1 use crate::check::{FnCtxt, Inherited};
2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
5 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
6 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
8 use rustc_hir::def_id::{DefId, LocalDefId};
9 use rustc_hir::intravisit as hir_visit;
10 use rustc_hir::intravisit::Visitor;
11 use rustc_hir::itemlikevisit::ParItemLikeVisitor;
12 use rustc_hir::lang_items::LangItem;
13 use rustc_hir::ItemKind;
14 use rustc_middle::hir::map as hir_map;
15 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
16 use rustc_middle::ty::trait_def::TraitSpecializationKind;
17 use rustc_middle::ty::{
18 self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
20 use rustc_session::parse::feature_err;
21 use rustc_span::symbol::{sym, Ident, Symbol};
23 use rustc_trait_selection::opaque_types::may_define_opaque_type;
24 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
25 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
27 use std::ops::ControlFlow;
29 /// Helper type of a temporary returned by `.for_item(...)`.
30 /// This is necessary because we can't write the following bound:
33 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
35 struct CheckWfFcxBuilder<'tcx> {
36 inherited: super::InheritedBuilder<'tcx>,
39 param_env: ty::ParamEnv<'tcx>,
42 impl<'tcx> CheckWfFcxBuilder<'tcx> {
43 fn with_fcx<F>(&mut self, f: F)
45 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
49 let param_env = self.param_env;
50 self.inherited.enter(|inh| {
51 let fcx = FnCtxt::new(&inh, param_env, id);
52 if !inh.tcx.features().trivial_bounds {
53 // As predicates are cached rather than obligations, this
54 // needsto be called first so that they are checked with an
56 check_false_global_bounds(&fcx, span, id);
58 let wf_tys = f(&fcx, fcx.tcx);
59 fcx.select_all_obligations_or_error();
60 fcx.regionck_item(id, span, &wf_tys);
65 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
66 /// well-formed, meaning that they do not require any constraints not declared in the struct
67 /// definition itself. For example, this definition would be illegal:
70 /// struct Ref<'a, T> { x: &'a T }
73 /// because the type did not declare that `T:'a`.
75 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
76 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
78 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
79 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
80 let item = tcx.hir().expect_item(hir_id);
83 "check_item_well_formed(it.hir_id={:?}, it.name={})",
85 tcx.def_path_str(def_id.to_def_id())
89 // Right now we check that every default trait implementation
90 // has an implementation of itself. Basically, a case like:
92 // impl Trait for T {}
94 // has a requirement of `T: Trait` which was required for default
95 // method implementations. Although this could be improved now that
96 // there's a better infrastructure in place for this, it's being left
97 // for a follow-up work.
99 // Since there's such a requirement, we need to check *just* positive
100 // implementations, otherwise things like:
102 // impl !Send for T {}
104 // won't be allowed unless there's an *explicit* implementation of `Send`
106 hir::ItemKind::Impl {
115 .impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
116 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
117 if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
118 let sp = of_trait.as_ref().map(|t| t.path.span).unwrap_or(item.span);
120 tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default");
121 err.span_labels(defaultness_span, "default because of this");
122 err.span_label(sp, "auto trait");
125 // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
126 match (tcx.impl_polarity(def_id), polarity) {
127 (ty::ImplPolarity::Positive, _) => {
128 check_impl(tcx, item, self_ty, of_trait);
130 (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => {
131 // FIXME(#27579): what amount of WF checking do we need for neg impls?
132 if let hir::Defaultness::Default { .. } = defaultness {
133 let mut spans = vec![span];
134 spans.extend(defaultness_span);
139 "negative impls cannot be default impls"
144 (ty::ImplPolarity::Reservation, _) => {
145 // FIXME: what amount of WF checking do we need for reservation impls?
150 hir::ItemKind::Fn(ref sig, ..) => {
151 check_item_fn(tcx, item.hir_id, item.ident, item.span, sig.decl);
153 hir::ItemKind::Static(ref ty, ..) => {
154 check_item_type(tcx, item.hir_id, ty.span, false);
156 hir::ItemKind::Const(ref ty, ..) => {
157 check_item_type(tcx, item.hir_id, ty.span, false);
159 hir::ItemKind::ForeignMod { items, .. } => {
160 for it in items.iter() {
161 let it = tcx.hir().foreign_item(it.id);
163 hir::ForeignItemKind::Fn(ref decl, ..) => {
164 check_item_fn(tcx, it.hir_id, it.ident, it.span, decl)
166 hir::ForeignItemKind::Static(ref ty, ..) => {
167 check_item_type(tcx, it.hir_id, ty.span, true)
169 hir::ForeignItemKind::Type => (),
173 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
174 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
176 check_variances_for_type_defn(tcx, item, ast_generics);
178 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
179 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
181 check_variances_for_type_defn(tcx, item, ast_generics);
183 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
184 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
186 check_variances_for_type_defn(tcx, item, ast_generics);
188 hir::ItemKind::Trait(..) => {
189 check_trait(tcx, item);
191 hir::ItemKind::TraitAlias(..) => {
192 check_trait(tcx, item);
198 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
199 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
200 let trait_item = tcx.hir().expect_trait_item(hir_id);
202 let method_sig = match trait_item.kind {
203 hir::TraitItemKind::Fn(ref sig, _) => Some(sig),
206 check_object_unsafe_self_trait_by_name(tcx, &trait_item);
207 check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
210 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
212 hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
213 [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
220 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
221 /// When this is done, suggest using `Self` instead.
222 fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
223 let (trait_name, trait_def_id) = match tcx.hir().get(tcx.hir().get_parent_item(item.hir_id)) {
224 hir::Node::Item(item) => match item.kind {
225 hir::ItemKind::Trait(..) => (item.ident, tcx.hir().local_def_id(item.hir_id)),
230 let mut trait_should_be_self = vec![];
232 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
233 if could_be_self(trait_def_id, ty) =>
235 trait_should_be_self.push(ty.span)
237 hir::TraitItemKind::Fn(sig, _) => {
238 for ty in sig.decl.inputs {
239 if could_be_self(trait_def_id, ty) {
240 trait_should_be_self.push(ty.span);
243 match sig.decl.output {
244 hir::FnRetTy::Return(ty) if could_be_self(trait_def_id, ty) => {
245 trait_should_be_self.push(ty.span);
252 if !trait_should_be_self.is_empty() {
253 if tcx.object_safety_violations(trait_def_id).is_empty() {
256 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
259 trait_should_be_self,
260 "associated item referring to unboxed trait object for its own trait",
262 .span_label(trait_name.span, "in this trait")
263 .multipart_suggestion(
264 "you might have meant to use `Self` to refer to the implementing type",
266 Applicability::MachineApplicable,
272 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
273 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
274 let impl_item = tcx.hir().expect_impl_item(hir_id);
276 let method_sig = match impl_item.kind {
277 hir::ImplItemKind::Fn(ref sig, _) => Some(sig),
281 check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
284 fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
286 // We currently only check wf of const params here.
287 hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (),
289 // Const parameters are well formed if their
290 // type is structural match.
291 hir::GenericParamKind::Const { ty: hir_ty } => {
292 let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id));
295 let mut is_ptr = true;
296 let err = if tcx.features().min_const_generics {
298 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None,
299 ty::FnPtr(_) => Some("function pointers"),
300 ty::RawPtr(_) => Some("raw pointers"),
303 err_ty_str = format!("`{}`", ty);
304 Some(err_ty_str.as_str())
308 match ty.peel_refs().kind() {
309 ty::FnPtr(_) => Some("function pointers"),
310 ty::RawPtr(_) => Some("raw pointers"),
314 if let Some(unsupported_type) = err {
319 "using {} as const generic parameters is forbidden",
328 "{} is forbidden as the type of a const generic parameter",
332 .note("the only supported types are integers, `bool` and `char`")
333 .help("more complex types are supported with `#[feature(const_generics)]`")
338 if traits::search_for_structural_match_violation(param.hir_id, param.span, tcx, ty)
341 // We use the same error code in both branches, because this is really the same
342 // issue: we just special-case the message for type parameters to make it
344 if let ty::Param(_) = ty.peel_refs().kind() {
345 // Const parameters may not have type parameters as their types,
346 // because we cannot be sure that the type parameter derives `PartialEq`
347 // and `Eq` (just implementing them is not enough for `structural_match`).
352 "`{}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
353 used as the type of a const parameter",
358 format!("`{}` may not derive both `PartialEq` and `Eq`", ty),
361 "it is not currently possible to use a type parameter as the type of a \
370 "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
371 the type of a const parameter",
376 format!("`{}` doesn't derive both `PartialEq` and `Eq`", ty),
385 fn check_associated_item(
389 sig_if_method: Option<&hir::FnSig<'_>>,
391 debug!("check_associated_item: {:?}", item_id);
393 let code = ObligationCauseCode::MiscObligation;
394 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
395 let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
397 let (mut implied_bounds, self_ty) = match item.container {
398 ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
399 ty::ImplContainer(def_id) => {
400 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
405 ty::AssocKind::Const => {
406 let ty = fcx.tcx.type_of(item.def_id);
407 let ty = fcx.normalize_associated_types_in(span, ty);
408 fcx.register_wf_obligation(ty.into(), span, code.clone());
410 ty::AssocKind::Fn => {
411 let sig = fcx.tcx.fn_sig(item.def_id);
412 let sig = fcx.normalize_associated_types_in(span, sig);
413 let hir_sig = sig_if_method.expect("bad signature for method");
423 check_method_receiver(fcx, hir_sig, &item, self_ty);
425 ty::AssocKind::Type => {
426 if let ty::AssocItemContainer::TraitContainer(_) = item.container {
427 check_associated_type_bounds(fcx, item, span)
429 if item.defaultness.has_value() {
430 let ty = fcx.tcx.type_of(item.def_id);
431 let ty = fcx.normalize_associated_types_in(span, ty);
432 fcx.register_wf_obligation(ty.into(), span, code.clone());
441 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
442 for_id(tcx, item.hir_id, item.span)
445 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
446 let def_id = tcx.hir().local_def_id(id);
448 inherited: Inherited::build(tcx, def_id),
451 param_env: tcx.param_env(def_id),
455 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
457 ItemKind::Struct(..) => Some(AdtKind::Struct),
458 ItemKind::Union(..) => Some(AdtKind::Union),
459 ItemKind::Enum(..) => Some(AdtKind::Enum),
464 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
465 fn check_type_defn<'tcx, F>(
467 item: &hir::Item<'tcx>,
469 mut lookup_fields: F,
471 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
473 for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
474 let variants = lookup_fields(fcx);
475 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
476 let packed = fcx.tcx.adt_def(def_id).repr.packed();
478 for variant in &variants {
479 // For DST, or when drop needs to copy things around, all
480 // intermediate types must be sized.
481 let needs_drop_copy = || {
483 let ty = variant.fields.last().unwrap().ty;
484 let ty = fcx.tcx.erase_regions(ty);
485 if ty.needs_infer() {
488 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
489 // Just treat unresolved type expression as if it needs drop.
492 ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
496 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
497 let unsized_len = if all_sized { 0 } else { 1 };
499 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
501 let last = idx == variant.fields.len() - 1;
504 fcx.tcx.require_lang_item(LangItem::Sized, None),
505 traits::ObligationCause::new(
509 adt_kind: match item_adt_kind(&item.kind) {
520 // All field types must be well-formed.
521 for field in &variant.fields {
522 fcx.register_wf_obligation(
525 ObligationCauseCode::MiscObligation,
529 // Explicit `enum` discriminant values must const-evaluate successfully.
530 if let Some(discr_def_id) = variant.explicit_discr {
532 InternalSubsts::identity_for_item(fcx.tcx, discr_def_id.to_def_id());
534 let cause = traits::ObligationCause::new(
535 fcx.tcx.def_span(discr_def_id),
537 traits::MiscObligation,
539 fcx.register_predicate(traits::Obligation::new(
542 ty::PredicateAtom::ConstEvaluatable(
543 ty::WithOptConstParam::unknown(discr_def_id.to_def_id()),
546 .to_predicate(fcx.tcx),
551 check_where_clauses(tcx, fcx, item.span, def_id.to_def_id(), None);
553 // No implied bounds in a struct definition.
558 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
559 debug!("check_trait: {:?}", item.hir_id);
561 let trait_def_id = tcx.hir().local_def_id(item.hir_id);
563 let trait_def = tcx.trait_def(trait_def_id);
564 if trait_def.is_marker
565 || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker)
567 for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
570 tcx.def_span(*associated_def_id),
572 "marker traits cannot have associated items",
578 for_item(tcx, item).with_fcx(|fcx, _| {
579 check_where_clauses(tcx, fcx, item.span, trait_def_id.to_def_id(), None);
585 /// Checks all associated type defaults of trait `trait_def_id`.
587 /// Assuming the defaults are used, check that all predicates (bounds on the
588 /// assoc type and where clauses on the trait) hold.
589 fn check_associated_type_bounds(fcx: &FnCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
592 let bounds = tcx.explicit_item_bounds(item.def_id);
594 debug!("check_associated_type_bounds: bounds={:?}", bounds);
595 let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
596 let normalized_bound = fcx.normalize_associated_types_in(span, bound);
597 traits::wf::predicate_obligations(
606 for obligation in wf_obligations {
607 debug!("next obligation cause: {:?}", obligation.cause);
608 fcx.register_predicate(obligation);
617 decl: &hir::FnDecl<'_>,
619 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
620 let def_id = fcx.tcx.hir().local_def_id(item_id);
621 let sig = fcx.tcx.fn_sig(def_id);
622 let sig = fcx.normalize_associated_types_in(span, sig);
623 let mut implied_bounds = vec![];
637 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
638 debug!("check_item_type: {:?}", item_id);
640 for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
641 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
642 let item_ty = fcx.normalize_associated_types_in(ty_span, ty);
644 let mut forbid_unsized = true;
645 if allow_foreign_ty {
646 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
647 if let ty::Foreign(_) = tail.kind() {
648 forbid_unsized = false;
652 fcx.register_wf_obligation(item_ty.into(), ty_span, ObligationCauseCode::MiscObligation);
656 fcx.tcx.require_lang_item(LangItem::Sized, None),
657 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
661 // No implied bounds in a const, etc.
668 item: &'tcx hir::Item<'tcx>,
669 ast_self_ty: &hir::Ty<'_>,
670 ast_trait_ref: &Option<hir::TraitRef<'_>>,
672 debug!("check_impl: {:?}", item);
674 for_item(tcx, item).with_fcx(|fcx, tcx| {
675 let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
677 match *ast_trait_ref {
678 Some(ref ast_trait_ref) => {
679 // `#[rustc_reservation_impl]` impls are not real impls and
680 // therefore don't need to be WF (the trait's `Self: Trait` predicate
682 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
684 fcx.normalize_associated_types_in(ast_trait_ref.path.span, trait_ref);
685 let obligations = traits::wf::trait_obligations(
690 ast_trait_ref.path.span,
693 for obligation in obligations {
694 fcx.register_predicate(obligation);
698 let self_ty = fcx.tcx.type_of(item_def_id);
699 let self_ty = fcx.normalize_associated_types_in(item.span, self_ty);
700 fcx.register_wf_obligation(
703 ObligationCauseCode::MiscObligation,
708 check_where_clauses(tcx, fcx, item.span, item_def_id.to_def_id(), None);
710 fcx.impl_implied_bounds(item_def_id.to_def_id(), item.span)
714 /// Checks where-clauses and inline bounds that are declared on `def_id`.
715 fn check_where_clauses<'tcx, 'fcx>(
717 fcx: &FnCtxt<'fcx, 'tcx>,
720 return_ty: Option<(Ty<'tcx>, Span)>,
722 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
724 let predicates = fcx.tcx.predicates_of(def_id);
725 let generics = tcx.generics_of(def_id);
727 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
728 GenericParamDefKind::Type { has_default, .. } => {
729 has_default && def.index >= generics.parent_count as u32
734 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
735 // For example, this forbids the declaration:
737 // struct Foo<T = Vec<[u32]>> { .. }
739 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
740 for param in &generics.params {
741 if let GenericParamDefKind::Type { .. } = param.kind {
742 if is_our_default(¶m) {
743 let ty = fcx.tcx.type_of(param.def_id);
744 // Ignore dependent defaults -- that is, where the default of one type
745 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
746 // be sure if it will error or not as user might always specify the other.
747 if !ty.needs_subst() {
748 fcx.register_wf_obligation(
750 fcx.tcx.def_span(param.def_id),
751 ObligationCauseCode::MiscObligation,
758 // Check that trait predicates are WF when params are substituted by their defaults.
759 // We don't want to overly constrain the predicates that may be written but we want to
760 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
761 // Therefore we check if a predicate which contains a single type param
762 // with a concrete default is WF with that default substituted.
763 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
765 // First we build the defaulted substitution.
766 let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
768 GenericParamDefKind::Lifetime => {
769 // All regions are identity.
770 fcx.tcx.mk_param_from_def(param)
773 GenericParamDefKind::Type { .. } => {
774 // If the param has a default, ...
775 if is_our_default(param) {
776 let default_ty = fcx.tcx.type_of(param.def_id);
777 // ... and it's not a dependent default, ...
778 if !default_ty.needs_subst() {
779 // ... then substitute it with the default.
780 return default_ty.into();
784 fcx.tcx.mk_param_from_def(param)
787 GenericParamDefKind::Const => {
788 // FIXME(const_generics:defaults)
789 fcx.tcx.mk_param_from_def(param)
794 // Now we build the substituted predicates.
795 let default_obligations = predicates
798 .flat_map(|&(pred, sp)| {
801 params: FxHashSet<u32>,
803 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
806 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
807 if let ty::Param(param) = t.kind() {
808 self.params.insert(param.index);
810 t.super_visit_with(self)
813 fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
817 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
818 if let ty::ConstKind::Param(param) = c.val {
819 self.params.insert(param.index);
821 c.super_visit_with(self)
824 let mut param_count = CountParams::default();
825 let has_region = pred.visit_with(&mut param_count).is_break();
826 let substituted_pred = pred.subst(fcx.tcx, substs);
827 // Don't check non-defaulted params, dependent defaults (including lifetimes)
828 // or preds with multiple params.
829 if substituted_pred.has_param_types_or_consts()
830 || param_count.params.len() > 1
834 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
835 // Avoid duplication of predicates that contain no parameters, for example.
838 Some((substituted_pred, sp))
842 // Convert each of those into an obligation. So if you have
843 // something like `struct Foo<T: Copy = String>`, we would
844 // take that predicate `T: Copy`, substitute to `String: Copy`
845 // (actually that happens in the previous `flat_map` call),
846 // and then try to prove it (in this case, we'll fail).
848 // Note the subtle difference from how we handle `predicates`
849 // below: there, we are not trying to prove those predicates
850 // to be *true* but merely *well-formed*.
851 let pred = fcx.normalize_associated_types_in(sp, pred);
853 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
854 traits::Obligation::new(cause, fcx.param_env, pred)
857 let predicates = predicates.instantiate_identity(fcx.tcx);
859 if let Some((mut return_ty, span)) = return_ty {
860 if return_ty.has_infer_types_or_consts() {
861 fcx.select_obligations_where_possible(false, |_| {});
862 return_ty = fcx.resolve_vars_if_possible(return_ty);
864 check_opaque_types(tcx, fcx, def_id.expect_local(), span, return_ty);
867 let predicates = fcx.normalize_associated_types_in(span, predicates);
869 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
870 assert_eq!(predicates.predicates.len(), predicates.spans.len());
872 predicates.predicates.iter().zip(predicates.spans.iter()).flat_map(|(&p, &sp)| {
873 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, sp)
876 for obligation in wf_obligations.chain(default_obligations) {
877 debug!("next obligation cause: {:?}", obligation.cause);
878 fcx.register_predicate(obligation);
882 fn check_fn_or_method<'fcx, 'tcx>(
884 fcx: &FnCtxt<'fcx, 'tcx>,
886 sig: ty::PolyFnSig<'tcx>,
887 hir_decl: &hir::FnDecl<'_>,
889 implied_bounds: &mut Vec<Ty<'tcx>>,
891 let sig = fcx.normalize_associated_types_in(span, sig);
892 let sig = fcx.tcx.liberate_late_bound_regions(def_id, sig);
894 for (&input_ty, span) in sig.inputs().iter().zip(hir_decl.inputs.iter().map(|t| t.span)) {
895 fcx.register_wf_obligation(input_ty.into(), span, ObligationCauseCode::MiscObligation);
897 implied_bounds.extend(sig.inputs());
899 fcx.register_wf_obligation(
901 hir_decl.output.span(),
902 ObligationCauseCode::ReturnType,
905 // FIXME(#25759) return types should not be implied bounds
906 implied_bounds.push(sig.output());
908 check_where_clauses(tcx, fcx, span, def_id, Some((sig.output(), hir_decl.output.span())));
911 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
912 /// laid for "higher-order pattern unification".
913 /// This ensures that inference is tractable.
914 /// In particular, definitions of opaque types can only use other generics as arguments,
915 /// and they cannot repeat an argument. Example:
918 /// type Foo<A, B> = impl Bar<A, B>;
920 /// // Okay -- `Foo` is applied to two distinct, generic types.
921 /// fn a<T, U>() -> Foo<T, U> { .. }
923 /// // Not okay -- `Foo` is applied to `T` twice.
924 /// fn b<T>() -> Foo<T, T> { .. }
926 /// // Not okay -- `Foo` is applied to a non-generic type.
927 /// fn b<T>() -> Foo<T, u32> { .. }
930 fn check_opaque_types<'fcx, 'tcx>(
932 fcx: &FnCtxt<'fcx, 'tcx>,
933 fn_def_id: LocalDefId,
937 trace!("check_opaque_types(ty={:?})", ty);
938 ty.fold_with(&mut ty::fold::BottomUpFolder {
941 if let ty::Opaque(def_id, substs) = *ty.kind() {
942 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
943 let generics = tcx.generics_of(def_id);
945 let opaque_hir_id = if let Some(local_id) = def_id.as_local() {
946 tcx.hir().local_def_id_to_hir_id(local_id)
948 // Opaque types from other crates won't have defining uses in this crate.
951 if let hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) =
952 tcx.hir().expect_item(opaque_hir_id).kind
954 // No need to check return position impl trait (RPIT)
955 // because for type and const parameters they are correct
956 // by construction: we convert
958 // fn foo<P0..Pn>() -> impl Trait
963 // fn foo<P0..Pn>() -> Foo<P0...Pn>.
965 // For lifetime parameters we convert
967 // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
971 // type foo::<'p0..'pn>::Foo<'q0..'qm>
972 // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
974 // which would error here on all of the `'static` args.
977 if !may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
980 trace!("check_opaque_types: may define, generics={:#?}", generics);
981 let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
982 for (i, arg) in substs.iter().enumerate() {
983 let arg_is_param = match arg.unpack() {
984 GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
986 GenericArgKind::Lifetime(region) => {
987 if let ty::ReStatic = region {
991 "non-defining opaque type use in defining scope",
994 tcx.def_span(generics.param_at(i, tcx).def_id),
995 "cannot use static lifetime; use a bound lifetime \
996 instead or remove the lifetime parameter from the \
1006 GenericArgKind::Const(ct) => matches!(ct.val, ty::ConstKind::Param(_)),
1010 seen_params.entry(arg).or_default().push(i);
1012 // Prevent `fn foo() -> Foo<u32>` from being defining.
1013 let opaque_param = generics.param_at(i, tcx);
1015 .struct_span_err(span, "non-defining opaque type use in defining scope")
1017 tcx.def_span(opaque_param.def_id),
1019 "used non-generic {} `{}` for generic parameter",
1020 opaque_param.kind.descr(),
1026 } // for (arg, param)
1028 for (_, indices) in seen_params {
1029 if indices.len() > 1 {
1030 let descr = generics.param_at(indices[0], tcx).kind.descr();
1031 let spans: Vec<_> = indices
1033 .map(|i| tcx.def_span(generics.param_at(i, tcx).def_id))
1036 .struct_span_err(span, "non-defining opaque type use in defining scope")
1037 .span_note(spans, &format!("{} used multiple times", descr))
1049 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
1050 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
1051 of the previous types except `Self`)";
1053 fn check_method_receiver<'fcx, 'tcx>(
1054 fcx: &FnCtxt<'fcx, 'tcx>,
1055 fn_sig: &hir::FnSig<'_>,
1056 method: &ty::AssocItem,
1059 // Check that the method has a valid receiver type, given the type `Self`.
1060 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
1062 if !method.fn_has_self_parameter {
1066 let span = fn_sig.decl.inputs[0].span;
1068 let sig = fcx.tcx.fn_sig(method.def_id);
1069 let sig = fcx.normalize_associated_types_in(span, sig);
1070 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, sig);
1072 debug!("check_method_receiver: sig={:?}", sig);
1074 let self_ty = fcx.normalize_associated_types_in(span, self_ty);
1075 let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, ty::Binder::bind(self_ty));
1077 let receiver_ty = sig.inputs()[0];
1079 let receiver_ty = fcx.normalize_associated_types_in(span, receiver_ty);
1081 fcx.tcx.liberate_late_bound_regions(method.def_id, ty::Binder::bind(receiver_ty));
1083 if fcx.tcx.features().arbitrary_self_types {
1084 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1085 // Report error; `arbitrary_self_types` was enabled.
1086 e0307(fcx, span, receiver_ty);
1089 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
1090 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
1091 // Report error; would have worked with `arbitrary_self_types`.
1093 &fcx.tcx.sess.parse_sess,
1094 sym::arbitrary_self_types,
1097 "`{}` cannot be used as the type of `self` without \
1098 the `arbitrary_self_types` feature",
1102 .help(HELP_FOR_SELF_TYPE)
1105 // Report error; would not have worked with `arbitrary_self_types`.
1106 e0307(fcx, span, receiver_ty);
1112 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
1114 fcx.tcx.sess.diagnostic(),
1117 "invalid `self` parameter type: {}",
1120 .note("type of `self` must be `Self` or a type that dereferences to it")
1121 .help(HELP_FOR_SELF_TYPE)
1125 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
1126 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
1127 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
1128 /// strict: `receiver_ty` must implement `Receiver` and directly implement
1129 /// `Deref<Target = self_ty>`.
1131 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
1132 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
1133 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
1134 fn receiver_is_valid<'fcx, 'tcx>(
1135 fcx: &FnCtxt<'fcx, 'tcx>,
1137 receiver_ty: Ty<'tcx>,
1139 arbitrary_self_types_enabled: bool,
1141 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
1143 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
1145 // `self: Self` is always valid.
1146 if can_eq_self(receiver_ty) {
1147 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
1153 let mut autoderef = fcx.autoderef(span, receiver_ty);
1155 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
1156 if arbitrary_self_types_enabled {
1157 autoderef = autoderef.include_raw_pointers();
1160 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
1163 let receiver_trait_def_id = fcx.tcx.require_lang_item(LangItem::Receiver, None);
1165 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
1167 if let Some((potential_self_ty, _)) = autoderef.next() {
1169 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
1170 potential_self_ty, self_ty
1173 if can_eq_self(potential_self_ty) {
1174 fcx.register_predicates(autoderef.into_obligations());
1176 if let Some(mut err) =
1177 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1184 // Without `feature(arbitrary_self_types)`, we require that each step in the
1185 // deref chain implement `receiver`
1186 if !arbitrary_self_types_enabled
1187 && !receiver_is_implemented(
1189 receiver_trait_def_id,
1198 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1199 // If he receiver already has errors reported due to it, consider it valid to avoid
1200 // unnecessary errors (#58712).
1201 return receiver_ty.references_error();
1205 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1206 if !arbitrary_self_types_enabled
1207 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1215 fn receiver_is_implemented(
1216 fcx: &FnCtxt<'_, 'tcx>,
1217 receiver_trait_def_id: DefId,
1218 cause: ObligationCause<'tcx>,
1219 receiver_ty: Ty<'tcx>,
1221 let trait_ref = ty::TraitRef {
1222 def_id: receiver_trait_def_id,
1223 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1226 let obligation = traits::Obligation::new(
1229 trait_ref.without_const().to_predicate(fcx.tcx),
1232 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1236 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1243 fn check_variances_for_type_defn<'tcx>(
1245 item: &hir::Item<'tcx>,
1246 hir_generics: &hir::Generics<'_>,
1248 let item_def_id = tcx.hir().local_def_id(item.hir_id);
1249 let ty = tcx.type_of(item_def_id);
1250 if tcx.has_error_field(ty) {
1254 let ty_predicates = tcx.predicates_of(item_def_id);
1255 assert_eq!(ty_predicates.parent, None);
1256 let variances = tcx.variances_of(item_def_id);
1258 let mut constrained_parameters: FxHashSet<_> = variances
1261 .filter(|&(_, &variance)| variance != ty::Bivariant)
1262 .map(|(index, _)| Parameter(index as u32))
1265 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1267 for (index, _) in variances.iter().enumerate() {
1268 if constrained_parameters.contains(&Parameter(index as u32)) {
1272 let param = &hir_generics.params[index];
1275 hir::ParamName::Error => {}
1276 _ => report_bivariance(tcx, param.span, param.name.ident().name),
1281 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) {
1282 let mut err = error_392(tcx, span, param_name);
1284 let suggested_marker_id = tcx.lang_items().phantom_data();
1285 // Help is available only in presence of lang items.
1286 let msg = if let Some(def_id) = suggested_marker_id {
1288 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1290 tcx.def_path_str(def_id),
1293 format!("consider removing `{}` or referring to it in a field", param_name)
1299 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1301 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1302 let empty_env = ty::ParamEnv::empty();
1304 let def_id = fcx.tcx.hir().local_def_id(id);
1305 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p);
1306 // Check elaborated bounds.
1307 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1309 for obligation in implied_obligations {
1310 let pred = obligation.predicate;
1311 // Match the existing behavior.
1312 if pred.is_global() && !pred.has_late_bound_regions() {
1313 let pred = fcx.normalize_associated_types_in(span, pred);
1314 let obligation = traits::Obligation::new(
1315 traits::ObligationCause::new(span, id, traits::TrivialBound),
1319 fcx.register_predicate(obligation);
1323 fcx.select_all_obligations_or_error();
1326 #[derive(Clone, Copy)]
1327 pub struct CheckTypeWellFormedVisitor<'tcx> {
1331 impl CheckTypeWellFormedVisitor<'tcx> {
1332 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1333 CheckTypeWellFormedVisitor { tcx }
1337 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1338 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1339 Visitor::visit_item(&mut self.clone(), i);
1342 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1343 Visitor::visit_trait_item(&mut self.clone(), trait_item);
1346 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1347 Visitor::visit_impl_item(&mut self.clone(), impl_item);
1350 fn visit_foreign_item(&self, foreign_item: &'tcx hir::ForeignItem<'tcx>) {
1351 Visitor::visit_foreign_item(&mut self.clone(), foreign_item)
1355 impl Visitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1356 type Map = hir_map::Map<'tcx>;
1358 fn nested_visit_map(&mut self) -> hir_visit::NestedVisitorMap<Self::Map> {
1359 hir_visit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
1362 fn visit_item(&mut self, i: &'tcx hir::Item<'tcx>) {
1363 debug!("visit_item: {:?}", i);
1364 let def_id = self.tcx.hir().local_def_id(i.hir_id);
1365 self.tcx.ensure().check_item_well_formed(def_id);
1366 hir_visit::walk_item(self, i);
1369 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1370 debug!("visit_trait_item: {:?}", trait_item);
1371 let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1372 self.tcx.ensure().check_trait_item_well_formed(def_id);
1373 hir_visit::walk_trait_item(self, trait_item);
1376 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1377 debug!("visit_impl_item: {:?}", impl_item);
1378 let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1379 self.tcx.ensure().check_impl_item_well_formed(def_id);
1380 hir_visit::walk_impl_item(self, impl_item);
1383 fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
1384 check_param_wf(self.tcx, p);
1385 hir_visit::walk_generic_param(self, p);
1389 ///////////////////////////////////////////////////////////////////////////
1392 // FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`.
1393 struct AdtVariant<'tcx> {
1394 /// Types of fields in the variant, that must be well-formed.
1395 fields: Vec<AdtField<'tcx>>,
1397 /// Explicit discriminant of this variant (e.g. `A = 123`),
1398 /// that must evaluate to a constant value.
1399 explicit_discr: Option<LocalDefId>,
1402 struct AdtField<'tcx> {
1407 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1408 // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`.
1409 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1410 let fields = struct_def
1414 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1415 let field_ty = self.normalize_associated_types_in(field.ty.span, field_ty);
1416 let field_ty = self.resolve_vars_if_possible(field_ty);
1417 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1418 AdtField { ty: field_ty, span: field.ty.span }
1421 AdtVariant { fields, explicit_discr: None }
1424 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1428 .map(|variant| AdtVariant {
1429 fields: self.non_enum_variant(&variant.data).fields,
1430 explicit_discr: variant
1432 .map(|explicit_discr| self.tcx.hir().local_def_id(explicit_discr.hir_id)),
1437 pub(super) fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1438 match self.tcx.impl_trait_ref(impl_def_id) {
1439 Some(trait_ref) => {
1440 // Trait impl: take implied bounds from all types that
1441 // appear in the trait reference.
1442 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1443 trait_ref.substs.types().collect()
1447 // Inherent impl: take implied bounds from the `self` type.
1448 let self_ty = self.tcx.type_of(impl_def_id);
1449 let self_ty = self.normalize_associated_types_in(span, self_ty);
1456 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: Symbol) -> DiagnosticBuilder<'_> {
1458 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1459 err.span_label(span, "unused parameter");