1 use crate::check::{FnCtxt, Inherited};
2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
5 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
6 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
8 use rustc_hir::def_id::{DefId, LocalDefId};
9 use rustc_hir::intravisit as hir_visit;
10 use rustc_hir::intravisit::Visitor;
11 use rustc_hir::itemlikevisit::ParItemLikeVisitor;
12 use rustc_hir::lang_items::LangItem;
13 use rustc_hir::ItemKind;
14 use rustc_middle::hir::map as hir_map;
15 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
16 use rustc_middle::ty::trait_def::TraitSpecializationKind;
17 use rustc_middle::ty::{
18 self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
20 use rustc_session::parse::feature_err;
21 use rustc_span::symbol::{sym, Ident, Symbol};
23 use rustc_trait_selection::opaque_types::may_define_opaque_type;
24 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
25 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
28 use std::ops::ControlFlow;
30 /// Helper type of a temporary returned by `.for_item(...)`.
31 /// This is necessary because we can't write the following bound:
34 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
36 struct CheckWfFcxBuilder<'tcx> {
37 inherited: super::InheritedBuilder<'tcx>,
40 param_env: ty::ParamEnv<'tcx>,
43 impl<'tcx> CheckWfFcxBuilder<'tcx> {
44 fn with_fcx<F>(&mut self, f: F)
46 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>) -> Vec<Ty<'tcx>>,
50 let param_env = self.param_env;
51 self.inherited.enter(|inh| {
52 let fcx = FnCtxt::new(&inh, param_env, id);
53 if !inh.tcx.features().trivial_bounds {
54 // As predicates are cached rather than obligations, this
55 // needs to be called first so that they are checked with an
57 check_false_global_bounds(&fcx, span, id);
60 fcx.select_all_obligations_or_error();
61 fcx.regionck_item(id, span, &wf_tys);
66 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
67 /// well-formed, meaning that they do not require any constraints not declared in the struct
68 /// definition itself. For example, this definition would be illegal:
71 /// struct Ref<'a, T> { x: &'a T }
74 /// because the type did not declare that `T:'a`.
76 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
77 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
79 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
80 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
81 let item = tcx.hir().expect_item(hir_id);
84 "check_item_well_formed(it.def_id={:?}, it.name={})",
86 tcx.def_path_str(def_id.to_def_id())
90 // Right now we check that every default trait implementation
91 // has an implementation of itself. Basically, a case like:
93 // impl Trait for T {}
95 // has a requirement of `T: Trait` which was required for default
96 // method implementations. Although this could be improved now that
97 // there's a better infrastructure in place for this, it's being left
98 // for a follow-up work.
100 // Since there's such a requirement, we need to check *just* positive
101 // implementations, otherwise things like:
103 // impl !Send for T {}
105 // won't be allowed unless there's an *explicit* implementation of `Send`
107 hir::ItemKind::Impl(ref impl_) => {
109 .impl_trait_ref(item.def_id)
110 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
111 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
112 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
114 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
115 err.span_labels(impl_.defaultness_span, "default because of this");
116 err.span_label(sp, "auto trait");
119 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
120 match (tcx.impl_polarity(def_id), impl_.polarity) {
121 (ty::ImplPolarity::Positive, _) => {
122 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait);
124 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
125 // FIXME(#27579): what amount of WF checking do we need for neg impls?
126 if let hir::Defaultness::Default { .. } = impl_.defaultness {
127 let mut spans = vec![span];
128 spans.extend(impl_.defaultness_span);
133 "negative impls cannot be default impls"
138 (ty::ImplPolarity::Reservation, _) => {
139 // FIXME: what amount of WF checking do we need for reservation impls?
144 hir::ItemKind::Fn(ref sig, ..) => {
145 check_item_fn(tcx, item.hir_id(), item.ident, item.span, sig.decl);
147 hir::ItemKind::Static(ref ty, ..) => {
148 check_item_type(tcx, item.hir_id(), ty.span, false);
150 hir::ItemKind::Const(ref ty, ..) => {
151 check_item_type(tcx, item.hir_id(), ty.span, false);
153 hir::ItemKind::ForeignMod { items, .. } => {
154 for it in items.iter() {
155 let it = tcx.hir().foreign_item(it.id);
157 hir::ForeignItemKind::Fn(ref decl, ..) => {
158 check_item_fn(tcx, it.hir_id(), it.ident, it.span, decl)
160 hir::ForeignItemKind::Static(ref ty, ..) => {
161 check_item_type(tcx, it.hir_id(), ty.span, true)
163 hir::ForeignItemKind::Type => (),
167 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
168 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
170 check_variances_for_type_defn(tcx, item, ast_generics);
172 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
173 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
175 check_variances_for_type_defn(tcx, item, ast_generics);
177 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
178 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
180 check_variances_for_type_defn(tcx, item, ast_generics);
182 hir::ItemKind::Trait(..) => {
183 check_trait(tcx, item);
185 hir::ItemKind::TraitAlias(..) => {
186 check_trait(tcx, item);
192 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
193 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
194 let trait_item = tcx.hir().expect_trait_item(hir_id);
196 let method_sig = match trait_item.kind {
197 hir::TraitItemKind::Fn(ref sig, _) => Some(sig),
200 check_object_unsafe_self_trait_by_name(tcx, &trait_item);
201 check_associated_item(tcx, trait_item.hir_id(), trait_item.span, method_sig);
204 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
206 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
207 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
214 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
215 /// When this is done, suggest using `Self` instead.
216 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
217 let (trait_name, trait_def_id) = match tcx.hir().get(tcx.hir().get_parent_item(item.hir_id())) {
218 hir::Node::Item(item) => match item.kind {
219 hir::ItemKind::Trait(..) => (item.ident, item.def_id),
224 let mut trait_should_be_self = vec![];
226 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
227 if could_be_self(trait_def_id, ty) =>
229 trait_should_be_self.push(ty.span)
231 hir::TraitItemKind::Fn(sig, _) => {
232 for ty in sig.decl.inputs {
233 if could_be_self(trait_def_id, ty) {
234 trait_should_be_self.push(ty.span);
237 match sig.decl.output {
238 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
239 trait_should_be_self.push(ty.span);
246 if !trait_should_be_self.is_empty() {
247 if tcx.object_safety_violations(trait_def_id).is_empty() {
250 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
253 trait_should_be_self,
254 "associated item referring to unboxed trait object for its own trait",
256 .span_label(trait_name.span, "in this trait")
257 .multipart_suggestion(
258 "you might have meant to use `Self` to refer to the implementing type",
260 Applicability::MachineApplicable,
266 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
267 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
268 let impl_item = tcx.hir().expect_impl_item(hir_id);
270 let method_sig = match impl_item.kind {
271 hir::ImplItemKind::Fn(ref sig, _) => Some(sig),
275 check_associated_item(tcx, impl_item.hir_id(), impl_item.span, method_sig);
278 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
280 // We currently only check wf of const params here.
281 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
283 // Const parameters are well formed if their type is structural match.
284 // FIXME(const_generics_defaults): we also need to check that the `default` is wf.
285 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
286 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
289 let mut is_ptr = true;
290 let err = if tcx.features().const_generics {
291 match ty.peel_refs().kind() {
292 ty::FnPtr(_) => Some("function pointers"),
293 ty::RawPtr(_) => Some("raw pointers"),
298 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
299 ty::FnPtr(_) => Some("function pointers"),
300 ty::RawPtr(_) => Some("raw pointers"),
303 err_ty_str = format!("`{}`", ty);
304 Some(err_ty_str.as_str())
308 if let Some(unsupported_type) = err {
313 "using {} as const generic parameters is forbidden",
318 let mut err = tcx.sess.struct_span_err(
321 "{} is forbidden as the type of a const generic parameter",
325 err.note("the only supported types are integers, `bool` and `char`");
326 if tcx.sess.is_nightly_build() {
328 "more complex types are supported with `#![feature(const_generics)]`",
335 if traits::search_for_structural_match_violation(param.hir_id, param.span, tcx, ty)
338 // We use the same error code in both branches, because this is really the same
339 // issue: we just special-case the message for type parameters to make it
341 if let ty::Param(_) = ty.peel_refs().kind() {
342 // Const parameters may not have type parameters as their types,
343 // because we cannot be sure that the type parameter derives `PartialEq`
344 // and `Eq` (just implementing them is not enough for `structural_match`).
349 "`{}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
350 used as the type of a const parameter",
355 format!("`{}` may not derive both `PartialEq` and `Eq`", ty),
358 "it is not currently possible to use a type parameter as the type of a \
367 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
368 the type of a const parameter",
373 format!("`{}` doesn't derive both `PartialEq` and `Eq`", ty),
382 fn check_associated_item(
386 sig_if_method: Option<&hir::FnSig<'_>>,
388 debug!("check_associated_item: {:?}", item_id);
390 let code = ObligationCauseCode::MiscObligation;
391 for_id(tcx, item_id, span).with_fcx(|fcx| {
392 let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
394 let (mut implied_bounds, self_ty) = match item.container {
395 ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
396 ty::ImplContainer(def_id) => {
397 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
402 ty::AssocKind::Const => {
403 let ty = fcx.tcx.type_of(item.def_id);
404 let ty = fcx.normalize_associated_types_in(span, ty);
405 fcx.register_wf_obligation(ty.into(), span, code.clone());
407 ty::AssocKind::Fn => {
408 let sig = fcx.tcx.fn_sig(item.def_id);
409 let sig = fcx.normalize_associated_types_in(span, sig);
410 let hir_sig = sig_if_method.expect("bad signature for method");
419 check_method_receiver(fcx, hir_sig, &item, self_ty);
421 ty::AssocKind::Type => {
422 if let ty::AssocItemContainer::TraitContainer(_) = item.container {
423 check_associated_type_bounds(fcx, item, span)
425 if item.defaultness.has_value() {
426 let ty = fcx.tcx.type_of(item.def_id);
427 let ty = fcx.normalize_associated_types_in(span, ty);
428 fcx.register_wf_obligation(ty.into(), span, code.clone());
437 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
438 for_id(tcx, item.hir_id(), item.span)
441 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
442 let def_id = tcx.hir().local_def_id(id);
444 inherited: Inherited::build(tcx, def_id),
447 param_env: tcx.param_env(def_id),
451 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
453 ItemKind::Struct(..) => Some(AdtKind::Struct),
454 ItemKind::Union(..) => Some(AdtKind::Union),
455 ItemKind::Enum(..) => Some(AdtKind::Enum),
460 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
461 fn check_type_defn<'tcx, F>(
463 item: &hir::Item<'tcx>,
465 mut lookup_fields: F,
467 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
469 for_item(tcx, item).with_fcx(|fcx| {
470 let variants = lookup_fields(fcx);
471 let packed = tcx.adt_def(item.def_id).repr.packed();
473 for variant in &variants {
474 // For DST, or when drop needs to copy things around, all
475 // intermediate types must be sized.
476 let needs_drop_copy = || {
478 let ty = variant.fields.last().unwrap().ty;
479 let ty = tcx.erase_regions(ty);
480 if ty.needs_infer() {
482 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
483 // Just treat unresolved type expression as if it needs drop.
486 ty.needs_drop(tcx, tcx.param_env(item.def_id))
490 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
491 let unsized_len = if all_sized { 0 } else { 1 };
493 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
495 let last = idx == variant.fields.len() - 1;
498 tcx.require_lang_item(LangItem::Sized, None),
499 traits::ObligationCause::new(
503 adt_kind: match item_adt_kind(&item.kind) {
514 // All field types must be well-formed.
515 for field in &variant.fields {
516 fcx.register_wf_obligation(
519 ObligationCauseCode::MiscObligation,
523 // Explicit `enum` discriminant values must const-evaluate successfully.
524 if let Some(discr_def_id) = variant.explicit_discr {
525 let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());
527 let cause = traits::ObligationCause::new(
528 tcx.def_span(discr_def_id),
530 traits::MiscObligation,
532 fcx.register_predicate(traits::Obligation::new(
535 ty::PredicateKind::ConstEvaluatable(
536 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
544 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
546 // No implied bounds in a struct definition.
551 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
552 debug!("check_trait: {:?}", item.def_id);
554 let trait_def = tcx.trait_def(item.def_id);
555 if trait_def.is_marker
556 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
558 for associated_def_id in &*tcx.associated_item_def_ids(item.def_id) {
561 tcx.def_span(*associated_def_id),
563 "marker traits cannot have associated items",
569 // FIXME: this shouldn't use an `FnCtxt` at all.
570 for_item(tcx, item).with_fcx(|fcx| {
571 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
577 /// Checks all associated type defaults of trait `trait_def_id`.
579 /// Assuming the defaults are used, check that all predicates (bounds on the
580 /// assoc type and where clauses on the trait) hold.
581 fn check_associated_type_bounds(fcx: &FnCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
584 let bounds = tcx.explicit_item_bounds(item.def_id);
586 debug!("check_associated_type_bounds: bounds={:?}", bounds);
587 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
588 let normalized_bound = fcx.normalize_associated_types_in(span, bound);
589 traits::wf::predicate_obligations(
598 for obligation in wf_obligations {
599 debug!("next obligation cause: {:?}", obligation.cause);
600 fcx.register_predicate(obligation);
609 decl: &hir::FnDecl<'_>,
611 for_id(tcx, item_id, span).with_fcx(|fcx| {
612 let def_id = tcx.hir().local_def_id(item_id);
613 let sig = tcx.fn_sig(def_id);
614 let sig = fcx.normalize_associated_types_in(span, sig);
615 let mut implied_bounds = vec![];
616 check_fn_or_method(fcx, ident.span, sig, decl, def_id.to_def_id(), &mut implied_bounds);
621 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
622 debug!("check_item_type: {:?}", item_id);
624 for_id(tcx, item_id, ty_span).with_fcx(|fcx| {
625 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
626 let item_ty = fcx.normalize_associated_types_in(ty_span, ty);
628 let mut forbid_unsized = true;
629 if allow_foreign_ty {
630 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
631 if let ty::Foreign(_) = tail.kind() {
632 forbid_unsized = false;
636 fcx.register_wf_obligation(item_ty.into(), ty_span, ObligationCauseCode::MiscObligation);
640 tcx.require_lang_item(LangItem::Sized, None),
641 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
645 // No implied bounds in a const, etc.
652 item: &'tcx hir::Item<'tcx>,
653 ast_self_ty: &hir::Ty<'_>,
654 ast_trait_ref: &Option<hir::TraitRef<'_>>,
656 debug!("check_impl: {:?}", item);
658 for_item(tcx, item).with_fcx(|fcx| {
659 match *ast_trait_ref {
660 Some(ref ast_trait_ref) => {
661 // `#[rustc_reservation_impl]` impls are not real impls and
662 // therefore don't need to be WF (the trait's `Self: Trait` predicate
664 let trait_ref = tcx.impl_trait_ref(item.def_id).unwrap();
666 fcx.normalize_associated_types_in(ast_trait_ref.path.span, trait_ref);
667 let obligations = traits::wf::trait_obligations(
672 ast_trait_ref.path.span,
675 for obligation in obligations {
676 fcx.register_predicate(obligation);
680 let self_ty = tcx.type_of(item.def_id);
681 let self_ty = fcx.normalize_associated_types_in(item.span, self_ty);
682 fcx.register_wf_obligation(
685 ObligationCauseCode::MiscObligation,
690 check_where_clauses(fcx, item.span, item.def_id.to_def_id(), None);
692 fcx.impl_implied_bounds(item.def_id.to_def_id(), item.span)
696 /// Checks where-clauses and inline bounds that are declared on `def_id`.
697 fn check_where_clauses<'tcx, 'fcx>(
698 fcx: &FnCtxt<'fcx, 'tcx>,
701 return_ty: Option<(Ty<'tcx>, Span)>,
703 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
706 let predicates = tcx.predicates_of(def_id);
707 let generics = tcx.generics_of(def_id);
709 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
710 GenericParamDefKind::Type { has_default, .. }
711 | GenericParamDefKind::Const { has_default } => {
712 has_default && def.index >= generics.parent_count as u32
714 GenericParamDefKind::Lifetime => unreachable!(),
717 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
718 // For example, this forbids the declaration:
720 // struct Foo<T = Vec<[u32]>> { .. }
722 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
723 for param in &generics.params {
725 GenericParamDefKind::Type { .. } => {
726 if is_our_default(¶m) {
727 let ty = tcx.type_of(param.def_id);
728 // Ignore dependent defaults -- that is, where the default of one type
729 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
730 // be sure if it will error or not as user might always specify the other.
731 if !ty.needs_subst() {
732 fcx.register_wf_obligation(
734 tcx.def_span(param.def_id),
735 ObligationCauseCode::MiscObligation,
740 GenericParamDefKind::Const { .. } => {
741 // FIXME(const_generics_defaults): Figure out if this
742 // is the behavior we want, see the comment further below.
743 if is_our_default(¶m) {
744 let default_ct = tcx.const_param_default(param.def_id);
745 fcx.register_wf_obligation(
747 tcx.def_span(param.def_id),
748 ObligationCauseCode::MiscObligation,
752 // Doesn't have defaults.
753 GenericParamDefKind::Lifetime => {}
757 // Check that trait predicates are WF when params are substituted by their defaults.
758 // We don't want to overly constrain the predicates that may be written but we want to
759 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
760 // Therefore we check if a predicate which contains a single type param
761 // with a concrete default is WF with that default substituted.
762 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
764 // First we build the defaulted substitution.
765 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
767 GenericParamDefKind::Lifetime => {
768 // All regions are identity.
769 tcx.mk_param_from_def(param)
772 GenericParamDefKind::Type { .. } => {
773 // If the param has a default, ...
774 if is_our_default(param) {
775 let default_ty = tcx.type_of(param.def_id);
776 // ... and it's not a dependent default, ...
777 if !default_ty.needs_subst() {
778 // ... then substitute it with the default.
779 return default_ty.into();
783 tcx.mk_param_from_def(param)
785 GenericParamDefKind::Const { .. } => {
786 // FIXME(const_generics_defaults): I(@lcnr) feel like always
787 // using the const parameter is the right choice here, even
788 // if it needs substs.
790 // Before stabilizing this we probably want to get some tests
791 // where this makes a difference and figure out what's the exact
792 // behavior we want here.
794 // If the param has a default, ...
795 if is_our_default(param) {
796 let default_ct = tcx.const_param_default(param.def_id);
797 // ... and it's not a dependent default, ...
798 if !default_ct.needs_subst() {
799 // ... then substitute it with the default.
800 return default_ct.into();
804 tcx.mk_param_from_def(param)
809 // Now we build the substituted predicates.
810 let default_obligations = predicates
813 .flat_map(|&(pred, sp)| {
816 params: FxHashSet<u32>,
818 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
821 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
822 if let ty::Param(param) = t.kind() {
823 self.params.insert(param.index);
825 t.super_visit_with(self)
828 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
832 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
833 if let ty::ConstKind::Param(param) = c.val {
834 self.params.insert(param.index);
836 c.super_visit_with(self)
839 let mut param_count = CountParams::default();
840 let has_region = pred.visit_with(&mut param_count).is_break();
841 let substituted_pred = pred.subst(tcx, substs);
842 // Don't check non-defaulted params, dependent defaults (including lifetimes)
843 // or preds with multiple params.
844 if substituted_pred.has_param_types_or_consts()
845 || param_count.params.len() > 1
849 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
850 // Avoid duplication of predicates that contain no parameters, for example.
853 Some((substituted_pred, sp))
857 // Convert each of those into an obligation. So if you have
858 // something like `struct Foo<T: Copy = String>`, we would
859 // take that predicate `T: Copy`, substitute to `String: Copy`
860 // (actually that happens in the previous `flat_map` call),
861 // and then try to prove it (in this case, we'll fail).
863 // Note the subtle difference from how we handle `predicates`
864 // below: there, we are not trying to prove those predicates
865 // to be *true* but merely *well-formed*.
866 let pred = fcx.normalize_associated_types_in(sp, pred);
868 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
869 traits::Obligation::new(cause, fcx.param_env, pred)
872 let predicates = predicates.instantiate_identity(tcx);
874 if let Some((mut return_ty, span)) = return_ty {
875 if return_ty.has_infer_types_or_consts() {
876 fcx.select_obligations_where_possible(false, |_| {});
877 return_ty = fcx.resolve_vars_if_possible(return_ty);
879 check_opaque_types(fcx, def_id.expect_local(), span, return_ty);
882 let predicates = fcx.normalize_associated_types_in(span, predicates);
884 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
885 assert_eq!(predicates.predicates.len(), predicates.spans.len());
887 iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| {
888 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
891 for obligation in wf_obligations.chain(default_obligations) {
892 debug!("next obligation cause: {:?}", obligation.cause);
893 fcx.register_predicate(obligation);
897 fn check_fn_or_method<'fcx, 'tcx>(
898 fcx: &FnCtxt<'fcx, 'tcx>,
900 sig: ty::PolyFnSig<'tcx>,
901 hir_decl: &hir::FnDecl<'_>,
903 implied_bounds: &mut Vec<Ty<'tcx>>,
905 let sig = fcx.normalize_associated_types_in(span, sig);
906 let sig = fcx.tcx.liberate_late_bound_regions(def_id, sig);
908 for (&input_ty, ty) in iter::zip(sig.inputs(), hir_decl.inputs) {
909 fcx.register_wf_obligation(input_ty.into(), ty.span, ObligationCauseCode::MiscObligation);
911 implied_bounds.extend(sig.inputs());
913 fcx.register_wf_obligation(
915 hir_decl.output.span(),
916 ObligationCauseCode::ReturnType,
919 // FIXME(#25759) return types should not be implied bounds
920 implied_bounds.push(sig.output());
922 check_where_clauses(fcx, span, def_id, Some((sig.output(), hir_decl.output.span())));
925 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
926 /// laid for "higher-order pattern unification".
927 /// This ensures that inference is tractable.
928 /// In particular, definitions of opaque types can only use other generics as arguments,
929 /// and they cannot repeat an argument. Example:
932 /// type Foo<A, B> = impl Bar<A, B>;
934 /// // Okay -- `Foo` is applied to two distinct, generic types.
935 /// fn a<T, U>() -> Foo<T, U> { .. }
937 /// // Not okay -- `Foo` is applied to `T` twice.
938 /// fn b<T>() -> Foo<T, T> { .. }
940 /// // Not okay -- `Foo` is applied to a non-generic type.
941 /// fn b<T>() -> Foo<T, u32> { .. }
944 fn check_opaque_types<'fcx, 'tcx>(
945 fcx: &FnCtxt<'fcx, 'tcx>,
946 fn_def_id: LocalDefId,
950 trace!("check_opaque_types(fn_def_id={:?}, ty={:?})", fn_def_id, ty);
953 ty.fold_with(&mut ty::fold::BottomUpFolder {
956 if let ty::Opaque(def_id, substs) = *ty.kind() {
957 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
958 let generics = tcx.generics_of(def_id);
960 let opaque_hir_id = if let Some(local_id) = def_id.as_local() {
961 tcx.hir().local_def_id_to_hir_id(local_id)
963 // Opaque types from other crates won't have defining uses in this crate.
966 if let hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) =
967 tcx.hir().expect_item(opaque_hir_id).kind
969 // No need to check return position impl trait (RPIT)
970 // because for type and const parameters they are correct
971 // by construction: we convert
973 // fn foo<P0..Pn>() -> impl Trait
978 // fn foo<P0..Pn>() -> Foo<P0...Pn>.
980 // For lifetime parameters we convert
982 // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
986 // type foo::<'p0..'pn>::Foo<'q0..'qm>
987 // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
989 // which would error here on all of the `'static` args.
992 if !may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
995 trace!("check_opaque_types: may define, generics={:#?}", generics);
996 let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
997 for (i, arg) in substs.iter().enumerate() {
998 let arg_is_param = match arg.unpack() {
999 GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
1001 GenericArgKind::Lifetime(region) => {
1002 if let ty::ReStatic = region {
1006 "non-defining opaque type use in defining scope",
1009 tcx.def_span(generics.param_at(i, tcx).def_id),
1010 "cannot use static lifetime; use a bound lifetime \
1011 instead or remove the lifetime parameter from the \
1021 GenericArgKind::Const(ct) => matches!(ct.val, ty::ConstKind::Param(_)),
1025 seen_params.entry(arg).or_default().push(i);
1027 // Prevent `fn foo() -> Foo<u32>` from being defining.
1028 let opaque_param = generics.param_at(i, tcx);
1030 .struct_span_err(span, "non-defining opaque type use in defining scope")
1032 tcx.def_span(opaque_param.def_id),
1034 "used non-generic {} `{}` for generic parameter",
1035 opaque_param.kind.descr(),
1041 } // for (arg, param)
1043 for (_, indices) in seen_params {
1044 if indices.len() > 1 {
1045 let descr = generics.param_at(indices[0], tcx).kind.descr();
1046 let spans: Vec<_> = indices
1048 .map(|i| tcx.def_span(generics.param_at(i, tcx).def_id))
1051 .struct_span_err(span, "non-defining opaque type use in defining scope")
1052 .span_note(spans, &format!("{} used multiple times", descr))
1064 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1065 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1066 of the previous types except `Self`)";
1068 fn check_method_receiver<'fcx, 'tcx>(
1069 fcx: &FnCtxt<'fcx, 'tcx>,
1070 fn_sig: &hir::FnSig<'_>,
1071 method: &ty::AssocItem,
1074 // Check that the method has a valid receiver type, given the type `Self`.
1075 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1077 if !method.fn_has_self_parameter {
1081 let span = fn_sig.decl.inputs[0].span;
1083 let sig = fcx.tcx.fn_sig(method.def_id);
1084 let sig = fcx.normalize_associated_types_in(span, sig);
1085 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, sig);
1087 debug!("check_method_receiver: sig={:?}", sig);
1089 let self_ty = fcx.normalize_associated_types_in(span, self_ty);
1091 fcx.tcx.liberate_late_bound_regions(method.def_id, ty::Binder::bind(self_ty, fcx.tcx));
1093 let receiver_ty = sig.inputs()[0];
1095 let receiver_ty = fcx.normalize_associated_types_in(span, receiver_ty);
1097 fcx.tcx.liberate_late_bound_regions(method.def_id, ty::Binder::bind(receiver_ty, fcx.tcx));
1099 if fcx.tcx.features().arbitrary_self_types {
1100 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1101 // Report error; `arbitrary_self_types` was enabled.
1102 e0307(fcx, span, receiver_ty);
1105 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1106 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1107 // Report error; would have worked with `arbitrary_self_types`.
1109 &fcx.tcx.sess.parse_sess,
1110 sym::arbitrary_self_types,
1113 "`{}` cannot be used as the type of `self` without \
1114 the `arbitrary_self_types` feature",
1118 .help(HELP_FOR_SELF_TYPE)
1121 // Report error; would not have worked with `arbitrary_self_types`.
1122 e0307(fcx, span, receiver_ty);
1128 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1130 fcx.tcx.sess.diagnostic(),
1133 "invalid `self` parameter type: {}",
1136 .note("type of `self` must be `Self` or a type that dereferences to it")
1137 .help(HELP_FOR_SELF_TYPE)
1141 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1142 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1143 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1144 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1145 /// `Deref<Target = self_ty>`.
1147 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1148 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1149 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1150 fn receiver_is_valid<'fcx, 'tcx>(
1151 fcx: &FnCtxt<'fcx, 'tcx>,
1153 receiver_ty: Ty<'tcx>,
1155 arbitrary_self_types_enabled: bool,
1157 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1159 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1161 // `self: Self` is always valid.
1162 if can_eq_self(receiver_ty) {
1163 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1169 let mut autoderef = fcx.autoderef(span, receiver_ty);
1171 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1172 if arbitrary_self_types_enabled {
1173 autoderef = autoderef.include_raw_pointers();
1176 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1179 let receiver_trait_def_id = fcx.tcx.require_lang_item(LangItem::Receiver, None);
1181 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1183 if let Some((potential_self_ty, _)) = autoderef.next() {
1185 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1186 potential_self_ty, self_ty
1189 if can_eq_self(potential_self_ty) {
1190 fcx.register_predicates(autoderef.into_obligations());
1192 if let Some(mut err) =
1193 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1200 // Without `feature(arbitrary_self_types)`, we require that each step in the
1201 // deref chain implement `receiver`
1202 if !arbitrary_self_types_enabled
1203 && !receiver_is_implemented(
1205 receiver_trait_def_id,
1214 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1215 // If he receiver already has errors reported due to it, consider it valid to avoid
1216 // unnecessary errors (#58712).
1217 return receiver_ty.references_error();
1221 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1222 if !arbitrary_self_types_enabled
1223 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1231 fn receiver_is_implemented(
1232 fcx: &FnCtxt<'_, 'tcx>,
1233 receiver_trait_def_id: DefId,
1234 cause: ObligationCause<'tcx>,
1235 receiver_ty: Ty<'tcx>,
1237 let trait_ref = ty::TraitRef {
1238 def_id: receiver_trait_def_id,
1239 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1242 let obligation = traits::Obligation::new(
1245 trait_ref.without_const().to_predicate(fcx.tcx),
1248 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1252 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1259 fn check_variances_for_type_defn<'tcx>(
1261 item: &hir::Item<'tcx>,
1262 hir_generics: &hir::Generics<'_>,
1264 let ty = tcx.type_of(item.def_id);
1265 if tcx.has_error_field(ty) {
1269 let ty_predicates = tcx.predicates_of(item.def_id);
1270 assert_eq!(ty_predicates.parent, None);
1271 let variances = tcx.variances_of(item.def_id);
1273 let mut constrained_parameters: FxHashSet<_> = variances
1276 .filter(|&(_, &variance)| variance != ty::Bivariant)
1277 .map(|(index, _)| Parameter(index as u32))
1280 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1282 for (index, _) in variances.iter().enumerate() {
1283 if constrained_parameters.contains(&Parameter(index as u32)) {
1287 let param = &hir_generics.params[index];
1290 hir::ParamName::Error => {}
1291 _ => report_bivariance(tcx, param),
1296 fn report_bivariance(tcx: TyCtxt<'_>, param: &rustc_hir::GenericParam<'_>) {
1297 let span = param.span;
1298 let param_name = param.name.ident().name;
1299 let mut err = error_392(tcx, span, param_name);
1301 let suggested_marker_id = tcx.lang_items().phantom_data();
1302 // Help is available only in presence of lang items.
1303 let msg = if let Some(def_id) = suggested_marker_id {
1305 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1307 tcx.def_path_str(def_id),
1310 format!("consider removing `{}` or referring to it in a field", param_name)
1314 if matches!(param.kind, rustc_hir::GenericParamKind::Type { .. }) {
1316 "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead",
1323 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1325 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1326 let empty_env = ty::ParamEnv::empty();
1328 let def_id = fcx.tcx.hir().local_def_id(id);
1329 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p);
1330 // Check elaborated bounds.
1331 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1333 for obligation in implied_obligations {
1334 let pred = obligation.predicate;
1335 // Match the existing behavior.
1336 if pred.is_global() && !pred.has_late_bound_regions() {
1337 let pred = fcx.normalize_associated_types_in(span, pred);
1338 let obligation = traits::Obligation::new(
1339 traits::ObligationCause::new(span, id, traits::TrivialBound),
1343 fcx.register_predicate(obligation);
1347 fcx.select_all_obligations_or_error();
1350 #[derive(Clone, Copy)]
1351 pub struct CheckTypeWellFormedVisitor<'tcx> {
1355 impl CheckTypeWellFormedVisitor<'tcx> {
1356 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1357 CheckTypeWellFormedVisitor { tcx }
1361 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1362 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1363 Visitor::visit_item(&mut self.clone(), i);
1366 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1367 Visitor::visit_trait_item(&mut self.clone(), trait_item);
1370 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1371 Visitor::visit_impl_item(&mut self.clone(), impl_item);
1374 fn visit_foreign_item(&self, foreign_item: &'tcx hir::ForeignItem<'tcx>) {
1375 Visitor::visit_foreign_item(&mut self.clone(), foreign_item)
1379 impl Visitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1380 type Map = hir_map::Map<'tcx>;
1382 fn nested_visit_map(&mut self) -> hir_visit::NestedVisitorMap<Self::Map> {
1383 hir_visit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
1386 fn visit_item(&mut self, i: &'tcx hir::Item<'tcx>) {
1387 debug!("visit_item: {:?}", i);
1388 self.tcx.ensure().check_item_well_formed(i.def_id);
1389 hir_visit::walk_item(self, i);
1392 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1393 debug!("visit_trait_item: {:?}", trait_item);
1394 self.tcx.ensure().check_trait_item_well_formed(trait_item.def_id);
1395 hir_visit::walk_trait_item(self, trait_item);
1398 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1399 debug!("visit_impl_item: {:?}", impl_item);
1400 self.tcx.ensure().check_impl_item_well_formed(impl_item.def_id);
1401 hir_visit::walk_impl_item(self, impl_item);
1404 fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
1405 check_param_wf(self.tcx, p);
1406 hir_visit::walk_generic_param(self, p);
1410 ///////////////////////////////////////////////////////////////////////////
1413 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1414 struct AdtVariant<'tcx> {
1415 /// Types of fields in the variant, that must be well-formed.
1416 fields: Vec<AdtField<'tcx>>,
1418 /// Explicit discriminant of this variant (e.g. `A = 123`),
1419 /// that must evaluate to a constant value.
1420 explicit_discr: Option<LocalDefId>,
1423 struct AdtField<'tcx> {
1428 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1429 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1430 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1431 let fields = struct_def
1435 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1436 let field_ty = self.normalize_associated_types_in(field.ty.span, field_ty);
1437 let field_ty = self.resolve_vars_if_possible(field_ty);
1438 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1439 AdtField { ty: field_ty, span: field.ty.span }
1442 AdtVariant { fields, explicit_discr: None }
1445 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1449 .map(|variant| AdtVariant {
1450 fields: self.non_enum_variant(&variant.data).fields,
1451 explicit_discr: variant
1453 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1458 pub(super) fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1459 match self.tcx.impl_trait_ref(impl_def_id) {
1460 Some(trait_ref) => {
1461 // Trait impl: take implied bounds from all types that
1462 // appear in the trait reference.
1463 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1464 trait_ref.substs.types().collect()
1468 // Inherent impl: take implied bounds from the `self` type.
1469 let self_ty = self.tcx.type_of(impl_def_id);
1470 let self_ty = self.normalize_associated_types_in(span, self_ty);
1477 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) -> DiagnosticBuilder<'_> {
1479 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1480 err.span_label(span, "unused parameter");