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_object_unsafe_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_object_unsafe_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();
235 trait_should_be_self,
236 "associated item referring to unboxed trait object for its own trait",
238 .span_label(trait_name.span, "in this trait")
239 .multipart_suggestion(
240 "you might have meant to use `Self` to refer to the implementing type",
242 Applicability::MachineApplicable,
248 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: DefId) {
249 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
250 let impl_item = tcx.hir().expect_impl_item(hir_id);
252 let method_sig = match impl_item.kind {
253 hir::ImplItemKind::Method(ref sig, _) => Some(sig),
257 check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
260 fn check_associated_item(
264 sig_if_method: Option<&hir::FnSig<'_>>,
266 debug!("check_associated_item: {:?}", item_id);
268 let code = ObligationCauseCode::MiscObligation;
269 for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
270 let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
272 let (mut implied_bounds, self_ty) = match item.container {
273 ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
274 ty::ImplContainer(def_id) => {
275 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
280 ty::AssocKind::Const => {
281 let ty = fcx.tcx.type_of(item.def_id);
282 let ty = fcx.normalize_associated_types_in(span, &ty);
283 fcx.register_wf_obligation(ty, span, code.clone());
285 ty::AssocKind::Method => {
286 let sig = fcx.tcx.fn_sig(item.def_id);
287 let sig = fcx.normalize_associated_types_in(span, &sig);
288 let hir_sig = sig_if_method.expect("bad signature for method");
298 check_method_receiver(fcx, hir_sig, &item, self_ty);
300 ty::AssocKind::Type => {
301 if item.defaultness.has_value() {
302 let ty = fcx.tcx.type_of(item.def_id);
303 let ty = fcx.normalize_associated_types_in(span, &ty);
304 fcx.register_wf_obligation(ty, span, code.clone());
307 ty::AssocKind::OpaqueTy => {
308 // Do nothing: opaque types check themselves.
316 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
317 for_id(tcx, item.hir_id, item.span)
320 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
321 let def_id = tcx.hir().local_def_id(id);
323 inherited: Inherited::build(tcx, def_id),
326 param_env: tcx.param_env(def_id),
330 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
332 ItemKind::Struct(..) => Some(AdtKind::Struct),
333 ItemKind::Union(..) => Some(AdtKind::Union),
334 ItemKind::Enum(..) => Some(AdtKind::Enum),
339 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
340 fn check_type_defn<'tcx, F>(
342 item: &hir::Item<'tcx>,
344 mut lookup_fields: F,
346 F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
348 for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
349 let variants = lookup_fields(fcx);
350 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
351 let packed = fcx.tcx.adt_def(def_id).repr.packed();
353 for variant in &variants {
354 // For DST, or when drop needs to copy things around, all
355 // intermediate types must be sized.
356 let needs_drop_copy = || {
358 let ty = variant.fields.last().unwrap().ty;
359 let ty = fcx.tcx.erase_regions(&ty);
360 if ty.has_local_value() {
363 .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
364 // Just treat unresolved type expression as if it needs drop.
367 ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
371 let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
372 let unsized_len = if all_sized { 0 } else { 1 };
374 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
376 let last = idx == variant.fields.len() - 1;
379 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
380 traits::ObligationCause::new(
384 adt_kind: match item_adt_kind(&item.kind) {
394 // All field types must be well-formed.
395 for field in &variant.fields {
396 fcx.register_wf_obligation(
399 ObligationCauseCode::MiscObligation,
404 check_where_clauses(tcx, fcx, item.span, def_id, None);
406 // No implied bounds in a struct definition.
411 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
412 debug!("check_trait: {:?}", item.hir_id);
414 let trait_def_id = tcx.hir().local_def_id(item.hir_id);
416 let trait_def = tcx.trait_def(trait_def_id);
417 if trait_def.is_marker {
418 for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
421 tcx.def_span(*associated_def_id),
423 "marker traits cannot have associated items",
429 for_item(tcx, item).with_fcx(|fcx, _| {
430 check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
435 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
436 for_item(tcx, item).with_fcx(|fcx, tcx| {
437 let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
438 let sig = fcx.tcx.fn_sig(def_id);
439 let sig = fcx.normalize_associated_types_in(item.span, &sig);
440 let mut implied_bounds = vec![];
441 let hir_sig = match &item.kind {
442 ItemKind::Fn(sig, ..) => sig,
443 _ => bug!("expected `ItemKind::Fn`, found `{:?}`", item.kind),
445 check_fn_or_method(tcx, fcx, item.ident.span, sig, hir_sig, def_id, &mut implied_bounds);
450 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
451 debug!("check_item_type: {:?}", item_id);
453 for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
454 let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
455 let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
457 let mut forbid_unsized = true;
458 if allow_foreign_ty {
459 let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
460 if let ty::Foreign(_) = tail.kind {
461 forbid_unsized = false;
465 fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
469 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
470 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
474 // No implied bounds in a const, etc.
481 item: &'tcx hir::Item<'tcx>,
482 ast_self_ty: &hir::Ty<'_>,
483 ast_trait_ref: &Option<hir::TraitRef<'_>>,
485 debug!("check_impl: {:?}", item);
487 for_item(tcx, item).with_fcx(|fcx, tcx| {
488 let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
490 match *ast_trait_ref {
491 Some(ref ast_trait_ref) => {
492 // `#[rustc_reservation_impl]` impls are not real impls and
493 // therefore don't need to be WF (the trait's `Self: Trait` predicate
495 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
497 fcx.normalize_associated_types_in(ast_trait_ref.path.span, &trait_ref);
498 let obligations = traits::wf::trait_obligations(
503 ast_trait_ref.path.span,
506 for obligation in obligations {
507 fcx.register_predicate(obligation);
511 let self_ty = fcx.tcx.type_of(item_def_id);
512 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
513 fcx.register_wf_obligation(
516 ObligationCauseCode::MiscObligation,
521 check_where_clauses(tcx, fcx, item.span, item_def_id, None);
523 fcx.impl_implied_bounds(item_def_id, item.span)
527 /// Checks where-clauses and inline bounds that are declared on `def_id`.
528 fn check_where_clauses<'tcx, 'fcx>(
530 fcx: &FnCtxt<'fcx, 'tcx>,
533 return_ty: Option<(Ty<'tcx>, Span)>,
535 debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
537 let predicates = fcx.tcx.predicates_of(def_id);
538 let generics = tcx.generics_of(def_id);
540 let is_our_default = |def: &ty::GenericParamDef| match def.kind {
541 GenericParamDefKind::Type { has_default, .. } => {
542 has_default && def.index >= generics.parent_count as u32
547 // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
548 // For example, this forbids the declaration:
550 // struct Foo<T = Vec<[u32]>> { .. }
552 // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
553 for param in &generics.params {
554 if let GenericParamDefKind::Type { .. } = param.kind {
555 if is_our_default(¶m) {
556 let ty = fcx.tcx.type_of(param.def_id);
557 // Ignore dependent defaults -- that is, where the default of one type
558 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
559 // be sure if it will error or not as user might always specify the other.
560 if !ty.needs_subst() {
561 fcx.register_wf_obligation(
563 fcx.tcx.def_span(param.def_id),
564 ObligationCauseCode::MiscObligation,
571 // Check that trait predicates are WF when params are substituted by their defaults.
572 // We don't want to overly constrain the predicates that may be written but we want to
573 // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
574 // Therefore we check if a predicate which contains a single type param
575 // with a concrete default is WF with that default substituted.
576 // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
578 // First we build the defaulted substitution.
579 let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
581 GenericParamDefKind::Lifetime => {
582 // All regions are identity.
583 fcx.tcx.mk_param_from_def(param)
586 GenericParamDefKind::Type { .. } => {
587 // If the param has a default, ...
588 if is_our_default(param) {
589 let default_ty = fcx.tcx.type_of(param.def_id);
590 // ... and it's not a dependent default, ...
591 if !default_ty.needs_subst() {
592 // ... then substitute it with the default.
593 return default_ty.into();
596 // Mark unwanted params as error.
597 fcx.tcx.types.err.into()
600 GenericParamDefKind::Const => {
601 // FIXME(const_generics:defaults)
602 fcx.tcx.consts.err.into()
607 // Now we build the substituted predicates.
608 let default_obligations = predicates
611 .flat_map(|&(pred, sp)| {
614 params: FxHashSet<u32>,
616 impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
617 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
618 if let ty::Param(param) = t.kind {
619 self.params.insert(param.index);
621 t.super_visit_with(self)
624 fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
628 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
629 if let ty::ConstKind::Param(param) = c.val {
630 self.params.insert(param.index);
632 c.super_visit_with(self)
635 let mut param_count = CountParams::default();
636 let has_region = pred.visit_with(&mut param_count);
637 let substituted_pred = pred.subst(fcx.tcx, substs);
638 // Don't check non-defaulted params, dependent defaults (including lifetimes)
639 // or preds with multiple params.
640 if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
642 } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
643 // Avoid duplication of predicates that contain no parameters, for example.
646 Some((substituted_pred, sp))
650 // Convert each of those into an obligation. So if you have
651 // something like `struct Foo<T: Copy = String>`, we would
652 // take that predicate `T: Copy`, substitute to `String: Copy`
653 // (actually that happens in the previous `flat_map` call),
654 // and then try to prove it (in this case, we'll fail).
656 // Note the subtle difference from how we handle `predicates`
657 // below: there, we are not trying to prove those predicates
658 // to be *true* but merely *well-formed*.
659 let pred = fcx.normalize_associated_types_in(sp, &pred);
661 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
662 traits::Obligation::new(cause, fcx.param_env, pred)
665 let mut predicates = predicates.instantiate_identity(fcx.tcx);
667 if let Some((return_ty, span)) = return_ty {
668 let opaque_types = check_opaque_types(tcx, fcx, def_id, span, return_ty);
669 for _ in 0..opaque_types.len() {
670 predicates.spans.push(span);
672 predicates.predicates.extend(opaque_types);
675 let predicates = fcx.normalize_associated_types_in(span, &predicates);
677 debug!("check_where_clauses: predicates={:?}", predicates.predicates);
678 assert_eq!(predicates.predicates.len(), predicates.spans.len());
680 predicates.predicates.iter().zip(predicates.spans.iter()).flat_map(|(p, sp)| {
681 traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, *sp)
684 for obligation in wf_obligations.chain(default_obligations) {
685 debug!("next obligation cause: {:?}", obligation.cause);
686 fcx.register_predicate(obligation);
690 fn check_fn_or_method<'fcx, 'tcx>(
692 fcx: &FnCtxt<'fcx, 'tcx>,
694 sig: ty::PolyFnSig<'tcx>,
695 hir_sig: &hir::FnSig<'_>,
697 implied_bounds: &mut Vec<Ty<'tcx>>,
699 let sig = fcx.normalize_associated_types_in(span, &sig);
700 let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
702 for (input_ty, span) in sig.inputs().iter().zip(hir_sig.decl.inputs.iter().map(|t| t.span)) {
703 fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
705 implied_bounds.extend(sig.inputs());
707 fcx.register_wf_obligation(
709 hir_sig.decl.output.span(),
710 ObligationCauseCode::ReturnType,
713 // FIXME(#25759) return types should not be implied bounds
714 implied_bounds.push(sig.output());
716 check_where_clauses(tcx, fcx, span, def_id, Some((sig.output(), hir_sig.decl.output.span())));
719 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
720 /// laid for "higher-order pattern unification".
721 /// This ensures that inference is tractable.
722 /// In particular, definitions of opaque types can only use other generics as arguments,
723 /// and they cannot repeat an argument. Example:
726 /// type Foo<A, B> = impl Bar<A, B>;
728 /// // Okay -- `Foo` is applied to two distinct, generic types.
729 /// fn a<T, U>() -> Foo<T, U> { .. }
731 /// // Not okay -- `Foo` is applied to `T` twice.
732 /// fn b<T>() -> Foo<T, T> { .. }
734 /// // Not okay -- `Foo` is applied to a non-generic type.
735 /// fn b<T>() -> Foo<T, u32> { .. }
738 fn check_opaque_types<'fcx, 'tcx>(
740 fcx: &FnCtxt<'fcx, 'tcx>,
744 ) -> Vec<ty::Predicate<'tcx>> {
745 trace!("check_opaque_types(ty={:?})", ty);
746 let mut substituted_predicates = Vec::new();
747 ty.fold_with(&mut ty::fold::BottomUpFolder {
750 if let ty::Opaque(def_id, substs) = ty.kind {
751 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
752 let generics = tcx.generics_of(def_id);
753 // Only check named `impl Trait` types defined in this crate.
754 if generics.parent.is_none() && def_id.is_local() {
755 let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
756 if may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
757 trace!("check_opaque_types: may define, generics={:#?}", generics);
758 let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
759 for (subst, param) in substs.iter().zip(&generics.params) {
760 match subst.unpack() {
761 ty::subst::GenericArgKind::Type(ty) => match ty.kind {
763 // Prevent `fn foo() -> Foo<u32>` from being defining.
768 "non-defining opaque type use \
772 tcx.def_span(param.def_id),
774 "used non-generic type {} for \
783 ty::subst::GenericArgKind::Lifetime(region) => {
784 let param_span = tcx.def_span(param.def_id);
785 if let ty::ReStatic = region {
789 "non-defining opaque type use \
794 "cannot use static lifetime; use a bound lifetime \
795 instead or remove the lifetime parameter from the \
800 seen.entry(region).or_default().push(param_span);
804 ty::subst::GenericArgKind::Const(ct) => match ct.val {
805 ty::ConstKind::Param(_) => {}
810 "non-defining opaque type use \
814 tcx.def_span(param.def_id),
816 "used non-generic const {} for \
825 } // for (subst, param)
826 for (_, spans) in seen {
831 "non-defining opaque type use \
834 .span_note(spans, "lifetime used multiple times")
838 } // if may_define_opaque_type
840 // Now register the bounds on the parameters of the opaque type
841 // so the parameters given by the function need to fulfill them.
843 // type Foo<T: Bar> = impl Baz + 'static;
844 // fn foo<U>() -> Foo<U> { .. *}
848 // type Foo<T: Bar> = impl Baz + 'static;
849 // fn foo<U: Bar>() -> Foo<U> { .. *}
850 let predicates = tcx.predicates_of(def_id);
851 trace!("check_opaque_types: may define, predicates={:#?}", predicates,);
852 for &(pred, _) in predicates.predicates {
853 let substituted_pred = pred.subst(fcx.tcx, substs);
854 // Avoid duplication of predicates that contain no parameters, for example.
855 if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
856 substituted_predicates.push(substituted_pred);
859 } // if is_named_opaque_type
866 substituted_predicates
869 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
870 `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
871 of the previous types except `Self`)";
873 fn check_method_receiver<'fcx, 'tcx>(
874 fcx: &FnCtxt<'fcx, 'tcx>,
875 fn_sig: &hir::FnSig<'_>,
876 method: &ty::AssocItem,
879 // Check that the method has a valid receiver type, given the type `Self`.
880 debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
882 if !method.method_has_self_argument {
886 let span = fn_sig.decl.inputs[0].span;
888 let sig = fcx.tcx.fn_sig(method.def_id);
889 let sig = fcx.normalize_associated_types_in(span, &sig);
890 let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
892 debug!("check_method_receiver: sig={:?}", sig);
894 let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
895 let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_ty));
897 let receiver_ty = sig.inputs()[0];
899 let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
901 fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(receiver_ty));
903 if fcx.tcx.features().arbitrary_self_types {
904 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
905 // Report error; `arbitrary_self_types` was enabled.
906 e0307(fcx, span, receiver_ty);
909 if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
910 if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
911 // Report error; would have worked with `arbitrary_self_types`.
913 &fcx.tcx.sess.parse_sess,
914 sym::arbitrary_self_types,
917 "`{}` cannot be used as the type of `self` without \
918 the `arbitrary_self_types` feature",
922 .help(HELP_FOR_SELF_TYPE)
925 // Report error; would not have worked with `arbitrary_self_types`.
926 e0307(fcx, span, receiver_ty);
932 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
934 fcx.tcx.sess.diagnostic(),
937 "invalid `self` parameter type: {:?}",
940 .note("type of `self` must be `Self` or a type that dereferences to it")
941 .help(HELP_FOR_SELF_TYPE)
945 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
946 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
947 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
948 /// strict: `receiver_ty` must implement `Receiver` and directly implement
949 /// `Deref<Target = self_ty>`.
951 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
952 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
953 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
954 fn receiver_is_valid<'fcx, 'tcx>(
955 fcx: &FnCtxt<'fcx, 'tcx>,
957 receiver_ty: Ty<'tcx>,
959 arbitrary_self_types_enabled: bool,
961 let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
963 let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
965 // `self: Self` is always valid.
966 if can_eq_self(receiver_ty) {
967 if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
973 let mut autoderef = fcx.autoderef(span, receiver_ty);
975 // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
976 if arbitrary_self_types_enabled {
977 autoderef = autoderef.include_raw_pointers();
980 // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
983 let receiver_trait_def_id = fcx.tcx.require_lang_item(lang_items::ReceiverTraitLangItem, None);
985 // Keep dereferencing `receiver_ty` until we get to `self_ty`.
987 if let Some((potential_self_ty, _)) = autoderef.next() {
989 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
990 potential_self_ty, self_ty
993 if can_eq_self(potential_self_ty) {
994 autoderef.finalize(fcx);
996 if let Some(mut err) =
997 fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
1004 // Without `feature(arbitrary_self_types)`, we require that each step in the
1005 // deref chain implement `receiver`
1006 if !arbitrary_self_types_enabled
1007 && !receiver_is_implemented(
1009 receiver_trait_def_id,
1018 debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
1019 // If he receiver already has errors reported due to it, consider it valid to avoid
1020 // unnecessary errors (#58712).
1021 return receiver_ty.references_error();
1025 // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
1026 if !arbitrary_self_types_enabled
1027 && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
1035 fn receiver_is_implemented(
1036 fcx: &FnCtxt<'_, 'tcx>,
1037 receiver_trait_def_id: DefId,
1038 cause: ObligationCause<'tcx>,
1039 receiver_ty: Ty<'tcx>,
1041 let trait_ref = ty::TraitRef {
1042 def_id: receiver_trait_def_id,
1043 substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
1047 traits::Obligation::new(cause, fcx.param_env, trait_ref.without_const().to_predicate());
1049 if fcx.predicate_must_hold_modulo_regions(&obligation) {
1053 "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
1060 fn check_variances_for_type_defn<'tcx>(
1062 item: &hir::Item<'tcx>,
1063 hir_generics: &hir::Generics<'_>,
1065 let item_def_id = tcx.hir().local_def_id(item.hir_id);
1066 let ty = tcx.type_of(item_def_id);
1067 if tcx.has_error_field(ty) {
1071 let ty_predicates = tcx.predicates_of(item_def_id);
1072 assert_eq!(ty_predicates.parent, None);
1073 let variances = tcx.variances_of(item_def_id);
1075 let mut constrained_parameters: FxHashSet<_> = variances
1078 .filter(|&(_, &variance)| variance != ty::Bivariant)
1079 .map(|(index, _)| Parameter(index as u32))
1082 identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
1084 for (index, _) in variances.iter().enumerate() {
1085 if constrained_parameters.contains(&Parameter(index as u32)) {
1089 let param = &hir_generics.params[index];
1092 hir::ParamName::Error => {}
1093 _ => report_bivariance(tcx, param.span, param.name.ident().name),
1098 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
1099 let mut err = error_392(tcx, span, param_name);
1101 let suggested_marker_id = tcx.lang_items().phantom_data();
1102 // Help is available only in presence of lang items.
1103 let msg = if let Some(def_id) = suggested_marker_id {
1105 "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1107 tcx.def_path_str(def_id),
1110 format!("consider removing `{}` or referring to it in a field", param_name)
1116 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1118 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1119 let empty_env = ty::ParamEnv::empty();
1121 let def_id = fcx.tcx.hir().local_def_id(id);
1122 let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p).collect();
1123 // Check elaborated bounds.
1124 let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1126 for pred in implied_obligations {
1127 // Match the existing behavior.
1128 if pred.is_global() && !pred.has_late_bound_regions() {
1129 let pred = fcx.normalize_associated_types_in(span, &pred);
1130 let obligation = traits::Obligation::new(
1131 traits::ObligationCause::new(span, id, traits::TrivialBound),
1135 fcx.register_predicate(obligation);
1139 fcx.select_all_obligations_or_error();
1142 pub struct CheckTypeWellFormedVisitor<'tcx> {
1146 impl CheckTypeWellFormedVisitor<'tcx> {
1147 pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1148 CheckTypeWellFormedVisitor { tcx }
1152 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1153 fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1154 debug!("visit_item: {:?}", i);
1155 let def_id = self.tcx.hir().local_def_id(i.hir_id);
1156 self.tcx.ensure().check_item_well_formed(def_id);
1159 fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1160 debug!("visit_trait_item: {:?}", trait_item);
1161 let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1162 self.tcx.ensure().check_trait_item_well_formed(def_id);
1165 fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1166 debug!("visit_impl_item: {:?}", impl_item);
1167 let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1168 self.tcx.ensure().check_impl_item_well_formed(def_id);
1172 ///////////////////////////////////////////////////////////////////////////
1175 struct AdtVariant<'tcx> {
1176 fields: Vec<AdtField<'tcx>>,
1179 struct AdtField<'tcx> {
1184 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1185 fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1186 let fields = struct_def
1190 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1191 let field_ty = self.normalize_associated_types_in(field.span, &field_ty);
1192 let field_ty = self.resolve_vars_if_possible(&field_ty);
1193 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1194 AdtField { ty: field_ty, span: field.span }
1197 AdtVariant { fields }
1200 fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1201 enum_def.variants.iter().map(|variant| self.non_enum_variant(&variant.data)).collect()
1204 fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1205 match self.tcx.impl_trait_ref(impl_def_id) {
1206 Some(ref trait_ref) => {
1207 // Trait impl: take implied bounds from all types that
1208 // appear in the trait reference.
1209 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1210 trait_ref.substs.types().collect()
1214 // Inherent impl: take implied bounds from the `self` type.
1215 let self_ty = self.tcx.type_of(impl_def_id);
1216 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1223 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) -> DiagnosticBuilder<'_> {
1225 struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1226 err.span_label(span, "unused parameter");