1 use crate::check::{FnCtxt, Inherited};
2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
4 use rustc::infer::opaque_types::may_define_opaque_type;
5 use rustc::middle::lang_items;
6 use rustc::session::parse::feature_err;
7 use rustc::traits::{self, ObligationCause, ObligationCauseCode};
8 use rustc::ty::subst::{InternalSubsts, Subst};
10 self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
12 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
13 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
14 use rustc_hir::def_id::DefId;
15 use rustc_hir::ItemKind;
16 use rustc_span::symbol::{sym, Ident};
21 use rustc_hir::itemlikevisit::ParItemLikeVisitor;
23 /// Helper type of a temporary returned by `.for_item(...)`.
24 /// This is necessary because we can't write the following bound:
27 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
29 struct CheckWfFcxBuilder<'tcx> {
30 inherited: super::InheritedBuilder<'tcx>,
33 param_env: ty::ParamEnv<'tcx>,
36 impl<'tcx> CheckWfFcxBuilder<'tcx> {
37 fn with_fcx<F>(&mut self, f: F)
39 F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
43 let param_env = self.param_env;
44 self.inherited.enter(|inh| {
45 let fcx = FnCtxt::new(&inh, param_env, id);
46 if !inh.tcx.features().trivial_bounds {
47 // As predicates are cached rather than obligations, this
48 // needsto be called first so that they are checked with an
50 check_false_global_bounds(&fcx, span, id);
52 let wf_tys = f(&fcx, fcx.tcx);
53 fcx.select_all_obligations_or_error();
54 fcx.regionck_item(id, span, &wf_tys);
59 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
60 /// well-formed, meaning that they do not require any constraints not declared in the struct
61 /// definition itself. For example, this definition would be illegal:
64 /// struct Ref<'a, T> { x: &'a T }
67 /// because the type did not declare that `T:'a`.
69 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
70 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
72 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: DefId) {
73 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
74 let item = tcx.hir().expect_item(hir_id);
77 "check_item_well_formed(it.hir_id={:?}, it.name={})",
79 tcx.def_path_str(def_id)
83 // Right now we check that every default trait implementation
84 // has an implementation of itself. Basically, a case like:
86 // impl Trait for T {}
88 // has a requirement of `T: Trait` which was required for default
89 // method implementations. Although this could be improved now that
90 // there's a better infrastructure in place for this, it's being left
91 // for a follow-up work.
93 // Since there's such a requirement, we need to check *just* positive
94 // implementations, otherwise things like:
96 // impl !Send for T {}
98 // won't be allowed unless there's an *explicit* implementation of `Send`
100 hir::ItemKind::Impl { defaultness, ref of_trait, ref self_ty, .. } => {
102 .impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
103 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
104 let polarity = tcx.impl_polarity(def_id);
105 if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
106 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
109 ty::ImplPolarity::Positive => {
110 check_impl(tcx, item, self_ty, of_trait);
112 ty::ImplPolarity::Negative => {
113 // FIXME(#27579): what amount of WF checking do we need for neg impls?
114 if of_trait.is_some() && !is_auto {
119 "negative impls are only allowed for \
120 auto traits (e.g., `Send` and `Sync`)"
125 ty::ImplPolarity::Reservation => {
126 // FIXME: what amount of WF checking do we need for reservation impls?
130 hir::ItemKind::Fn(..) => {
131 check_item_fn(tcx, item);
133 hir::ItemKind::Static(ref ty, ..) => {
134 check_item_type(tcx, item.hir_id, ty.span, false);
136 hir::ItemKind::Const(ref ty, ..) => {
137 check_item_type(tcx, item.hir_id, ty.span, false);
139 hir::ItemKind::ForeignMod(ref module) => {
140 for it in module.items.iter() {
141 if let hir::ForeignItemKind::Static(ref ty, ..) = it.kind {
142 check_item_type(tcx, it.hir_id, ty.span, true);
146 hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
147 check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
149 check_variances_for_type_defn(tcx, item, ast_generics);
151 hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
152 check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
154 check_variances_for_type_defn(tcx, item, ast_generics);
156 hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
157 check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
159 check_variances_for_type_defn(tcx, item, ast_generics);
161 hir::ItemKind::Trait(..) => {
162 check_trait(tcx, item);
164 hir::ItemKind::TraitAlias(..) => {
165 check_trait(tcx, item);
171 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: DefId) {
172 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
173 let trait_item = tcx.hir().expect_trait_item(hir_id);
175 let method_sig = match trait_item.kind {
176 hir::TraitItemKind::Method(ref sig, _) => Some(sig),
179 check_bare_self_trait_by_name(tcx, &trait_item);
180 check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
183 fn could_be_self(trait_name: Ident, ty: &hir::Ty<'_>) -> bool {
185 hir::TyKind::TraitObject([trait_ref], ..) => {
186 let mut p = trait_ref.trait_ref.path.segments.iter().map(|s| s.ident);
187 match (p.next(), p.next()) {
188 (Some(ident), None) => ident == trait_name,
196 /// Detect when an object unsafe trait is referring to itself in one of its associated items.
197 /// When this is done, suggest using `Self` instead.
198 fn check_bare_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) {
199 let (trait_name, trait_def_id) = match tcx.hir().get(tcx.hir().get_parent_item(item.hir_id)) {
200 hir::Node::Item(item) => match item.kind {
201 hir::ItemKind::Trait(..) => (item.ident, tcx.hir().local_def_id(item.hir_id)),
206 let mut trait_should_be_self = vec![];
208 hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty))
209 if could_be_self(trait_name, ty) =>
211 trait_should_be_self.push(ty.span)
213 hir::TraitItemKind::Method(sig, _) => {
214 for ty in sig.decl.inputs {
215 if could_be_self(trait_name, ty) {
216 trait_should_be_self.push(ty.span);
219 match sig.decl.output {
220 hir::FunctionRetTy::Return(ty) if could_be_self(trait_name, ty) => {
221 trait_should_be_self.push(ty.span);
228 if !trait_should_be_self.is_empty() {
229 if rustc::traits::object_safety_violations(tcx, trait_def_id).is_empty() {
232 let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect();
233 let mut err = tcx.sess.struct_span_err(
234 trait_should_be_self,
235 "associated item referring to unboxed trait object for its own trait",
237 err.span_label(trait_name.span, "in this trait");
238 err.multipart_suggestion(
239 "you might have meant to use `Self` to refer to the materialized type",
241 Applicability::MachineApplicable,
247 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: DefId) {
248 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
249 let impl_item = tcx.hir().expect_impl_item(hir_id);
251 let method_sig = match impl_item.kind {
252 hir::ImplItemKind::Method(ref sig, _) => Some(sig),
256 check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
259 fn check_associated_item(
263 sig_if_method: Option<&hir::FnSig<'_>>,
265 debug!("check_associated_item: {:?}", item_id);
267 let code = ObligationCauseCode::MiscObligation;
268 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
269 let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
271 let (mut implied_bounds, self_ty) = match item.container {
272 ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
273 ty::ImplContainer(def_id) => {
274 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
279 ty::AssocKind::Const => {
280 let ty = fcx.tcx.type_of(item.def_id);
281 let ty = fcx.normalize_associated_types_in(span, &ty);
282 fcx.register_wf_obligation(ty, span, code.clone());
284 ty::AssocKind::Method => {
285 let sig = fcx.tcx.fn_sig(item.def_id);
286 let sig = fcx.normalize_associated_types_in(span, &sig);
287 let hir_sig = sig_if_method.expect("bad signature for method");
297 check_method_receiver(fcx, hir_sig, &item, self_ty);
299 ty::AssocKind::Type => {
300 if item.defaultness.has_value() {
301 let ty = fcx.tcx.type_of(item.def_id);
302 let ty = fcx.normalize_associated_types_in(span, &ty);
303 fcx.register_wf_obligation(ty, span, code.clone());
306 ty::AssocKind::OpaqueTy => {
307 // Do nothing: opaque types check themselves.
315 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
316 for_id(tcx, item.hir_id, item.span)
319 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
320 let def_id = tcx.hir().local_def_id(id);
322 inherited: Inherited::build(tcx, def_id),
325 param_env: tcx.param_env(def_id),
329 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
331 ItemKind::Struct(..) => Some(AdtKind::Struct),
332 ItemKind::Union(..) => Some(AdtKind::Union),
333 ItemKind::Enum(..) => Some(AdtKind::Enum),
338 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
339 fn check_type_defn<'tcx, F>(
341 item: &hir::Item<'tcx>,
343 mut lookup_fields: F,
345 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
347 for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
348 let variants = lookup_fields(fcx);
349 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
350 let packed = fcx.tcx.adt_def(def_id).repr.packed();
352 for variant in &variants {
353 // For DST, or when drop needs to copy things around, all
354 // intermediate types must be sized.
355 let needs_drop_copy = || {
357 let ty = variant.fields.last().unwrap().ty;
358 let ty = fcx.tcx.erase_regions(&ty);
359 if ty.has_local_value() {
362 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
363 // Just treat unresolved type expression as if it needs drop.
366 ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
370 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
371 let unsized_len = if all_sized { 0 } else { 1 };
373 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
375 let last = idx == variant.fields.len() - 1;
378 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
379 traits::ObligationCause::new(
383 adt_kind: match item_adt_kind(&item.kind) {
393 // All field types must be well-formed.
394 for field in &variant.fields {
395 fcx.register_wf_obligation(
398 ObligationCauseCode::MiscObligation,
403 check_where_clauses(tcx, fcx, item.span, def_id, None);
405 // No implied bounds in a struct definition.
410 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
411 debug!("check_trait: {:?}", item.hir_id);
413 let trait_def_id = tcx.hir().local_def_id(item.hir_id);
415 let trait_def = tcx.trait_def(trait_def_id);
416 if trait_def.is_marker {
417 for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
420 tcx.def_span(*associated_def_id),
422 "marker traits cannot have associated items",
428 for_item(tcx, item).with_fcx(|fcx, _| {
429 check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
434 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
435 for_item(tcx, item).with_fcx(|fcx, tcx| {
436 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
437 let sig = fcx.tcx.fn_sig(def_id);
438 let sig = fcx.normalize_associated_types_in(item.span, &sig);
439 let mut implied_bounds = vec![];
440 let hir_sig = match &item.kind {
441 ItemKind::Fn(sig, ..) => sig,
442 _ => bug!("expected `ItemKind::Fn`, found `{:?}`", item.kind),
444 check_fn_or_method(tcx, fcx, item.ident.span, sig, hir_sig, def_id, &mut implied_bounds);
449 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
450 debug!("check_item_type: {:?}", item_id);
452 for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
453 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
454 let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
456 let mut forbid_unsized = true;
457 if allow_foreign_ty {
458 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
459 if let ty::Foreign(_) = tail.kind {
460 forbid_unsized = false;
464 fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
468 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
469 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
473 // No implied bounds in a const, etc.
480 item: &'tcx hir::Item<'tcx>,
481 ast_self_ty: &hir::Ty<'_>,
482 ast_trait_ref: &Option<hir::TraitRef<'_>>,
484 debug!("check_impl: {:?}", item);
486 for_item(tcx, item).with_fcx(|fcx, tcx| {
487 let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
489 match *ast_trait_ref {
490 Some(ref ast_trait_ref) => {
491 // `#[rustc_reservation_impl]` impls are not real impls and
492 // therefore don't need to be WF (the trait's `Self: Trait` predicate
494 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
496 fcx.normalize_associated_types_in(ast_trait_ref.path.span, &trait_ref);
497 let obligations = traits::wf::trait_obligations(
502 ast_trait_ref.path.span,
505 for obligation in obligations {
506 fcx.register_predicate(obligation);
510 let self_ty = fcx.tcx.type_of(item_def_id);
511 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
512 fcx.register_wf_obligation(
515 ObligationCauseCode::MiscObligation,
520 check_where_clauses(tcx, fcx, item.span, item_def_id, None);
522 fcx.impl_implied_bounds(item_def_id, item.span)
526 /// Checks where-clauses and inline bounds that are declared on `def_id`.
527 fn check_where_clauses<'tcx, 'fcx>(
529 fcx: &FnCtxt<'fcx, 'tcx>,
532 return_ty: Option<Ty<'tcx>>,
534 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
536 let predicates = fcx.tcx.predicates_of(def_id);
537 let generics = tcx.generics_of(def_id);
539 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
540 GenericParamDefKind::Type { has_default, .. } => {
541 has_default && def.index >= generics.parent_count as u32
546 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
547 // For example, this forbids the declaration:
549 // struct Foo<T = Vec<[u32]>> { .. }
551 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
552 for param in &generics.params {
553 if let GenericParamDefKind::Type { .. } = param.kind {
554 if is_our_default(¶m) {
555 let ty = fcx.tcx.type_of(param.def_id);
556 // Ignore dependent defaults -- that is, where the default of one type
557 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
558 // be sure if it will error or not as user might always specify the other.
559 if !ty.needs_subst() {
560 fcx.register_wf_obligation(
562 fcx.tcx.def_span(param.def_id),
563 ObligationCauseCode::MiscObligation,
570 // Check that trait predicates are WF when params are substituted by their defaults.
571 // We don't want to overly constrain the predicates that may be written but we want to
572 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
573 // Therefore we check if a predicate which contains a single type param
574 // with a concrete default is WF with that default substituted.
575 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
577 // First we build the defaulted substitution.
578 let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
580 GenericParamDefKind::Lifetime => {
581 // All regions are identity.
582 fcx.tcx.mk_param_from_def(param)
585 GenericParamDefKind::Type { .. } => {
586 // If the param has a default, ...
587 if is_our_default(param) {
588 let default_ty = fcx.tcx.type_of(param.def_id);
589 // ... and it's not a dependent default, ...
590 if !default_ty.needs_subst() {
591 // ... then substitute it with the default.
592 return default_ty.into();
595 // Mark unwanted params as error.
596 fcx.tcx.types.err.into()
599 GenericParamDefKind::Const => {
600 // FIXME(const_generics:defaults)
601 fcx.tcx.consts.err.into()
606 // Now we build the substituted predicates.
607 let default_obligations = predicates
610 .flat_map(|&(pred, sp)| {
613 params: FxHashSet<u32>,
615 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
616 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
617 if let ty::Param(param) = t.kind {
618 self.params.insert(param.index);
620 t.super_visit_with(self)
623 fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
627 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
628 if let ty::ConstKind::Param(param) = c.val {
629 self.params.insert(param.index);
631 c.super_visit_with(self)
634 let mut param_count = CountParams::default();
635 let has_region = pred.visit_with(&mut param_count);
636 let substituted_pred = pred.subst(fcx.tcx, substs);
637 // Don't check non-defaulted params, dependent defaults (including lifetimes)
638 // or preds with multiple params.
639 if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
641 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
642 // Avoid duplication of predicates that contain no parameters, for example.
645 Some((substituted_pred, sp))
649 // Convert each of those into an obligation. So if you have
650 // something like `struct Foo<T: Copy = String>`, we would
651 // take that predicate `T: Copy`, substitute to `String: Copy`
652 // (actually that happens in the previous `flat_map` call),
653 // and then try to prove it (in this case, we'll fail).
655 // Note the subtle difference from how we handle `predicates`
656 // below: there, we are not trying to prove those predicates
657 // to be *true* but merely *well-formed*.
658 let pred = fcx.normalize_associated_types_in(sp, &pred);
660 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
661 traits::Obligation::new(cause, fcx.param_env, pred)
664 let mut predicates = predicates.instantiate_identity(fcx.tcx);
666 if let Some(return_ty) = return_ty {
667 predicates.predicates.extend(check_opaque_types(tcx, fcx, def_id, span, return_ty));
670 let predicates = fcx.normalize_associated_types_in(span, &predicates);
672 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
673 let wf_obligations = predicates
676 .flat_map(|p| traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, span));
678 for obligation in wf_obligations.chain(default_obligations) {
679 debug!("next obligation cause: {:?}", obligation.cause);
680 fcx.register_predicate(obligation);
684 fn check_fn_or_method<'fcx, 'tcx>(
686 fcx: &FnCtxt<'fcx, 'tcx>,
688 sig: ty::PolyFnSig<'tcx>,
689 hir_sig: &hir::FnSig<'_>,
691 implied_bounds: &mut Vec<Ty<'tcx>>,
693 let sig = fcx.normalize_associated_types_in(span, &sig);
694 let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
696 for (input_ty, span) in sig.inputs().iter().zip(hir_sig.decl.inputs.iter().map(|t| t.span)) {
697 fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
699 implied_bounds.extend(sig.inputs());
701 fcx.register_wf_obligation(
703 hir_sig.decl.output.span(),
704 ObligationCauseCode::ReturnType,
707 // FIXME(#25759) return types should not be implied bounds
708 implied_bounds.push(sig.output());
710 check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
713 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
714 /// laid for "higher-order pattern unification".
715 /// This ensures that inference is tractable.
716 /// In particular, definitions of opaque types can only use other generics as arguments,
717 /// and they cannot repeat an argument. Example:
720 /// type Foo<A, B> = impl Bar<A, B>;
722 /// // Okay -- `Foo` is applied to two distinct, generic types.
723 /// fn a<T, U>() -> Foo<T, U> { .. }
725 /// // Not okay -- `Foo` is applied to `T` twice.
726 /// fn b<T>() -> Foo<T, T> { .. }
728 /// // Not okay -- `Foo` is applied to a non-generic type.
729 /// fn b<T>() -> Foo<T, u32> { .. }
732 fn check_opaque_types<'fcx, 'tcx>(
734 fcx: &FnCtxt<'fcx, 'tcx>,
738 ) -> Vec<ty::Predicate<'tcx>> {
739 trace!("check_opaque_types(ty={:?})", ty);
740 let mut substituted_predicates = Vec::new();
741 ty.fold_with(&mut ty::fold::BottomUpFolder {
744 if let ty::Opaque(def_id, substs) = ty.kind {
745 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
746 let generics = tcx.generics_of(def_id);
747 // Only check named `impl Trait` types defined in this crate.
748 if generics.parent.is_none() && def_id.is_local() {
749 let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
750 if may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
751 trace!("check_opaque_types: may define, generics={:#?}", generics);
752 let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
753 for (subst, param) in substs.iter().zip(&generics.params) {
754 match subst.unpack() {
755 ty::subst::GenericArgKind::Type(ty) => match ty.kind {
757 // Prevent `fn foo() -> Foo<u32>` from being defining.
762 "non-defining opaque type use \
766 tcx.def_span(param.def_id),
768 "used non-generic type {} for \
777 ty::subst::GenericArgKind::Lifetime(region) => {
778 let param_span = tcx.def_span(param.def_id);
779 if let ty::ReStatic = region {
783 "non-defining opaque type use \
788 "cannot use static lifetime; use a bound lifetime \
789 instead or remove the lifetime parameter from the \
794 seen.entry(region).or_default().push(param_span);
798 ty::subst::GenericArgKind::Const(ct) => match ct.val {
799 ty::ConstKind::Param(_) => {}
804 "non-defining opaque type use \
808 tcx.def_span(param.def_id),
810 "used non-generic const {} for \
819 } // for (subst, param)
820 for (_, spans) in seen {
825 "non-defining opaque type use \
828 .span_note(spans, "lifetime used multiple times")
832 } // if may_define_opaque_type
834 // Now register the bounds on the parameters of the opaque type
835 // so the parameters given by the function need to fulfill them.
837 // type Foo<T: Bar> = impl Baz + 'static;
838 // fn foo<U>() -> Foo<U> { .. *}
842 // type Foo<T: Bar> = impl Baz + 'static;
843 // fn foo<U: Bar>() -> Foo<U> { .. *}
844 let predicates = tcx.predicates_of(def_id);
845 trace!("check_opaque_types: may define, predicates={:#?}", predicates,);
846 for &(pred, _) in predicates.predicates {
847 let substituted_pred = pred.subst(fcx.tcx, substs);
848 // Avoid duplication of predicates that contain no parameters, for example.
849 if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
850 substituted_predicates.push(substituted_pred);
853 } // if is_named_opaque_type
860 substituted_predicates
863 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
864 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
865 of the previous types except `Self`)";
867 fn check_method_receiver<'fcx, 'tcx>(
868 fcx: &FnCtxt<'fcx, 'tcx>,
869 fn_sig: &hir::FnSig<'_>,
870 method: &ty::AssocItem,
873 // Check that the method has a valid receiver type, given the type `Self`.
874 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
876 if !method.method_has_self_argument {
880 let span = fn_sig.decl.inputs[0].span;
882 let sig = fcx.tcx.fn_sig(method.def_id);
883 let sig = fcx.normalize_associated_types_in(span, &sig);
884 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
886 debug!("check_method_receiver: sig={:?}", sig);
888 let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
889 let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_ty));
891 let receiver_ty = sig.inputs()[0];
893 let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
895 fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(receiver_ty));
897 if fcx.tcx.features().arbitrary_self_types {
898 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
899 // Report error; `arbitrary_self_types` was enabled.
900 e0307(fcx, span, receiver_ty);
903 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
904 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
905 // Report error; would have worked with `arbitrary_self_types`.
907 &fcx.tcx.sess.parse_sess,
908 sym::arbitrary_self_types,
911 "`{}` cannot be used as the type of `self` without \
912 the `arbitrary_self_types` feature",
916 .help(HELP_FOR_SELF_TYPE)
919 // Report error; would not have worked with `arbitrary_self_types`.
920 e0307(fcx, span, receiver_ty);
926 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
928 fcx.tcx.sess.diagnostic(),
931 "invalid `self` parameter type: {:?}",
934 .note("type of `self` must be `Self` or a type that dereferences to it")
935 .help(HELP_FOR_SELF_TYPE)
939 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
940 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
941 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
942 /// strict: `receiver_ty` must implement `Receiver` and directly implement
943 /// `Deref<Target = self_ty>`.
945 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
946 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
947 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
948 fn receiver_is_valid<'fcx, 'tcx>(
949 fcx: &FnCtxt<'fcx, 'tcx>,
951 receiver_ty: Ty<'tcx>,
953 arbitrary_self_types_enabled: bool,
955 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
957 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
959 // `self: Self` is always valid.
960 if can_eq_self(receiver_ty) {
961 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
967 let mut autoderef = fcx.autoderef(span, receiver_ty);
969 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
970 if arbitrary_self_types_enabled {
971 autoderef = autoderef.include_raw_pointers();
974 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
977 let receiver_trait_def_id = fcx.tcx.require_lang_item(lang_items::ReceiverTraitLangItem, None);
979 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
981 if let Some((potential_self_ty, _)) = autoderef.next() {
983 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
984 potential_self_ty, self_ty
987 if can_eq_self(potential_self_ty) {
988 autoderef.finalize(fcx);
990 if let Some(mut err) =
991 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
998 // Without `feature(arbitrary_self_types)`, we require that each step in the
999 // deref chain implement `receiver`
1000 if !arbitrary_self_types_enabled
1001 && !receiver_is_implemented(
1003 receiver_trait_def_id,
1012 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1013 // If he receiver already has errors reported due to it, consider it valid to avoid
1014 // unnecessary errors (#58712).
1015 return receiver_ty.references_error();
1019 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1020 if !arbitrary_self_types_enabled
1021 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1029 fn receiver_is_implemented(
1030 fcx: &FnCtxt<'_, 'tcx>,
1031 receiver_trait_def_id: DefId,
1032 cause: ObligationCause<'tcx>,
1033 receiver_ty: Ty<'tcx>,
1035 let trait_ref = ty::TraitRef {
1036 def_id: receiver_trait_def_id,
1037 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1041 traits::Obligation::new(cause, fcx.param_env, trait_ref.without_const().to_predicate());
1043 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1047 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1054 fn check_variances_for_type_defn<'tcx>(
1056 item: &hir::Item<'tcx>,
1057 hir_generics: &hir::Generics<'_>,
1059 let item_def_id = tcx.hir().local_def_id(item.hir_id);
1060 let ty = tcx.type_of(item_def_id);
1061 if tcx.has_error_field(ty) {
1065 let ty_predicates = tcx.predicates_of(item_def_id);
1066 assert_eq!(ty_predicates.parent, None);
1067 let variances = tcx.variances_of(item_def_id);
1069 let mut constrained_parameters: FxHashSet<_> = variances
1072 .filter(|&(_, &variance)| variance != ty::Bivariant)
1073 .map(|(index, _)| Parameter(index as u32))
1076 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1078 for (index, _) in variances.iter().enumerate() {
1079 if constrained_parameters.contains(&Parameter(index as u32)) {
1083 let param = &hir_generics.params[index];
1086 hir::ParamName::Error => {}
1087 _ => report_bivariance(tcx, param.span, param.name.ident().name),
1092 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
1093 let mut err = error_392(tcx, span, param_name);
1095 let suggested_marker_id = tcx.lang_items().phantom_data();
1096 // Help is available only in presence of lang items.
1097 let msg = if let Some(def_id) = suggested_marker_id {
1099 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1101 tcx.def_path_str(def_id),
1104 format!("consider removing `{}` or referring to it in a field", param_name)
1110 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1112 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1113 let empty_env = ty::ParamEnv::empty();
1115 let def_id = fcx.tcx.hir().local_def_id(id);
1116 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p).collect();
1117 // Check elaborated bounds.
1118 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1120 for pred in implied_obligations {
1121 // Match the existing behavior.
1122 if pred.is_global() && !pred.has_late_bound_regions() {
1123 let pred = fcx.normalize_associated_types_in(span, &pred);
1124 let obligation = traits::Obligation::new(
1125 traits::ObligationCause::new(span, id, traits::TrivialBound),
1129 fcx.register_predicate(obligation);
1133 fcx.select_all_obligations_or_error();
1136 pub struct CheckTypeWellFormedVisitor<'tcx> {
1140 impl CheckTypeWellFormedVisitor<'tcx> {
1141 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1142 CheckTypeWellFormedVisitor { tcx }
1146 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1147 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1148 debug!("visit_item: {:?}", i);
1149 let def_id = self.tcx.hir().local_def_id(i.hir_id);
1150 self.tcx.ensure().check_item_well_formed(def_id);
1153 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1154 debug!("visit_trait_item: {:?}", trait_item);
1155 let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1156 self.tcx.ensure().check_trait_item_well_formed(def_id);
1159 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1160 debug!("visit_impl_item: {:?}", impl_item);
1161 let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1162 self.tcx.ensure().check_impl_item_well_formed(def_id);
1166 ///////////////////////////////////////////////////////////////////////////
1169 struct AdtVariant<'tcx> {
1170 fields: Vec<AdtField<'tcx>>,
1173 struct AdtField<'tcx> {
1178 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1179 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1180 let fields = struct_def
1184 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1185 let field_ty = self.normalize_associated_types_in(field.span, &field_ty);
1186 let field_ty = self.resolve_vars_if_possible(&field_ty);
1187 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1188 AdtField { ty: field_ty, span: field.span }
1191 AdtVariant { fields }
1194 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1195 enum_def.variants.iter().map(|variant| self.non_enum_variant(&variant.data)).collect()
1198 fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1199 match self.tcx.impl_trait_ref(impl_def_id) {
1200 Some(ref trait_ref) => {
1201 // Trait impl: take implied bounds from all types that
1202 // appear in the trait reference.
1203 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1204 trait_ref.substs.types().collect()
1208 // Inherent impl: take implied bounds from the `self` type.
1209 let self_ty = self.tcx.type_of(impl_def_id);
1210 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1217 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) -> DiagnosticBuilder<'_> {
1219 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1220 err.span_label(span, "unused parameter");