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;
9 use rustc_hir::itemlikevisit::ParItemLikeVisitor;
10 use rustc_hir::ItemKind;
11 use rustc_middle::middle::lang_items;
12 use rustc_middle::ty::subst::{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;
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: DefId) {
74 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
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)
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: DefId) {
187 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
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: DefId, 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),
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: DefId) {
261 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
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, span, code.clone());
297 ty::AssocKind::Method => {
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, span, code.clone());
319 ty::AssocKind::OpaqueTy => {
320 // Do nothing: opaque types check themselves.
328 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
329 for_id(tcx, item.hir_id, item.span)
332 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
333 let def_id = tcx.hir().local_def_id(id).expect_local();
335 inherited: Inherited::build(tcx, def_id),
338 param_env: tcx.param_env(def_id.to_def_id()),
342 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
344 ItemKind::Struct(..) => Some(AdtKind::Struct),
345 ItemKind::Union(..) => Some(AdtKind::Union),
346 ItemKind::Enum(..) => Some(AdtKind::Enum),
351 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
352 fn check_type_defn<'tcx, F>(
354 item: &hir::Item<'tcx>,
356 mut lookup_fields: F,
358 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
360 for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
361 let variants = lookup_fields(fcx);
362 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
363 let packed = fcx.tcx.adt_def(def_id).repr.packed();
365 for variant in &variants {
366 // For DST, or when drop needs to copy things around, all
367 // intermediate types must be sized.
368 let needs_drop_copy = || {
370 let ty = variant.fields.last().unwrap().ty;
371 let ty = fcx.tcx.erase_regions(&ty);
372 if ty.has_local_value() {
375 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
376 // Just treat unresolved type expression as if it needs drop.
379 ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
383 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
384 let unsized_len = if all_sized { 0 } else { 1 };
386 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
388 let last = idx == variant.fields.len() - 1;
391 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
392 traits::ObligationCause::new(
396 adt_kind: match item_adt_kind(&item.kind) {
406 // All field types must be well-formed.
407 for field in &variant.fields {
408 fcx.register_wf_obligation(
411 ObligationCauseCode::MiscObligation,
416 check_where_clauses(tcx, fcx, item.span, def_id, None);
418 // No implied bounds in a struct definition.
423 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
424 debug!("check_trait: {:?}", item.hir_id);
426 let trait_def_id = tcx.hir().local_def_id(item.hir_id);
428 let trait_def = tcx.trait_def(trait_def_id);
429 if trait_def.is_marker
430 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
432 for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
435 tcx.def_span(*associated_def_id),
437 "marker traits cannot have associated items",
443 for_item(tcx, item).with_fcx(|fcx, _| {
444 check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
445 check_associated_type_defaults(fcx, trait_def_id);
451 /// Checks all associated type defaults of trait `trait_def_id`.
453 /// Assuming the defaults are used, check that all predicates (bounds on the
454 /// assoc type and where clauses on the trait) hold.
455 fn check_associated_type_defaults(fcx: &FnCtxt<'_, '_>, trait_def_id: DefId) {
457 let substs = InternalSubsts::identity_for_item(tcx, trait_def_id);
459 // For all assoc. types with defaults, build a map from
460 // `<Self as Trait<...>>::Assoc` to the default type.
462 .associated_items(trait_def_id)
463 .in_definition_order()
465 if item.kind == ty::AssocKind::Type && item.defaultness.has_value() {
466 // `<Self as Trait<...>>::Assoc`
467 let proj = ty::ProjectionTy { substs, item_def_id: item.def_id };
468 let default_ty = tcx.type_of(item.def_id);
469 debug!("assoc. type default mapping: {} -> {}", proj, default_ty);
470 Some((proj, default_ty))
475 .collect::<FxHashMap<_, _>>();
477 /// Replaces projections of associated types with their default types.
479 /// This does a "shallow substitution", meaning that defaults that refer to
480 /// other defaulted assoc. types will still refer to the projection
481 /// afterwards, not to the other default. For example:
485 /// type A: Clone = Vec<Self::B>;
490 /// This will end up replacing the bound `Self::A: Clone` with
491 /// `Vec<Self::B>: Clone`, not with `Vec<u8>: Clone`. If we did a deep
492 /// substitution and ended up with the latter, the trait would be accepted.
493 /// If an `impl` then replaced `B` with something that isn't `Clone`,
494 /// suddenly the default for `A` is no longer valid. The shallow
495 /// substitution forces the trait to add a `B: Clone` bound to be accepted,
496 /// which means that an `impl` can replace any default without breaking
499 /// Note that this isn't needed for soundness: The defaults would still be
500 /// checked in any impl that doesn't override them.
501 struct DefaultNormalizer<'tcx> {
503 map: FxHashMap<ty::ProjectionTy<'tcx>, Ty<'tcx>>,
506 impl<'tcx> ty::fold::TypeFolder<'tcx> for DefaultNormalizer<'tcx> {
507 fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
511 fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
513 ty::Projection(proj_ty) => {
514 if let Some(default) = self.map.get(&proj_ty) {
517 t.super_fold_with(self)
520 _ => t.super_fold_with(self),
525 // Now take all predicates defined on the trait, replace any mention of
526 // the assoc. types with their default, and prove them.
527 // We only consider predicates that directly mention the assoc. type.
528 let mut norm = DefaultNormalizer { tcx, map };
529 let predicates = fcx.tcx.predicates_of(trait_def_id);
530 for &(orig_pred, span) in predicates.predicates.iter() {
531 let pred = orig_pred.fold_with(&mut norm);
532 if pred != orig_pred {
533 // Mentions one of the defaulted assoc. types
534 debug!("default suitability check: proving predicate: {} -> {}", orig_pred, pred);
535 let pred = fcx.normalize_associated_types_in(span, &pred);
536 let cause = traits::ObligationCause::new(
539 traits::ItemObligation(trait_def_id),
541 let obligation = traits::Obligation::new(cause, fcx.param_env, pred);
543 fcx.register_predicate(obligation);
548 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
549 for_item(tcx, item).with_fcx(|fcx, tcx| {
550 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
551 let sig = fcx.tcx.fn_sig(def_id);
552 let sig = fcx.normalize_associated_types_in(item.span, &sig);
553 let mut implied_bounds = vec![];
554 let hir_sig = match &item.kind {
555 ItemKind::Fn(sig, ..) => sig,
556 _ => bug!("expected `ItemKind::Fn`, found `{:?}`", item.kind),
558 check_fn_or_method(tcx, fcx, item.ident.span, sig, hir_sig, def_id, &mut implied_bounds);
563 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
564 debug!("check_item_type: {:?}", item_id);
566 for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
567 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
568 let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
570 let mut forbid_unsized = true;
571 if allow_foreign_ty {
572 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
573 if let ty::Foreign(_) = tail.kind {
574 forbid_unsized = false;
578 fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
582 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
583 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
587 // No implied bounds in a const, etc.
594 item: &'tcx hir::Item<'tcx>,
595 ast_self_ty: &hir::Ty<'_>,
596 ast_trait_ref: &Option<hir::TraitRef<'_>>,
598 debug!("check_impl: {:?}", item);
600 for_item(tcx, item).with_fcx(|fcx, tcx| {
601 let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
603 match *ast_trait_ref {
604 Some(ref ast_trait_ref) => {
605 // `#[rustc_reservation_impl]` impls are not real impls and
606 // therefore don't need to be WF (the trait's `Self: Trait` predicate
608 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
610 fcx.normalize_associated_types_in(ast_trait_ref.path.span, &trait_ref);
611 let obligations = traits::wf::trait_obligations(
616 ast_trait_ref.path.span,
619 for obligation in obligations {
620 fcx.register_predicate(obligation);
624 let self_ty = fcx.tcx.type_of(item_def_id);
625 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
626 fcx.register_wf_obligation(
629 ObligationCauseCode::MiscObligation,
634 check_where_clauses(tcx, fcx, item.span, item_def_id, None);
636 fcx.impl_implied_bounds(item_def_id, item.span)
640 /// Checks where-clauses and inline bounds that are declared on `def_id`.
641 fn check_where_clauses<'tcx, 'fcx>(
643 fcx: &FnCtxt<'fcx, 'tcx>,
646 return_ty: Option<(Ty<'tcx>, Span)>,
648 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
650 let predicates = fcx.tcx.predicates_of(def_id);
651 let generics = tcx.generics_of(def_id);
653 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
654 GenericParamDefKind::Type { has_default, .. } => {
655 has_default && def.index >= generics.parent_count as u32
660 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
661 // For example, this forbids the declaration:
663 // struct Foo<T = Vec<[u32]>> { .. }
665 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
666 for param in &generics.params {
667 if let GenericParamDefKind::Type { .. } = param.kind {
668 if is_our_default(¶m) {
669 let ty = fcx.tcx.type_of(param.def_id);
670 // Ignore dependent defaults -- that is, where the default of one type
671 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
672 // be sure if it will error or not as user might always specify the other.
673 if !ty.needs_subst() {
674 fcx.register_wf_obligation(
676 fcx.tcx.def_span(param.def_id),
677 ObligationCauseCode::MiscObligation,
684 // Check that trait predicates are WF when params are substituted by their defaults.
685 // We don't want to overly constrain the predicates that may be written but we want to
686 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
687 // Therefore we check if a predicate which contains a single type param
688 // with a concrete default is WF with that default substituted.
689 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
691 // First we build the defaulted substitution.
692 let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
694 GenericParamDefKind::Lifetime => {
695 // All regions are identity.
696 fcx.tcx.mk_param_from_def(param)
699 GenericParamDefKind::Type { .. } => {
700 // If the param has a default, ...
701 if is_our_default(param) {
702 let default_ty = fcx.tcx.type_of(param.def_id);
703 // ... and it's not a dependent default, ...
704 if !default_ty.needs_subst() {
705 // ... then substitute it with the default.
706 return default_ty.into();
709 // Mark unwanted params as error.
710 fcx.tcx.types.err.into()
713 GenericParamDefKind::Const => {
714 // FIXME(const_generics:defaults)
715 fcx.tcx.consts.err.into()
720 // Now we build the substituted predicates.
721 let default_obligations = predicates
724 .flat_map(|&(pred, sp)| {
727 params: FxHashSet<u32>,
729 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
730 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
731 if let ty::Param(param) = t.kind {
732 self.params.insert(param.index);
734 t.super_visit_with(self)
737 fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
741 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
742 if let ty::ConstKind::Param(param) = c.val {
743 self.params.insert(param.index);
745 c.super_visit_with(self)
748 let mut param_count = CountParams::default();
749 let has_region = pred.visit_with(&mut param_count);
750 let substituted_pred = pred.subst(fcx.tcx, substs);
751 // Don't check non-defaulted params, dependent defaults (including lifetimes)
752 // or preds with multiple params.
753 if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
755 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
756 // Avoid duplication of predicates that contain no parameters, for example.
759 Some((substituted_pred, sp))
763 // Convert each of those into an obligation. So if you have
764 // something like `struct Foo<T: Copy = String>`, we would
765 // take that predicate `T: Copy`, substitute to `String: Copy`
766 // (actually that happens in the previous `flat_map` call),
767 // and then try to prove it (in this case, we'll fail).
769 // Note the subtle difference from how we handle `predicates`
770 // below: there, we are not trying to prove those predicates
771 // to be *true* but merely *well-formed*.
772 let pred = fcx.normalize_associated_types_in(sp, &pred);
774 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
775 traits::Obligation::new(cause, fcx.param_env, pred)
778 let mut predicates = predicates.instantiate_identity(fcx.tcx);
780 if let Some((return_ty, span)) = return_ty {
781 let opaque_types = check_opaque_types(tcx, fcx, def_id, span, return_ty);
782 for _ in 0..opaque_types.len() {
783 predicates.spans.push(span);
785 predicates.predicates.extend(opaque_types);
788 let predicates = fcx.normalize_associated_types_in(span, &predicates);
790 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
791 assert_eq!(predicates.predicates.len(), predicates.spans.len());
793 predicates.predicates.iter().zip(predicates.spans.iter()).flat_map(|(p, sp)| {
794 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, *sp)
797 for obligation in wf_obligations.chain(default_obligations) {
798 debug!("next obligation cause: {:?}", obligation.cause);
799 fcx.register_predicate(obligation);
803 fn check_fn_or_method<'fcx, 'tcx>(
805 fcx: &FnCtxt<'fcx, 'tcx>,
807 sig: ty::PolyFnSig<'tcx>,
808 hir_sig: &hir::FnSig<'_>,
810 implied_bounds: &mut Vec<Ty<'tcx>>,
812 let sig = fcx.normalize_associated_types_in(span, &sig);
813 let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
815 for (input_ty, span) in sig.inputs().iter().zip(hir_sig.decl.inputs.iter().map(|t| t.span)) {
816 fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
818 implied_bounds.extend(sig.inputs());
820 fcx.register_wf_obligation(
822 hir_sig.decl.output.span(),
823 ObligationCauseCode::ReturnType,
826 // FIXME(#25759) return types should not be implied bounds
827 implied_bounds.push(sig.output());
829 check_where_clauses(tcx, fcx, span, def_id, Some((sig.output(), hir_sig.decl.output.span())));
832 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
833 /// laid for "higher-order pattern unification".
834 /// This ensures that inference is tractable.
835 /// In particular, definitions of opaque types can only use other generics as arguments,
836 /// and they cannot repeat an argument. Example:
839 /// type Foo<A, B> = impl Bar<A, B>;
841 /// // Okay -- `Foo` is applied to two distinct, generic types.
842 /// fn a<T, U>() -> Foo<T, U> { .. }
844 /// // Not okay -- `Foo` is applied to `T` twice.
845 /// fn b<T>() -> Foo<T, T> { .. }
847 /// // Not okay -- `Foo` is applied to a non-generic type.
848 /// fn b<T>() -> Foo<T, u32> { .. }
851 fn check_opaque_types<'fcx, 'tcx>(
853 fcx: &FnCtxt<'fcx, 'tcx>,
857 ) -> Vec<ty::Predicate<'tcx>> {
858 trace!("check_opaque_types(ty={:?})", ty);
859 let mut substituted_predicates = Vec::new();
860 ty.fold_with(&mut ty::fold::BottomUpFolder {
863 if let ty::Opaque(def_id, substs) = ty.kind {
864 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
865 let generics = tcx.generics_of(def_id);
866 // Only check named `impl Trait` types defined in this crate.
867 if generics.parent.is_none() && def_id.is_local() {
868 let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
869 if may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
870 trace!("check_opaque_types: may define, generics={:#?}", generics);
871 let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
872 for (subst, param) in substs.iter().zip(&generics.params) {
873 match subst.unpack() {
874 ty::subst::GenericArgKind::Type(ty) => match ty.kind {
876 // Prevent `fn foo() -> Foo<u32>` from being defining.
881 "non-defining opaque type use \
885 tcx.def_span(param.def_id),
887 "used non-generic type {} for \
896 ty::subst::GenericArgKind::Lifetime(region) => {
897 let param_span = tcx.def_span(param.def_id);
898 if let ty::ReStatic = region {
902 "non-defining opaque type use \
907 "cannot use static lifetime; use a bound lifetime \
908 instead or remove the lifetime parameter from the \
913 seen.entry(region).or_default().push(param_span);
917 ty::subst::GenericArgKind::Const(ct) => match ct.val {
918 ty::ConstKind::Param(_) => {}
923 "non-defining opaque type use \
927 tcx.def_span(param.def_id),
929 "used non-generic const {} for \
938 } // for (subst, param)
939 for (_, spans) in seen {
944 "non-defining opaque type use \
947 .span_note(spans, "lifetime used multiple times")
951 } // if may_define_opaque_type
953 // Now register the bounds on the parameters of the opaque type
954 // so the parameters given by the function need to fulfill them.
956 // type Foo<T: Bar> = impl Baz + 'static;
957 // fn foo<U>() -> Foo<U> { .. *}
961 // type Foo<T: Bar> = impl Baz + 'static;
962 // fn foo<U: Bar>() -> Foo<U> { .. *}
963 let predicates = tcx.predicates_of(def_id);
964 trace!("check_opaque_types: may define, predicates={:#?}", predicates,);
965 for &(pred, _) in predicates.predicates {
966 let substituted_pred = pred.subst(fcx.tcx, substs);
967 // Avoid duplication of predicates that contain no parameters, for example.
968 if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
969 substituted_predicates.push(substituted_pred);
972 } // if is_named_opaque_type
979 substituted_predicates
982 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
983 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
984 of the previous types except `Self`)";
986 fn check_method_receiver<'fcx, 'tcx>(
987 fcx: &FnCtxt<'fcx, 'tcx>,
988 fn_sig: &hir::FnSig<'_>,
989 method: &ty::AssocItem,
992 // Check that the method has a valid receiver type, given the type `Self`.
993 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
995 if !method.method_has_self_argument {
999 let span = fn_sig.decl.inputs[0].span;
1001 let sig = fcx.tcx.fn_sig(method.def_id);
1002 let sig = fcx.normalize_associated_types_in(span, &sig);
1003 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
1005 debug!("check_method_receiver: sig={:?}", sig);
1007 let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
1008 let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_ty));
1010 let receiver_ty = sig.inputs()[0];
1012 let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
1014 fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(receiver_ty));
1016 if fcx.tcx.features().arbitrary_self_types {
1017 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1018 // Report error; `arbitrary_self_types` was enabled.
1019 e0307(fcx, span, receiver_ty);
1022 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1023 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1024 // Report error; would have worked with `arbitrary_self_types`.
1026 &fcx.tcx.sess.parse_sess,
1027 sym::arbitrary_self_types,
1030 "`{}` cannot be used as the type of `self` without \
1031 the `arbitrary_self_types` feature",
1035 .help(HELP_FOR_SELF_TYPE)
1038 // Report error; would not have worked with `arbitrary_self_types`.
1039 e0307(fcx, span, receiver_ty);
1045 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1047 fcx.tcx.sess.diagnostic(),
1050 "invalid `self` parameter type: {:?}",
1053 .note("type of `self` must be `Self` or a type that dereferences to it")
1054 .help(HELP_FOR_SELF_TYPE)
1058 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1059 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1060 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1061 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1062 /// `Deref<Target = self_ty>`.
1064 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1065 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1066 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1067 fn receiver_is_valid<'fcx, 'tcx>(
1068 fcx: &FnCtxt<'fcx, 'tcx>,
1070 receiver_ty: Ty<'tcx>,
1072 arbitrary_self_types_enabled: bool,
1074 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1076 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1078 // `self: Self` is always valid.
1079 if can_eq_self(receiver_ty) {
1080 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1086 let mut autoderef = fcx.autoderef(span, receiver_ty);
1088 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1089 if arbitrary_self_types_enabled {
1090 autoderef = autoderef.include_raw_pointers();
1093 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1096 let receiver_trait_def_id = fcx.tcx.require_lang_item(lang_items::ReceiverTraitLangItem, None);
1098 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1100 if let Some((potential_self_ty, _)) = autoderef.next() {
1102 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1103 potential_self_ty, self_ty
1106 if can_eq_self(potential_self_ty) {
1107 autoderef.finalize(fcx);
1109 if let Some(mut err) =
1110 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1117 // Without `feature(arbitrary_self_types)`, we require that each step in the
1118 // deref chain implement `receiver`
1119 if !arbitrary_self_types_enabled
1120 && !receiver_is_implemented(
1122 receiver_trait_def_id,
1131 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1132 // If he receiver already has errors reported due to it, consider it valid to avoid
1133 // unnecessary errors (#58712).
1134 return receiver_ty.references_error();
1138 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1139 if !arbitrary_self_types_enabled
1140 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1148 fn receiver_is_implemented(
1149 fcx: &FnCtxt<'_, 'tcx>,
1150 receiver_trait_def_id: DefId,
1151 cause: ObligationCause<'tcx>,
1152 receiver_ty: Ty<'tcx>,
1154 let trait_ref = ty::TraitRef {
1155 def_id: receiver_trait_def_id,
1156 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1160 traits::Obligation::new(cause, fcx.param_env, trait_ref.without_const().to_predicate());
1162 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1166 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1173 fn check_variances_for_type_defn<'tcx>(
1175 item: &hir::Item<'tcx>,
1176 hir_generics: &hir::Generics<'_>,
1178 let item_def_id = tcx.hir().local_def_id(item.hir_id);
1179 let ty = tcx.type_of(item_def_id);
1180 if tcx.has_error_field(ty) {
1184 let ty_predicates = tcx.predicates_of(item_def_id);
1185 assert_eq!(ty_predicates.parent, None);
1186 let variances = tcx.variances_of(item_def_id);
1188 let mut constrained_parameters: FxHashSet<_> = variances
1191 .filter(|&(_, &variance)| variance != ty::Bivariant)
1192 .map(|(index, _)| Parameter(index as u32))
1195 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1197 for (index, _) in variances.iter().enumerate() {
1198 if constrained_parameters.contains(&Parameter(index as u32)) {
1202 let param = &hir_generics.params[index];
1205 hir::ParamName::Error => {}
1206 _ => report_bivariance(tcx, param.span, param.name.ident().name),
1211 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
1212 let mut err = error_392(tcx, span, param_name);
1214 let suggested_marker_id = tcx.lang_items().phantom_data();
1215 // Help is available only in presence of lang items.
1216 let msg = if let Some(def_id) = suggested_marker_id {
1218 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1220 tcx.def_path_str(def_id),
1223 format!("consider removing `{}` or referring to it in a field", param_name)
1229 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1231 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1232 let empty_env = ty::ParamEnv::empty();
1234 let def_id = fcx.tcx.hir().local_def_id(id);
1235 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p).collect();
1236 // Check elaborated bounds.
1237 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1239 for pred in implied_obligations {
1240 // Match the existing behavior.
1241 if pred.is_global() && !pred.has_late_bound_regions() {
1242 let pred = fcx.normalize_associated_types_in(span, &pred);
1243 let obligation = traits::Obligation::new(
1244 traits::ObligationCause::new(span, id, traits::TrivialBound),
1248 fcx.register_predicate(obligation);
1252 fcx.select_all_obligations_or_error();
1255 pub struct CheckTypeWellFormedVisitor<'tcx> {
1259 impl CheckTypeWellFormedVisitor<'tcx> {
1260 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1261 CheckTypeWellFormedVisitor { tcx }
1265 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1266 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1267 debug!("visit_item: {:?}", i);
1268 let def_id = self.tcx.hir().local_def_id(i.hir_id);
1269 self.tcx.ensure().check_item_well_formed(def_id);
1272 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1273 debug!("visit_trait_item: {:?}", trait_item);
1274 let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1275 self.tcx.ensure().check_trait_item_well_formed(def_id);
1278 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1279 debug!("visit_impl_item: {:?}", impl_item);
1280 let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1281 self.tcx.ensure().check_impl_item_well_formed(def_id);
1285 ///////////////////////////////////////////////////////////////////////////
1288 struct AdtVariant<'tcx> {
1289 fields: Vec<AdtField<'tcx>>,
1292 struct AdtField<'tcx> {
1297 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1298 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1299 let fields = struct_def
1303 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1304 let field_ty = self.normalize_associated_types_in(field.span, &field_ty);
1305 let field_ty = self.resolve_vars_if_possible(&field_ty);
1306 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1307 AdtField { ty: field_ty, span: field.span }
1310 AdtVariant { fields }
1313 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1314 enum_def.variants.iter().map(|variant| self.non_enum_variant(&variant.data)).collect()
1317 fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1318 match self.tcx.impl_trait_ref(impl_def_id) {
1319 Some(ref trait_ref) => {
1320 // Trait impl: take implied bounds from all types that
1321 // appear in the trait reference.
1322 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1323 trait_ref.substs.types().collect()
1327 // Inherent impl: take implied bounds from the `self` type.
1328 let self_ty = self.tcx.type_of(impl_def_id);
1329 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1336 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) -> DiagnosticBuilder<'_> {
1338 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1339 err.span_label(span, "unused parameter");