = method_sig {
227 if let [self_ty, _] = decl.inputs {
228 if !matches!(self_ty.kind, hir::TyKind::Rptr(_, _)) {
233 "first argument of `call` in `{}` lang item must be a reference",
244 "`call` function in `{}` lang item takes exactly two arguments",
255 "`call` trait item in `{}` lang item must be a function",
264 /// Require that the user writes where clauses on GATs for the implicit
265 /// outlives bounds involving trait parameters in trait functions and
266 /// lifetimes passed as GAT substs. See `self-outlives-lint` test.
268 /// We use the following trait as an example throughout this function:
269 /// ```rust,ignore (this code fails due to this lint)
271 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
273 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
276 fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
277 // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
278 let mut required_bounds_by_item = FxHashMap::default();
280 // Loop over all GATs together, because if this lint suggests adding a where-clause bound
281 // to one GAT, it might then require us to an additional bound on another GAT.
282 // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which
283 // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between
286 let mut should_continue = false;
287 for gat_item in associated_items {
288 let gat_def_id = gat_item.id.def_id;
289 let gat_item = tcx.associated_item(gat_def_id);
290 // If this item is not an assoc ty, or has no substs, then it's not a GAT
291 if gat_item.kind != ty::AssocKind::Type {
294 let gat_generics = tcx.generics_of(gat_def_id);
295 // FIXME(jackh726): we can also warn in the more general case
296 if gat_generics.params.is_empty() {
300 // Gather the bounds with which all other items inside of this trait constrain the GAT.
301 // This is calculated by taking the intersection of the bounds that each item
302 // constrains the GAT with individually.
303 let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
304 for item in associated_items {
305 let item_def_id = item.id.def_id;
306 // Skip our own GAT, since it does not constrain itself at all.
307 if item_def_id == gat_def_id {
311 let item_hir_id = item.id.hir_id();
312 let param_env = tcx.param_env(item_def_id);
314 let item_required_bounds = match item.kind {
315 // In our example, this corresponds to `into_iter` method
316 hir::AssocItemKind::Fn { .. } => {
317 // For methods, we check the function signature's return type for any GATs
318 // to constrain. In the `into_iter` case, we see that the return type
319 // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
320 let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions(
321 item_def_id.to_def_id(),
322 tcx.fn_sig(item_def_id),
329 // We also assume that all of the function signature's parameter types
331 &sig.inputs().iter().copied().collect(),
336 // In our example, this corresponds to the `Iter` and `Item` associated types
337 hir::AssocItemKind::Type => {
338 // If our associated item is a GAT with missing bounds, add them to
339 // the param-env here. This allows this GAT to propagate missing bounds
341 let param_env = augment_param_env(
344 required_bounds_by_item.get(&item_def_id),
350 tcx.explicit_item_bounds(item_def_id)
353 .collect::<Vec<_>>(),
354 &FxHashSet::default(),
359 hir::AssocItemKind::Const => None,
362 if let Some(item_required_bounds) = item_required_bounds {
363 // Take the intersection of the required bounds for this GAT, and
364 // the item_required_bounds which are the ones implied by just
366 // This is why we use an Option<_>, since we need to distinguish
367 // the empty set of bounds from the _uninitialized_ set of bounds.
368 if let Some(new_required_bounds) = &mut new_required_bounds {
369 new_required_bounds.retain(|b| item_required_bounds.contains(b));
371 new_required_bounds = Some(item_required_bounds);
376 if let Some(new_required_bounds) = new_required_bounds {
377 let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default();
378 if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) {
379 // Iterate until our required_bounds no longer change
380 // Since they changed here, we should continue the loop
381 should_continue = true;
385 // We know that this loop will eventually halt, since we only set `should_continue` if the
386 // `required_bounds` for this item grows. Since we are not creating any new region or type
387 // variables, the set of all region and type bounds that we could ever insert are limited
388 // by the number of unique types and regions we observe in a given item.
389 if !should_continue {
394 for (gat_def_id, required_bounds) in required_bounds_by_item {
395 let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id);
396 debug!(?required_bounds);
397 let param_env = tcx.param_env(gat_def_id);
398 let gat_hir = gat_item_hir.hir_id();
400 let mut unsatisfied_bounds: Vec<_> = required_bounds
402 .filter(|clause| match clause.kind().skip_binder() {
403 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
404 !region_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
406 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
407 !ty_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
409 _ => bug!("Unexpected PredicateKind"),
411 .map(|clause| clause.to_string())
414 // We sort so that order is predictable
415 unsatisfied_bounds.sort();
417 if !unsatisfied_bounds.is_empty() {
418 let plural = if unsatisfied_bounds.len() > 1 { "s" } else { "" };
419 let mut err = tcx.sess.struct_span_err(
421 &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
424 let suggestion = format!(
426 if !gat_item_hir.generics.where_clause.predicates.is_empty() {
431 unsatisfied_bounds.join(", "),
434 gat_item_hir.generics.where_clause.tail_span_for_suggestion(),
435 &format!("add the required where clause{}", plural),
437 Applicability::MachineApplicable,
441 if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
443 "{} currently required to ensure that impls have maximum flexibility",
447 "we are soliciting feedback, see issue #87479 \
448 <https://github.com/rust-lang/rust/issues/87479> \
449 for more information",
457 /// Add a new set of predicates to the caller_bounds of an existing param_env.
458 fn augment_param_env<'tcx>(
460 param_env: ty::ParamEnv<'tcx>,
461 new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
462 ) -> ty::ParamEnv<'tcx> {
463 let Some(new_predicates) = new_predicates else {
467 if new_predicates.is_empty() {
472 tcx.mk_predicates(param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()));
473 // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
474 // i.e. traits::normalize_param_env_or_error
475 ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness())
478 /// We use the following trait as an example throughout this function.
479 /// Specifically, let's assume that `to_check` here is the return type
480 /// of `into_iter`, and the GAT we are checking this for is `Iter`.
481 /// ```rust,ignore (this code fails due to this lint)
483 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
485 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
488 fn gather_gat_bounds<'tcx, T: TypeFoldable<'tcx>>(
490 param_env: ty::ParamEnv<'tcx>,
491 item_hir: hir::HirId,
493 wf_tys: &FxHashSet<Ty<'tcx>>,
494 gat_def_id: LocalDefId,
495 gat_generics: &'tcx ty::Generics,
496 ) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
497 // The bounds we that we would require from `to_check`
498 let mut bounds = FxHashSet::default();
500 let (regions, types) = GATSubstCollector::visit(tcx, gat_def_id.to_def_id(), to_check);
502 // If both regions and types are empty, then this GAT isn't in the
503 // set of types we are checking, and we shouldn't try to do clause analysis
504 // (particularly, doing so would end up with an empty set of clauses,
505 // since the current method would require none, and we take the
506 // intersection of requirements of all methods)
507 if types.is_empty() && regions.is_empty() {
511 for (region_a, region_a_idx) in ®ions {
512 // Ignore `'static` lifetimes for the purpose of this lint: it's
513 // because we know it outlives everything and so doesn't give meaninful
515 if let ty::ReStatic = **region_a {
518 // For each region argument (e.g., `'a` in our example), check for a
519 // relationship to the type arguments (e.g., `Self`). If there is an
520 // outlives relationship (`Self: 'a`), then we want to ensure that is
521 // reflected in a where clause on the GAT itself.
522 for (ty, ty_idx) in &types {
523 // In our example, requires that `Self: 'a`
524 if ty_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *ty, *region_a) {
525 debug!(?ty_idx, ?region_a_idx);
526 debug!("required clause: {} must outlive {}", ty, region_a);
527 // Translate into the generic parameters of the GAT. In
528 // our example, the type was `Self`, which will also be
529 // `Self` in the GAT.
530 let ty_param = gat_generics.param_at(*ty_idx, tcx);
532 .mk_ty(ty::Param(ty::ParamTy { index: ty_param.index, name: ty_param.name }));
533 // Same for the region. In our example, 'a corresponds
534 // to the 'me parameter.
535 let region_param = gat_generics.param_at(*region_a_idx, tcx);
537 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
538 def_id: region_param.def_id,
539 index: region_param.index,
540 name: region_param.name,
542 // The predicate we expect to see. (In our example,
545 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param));
546 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
547 bounds.insert(clause);
551 // For each region argument (e.g., `'a` in our example), also check for a
552 // relationship to the other region arguments. If there is an outlives
553 // relationship, then we want to ensure that is reflected in the where clause
554 // on the GAT itself.
555 for (region_b, region_b_idx) in ®ions {
556 // Again, skip `'static` because it outlives everything. Also, we trivially
557 // know that a region outlives itself.
558 if ty::ReStatic == **region_b || region_a == region_b {
561 if region_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *region_a, *region_b) {
562 debug!(?region_a_idx, ?region_b_idx);
563 debug!("required clause: {} must outlive {}", region_a, region_b);
564 // Translate into the generic parameters of the GAT.
565 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
567 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
568 def_id: region_a_param.def_id,
569 index: region_a_param.index,
570 name: region_a_param.name,
572 // Same for the region.
573 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
575 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
576 def_id: region_b_param.def_id,
577 index: region_b_param.index,
578 name: region_b_param.name,
580 // The predicate we expect to see.
581 let clause = ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(
585 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
586 bounds.insert(clause);
594 /// Given a known `param_env` and a set of well formed types, can we prove that
595 /// `ty` outlives `region`.
596 fn ty_known_to_outlive<'tcx>(
599 param_env: ty::ParamEnv<'tcx>,
600 wf_tys: &FxHashSet<Ty<'tcx>>,
602 region: ty::Region<'tcx>,
604 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| {
605 let origin = infer::RelateParamBound(DUMMY_SP, ty, None);
606 let outlives = &mut TypeOutlives::new(
610 Some(infcx.tcx.lifetimes.re_root_empty),
613 outlives.type_must_outlive(origin, ty, region);
617 /// Given a known `param_env` and a set of well formed types, can we prove that
618 /// `region_a` outlives `region_b`
619 fn region_known_to_outlive<'tcx>(
622 param_env: ty::ParamEnv<'tcx>,
623 wf_tys: &FxHashSet<Ty<'tcx>>,
624 region_a: ty::Region<'tcx>,
625 region_b: ty::Region<'tcx>,
627 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| {
628 use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
629 let origin = infer::RelateRegionParamBound(DUMMY_SP);
630 // `region_a: region_b` -> `region_b <= region_a`
631 infcx.push_sub_region_constraint(origin, region_b, region_a);
635 /// Given a known `param_env` and a set of well formed types, set up an
636 /// `InferCtxt`, call the passed function (to e.g. set up region constraints
637 /// to be tested), then resolve region and return errors
638 fn resolve_regions_with_wf_tys<'tcx>(
641 param_env: ty::ParamEnv<'tcx>,
642 wf_tys: &FxHashSet<Ty<'tcx>>,
643 add_constraints: impl for<'a> FnOnce(
644 &'a InferCtxt<'a, 'tcx>,
645 &'a Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>,
648 // Unfortunately, we have to use a new `InferCtxt` each call, because
649 // region constraints get added and solved there and we need to test each
650 // call individually.
651 tcx.infer_ctxt().enter(|infcx| {
652 let mut outlives_environment = OutlivesEnvironment::new(param_env);
653 outlives_environment.add_implied_bounds(&infcx, wf_tys.clone(), id, DUMMY_SP);
654 outlives_environment.save_implied_bounds(id);
655 let region_bound_pairs = outlives_environment.region_bound_pairs_map().get(&id).unwrap();
657 add_constraints(&infcx, region_bound_pairs);
659 let errors = infcx.resolve_regions(
660 id.expect_owner().to_def_id(),
661 &outlives_environment,
662 RegionckMode::default(),
665 debug!(?errors, "errors");
667 // If we were able to prove that the type outlives the region without
668 // an error, it must be because of the implied or explicit bounds...
673 /// TypeVisitor that looks for uses of GATs like
674 /// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into
675 /// the two vectors, `regions` and `types` (depending on their kind). For each
676 /// parameter `Pi` also track the index `i`.
677 struct GATSubstCollector<'tcx> {
680 // Which region appears and which parameter index its subsituted for
681 regions: FxHashSet<(ty::Region<'tcx>, usize)>,
682 // Which params appears and which parameter index its subsituted for
683 types: FxHashSet<(Ty<'tcx>, usize)>,
686 impl<'tcx> GATSubstCollector<'tcx> {
687 fn visit<T: TypeFoldable<'tcx>>(
691 ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) {
692 let mut visitor = GATSubstCollector {
695 regions: FxHashSet::default(),
696 types: FxHashSet::default(),
698 t.visit_with(&mut visitor);
699 (visitor.regions, visitor.types)
703 impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
706 fn visit_binder<T: TypeFoldable<'tcx>>(
708 t: &ty::Binder<'tcx, T>,
709 ) -> ControlFlow<Self::BreakTy> {
710 self.tcx.liberate_late_bound_regions(self.gat, t.clone()).visit_with(self)
713 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
715 ty::Projection(p) if p.item_def_id == self.gat => {
716 for (idx, subst) in p.substs.iter().enumerate() {
717 match subst.unpack() {
718 GenericArgKind::Lifetime(lt) => {
719 self.regions.insert((lt, idx));
721 GenericArgKind::Type(t) => {
722 self.types.insert((t, idx));
730 t.super_visit_with(self)
734 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
736 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
737 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
744 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
745 /// When this is done, suggest using `Self` instead.
746 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
747 let (trait_name, trait_def_id) =
748 match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id())) {
749 hir::Node::Item(item) => match item.kind {
750 hir::ItemKind::Trait(..) => (item.ident, item.def_id),
755 let mut trait_should_be_self = vec![];
757 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
758 if could_be_self(trait_def_id, ty) =>
760 trait_should_be_self.push(ty.span)
762 hir::TraitItemKind::Fn(sig, _) => {
763 for ty in sig.decl.inputs {
764 if could_be_self(trait_def_id, ty) {
765 trait_should_be_self.push(ty.span);
768 match sig.decl.output {
769 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
770 trait_should_be_self.push(ty.span);
777 if !trait_should_be_self.is_empty() {
778 if tcx.object_safety_violations(trait_def_id).is_empty() {
781 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
784 trait_should_be_self,
785 "associated item referring to unboxed trait object for its own trait",
787 .span_label(trait_name.span, "in this trait")
788 .multipart_suggestion(
789 "you might have meant to use `Self` to refer to the implementing type",
791 Applicability::MachineApplicable,
797 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
798 let impl_item = tcx.hir().expect_impl_item(def_id);
800 let (method_sig, span) = match impl_item.kind {
801 hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span),
802 // Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`.
803 hir::ImplItemKind::TyAlias(ty) if ty.span != DUMMY_SP => (None, ty.span),
804 _ => (None, impl_item.span),
807 check_associated_item(tcx, impl_item.def_id, span, method_sig);
810 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
812 // We currently only check wf of const params here.
813 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
815 // Const parameters are well formed if their type is structural match.
816 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
817 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
820 let mut is_ptr = true;
821 let err = if tcx.features().adt_const_params {
822 match ty.peel_refs().kind() {
823 ty::FnPtr(_) => Some("function pointers"),
824 ty::RawPtr(_) => Some("raw pointers"),
829 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
830 ty::FnPtr(_) => Some("function pointers"),
831 ty::RawPtr(_) => Some("raw pointers"),
834 err_ty_str = format!("`{}`", ty);
835 Some(err_ty_str.as_str())
839 if let Some(unsupported_type) = err {
844 "using {} as const generic parameters is forbidden",
849 let mut err = tcx.sess.struct_span_err(
852 "{} is forbidden as the type of a const generic parameter",
856 err.note("the only supported types are integers, `bool` and `char`");
857 if tcx.sess.is_nightly_build() {
859 "more complex types are supported with `#![feature(adt_const_params)]`",
866 if traits::search_for_structural_match_violation(param.span, tcx, ty).is_some() {
867 // We use the same error code in both branches, because this is really the same
868 // issue: we just special-case the message for type parameters to make it
870 if let ty::Param(_) = ty.peel_refs().kind() {
871 // Const parameters may not have type parameters as their types,
872 // because we cannot be sure that the type parameter derives `PartialEq`
873 // and `Eq` (just implementing them is not enough for `structural_match`).
878 "`{}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
879 used as the type of a const parameter",
884 format!("`{}` may not derive both `PartialEq` and `Eq`", ty),
887 "it is not currently possible to use a type parameter as the type of a \
896 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
897 the type of a const parameter",
902 format!("`{}` doesn't derive both `PartialEq` and `Eq`", ty),
911 #[tracing::instrument(level = "debug", skip(tcx, span, sig_if_method))]
912 fn check_associated_item(
916 sig_if_method: Option<&hir::FnSig<'_>>,
918 let code = ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(item_id)));
919 for_id(tcx, item_id, span).with_fcx(|fcx| {
920 let item = fcx.tcx.associated_item(item_id);
922 let (mut implied_bounds, self_ty) = match item.container {
923 ty::TraitContainer(_) => (FxHashSet::default(), fcx.tcx.types.self_param),
924 ty::ImplContainer(def_id) => {
925 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
930 ty::AssocKind::Const => {
931 let ty = fcx.tcx.type_of(item.def_id);
932 let ty = fcx.normalize_associated_types_in_wf(span, ty, WellFormedLoc::Ty(item_id));
933 fcx.register_wf_obligation(ty.into(), span, code.clone());
935 ty::AssocKind::Fn => {
936 let sig = fcx.tcx.fn_sig(item.def_id);
937 let hir_sig = sig_if_method.expect("bad signature for method");
940 item.ident(fcx.tcx).span,
946 check_method_receiver(fcx, hir_sig, item, self_ty);
948 ty::AssocKind::Type => {
949 if let ty::AssocItemContainer::TraitContainer(_) = item.container {
950 check_associated_type_bounds(fcx, item, span)
952 if item.defaultness.has_value() {
953 let ty = fcx.tcx.type_of(item.def_id);
955 fcx.normalize_associated_types_in_wf(span, ty, WellFormedLoc::Ty(item_id));
956 fcx.register_wf_obligation(ty.into(), span, code.clone());
965 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
966 for_id(tcx, item.def_id, item.span)
969 fn for_id(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) -> CheckWfFcxBuilder<'_> {
971 inherited: Inherited::build(tcx, def_id),
972 id: hir::HirId::make_owner(def_id),
974 param_env: tcx.param_env(def_id),
978 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
980 ItemKind::Struct(..) => Some(AdtKind::Struct),
981 ItemKind::Union(..) => Some(AdtKind::Union),
982 ItemKind::Enum(..) => Some(AdtKind::Enum),
987 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
988 fn check_type_defn<'tcx, F>(
990 item: &hir::Item<'tcx>,
992 mut lookup_fields: F,
994 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
996 for_item(tcx, item).with_fcx(|fcx| {
997 let variants = lookup_fields(fcx);
998 let packed = tcx.adt_def(item.def_id).repr().packed();
1000 for variant in &variants {
1001 // For DST, or when drop needs to copy things around, all
1002 // intermediate types must be sized.
1003 let needs_drop_copy = || {
1005 let ty = variant.fields.last().unwrap().ty;
1006 let ty = tcx.erase_regions(ty);
1007 if ty.needs_infer() {
1009 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
1010 // Just treat unresolved type expression as if it needs drop.
1013 ty.needs_drop(tcx, tcx.param_env(item.def_id))
1017 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
1018 let unsized_len = if all_sized { 0 } else { 1 };
1020 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
1022 let last = idx == variant.fields.len() - 1;
1025 tcx.require_lang_item(LangItem::Sized, None),
1026 traits::ObligationCause::new(
1029 traits::FieldSized {
1030 adt_kind: match item_adt_kind(&item.kind) {
1041 // All field types must be well-formed.
1042 for field in &variant.fields {
1043 fcx.register_wf_obligation(
1046 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(field.def_id))),
1050 // Explicit `enum` discriminant values must const-evaluate successfully.
1051 if let Some(discr_def_id) = variant.explicit_discr {
1052 let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());
1054 let cause = traits::ObligationCause::new(
1055 tcx.def_span(discr_def_id),
1057 traits::MiscObligation,
1059 fcx.register_predicate(traits::Obligation::new(
1062 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ty::Unevaluated::new(
1063 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
1071 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
1073 // No implied bounds in a struct definition.
1074 FxHashSet::default()
1078 #[instrument(skip(tcx, item))]
1079 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
1080 debug!(?item.def_id);
1082 let trait_def = tcx.trait_def(item.def_id);
1083 if trait_def.is_marker
1084 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
1086 for associated_def_id in &*tcx.associated_item_def_ids(item.def_id) {
1089 tcx.def_span(*associated_def_id),
1091 "marker traits cannot have associated items",
1097 // FIXME: this shouldn't use an `FnCtxt` at all.
1098 for_item(tcx, item).with_fcx(|fcx| {
1099 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
1101 FxHashSet::default()
1104 // Only check traits, don't check trait aliases
1105 if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
1106 check_gat_where_clauses(tcx, items);
1110 /// Checks all associated type defaults of trait `trait_def_id`.
1112 /// Assuming the defaults are used, check that all predicates (bounds on the
1113 /// assoc type and where clauses on the trait) hold.
1114 fn check_associated_type_bounds(fcx: &FnCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
1117 let bounds = tcx.explicit_item_bounds(item.def_id);
1119 debug!("check_associated_type_bounds: bounds={:?}", bounds);
1120 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1121 let normalized_bound = fcx.normalize_associated_types_in(span, bound);
1122 traits::wf::predicate_obligations(
1131 for obligation in wf_obligations {
1132 debug!("next obligation cause: {:?}", obligation.cause);
1133 fcx.register_predicate(obligation);
1142 decl: &hir::FnDecl<'_>,
1144 for_id(tcx, def_id, span).with_fcx(|fcx| {
1145 let sig = tcx.fn_sig(def_id);
1146 let mut implied_bounds = FxHashSet::default();
1147 check_fn_or_method(fcx, ident.span, sig, decl, def_id.to_def_id(), &mut implied_bounds);
1152 fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) {
1153 debug!("check_item_type: {:?}", item_id);
1155 for_id(tcx, item_id, ty_span).with_fcx(|fcx| {
1156 let ty = tcx.type_of(item_id);
1157 let item_ty = fcx.normalize_associated_types_in_wf(ty_span, ty, WellFormedLoc::Ty(item_id));
1159 let mut forbid_unsized = true;
1160 if allow_foreign_ty {
1161 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
1162 if let ty::Foreign(_) = tail.kind() {
1163 forbid_unsized = false;
1167 fcx.register_wf_obligation(
1170 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(item_id))),
1175 tcx.require_lang_item(LangItem::Sized, None),
1176 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
1180 // Ensure that the end result is `Sync` in a non-thread local `static`.
1181 let should_check_for_sync = tcx.static_mutability(item_id.to_def_id())
1182 == Some(hir::Mutability::Not)
1183 && !tcx.is_foreign_item(item_id.to_def_id())
1184 && !tcx.is_thread_local_static(item_id.to_def_id());
1186 if should_check_for_sync {
1189 tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
1190 traits::ObligationCause::new(ty_span, fcx.body_id, traits::SharedStatic),
1194 // No implied bounds in a const, etc.
1195 FxHashSet::default()
1199 #[tracing::instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))]
1200 fn check_impl<'tcx>(
1202 item: &'tcx hir::Item<'tcx>,
1203 ast_self_ty: &hir::Ty<'_>,
1204 ast_trait_ref: &Option<hir::TraitRef<'_>>,
1206 for_item(tcx, item).with_fcx(|fcx| {
1207 match *ast_trait_ref {
1208 Some(ref ast_trait_ref) => {
1209 // `#[rustc_reservation_impl]` impls are not real impls and
1210 // therefore don't need to be WF (the trait's `Self: Trait` predicate
1212 let trait_ref = tcx.impl_trait_ref(item.def_id).unwrap();
1214 fcx.normalize_associated_types_in(ast_trait_ref.path.span, trait_ref);
1215 let obligations = traits::wf::trait_obligations(
1220 ast_trait_ref.path.span,
1223 debug!(?obligations);
1224 for obligation in obligations {
1225 fcx.register_predicate(obligation);
1229 let self_ty = tcx.type_of(item.def_id);
1230 let self_ty = fcx.normalize_associated_types_in(item.span, self_ty);
1231 fcx.register_wf_obligation(
1234 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(
1235 item.hir_id().expect_owner(),
1241 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
1243 fcx.impl_implied_bounds(item.def_id.to_def_id(), item.span)
1247 /// Checks where-clauses and inline bounds that are declared on `def_id`.
1248 #[instrument(skip(fcx), level = "debug")]
1249 fn check_where_clauses<'tcx, 'fcx>(
1250 fcx: &FnCtxt<'fcx, 'tcx>,
1253 return_ty: Option<(Ty<'tcx>, Span)>,
1257 let predicates = tcx.predicates_of(def_id);
1258 let generics = tcx.generics_of(def_id);
1260 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
1261 GenericParamDefKind::Type { has_default, .. }
1262 | GenericParamDefKind::Const { has_default } => {
1263 has_default && def.index >= generics.parent_count as u32
1265 GenericParamDefKind::Lifetime => unreachable!(),
1268 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
1269 // For example, this forbids the declaration:
1271 // struct Foo<T = Vec<[u32]>> { .. }
1273 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
1274 for param in &generics.params {
1276 GenericParamDefKind::Type { .. } => {
1277 if is_our_default(param) {
1278 let ty = tcx.type_of(param.def_id);
1279 // Ignore dependent defaults -- that is, where the default of one type
1280 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
1281 // be sure if it will error or not as user might always specify the other.
1282 if !ty.needs_subst() {
1283 fcx.register_wf_obligation(
1285 tcx.def_span(param.def_id),
1286 ObligationCauseCode::MiscObligation,
1291 GenericParamDefKind::Const { .. } => {
1292 if is_our_default(param) {
1293 // FIXME(const_generics_defaults): This
1294 // is incorrect when dealing with unused substs, for example
1295 // for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
1296 // we should eagerly error.
1297 let default_ct = tcx.const_param_default(param.def_id);
1298 if !default_ct.needs_subst() {
1299 fcx.register_wf_obligation(
1301 tcx.def_span(param.def_id),
1302 ObligationCauseCode::WellFormed(None),
1307 // Doesn't have defaults.
1308 GenericParamDefKind::Lifetime => {}
1312 // Check that trait predicates are WF when params are substituted by their defaults.
1313 // We don't want to overly constrain the predicates that may be written but we want to
1314 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
1315 // Therefore we check if a predicate which contains a single type param
1316 // with a concrete default is WF with that default substituted.
1317 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
1319 // First we build the defaulted substitution.
1320 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
1322 GenericParamDefKind::Lifetime => {
1323 // All regions are identity.
1324 tcx.mk_param_from_def(param)
1327 GenericParamDefKind::Type { .. } => {
1328 // If the param has a default, ...
1329 if is_our_default(param) {
1330 let default_ty = tcx.type_of(param.def_id);
1331 // ... and it's not a dependent default, ...
1332 if !default_ty.needs_subst() {
1333 // ... then substitute it with the default.
1334 return default_ty.into();
1338 tcx.mk_param_from_def(param)
1340 GenericParamDefKind::Const { .. } => {
1341 // If the param has a default, ...
1342 if is_our_default(param) {
1343 let default_ct = tcx.const_param_default(param.def_id);
1344 // ... and it's not a dependent default, ...
1345 if !default_ct.needs_subst() {
1346 // ... then substitute it with the default.
1347 return default_ct.into();
1351 tcx.mk_param_from_def(param)
1356 // Now we build the substituted predicates.
1357 let default_obligations = predicates
1360 .flat_map(|&(pred, sp)| {
1362 struct CountParams {
1363 params: FxHashSet<u32>,
1365 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
1368 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1369 if let ty::Param(param) = t.kind() {
1370 self.params.insert(param.index);
1372 t.super_visit_with(self)
1375 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1379 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1380 if let ty::ConstKind::Param(param) = c.val() {
1381 self.params.insert(param.index);
1383 c.super_visit_with(self)
1386 let mut param_count = CountParams::default();
1387 let has_region = pred.visit_with(&mut param_count).is_break();
1388 let substituted_pred = pred.subst(tcx, substs);
1389 // Don't check non-defaulted params, dependent defaults (including lifetimes)
1390 // or preds with multiple params.
1391 if substituted_pred.has_param_types_or_consts()
1392 || param_count.params.len() > 1
1396 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
1397 // Avoid duplication of predicates that contain no parameters, for example.
1400 Some((substituted_pred, sp))
1404 // Convert each of those into an obligation. So if you have
1405 // something like `struct Foo<T: Copy = String>`, we would
1406 // take that predicate `T: Copy`, substitute to `String: Copy`
1407 // (actually that happens in the previous `flat_map` call),
1408 // and then try to prove it (in this case, we'll fail).
1410 // Note the subtle difference from how we handle `predicates`
1411 // below: there, we are not trying to prove those predicates
1412 // to be *true* but merely *well-formed*.
1413 let pred = fcx.normalize_associated_types_in(sp, pred);
1415 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
1416 traits::Obligation::new(cause, fcx.param_env, pred)
1419 let predicates = predicates.instantiate_identity(tcx);
1421 if let Some((return_ty, _)) = return_ty {
1422 if return_ty.has_infer_types_or_consts() {
1423 fcx.select_obligations_where_possible(false, |_| {});
1427 let predicates = fcx.normalize_associated_types_in(span, predicates);
1429 debug!(?predicates.predicates);
1430 assert_eq!(predicates.predicates.len(), predicates.spans.len());
1431 let wf_obligations =
1432 iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| {
1433 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
1436 for obligation in wf_obligations.chain(default_obligations) {
1437 debug!("next obligation cause: {:?}", obligation.cause);
1438 fcx.register_predicate(obligation);
1442 #[tracing::instrument(level = "debug", skip(fcx, span, hir_decl))]
1443 fn check_fn_or_method<'fcx, 'tcx>(
1444 fcx: &FnCtxt<'fcx, 'tcx>,
1446 sig: ty::PolyFnSig<'tcx>,
1447 hir_decl: &hir::FnDecl<'_>,
1449 implied_bounds: &mut FxHashSet<Ty<'tcx>>,
1451 let sig = fcx.tcx.liberate_late_bound_regions(def_id, sig);
1453 // Normalize the input and output types one at a time, using a different
1454 // `WellFormedLoc` for each. We cannot call `normalize_associated_types`
1455 // on the entire `FnSig`, since this would use the same `WellFormedLoc`
1456 // for each type, preventing the HIR wf check from generating
1457 // a nice error message.
1458 let ty::FnSig { mut inputs_and_output, c_variadic, unsafety, abi } = sig;
1460 fcx.tcx.mk_type_list(inputs_and_output.iter().enumerate().map(|(i, ty)| {
1461 fcx.normalize_associated_types_in_wf(
1464 WellFormedLoc::Param {
1465 function: def_id.expect_local(),
1466 // Note that the `param_idx` of the output type is
1467 // one greater than the index of the last input type.
1468 param_idx: i.try_into().unwrap(),
1472 // Manually call `normalize_assocaited_types_in` on the other types
1473 // in `FnSig`. This ensures that if the types of these fields
1474 // ever change to include projections, we will start normalizing
1475 // them automatically.
1476 let sig = ty::FnSig {
1478 c_variadic: fcx.normalize_associated_types_in(span, c_variadic),
1479 unsafety: fcx.normalize_associated_types_in(span, unsafety),
1480 abi: fcx.normalize_associated_types_in(span, abi),
1483 for (i, (&input_ty, ty)) in iter::zip(sig.inputs(), hir_decl.inputs).enumerate() {
1484 fcx.register_wf_obligation(
1487 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Param {
1488 function: def_id.expect_local(),
1489 param_idx: i.try_into().unwrap(),
1494 implied_bounds.extend(sig.inputs());
1496 fcx.register_wf_obligation(
1497 sig.output().into(),
1498 hir_decl.output.span(),
1499 ObligationCauseCode::ReturnType,
1502 // FIXME(#27579) return types should not be implied bounds
1503 implied_bounds.insert(sig.output());
1505 debug!(?implied_bounds);
1507 check_where_clauses(fcx, span, def_id, Some((sig.output(), hir_decl.output.span())));
1510 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1511 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1512 of the previous types except `Self`)";
1514 #[tracing::instrument(level = "debug", skip(fcx))]
1515 fn check_method_receiver<'fcx, 'tcx>(
1516 fcx: &FnCtxt<'fcx, 'tcx>,
1517 fn_sig: &hir::FnSig<'_>,
1518 method: &ty::AssocItem,
1521 // Check that the method has a valid receiver type, given the type `Self`.
1522 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1524 if !method.fn_has_self_parameter {
1528 let span = fn_sig.decl.inputs[0].span;
1530 let sig = fcx.tcx.fn_sig(method.def_id);
1531 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, sig);
1532 let sig = fcx.normalize_associated_types_in(span, sig);
1534 debug!("check_method_receiver: sig={:?}", sig);
1536 let self_ty = fcx.normalize_associated_types_in(span, self_ty);
1538 let receiver_ty = sig.inputs()[0];
1539 let receiver_ty = fcx.normalize_associated_types_in(span, receiver_ty);
1541 if fcx.tcx.features().arbitrary_self_types {
1542 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1543 // Report error; `arbitrary_self_types` was enabled.
1544 e0307(fcx, span, receiver_ty);
1547 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1548 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1549 // Report error; would have worked with `arbitrary_self_types`.
1551 &fcx.tcx.sess.parse_sess,
1552 sym::arbitrary_self_types,
1555 "`{}` cannot be used as the type of `self` without \
1556 the `arbitrary_self_types` feature",
1560 .help(HELP_FOR_SELF_TYPE)
1563 // Report error; would not have worked with `arbitrary_self_types`.
1564 e0307(fcx, span, receiver_ty);
1570 fn e0307<'tcx>(fcx: &FnCtxt<'_, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1572 fcx.tcx.sess.diagnostic(),
1575 "invalid `self` parameter type: {}",
1578 .note("type of `self` must be `Self` or a type that dereferences to it")
1579 .help(HELP_FOR_SELF_TYPE)
1583 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1584 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1585 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1586 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1587 /// `Deref<Target = self_ty>`.
1589 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1590 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1591 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1592 fn receiver_is_valid<'fcx, 'tcx>(
1593 fcx: &FnCtxt<'fcx, 'tcx>,
1595 receiver_ty: Ty<'tcx>,
1597 arbitrary_self_types_enabled: bool,
1599 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1601 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1603 // `self: Self` is always valid.
1604 if can_eq_self(receiver_ty) {
1605 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1611 let mut autoderef = fcx.autoderef(span, receiver_ty);
1613 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1614 if arbitrary_self_types_enabled {
1615 autoderef = autoderef.include_raw_pointers();
1618 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1621 let receiver_trait_def_id = fcx.tcx.require_lang_item(LangItem::Receiver, None);
1623 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1625 if let Some((potential_self_ty, _)) = autoderef.next() {
1627 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1628 potential_self_ty, self_ty
1631 if can_eq_self(potential_self_ty) {
1632 fcx.register_predicates(autoderef.into_obligations());
1634 if let Some(mut err) =
1635 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1642 // Without `feature(arbitrary_self_types)`, we require that each step in the
1643 // deref chain implement `receiver`
1644 if !arbitrary_self_types_enabled
1645 && !receiver_is_implemented(
1647 receiver_trait_def_id,
1656 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1657 // If he receiver already has errors reported due to it, consider it valid to avoid
1658 // unnecessary errors (#58712).
1659 return receiver_ty.references_error();
1663 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1664 if !arbitrary_self_types_enabled
1665 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1673 fn receiver_is_implemented<'tcx>(
1674 fcx: &FnCtxt<'_, 'tcx>,
1675 receiver_trait_def_id: DefId,
1676 cause: ObligationCause<'tcx>,
1677 receiver_ty: Ty<'tcx>,
1679 let trait_ref = ty::Binder::dummy(ty::TraitRef {
1680 def_id: receiver_trait_def_id,
1681 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1684 let obligation = traits::Obligation::new(
1687 trait_ref.without_const().to_predicate(fcx.tcx),
1690 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1694 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1701 fn check_variances_for_type_defn<'tcx>(
1703 item: &hir::Item<'tcx>,
1704 hir_generics: &hir::Generics<'_>,
1706 let ty = tcx.type_of(item.def_id);
1707 if tcx.has_error_field(ty) {
1711 let ty_predicates = tcx.predicates_of(item.def_id);
1712 assert_eq!(ty_predicates.parent, None);
1713 let variances = tcx.variances_of(item.def_id);
1715 let mut constrained_parameters: FxHashSet<_> = variances
1718 .filter(|&(_, &variance)| variance != ty::Bivariant)
1719 .map(|(index, _)| Parameter(index as u32))
1722 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1724 // Lazily calculated because it is only needed in case of an error.
1725 let explicitly_bounded_params = Lazy::new(|| {
1726 let icx = crate::collect::ItemCtxt::new(tcx, item.def_id.to_def_id());
1731 .filter_map(|predicate| match predicate {
1732 hir::WherePredicate::BoundPredicate(predicate) => {
1733 match icx.to_ty(predicate.bounded_ty).kind() {
1734 ty::Param(data) => Some(Parameter(data.index)),
1740 .collect::<FxHashSet<_>>()
1743 for (index, _) in variances.iter().enumerate() {
1744 let parameter = Parameter(index as u32);
1746 if constrained_parameters.contains(¶meter) {
1750 let param = &hir_generics.params[index];
1753 hir::ParamName::Error => {}
1755 let has_explicit_bounds =
1756 !param.bounds.is_empty() || explicitly_bounded_params.contains(¶meter);
1757 report_bivariance(tcx, param, has_explicit_bounds);
1763 fn report_bivariance(
1765 param: &rustc_hir::GenericParam<'_>,
1766 has_explicit_bounds: bool,
1767 ) -> ErrorGuaranteed {
1768 let span = param.span;
1769 let param_name = param.name.ident().name;
1770 let mut err = error_392(tcx, span, param_name);
1772 let suggested_marker_id = tcx.lang_items().phantom_data();
1773 // Help is available only in presence of lang items.
1774 let msg = if let Some(def_id) = suggested_marker_id {
1776 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1778 tcx.def_path_str(def_id),
1781 format!("consider removing `{}` or referring to it in a field", param_name)
1785 if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds {
1787 "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
1794 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1796 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, mut span: Span, id: hir::HirId) {
1797 let empty_env = ty::ParamEnv::empty();
1799 let def_id = fcx.tcx.hir().local_def_id(id);
1800 let predicates_with_span =
1801 fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, span)| (*p, *span));
1802 // Check elaborated bounds.
1803 let implied_obligations = traits::elaborate_predicates_with_span(fcx.tcx, predicates_with_span);
1805 for obligation in implied_obligations {
1806 let pred = obligation.predicate;
1807 // Match the existing behavior.
1808 if pred.is_global() && !pred.has_late_bound_regions() {
1809 let pred = fcx.normalize_associated_types_in(span, pred);
1810 let hir_node = fcx.tcx.hir().find(id);
1812 // only use the span of the predicate clause (#90869)
1814 if let Some(hir::Generics { where_clause, .. }) =
1815 hir_node.and_then(|node| node.generics())
1817 let obligation_span = obligation.cause.span(fcx.tcx);
1822 // There seems to be no better way to find out which predicate we are in
1823 .find(|pred| pred.span().contains(obligation_span))
1824 .map(|pred| pred.span())
1825 .unwrap_or(obligation_span);
1828 let obligation = traits::Obligation::new(
1829 traits::ObligationCause::new(span, id, traits::TrivialBound),
1833 fcx.register_predicate(obligation);
1837 fcx.select_all_obligations_or_error();
1840 #[derive(Clone, Copy)]
1841 pub struct CheckTypeWellFormedVisitor<'tcx> {
1845 impl<'tcx> CheckTypeWellFormedVisitor<'tcx> {
1846 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1847 CheckTypeWellFormedVisitor { tcx }
1851 impl<'tcx> ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1852 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1853 Visitor::visit_item(&mut self.clone(), i);
1856 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1857 Visitor::visit_trait_item(&mut self.clone(), trait_item);
1860 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1861 Visitor::visit_impl_item(&mut self.clone(), impl_item);
1864 fn visit_foreign_item(&self, foreign_item: &'tcx hir::ForeignItem<'tcx>) {
1865 Visitor::visit_foreign_item(&mut self.clone(), foreign_item)
1869 impl<'tcx> Visitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1870 type NestedFilter = nested_filter::OnlyBodies;
1872 fn nested_visit_map(&mut self) -> Self::Map {
1876 #[instrument(skip(self, i), level = "debug")]
1877 fn visit_item(&mut self, i: &'tcx hir::Item<'tcx>) {
1879 self.tcx.ensure().check_item_well_formed(i.def_id);
1880 hir_visit::walk_item(self, i);
1883 #[instrument(skip(self, trait_item), level = "debug")]
1884 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1885 trace!(?trait_item);
1886 self.tcx.ensure().check_trait_item_well_formed(trait_item.def_id);
1887 hir_visit::walk_trait_item(self, trait_item);
1890 #[instrument(skip(self, impl_item), level = "debug")]
1891 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1893 self.tcx.ensure().check_impl_item_well_formed(impl_item.def_id);
1894 hir_visit::walk_impl_item(self, impl_item);
1897 fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
1898 check_param_wf(self.tcx, p);
1899 hir_visit::walk_generic_param(self, p);
1903 ///////////////////////////////////////////////////////////////////////////
1906 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1907 struct AdtVariant<'tcx> {
1908 /// Types of fields in the variant, that must be well-formed.
1909 fields: Vec<AdtField<'tcx>>,
1911 /// Explicit discriminant of this variant (e.g. `A = 123`),
1912 /// that must evaluate to a constant value.
1913 explicit_discr: Option<LocalDefId>,
1916 struct AdtField<'tcx> {
1922 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1923 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1924 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1925 let fields = struct_def
1929 let def_id = self.tcx.hir().local_def_id(field.hir_id);
1930 let field_ty = self.tcx.type_of(def_id);
1931 let field_ty = self.normalize_associated_types_in(field.ty.span, field_ty);
1932 let field_ty = self.resolve_vars_if_possible(field_ty);
1933 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1934 AdtField { ty: field_ty, span: field.ty.span, def_id }
1937 AdtVariant { fields, explicit_discr: None }
1940 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1944 .map(|variant| AdtVariant {
1945 fields: self.non_enum_variant(&variant.data).fields,
1946 explicit_discr: variant
1948 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1953 pub(super) fn impl_implied_bounds(
1957 ) -> FxHashSet<Ty<'tcx>> {
1958 match self.tcx.impl_trait_ref(impl_def_id) {
1959 Some(trait_ref) => {
1960 // Trait impl: take implied bounds from all types that
1961 // appear in the trait reference.
1962 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1963 trait_ref.substs.types().collect()
1967 // Inherent impl: take implied bounds from the `self` type.
1968 let self_ty = self.tcx.type_of(impl_def_id);
1969 let self_ty = self.normalize_associated_types_in(span, self_ty);
1970 FxHashSet::from_iter([self_ty])
1980 ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
1982 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1983 err.span_label(span, "unused parameter");