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};
27 use std::ops::ControlFlow;
29 /// Helper type of a temporary returned by `.for_item(...)`.
30 /// This is necessary because we can't write the following bound:
33 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
35 struct CheckWfFcxBuilder<'tcx> {
36 inherited: super::InheritedBuilder<'tcx>,
39 param_env: ty::ParamEnv<'tcx>,
42 impl<'tcx> CheckWfFcxBuilder<'tcx> {
43 fn with_fcx<F>(&mut self, f: F)
45 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
49 let param_env = self.param_env;
50 self.inherited.enter(|inh| {
51 let fcx = FnCtxt::new(&inh, param_env, id);
52 if !inh.tcx.features().trivial_bounds {
53 // As predicates are cached rather than obligations, this
54 // needs to be called first so that they are checked with an
56 check_false_global_bounds(&fcx, span, id);
58 let wf_tys = f(&fcx, fcx.tcx);
59 fcx.select_all_obligations_or_error();
60 fcx.regionck_item(id, span, &wf_tys);
65 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
66 /// well-formed, meaning that they do not require any constraints not declared in the struct
67 /// definition itself. For example, this definition would be illegal:
70 /// struct Ref<'a, T> { x: &'a T }
73 /// because the type did not declare that `T:'a`.
75 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
76 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
78 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
79 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
80 let item = tcx.hir().expect_item(hir_id);
83 "check_item_well_formed(it.hir_id={:?}, it.name={})",
85 tcx.def_path_str(def_id.to_def_id())
89 // Right now we check that every default trait implementation
90 // has an implementation of itself. Basically, a case like:
92 // impl Trait for T {}
94 // has a requirement of `T: Trait` which was required for default
95 // method implementations. Although this could be improved now that
96 // there's a better infrastructure in place for this, it's being left
97 // for a follow-up work.
99 // Since there's such a requirement, we need to check *just* positive
100 // implementations, otherwise things like:
102 // impl !Send for T {}
104 // won't be allowed unless there's an *explicit* implementation of `Send`
106 hir::ItemKind::Impl(ref impl_) => {
108 .impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
109 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
110 if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
111 let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
113 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
114 err.span_labels(impl_.defaultness_span, "default because of this");
115 err.span_label(sp, "auto trait");
118 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
119 match (tcx.impl_polarity(def_id), impl_.polarity) {
120 (ty::ImplPolarity::Positive, _) => {
121 check_impl(tcx, item, impl_.self_ty, &impl_.of_trait);
123 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
124 // FIXME(#27579): what amount of WF checking do we need for neg impls?
125 if let hir::Defaultness::Default { .. } = impl_.defaultness {
126 let mut spans = vec![span];
127 spans.extend(impl_.defaultness_span);
132 "negative impls cannot be default impls"
137 (ty::ImplPolarity::Reservation, _) => {
138 // FIXME: what amount of WF checking do we need for reservation impls?
143 hir::ItemKind::Fn(ref sig, ..) => {
144 check_item_fn(tcx, item.hir_id, item.ident, item.span, sig.decl);
146 hir::ItemKind::Static(ref ty, ..) => {
147 check_item_type(tcx, item.hir_id, ty.span, false);
149 hir::ItemKind::Const(ref ty, ..) => {
150 check_item_type(tcx, item.hir_id, ty.span, false);
152 hir::ItemKind::ForeignMod { items, .. } => {
153 for it in items.iter() {
154 let it = tcx.hir().foreign_item(it.id);
156 hir::ForeignItemKind::Fn(ref decl, ..) => {
157 check_item_fn(tcx, it.hir_id, it.ident, it.span, decl)
159 hir::ForeignItemKind::Static(ref ty, ..) => {
160 check_item_type(tcx, it.hir_id, ty.span, true)
162 hir::ForeignItemKind::Type => (),
166 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
167 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
169 check_variances_for_type_defn(tcx, item, ast_generics);
171 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
172 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
174 check_variances_for_type_defn(tcx, item, ast_generics);
176 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
177 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
179 check_variances_for_type_defn(tcx, item, ast_generics);
181 hir::ItemKind::Trait(..) => {
182 check_trait(tcx, item);
184 hir::ItemKind::TraitAlias(..) => {
185 check_trait(tcx, item);
191 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
192 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
193 let trait_item = tcx.hir().expect_trait_item(hir_id);
195 let method_sig = match trait_item.kind {
196 hir::TraitItemKind::Fn(ref sig, _) => Some(sig),
199 check_object_unsafe_self_trait_by_name(tcx, &trait_item);
200 check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
203 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
205 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
206 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
213 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
214 /// When this is done, suggest using `Self` instead.
215 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
216 let (trait_name, trait_def_id) = match tcx.hir().get(tcx.hir().get_parent_item(item.hir_id)) {
217 hir::Node::Item(item) => match item.kind {
218 hir::ItemKind::Trait(..) => (item.ident, tcx.hir().local_def_id(item.hir_id)),
223 let mut trait_should_be_self = vec![];
225 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
226 if could_be_self(trait_def_id, ty) =>
228 trait_should_be_self.push(ty.span)
230 hir::TraitItemKind::Fn(sig, _) => {
231 for ty in sig.decl.inputs {
232 if could_be_self(trait_def_id, ty) {
233 trait_should_be_self.push(ty.span);
236 match sig.decl.output {
237 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
238 trait_should_be_self.push(ty.span);
245 if !trait_should_be_self.is_empty() {
246 if tcx.object_safety_violations(trait_def_id).is_empty() {
249 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
252 trait_should_be_self,
253 "associated item referring to unboxed trait object for its own trait",
255 .span_label(trait_name.span, "in this trait")
256 .multipart_suggestion(
257 "you might have meant to use `Self` to refer to the implementing type",
259 Applicability::MachineApplicable,
265 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
266 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
267 let impl_item = tcx.hir().expect_impl_item(hir_id);
269 let method_sig = match impl_item.kind {
270 hir::ImplItemKind::Fn(ref sig, _) => Some(sig),
274 check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
277 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
279 // We currently only check wf of const params here.
280 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
282 // Const parameters are well formed if their type is structural match.
283 // FIXME(const_generics_defaults): we also need to check that the `default` is wf.
284 hir::GenericParamKind::Const { ty: hir_ty, default: _ } => {
285 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
288 let mut is_ptr = true;
289 let err = if tcx.features().const_generics {
290 match ty.peel_refs().kind() {
291 ty::FnPtr(_) => Some("function pointers"),
292 ty::RawPtr(_) => Some("raw pointers"),
297 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
298 ty::FnPtr(_) => Some("function pointers"),
299 ty::RawPtr(_) => Some("raw pointers"),
302 err_ty_str = format!("`{}`", ty);
303 Some(err_ty_str.as_str())
307 if let Some(unsupported_type) = err {
312 "using {} as const generic parameters is forbidden",
321 "{} is forbidden as the type of a const generic parameter",
325 .note("the only supported types are integers, `bool` and `char`")
326 .help("more complex types are supported with `#![feature(const_generics)]`")
331 if traits::search_for_structural_match_violation(param.hir_id, param.span, tcx, ty)
334 // We use the same error code in both branches, because this is really the same
335 // issue: we just special-case the message for type parameters to make it
337 if let ty::Param(_) = ty.peel_refs().kind() {
338 // Const parameters may not have type parameters as their types,
339 // because we cannot be sure that the type parameter derives `PartialEq`
340 // and `Eq` (just implementing them is not enough for `structural_match`).
345 "`{}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
346 used as the type of a const parameter",
351 format!("`{}` may not derive both `PartialEq` and `Eq`", ty),
354 "it is not currently possible to use a type parameter as the type of a \
363 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
364 the type of a const parameter",
369 format!("`{}` doesn't derive both `PartialEq` and `Eq`", ty),
378 fn check_associated_item(
382 sig_if_method: Option<&hir::FnSig<'_>>,
384 debug!("check_associated_item: {:?}", item_id);
386 let code = ObligationCauseCode::MiscObligation;
387 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
388 let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
390 let (mut implied_bounds, self_ty) = match item.container {
391 ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
392 ty::ImplContainer(def_id) => {
393 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
398 ty::AssocKind::Const => {
399 let ty = fcx.tcx.type_of(item.def_id);
400 let ty = fcx.normalize_associated_types_in(span, ty);
401 fcx.register_wf_obligation(ty.into(), span, code.clone());
403 ty::AssocKind::Fn => {
404 let sig = fcx.tcx.fn_sig(item.def_id);
405 let sig = fcx.normalize_associated_types_in(span, sig);
406 let hir_sig = sig_if_method.expect("bad signature for method");
416 check_method_receiver(fcx, hir_sig, &item, self_ty);
418 ty::AssocKind::Type => {
419 if let ty::AssocItemContainer::TraitContainer(_) = item.container {
420 check_associated_type_bounds(fcx, item, span)
422 if item.defaultness.has_value() {
423 let ty = fcx.tcx.type_of(item.def_id);
424 let ty = fcx.normalize_associated_types_in(span, ty);
425 fcx.register_wf_obligation(ty.into(), span, code.clone());
434 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
435 for_id(tcx, item.hir_id, item.span)
438 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
439 let def_id = tcx.hir().local_def_id(id);
441 inherited: Inherited::build(tcx, def_id),
444 param_env: tcx.param_env(def_id),
448 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
450 ItemKind::Struct(..) => Some(AdtKind::Struct),
451 ItemKind::Union(..) => Some(AdtKind::Union),
452 ItemKind::Enum(..) => Some(AdtKind::Enum),
457 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
458 fn check_type_defn<'tcx, F>(
460 item: &hir::Item<'tcx>,
462 mut lookup_fields: F,
464 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
466 for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
467 let variants = lookup_fields(fcx);
468 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
469 let packed = fcx.tcx.adt_def(def_id).repr.packed();
471 for variant in &variants {
472 // For DST, or when drop needs to copy things around, all
473 // intermediate types must be sized.
474 let needs_drop_copy = || {
476 let ty = variant.fields.last().unwrap().ty;
477 let ty = fcx.tcx.erase_regions(ty);
478 if ty.needs_infer() {
481 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
482 // Just treat unresolved type expression as if it needs drop.
485 ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
489 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
490 let unsized_len = if all_sized { 0 } else { 1 };
492 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
494 let last = idx == variant.fields.len() - 1;
497 fcx.tcx.require_lang_item(LangItem::Sized, None),
498 traits::ObligationCause::new(
502 adt_kind: match item_adt_kind(&item.kind) {
513 // All field types must be well-formed.
514 for field in &variant.fields {
515 fcx.register_wf_obligation(
518 ObligationCauseCode::MiscObligation,
522 // Explicit `enum` discriminant values must const-evaluate successfully.
523 if let Some(discr_def_id) = variant.explicit_discr {
525 InternalSubsts::identity_for_item(fcx.tcx, discr_def_id.to_def_id());
527 let cause = traits::ObligationCause::new(
528 fcx.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()),
539 .to_predicate(fcx.tcx),
544 check_where_clauses(tcx, fcx, item.span, 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.hir_id);
554 let trait_def_id = tcx.hir().local_def_id(item.hir_id);
556 let trait_def = tcx.trait_def(trait_def_id);
557 if trait_def.is_marker
558 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
560 for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
563 tcx.def_span(*associated_def_id),
565 "marker traits cannot have associated items",
571 for_item(tcx, item).with_fcx(|fcx, _| {
572 check_where_clauses(tcx, fcx, item.span, trait_def_id.to_def_id(), None);
578 /// Checks all associated type defaults of trait `trait_def_id`.
580 /// Assuming the defaults are used, check that all predicates (bounds on the
581 /// assoc type and where clauses on the trait) hold.
582 fn check_associated_type_bounds(fcx: &FnCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
585 let bounds = tcx.explicit_item_bounds(item.def_id);
587 debug!("check_associated_type_bounds: bounds={:?}", bounds);
588 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
589 let normalized_bound = fcx.normalize_associated_types_in(span, bound);
590 traits::wf::predicate_obligations(
599 for obligation in wf_obligations {
600 debug!("next obligation cause: {:?}", obligation.cause);
601 fcx.register_predicate(obligation);
610 decl: &hir::FnDecl<'_>,
612 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
613 let def_id = fcx.tcx.hir().local_def_id(item_id);
614 let sig = fcx.tcx.fn_sig(def_id);
615 let sig = fcx.normalize_associated_types_in(span, sig);
616 let mut implied_bounds = vec![];
630 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
631 debug!("check_item_type: {:?}", item_id);
633 for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
634 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
635 let item_ty = fcx.normalize_associated_types_in(ty_span, ty);
637 let mut forbid_unsized = true;
638 if allow_foreign_ty {
639 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
640 if let ty::Foreign(_) = tail.kind() {
641 forbid_unsized = false;
645 fcx.register_wf_obligation(item_ty.into(), ty_span, ObligationCauseCode::MiscObligation);
649 fcx.tcx.require_lang_item(LangItem::Sized, None),
650 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
654 // No implied bounds in a const, etc.
661 item: &'tcx hir::Item<'tcx>,
662 ast_self_ty: &hir::Ty<'_>,
663 ast_trait_ref: &Option<hir::TraitRef<'_>>,
665 debug!("check_impl: {:?}", item);
667 for_item(tcx, item).with_fcx(|fcx, tcx| {
668 let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
670 match *ast_trait_ref {
671 Some(ref ast_trait_ref) => {
672 // `#[rustc_reservation_impl]` impls are not real impls and
673 // therefore don't need to be WF (the trait's `Self: Trait` predicate
675 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
677 fcx.normalize_associated_types_in(ast_trait_ref.path.span, trait_ref);
678 let obligations = traits::wf::trait_obligations(
683 ast_trait_ref.path.span,
686 for obligation in obligations {
687 fcx.register_predicate(obligation);
691 let self_ty = fcx.tcx.type_of(item_def_id);
692 let self_ty = fcx.normalize_associated_types_in(item.span, self_ty);
693 fcx.register_wf_obligation(
696 ObligationCauseCode::MiscObligation,
701 check_where_clauses(tcx, fcx, item.span, item_def_id.to_def_id(), None);
703 fcx.impl_implied_bounds(item_def_id.to_def_id(), item.span)
707 /// Checks where-clauses and inline bounds that are declared on `def_id`.
708 fn check_where_clauses<'tcx, 'fcx>(
710 fcx: &FnCtxt<'fcx, 'tcx>,
713 return_ty: Option<(Ty<'tcx>, Span)>,
715 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
717 let predicates = fcx.tcx.predicates_of(def_id);
718 let generics = tcx.generics_of(def_id);
720 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
721 GenericParamDefKind::Type { has_default, .. } => {
722 has_default && def.index >= generics.parent_count as u32
727 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
728 // For example, this forbids the declaration:
730 // struct Foo<T = Vec<[u32]>> { .. }
732 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
733 for param in &generics.params {
734 if let GenericParamDefKind::Type { .. } = param.kind {
735 if is_our_default(¶m) {
736 let ty = fcx.tcx.type_of(param.def_id);
737 // Ignore dependent defaults -- that is, where the default of one type
738 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
739 // be sure if it will error or not as user might always specify the other.
740 if !ty.needs_subst() {
741 fcx.register_wf_obligation(
743 fcx.tcx.def_span(param.def_id),
744 ObligationCauseCode::MiscObligation,
751 // Check that trait predicates are WF when params are substituted by their defaults.
752 // We don't want to overly constrain the predicates that may be written but we want to
753 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
754 // Therefore we check if a predicate which contains a single type param
755 // with a concrete default is WF with that default substituted.
756 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
758 // First we build the defaulted substitution.
759 let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
761 GenericParamDefKind::Lifetime => {
762 // All regions are identity.
763 fcx.tcx.mk_param_from_def(param)
766 GenericParamDefKind::Type { .. } => {
767 // If the param has a default, ...
768 if is_our_default(param) {
769 let default_ty = fcx.tcx.type_of(param.def_id);
770 // ... and it's not a dependent default, ...
771 if !default_ty.needs_subst() {
772 // ... then substitute it with the default.
773 return default_ty.into();
777 fcx.tcx.mk_param_from_def(param)
780 GenericParamDefKind::Const => {
781 // FIXME(const_generics_defaults)
782 fcx.tcx.mk_param_from_def(param)
787 // Now we build the substituted predicates.
788 let default_obligations = predicates
791 .flat_map(|&(pred, sp)| {
794 params: FxHashSet<u32>,
796 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
799 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
800 if let ty::Param(param) = t.kind() {
801 self.params.insert(param.index);
803 t.super_visit_with(self)
806 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
810 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
811 if let ty::ConstKind::Param(param) = c.val {
812 self.params.insert(param.index);
814 c.super_visit_with(self)
817 let mut param_count = CountParams::default();
818 let has_region = pred.visit_with(&mut param_count).is_break();
819 let substituted_pred = pred.subst(fcx.tcx, substs);
820 // Don't check non-defaulted params, dependent defaults (including lifetimes)
821 // or preds with multiple params.
822 if substituted_pred.has_param_types_or_consts()
823 || param_count.params.len() > 1
827 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
828 // Avoid duplication of predicates that contain no parameters, for example.
831 Some((substituted_pred, sp))
835 // Convert each of those into an obligation. So if you have
836 // something like `struct Foo<T: Copy = String>`, we would
837 // take that predicate `T: Copy`, substitute to `String: Copy`
838 // (actually that happens in the previous `flat_map` call),
839 // and then try to prove it (in this case, we'll fail).
841 // Note the subtle difference from how we handle `predicates`
842 // below: there, we are not trying to prove those predicates
843 // to be *true* but merely *well-formed*.
844 let pred = fcx.normalize_associated_types_in(sp, pred);
846 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
847 traits::Obligation::new(cause, fcx.param_env, pred)
850 let predicates = predicates.instantiate_identity(fcx.tcx);
852 if let Some((mut return_ty, span)) = return_ty {
853 if return_ty.has_infer_types_or_consts() {
854 fcx.select_obligations_where_possible(false, |_| {});
855 return_ty = fcx.resolve_vars_if_possible(return_ty);
857 check_opaque_types(tcx, fcx, def_id.expect_local(), span, return_ty);
860 let predicates = fcx.normalize_associated_types_in(span, predicates);
862 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
863 assert_eq!(predicates.predicates.len(), predicates.spans.len());
865 predicates.predicates.iter().zip(predicates.spans.iter()).flat_map(|(&p, &sp)| {
866 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
869 for obligation in wf_obligations.chain(default_obligations) {
870 debug!("next obligation cause: {:?}", obligation.cause);
871 fcx.register_predicate(obligation);
875 fn check_fn_or_method<'fcx, 'tcx>(
877 fcx: &FnCtxt<'fcx, 'tcx>,
879 sig: ty::PolyFnSig<'tcx>,
880 hir_decl: &hir::FnDecl<'_>,
882 implied_bounds: &mut Vec<Ty<'tcx>>,
884 let sig = fcx.normalize_associated_types_in(span, sig);
885 let sig = fcx.tcx.liberate_late_bound_regions(def_id, sig);
887 for (&input_ty, span) in sig.inputs().iter().zip(hir_decl.inputs.iter().map(|t| t.span)) {
888 fcx.register_wf_obligation(input_ty.into(), span, ObligationCauseCode::MiscObligation);
890 implied_bounds.extend(sig.inputs());
892 fcx.register_wf_obligation(
894 hir_decl.output.span(),
895 ObligationCauseCode::ReturnType,
898 // FIXME(#25759) return types should not be implied bounds
899 implied_bounds.push(sig.output());
901 check_where_clauses(tcx, fcx, span, def_id, Some((sig.output(), hir_decl.output.span())));
904 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
905 /// laid for "higher-order pattern unification".
906 /// This ensures that inference is tractable.
907 /// In particular, definitions of opaque types can only use other generics as arguments,
908 /// and they cannot repeat an argument. Example:
911 /// type Foo<A, B> = impl Bar<A, B>;
913 /// // Okay -- `Foo` is applied to two distinct, generic types.
914 /// fn a<T, U>() -> Foo<T, U> { .. }
916 /// // Not okay -- `Foo` is applied to `T` twice.
917 /// fn b<T>() -> Foo<T, T> { .. }
919 /// // Not okay -- `Foo` is applied to a non-generic type.
920 /// fn b<T>() -> Foo<T, u32> { .. }
923 fn check_opaque_types<'fcx, 'tcx>(
925 fcx: &FnCtxt<'fcx, 'tcx>,
926 fn_def_id: LocalDefId,
930 trace!("check_opaque_types(ty={:?})", ty);
931 ty.fold_with(&mut ty::fold::BottomUpFolder {
934 if let ty::Opaque(def_id, substs) = *ty.kind() {
935 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
936 let generics = tcx.generics_of(def_id);
938 let opaque_hir_id = if let Some(local_id) = def_id.as_local() {
939 tcx.hir().local_def_id_to_hir_id(local_id)
941 // Opaque types from other crates won't have defining uses in this crate.
944 if let hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) =
945 tcx.hir().expect_item(opaque_hir_id).kind
947 // No need to check return position impl trait (RPIT)
948 // because for type and const parameters they are correct
949 // by construction: we convert
951 // fn foo<P0..Pn>() -> impl Trait
956 // fn foo<P0..Pn>() -> Foo<P0...Pn>.
958 // For lifetime parameters we convert
960 // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
964 // type foo::<'p0..'pn>::Foo<'q0..'qm>
965 // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
967 // which would error here on all of the `'static` args.
970 if !may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
973 trace!("check_opaque_types: may define, generics={:#?}", generics);
974 let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
975 for (i, arg) in substs.iter().enumerate() {
976 let arg_is_param = match arg.unpack() {
977 GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
979 GenericArgKind::Lifetime(region) => {
980 if let ty::ReStatic = region {
984 "non-defining opaque type use in defining scope",
987 tcx.def_span(generics.param_at(i, tcx).def_id),
988 "cannot use static lifetime; use a bound lifetime \
989 instead or remove the lifetime parameter from the \
999 GenericArgKind::Const(ct) => matches!(ct.val, ty::ConstKind::Param(_)),
1003 seen_params.entry(arg).or_default().push(i);
1005 // Prevent `fn foo() -> Foo<u32>` from being defining.
1006 let opaque_param = generics.param_at(i, tcx);
1008 .struct_span_err(span, "non-defining opaque type use in defining scope")
1010 tcx.def_span(opaque_param.def_id),
1012 "used non-generic {} `{}` for generic parameter",
1013 opaque_param.kind.descr(),
1019 } // for (arg, param)
1021 for (_, indices) in seen_params {
1022 if indices.len() > 1 {
1023 let descr = generics.param_at(indices[0], tcx).kind.descr();
1024 let spans: Vec<_> = indices
1026 .map(|i| tcx.def_span(generics.param_at(i, tcx).def_id))
1029 .struct_span_err(span, "non-defining opaque type use in defining scope")
1030 .span_note(spans, &format!("{} used multiple times", descr))
1042 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1043 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1044 of the previous types except `Self`)";
1046 fn check_method_receiver<'fcx, 'tcx>(
1047 fcx: &FnCtxt<'fcx, 'tcx>,
1048 fn_sig: &hir::FnSig<'_>,
1049 method: &ty::AssocItem,
1052 // Check that the method has a valid receiver type, given the type `Self`.
1053 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1055 if !method.fn_has_self_parameter {
1059 let span = fn_sig.decl.inputs[0].span;
1061 let sig = fcx.tcx.fn_sig(method.def_id);
1062 let sig = fcx.normalize_associated_types_in(span, sig);
1063 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, sig);
1065 debug!("check_method_receiver: sig={:?}", sig);
1067 let self_ty = fcx.normalize_associated_types_in(span, self_ty);
1068 let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, ty::Binder::bind(self_ty));
1070 let receiver_ty = sig.inputs()[0];
1072 let receiver_ty = fcx.normalize_associated_types_in(span, receiver_ty);
1074 fcx.tcx.liberate_late_bound_regions(method.def_id, ty::Binder::bind(receiver_ty));
1076 if fcx.tcx.features().arbitrary_self_types {
1077 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1078 // Report error; `arbitrary_self_types` was enabled.
1079 e0307(fcx, span, receiver_ty);
1082 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1083 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1084 // Report error; would have worked with `arbitrary_self_types`.
1086 &fcx.tcx.sess.parse_sess,
1087 sym::arbitrary_self_types,
1090 "`{}` cannot be used as the type of `self` without \
1091 the `arbitrary_self_types` feature",
1095 .help(HELP_FOR_SELF_TYPE)
1098 // Report error; would not have worked with `arbitrary_self_types`.
1099 e0307(fcx, span, receiver_ty);
1105 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1107 fcx.tcx.sess.diagnostic(),
1110 "invalid `self` parameter type: {}",
1113 .note("type of `self` must be `Self` or a type that dereferences to it")
1114 .help(HELP_FOR_SELF_TYPE)
1118 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1119 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1120 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1121 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1122 /// `Deref<Target = self_ty>`.
1124 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1125 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1126 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1127 fn receiver_is_valid<'fcx, 'tcx>(
1128 fcx: &FnCtxt<'fcx, 'tcx>,
1130 receiver_ty: Ty<'tcx>,
1132 arbitrary_self_types_enabled: bool,
1134 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1136 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1138 // `self: Self` is always valid.
1139 if can_eq_self(receiver_ty) {
1140 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1146 let mut autoderef = fcx.autoderef(span, receiver_ty);
1148 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1149 if arbitrary_self_types_enabled {
1150 autoderef = autoderef.include_raw_pointers();
1153 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1156 let receiver_trait_def_id = fcx.tcx.require_lang_item(LangItem::Receiver, None);
1158 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1160 if let Some((potential_self_ty, _)) = autoderef.next() {
1162 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1163 potential_self_ty, self_ty
1166 if can_eq_self(potential_self_ty) {
1167 fcx.register_predicates(autoderef.into_obligations());
1169 if let Some(mut err) =
1170 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1177 // Without `feature(arbitrary_self_types)`, we require that each step in the
1178 // deref chain implement `receiver`
1179 if !arbitrary_self_types_enabled
1180 && !receiver_is_implemented(
1182 receiver_trait_def_id,
1191 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1192 // If he receiver already has errors reported due to it, consider it valid to avoid
1193 // unnecessary errors (#58712).
1194 return receiver_ty.references_error();
1198 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1199 if !arbitrary_self_types_enabled
1200 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1208 fn receiver_is_implemented(
1209 fcx: &FnCtxt<'_, 'tcx>,
1210 receiver_trait_def_id: DefId,
1211 cause: ObligationCause<'tcx>,
1212 receiver_ty: Ty<'tcx>,
1214 let trait_ref = ty::TraitRef {
1215 def_id: receiver_trait_def_id,
1216 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1219 let obligation = traits::Obligation::new(
1222 trait_ref.without_const().to_predicate(fcx.tcx),
1225 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1229 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1236 fn check_variances_for_type_defn<'tcx>(
1238 item: &hir::Item<'tcx>,
1239 hir_generics: &hir::Generics<'_>,
1241 let item_def_id = tcx.hir().local_def_id(item.hir_id);
1242 let ty = tcx.type_of(item_def_id);
1243 if tcx.has_error_field(ty) {
1247 let ty_predicates = tcx.predicates_of(item_def_id);
1248 assert_eq!(ty_predicates.parent, None);
1249 let variances = tcx.variances_of(item_def_id);
1251 let mut constrained_parameters: FxHashSet<_> = variances
1254 .filter(|&(_, &variance)| variance != ty::Bivariant)
1255 .map(|(index, _)| Parameter(index as u32))
1258 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1260 for (index, _) in variances.iter().enumerate() {
1261 if constrained_parameters.contains(&Parameter(index as u32)) {
1265 let param = &hir_generics.params[index];
1268 hir::ParamName::Error => {}
1269 _ => report_bivariance(tcx, param.span, param.name.ident().name),
1274 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) {
1275 let mut err = error_392(tcx, span, param_name);
1277 let suggested_marker_id = tcx.lang_items().phantom_data();
1278 // Help is available only in presence of lang items.
1279 let msg = if let Some(def_id) = suggested_marker_id {
1281 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1283 tcx.def_path_str(def_id),
1286 format!("consider removing `{}` or referring to it in a field", param_name)
1292 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1294 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1295 let empty_env = ty::ParamEnv::empty();
1297 let def_id = fcx.tcx.hir().local_def_id(id);
1298 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p);
1299 // Check elaborated bounds.
1300 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1302 for obligation in implied_obligations {
1303 let pred = obligation.predicate;
1304 // Match the existing behavior.
1305 if pred.is_global() && !pred.has_late_bound_regions() {
1306 let pred = fcx.normalize_associated_types_in(span, pred);
1307 let obligation = traits::Obligation::new(
1308 traits::ObligationCause::new(span, id, traits::TrivialBound),
1312 fcx.register_predicate(obligation);
1316 fcx.select_all_obligations_or_error();
1319 #[derive(Clone, Copy)]
1320 pub struct CheckTypeWellFormedVisitor<'tcx> {
1324 impl CheckTypeWellFormedVisitor<'tcx> {
1325 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1326 CheckTypeWellFormedVisitor { tcx }
1330 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1331 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1332 Visitor::visit_item(&mut self.clone(), i);
1335 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1336 Visitor::visit_trait_item(&mut self.clone(), trait_item);
1339 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1340 Visitor::visit_impl_item(&mut self.clone(), impl_item);
1343 fn visit_foreign_item(&self, foreign_item: &'tcx hir::ForeignItem<'tcx>) {
1344 Visitor::visit_foreign_item(&mut self.clone(), foreign_item)
1348 impl Visitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1349 type Map = hir_map::Map<'tcx>;
1351 fn nested_visit_map(&mut self) -> hir_visit::NestedVisitorMap<Self::Map> {
1352 hir_visit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
1355 fn visit_item(&mut self, i: &'tcx hir::Item<'tcx>) {
1356 debug!("visit_item: {:?}", i);
1357 let def_id = self.tcx.hir().local_def_id(i.hir_id);
1358 self.tcx.ensure().check_item_well_formed(def_id);
1359 hir_visit::walk_item(self, i);
1362 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1363 debug!("visit_trait_item: {:?}", trait_item);
1364 let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1365 self.tcx.ensure().check_trait_item_well_formed(def_id);
1366 hir_visit::walk_trait_item(self, trait_item);
1369 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1370 debug!("visit_impl_item: {:?}", impl_item);
1371 let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1372 self.tcx.ensure().check_impl_item_well_formed(def_id);
1373 hir_visit::walk_impl_item(self, impl_item);
1376 fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
1377 check_param_wf(self.tcx, p);
1378 hir_visit::walk_generic_param(self, p);
1382 ///////////////////////////////////////////////////////////////////////////
1385 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1386 struct AdtVariant<'tcx> {
1387 /// Types of fields in the variant, that must be well-formed.
1388 fields: Vec<AdtField<'tcx>>,
1390 /// Explicit discriminant of this variant (e.g. `A = 123`),
1391 /// that must evaluate to a constant value.
1392 explicit_discr: Option<LocalDefId>,
1395 struct AdtField<'tcx> {
1400 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1401 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1402 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1403 let fields = struct_def
1407 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1408 let field_ty = self.normalize_associated_types_in(field.ty.span, field_ty);
1409 let field_ty = self.resolve_vars_if_possible(field_ty);
1410 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1411 AdtField { ty: field_ty, span: field.ty.span }
1414 AdtVariant { fields, explicit_discr: None }
1417 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1421 .map(|variant| AdtVariant {
1422 fields: self.non_enum_variant(&variant.data).fields,
1423 explicit_discr: variant
1425 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1430 pub(super) fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1431 match self.tcx.impl_trait_ref(impl_def_id) {
1432 Some(trait_ref) => {
1433 // Trait impl: take implied bounds from all types that
1434 // appear in the trait reference.
1435 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1436 trait_ref.substs.types().collect()
1440 // Inherent impl: take implied bounds from the `self` type.
1441 let self_ty = self.tcx.type_of(impl_def_id);
1442 let self_ty = self.normalize_associated_types_in(span, self_ty);
1449 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) -> DiagnosticBuilder<'_> {
1451 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1452 err.span_label(span, "unused parameter");