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::lang_items::LangItem;
11 use rustc_hir::ItemKind;
12 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
13 use rustc_infer::infer::outlives::obligations::TypeOutlives;
14 use rustc_infer::infer::region_constraints::GenericKind;
15 use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
16 use rustc_middle::ty::query::Providers;
17 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
18 use rustc_middle::ty::trait_def::TraitSpecializationKind;
19 use rustc_middle::ty::{
20 self, AdtKind, DefIdTree, EarlyBinder, GenericParamDefKind, ToPredicate, Ty, TyCtxt,
21 TypeFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitor,
23 use rustc_session::parse::feature_err;
24 use rustc_span::symbol::{sym, Ident, Symbol};
25 use rustc_span::{Span, DUMMY_SP};
26 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
27 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode, WellFormedLoc};
29 use std::cell::LazyCell;
30 use std::convert::TryInto;
32 use std::ops::ControlFlow;
34 /// Helper type of a temporary returned by `.for_item(...)`.
35 /// This is necessary because we can't write the following bound:
37 /// ```ignore (illustrative)
38 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
40 pub(super) struct CheckWfFcxBuilder<'tcx> {
41 inherited: super::InheritedBuilder<'tcx>,
44 param_env: ty::ParamEnv<'tcx>,
47 impl<'tcx> CheckWfFcxBuilder<'tcx> {
48 pub(super) fn with_fcx<F>(&mut self, f: F)
50 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>) -> FxHashSet<Ty<'tcx>>,
54 let param_env = self.param_env;
55 self.inherited.enter(|inh| {
56 let fcx = FnCtxt::new(&inh, param_env, id);
57 if !inh.tcx.features().trivial_bounds {
58 // As predicates are cached rather than obligations, this
59 // needs to be called first so that they are checked with an
61 check_false_global_bounds(&fcx, span, id);
64 fcx.select_all_obligations_or_error();
66 let mut outlives_environment = OutlivesEnvironment::new(param_env);
67 outlives_environment.add_implied_bounds(&fcx.infcx, wf_tys, id);
68 fcx.infcx.check_region_obligations_and_report_errors(&outlives_environment);
73 fn check_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
74 let node = tcx.hir().expect_owner(def_id);
76 hir::OwnerNode::Crate(_) => {}
77 hir::OwnerNode::Item(item) => check_item(tcx, item),
78 hir::OwnerNode::TraitItem(item) => check_trait_item(tcx, item),
79 hir::OwnerNode::ImplItem(item) => check_impl_item(tcx, item),
80 hir::OwnerNode::ForeignItem(item) => check_foreign_item(tcx, item),
83 if let Some(generics) = node.generics() {
84 for param in generics.params {
85 check_param_wf(tcx, param)
90 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
91 /// well-formed, meaning that they do not require any constraints not declared in the struct
92 /// definition itself. For example, this definition would be illegal:
95 /// struct Ref<'a, T> { x: &'a T }
98 /// because the type did not declare that `T:'a`.
100 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
101 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
103 #[instrument(skip(tcx), level = "debug")]
104 fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
105 let def_id = item.def_id;
109 item.name = ? tcx.def_path_str(def_id.to_def_id())
113 // Right now we check that every default trait implementation
114 // has an implementation of itself. Basically, a case like:
116 // impl Trait for T {}
118 // has a requirement of `T: Trait` which was required for default
119 // method implementations. Although this could be improved now that
120 // there's a better infrastructure in place for this, it's being left
121 // for a follow-up work.
123 // Since there's such a requirement, we need to check *just* positive
124 // implementations, otherwise things like:
126 // impl !Send for T {}
128 // won't be allowed unless there's an *explicit* implementation of `Send`
130 hir::ItemKind::Impl(ref impl_) => {
132 .impl_trait_ref(item.def_id)
133 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
134 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
135 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
137 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
138 err.span_labels(impl_.defaultness_span, "default because of this");
139 err.span_label(sp, "auto trait");
142 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
143 match (tcx.impl_polarity(def_id), impl_.polarity) {
144 (ty::ImplPolarity::Positive, _) => {
145 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait);
147 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
148 // FIXME(#27579): what amount of WF checking do we need for neg impls?
149 if let hir::Defaultness::Default { .. } = impl_.defaultness {
150 let mut spans = vec![span];
151 spans.extend(impl_.defaultness_span);
156 "negative impls cannot be default impls"
161 (ty::ImplPolarity::Reservation, _) => {
162 // FIXME: what amount of WF checking do we need for reservation impls?
167 hir::ItemKind::Fn(ref sig, ..) => {
168 check_item_fn(tcx, item.def_id, item.ident, item.span, sig.decl);
170 hir::ItemKind::Static(ty, ..) => {
171 check_item_type(tcx, item.def_id, ty.span, false);
173 hir::ItemKind::Const(ty, ..) => {
174 check_item_type(tcx, item.def_id, ty.span, false);
176 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
177 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
179 check_variances_for_type_defn(tcx, item, ast_generics);
181 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
182 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
184 check_variances_for_type_defn(tcx, item, ast_generics);
186 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
187 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
189 check_variances_for_type_defn(tcx, item, ast_generics);
191 hir::ItemKind::Trait(..) => {
192 check_trait(tcx, item);
194 hir::ItemKind::TraitAlias(..) => {
195 check_trait(tcx, item);
197 // `ForeignItem`s are handled separately.
198 hir::ItemKind::ForeignMod { .. } => {}
203 fn check_foreign_item(tcx: TyCtxt<'_>, item: &hir::ForeignItem<'_>) {
204 let def_id = item.def_id;
208 item.name = ? tcx.def_path_str(def_id.to_def_id())
212 hir::ForeignItemKind::Fn(decl, ..) => {
213 check_item_fn(tcx, item.def_id, item.ident, item.span, decl)
215 hir::ForeignItemKind::Static(ty, ..) => check_item_type(tcx, item.def_id, ty.span, true),
216 hir::ForeignItemKind::Type => (),
220 fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) {
221 let def_id = trait_item.def_id;
223 let (method_sig, span) = match trait_item.kind {
224 hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span),
225 hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span),
226 _ => (None, trait_item.span),
228 check_object_unsafe_self_trait_by_name(tcx, trait_item);
229 check_associated_item(tcx, trait_item.def_id, span, method_sig);
231 let encl_trait_def_id = tcx.local_parent(def_id);
232 let encl_trait = tcx.hir().expect_item(encl_trait_def_id);
233 let encl_trait_def_id = encl_trait.def_id.to_def_id();
234 let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() {
236 } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() {
242 if let (Some(fn_lang_item_name), "call") =
243 (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str())
245 // We are looking at the `call` function of the `fn` or `fn_mut` lang item.
246 // Do some rudimentary sanity checking to avoid an ICE later (issue #83471).
247 if let Some(hir::FnSig { decl, span, .. }) = method_sig {
248 if let [self_ty, _] = decl.inputs {
249 if !matches!(self_ty.kind, hir::TyKind::Rptr(_, _)) {
254 "first argument of `call` in `{fn_lang_item_name}` lang item must be a reference",
264 "`call` function in `{fn_lang_item_name}` lang item takes exactly two arguments",
274 "`call` trait item in `{fn_lang_item_name}` lang item must be a function",
282 /// Require that the user writes where clauses on GATs for the implicit
283 /// outlives bounds involving trait parameters in trait functions and
284 /// lifetimes passed as GAT substs. See `self-outlives-lint` test.
286 /// We use the following trait as an example throughout this function:
287 /// ```rust,ignore (this code fails due to this lint)
289 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
291 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
294 fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
295 // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint.
296 let mut required_bounds_by_item = FxHashMap::default();
298 // Loop over all GATs together, because if this lint suggests adding a where-clause bound
299 // to one GAT, it might then require us to an additional bound on another GAT.
300 // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which
301 // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between
304 let mut should_continue = false;
305 for gat_item in associated_items {
306 let gat_def_id = gat_item.id.def_id;
307 let gat_item = tcx.associated_item(gat_def_id);
308 // If this item is not an assoc ty, or has no substs, then it's not a GAT
309 if gat_item.kind != ty::AssocKind::Type {
312 let gat_generics = tcx.generics_of(gat_def_id);
313 // FIXME(jackh726): we can also warn in the more general case
314 if gat_generics.params.is_empty() {
318 // Gather the bounds with which all other items inside of this trait constrain the GAT.
319 // This is calculated by taking the intersection of the bounds that each item
320 // constrains the GAT with individually.
321 let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
322 for item in associated_items {
323 let item_def_id = item.id.def_id;
324 // Skip our own GAT, since it does not constrain itself at all.
325 if item_def_id == gat_def_id {
329 let item_hir_id = item.id.hir_id();
330 let param_env = tcx.param_env(item_def_id);
332 let item_required_bounds = match item.kind {
333 // In our example, this corresponds to `into_iter` method
334 hir::AssocItemKind::Fn { .. } => {
335 // For methods, we check the function signature's return type for any GATs
336 // to constrain. In the `into_iter` case, we see that the return type
337 // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from.
338 let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions(
339 item_def_id.to_def_id(),
340 tcx.fn_sig(item_def_id),
347 // We also assume that all of the function signature's parameter types
349 &sig.inputs().iter().copied().collect(),
354 // In our example, this corresponds to the `Iter` and `Item` associated types
355 hir::AssocItemKind::Type => {
356 // If our associated item is a GAT with missing bounds, add them to
357 // the param-env here. This allows this GAT to propagate missing bounds
359 let param_env = augment_param_env(
362 required_bounds_by_item.get(&item_def_id),
368 tcx.explicit_item_bounds(item_def_id)
371 .collect::<Vec<_>>(),
372 &FxHashSet::default(),
377 hir::AssocItemKind::Const => None,
380 if let Some(item_required_bounds) = item_required_bounds {
381 // Take the intersection of the required bounds for this GAT, and
382 // the item_required_bounds which are the ones implied by just
384 // This is why we use an Option<_>, since we need to distinguish
385 // the empty set of bounds from the _uninitialized_ set of bounds.
386 if let Some(new_required_bounds) = &mut new_required_bounds {
387 new_required_bounds.retain(|b| item_required_bounds.contains(b));
389 new_required_bounds = Some(item_required_bounds);
394 if let Some(new_required_bounds) = new_required_bounds {
395 let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default();
396 if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) {
397 // Iterate until our required_bounds no longer change
398 // Since they changed here, we should continue the loop
399 should_continue = true;
403 // We know that this loop will eventually halt, since we only set `should_continue` if the
404 // `required_bounds` for this item grows. Since we are not creating any new region or type
405 // variables, the set of all region and type bounds that we could ever insert are limited
406 // by the number of unique types and regions we observe in a given item.
407 if !should_continue {
412 for (gat_def_id, required_bounds) in required_bounds_by_item {
413 let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id);
414 debug!(?required_bounds);
415 let param_env = tcx.param_env(gat_def_id);
416 let gat_hir = gat_item_hir.hir_id();
418 let mut unsatisfied_bounds: Vec<_> = required_bounds
420 .filter(|clause| match clause.kind().skip_binder() {
421 ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
422 !region_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
424 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
425 !ty_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
427 _ => bug!("Unexpected PredicateKind"),
429 .map(|clause| clause.to_string())
432 // We sort so that order is predictable
433 unsatisfied_bounds.sort();
435 if !unsatisfied_bounds.is_empty() {
436 let plural = if unsatisfied_bounds.len() > 1 { "s" } else { "" };
437 let mut err = tcx.sess.struct_span_err(
439 &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
442 let suggestion = format!(
444 gat_item_hir.generics.add_where_or_trailing_comma(),
445 unsatisfied_bounds.join(", "),
448 gat_item_hir.generics.tail_span_for_predicate_suggestion(),
449 &format!("add the required where clause{plural}"),
451 Applicability::MachineApplicable,
455 if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
457 "{} currently required to ensure that impls have maximum flexibility",
461 "we are soliciting feedback, see issue #87479 \
462 <https://github.com/rust-lang/rust/issues/87479> \
463 for more information",
471 /// Add a new set of predicates to the caller_bounds of an existing param_env.
472 fn augment_param_env<'tcx>(
474 param_env: ty::ParamEnv<'tcx>,
475 new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
476 ) -> ty::ParamEnv<'tcx> {
477 let Some(new_predicates) = new_predicates else {
481 if new_predicates.is_empty() {
486 tcx.mk_predicates(param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()));
487 // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
488 // i.e. traits::normalize_param_env_or_error
489 ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness())
492 /// We use the following trait as an example throughout this function.
493 /// Specifically, let's assume that `to_check` here is the return type
494 /// of `into_iter`, and the GAT we are checking this for is `Iter`.
495 /// ```rust,ignore (this code fails due to this lint)
497 /// type Iter<'a>: Iterator<Item = Self::Item<'a>>;
499 /// fn into_iter<'a>(&'a self) -> Self::Iter<'a>;
502 fn gather_gat_bounds<'tcx, T: TypeFoldable<'tcx>>(
504 param_env: ty::ParamEnv<'tcx>,
505 item_hir: hir::HirId,
507 wf_tys: &FxHashSet<Ty<'tcx>>,
508 gat_def_id: LocalDefId,
509 gat_generics: &'tcx ty::Generics,
510 ) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
511 // The bounds we that we would require from `to_check`
512 let mut bounds = FxHashSet::default();
514 let (regions, types) = GATSubstCollector::visit(gat_def_id.to_def_id(), to_check);
516 // If both regions and types are empty, then this GAT isn't in the
517 // set of types we are checking, and we shouldn't try to do clause analysis
518 // (particularly, doing so would end up with an empty set of clauses,
519 // since the current method would require none, and we take the
520 // intersection of requirements of all methods)
521 if types.is_empty() && regions.is_empty() {
525 for (region_a, region_a_idx) in ®ions {
526 // Ignore `'static` lifetimes for the purpose of this lint: it's
527 // because we know it outlives everything and so doesn't give meaningful
529 if let ty::ReStatic = **region_a {
532 // For each region argument (e.g., `'a` in our example), check for a
533 // relationship to the type arguments (e.g., `Self`). If there is an
534 // outlives relationship (`Self: 'a`), then we want to ensure that is
535 // reflected in a where clause on the GAT itself.
536 for (ty, ty_idx) in &types {
537 // In our example, requires that `Self: 'a`
538 if ty_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *ty, *region_a) {
539 debug!(?ty_idx, ?region_a_idx);
540 debug!("required clause: {ty} must outlive {region_a}");
541 // Translate into the generic parameters of the GAT. In
542 // our example, the type was `Self`, which will also be
543 // `Self` in the GAT.
544 let ty_param = gat_generics.param_at(*ty_idx, tcx);
546 .mk_ty(ty::Param(ty::ParamTy { index: ty_param.index, name: ty_param.name }));
547 // Same for the region. In our example, 'a corresponds
548 // to the 'me parameter.
549 let region_param = gat_generics.param_at(*region_a_idx, tcx);
551 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
552 def_id: region_param.def_id,
553 index: region_param.index,
554 name: region_param.name,
556 // The predicate we expect to see. (In our example,
559 ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param));
560 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
561 bounds.insert(clause);
565 // For each region argument (e.g., `'a` in our example), also check for a
566 // relationship to the other region arguments. If there is an outlives
567 // relationship, then we want to ensure that is reflected in the where clause
568 // on the GAT itself.
569 for (region_b, region_b_idx) in ®ions {
570 // Again, skip `'static` because it outlives everything. Also, we trivially
571 // know that a region outlives itself.
572 if ty::ReStatic == **region_b || region_a == region_b {
575 if region_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *region_a, *region_b) {
576 debug!(?region_a_idx, ?region_b_idx);
577 debug!("required clause: {region_a} must outlive {region_b}");
578 // Translate into the generic parameters of the GAT.
579 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
581 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
582 def_id: region_a_param.def_id,
583 index: region_a_param.index,
584 name: region_a_param.name,
586 // Same for the region.
587 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
589 tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion {
590 def_id: region_b_param.def_id,
591 index: region_b_param.index,
592 name: region_b_param.name,
594 // The predicate we expect to see.
595 let clause = ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(
599 let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
600 bounds.insert(clause);
608 /// Given a known `param_env` and a set of well formed types, can we prove that
609 /// `ty` outlives `region`.
610 fn ty_known_to_outlive<'tcx>(
613 param_env: ty::ParamEnv<'tcx>,
614 wf_tys: &FxHashSet<Ty<'tcx>>,
616 region: ty::Region<'tcx>,
618 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| {
619 let origin = infer::RelateParamBound(DUMMY_SP, ty, None);
620 let outlives = &mut TypeOutlives::new(infcx, tcx, region_bound_pairs, None, param_env);
621 outlives.type_must_outlive(origin, ty, region);
625 /// Given a known `param_env` and a set of well formed types, can we prove that
626 /// `region_a` outlives `region_b`
627 fn region_known_to_outlive<'tcx>(
630 param_env: ty::ParamEnv<'tcx>,
631 wf_tys: &FxHashSet<Ty<'tcx>>,
632 region_a: ty::Region<'tcx>,
633 region_b: ty::Region<'tcx>,
635 resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| {
636 use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
637 let origin = infer::RelateRegionParamBound(DUMMY_SP);
638 // `region_a: region_b` -> `region_b <= region_a`
639 infcx.push_sub_region_constraint(origin, region_b, region_a);
643 /// Given a known `param_env` and a set of well formed types, set up an
644 /// `InferCtxt`, call the passed function (to e.g. set up region constraints
645 /// to be tested), then resolve region and return errors
646 fn resolve_regions_with_wf_tys<'tcx>(
649 param_env: ty::ParamEnv<'tcx>,
650 wf_tys: &FxHashSet<Ty<'tcx>>,
651 add_constraints: impl for<'a> FnOnce(
652 &'a InferCtxt<'a, 'tcx>,
653 &'a Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>,
656 // Unfortunately, we have to use a new `InferCtxt` each call, because
657 // region constraints get added and solved there and we need to test each
658 // call individually.
659 tcx.infer_ctxt().enter(|infcx| {
660 let mut outlives_environment = OutlivesEnvironment::new(param_env);
661 outlives_environment.add_implied_bounds(&infcx, wf_tys.clone(), id);
662 let region_bound_pairs = outlives_environment.region_bound_pairs();
664 add_constraints(&infcx, region_bound_pairs);
666 let errors = infcx.resolve_regions(&outlives_environment);
668 debug!(?errors, "errors");
670 // If we were able to prove that the type outlives the region without
671 // an error, it must be because of the implied or explicit bounds...
676 /// TypeVisitor that looks for uses of GATs like
677 /// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into
678 /// the two vectors, `regions` and `types` (depending on their kind). For each
679 /// parameter `Pi` also track the index `i`.
680 struct GATSubstCollector<'tcx> {
682 // Which region appears and which parameter index its substituted for
683 regions: FxHashSet<(ty::Region<'tcx>, usize)>,
684 // Which params appears and which parameter index its substituted for
685 types: FxHashSet<(Ty<'tcx>, usize)>,
688 impl<'tcx> GATSubstCollector<'tcx> {
689 fn visit<T: TypeFoldable<'tcx>>(
692 ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) {
694 GATSubstCollector { gat, regions: FxHashSet::default(), types: FxHashSet::default() };
695 t.visit_with(&mut visitor);
696 (visitor.regions, visitor.types)
700 impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
703 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
705 ty::Projection(p) if p.item_def_id == self.gat => {
706 for (idx, subst) in p.substs.iter().enumerate() {
707 match subst.unpack() {
708 GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => {
709 self.regions.insert((lt, idx));
711 GenericArgKind::Type(t) => {
712 self.types.insert((t, idx));
720 t.super_visit_with(self)
724 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
726 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
727 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
734 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
735 /// When this is done, suggest using `Self` instead.
736 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
737 let (trait_name, trait_def_id) =
738 match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id())) {
739 hir::Node::Item(item) => match item.kind {
740 hir::ItemKind::Trait(..) => (item.ident, item.def_id),
745 let mut trait_should_be_self = vec![];
747 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
748 if could_be_self(trait_def_id, ty) =>
750 trait_should_be_self.push(ty.span)
752 hir::TraitItemKind::Fn(sig, _) => {
753 for ty in sig.decl.inputs {
754 if could_be_self(trait_def_id, ty) {
755 trait_should_be_self.push(ty.span);
758 match sig.decl.output {
759 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
760 trait_should_be_self.push(ty.span);
767 if !trait_should_be_self.is_empty() {
768 if tcx.object_safety_violations(trait_def_id).is_empty() {
771 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
774 trait_should_be_self,
775 "associated item referring to unboxed trait object for its own trait",
777 .span_label(trait_name.span, "in this trait")
778 .multipart_suggestion(
779 "you might have meant to use `Self` to refer to the implementing type",
781 Applicability::MachineApplicable,
787 fn check_impl_item(tcx: TyCtxt<'_>, impl_item: &hir::ImplItem<'_>) {
788 let def_id = impl_item.def_id;
790 let (method_sig, span) = match impl_item.kind {
791 hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span),
792 // Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`.
793 hir::ImplItemKind::TyAlias(ty) if ty.span != DUMMY_SP => (None, ty.span),
794 _ => (None, impl_item.span),
797 check_associated_item(tcx, def_id, span, method_sig);
800 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
802 // We currently only check wf of const params here.
803 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
805 // Const parameters are well formed if their type is structural match.
806 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
807 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
809 if tcx.features().adt_const_params {
810 let err = match ty.peel_refs().kind() {
811 ty::FnPtr(_) => Some("function pointers"),
812 ty::RawPtr(_) => Some("raw pointers"),
816 if let Some(unsupported_type) = err {
820 "using {} as const generic parameters is forbidden",
826 if let Some(non_structural_match_ty) =
827 traits::search_for_structural_match_violation(param.span, tcx, ty)
829 // We use the same error code in both branches, because this is really the same
830 // issue: we just special-case the message for type parameters to make it
832 if let ty::Param(_) = ty.peel_refs().kind() {
833 // Const parameters may not have type parameters as their types,
834 // because we cannot be sure that the type parameter derives `PartialEq`
835 // and `Eq` (just implementing them is not enough for `structural_match`).
840 "`{}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
841 used as the type of a const parameter",
846 format!("`{}` may not derive both `PartialEq` and `Eq`", ty),
849 "it is not currently possible to use a type parameter as the type of a \
854 let mut diag = struct_span_err!(
858 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
859 the type of a const parameter",
860 non_structural_match_ty.ty,
863 if ty == non_structural_match_ty.ty {
866 format!("`{ty}` doesn't derive both `PartialEq` and `Eq`"),
875 let mut is_ptr = true;
877 let err = match ty.kind() {
878 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
879 ty::FnPtr(_) => Some("function pointers"),
880 ty::RawPtr(_) => Some("raw pointers"),
883 err_ty_str = format!("`{ty}`");
884 Some(err_ty_str.as_str())
888 if let Some(unsupported_type) = err {
893 "using {unsupported_type} as const generic parameters is forbidden",
897 let mut err = tcx.sess.struct_span_err(
900 "{unsupported_type} is forbidden as the type of a const generic parameter",
903 err.note("the only supported types are integers, `bool` and `char`");
904 if tcx.sess.is_nightly_build() {
906 "more complex types are supported with `#![feature(adt_const_params)]`",
917 #[tracing::instrument(level = "debug", skip(tcx, span, sig_if_method))]
918 fn check_associated_item(
922 sig_if_method: Option<&hir::FnSig<'_>>,
924 let code = ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(item_id)));
925 for_id(tcx, item_id, span).with_fcx(|fcx| {
926 let item = fcx.tcx.associated_item(item_id);
928 let (mut implied_bounds, self_ty) = match item.container {
929 ty::TraitContainer(_) => (FxHashSet::default(), fcx.tcx.types.self_param),
930 ty::ImplContainer(def_id) => {
931 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
936 ty::AssocKind::Const => {
937 let ty = fcx.tcx.type_of(item.def_id);
938 let ty = fcx.normalize_associated_types_in_wf(span, ty, WellFormedLoc::Ty(item_id));
939 fcx.register_wf_obligation(ty.into(), span, code.clone());
941 ty::AssocKind::Fn => {
942 let sig = fcx.tcx.fn_sig(item.def_id);
943 let hir_sig = sig_if_method.expect("bad signature for method");
946 item.ident(fcx.tcx).span,
949 item.def_id.expect_local(),
952 check_method_receiver(fcx, hir_sig, item, self_ty);
954 ty::AssocKind::Type => {
955 if let ty::AssocItemContainer::TraitContainer(_) = item.container {
956 check_associated_type_bounds(fcx, item, span)
958 if item.defaultness.has_value() {
959 let ty = fcx.tcx.type_of(item.def_id);
961 fcx.normalize_associated_types_in_wf(span, ty, WellFormedLoc::Ty(item_id));
962 fcx.register_wf_obligation(ty.into(), span, code.clone());
971 pub(super) fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
972 for_id(tcx, item.def_id, item.span)
975 fn for_id(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) -> CheckWfFcxBuilder<'_> {
977 inherited: Inherited::build(tcx, def_id),
978 id: hir::HirId::make_owner(def_id),
980 param_env: tcx.param_env(def_id),
984 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
986 ItemKind::Struct(..) => Some(AdtKind::Struct),
987 ItemKind::Union(..) => Some(AdtKind::Union),
988 ItemKind::Enum(..) => Some(AdtKind::Enum),
993 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
994 fn check_type_defn<'tcx, F>(
996 item: &hir::Item<'tcx>,
998 mut lookup_fields: F,
1000 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
1002 for_item(tcx, item).with_fcx(|fcx| {
1003 let variants = lookup_fields(fcx);
1004 let packed = tcx.adt_def(item.def_id).repr().packed();
1006 for variant in &variants {
1007 // All field types must be well-formed.
1008 for field in &variant.fields {
1009 fcx.register_wf_obligation(
1012 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(field.def_id))),
1016 // For DST, or when drop needs to copy things around, all
1017 // intermediate types must be sized.
1018 let needs_drop_copy = || {
1020 let ty = variant.fields.last().unwrap().ty;
1021 let ty = tcx.erase_regions(ty);
1022 if ty.needs_infer() {
1024 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
1025 // Just treat unresolved type expression as if it needs drop.
1028 ty.needs_drop(tcx, tcx.param_env(item.def_id))
1032 // All fields (except for possibly the last) should be sized.
1033 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
1034 let unsized_len = if all_sized { 0 } else { 1 };
1036 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
1038 let last = idx == variant.fields.len() - 1;
1041 tcx.require_lang_item(LangItem::Sized, None),
1042 traits::ObligationCause::new(
1045 traits::FieldSized {
1046 adt_kind: match item_adt_kind(&item.kind) {
1057 // Explicit `enum` discriminant values must const-evaluate successfully.
1058 if let Some(discr_def_id) = variant.explicit_discr {
1059 let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());
1061 let cause = traits::ObligationCause::new(
1062 tcx.def_span(discr_def_id),
1064 traits::MiscObligation,
1066 fcx.register_predicate(traits::Obligation::new(
1069 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ty::Unevaluated::new(
1070 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
1078 check_where_clauses(fcx, item.span, item.def_id, None);
1080 // No implied bounds in a struct definition.
1081 FxHashSet::default()
1085 #[instrument(skip(tcx, item))]
1086 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
1087 debug!(?item.def_id);
1089 let trait_def = tcx.trait_def(item.def_id);
1090 if trait_def.is_marker
1091 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
1093 for associated_def_id in &*tcx.associated_item_def_ids(item.def_id) {
1096 tcx.def_span(*associated_def_id),
1098 "marker traits cannot have associated items",
1104 // FIXME: this shouldn't use an `FnCtxt` at all.
1105 for_item(tcx, item).with_fcx(|fcx| {
1106 check_where_clauses(fcx, item.span, item.def_id, None);
1108 FxHashSet::default()
1111 // Only check traits, don't check trait aliases
1112 if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
1113 check_gat_where_clauses(tcx, items);
1117 /// Checks all associated type defaults of trait `trait_def_id`.
1119 /// Assuming the defaults are used, check that all predicates (bounds on the
1120 /// assoc type and where clauses on the trait) hold.
1121 fn check_associated_type_bounds(fcx: &FnCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
1124 let bounds = tcx.explicit_item_bounds(item.def_id);
1126 debug!("check_associated_type_bounds: bounds={:?}", bounds);
1127 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
1128 let normalized_bound = fcx.normalize_associated_types_in(span, bound);
1129 traits::wf::predicate_obligations(
1138 for obligation in wf_obligations {
1139 debug!("next obligation cause: {:?}", obligation.cause);
1140 fcx.register_predicate(obligation);
1149 decl: &hir::FnDecl<'_>,
1151 for_id(tcx, def_id, span).with_fcx(|fcx| {
1152 let sig = tcx.fn_sig(def_id);
1153 let mut implied_bounds = FxHashSet::default();
1154 check_fn_or_method(fcx, ident.span, sig, decl, def_id, &mut implied_bounds);
1159 fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) {
1160 debug!("check_item_type: {:?}", item_id);
1162 for_id(tcx, item_id, ty_span).with_fcx(|fcx| {
1163 let ty = tcx.type_of(item_id);
1164 let item_ty = fcx.normalize_associated_types_in_wf(ty_span, ty, WellFormedLoc::Ty(item_id));
1166 let mut forbid_unsized = true;
1167 if allow_foreign_ty {
1168 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
1169 if let ty::Foreign(_) = tail.kind() {
1170 forbid_unsized = false;
1174 fcx.register_wf_obligation(
1177 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(item_id))),
1182 tcx.require_lang_item(LangItem::Sized, None),
1183 traits::ObligationCause::new(ty_span, fcx.body_id, traits::WellFormed(None)),
1187 // Ensure that the end result is `Sync` in a non-thread local `static`.
1188 let should_check_for_sync = tcx.static_mutability(item_id.to_def_id())
1189 == Some(hir::Mutability::Not)
1190 && !tcx.is_foreign_item(item_id.to_def_id())
1191 && !tcx.is_thread_local_static(item_id.to_def_id());
1193 if should_check_for_sync {
1196 tcx.require_lang_item(LangItem::Sync, Some(ty_span)),
1197 traits::ObligationCause::new(ty_span, fcx.body_id, traits::SharedStatic),
1201 // No implied bounds in a const, etc.
1202 FxHashSet::default()
1206 #[tracing::instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))]
1207 fn check_impl<'tcx>(
1209 item: &'tcx hir::Item<'tcx>,
1210 ast_self_ty: &hir::Ty<'_>,
1211 ast_trait_ref: &Option<hir::TraitRef<'_>>,
1213 for_item(tcx, item).with_fcx(|fcx| {
1214 match *ast_trait_ref {
1215 Some(ref ast_trait_ref) => {
1216 // `#[rustc_reservation_impl]` impls are not real impls and
1217 // therefore don't need to be WF (the trait's `Self: Trait` predicate
1219 let trait_ref = tcx.impl_trait_ref(item.def_id).unwrap();
1221 fcx.normalize_associated_types_in(ast_trait_ref.path.span, trait_ref);
1222 let obligations = traits::wf::trait_obligations(
1227 ast_trait_ref.path.span,
1230 debug!(?obligations);
1231 for obligation in obligations {
1232 fcx.register_predicate(obligation);
1236 let self_ty = tcx.type_of(item.def_id);
1237 let self_ty = fcx.normalize_associated_types_in(item.span, self_ty);
1238 fcx.register_wf_obligation(
1241 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(
1242 item.hir_id().expect_owner(),
1248 check_where_clauses(fcx, item.span, item.def_id, None);
1250 fcx.impl_implied_bounds(item.def_id.to_def_id(), item.span)
1254 /// Checks where-clauses and inline bounds that are declared on `def_id`.
1255 #[instrument(skip(fcx), level = "debug")]
1256 fn check_where_clauses<'tcx, 'fcx>(
1257 fcx: &FnCtxt<'fcx, 'tcx>,
1260 return_ty: Option<(Ty<'tcx>, Span)>,
1264 let predicates = tcx.predicates_of(def_id);
1265 let generics = tcx.generics_of(def_id);
1267 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
1268 GenericParamDefKind::Type { has_default, .. }
1269 | GenericParamDefKind::Const { has_default } => {
1270 has_default && def.index >= generics.parent_count as u32
1272 GenericParamDefKind::Lifetime => unreachable!(),
1275 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
1276 // For example, this forbids the declaration:
1278 // struct Foo<T = Vec<[u32]>> { .. }
1280 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
1281 for param in &generics.params {
1283 GenericParamDefKind::Type { .. } => {
1284 if is_our_default(param) {
1285 let ty = tcx.type_of(param.def_id);
1286 // Ignore dependent defaults -- that is, where the default of one type
1287 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
1288 // be sure if it will error or not as user might always specify the other.
1289 if !ty.needs_subst() {
1290 fcx.register_wf_obligation(
1292 tcx.def_span(param.def_id),
1293 ObligationCauseCode::MiscObligation,
1298 GenericParamDefKind::Const { .. } => {
1299 if is_our_default(param) {
1300 // FIXME(const_generics_defaults): This
1301 // is incorrect when dealing with unused substs, for example
1302 // for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>`
1303 // we should eagerly error.
1304 let default_ct = tcx.const_param_default(param.def_id);
1305 if !default_ct.needs_subst() {
1306 fcx.register_wf_obligation(
1308 tcx.def_span(param.def_id),
1309 ObligationCauseCode::WellFormed(None),
1314 // Doesn't have defaults.
1315 GenericParamDefKind::Lifetime => {}
1319 // Check that trait predicates are WF when params are substituted by their defaults.
1320 // We don't want to overly constrain the predicates that may be written but we want to
1321 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
1322 // Therefore we check if a predicate which contains a single type param
1323 // with a concrete default is WF with that default substituted.
1324 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
1326 // First we build the defaulted substitution.
1327 let substs = InternalSubsts::for_item(tcx, def_id.to_def_id(), |param, _| {
1329 GenericParamDefKind::Lifetime => {
1330 // All regions are identity.
1331 tcx.mk_param_from_def(param)
1334 GenericParamDefKind::Type { .. } => {
1335 // If the param has a default, ...
1336 if is_our_default(param) {
1337 let default_ty = tcx.type_of(param.def_id);
1338 // ... and it's not a dependent default, ...
1339 if !default_ty.needs_subst() {
1340 // ... then substitute it with the default.
1341 return default_ty.into();
1345 tcx.mk_param_from_def(param)
1347 GenericParamDefKind::Const { .. } => {
1348 // If the param has a default, ...
1349 if is_our_default(param) {
1350 let default_ct = tcx.const_param_default(param.def_id);
1351 // ... and it's not a dependent default, ...
1352 if !default_ct.needs_subst() {
1353 // ... then substitute it with the default.
1354 return default_ct.into();
1358 tcx.mk_param_from_def(param)
1363 // Now we build the substituted predicates.
1364 let default_obligations = predicates
1367 .flat_map(|&(pred, sp)| {
1369 struct CountParams {
1370 params: FxHashSet<u32>,
1372 impl<'tcx> ty::visit::TypeVisitor<'tcx> for CountParams {
1375 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
1376 if let ty::Param(param) = t.kind() {
1377 self.params.insert(param.index);
1379 t.super_visit_with(self)
1382 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
1386 fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
1387 if let ty::ConstKind::Param(param) = c.kind() {
1388 self.params.insert(param.index);
1390 c.super_visit_with(self)
1393 let mut param_count = CountParams::default();
1394 let has_region = pred.visit_with(&mut param_count).is_break();
1395 let substituted_pred = EarlyBinder(pred).subst(tcx, substs);
1396 // Don't check non-defaulted params, dependent defaults (including lifetimes)
1397 // or preds with multiple params.
1398 if substituted_pred.has_param_types_or_consts()
1399 || param_count.params.len() > 1
1403 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
1404 // Avoid duplication of predicates that contain no parameters, for example.
1407 Some((substituted_pred, sp))
1411 // Convert each of those into an obligation. So if you have
1412 // something like `struct Foo<T: Copy = String>`, we would
1413 // take that predicate `T: Copy`, substitute to `String: Copy`
1414 // (actually that happens in the previous `flat_map` call),
1415 // and then try to prove it (in this case, we'll fail).
1417 // Note the subtle difference from how we handle `predicates`
1418 // below: there, we are not trying to prove those predicates
1419 // to be *true* but merely *well-formed*.
1420 let pred = fcx.normalize_associated_types_in(sp, pred);
1421 let cause = traits::ObligationCause::new(
1424 traits::ItemObligation(def_id.to_def_id()),
1426 traits::Obligation::new(cause, fcx.param_env, pred)
1429 let predicates = predicates.instantiate_identity(tcx);
1431 if let Some((return_ty, _)) = return_ty {
1432 if return_ty.has_infer_types_or_consts() {
1433 fcx.select_obligations_where_possible(false, |_| {});
1437 let predicates = fcx.normalize_associated_types_in(span, predicates);
1439 debug!(?predicates.predicates);
1440 assert_eq!(predicates.predicates.len(), predicates.spans.len());
1441 let wf_obligations =
1442 iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| {
1443 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
1446 for obligation in wf_obligations.chain(default_obligations) {
1447 debug!("next obligation cause: {:?}", obligation.cause);
1448 fcx.register_predicate(obligation);
1452 #[tracing::instrument(level = "debug", skip(fcx, span, hir_decl))]
1453 fn check_fn_or_method<'fcx, 'tcx>(
1454 fcx: &FnCtxt<'fcx, 'tcx>,
1456 sig: ty::PolyFnSig<'tcx>,
1457 hir_decl: &hir::FnDecl<'_>,
1459 implied_bounds: &mut FxHashSet<Ty<'tcx>>,
1461 let sig = fcx.tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
1463 // Normalize the input and output types one at a time, using a different
1464 // `WellFormedLoc` for each. We cannot call `normalize_associated_types`
1465 // on the entire `FnSig`, since this would use the same `WellFormedLoc`
1466 // for each type, preventing the HIR wf check from generating
1467 // a nice error message.
1468 let ty::FnSig { mut inputs_and_output, c_variadic, unsafety, abi } = sig;
1470 fcx.tcx.mk_type_list(inputs_and_output.iter().enumerate().map(|(i, ty)| {
1471 fcx.normalize_associated_types_in_wf(
1474 WellFormedLoc::Param {
1476 // Note that the `param_idx` of the output type is
1477 // one greater than the index of the last input type.
1478 param_idx: i.try_into().unwrap(),
1482 // Manually call `normalize_associated_types_in` on the other types
1483 // in `FnSig`. This ensures that if the types of these fields
1484 // ever change to include projections, we will start normalizing
1485 // them automatically.
1486 let sig = ty::FnSig {
1488 c_variadic: fcx.normalize_associated_types_in(span, c_variadic),
1489 unsafety: fcx.normalize_associated_types_in(span, unsafety),
1490 abi: fcx.normalize_associated_types_in(span, abi),
1493 for (i, (&input_ty, ty)) in iter::zip(sig.inputs(), hir_decl.inputs).enumerate() {
1494 fcx.register_wf_obligation(
1497 ObligationCauseCode::WellFormed(Some(WellFormedLoc::Param {
1499 param_idx: i.try_into().unwrap(),
1504 implied_bounds.extend(sig.inputs());
1506 fcx.register_wf_obligation(
1507 sig.output().into(),
1508 hir_decl.output.span(),
1509 ObligationCauseCode::ReturnType,
1512 // FIXME(#27579) return types should not be implied bounds
1513 implied_bounds.insert(sig.output());
1515 debug!(?implied_bounds);
1517 check_where_clauses(fcx, span, def_id, Some((sig.output(), hir_decl.output.span())));
1520 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1521 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1522 of the previous types except `Self`)";
1524 #[tracing::instrument(level = "debug", skip(fcx))]
1525 fn check_method_receiver<'fcx, 'tcx>(
1526 fcx: &FnCtxt<'fcx, 'tcx>,
1527 fn_sig: &hir::FnSig<'_>,
1528 method: &ty::AssocItem,
1531 // Check that the method has a valid receiver type, given the type `Self`.
1532 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1534 if !method.fn_has_self_parameter {
1538 let span = fn_sig.decl.inputs[0].span;
1540 let sig = fcx.tcx.fn_sig(method.def_id);
1541 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, sig);
1542 let sig = fcx.normalize_associated_types_in(span, sig);
1544 debug!("check_method_receiver: sig={:?}", sig);
1546 let self_ty = fcx.normalize_associated_types_in(span, self_ty);
1548 let receiver_ty = sig.inputs()[0];
1549 let receiver_ty = fcx.normalize_associated_types_in(span, receiver_ty);
1551 if fcx.tcx.features().arbitrary_self_types {
1552 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1553 // Report error; `arbitrary_self_types` was enabled.
1554 e0307(fcx, span, receiver_ty);
1557 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1558 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1559 // Report error; would have worked with `arbitrary_self_types`.
1561 &fcx.tcx.sess.parse_sess,
1562 sym::arbitrary_self_types,
1565 "`{receiver_ty}` cannot be used as the type of `self` without \
1566 the `arbitrary_self_types` feature",
1569 .help(HELP_FOR_SELF_TYPE)
1572 // Report error; would not have worked with `arbitrary_self_types`.
1573 e0307(fcx, span, receiver_ty);
1579 fn e0307<'tcx>(fcx: &FnCtxt<'_, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1581 fcx.tcx.sess.diagnostic(),
1584 "invalid `self` parameter type: {receiver_ty}"
1586 .note("type of `self` must be `Self` or a type that dereferences to it")
1587 .help(HELP_FOR_SELF_TYPE)
1591 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1592 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1593 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1594 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1595 /// `Deref<Target = self_ty>`.
1597 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1598 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1599 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1600 fn receiver_is_valid<'fcx, 'tcx>(
1601 fcx: &FnCtxt<'fcx, 'tcx>,
1603 receiver_ty: Ty<'tcx>,
1605 arbitrary_self_types_enabled: bool,
1607 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1609 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1611 // `self: Self` is always valid.
1612 if can_eq_self(receiver_ty) {
1613 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1619 let mut autoderef = fcx.autoderef(span, receiver_ty);
1621 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1622 if arbitrary_self_types_enabled {
1623 autoderef = autoderef.include_raw_pointers();
1626 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1629 let receiver_trait_def_id = fcx.tcx.require_lang_item(LangItem::Receiver, None);
1631 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1633 if let Some((potential_self_ty, _)) = autoderef.next() {
1635 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1636 potential_self_ty, self_ty
1639 if can_eq_self(potential_self_ty) {
1640 fcx.register_predicates(autoderef.into_obligations());
1642 if let Some(mut err) =
1643 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1650 // Without `feature(arbitrary_self_types)`, we require that each step in the
1651 // deref chain implement `receiver`
1652 if !arbitrary_self_types_enabled
1653 && !receiver_is_implemented(
1655 receiver_trait_def_id,
1664 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1665 // If the receiver already has errors reported due to it, consider it valid to avoid
1666 // unnecessary errors (#58712).
1667 return receiver_ty.references_error();
1671 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1672 if !arbitrary_self_types_enabled
1673 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1681 fn receiver_is_implemented<'tcx>(
1682 fcx: &FnCtxt<'_, 'tcx>,
1683 receiver_trait_def_id: DefId,
1684 cause: ObligationCause<'tcx>,
1685 receiver_ty: Ty<'tcx>,
1687 let trait_ref = ty::Binder::dummy(ty::TraitRef {
1688 def_id: receiver_trait_def_id,
1689 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1692 let obligation = traits::Obligation::new(
1695 trait_ref.without_const().to_predicate(fcx.tcx),
1698 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1702 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1709 fn check_variances_for_type_defn<'tcx>(
1711 item: &hir::Item<'tcx>,
1712 hir_generics: &hir::Generics<'_>,
1714 let ty = tcx.type_of(item.def_id);
1715 if tcx.has_error_field(ty) {
1719 let ty_predicates = tcx.predicates_of(item.def_id);
1720 assert_eq!(ty_predicates.parent, None);
1721 let variances = tcx.variances_of(item.def_id);
1723 let mut constrained_parameters: FxHashSet<_> = variances
1726 .filter(|&(_, &variance)| variance != ty::Bivariant)
1727 .map(|(index, _)| Parameter(index as u32))
1730 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1732 // Lazily calculated because it is only needed in case of an error.
1733 let explicitly_bounded_params = LazyCell::new(|| {
1734 let icx = crate::collect::ItemCtxt::new(tcx, item.def_id.to_def_id());
1738 .filter_map(|predicate| match predicate {
1739 hir::WherePredicate::BoundPredicate(predicate) => {
1740 match icx.to_ty(predicate.bounded_ty).kind() {
1741 ty::Param(data) => Some(Parameter(data.index)),
1747 .collect::<FxHashSet<_>>()
1750 for (index, _) in variances.iter().enumerate() {
1751 let parameter = Parameter(index as u32);
1753 if constrained_parameters.contains(¶meter) {
1757 let param = &hir_generics.params[index];
1760 hir::ParamName::Error => {}
1762 let has_explicit_bounds = explicitly_bounded_params.contains(¶meter);
1763 report_bivariance(tcx, param, has_explicit_bounds);
1769 fn report_bivariance(
1771 param: &rustc_hir::GenericParam<'_>,
1772 has_explicit_bounds: bool,
1773 ) -> ErrorGuaranteed {
1774 let span = param.span;
1775 let param_name = param.name.ident().name;
1776 let mut err = error_392(tcx, span, param_name);
1778 let suggested_marker_id = tcx.lang_items().phantom_data();
1779 // Help is available only in presence of lang items.
1780 let msg = if let Some(def_id) = suggested_marker_id {
1782 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1784 tcx.def_path_str(def_id),
1787 format!("consider removing `{param_name}` or referring to it in a field")
1791 if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds {
1793 "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
1800 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1802 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, mut span: Span, id: hir::HirId) {
1803 let empty_env = ty::ParamEnv::empty();
1805 let def_id = fcx.tcx.hir().local_def_id(id);
1806 let predicates_with_span =
1807 fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, span)| (*p, *span));
1808 // Check elaborated bounds.
1809 let implied_obligations = traits::elaborate_predicates_with_span(fcx.tcx, predicates_with_span);
1811 for obligation in implied_obligations {
1812 // We lower empty bounds like `Vec<dyn Copy>:` as
1813 // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
1814 // regular WF checking
1815 if let ty::PredicateKind::WellFormed(..) = obligation.predicate.kind().skip_binder() {
1818 let pred = obligation.predicate;
1819 // Match the existing behavior.
1820 if pred.is_global() && !pred.has_late_bound_regions() {
1821 let pred = fcx.normalize_associated_types_in(span, pred);
1822 let hir_node = fcx.tcx.hir().find(id);
1824 // only use the span of the predicate clause (#90869)
1826 if let Some(hir::Generics { predicates, .. }) =
1827 hir_node.and_then(|node| node.generics())
1829 let obligation_span = obligation.cause.span(fcx.tcx);
1833 // There seems to be no better way to find out which predicate we are in
1834 .find(|pred| pred.span().contains(obligation_span))
1835 .map(|pred| pred.span())
1836 .unwrap_or(obligation_span);
1839 let obligation = traits::Obligation::new(
1840 traits::ObligationCause::new(span, id, traits::TrivialBound),
1844 fcx.register_predicate(obligation);
1848 fcx.select_all_obligations_or_error();
1851 fn check_mod_type_wf(tcx: TyCtxt<'_>, module: LocalDefId) {
1852 let items = tcx.hir_module_items(module);
1853 items.par_items(|item| tcx.ensure().check_well_formed(item.def_id));
1854 items.par_impl_items(|item| tcx.ensure().check_well_formed(item.def_id));
1855 items.par_trait_items(|item| tcx.ensure().check_well_formed(item.def_id));
1856 items.par_foreign_items(|item| tcx.ensure().check_well_formed(item.def_id));
1859 ///////////////////////////////////////////////////////////////////////////
1862 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1863 struct AdtVariant<'tcx> {
1864 /// Types of fields in the variant, that must be well-formed.
1865 fields: Vec<AdtField<'tcx>>,
1867 /// Explicit discriminant of this variant (e.g. `A = 123`),
1868 /// that must evaluate to a constant value.
1869 explicit_discr: Option<LocalDefId>,
1872 struct AdtField<'tcx> {
1878 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1879 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1880 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1881 let fields = struct_def
1885 let def_id = self.tcx.hir().local_def_id(field.hir_id);
1886 let field_ty = self.tcx.type_of(def_id);
1887 let field_ty = self.normalize_associated_types_in(field.ty.span, field_ty);
1888 let field_ty = self.resolve_vars_if_possible(field_ty);
1889 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1890 AdtField { ty: field_ty, span: field.ty.span, def_id }
1893 AdtVariant { fields, explicit_discr: None }
1896 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1900 .map(|variant| AdtVariant {
1901 fields: self.non_enum_variant(&variant.data).fields,
1902 explicit_discr: variant
1904 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1909 pub(super) fn impl_implied_bounds(
1913 ) -> FxHashSet<Ty<'tcx>> {
1914 match self.tcx.impl_trait_ref(impl_def_id) {
1915 Some(trait_ref) => {
1916 // Trait impl: take implied bounds from all types that
1917 // appear in the trait reference.
1918 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1919 trait_ref.substs.types().collect()
1923 // Inherent impl: take implied bounds from the `self` type.
1924 let self_ty = self.tcx.type_of(impl_def_id);
1925 let self_ty = self.normalize_associated_types_in(span, self_ty);
1926 FxHashSet::from_iter([self_ty])
1936 ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
1937 let mut err = struct_span_err!(tcx.sess, span, E0392, "parameter `{param_name}` is never used");
1938 err.span_label(span, "unused parameter");
1942 pub fn provide(providers: &mut Providers) {
1943 *providers = Providers { check_mod_type_wf, check_well_formed, ..*providers };