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::itemlikevisit::ParItemLikeVisitor;
10 use rustc_hir::lang_items;
11 use rustc_hir::ItemKind;
12 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
13 use rustc_middle::ty::trait_def::TraitSpecializationKind;
14 use rustc_middle::ty::{
15 self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
17 use rustc_session::parse::feature_err;
18 use rustc_span::symbol::{sym, Symbol};
20 use rustc_trait_selection::opaque_types::may_define_opaque_type;
21 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
22 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
24 /// Helper type of a temporary returned by `.for_item(...)`.
25 /// This is necessary because we can't write the following bound:
28 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
30 struct CheckWfFcxBuilder<'tcx> {
31 inherited: super::InheritedBuilder<'tcx>,
34 param_env: ty::ParamEnv<'tcx>,
37 impl<'tcx> CheckWfFcxBuilder<'tcx> {
38 fn with_fcx<F>(&mut self, f: F)
40 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
44 let param_env = self.param_env;
45 self.inherited.enter(|inh| {
46 let fcx = FnCtxt::new(&inh, param_env, id);
47 if !inh.tcx.features().trivial_bounds {
48 // As predicates are cached rather than obligations, this
49 // needsto be called first so that they are checked with an
51 check_false_global_bounds(&fcx, span, id);
53 let wf_tys = f(&fcx, fcx.tcx);
54 fcx.select_all_obligations_or_error();
55 fcx.regionck_item(id, span, &wf_tys);
60 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
61 /// well-formed, meaning that they do not require any constraints not declared in the struct
62 /// definition itself. For example, this definition would be illegal:
65 /// struct Ref<'a, T> { x: &'a T }
68 /// because the type did not declare that `T:'a`.
70 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
71 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
73 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
74 let hir_id = tcx.hir().as_local_hir_id(def_id);
75 let item = tcx.hir().expect_item(hir_id);
78 "check_item_well_formed(it.hir_id={:?}, it.name={})",
80 tcx.def_path_str(def_id.to_def_id())
84 // Right now we check that every default trait implementation
85 // has an implementation of itself. Basically, a case like:
87 // impl Trait for T {}
89 // has a requirement of `T: Trait` which was required for default
90 // method implementations. Although this could be improved now that
91 // there's a better infrastructure in place for this, it's being left
92 // for a follow-up work.
94 // Since there's such a requirement, we need to check *just* positive
95 // implementations, otherwise things like:
97 // impl !Send for T {}
99 // won't be allowed unless there's an *explicit* implementation of `Send`
101 hir::ItemKind::Impl {
110 .impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
111 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
112 if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
113 let sp = of_trait.as_ref().map(|t| t.path.span).unwrap_or(item.span);
115 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
116 err.span_labels(defaultness_span, "default because of this");
117 err.span_label(sp, "auto trait");
120 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
121 match (tcx.impl_polarity(def_id), polarity) {
122 (ty::ImplPolarity::Positive, _) => {
123 check_impl(tcx, item, self_ty, of_trait);
125 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
126 // FIXME(#27579): what amount of WF checking do we need for neg impls?
127 if let hir::Defaultness::Default { .. } = defaultness {
128 let mut spans = vec![span];
129 spans.extend(defaultness_span);
134 "negative impls cannot be default impls"
139 (ty::ImplPolarity::Reservation, _) => {
140 // FIXME: what amount of WF checking do we need for reservation impls?
145 hir::ItemKind::Fn(..) => {
146 check_item_fn(tcx, item);
148 hir::ItemKind::Static(ref ty, ..) => {
149 check_item_type(tcx, item.hir_id, ty.span, false);
151 hir::ItemKind::Const(ref ty, ..) => {
152 check_item_type(tcx, item.hir_id, ty.span, false);
154 hir::ItemKind::ForeignMod(ref module) => {
155 for it in module.items.iter() {
156 if let hir::ForeignItemKind::Static(ref ty, ..) = it.kind {
157 check_item_type(tcx, it.hir_id, ty.span, true);
161 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
162 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
164 check_variances_for_type_defn(tcx, item, ast_generics);
166 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
167 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
169 check_variances_for_type_defn(tcx, item, ast_generics);
171 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
172 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
174 check_variances_for_type_defn(tcx, item, ast_generics);
176 hir::ItemKind::Trait(..) => {
177 check_trait(tcx, item);
179 hir::ItemKind::TraitAlias(..) => {
180 check_trait(tcx, item);
186 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
187 let hir_id = tcx.hir().as_local_hir_id(def_id);
188 let trait_item = tcx.hir().expect_trait_item(hir_id);
190 let method_sig = match trait_item.kind {
191 hir::TraitItemKind::Fn(ref sig, _) => Some(sig),
194 check_object_unsafe_self_trait_by_name(tcx, &trait_item);
195 check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
198 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
200 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
201 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
208 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
209 /// When this is done, suggest using `Self` instead.
210 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
211 let (trait_name, trait_def_id) = match tcx.hir().get(tcx.hir().get_parent_item(item.hir_id)) {
212 hir::Node::Item(item) => match item.kind {
213 hir::ItemKind::Trait(..) => (item.ident, tcx.hir().local_def_id(item.hir_id)),
218 let mut trait_should_be_self = vec![];
220 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
221 if could_be_self(trait_def_id, ty) =>
223 trait_should_be_self.push(ty.span)
225 hir::TraitItemKind::Fn(sig, _) => {
226 for ty in sig.decl.inputs {
227 if could_be_self(trait_def_id, ty) {
228 trait_should_be_self.push(ty.span);
231 match sig.decl.output {
232 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
233 trait_should_be_self.push(ty.span);
240 if !trait_should_be_self.is_empty() {
241 if tcx.object_safety_violations(trait_def_id).is_empty() {
244 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
247 trait_should_be_self,
248 "associated item referring to unboxed trait object for its own trait",
250 .span_label(trait_name.span, "in this trait")
251 .multipart_suggestion(
252 "you might have meant to use `Self` to refer to the implementing type",
254 Applicability::MachineApplicable,
260 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
261 let hir_id = tcx.hir().as_local_hir_id(def_id);
262 let impl_item = tcx.hir().expect_impl_item(hir_id);
264 let method_sig = match impl_item.kind {
265 hir::ImplItemKind::Fn(ref sig, _) => Some(sig),
269 check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
272 fn check_associated_item(
276 sig_if_method: Option<&hir::FnSig<'_>>,
278 debug!("check_associated_item: {:?}", item_id);
280 let code = ObligationCauseCode::MiscObligation;
281 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
282 let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
284 let (mut implied_bounds, self_ty) = match item.container {
285 ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
286 ty::ImplContainer(def_id) => {
287 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
292 ty::AssocKind::Const => {
293 let ty = fcx.tcx.type_of(item.def_id);
294 let ty = fcx.normalize_associated_types_in(span, &ty);
295 fcx.register_wf_obligation(ty.into(), span, code.clone());
297 ty::AssocKind::Fn => {
298 let sig = fcx.tcx.fn_sig(item.def_id);
299 let sig = fcx.normalize_associated_types_in(span, &sig);
300 let hir_sig = sig_if_method.expect("bad signature for method");
310 check_method_receiver(fcx, hir_sig, &item, self_ty);
312 ty::AssocKind::Type => {
313 if item.defaultness.has_value() {
314 let ty = fcx.tcx.type_of(item.def_id);
315 let ty = fcx.normalize_associated_types_in(span, &ty);
316 fcx.register_wf_obligation(ty.into(), span, code.clone());
325 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
326 for_id(tcx, item.hir_id, item.span)
329 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
330 let def_id = tcx.hir().local_def_id(id);
332 inherited: Inherited::build(tcx, def_id),
335 param_env: tcx.param_env(def_id),
339 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
341 ItemKind::Struct(..) => Some(AdtKind::Struct),
342 ItemKind::Union(..) => Some(AdtKind::Union),
343 ItemKind::Enum(..) => Some(AdtKind::Enum),
348 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
349 fn check_type_defn<'tcx, F>(
351 item: &hir::Item<'tcx>,
353 mut lookup_fields: F,
355 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
357 for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
358 let variants = lookup_fields(fcx);
359 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
360 let packed = fcx.tcx.adt_def(def_id).repr.packed();
362 for variant in &variants {
363 // For DST, or when drop needs to copy things around, all
364 // intermediate types must be sized.
365 let needs_drop_copy = || {
367 let ty = variant.fields.last().unwrap().ty;
368 let ty = fcx.tcx.erase_regions(&ty);
369 if ty.needs_infer() {
372 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
373 // Just treat unresolved type expression as if it needs drop.
376 ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
380 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
381 let unsized_len = if all_sized { 0 } else { 1 };
383 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
385 let last = idx == variant.fields.len() - 1;
388 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
389 traits::ObligationCause::new(
393 adt_kind: match item_adt_kind(&item.kind) {
404 // All field types must be well-formed.
405 for field in &variant.fields {
406 fcx.register_wf_obligation(
409 ObligationCauseCode::MiscObligation,
413 // Explicit `enum` discriminant values must const-evaluate successfully.
414 if let Some(discr_def_id) = variant.explicit_discr {
416 InternalSubsts::identity_for_item(fcx.tcx, discr_def_id.to_def_id());
418 let cause = traits::ObligationCause::new(
419 fcx.tcx.def_span(discr_def_id),
421 traits::MiscObligation,
423 fcx.register_predicate(traits::Obligation::new(
426 ty::PredicateKind::ConstEvaluatable(
427 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
430 .to_predicate(fcx.tcx),
435 check_where_clauses(tcx, fcx, item.span, def_id.to_def_id(), None);
437 // No implied bounds in a struct definition.
442 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
443 debug!("check_trait: {:?}", item.hir_id);
445 let trait_def_id = tcx.hir().local_def_id(item.hir_id);
447 let trait_def = tcx.trait_def(trait_def_id);
448 if trait_def.is_marker
449 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
451 for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
454 tcx.def_span(*associated_def_id),
456 "marker traits cannot have associated items",
462 for_item(tcx, item).with_fcx(|fcx, _| {
463 check_where_clauses(tcx, fcx, item.span, trait_def_id.to_def_id(), None);
464 check_associated_type_defaults(fcx, trait_def_id.to_def_id());
470 /// Checks all associated type defaults of trait `trait_def_id`.
472 /// Assuming the defaults are used, check that all predicates (bounds on the
473 /// assoc type and where clauses on the trait) hold.
474 fn check_associated_type_defaults(fcx: &FnCtxt<'_, '_>, trait_def_id: DefId) {
476 let substs = InternalSubsts::identity_for_item(tcx, trait_def_id);
478 // For all assoc. types with defaults, build a map from
479 // `<Self as Trait<...>>::Assoc` to the default type.
481 .associated_items(trait_def_id)
482 .in_definition_order()
484 if item.kind == ty::AssocKind::Type && item.defaultness.has_value() {
485 // `<Self as Trait<...>>::Assoc`
486 let proj = ty::ProjectionTy { substs, item_def_id: item.def_id };
487 let default_ty = tcx.type_of(item.def_id);
488 debug!("assoc. type default mapping: {} -> {}", proj, default_ty);
489 Some((proj, default_ty))
494 .collect::<FxHashMap<_, _>>();
496 /// Replaces projections of associated types with their default types.
498 /// This does a "shallow substitution", meaning that defaults that refer to
499 /// other defaulted assoc. types will still refer to the projection
500 /// afterwards, not to the other default. For example:
504 /// type A: Clone = Vec<Self::B>;
509 /// This will end up replacing the bound `Self::A: Clone` with
510 /// `Vec<Self::B>: Clone`, not with `Vec<u8>: Clone`. If we did a deep
511 /// substitution and ended up with the latter, the trait would be accepted.
512 /// If an `impl` then replaced `B` with something that isn't `Clone`,
513 /// suddenly the default for `A` is no longer valid. The shallow
514 /// substitution forces the trait to add a `B: Clone` bound to be accepted,
515 /// which means that an `impl` can replace any default without breaking
518 /// Note that this isn't needed for soundness: The defaults would still be
519 /// checked in any impl that doesn't override them.
520 struct DefaultNormalizer<'tcx> {
522 map: FxHashMap<ty::ProjectionTy<'tcx>, Ty<'tcx>>,
525 impl<'tcx> ty::fold::TypeFolder<'tcx> for DefaultNormalizer<'tcx> {
526 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
530 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
532 ty::Projection(proj_ty) => {
533 if let Some(default) = self.map.get(&proj_ty) {
536 t.super_fold_with(self)
539 _ => t.super_fold_with(self),
544 // Now take all predicates defined on the trait, replace any mention of
545 // the assoc. types with their default, and prove them.
546 // We only consider predicates that directly mention the assoc. type.
547 let mut norm = DefaultNormalizer { tcx, map };
548 let predicates = fcx.tcx.predicates_of(trait_def_id);
549 for &(orig_pred, span) in predicates.predicates.iter() {
550 let pred = orig_pred.fold_with(&mut norm);
551 if pred != orig_pred {
552 // Mentions one of the defaulted assoc. types
553 debug!("default suitability check: proving predicate: {} -> {}", orig_pred, pred);
554 let pred = fcx.normalize_associated_types_in(span, &pred);
555 let cause = traits::ObligationCause::new(
558 traits::ItemObligation(trait_def_id),
560 let obligation = traits::Obligation::new(cause, fcx.param_env, pred);
562 fcx.register_predicate(obligation);
567 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
568 for_item(tcx, item).with_fcx(|fcx, tcx| {
569 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
570 let sig = fcx.tcx.fn_sig(def_id);
571 let sig = fcx.normalize_associated_types_in(item.span, &sig);
572 let mut implied_bounds = vec![];
573 let hir_sig = match &item.kind {
574 ItemKind::Fn(sig, ..) => sig,
575 _ => bug!("expected `ItemKind::Fn`, found `{:?}`", item.kind),
590 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
591 debug!("check_item_type: {:?}", item_id);
593 for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
594 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
595 let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
597 let mut forbid_unsized = true;
598 if allow_foreign_ty {
599 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
600 if let ty::Foreign(_) = tail.kind {
601 forbid_unsized = false;
605 fcx.register_wf_obligation(item_ty.into(), ty_span, ObligationCauseCode::MiscObligation);
609 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
610 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
614 // No implied bounds in a const, etc.
621 item: &'tcx hir::Item<'tcx>,
622 ast_self_ty: &hir::Ty<'_>,
623 ast_trait_ref: &Option<hir::TraitRef<'_>>,
625 debug!("check_impl: {:?}", item);
627 for_item(tcx, item).with_fcx(|fcx, tcx| {
628 let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
630 match *ast_trait_ref {
631 Some(ref ast_trait_ref) => {
632 // `#[rustc_reservation_impl]` impls are not real impls and
633 // therefore don't need to be WF (the trait's `Self: Trait` predicate
635 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
637 fcx.normalize_associated_types_in(ast_trait_ref.path.span, &trait_ref);
638 let obligations = traits::wf::trait_obligations(
643 ast_trait_ref.path.span,
646 for obligation in obligations {
647 fcx.register_predicate(obligation);
651 let self_ty = fcx.tcx.type_of(item_def_id);
652 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
653 fcx.register_wf_obligation(
656 ObligationCauseCode::MiscObligation,
661 check_where_clauses(tcx, fcx, item.span, item_def_id.to_def_id(), None);
663 fcx.impl_implied_bounds(item_def_id.to_def_id(), item.span)
667 /// Checks where-clauses and inline bounds that are declared on `def_id`.
668 fn check_where_clauses<'tcx, 'fcx>(
670 fcx: &FnCtxt<'fcx, 'tcx>,
673 return_ty: Option<(Ty<'tcx>, Span)>,
675 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
677 let predicates = fcx.tcx.predicates_of(def_id);
678 let generics = tcx.generics_of(def_id);
680 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
681 GenericParamDefKind::Type { has_default, .. } => {
682 has_default && def.index >= generics.parent_count as u32
687 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
688 // For example, this forbids the declaration:
690 // struct Foo<T = Vec<[u32]>> { .. }
692 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
693 for param in &generics.params {
694 if let GenericParamDefKind::Type { .. } = param.kind {
695 if is_our_default(¶m) {
696 let ty = fcx.tcx.type_of(param.def_id);
697 // Ignore dependent defaults -- that is, where the default of one type
698 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
699 // be sure if it will error or not as user might always specify the other.
700 if !ty.needs_subst() {
701 fcx.register_wf_obligation(
703 fcx.tcx.def_span(param.def_id),
704 ObligationCauseCode::MiscObligation,
711 // Check that trait predicates are WF when params are substituted by their defaults.
712 // We don't want to overly constrain the predicates that may be written but we want to
713 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
714 // Therefore we check if a predicate which contains a single type param
715 // with a concrete default is WF with that default substituted.
716 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
718 // First we build the defaulted substitution.
719 let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
721 GenericParamDefKind::Lifetime => {
722 // All regions are identity.
723 fcx.tcx.mk_param_from_def(param)
726 GenericParamDefKind::Type { .. } => {
727 // If the param has a default, ...
728 if is_our_default(param) {
729 let default_ty = fcx.tcx.type_of(param.def_id);
730 // ... and it's not a dependent default, ...
731 if !default_ty.needs_subst() {
732 // ... then substitute it with the default.
733 return default_ty.into();
737 fcx.tcx.mk_param_from_def(param)
740 GenericParamDefKind::Const => {
741 // FIXME(const_generics:defaults)
742 fcx.tcx.mk_param_from_def(param)
747 // Now we build the substituted predicates.
748 let default_obligations = predicates
751 .flat_map(|&(pred, sp)| {
754 params: FxHashSet<u32>,
756 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
757 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
758 if let ty::Param(param) = t.kind {
759 self.params.insert(param.index);
761 t.super_visit_with(self)
764 fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
768 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
769 if let ty::ConstKind::Param(param) = c.val {
770 self.params.insert(param.index);
772 c.super_visit_with(self)
775 let mut param_count = CountParams::default();
776 let has_region = pred.visit_with(&mut param_count);
777 let substituted_pred = pred.subst(fcx.tcx, substs);
778 // Don't check non-defaulted params, dependent defaults (including lifetimes)
779 // or preds with multiple params.
780 if substituted_pred.has_param_types_or_consts()
781 || param_count.params.len() > 1
785 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
786 // Avoid duplication of predicates that contain no parameters, for example.
789 Some((substituted_pred, sp))
793 // Convert each of those into an obligation. So if you have
794 // something like `struct Foo<T: Copy = String>`, we would
795 // take that predicate `T: Copy`, substitute to `String: Copy`
796 // (actually that happens in the previous `flat_map` call),
797 // and then try to prove it (in this case, we'll fail).
799 // Note the subtle difference from how we handle `predicates`
800 // below: there, we are not trying to prove those predicates
801 // to be *true* but merely *well-formed*.
802 let pred = fcx.normalize_associated_types_in(sp, &pred);
804 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
805 traits::Obligation::new(cause, fcx.param_env, pred)
808 let predicates = predicates.instantiate_identity(fcx.tcx);
810 if let Some((mut return_ty, span)) = return_ty {
811 if return_ty.has_infer_types_or_consts() {
812 fcx.select_obligations_where_possible(false, |_| {});
813 return_ty = fcx.resolve_vars_if_possible(&return_ty);
815 check_opaque_types(tcx, fcx, def_id.expect_local(), span, return_ty);
818 let predicates = fcx.normalize_associated_types_in(span, &predicates);
820 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
821 assert_eq!(predicates.predicates.len(), predicates.spans.len());
823 predicates.predicates.iter().zip(predicates.spans.iter()).flat_map(|(&p, &sp)| {
824 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
827 for obligation in wf_obligations.chain(default_obligations) {
828 debug!("next obligation cause: {:?}", obligation.cause);
829 fcx.register_predicate(obligation);
833 fn check_fn_or_method<'fcx, 'tcx>(
835 fcx: &FnCtxt<'fcx, 'tcx>,
837 sig: ty::PolyFnSig<'tcx>,
838 hir_sig: &hir::FnSig<'_>,
840 implied_bounds: &mut Vec<Ty<'tcx>>,
842 let sig = fcx.normalize_associated_types_in(span, &sig);
843 let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
845 for (&input_ty, span) in sig.inputs().iter().zip(hir_sig.decl.inputs.iter().map(|t| t.span)) {
846 fcx.register_wf_obligation(input_ty.into(), span, ObligationCauseCode::MiscObligation);
848 implied_bounds.extend(sig.inputs());
850 fcx.register_wf_obligation(
852 hir_sig.decl.output.span(),
853 ObligationCauseCode::ReturnType,
856 // FIXME(#25759) return types should not be implied bounds
857 implied_bounds.push(sig.output());
859 check_where_clauses(tcx, fcx, span, def_id, Some((sig.output(), hir_sig.decl.output.span())));
862 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
863 /// laid for "higher-order pattern unification".
864 /// This ensures that inference is tractable.
865 /// In particular, definitions of opaque types can only use other generics as arguments,
866 /// and they cannot repeat an argument. Example:
869 /// type Foo<A, B> = impl Bar<A, B>;
871 /// // Okay -- `Foo` is applied to two distinct, generic types.
872 /// fn a<T, U>() -> Foo<T, U> { .. }
874 /// // Not okay -- `Foo` is applied to `T` twice.
875 /// fn b<T>() -> Foo<T, T> { .. }
877 /// // Not okay -- `Foo` is applied to a non-generic type.
878 /// fn b<T>() -> Foo<T, u32> { .. }
881 fn check_opaque_types<'fcx, 'tcx>(
883 fcx: &FnCtxt<'fcx, 'tcx>,
884 fn_def_id: LocalDefId,
888 trace!("check_opaque_types(ty={:?})", ty);
889 ty.fold_with(&mut ty::fold::BottomUpFolder {
892 if let ty::Opaque(def_id, substs) = ty.kind {
893 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
894 let generics = tcx.generics_of(def_id);
896 let opaque_hir_id = if let Some(local_id) = def_id.as_local() {
897 tcx.hir().as_local_hir_id(local_id)
899 // Opaque types from other crates won't have defining uses in this crate.
902 if let hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) =
903 tcx.hir().expect_item(opaque_hir_id).kind
905 // No need to check return position impl trait (RPIT)
906 // because for type and const parameters they are correct
907 // by construction: we convert
909 // fn foo<P0..Pn>() -> impl Trait
914 // fn foo<P0..Pn>() -> Foo<P0...Pn>.
916 // For lifetime parameters we convert
918 // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
922 // type foo::<'p0..'pn>::Foo<'q0..'qm>
923 // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
925 // which would error here on all of the `'static` args.
928 if !may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
931 trace!("check_opaque_types: may define, generics={:#?}", generics);
932 let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
933 for (i, arg) in substs.iter().enumerate() {
934 let arg_is_param = match arg.unpack() {
935 GenericArgKind::Type(ty) => matches!(ty.kind, ty::Param(_)),
937 GenericArgKind::Lifetime(region) => {
938 if let ty::ReStatic = region {
942 "non-defining opaque type use in defining scope",
945 tcx.def_span(generics.param_at(i, tcx).def_id),
946 "cannot use static lifetime; use a bound lifetime \
947 instead or remove the lifetime parameter from the \
957 GenericArgKind::Const(ct) => matches!(ct.val, ty::ConstKind::Param(_)),
961 seen_params.entry(arg).or_default().push(i);
963 // Prevent `fn foo() -> Foo<u32>` from being defining.
964 let opaque_param = generics.param_at(i, tcx);
966 .struct_span_err(span, "non-defining opaque type use in defining scope")
968 tcx.def_span(opaque_param.def_id),
970 "used non-generic {} `{}` for generic parameter",
971 opaque_param.kind.descr(),
977 } // for (arg, param)
979 for (_, indices) in seen_params {
980 if indices.len() > 1 {
981 let descr = generics.param_at(indices[0], tcx).kind.descr();
982 let spans: Vec<_> = indices
984 .map(|i| tcx.def_span(generics.param_at(i, tcx).def_id))
987 .struct_span_err(span, "non-defining opaque type use in defining scope")
988 .span_note(spans, &format!("{} used multiple times", descr))
1000 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1001 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1002 of the previous types except `Self`)";
1004 fn check_method_receiver<'fcx, 'tcx>(
1005 fcx: &FnCtxt<'fcx, 'tcx>,
1006 fn_sig: &hir::FnSig<'_>,
1007 method: &ty::AssocItem,
1010 // Check that the method has a valid receiver type, given the type `Self`.
1011 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1013 if !method.fn_has_self_parameter {
1017 let span = fn_sig.decl.inputs[0].span;
1019 let sig = fcx.tcx.fn_sig(method.def_id);
1020 let sig = fcx.normalize_associated_types_in(span, &sig);
1021 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
1023 debug!("check_method_receiver: sig={:?}", sig);
1025 let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
1026 let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_ty));
1028 let receiver_ty = sig.inputs()[0];
1030 let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
1032 fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(receiver_ty));
1034 if fcx.tcx.features().arbitrary_self_types {
1035 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1036 // Report error; `arbitrary_self_types` was enabled.
1037 e0307(fcx, span, receiver_ty);
1040 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1041 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1042 // Report error; would have worked with `arbitrary_self_types`.
1044 &fcx.tcx.sess.parse_sess,
1045 sym::arbitrary_self_types,
1048 "`{}` cannot be used as the type of `self` without \
1049 the `arbitrary_self_types` feature",
1053 .help(HELP_FOR_SELF_TYPE)
1056 // Report error; would not have worked with `arbitrary_self_types`.
1057 e0307(fcx, span, receiver_ty);
1063 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1065 fcx.tcx.sess.diagnostic(),
1068 "invalid `self` parameter type: {:?}",
1071 .note("type of `self` must be `Self` or a type that dereferences to it")
1072 .help(HELP_FOR_SELF_TYPE)
1076 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1077 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1078 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1079 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1080 /// `Deref<Target = self_ty>`.
1082 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1083 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1084 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1085 fn receiver_is_valid<'fcx, 'tcx>(
1086 fcx: &FnCtxt<'fcx, 'tcx>,
1088 receiver_ty: Ty<'tcx>,
1090 arbitrary_self_types_enabled: bool,
1092 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1094 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1096 // `self: Self` is always valid.
1097 if can_eq_self(receiver_ty) {
1098 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1104 let mut autoderef = fcx.autoderef(span, receiver_ty);
1106 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1107 if arbitrary_self_types_enabled {
1108 autoderef = autoderef.include_raw_pointers();
1111 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1114 let receiver_trait_def_id = fcx.tcx.require_lang_item(lang_items::ReceiverTraitLangItem, None);
1116 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1118 if let Some((potential_self_ty, _)) = autoderef.next() {
1120 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1121 potential_self_ty, self_ty
1124 if can_eq_self(potential_self_ty) {
1125 fcx.register_predicates(autoderef.into_obligations());
1127 if let Some(mut err) =
1128 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1135 // Without `feature(arbitrary_self_types)`, we require that each step in the
1136 // deref chain implement `receiver`
1137 if !arbitrary_self_types_enabled
1138 && !receiver_is_implemented(
1140 receiver_trait_def_id,
1149 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1150 // If he receiver already has errors reported due to it, consider it valid to avoid
1151 // unnecessary errors (#58712).
1152 return receiver_ty.references_error();
1156 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1157 if !arbitrary_self_types_enabled
1158 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1166 fn receiver_is_implemented(
1167 fcx: &FnCtxt<'_, 'tcx>,
1168 receiver_trait_def_id: DefId,
1169 cause: ObligationCause<'tcx>,
1170 receiver_ty: Ty<'tcx>,
1172 let trait_ref = ty::TraitRef {
1173 def_id: receiver_trait_def_id,
1174 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1177 let obligation = traits::Obligation::new(
1180 trait_ref.without_const().to_predicate(fcx.tcx),
1183 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1187 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1194 fn check_variances_for_type_defn<'tcx>(
1196 item: &hir::Item<'tcx>,
1197 hir_generics: &hir::Generics<'_>,
1199 let item_def_id = tcx.hir().local_def_id(item.hir_id);
1200 let ty = tcx.type_of(item_def_id);
1201 if tcx.has_error_field(ty) {
1205 let ty_predicates = tcx.predicates_of(item_def_id);
1206 assert_eq!(ty_predicates.parent, None);
1207 let variances = tcx.variances_of(item_def_id);
1209 let mut constrained_parameters: FxHashSet<_> = variances
1212 .filter(|&(_, &variance)| variance != ty::Bivariant)
1213 .map(|(index, _)| Parameter(index as u32))
1216 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1218 for (index, _) in variances.iter().enumerate() {
1219 if constrained_parameters.contains(&Parameter(index as u32)) {
1223 let param = &hir_generics.params[index];
1226 hir::ParamName::Error => {}
1227 _ => report_bivariance(tcx, param.span, param.name.ident().name),
1232 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) {
1233 let mut err = error_392(tcx, span, param_name);
1235 let suggested_marker_id = tcx.lang_items().phantom_data();
1236 // Help is available only in presence of lang items.
1237 let msg = if let Some(def_id) = suggested_marker_id {
1239 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1241 tcx.def_path_str(def_id),
1244 format!("consider removing `{}` or referring to it in a field", param_name)
1250 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1252 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1253 let empty_env = ty::ParamEnv::empty();
1255 let def_id = fcx.tcx.hir().local_def_id(id);
1256 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p);
1257 // Check elaborated bounds.
1258 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1260 for obligation in implied_obligations {
1261 let pred = obligation.predicate;
1262 // Match the existing behavior.
1263 if pred.is_global() && !pred.has_late_bound_regions() {
1264 let pred = fcx.normalize_associated_types_in(span, &pred);
1265 let obligation = traits::Obligation::new(
1266 traits::ObligationCause::new(span, id, traits::TrivialBound),
1270 fcx.register_predicate(obligation);
1274 fcx.select_all_obligations_or_error();
1277 pub struct CheckTypeWellFormedVisitor<'tcx> {
1281 impl CheckTypeWellFormedVisitor<'tcx> {
1282 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1283 CheckTypeWellFormedVisitor { tcx }
1287 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1288 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1289 debug!("visit_item: {:?}", i);
1290 let def_id = self.tcx.hir().local_def_id(i.hir_id);
1291 self.tcx.ensure().check_item_well_formed(def_id);
1294 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1295 debug!("visit_trait_item: {:?}", trait_item);
1296 let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1297 self.tcx.ensure().check_trait_item_well_formed(def_id);
1300 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1301 debug!("visit_impl_item: {:?}", impl_item);
1302 let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1303 self.tcx.ensure().check_impl_item_well_formed(def_id);
1307 ///////////////////////////////////////////////////////////////////////////
1310 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1311 struct AdtVariant<'tcx> {
1312 /// Types of fields in the variant, that must be well-formed.
1313 fields: Vec<AdtField<'tcx>>,
1315 /// Explicit discriminant of this variant (e.g. `A = 123`),
1316 /// that must evaluate to a constant value.
1317 explicit_discr: Option<LocalDefId>,
1320 struct AdtField<'tcx> {
1325 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1326 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1327 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1328 let fields = struct_def
1332 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1333 let field_ty = self.normalize_associated_types_in(field.ty.span, &field_ty);
1334 let field_ty = self.resolve_vars_if_possible(&field_ty);
1335 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1336 AdtField { ty: field_ty, span: field.ty.span }
1339 AdtVariant { fields, explicit_discr: None }
1342 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1346 .map(|variant| AdtVariant {
1347 fields: self.non_enum_variant(&variant.data).fields,
1348 explicit_discr: variant
1350 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1355 fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1356 match self.tcx.impl_trait_ref(impl_def_id) {
1357 Some(ref trait_ref) => {
1358 // Trait impl: take implied bounds from all types that
1359 // appear in the trait reference.
1360 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1361 trait_ref.substs.types().collect()
1365 // Inherent impl: take implied bounds from the `self` type.
1366 let self_ty = self.tcx.type_of(impl_def_id);
1367 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1374 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) -> DiagnosticBuilder<'_> {
1376 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1377 err.span_label(span, "unused parameter");