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 /// Helper type of a temporary returned by `.for_item(...)`.
28 /// This is necessary because we can't write the following bound:
31 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
33 struct CheckWfFcxBuilder<'tcx> {
34 inherited: super::InheritedBuilder<'tcx>,
37 param_env: ty::ParamEnv<'tcx>,
40 impl<'tcx> CheckWfFcxBuilder<'tcx> {
41 fn with_fcx<F>(&mut self, f: F)
43 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
47 let param_env = self.param_env;
48 self.inherited.enter(|inh| {
49 let fcx = FnCtxt::new(&inh, param_env, id);
50 if !inh.tcx.features().trivial_bounds {
51 // As predicates are cached rather than obligations, this
52 // needsto be called first so that they are checked with an
54 check_false_global_bounds(&fcx, span, id);
56 let wf_tys = f(&fcx, fcx.tcx);
57 fcx.select_all_obligations_or_error();
58 fcx.regionck_item(id, span, &wf_tys);
63 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
64 /// well-formed, meaning that they do not require any constraints not declared in the struct
65 /// definition itself. For example, this definition would be illegal:
68 /// struct Ref<'a, T> { x: &'a T }
71 /// because the type did not declare that `T:'a`.
73 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
74 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
76 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
77 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
78 let item = tcx.hir().expect_item(hir_id);
81 "check_item_well_formed(it.hir_id={:?}, it.name={})",
83 tcx.def_path_str(def_id.to_def_id())
87 // Right now we check that every default trait implementation
88 // has an implementation of itself. Basically, a case like:
90 // impl Trait for T {}
92 // has a requirement of `T: Trait` which was required for default
93 // method implementations. Although this could be improved now that
94 // there's a better infrastructure in place for this, it's being left
95 // for a follow-up work.
97 // Since there's such a requirement, we need to check *just* positive
98 // implementations, otherwise things like:
100 // impl !Send for T {}
102 // won't be allowed unless there's an *explicit* implementation of `Send`
104 hir::ItemKind::Impl {
113 .impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
114 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
115 if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
116 let sp = of_trait.as_ref().map(|t| t.path.span).unwrap_or(item.span);
118 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
119 err.span_labels(defaultness_span, "default because of this");
120 err.span_label(sp, "auto trait");
123 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
124 match (tcx.impl_polarity(def_id), polarity) {
125 (ty::ImplPolarity::Positive, _) => {
126 check_impl(tcx, item, self_ty, of_trait);
128 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
129 // FIXME(#27579): what amount of WF checking do we need for neg impls?
130 if let hir::Defaultness::Default { .. } = defaultness {
131 let mut spans = vec![span];
132 spans.extend(defaultness_span);
137 "negative impls cannot be default impls"
142 (ty::ImplPolarity::Reservation, _) => {
143 // FIXME: what amount of WF checking do we need for reservation impls?
148 hir::ItemKind::Fn(ref sig, ..) => {
149 check_item_fn(tcx, item.hir_id, item.ident, item.span, sig.decl);
151 hir::ItemKind::Static(ref ty, ..) => {
152 check_item_type(tcx, item.hir_id, ty.span, false);
154 hir::ItemKind::Const(ref ty, ..) => {
155 check_item_type(tcx, item.hir_id, ty.span, false);
157 hir::ItemKind::ForeignMod(ref module) => {
158 for it in module.items.iter() {
160 hir::ForeignItemKind::Fn(ref decl, ..) => {
161 check_item_fn(tcx, it.hir_id, it.ident, it.span, decl)
163 hir::ForeignItemKind::Static(ref ty, ..) => {
164 check_item_type(tcx, it.hir_id, ty.span, true)
166 hir::ForeignItemKind::Type => (),
170 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
171 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
173 check_variances_for_type_defn(tcx, item, ast_generics);
175 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
176 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
178 check_variances_for_type_defn(tcx, item, ast_generics);
180 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
181 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
183 check_variances_for_type_defn(tcx, item, ast_generics);
185 hir::ItemKind::Trait(..) => {
186 check_trait(tcx, item);
188 hir::ItemKind::TraitAlias(..) => {
189 check_trait(tcx, item);
195 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
196 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
197 let trait_item = tcx.hir().expect_trait_item(hir_id);
199 let method_sig = match trait_item.kind {
200 hir::TraitItemKind::Fn(ref sig, _) => Some(sig),
203 check_object_unsafe_self_trait_by_name(tcx, &trait_item);
204 check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
207 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
209 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
210 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
217 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
218 /// When this is done, suggest using `Self` instead.
219 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
220 let (trait_name, trait_def_id) = match tcx.hir().get(tcx.hir().get_parent_item(item.hir_id)) {
221 hir::Node::Item(item) => match item.kind {
222 hir::ItemKind::Trait(..) => (item.ident, tcx.hir().local_def_id(item.hir_id)),
227 let mut trait_should_be_self = vec![];
229 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
230 if could_be_self(trait_def_id, ty) =>
232 trait_should_be_self.push(ty.span)
234 hir::TraitItemKind::Fn(sig, _) => {
235 for ty in sig.decl.inputs {
236 if could_be_self(trait_def_id, ty) {
237 trait_should_be_self.push(ty.span);
240 match sig.decl.output {
241 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
242 trait_should_be_self.push(ty.span);
249 if !trait_should_be_self.is_empty() {
250 if tcx.object_safety_violations(trait_def_id).is_empty() {
253 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
256 trait_should_be_self,
257 "associated item referring to unboxed trait object for its own trait",
259 .span_label(trait_name.span, "in this trait")
260 .multipart_suggestion(
261 "you might have meant to use `Self` to refer to the implementing type",
263 Applicability::MachineApplicable,
269 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
270 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
271 let impl_item = tcx.hir().expect_impl_item(hir_id);
273 let method_sig = match impl_item.kind {
274 hir::ImplItemKind::Fn(ref sig, _) => Some(sig),
278 check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
281 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
283 // We currently only check wf of const params here.
284 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
286 // Const parameters are well formed if their
287 // type is structural match.
288 hir::GenericParamKind::Const { ty: hir_ty } => {
289 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
292 let mut is_ptr = true;
293 let err = if tcx.features().min_const_generics {
295 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
296 ty::FnPtr(_) => Some("function pointers"),
297 ty::RawPtr(_) => Some("raw pointers"),
300 err_ty_str = format!("`{}`", ty);
301 Some(err_ty_str.as_str())
305 match ty.peel_refs().kind {
306 ty::FnPtr(_) => Some("function pointers"),
307 ty::RawPtr(_) => Some("raw pointers"),
311 if let Some(unsupported_type) = err {
316 "using {} as const generic parameters is forbidden",
325 "{} is forbidden as the type of a const generic parameter",
329 .note("the only supported types are integers, `bool` and `char`")
330 .note("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, tcx| {
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");
420 check_method_receiver(fcx, hir_sig, &item, self_ty);
422 ty::AssocKind::Type => {
423 if item.defaultness.has_value() {
424 let ty = fcx.tcx.type_of(item.def_id);
425 let ty = fcx.normalize_associated_types_in(span, &ty);
426 fcx.register_wf_obligation(ty.into(), span, code.clone());
435 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
436 for_id(tcx, item.hir_id, item.span)
439 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
440 let def_id = tcx.hir().local_def_id(id);
442 inherited: Inherited::build(tcx, def_id),
445 param_env: tcx.param_env(def_id),
449 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
451 ItemKind::Struct(..) => Some(AdtKind::Struct),
452 ItemKind::Union(..) => Some(AdtKind::Union),
453 ItemKind::Enum(..) => Some(AdtKind::Enum),
458 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
459 fn check_type_defn<'tcx, F>(
461 item: &hir::Item<'tcx>,
463 mut lookup_fields: F,
465 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
467 for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
468 let variants = lookup_fields(fcx);
469 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
470 let packed = fcx.tcx.adt_def(def_id).repr.packed();
472 for variant in &variants {
473 // For DST, or when drop needs to copy things around, all
474 // intermediate types must be sized.
475 let needs_drop_copy = || {
477 let ty = variant.fields.last().unwrap().ty;
478 let ty = fcx.tcx.erase_regions(&ty);
479 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(fcx_tcx, fcx_tcx.param_env(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 fcx.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 {
526 InternalSubsts::identity_for_item(fcx.tcx, discr_def_id.to_def_id());
528 let cause = traits::ObligationCause::new(
529 fcx.tcx.def_span(discr_def_id),
531 traits::MiscObligation,
533 fcx.register_predicate(traits::Obligation::new(
536 ty::PredicateAtom::ConstEvaluatable(
537 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
540 .to_predicate(fcx.tcx),
545 check_where_clauses(tcx, fcx, item.span, def_id.to_def_id(), None);
547 // No implied bounds in a struct definition.
552 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
553 debug!("check_trait: {:?}", item.hir_id);
555 let trait_def_id = tcx.hir().local_def_id(item.hir_id);
557 let trait_def = tcx.trait_def(trait_def_id);
558 if trait_def.is_marker
559 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
561 for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
564 tcx.def_span(*associated_def_id),
566 "marker traits cannot have associated items",
572 for_item(tcx, item).with_fcx(|fcx, _| {
573 check_where_clauses(tcx, fcx, item.span, trait_def_id.to_def_id(), None);
574 check_associated_type_defaults(fcx, trait_def_id.to_def_id());
580 /// Checks all associated type defaults of trait `trait_def_id`.
582 /// Assuming the defaults are used, check that all predicates (bounds on the
583 /// assoc type and where clauses on the trait) hold.
584 fn check_associated_type_defaults(fcx: &FnCtxt<'_, '_>, trait_def_id: DefId) {
586 let substs = InternalSubsts::identity_for_item(tcx, trait_def_id);
588 // For all assoc. types with defaults, build a map from
589 // `<Self as Trait<...>>::Assoc` to the default type.
591 .associated_items(trait_def_id)
592 .in_definition_order()
594 if item.kind == ty::AssocKind::Type && item.defaultness.has_value() {
595 // `<Self as Trait<...>>::Assoc`
596 let proj = ty::ProjectionTy { substs, item_def_id: item.def_id };
597 let default_ty = tcx.type_of(item.def_id);
598 debug!("assoc. type default mapping: {} -> {}", proj, default_ty);
599 Some((proj, default_ty))
604 .collect::<FxHashMap<_, _>>();
606 /// Replaces projections of associated types with their default types.
608 /// This does a "shallow substitution", meaning that defaults that refer to
609 /// other defaulted assoc. types will still refer to the projection
610 /// afterwards, not to the other default. For example:
614 /// type A: Clone = Vec<Self::B>;
619 /// This will end up replacing the bound `Self::A: Clone` with
620 /// `Vec<Self::B>: Clone`, not with `Vec<u8>: Clone`. If we did a deep
621 /// substitution and ended up with the latter, the trait would be accepted.
622 /// If an `impl` then replaced `B` with something that isn't `Clone`,
623 /// suddenly the default for `A` is no longer valid. The shallow
624 /// substitution forces the trait to add a `B: Clone` bound to be accepted,
625 /// which means that an `impl` can replace any default without breaking
628 /// Note that this isn't needed for soundness: The defaults would still be
629 /// checked in any impl that doesn't override them.
630 struct DefaultNormalizer<'tcx> {
632 map: FxHashMap<ty::ProjectionTy<'tcx>, Ty<'tcx>>,
635 impl<'tcx> ty::fold::TypeFolder<'tcx> for DefaultNormalizer<'tcx> {
636 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
640 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
642 ty::Projection(proj_ty) => {
643 if let Some(default) = self.map.get(&proj_ty) {
646 t.super_fold_with(self)
649 _ => t.super_fold_with(self),
654 // Now take all predicates defined on the trait, replace any mention of
655 // the assoc. types with their default, and prove them.
656 // We only consider predicates that directly mention the assoc. type.
657 let mut norm = DefaultNormalizer { tcx, map };
658 let predicates = fcx.tcx.predicates_of(trait_def_id);
659 for &(orig_pred, span) in predicates.predicates.iter() {
660 let pred = orig_pred.fold_with(&mut norm);
661 if pred != orig_pred {
662 // Mentions one of the defaulted assoc. types
663 debug!("default suitability check: proving predicate: {} -> {}", orig_pred, pred);
664 let pred = fcx.normalize_associated_types_in(span, &pred);
665 let cause = traits::ObligationCause::new(
668 traits::ItemObligation(trait_def_id),
670 let obligation = traits::Obligation::new(cause, fcx.param_env, pred);
672 fcx.register_predicate(obligation);
682 decl: &hir::FnDecl<'_>,
684 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
685 let def_id = fcx.tcx.hir().local_def_id(item_id);
686 let sig = fcx.tcx.fn_sig(def_id);
687 let sig = fcx.normalize_associated_types_in(span, &sig);
688 let mut implied_bounds = vec![];
702 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
703 debug!("check_item_type: {:?}", item_id);
705 for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
706 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
707 let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
709 let mut forbid_unsized = true;
710 if allow_foreign_ty {
711 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
712 if let ty::Foreign(_) = tail.kind {
713 forbid_unsized = false;
717 fcx.register_wf_obligation(item_ty.into(), ty_span, ObligationCauseCode::MiscObligation);
721 fcx.tcx.require_lang_item(LangItem::Sized, None),
722 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
726 // No implied bounds in a const, etc.
733 item: &'tcx hir::Item<'tcx>,
734 ast_self_ty: &hir::Ty<'_>,
735 ast_trait_ref: &Option<hir::TraitRef<'_>>,
737 debug!("check_impl: {:?}", item);
739 for_item(tcx, item).with_fcx(|fcx, tcx| {
740 let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
742 match *ast_trait_ref {
743 Some(ref ast_trait_ref) => {
744 // `#[rustc_reservation_impl]` impls are not real impls and
745 // therefore don't need to be WF (the trait's `Self: Trait` predicate
747 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
749 fcx.normalize_associated_types_in(ast_trait_ref.path.span, &trait_ref);
750 let obligations = traits::wf::trait_obligations(
755 ast_trait_ref.path.span,
758 for obligation in obligations {
759 fcx.register_predicate(obligation);
763 let self_ty = fcx.tcx.type_of(item_def_id);
764 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
765 fcx.register_wf_obligation(
768 ObligationCauseCode::MiscObligation,
773 check_where_clauses(tcx, fcx, item.span, item_def_id.to_def_id(), None);
775 fcx.impl_implied_bounds(item_def_id.to_def_id(), item.span)
779 /// Checks where-clauses and inline bounds that are declared on `def_id`.
780 fn check_where_clauses<'tcx, 'fcx>(
782 fcx: &FnCtxt<'fcx, 'tcx>,
785 return_ty: Option<(Ty<'tcx>, Span)>,
787 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
789 let predicates = fcx.tcx.predicates_of(def_id);
790 let generics = tcx.generics_of(def_id);
792 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
793 GenericParamDefKind::Type { has_default, .. } => {
794 has_default && def.index >= generics.parent_count as u32
799 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
800 // For example, this forbids the declaration:
802 // struct Foo<T = Vec<[u32]>> { .. }
804 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
805 for param in &generics.params {
806 if let GenericParamDefKind::Type { .. } = param.kind {
807 if is_our_default(¶m) {
808 let ty = fcx.tcx.type_of(param.def_id);
809 // Ignore dependent defaults -- that is, where the default of one type
810 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
811 // be sure if it will error or not as user might always specify the other.
812 if !ty.needs_subst() {
813 fcx.register_wf_obligation(
815 fcx.tcx.def_span(param.def_id),
816 ObligationCauseCode::MiscObligation,
823 // Check that trait predicates are WF when params are substituted by their defaults.
824 // We don't want to overly constrain the predicates that may be written but we want to
825 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
826 // Therefore we check if a predicate which contains a single type param
827 // with a concrete default is WF with that default substituted.
828 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
830 // First we build the defaulted substitution.
831 let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
833 GenericParamDefKind::Lifetime => {
834 // All regions are identity.
835 fcx.tcx.mk_param_from_def(param)
838 GenericParamDefKind::Type { .. } => {
839 // If the param has a default, ...
840 if is_our_default(param) {
841 let default_ty = fcx.tcx.type_of(param.def_id);
842 // ... and it's not a dependent default, ...
843 if !default_ty.needs_subst() {
844 // ... then substitute it with the default.
845 return default_ty.into();
849 fcx.tcx.mk_param_from_def(param)
852 GenericParamDefKind::Const => {
853 // FIXME(const_generics:defaults)
854 fcx.tcx.mk_param_from_def(param)
859 // Now we build the substituted predicates.
860 let default_obligations = predicates
863 .flat_map(|&(pred, sp)| {
866 params: FxHashSet<u32>,
868 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
869 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
870 if let ty::Param(param) = t.kind {
871 self.params.insert(param.index);
873 t.super_visit_with(self)
876 fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
880 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
881 if let ty::ConstKind::Param(param) = c.val {
882 self.params.insert(param.index);
884 c.super_visit_with(self)
887 let mut param_count = CountParams::default();
888 let has_region = pred.visit_with(&mut param_count);
889 let substituted_pred = pred.subst(fcx.tcx, substs);
890 // Don't check non-defaulted params, dependent defaults (including lifetimes)
891 // or preds with multiple params.
892 if substituted_pred.has_param_types_or_consts()
893 || param_count.params.len() > 1
897 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
898 // Avoid duplication of predicates that contain no parameters, for example.
901 Some((substituted_pred, sp))
905 // Convert each of those into an obligation. So if you have
906 // something like `struct Foo<T: Copy = String>`, we would
907 // take that predicate `T: Copy`, substitute to `String: Copy`
908 // (actually that happens in the previous `flat_map` call),
909 // and then try to prove it (in this case, we'll fail).
911 // Note the subtle difference from how we handle `predicates`
912 // below: there, we are not trying to prove those predicates
913 // to be *true* but merely *well-formed*.
914 let pred = fcx.normalize_associated_types_in(sp, &pred);
916 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
917 traits::Obligation::new(cause, fcx.param_env, pred)
920 let predicates = predicates.instantiate_identity(fcx.tcx);
922 if let Some((mut return_ty, span)) = return_ty {
923 if return_ty.has_infer_types_or_consts() {
924 fcx.select_obligations_where_possible(false, |_| {});
925 return_ty = fcx.resolve_vars_if_possible(&return_ty);
927 check_opaque_types(tcx, fcx, def_id.expect_local(), span, return_ty);
930 let predicates = fcx.normalize_associated_types_in(span, &predicates);
932 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
933 assert_eq!(predicates.predicates.len(), predicates.spans.len());
935 predicates.predicates.iter().zip(predicates.spans.iter()).flat_map(|(&p, &sp)| {
936 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
939 for obligation in wf_obligations.chain(default_obligations) {
940 debug!("next obligation cause: {:?}", obligation.cause);
941 fcx.register_predicate(obligation);
945 fn check_fn_or_method<'fcx, 'tcx>(
947 fcx: &FnCtxt<'fcx, 'tcx>,
949 sig: ty::PolyFnSig<'tcx>,
950 hir_decl: &hir::FnDecl<'_>,
952 implied_bounds: &mut Vec<Ty<'tcx>>,
954 let sig = fcx.normalize_associated_types_in(span, &sig);
955 let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
957 for (&input_ty, span) in sig.inputs().iter().zip(hir_decl.inputs.iter().map(|t| t.span)) {
958 fcx.register_wf_obligation(input_ty.into(), span, ObligationCauseCode::MiscObligation);
960 implied_bounds.extend(sig.inputs());
962 fcx.register_wf_obligation(
964 hir_decl.output.span(),
965 ObligationCauseCode::ReturnType,
968 // FIXME(#25759) return types should not be implied bounds
969 implied_bounds.push(sig.output());
971 check_where_clauses(tcx, fcx, span, def_id, Some((sig.output(), hir_decl.output.span())));
974 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
975 /// laid for "higher-order pattern unification".
976 /// This ensures that inference is tractable.
977 /// In particular, definitions of opaque types can only use other generics as arguments,
978 /// and they cannot repeat an argument. Example:
981 /// type Foo<A, B> = impl Bar<A, B>;
983 /// // Okay -- `Foo` is applied to two distinct, generic types.
984 /// fn a<T, U>() -> Foo<T, U> { .. }
986 /// // Not okay -- `Foo` is applied to `T` twice.
987 /// fn b<T>() -> Foo<T, T> { .. }
989 /// // Not okay -- `Foo` is applied to a non-generic type.
990 /// fn b<T>() -> Foo<T, u32> { .. }
993 fn check_opaque_types<'fcx, 'tcx>(
995 fcx: &FnCtxt<'fcx, 'tcx>,
996 fn_def_id: LocalDefId,
1000 trace!("check_opaque_types(ty={:?})", ty);
1001 ty.fold_with(&mut ty::fold::BottomUpFolder {
1004 if let ty::Opaque(def_id, substs) = ty.kind {
1005 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
1006 let generics = tcx.generics_of(def_id);
1008 let opaque_hir_id = if let Some(local_id) = def_id.as_local() {
1009 tcx.hir().local_def_id_to_hir_id(local_id)
1011 // Opaque types from other crates won't have defining uses in this crate.
1014 if let hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) =
1015 tcx.hir().expect_item(opaque_hir_id).kind
1017 // No need to check return position impl trait (RPIT)
1018 // because for type and const parameters they are correct
1019 // by construction: we convert
1021 // fn foo<P0..Pn>() -> impl Trait
1025 // type Foo<P0...Pn>
1026 // fn foo<P0..Pn>() -> Foo<P0...Pn>.
1028 // For lifetime parameters we convert
1030 // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
1034 // type foo::<'p0..'pn>::Foo<'q0..'qm>
1035 // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
1037 // which would error here on all of the `'static` args.
1040 if !may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
1043 trace!("check_opaque_types: may define, generics={:#?}", generics);
1044 let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
1045 for (i, arg) in substs.iter().enumerate() {
1046 let arg_is_param = match arg.unpack() {
1047 GenericArgKind::Type(ty) => matches!(ty.kind, ty::Param(_)),
1049 GenericArgKind::Lifetime(region) => {
1050 if let ty::ReStatic = region {
1054 "non-defining opaque type use in defining scope",
1057 tcx.def_span(generics.param_at(i, tcx).def_id),
1058 "cannot use static lifetime; use a bound lifetime \
1059 instead or remove the lifetime parameter from the \
1069 GenericArgKind::Const(ct) => matches!(ct.val, ty::ConstKind::Param(_)),
1073 seen_params.entry(arg).or_default().push(i);
1075 // Prevent `fn foo() -> Foo<u32>` from being defining.
1076 let opaque_param = generics.param_at(i, tcx);
1078 .struct_span_err(span, "non-defining opaque type use in defining scope")
1080 tcx.def_span(opaque_param.def_id),
1082 "used non-generic {} `{}` for generic parameter",
1083 opaque_param.kind.descr(),
1089 } // for (arg, param)
1091 for (_, indices) in seen_params {
1092 if indices.len() > 1 {
1093 let descr = generics.param_at(indices[0], tcx).kind.descr();
1094 let spans: Vec<_> = indices
1096 .map(|i| tcx.def_span(generics.param_at(i, tcx).def_id))
1099 .struct_span_err(span, "non-defining opaque type use in defining scope")
1100 .span_note(spans, &format!("{} used multiple times", descr))
1112 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1113 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1114 of the previous types except `Self`)";
1116 fn check_method_receiver<'fcx, 'tcx>(
1117 fcx: &FnCtxt<'fcx, 'tcx>,
1118 fn_sig: &hir::FnSig<'_>,
1119 method: &ty::AssocItem,
1122 // Check that the method has a valid receiver type, given the type `Self`.
1123 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1125 if !method.fn_has_self_parameter {
1129 let span = fn_sig.decl.inputs[0].span;
1131 let sig = fcx.tcx.fn_sig(method.def_id);
1132 let sig = fcx.normalize_associated_types_in(span, &sig);
1133 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
1135 debug!("check_method_receiver: sig={:?}", sig);
1137 let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
1138 let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_ty));
1140 let receiver_ty = sig.inputs()[0];
1142 let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
1144 fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(receiver_ty));
1146 if fcx.tcx.features().arbitrary_self_types {
1147 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1148 // Report error; `arbitrary_self_types` was enabled.
1149 e0307(fcx, span, receiver_ty);
1152 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1153 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1154 // Report error; would have worked with `arbitrary_self_types`.
1156 &fcx.tcx.sess.parse_sess,
1157 sym::arbitrary_self_types,
1160 "`{}` cannot be used as the type of `self` without \
1161 the `arbitrary_self_types` feature",
1165 .help(HELP_FOR_SELF_TYPE)
1168 // Report error; would not have worked with `arbitrary_self_types`.
1169 e0307(fcx, span, receiver_ty);
1175 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1177 fcx.tcx.sess.diagnostic(),
1180 "invalid `self` parameter type: {:?}",
1183 .note("type of `self` must be `Self` or a type that dereferences to it")
1184 .help(HELP_FOR_SELF_TYPE)
1188 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1189 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1190 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1191 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1192 /// `Deref<Target = self_ty>`.
1194 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1195 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1196 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1197 fn receiver_is_valid<'fcx, 'tcx>(
1198 fcx: &FnCtxt<'fcx, 'tcx>,
1200 receiver_ty: Ty<'tcx>,
1202 arbitrary_self_types_enabled: bool,
1204 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1206 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1208 // `self: Self` is always valid.
1209 if can_eq_self(receiver_ty) {
1210 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1216 let mut autoderef = fcx.autoderef(span, receiver_ty);
1218 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1219 if arbitrary_self_types_enabled {
1220 autoderef = autoderef.include_raw_pointers();
1223 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1226 let receiver_trait_def_id = fcx.tcx.require_lang_item(LangItem::Receiver, None);
1228 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1230 if let Some((potential_self_ty, _)) = autoderef.next() {
1232 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1233 potential_self_ty, self_ty
1236 if can_eq_self(potential_self_ty) {
1237 fcx.register_predicates(autoderef.into_obligations());
1239 if let Some(mut err) =
1240 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1247 // Without `feature(arbitrary_self_types)`, we require that each step in the
1248 // deref chain implement `receiver`
1249 if !arbitrary_self_types_enabled
1250 && !receiver_is_implemented(
1252 receiver_trait_def_id,
1261 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1262 // If he receiver already has errors reported due to it, consider it valid to avoid
1263 // unnecessary errors (#58712).
1264 return receiver_ty.references_error();
1268 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1269 if !arbitrary_self_types_enabled
1270 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1278 fn receiver_is_implemented(
1279 fcx: &FnCtxt<'_, 'tcx>,
1280 receiver_trait_def_id: DefId,
1281 cause: ObligationCause<'tcx>,
1282 receiver_ty: Ty<'tcx>,
1284 let trait_ref = ty::TraitRef {
1285 def_id: receiver_trait_def_id,
1286 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1289 let obligation = traits::Obligation::new(
1292 trait_ref.without_const().to_predicate(fcx.tcx),
1295 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1299 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1306 fn check_variances_for_type_defn<'tcx>(
1308 item: &hir::Item<'tcx>,
1309 hir_generics: &hir::Generics<'_>,
1311 let item_def_id = tcx.hir().local_def_id(item.hir_id);
1312 let ty = tcx.type_of(item_def_id);
1313 if tcx.has_error_field(ty) {
1317 let ty_predicates = tcx.predicates_of(item_def_id);
1318 assert_eq!(ty_predicates.parent, None);
1319 let variances = tcx.variances_of(item_def_id);
1321 let mut constrained_parameters: FxHashSet<_> = variances
1324 .filter(|&(_, &variance)| variance != ty::Bivariant)
1325 .map(|(index, _)| Parameter(index as u32))
1328 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1330 for (index, _) in variances.iter().enumerate() {
1331 if constrained_parameters.contains(&Parameter(index as u32)) {
1335 let param = &hir_generics.params[index];
1338 hir::ParamName::Error => {}
1339 _ => report_bivariance(tcx, param.span, param.name.ident().name),
1344 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) {
1345 let mut err = error_392(tcx, span, param_name);
1347 let suggested_marker_id = tcx.lang_items().phantom_data();
1348 // Help is available only in presence of lang items.
1349 let msg = if let Some(def_id) = suggested_marker_id {
1351 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1353 tcx.def_path_str(def_id),
1356 format!("consider removing `{}` or referring to it in a field", param_name)
1362 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1364 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1365 let empty_env = ty::ParamEnv::empty();
1367 let def_id = fcx.tcx.hir().local_def_id(id);
1368 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p);
1369 // Check elaborated bounds.
1370 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1372 for obligation in implied_obligations {
1373 let pred = obligation.predicate;
1374 // Match the existing behavior.
1375 if pred.is_global() && !pred.has_late_bound_regions() {
1376 let pred = fcx.normalize_associated_types_in(span, &pred);
1377 let obligation = traits::Obligation::new(
1378 traits::ObligationCause::new(span, id, traits::TrivialBound),
1382 fcx.register_predicate(obligation);
1386 fcx.select_all_obligations_or_error();
1389 #[derive(Clone, Copy)]
1390 pub struct CheckTypeWellFormedVisitor<'tcx> {
1394 impl CheckTypeWellFormedVisitor<'tcx> {
1395 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1396 CheckTypeWellFormedVisitor { tcx }
1400 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1401 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1402 Visitor::visit_item(&mut self.clone(), i);
1405 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1406 Visitor::visit_trait_item(&mut self.clone(), trait_item);
1409 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1410 Visitor::visit_impl_item(&mut self.clone(), impl_item);
1414 impl Visitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1415 type Map = hir_map::Map<'tcx>;
1417 fn nested_visit_map(&mut self) -> hir_visit::NestedVisitorMap<Self::Map> {
1418 hir_visit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
1421 fn visit_item(&mut self, i: &'tcx hir::Item<'tcx>) {
1422 debug!("visit_item: {:?}", i);
1423 let def_id = self.tcx.hir().local_def_id(i.hir_id);
1424 self.tcx.ensure().check_item_well_formed(def_id);
1425 hir_visit::walk_item(self, i);
1428 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1429 debug!("visit_trait_item: {:?}", trait_item);
1430 let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1431 self.tcx.ensure().check_trait_item_well_formed(def_id);
1432 hir_visit::walk_trait_item(self, trait_item);
1435 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1436 debug!("visit_impl_item: {:?}", impl_item);
1437 let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1438 self.tcx.ensure().check_impl_item_well_formed(def_id);
1439 hir_visit::walk_impl_item(self, impl_item);
1442 fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
1443 check_param_wf(self.tcx, p);
1444 hir_visit::walk_generic_param(self, p);
1448 ///////////////////////////////////////////////////////////////////////////
1451 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1452 struct AdtVariant<'tcx> {
1453 /// Types of fields in the variant, that must be well-formed.
1454 fields: Vec<AdtField<'tcx>>,
1456 /// Explicit discriminant of this variant (e.g. `A = 123`),
1457 /// that must evaluate to a constant value.
1458 explicit_discr: Option<LocalDefId>,
1461 struct AdtField<'tcx> {
1466 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1467 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1468 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1469 let fields = struct_def
1473 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1474 let field_ty = self.normalize_associated_types_in(field.ty.span, &field_ty);
1475 let field_ty = self.resolve_vars_if_possible(&field_ty);
1476 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1477 AdtField { ty: field_ty, span: field.ty.span }
1480 AdtVariant { fields, explicit_discr: None }
1483 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1487 .map(|variant| AdtVariant {
1488 fields: self.non_enum_variant(&variant.data).fields,
1489 explicit_discr: variant
1491 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1496 fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1497 match self.tcx.impl_trait_ref(impl_def_id) {
1498 Some(ref trait_ref) => {
1499 // Trait impl: take implied bounds from all types that
1500 // appear in the trait reference.
1501 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1502 trait_ref.substs.types().collect()
1506 // Inherent impl: take implied bounds from the `self` type.
1507 let self_ty = self.tcx.type_of(impl_def_id);
1508 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1515 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) -> DiagnosticBuilder<'_> {
1517 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1518 err.span_label(span, "unused parameter");