diff options
Diffstat (limited to 'compiler/rustc_hir_analysis/src/check/wfcheck.rs')
| -rw-r--r-- | compiler/rustc_hir_analysis/src/check/wfcheck.rs | 1990 |
1 files changed, 1990 insertions, 0 deletions
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs new file mode 100644 index 00000000000..7965ec1b43f --- /dev/null +++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs @@ -0,0 +1,1990 @@ +use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter}; +use hir::def::DefKind; +use rustc_ast as ast; +use rustc_data_structures::fx::{FxHashMap, FxHashSet}; +use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed}; +use rustc_hir as hir; +use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_hir::lang_items::LangItem; +use rustc_hir::ItemKind; +use rustc_infer::infer::outlives::env::{OutlivesEnvironment, RegionBoundPairs}; +use rustc_infer::infer::outlives::obligations::TypeOutlives; +use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt}; +use rustc_middle::mir::ConstraintCategory; +use rustc_middle::ty::query::Providers; +use rustc_middle::ty::trait_def::TraitSpecializationKind; +use rustc_middle::ty::{ + self, AdtKind, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, + TypeSuperVisitable, TypeVisitable, TypeVisitor, +}; +use rustc_middle::ty::{GenericArgKind, InternalSubsts}; +use rustc_session::parse::feature_err; +use rustc_span::symbol::{sym, Ident, Symbol}; +use rustc_span::{Span, DUMMY_SP}; +use rustc_trait_selection::autoderef::Autoderef; +use rustc_trait_selection::traits::error_reporting::InferCtxtExt; +use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _; +use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _; +use rustc_trait_selection::traits::{ + self, ObligationCause, ObligationCauseCode, ObligationCtxt, WellFormedLoc, +}; + +use std::cell::LazyCell; +use std::convert::TryInto; +use std::iter; +use std::ops::{ControlFlow, Deref}; + +pub(super) struct WfCheckingCtxt<'a, 'tcx> { + pub(super) ocx: ObligationCtxt<'a, 'tcx>, + span: Span, + body_id: hir::HirId, + param_env: ty::ParamEnv<'tcx>, +} +impl<'a, 'tcx> Deref for WfCheckingCtxt<'a, 'tcx> { + type Target = ObligationCtxt<'a, 'tcx>; + fn deref(&self) -> &Self::Target { + &self.ocx + } +} + +impl<'tcx> WfCheckingCtxt<'_, 'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.ocx.infcx.tcx + } + + fn normalize<T>(&self, span: Span, loc: Option<WellFormedLoc>, value: T) -> T + where + T: TypeFoldable<'tcx>, + { + self.ocx.normalize( + ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc)), + self.param_env, + value, + ) + } + + fn register_wf_obligation( + &self, + span: Span, + loc: Option<WellFormedLoc>, + arg: ty::GenericArg<'tcx>, + ) { + let cause = + traits::ObligationCause::new(span, self.body_id, ObligationCauseCode::WellFormed(loc)); + // for a type to be WF, we do not need to check if const trait predicates satisfy. + let param_env = self.param_env.without_const(); + self.ocx.register_obligation(traits::Obligation::new( + cause, + param_env, + ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)).to_predicate(self.tcx()), + )); + } +} + +pub(super) fn enter_wf_checking_ctxt<'tcx, F>( + tcx: TyCtxt<'tcx>, + span: Span, + body_def_id: LocalDefId, + f: F, +) where + F: for<'a> FnOnce(&WfCheckingCtxt<'a, 'tcx>), +{ + let param_env = tcx.param_env(body_def_id); + let body_id = tcx.hir().local_def_id_to_hir_id(body_def_id); + tcx.infer_ctxt().enter(|ref infcx| { + let ocx = ObligationCtxt::new(infcx); + + let assumed_wf_types = ocx.assumed_wf_types(param_env, span, body_def_id); + + let mut wfcx = WfCheckingCtxt { ocx, span, body_id, param_env }; + + if !tcx.features().trivial_bounds { + wfcx.check_false_global_bounds() + } + f(&mut wfcx); + let errors = wfcx.select_all_or_error(); + if !errors.is_empty() { + infcx.report_fulfillment_errors(&errors, None, false); + return; + } + + let implied_bounds = infcx.implied_bounds_tys(param_env, body_id, assumed_wf_types); + let outlives_environment = + OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds); + + infcx.check_region_obligations_and_report_errors(body_def_id, &outlives_environment); + }) +} + +fn check_well_formed(tcx: TyCtxt<'_>, def_id: hir::OwnerId) { + let node = tcx.hir().expect_owner(def_id); + match node { + hir::OwnerNode::Crate(_) => {} + hir::OwnerNode::Item(item) => check_item(tcx, item), + hir::OwnerNode::TraitItem(item) => check_trait_item(tcx, item), + hir::OwnerNode::ImplItem(item) => check_impl_item(tcx, item), + hir::OwnerNode::ForeignItem(item) => check_foreign_item(tcx, item), + } + + if let Some(generics) = node.generics() { + for param in generics.params { + check_param_wf(tcx, param) + } + } +} + +/// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are +/// well-formed, meaning that they do not require any constraints not declared in the struct +/// definition itself. For example, this definition would be illegal: +/// +/// ```rust +/// struct Ref<'a, T> { x: &'a T } +/// ``` +/// +/// because the type did not declare that `T:'a`. +/// +/// We do this check as a pre-pass before checking fn bodies because if these constraints are +/// not included it frequently leads to confusing errors in fn bodies. So it's better to check +/// the types first. +#[instrument(skip(tcx), level = "debug")] +fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) { + let def_id = item.def_id.def_id; + + debug!( + ?item.def_id, + item.name = ? tcx.def_path_str(def_id.to_def_id()) + ); + + match item.kind { + // Right now we check that every default trait implementation + // has an implementation of itself. Basically, a case like: + // + // impl Trait for T {} + // + // has a requirement of `T: Trait` which was required for default + // method implementations. Although this could be improved now that + // there's a better infrastructure in place for this, it's being left + // for a follow-up work. + // + // Since there's such a requirement, we need to check *just* positive + // implementations, otherwise things like: + // + // impl !Send for T {} + // + // won't be allowed unless there's an *explicit* implementation of `Send` + // for `T` + hir::ItemKind::Impl(ref impl_) => { + let is_auto = tcx + .impl_trait_ref(def_id) + .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id)); + if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) { + let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span); + let mut err = + tcx.sess.struct_span_err(sp, "impls of auto traits cannot be default"); + err.span_labels(impl_.defaultness_span, "default because of this"); + err.span_label(sp, "auto trait"); + err.emit(); + } + // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span. + match (tcx.impl_polarity(def_id), impl_.polarity) { + (ty::ImplPolarity::Positive, _) => { + check_impl(tcx, item, impl_.self_ty, &impl_.of_trait, impl_.constness); + } + (ty::ImplPolarity::Negative, ast::ImplPolarity::Negative(span)) => { + // FIXME(#27579): what amount of WF checking do we need for neg impls? + if let hir::Defaultness::Default { .. } = impl_.defaultness { + let mut spans = vec![span]; + spans.extend(impl_.defaultness_span); + struct_span_err!( + tcx.sess, + spans, + E0750, + "negative impls cannot be default impls" + ) + .emit(); + } + } + (ty::ImplPolarity::Reservation, _) => { + // FIXME: what amount of WF checking do we need for reservation impls? + } + _ => unreachable!(), + } + } + hir::ItemKind::Fn(ref sig, ..) => { + check_item_fn(tcx, def_id, item.ident, item.span, sig.decl); + } + hir::ItemKind::Static(ty, ..) => { + check_item_type(tcx, def_id, ty.span, false); + } + hir::ItemKind::Const(ty, ..) => { + check_item_type(tcx, def_id, ty.span, false); + } + hir::ItemKind::Struct(ref struct_def, ref ast_generics) => { + check_type_defn(tcx, item, false, |wfcx| vec![wfcx.non_enum_variant(struct_def)]); + + check_variances_for_type_defn(tcx, item, ast_generics); + } + hir::ItemKind::Union(ref struct_def, ref ast_generics) => { + check_type_defn(tcx, item, true, |wfcx| vec![wfcx.non_enum_variant(struct_def)]); + + check_variances_for_type_defn(tcx, item, ast_generics); + } + hir::ItemKind::Enum(ref enum_def, ref ast_generics) => { + check_type_defn(tcx, item, true, |wfcx| wfcx.enum_variants(enum_def)); + + check_variances_for_type_defn(tcx, item, ast_generics); + } + hir::ItemKind::Trait(..) => { + check_trait(tcx, item); + } + hir::ItemKind::TraitAlias(..) => { + check_trait(tcx, item); + } + // `ForeignItem`s are handled separately. + hir::ItemKind::ForeignMod { .. } => {} + _ => {} + } +} + +fn check_foreign_item(tcx: TyCtxt<'_>, item: &hir::ForeignItem<'_>) { + let def_id = item.def_id.def_id; + + debug!( + ?item.def_id, + item.name = ? tcx.def_path_str(def_id.to_def_id()) + ); + + match item.kind { + hir::ForeignItemKind::Fn(decl, ..) => { + check_item_fn(tcx, def_id, item.ident, item.span, decl) + } + hir::ForeignItemKind::Static(ty, ..) => check_item_type(tcx, def_id, ty.span, true), + hir::ForeignItemKind::Type => (), + } +} + +fn check_trait_item(tcx: TyCtxt<'_>, trait_item: &hir::TraitItem<'_>) { + let def_id = trait_item.def_id.def_id; + + let (method_sig, span) = match trait_item.kind { + hir::TraitItemKind::Fn(ref sig, _) => (Some(sig), trait_item.span), + hir::TraitItemKind::Type(_bounds, Some(ty)) => (None, ty.span), + _ => (None, trait_item.span), + }; + check_object_unsafe_self_trait_by_name(tcx, trait_item); + check_associated_item(tcx, def_id, span, method_sig); + + let encl_trait_def_id = tcx.local_parent(def_id); + let encl_trait = tcx.hir().expect_item(encl_trait_def_id); + let encl_trait_def_id = encl_trait.def_id.to_def_id(); + let fn_lang_item_name = if Some(encl_trait_def_id) == tcx.lang_items().fn_trait() { + Some("fn") + } else if Some(encl_trait_def_id) == tcx.lang_items().fn_mut_trait() { + Some("fn_mut") + } else { + None + }; + + if let (Some(fn_lang_item_name), "call") = + (fn_lang_item_name, trait_item.ident.name.to_ident_string().as_str()) + { + // We are looking at the `call` function of the `fn` or `fn_mut` lang item. + // Do some rudimentary sanity checking to avoid an ICE later (issue #83471). + if let Some(hir::FnSig { decl, span, .. }) = method_sig { + if let [self_ty, _] = decl.inputs { + if !matches!(self_ty.kind, hir::TyKind::Rptr(_, _)) { + tcx.sess + .struct_span_err( + self_ty.span, + &format!( + "first argument of `call` in `{fn_lang_item_name}` lang item must be a reference", + ), + ) + .emit(); + } + } else { + tcx.sess + .struct_span_err( + *span, + &format!( + "`call` function in `{fn_lang_item_name}` lang item takes exactly two arguments", + ), + ) + .emit(); + } + } else { + tcx.sess + .struct_span_err( + trait_item.span, + &format!( + "`call` trait item in `{fn_lang_item_name}` lang item must be a function", + ), + ) + .emit(); + } + } +} + +/// Require that the user writes where clauses on GATs for the implicit +/// outlives bounds involving trait parameters in trait functions and +/// lifetimes passed as GAT substs. See `self-outlives-lint` test. +/// +/// We use the following trait as an example throughout this function: +/// ```rust,ignore (this code fails due to this lint) +/// trait IntoIter { +/// type Iter<'a>: Iterator<Item = Self::Item<'a>>; +/// type Item<'a>; +/// fn into_iter<'a>(&'a self) -> Self::Iter<'a>; +/// } +/// ``` +fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) { + // Associates every GAT's def_id to a list of possibly missing bounds detected by this lint. + let mut required_bounds_by_item = FxHashMap::default(); + + // Loop over all GATs together, because if this lint suggests adding a where-clause bound + // to one GAT, it might then require us to an additional bound on another GAT. + // In our `IntoIter` example, we discover a missing `Self: 'a` bound on `Iter<'a>`, which + // then in a second loop adds a `Self: 'a` bound to `Item` due to the relationship between + // those GATs. + loop { + let mut should_continue = false; + for gat_item in associated_items { + let gat_def_id = gat_item.id.def_id; + let gat_item = tcx.associated_item(gat_def_id); + // If this item is not an assoc ty, or has no substs, then it's not a GAT + if gat_item.kind != ty::AssocKind::Type { + continue; + } + let gat_generics = tcx.generics_of(gat_def_id); + // FIXME(jackh726): we can also warn in the more general case + if gat_generics.params.is_empty() { + continue; + } + + // Gather the bounds with which all other items inside of this trait constrain the GAT. + // This is calculated by taking the intersection of the bounds that each item + // constrains the GAT with individually. + let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None; + for item in associated_items { + let item_def_id = item.id.def_id; + // Skip our own GAT, since it does not constrain itself at all. + if item_def_id == gat_def_id { + continue; + } + + let item_hir_id = item.id.hir_id(); + let param_env = tcx.param_env(item_def_id); + + let item_required_bounds = match item.kind { + // In our example, this corresponds to `into_iter` method + hir::AssocItemKind::Fn { .. } => { + // For methods, we check the function signature's return type for any GATs + // to constrain. In the `into_iter` case, we see that the return type + // `Self::Iter<'a>` is a GAT we want to gather any potential missing bounds from. + let sig: ty::FnSig<'_> = tcx.liberate_late_bound_regions( + item_def_id.to_def_id(), + tcx.fn_sig(item_def_id), + ); + gather_gat_bounds( + tcx, + param_env, + item_hir_id, + sig.inputs_and_output, + // We also assume that all of the function signature's parameter types + // are well formed. + &sig.inputs().iter().copied().collect(), + gat_def_id.def_id, + gat_generics, + ) + } + // In our example, this corresponds to the `Iter` and `Item` associated types + hir::AssocItemKind::Type => { + // If our associated item is a GAT with missing bounds, add them to + // the param-env here. This allows this GAT to propagate missing bounds + // to other GATs. + let param_env = augment_param_env( + tcx, + param_env, + required_bounds_by_item.get(&item_def_id), + ); + gather_gat_bounds( + tcx, + param_env, + item_hir_id, + tcx.explicit_item_bounds(item_def_id) + .iter() + .copied() + .collect::<Vec<_>>(), + &FxHashSet::default(), + gat_def_id.def_id, + gat_generics, + ) + } + hir::AssocItemKind::Const => None, + }; + + if let Some(item_required_bounds) = item_required_bounds { + // Take the intersection of the required bounds for this GAT, and + // the item_required_bounds which are the ones implied by just + // this item alone. + // This is why we use an Option<_>, since we need to distinguish + // the empty set of bounds from the _uninitialized_ set of bounds. + if let Some(new_required_bounds) = &mut new_required_bounds { + new_required_bounds.retain(|b| item_required_bounds.contains(b)); + } else { + new_required_bounds = Some(item_required_bounds); + } + } + } + + if let Some(new_required_bounds) = new_required_bounds { + let required_bounds = required_bounds_by_item.entry(gat_def_id).or_default(); + if new_required_bounds.into_iter().any(|p| required_bounds.insert(p)) { + // Iterate until our required_bounds no longer change + // Since they changed here, we should continue the loop + should_continue = true; + } + } + } + // We know that this loop will eventually halt, since we only set `should_continue` if the + // `required_bounds` for this item grows. Since we are not creating any new region or type + // variables, the set of all region and type bounds that we could ever insert are limited + // by the number of unique types and regions we observe in a given item. + if !should_continue { + break; + } + } + + for (gat_def_id, required_bounds) in required_bounds_by_item { + let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id.def_id); + debug!(?required_bounds); + let param_env = tcx.param_env(gat_def_id); + let gat_hir = gat_item_hir.hir_id(); + + let mut unsatisfied_bounds: Vec<_> = required_bounds + .into_iter() + .filter(|clause| match clause.kind().skip_binder() { + ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => { + !region_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b) + } + ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => { + !ty_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b) + } + _ => bug!("Unexpected PredicateKind"), + }) + .map(|clause| clause.to_string()) + .collect(); + + // We sort so that order is predictable + unsatisfied_bounds.sort(); + + if !unsatisfied_bounds.is_empty() { + let plural = pluralize!(unsatisfied_bounds.len()); + let mut err = tcx.sess.struct_span_err( + gat_item_hir.span, + &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident), + ); + + let suggestion = format!( + "{} {}", + gat_item_hir.generics.add_where_or_trailing_comma(), + unsatisfied_bounds.join(", "), + ); + err.span_suggestion( + gat_item_hir.generics.tail_span_for_predicate_suggestion(), + &format!("add the required where clause{plural}"), + suggestion, + Applicability::MachineApplicable, + ); + + let bound = + if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" }; + err.note(&format!( + "{} currently required to ensure that impls have maximum flexibility", + bound + )); + err.note( + "we are soliciting feedback, see issue #87479 \ + <https://github.com/rust-lang/rust/issues/87479> \ + for more information", + ); + + err.emit(); + } + } +} + +/// Add a new set of predicates to the caller_bounds of an existing param_env. +fn augment_param_env<'tcx>( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>, +) -> ty::ParamEnv<'tcx> { + let Some(new_predicates) = new_predicates else { + return param_env; + }; + + if new_predicates.is_empty() { + return param_env; + } + + let bounds = + tcx.mk_predicates(param_env.caller_bounds().iter().chain(new_predicates.iter().cloned())); + // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this + // i.e. traits::normalize_param_env_or_error + ty::ParamEnv::new(bounds, param_env.reveal(), param_env.constness()) +} + +/// We use the following trait as an example throughout this function. +/// Specifically, let's assume that `to_check` here is the return type +/// of `into_iter`, and the GAT we are checking this for is `Iter`. +/// ```rust,ignore (this code fails due to this lint) +/// trait IntoIter { +/// type Iter<'a>: Iterator<Item = Self::Item<'a>>; +/// type Item<'a>; +/// fn into_iter<'a>(&'a self) -> Self::Iter<'a>; +/// } +/// ``` +fn gather_gat_bounds<'tcx, T: TypeFoldable<'tcx>>( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + item_hir: hir::HirId, + to_check: T, + wf_tys: &FxHashSet<Ty<'tcx>>, + gat_def_id: LocalDefId, + gat_generics: &'tcx ty::Generics, +) -> Option<FxHashSet<ty::Predicate<'tcx>>> { + // The bounds we that we would require from `to_check` + let mut bounds = FxHashSet::default(); + + let (regions, types) = GATSubstCollector::visit(gat_def_id.to_def_id(), to_check); + + // If both regions and types are empty, then this GAT isn't in the + // set of types we are checking, and we shouldn't try to do clause analysis + // (particularly, doing so would end up with an empty set of clauses, + // since the current method would require none, and we take the + // intersection of requirements of all methods) + if types.is_empty() && regions.is_empty() { + return None; + } + + for (region_a, region_a_idx) in ®ions { + // Ignore `'static` lifetimes for the purpose of this lint: it's + // because we know it outlives everything and so doesn't give meaningful + // clues + if let ty::ReStatic = **region_a { + continue; + } + // For each region argument (e.g., `'a` in our example), check for a + // relationship to the type arguments (e.g., `Self`). If there is an + // outlives relationship (`Self: 'a`), then we want to ensure that is + // reflected in a where clause on the GAT itself. + for (ty, ty_idx) in &types { + // In our example, requires that `Self: 'a` + if ty_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *ty, *region_a) { + debug!(?ty_idx, ?region_a_idx); + debug!("required clause: {ty} must outlive {region_a}"); + // Translate into the generic parameters of the GAT. In + // our example, the type was `Self`, which will also be + // `Self` in the GAT. + let ty_param = gat_generics.param_at(*ty_idx, tcx); + let ty_param = tcx + .mk_ty(ty::Param(ty::ParamTy { index: ty_param.index, name: ty_param.name })); + // Same for the region. In our example, 'a corresponds + // to the 'me parameter. + let region_param = gat_generics.param_at(*region_a_idx, tcx); + let region_param = + tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion { + def_id: region_param.def_id, + index: region_param.index, + name: region_param.name, + })); + // The predicate we expect to see. (In our example, + // `Self: 'me`.) + let clause = + ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param)); + let clause = tcx.mk_predicate(ty::Binder::dummy(clause)); + bounds.insert(clause); + } + } + + // For each region argument (e.g., `'a` in our example), also check for a + // relationship to the other region arguments. If there is an outlives + // relationship, then we want to ensure that is reflected in the where clause + // on the GAT itself. + for (region_b, region_b_idx) in ®ions { + // Again, skip `'static` because it outlives everything. Also, we trivially + // know that a region outlives itself. + if ty::ReStatic == **region_b || region_a == region_b { + continue; + } + if region_known_to_outlive(tcx, item_hir, param_env, &wf_tys, *region_a, *region_b) { + debug!(?region_a_idx, ?region_b_idx); + debug!("required clause: {region_a} must outlive {region_b}"); + // Translate into the generic parameters of the GAT. + let region_a_param = gat_generics.param_at(*region_a_idx, tcx); + let region_a_param = + tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion { + def_id: region_a_param.def_id, + index: region_a_param.index, + name: region_a_param.name, + })); + // Same for the region. + let region_b_param = gat_generics.param_at(*region_b_idx, tcx); + let region_b_param = + tcx.mk_region(ty::RegionKind::ReEarlyBound(ty::EarlyBoundRegion { + def_id: region_b_param.def_id, + index: region_b_param.index, + name: region_b_param.name, + })); + // The predicate we expect to see. + let clause = ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate( + region_a_param, + region_b_param, + )); + let clause = tcx.mk_predicate(ty::Binder::dummy(clause)); + bounds.insert(clause); + } + } + } + + Some(bounds) +} + +/// Given a known `param_env` and a set of well formed types, can we prove that +/// `ty` outlives `region`. +fn ty_known_to_outlive<'tcx>( + tcx: TyCtxt<'tcx>, + id: hir::HirId, + param_env: ty::ParamEnv<'tcx>, + wf_tys: &FxHashSet<Ty<'tcx>>, + ty: Ty<'tcx>, + region: ty::Region<'tcx>, +) -> bool { + resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |infcx, region_bound_pairs| { + let origin = infer::RelateParamBound(DUMMY_SP, ty, None); + let outlives = &mut TypeOutlives::new(infcx, tcx, region_bound_pairs, None, param_env); + outlives.type_must_outlive(origin, ty, region, ConstraintCategory::BoringNoLocation); + }) +} + +/// Given a known `param_env` and a set of well formed types, can we prove that +/// `region_a` outlives `region_b` +fn region_known_to_outlive<'tcx>( + tcx: TyCtxt<'tcx>, + id: hir::HirId, + param_env: ty::ParamEnv<'tcx>, + wf_tys: &FxHashSet<Ty<'tcx>>, + region_a: ty::Region<'tcx>, + region_b: ty::Region<'tcx>, +) -> bool { + resolve_regions_with_wf_tys(tcx, id, param_env, &wf_tys, |mut infcx, _| { + use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate; + let origin = infer::RelateRegionParamBound(DUMMY_SP); + // `region_a: region_b` -> `region_b <= region_a` + infcx.push_sub_region_constraint( + origin, + region_b, + region_a, + ConstraintCategory::BoringNoLocation, + ); + }) +} + +/// Given a known `param_env` and a set of well formed types, set up an +/// `InferCtxt`, call the passed function (to e.g. set up region constraints +/// to be tested), then resolve region and return errors +fn resolve_regions_with_wf_tys<'tcx>( + tcx: TyCtxt<'tcx>, + id: hir::HirId, + param_env: ty::ParamEnv<'tcx>, + wf_tys: &FxHashSet<Ty<'tcx>>, + add_constraints: impl for<'a> FnOnce(&'a InferCtxt<'a, 'tcx>, &'a RegionBoundPairs<'tcx>), +) -> bool { + // Unfortunately, we have to use a new `InferCtxt` each call, because + // region constraints get added and solved there and we need to test each + // call individually. + tcx.infer_ctxt().enter(|infcx| { + let outlives_environment = OutlivesEnvironment::with_bounds( + param_env, + Some(&infcx), + infcx.implied_bounds_tys(param_env, id, wf_tys.clone()), + ); + let region_bound_pairs = outlives_environment.region_bound_pairs(); + + add_constraints(&infcx, region_bound_pairs); + + let errors = infcx.resolve_regions(&outlives_environment); + + debug!(?errors, "errors"); + + // If we were able to prove that the type outlives the region without + // an error, it must be because of the implied or explicit bounds... + errors.is_empty() + }) +} + +/// TypeVisitor that looks for uses of GATs like +/// `<P0 as Trait<P1..Pn>>::GAT<Pn..Pm>` and adds the arguments `P0..Pm` into +/// the two vectors, `regions` and `types` (depending on their kind). For each +/// parameter `Pi` also track the index `i`. +struct GATSubstCollector<'tcx> { + gat: DefId, + // Which region appears and which parameter index its substituted for + regions: FxHashSet<(ty::Region<'tcx>, usize)>, + // Which params appears and which parameter index its substituted for + types: FxHashSet<(Ty<'tcx>, usize)>, +} + +impl<'tcx> GATSubstCollector<'tcx> { + fn visit<T: TypeFoldable<'tcx>>( + gat: DefId, + t: T, + ) -> (FxHashSet<(ty::Region<'tcx>, usize)>, FxHashSet<(Ty<'tcx>, usize)>) { + let mut visitor = + GATSubstCollector { gat, regions: FxHashSet::default(), types: FxHashSet::default() }; + t.visit_with(&mut visitor); + (visitor.regions, visitor.types) + } +} + +impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> { + type BreakTy = !; + + fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { + match t.kind() { + ty::Projection(p) if p.item_def_id == self.gat => { + for (idx, subst) in p.substs.iter().enumerate() { + match subst.unpack() { + GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => { + self.regions.insert((lt, idx)); + } + GenericArgKind::Type(t) => { + self.types.insert((t, idx)); + } + _ => {} + } + } + } + _ => {} + } + t.super_visit_with(self) + } +} + +fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool { + match ty.kind { + hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments { + [s] => s.res.opt_def_id() == Some(trait_def_id.to_def_id()), + _ => false, + }, + _ => false, + } +} + +/// Detect when an object unsafe trait is referring to itself in one of its associated items. +/// When this is done, suggest using `Self` instead. +fn check_object_unsafe_self_trait_by_name(tcx: TyCtxt<'_>, item: &hir::TraitItem<'_>) { + let (trait_name, trait_def_id) = + match tcx.hir().get_by_def_id(tcx.hir().get_parent_item(item.hir_id()).def_id) { + hir::Node::Item(item) => match item.kind { + hir::ItemKind::Trait(..) => (item.ident, item.def_id), + _ => return, + }, + _ => return, + }; + let mut trait_should_be_self = vec![]; + match &item.kind { + hir::TraitItemKind::Const(ty, _) | hir::TraitItemKind::Type(_, Some(ty)) + if could_be_self(trait_def_id.def_id, ty) => + { + trait_should_be_self.push(ty.span) + } + hir::TraitItemKind::Fn(sig, _) => { + for ty in sig.decl.inputs { + if could_be_self(trait_def_id.def_id, ty) { + trait_should_be_self.push(ty.span); + } + } + match sig.decl.output { + hir::FnRetTy::Return(ty) if could_be_self(trait_def_id.def_id, ty) => { + trait_should_be_self.push(ty.span); + } + _ => {} + } + } + _ => {} + } + if !trait_should_be_self.is_empty() { + if tcx.object_safety_violations(trait_def_id).is_empty() { + return; + } + let sugg = trait_should_be_self.iter().map(|span| (*span, "Self".to_string())).collect(); + tcx.sess + .struct_span_err( + trait_should_be_self, + "associated item referring to unboxed trait object for its own trait", + ) + .span_label(trait_name.span, "in this trait") + .multipart_suggestion( + "you might have meant to use `Self` to refer to the implementing type", + sugg, + Applicability::MachineApplicable, + ) + .emit(); + } +} + +fn check_impl_item(tcx: TyCtxt<'_>, impl_item: &hir::ImplItem<'_>) { + let (method_sig, span) = match impl_item.kind { + hir::ImplItemKind::Fn(ref sig, _) => (Some(sig), impl_item.span), + // Constrain binding and overflow error spans to `<Ty>` in `type foo = <Ty>`. + hir::ImplItemKind::TyAlias(ty) if ty.span != DUMMY_SP => (None, ty.span), + _ => (None, impl_item.span), + }; + + check_associated_item(tcx, impl_item.def_id.def_id, span, method_sig); +} + +fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) { + match param.kind { + // We currently only check wf of const params here. + hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. } => (), + + // Const parameters are well formed if their type is structural match. + hir::GenericParamKind::Const { ty: hir_ty, default: _ } => { + let ty = tcx.type_of(tcx.hir().local_def_id(param.hir_id)); + + if tcx.features().adt_const_params { + if let Some(non_structural_match_ty) = + traits::search_for_adt_const_param_violation(param.span, tcx, ty) + { + // We use the same error code in both branches, because this is really the same + // issue: we just special-case the message for type parameters to make it + // clearer. + match non_structural_match_ty.kind() { + ty::Param(_) => { + // Const parameters may not have type parameters as their types, + // because we cannot be sure that the type parameter derives `PartialEq` + // and `Eq` (just implementing them is not enough for `structural_match`). + struct_span_err!( + tcx.sess, + hir_ty.span, + E0741, + "`{ty}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \ + used as the type of a const parameter", + ) + .span_label( + hir_ty.span, + format!("`{ty}` may not derive both `PartialEq` and `Eq`"), + ) + .note( + "it is not currently possible to use a type parameter as the type of a \ + const parameter", + ) + .emit(); + } + ty::Float(_) => { + struct_span_err!( + tcx.sess, + hir_ty.span, + E0741, + "`{ty}` is forbidden as the type of a const generic parameter", + ) + .note("floats do not derive `Eq` or `Ord`, which are required for const parameters") + .emit(); + } + ty::FnPtr(_) => { + struct_span_err!( + tcx.sess, + hir_ty.span, + E0741, + "using function pointers as const generic parameters is forbidden", + ) + .emit(); + } + ty::RawPtr(_) => { + struct_span_err!( + tcx.sess, + hir_ty.span, + E0741, + "using raw pointers as const generic parameters is forbidden", + ) + .emit(); + } + _ => { + let mut diag = struct_span_err!( + tcx.sess, + hir_ty.span, + E0741, + "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \ + the type of a const parameter", + non_structural_match_ty, + ); + + if ty == non_structural_match_ty { + diag.span_label( + hir_ty.span, + format!("`{ty}` doesn't derive both `PartialEq` and `Eq`"), + ); + } + + diag.emit(); + } + } + } + } else { + let err_ty_str; + let mut is_ptr = true; + + let err = match ty.kind() { + ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => None, + ty::FnPtr(_) => Some("function pointers"), + ty::RawPtr(_) => Some("raw pointers"), + _ => { + is_ptr = false; + err_ty_str = format!("`{ty}`"); + Some(err_ty_str.as_str()) + } + }; + + if let Some(unsupported_type) = err { + if is_ptr { + tcx.sess.span_err( + hir_ty.span, + &format!( + "using {unsupported_type} as const generic parameters is forbidden", + ), + ); + } else { + let mut err = tcx.sess.struct_span_err( + hir_ty.span, + &format!( + "{unsupported_type} is forbidden as the type of a const generic parameter", + ), + ); + err.note("the only supported types are integers, `bool` and `char`"); + if tcx.sess.is_nightly_build() { + err.help( + "more complex types are supported with `#![feature(adt_const_params)]`", + ); + } + err.emit(); + } + } + } + } + } +} + +#[instrument(level = "debug", skip(tcx, span, sig_if_method))] +fn check_associated_item( + tcx: TyCtxt<'_>, + item_id: LocalDefId, + span: Span, + sig_if_method: Option<&hir::FnSig<'_>>, +) { + let loc = Some(WellFormedLoc::Ty(item_id)); + enter_wf_checking_ctxt(tcx, span, item_id, |wfcx| { + let item = tcx.associated_item(item_id); + + let self_ty = match item.container { + ty::TraitContainer => tcx.types.self_param, + ty::ImplContainer => tcx.type_of(item.container_id(tcx)), + }; + + match item.kind { + ty::AssocKind::Const => { + let ty = tcx.type_of(item.def_id); + let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty); + wfcx.register_wf_obligation(span, loc, ty.into()); + } + ty::AssocKind::Fn => { + let sig = tcx.fn_sig(item.def_id); + let hir_sig = sig_if_method.expect("bad signature for method"); + check_fn_or_method( + wfcx, + item.ident(tcx).span, + sig, + hir_sig.decl, + item.def_id.expect_local(), + ); + check_method_receiver(wfcx, hir_sig, item, self_ty); + } + ty::AssocKind::Type => { + if let ty::AssocItemContainer::TraitContainer = item.container { + check_associated_type_bounds(wfcx, item, span) + } + if item.defaultness(tcx).has_value() { + let ty = tcx.type_of(item.def_id); + let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty); + wfcx.register_wf_obligation(span, loc, ty.into()); + } + } + } + }) +} + +fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> { + match kind { + ItemKind::Struct(..) => Some(AdtKind::Struct), + ItemKind::Union(..) => Some(AdtKind::Union), + ItemKind::Enum(..) => Some(AdtKind::Enum), + _ => None, + } +} + +/// In a type definition, we check that to ensure that the types of the fields are well-formed. +fn check_type_defn<'tcx, F>( + tcx: TyCtxt<'tcx>, + item: &hir::Item<'tcx>, + all_sized: bool, + mut lookup_fields: F, +) where + F: FnMut(&WfCheckingCtxt<'_, 'tcx>) -> Vec<AdtVariant<'tcx>>, +{ + enter_wf_checking_ctxt(tcx, item.span, item.def_id.def_id, |wfcx| { + let variants = lookup_fields(wfcx); + let packed = tcx.adt_def(item.def_id).repr().packed(); + + for variant in &variants { + // All field types must be well-formed. + for field in &variant.fields { + wfcx.register_wf_obligation( + field.span, + Some(WellFormedLoc::Ty(field.def_id)), + field.ty.into(), + ) + } + + // For DST, or when drop needs to copy things around, all + // intermediate types must be sized. + let needs_drop_copy = || { + packed && { + let ty = variant.fields.last().unwrap().ty; + let ty = tcx.erase_regions(ty); + if ty.needs_infer() { + tcx.sess + .delay_span_bug(item.span, &format!("inference variables in {:?}", ty)); + // Just treat unresolved type expression as if it needs drop. + true + } else { + ty.needs_drop(tcx, tcx.param_env(item.def_id)) + } + } + }; + // All fields (except for possibly the last) should be sized. + let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy(); + let unsized_len = if all_sized { 0 } else { 1 }; + for (idx, field) in + variant.fields[..variant.fields.len() - unsized_len].iter().enumerate() + { + let last = idx == variant.fields.len() - 1; + wfcx.register_bound( + traits::ObligationCause::new( + field.span, + wfcx.body_id, + traits::FieldSized { + adt_kind: match item_adt_kind(&item.kind) { + Some(i) => i, + None => bug!(), + }, + span: field.span, + last, + }, + ), + wfcx.param_env, + field.ty, + tcx.require_lang_item(LangItem::Sized, None), + ); + } + + // Explicit `enum` discriminant values must const-evaluate successfully. + if let Some(discr_def_id) = variant.explicit_discr { + let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id()); + + let cause = traits::ObligationCause::new( + tcx.def_span(discr_def_id), + wfcx.body_id, + traits::MiscObligation, + ); + wfcx.register_obligation(traits::Obligation::new( + cause, + wfcx.param_env, + ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable( + ty::UnevaluatedConst::new( + ty::WithOptConstParam::unknown(discr_def_id.to_def_id()), + discr_substs, + ), + )) + .to_predicate(tcx), + )); + } + } + + check_where_clauses(wfcx, item.span, item.def_id.def_id); + }); +} + +#[instrument(skip(tcx, item))] +fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) { + debug!(?item.def_id); + + let def_id = item.def_id.def_id; + let trait_def = tcx.trait_def(def_id); + if trait_def.is_marker + || matches!(trait_def.specialization_kind, TraitSpecializationKind::Marker) + { + for associated_def_id in &*tcx.associated_item_def_ids(def_id) { + struct_span_err!( + tcx.sess, + tcx.def_span(*associated_def_id), + E0714, + "marker traits cannot have associated items", + ) + .emit(); + } + } + + enter_wf_checking_ctxt(tcx, item.span, def_id, |wfcx| { + check_where_clauses(wfcx, item.span, def_id) + }); + + // Only check traits, don't check trait aliases + if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind { + check_gat_where_clauses(tcx, items); + } +} + +/// Checks all associated type defaults of trait `trait_def_id`. +/// +/// Assuming the defaults are used, check that all predicates (bounds on the +/// assoc type and where clauses on the trait) hold. +fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: &ty::AssocItem, span: Span) { + let bounds = wfcx.tcx().explicit_item_bounds(item.def_id); + + debug!("check_associated_type_bounds: bounds={:?}", bounds); + let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| { + let normalized_bound = wfcx.normalize(span, None, bound); + traits::wf::predicate_obligations( + wfcx.infcx, + wfcx.param_env, + wfcx.body_id, + normalized_bound, + bound_span, + ) + }); + + wfcx.register_obligations(wf_obligations); +} + +fn check_item_fn( + tcx: TyCtxt<'_>, + def_id: LocalDefId, + ident: Ident, + span: Span, + decl: &hir::FnDecl<'_>, +) { + enter_wf_checking_ctxt(tcx, span, def_id, |wfcx| { + let sig = tcx.fn_sig(def_id); + check_fn_or_method(wfcx, ident.span, sig, decl, def_id); + }) +} + +fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) { + debug!("check_item_type: {:?}", item_id); + + enter_wf_checking_ctxt(tcx, ty_span, item_id, |wfcx| { + let ty = tcx.type_of(item_id); + let item_ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(item_id)), ty); + + let mut forbid_unsized = true; + if allow_foreign_ty { + let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env); + if let ty::Foreign(_) = tail.kind() { + forbid_unsized = false; + } + } + + wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(item_id)), item_ty.into()); + if forbid_unsized { + wfcx.register_bound( + traits::ObligationCause::new(ty_span, wfcx.body_id, traits::WellFormed(None)), + wfcx.param_env, + item_ty, + tcx.require_lang_item(LangItem::Sized, None), + ); + } + + // Ensure that the end result is `Sync` in a non-thread local `static`. + let should_check_for_sync = tcx.static_mutability(item_id.to_def_id()) + == Some(hir::Mutability::Not) + && !tcx.is_foreign_item(item_id.to_def_id()) + && !tcx.is_thread_local_static(item_id.to_def_id()); + + if should_check_for_sync { + wfcx.register_bound( + traits::ObligationCause::new(ty_span, wfcx.body_id, traits::SharedStatic), + wfcx.param_env, + item_ty, + tcx.require_lang_item(LangItem::Sync, Some(ty_span)), + ); + } + }); +} + +#[instrument(level = "debug", skip(tcx, ast_self_ty, ast_trait_ref))] +fn check_impl<'tcx>( + tcx: TyCtxt<'tcx>, + item: &'tcx hir::Item<'tcx>, + ast_self_ty: &hir::Ty<'_>, + ast_trait_ref: &Option<hir::TraitRef<'_>>, + constness: hir::Constness, +) { + enter_wf_checking_ctxt(tcx, item.span, item.def_id.def_id, |wfcx| { + match *ast_trait_ref { + Some(ref ast_trait_ref) => { + // `#[rustc_reservation_impl]` impls are not real impls and + // therefore don't need to be WF (the trait's `Self: Trait` predicate + // won't hold). + let trait_ref = tcx.impl_trait_ref(item.def_id).unwrap(); + let trait_ref = wfcx.normalize(ast_trait_ref.path.span, None, trait_ref); + let trait_pred = ty::TraitPredicate { + trait_ref, + constness: match constness { + hir::Constness::Const => ty::BoundConstness::ConstIfConst, + hir::Constness::NotConst => ty::BoundConstness::NotConst, + }, + polarity: ty::ImplPolarity::Positive, + }; + let obligations = traits::wf::trait_obligations( + wfcx.infcx, + wfcx.param_env, + wfcx.body_id, + &trait_pred, + ast_trait_ref.path.span, + item, + ); + debug!(?obligations); + wfcx.register_obligations(obligations); + } + None => { + let self_ty = tcx.type_of(item.def_id); + let self_ty = wfcx.normalize( + item.span, + Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)), + self_ty, + ); + wfcx.register_wf_obligation( + ast_self_ty.span, + Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)), + self_ty.into(), + ); + } + } + + check_where_clauses(wfcx, item.span, item.def_id.def_id); + }); +} + +/// Checks where-clauses and inline bounds that are declared on `def_id`. +#[instrument(level = "debug", skip(wfcx))] +fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id: LocalDefId) { + let infcx = wfcx.infcx; + let tcx = wfcx.tcx(); + + let predicates = tcx.bound_predicates_of(def_id.to_def_id()); + let generics = tcx.generics_of(def_id); + + let is_our_default = |def: &ty::GenericParamDef| match def.kind { + GenericParamDefKind::Type { has_default, .. } + | GenericParamDefKind::Const { has_default } => { + has_default && def.index >= generics.parent_count as u32 + } + GenericParamDefKind::Lifetime => unreachable!(), + }; + + // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`. + // For example, this forbids the declaration: + // + // struct Foo<T = Vec<[u32]>> { .. } + // + // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold. + for param in &generics.params { + match param.kind { + GenericParamDefKind::Type { .. } => { + if is_our_default(param) { + let ty = tcx.type_of(param.def_id); + // Ignore dependent defaults -- that is, where the default of one type + // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't + // be sure if it will error or not as user might always specify the other. + if !ty.needs_subst() { + wfcx.register_wf_obligation( + tcx.def_span(param.def_id), + Some(WellFormedLoc::Ty(param.def_id.expect_local())), + ty.into(), + ); + } + } + } + GenericParamDefKind::Const { .. } => { + if is_our_default(param) { + // FIXME(const_generics_defaults): This + // is incorrect when dealing with unused substs, for example + // for `struct Foo<const N: usize, const M: usize = { 1 - 2 }>` + // we should eagerly error. + let default_ct = tcx.const_param_default(param.def_id); + if !default_ct.needs_subst() { + wfcx.register_wf_obligation( + tcx.def_span(param.def_id), + None, + default_ct.into(), + ); + } + } + } + // Doesn't have defaults. + GenericParamDefKind::Lifetime => {} + } + } + + // Check that trait predicates are WF when params are substituted by their defaults. + // We don't want to overly constrain the predicates that may be written but we want to + // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`. + // Therefore we check if a predicate which contains a single type param + // with a concrete default is WF with that default substituted. + // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`. + // + // First we build the defaulted substitution. + let substs = InternalSubsts::for_item(tcx, def_id.to_def_id(), |param, _| { + match param.kind { + GenericParamDefKind::Lifetime => { + // All regions are identity. + tcx.mk_param_from_def(param) + } + + GenericParamDefKind::Type { .. } => { + // If the param has a default, ... + if is_our_default(param) { + let default_ty = tcx.type_of(param.def_id); + // ... and it's not a dependent default, ... + if !default_ty.needs_subst() { + // ... then substitute it with the default. + return default_ty.into(); + } + } + + tcx.mk_param_from_def(param) + } + GenericParamDefKind::Const { .. } => { + // If the param has a default, ... + if is_our_default(param) { + let default_ct = tcx.const_param_default(param.def_id); + // ... and it's not a dependent default, ... + if !default_ct.needs_subst() { + // ... then substitute it with the default. + return default_ct.into(); + } + } + + tcx.mk_param_from_def(param) + } + } + }); + + // Now we build the substituted predicates. + let default_obligations = predicates + .0 + .predicates + .iter() + .flat_map(|&(pred, sp)| { + #[derive(Default)] + struct CountParams { + params: FxHashSet<u32>, + } + impl<'tcx> ty::visit::TypeVisitor<'tcx> for CountParams { + type BreakTy = (); + + fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { + if let ty::Param(param) = t.kind() { + self.params.insert(param.index); + } + t.super_visit_with(self) + } + + fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> { + ControlFlow::BREAK + } + + fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> { + if let ty::ConstKind::Param(param) = c.kind() { + self.params.insert(param.index); + } + c.super_visit_with(self) + } + } + let mut param_count = CountParams::default(); + let has_region = pred.visit_with(&mut param_count).is_break(); + let substituted_pred = predicates.rebind(pred).subst(tcx, substs); + // Don't check non-defaulted params, dependent defaults (including lifetimes) + // or preds with multiple params. + if substituted_pred.has_param_types_or_consts() + || param_count.params.len() > 1 + || has_region + { + None + } else if predicates.0.predicates.iter().any(|&(p, _)| p == substituted_pred) { + // Avoid duplication of predicates that contain no parameters, for example. + None + } else { + Some((substituted_pred, sp)) + } + }) + .map(|(pred, sp)| { + // Convert each of those into an obligation. So if you have + // something like `struct Foo<T: Copy = String>`, we would + // take that predicate `T: Copy`, substitute to `String: Copy` + // (actually that happens in the previous `flat_map` call), + // and then try to prove it (in this case, we'll fail). + // + // Note the subtle difference from how we handle `predicates` + // below: there, we are not trying to prove those predicates + // to be *true* but merely *well-formed*. + let pred = wfcx.normalize(sp, None, pred); + let cause = traits::ObligationCause::new( + sp, + wfcx.body_id, + traits::ItemObligation(def_id.to_def_id()), + ); + traits::Obligation::new(cause, wfcx.param_env, pred) + }); + + let predicates = predicates.0.instantiate_identity(tcx); + + let predicates = wfcx.normalize(span, None, predicates); + + debug!(?predicates.predicates); + assert_eq!(predicates.predicates.len(), predicates.spans.len()); + let wf_obligations = + iter::zip(&predicates.predicates, &predicates.spans).flat_map(|(&p, &sp)| { + traits::wf::predicate_obligations( + infcx, + wfcx.param_env.without_const(), + wfcx.body_id, + p, + sp, + ) + }); + + let obligations: Vec<_> = wf_obligations.chain(default_obligations).collect(); + wfcx.register_obligations(obligations); +} + +#[instrument(level = "debug", skip(wfcx, span, hir_decl))] +fn check_fn_or_method<'tcx>( + wfcx: &WfCheckingCtxt<'_, 'tcx>, + span: Span, + sig: ty::PolyFnSig<'tcx>, + hir_decl: &hir::FnDecl<'_>, + def_id: LocalDefId, +) { + let tcx = wfcx.tcx(); + let sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig); + + // Normalize the input and output types one at a time, using a different + // `WellFormedLoc` for each. We cannot call `normalize_associated_types` + // on the entire `FnSig`, since this would use the same `WellFormedLoc` + // for each type, preventing the HIR wf check from generating + // a nice error message. + let ty::FnSig { mut inputs_and_output, c_variadic, unsafety, abi } = sig; + inputs_and_output = tcx.mk_type_list(inputs_and_output.iter().enumerate().map(|(i, ty)| { + wfcx.normalize( + span, + Some(WellFormedLoc::Param { + function: def_id, + // Note that the `param_idx` of the output type is + // one greater than the index of the last input type. + param_idx: i.try_into().unwrap(), + }), + ty, + ) + })); + // Manually call `normalize_associated_types_in` on the other types + // in `FnSig`. This ensures that if the types of these fields + // ever change to include projections, we will start normalizing + // them automatically. + let sig = ty::FnSig { + inputs_and_output, + c_variadic: wfcx.normalize(span, None, c_variadic), + unsafety: wfcx.normalize(span, None, unsafety), + abi: wfcx.normalize(span, None, abi), + }; + + for (i, (&input_ty, ty)) in iter::zip(sig.inputs(), hir_decl.inputs).enumerate() { + wfcx.register_wf_obligation( + ty.span, + Some(WellFormedLoc::Param { function: def_id, param_idx: i.try_into().unwrap() }), + input_ty.into(), + ); + } + + wfcx.register_wf_obligation( + hir_decl.output.span(), + Some(WellFormedLoc::Param { + function: def_id, + param_idx: sig.inputs().len().try_into().unwrap(), + }), + sig.output().into(), + ); + + check_where_clauses(wfcx, span, def_id); + + check_return_position_impl_trait_in_trait_bounds( + tcx, + wfcx, + def_id, + sig.output(), + hir_decl.output.span(), + ); +} + +/// Basically `check_associated_type_bounds`, but separated for now and should be +/// deduplicated when RPITITs get lowered into real associated items. +fn check_return_position_impl_trait_in_trait_bounds<'tcx>( + tcx: TyCtxt<'tcx>, + wfcx: &WfCheckingCtxt<'_, 'tcx>, + fn_def_id: LocalDefId, + fn_output: Ty<'tcx>, + span: Span, +) { + if let Some(assoc_item) = tcx.opt_associated_item(fn_def_id.to_def_id()) + && assoc_item.container == ty::AssocItemContainer::TraitContainer + { + for arg in fn_output.walk() { + if let ty::GenericArgKind::Type(ty) = arg.unpack() + && let ty::Projection(proj) = ty.kind() + && tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder + && tcx.impl_trait_in_trait_parent(proj.item_def_id) == fn_def_id.to_def_id() + { + let bounds = wfcx.tcx().explicit_item_bounds(proj.item_def_id); + let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| { + let normalized_bound = wfcx.normalize(span, None, bound); + traits::wf::predicate_obligations( + wfcx.infcx, + wfcx.param_env, + wfcx.body_id, + normalized_bound, + bound_span, + ) + }); + wfcx.register_obligations(wf_obligations); + } + } + } +} + +const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \ + `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \ + of the previous types except `Self`)"; + +#[instrument(level = "debug", skip(wfcx))] +fn check_method_receiver<'tcx>( + wfcx: &WfCheckingCtxt<'_, 'tcx>, + fn_sig: &hir::FnSig<'_>, + method: &ty::AssocItem, + self_ty: Ty<'tcx>, +) { + let tcx = wfcx.tcx(); + + if !method.fn_has_self_parameter { + return; + } + + let span = fn_sig.decl.inputs[0].span; + + let sig = tcx.fn_sig(method.def_id); + let sig = tcx.liberate_late_bound_regions(method.def_id, sig); + let sig = wfcx.normalize(span, None, sig); + + debug!("check_method_receiver: sig={:?}", sig); + + let self_ty = wfcx.normalize(span, None, self_ty); + + let receiver_ty = sig.inputs()[0]; + let receiver_ty = wfcx.normalize(span, None, receiver_ty); + + if tcx.features().arbitrary_self_types { + if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) { + // Report error; `arbitrary_self_types` was enabled. + e0307(tcx, span, receiver_ty); + } + } else { + if !receiver_is_valid(wfcx, span, receiver_ty, self_ty, false) { + if receiver_is_valid(wfcx, span, receiver_ty, self_ty, true) { + // Report error; would have worked with `arbitrary_self_types`. + feature_err( + &tcx.sess.parse_sess, + sym::arbitrary_self_types, + span, + &format!( + "`{receiver_ty}` cannot be used as the type of `self` without \ + the `arbitrary_self_types` feature", + ), + ) + .help(HELP_FOR_SELF_TYPE) + .emit(); + } else { + // Report error; would not have worked with `arbitrary_self_types`. + e0307(tcx, span, receiver_ty); + } + } + } +} + +fn e0307<'tcx>(tcx: TyCtxt<'tcx>, span: Span, receiver_ty: Ty<'_>) { + struct_span_err!( + tcx.sess.diagnostic(), + span, + E0307, + "invalid `self` parameter type: {receiver_ty}" + ) + .note("type of `self` must be `Self` or a type that dereferences to it") + .help(HELP_FOR_SELF_TYPE) + .emit(); +} + +/// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If +/// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly +/// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more +/// strict: `receiver_ty` must implement `Receiver` and directly implement +/// `Deref<Target = self_ty>`. +/// +/// N.B., there are cases this function returns `true` but causes an error to be emitted, +/// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the +/// wrong lifetime. Be careful of this if you are calling this function speculatively. +fn receiver_is_valid<'tcx>( + wfcx: &WfCheckingCtxt<'_, 'tcx>, + span: Span, + receiver_ty: Ty<'tcx>, + self_ty: Ty<'tcx>, + arbitrary_self_types_enabled: bool, +) -> bool { + let infcx = wfcx.infcx; + let tcx = wfcx.tcx(); + let cause = + ObligationCause::new(span, wfcx.body_id, traits::ObligationCauseCode::MethodReceiver); + + let can_eq_self = |ty| infcx.can_eq(wfcx.param_env, self_ty, ty).is_ok(); + + // `self: Self` is always valid. + if can_eq_self(receiver_ty) { + if let Err(err) = wfcx.equate_types(&cause, wfcx.param_env, self_ty, receiver_ty) { + infcx.report_mismatched_types(&cause, self_ty, receiver_ty, err).emit(); + } + return true; + } + + let mut autoderef = + Autoderef::new(infcx, wfcx.param_env, wfcx.body_id, span, receiver_ty, span); + + // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`. + if arbitrary_self_types_enabled { + autoderef = autoderef.include_raw_pointers(); + } + + // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it. + autoderef.next(); + + let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, None); + + // Keep dereferencing `receiver_ty` until we get to `self_ty`. + loop { + if let Some((potential_self_ty, _)) = autoderef.next() { + debug!( + "receiver_is_valid: potential self type `{:?}` to match `{:?}`", + potential_self_ty, self_ty + ); + + if can_eq_self(potential_self_ty) { + wfcx.register_obligations(autoderef.into_obligations()); + + if let Err(err) = + wfcx.equate_types(&cause, wfcx.param_env, self_ty, potential_self_ty) + { + infcx.report_mismatched_types(&cause, self_ty, potential_self_ty, err).emit(); + } + + break; + } else { + // Without `feature(arbitrary_self_types)`, we require that each step in the + // deref chain implement `receiver` + if !arbitrary_self_types_enabled + && !receiver_is_implemented( + wfcx, + receiver_trait_def_id, + cause.clone(), + potential_self_ty, + ) + { + return false; + } + } + } else { + debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty); + // If the receiver already has errors reported due to it, consider it valid to avoid + // unnecessary errors (#58712). + return receiver_ty.references_error(); + } + } + + // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`. + if !arbitrary_self_types_enabled + && !receiver_is_implemented(wfcx, receiver_trait_def_id, cause.clone(), receiver_ty) + { + return false; + } + + true +} + +fn receiver_is_implemented<'tcx>( + wfcx: &WfCheckingCtxt<'_, 'tcx>, + receiver_trait_def_id: DefId, + cause: ObligationCause<'tcx>, + receiver_ty: Ty<'tcx>, +) -> bool { + let tcx = wfcx.tcx(); + let trait_ref = ty::Binder::dummy(ty::TraitRef { + def_id: receiver_trait_def_id, + substs: tcx.mk_substs_trait(receiver_ty, &[]), + }); + + let obligation = + traits::Obligation::new(cause, wfcx.param_env, trait_ref.without_const().to_predicate(tcx)); + + if wfcx.infcx.predicate_must_hold_modulo_regions(&obligation) { + true + } else { + debug!( + "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait", + receiver_ty + ); + false + } +} + +fn check_variances_for_type_defn<'tcx>( + tcx: TyCtxt<'tcx>, + item: &hir::Item<'tcx>, + hir_generics: &hir::Generics<'_>, +) { + let ty = tcx.type_of(item.def_id); + if tcx.has_error_field(ty) { + return; + } + + let ty_predicates = tcx.predicates_of(item.def_id); + assert_eq!(ty_predicates.parent, None); + let variances = tcx.variances_of(item.def_id); + + let mut constrained_parameters: FxHashSet<_> = variances + .iter() + .enumerate() + .filter(|&(_, &variance)| variance != ty::Bivariant) + .map(|(index, _)| Parameter(index as u32)) + .collect(); + + identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters); + + // Lazily calculated because it is only needed in case of an error. + let explicitly_bounded_params = LazyCell::new(|| { + let icx = crate::collect::ItemCtxt::new(tcx, item.def_id.to_def_id()); + hir_generics + .predicates + .iter() + .filter_map(|predicate| match predicate { + hir::WherePredicate::BoundPredicate(predicate) => { + match icx.to_ty(predicate.bounded_ty).kind() { + ty::Param(data) => Some(Parameter(data.index)), + _ => None, + } + } + _ => None, + }) + .collect::<FxHashSet<_>>() + }); + + for (index, _) in variances.iter().enumerate() { + let parameter = Parameter(index as u32); + + if constrained_parameters.contains(¶meter) { + continue; + } + + let param = &hir_generics.params[index]; + + match param.name { + hir::ParamName::Error => {} + _ => { + let has_explicit_bounds = explicitly_bounded_params.contains(¶meter); + report_bivariance(tcx, param, has_explicit_bounds); + } + } + } +} + +fn report_bivariance( + tcx: TyCtxt<'_>, + param: &rustc_hir::GenericParam<'_>, + has_explicit_bounds: bool, +) -> ErrorGuaranteed { + let span = param.span; + let param_name = param.name.ident().name; + let mut err = error_392(tcx, span, param_name); + + let suggested_marker_id = tcx.lang_items().phantom_data(); + // Help is available only in presence of lang items. + let msg = if let Some(def_id) = suggested_marker_id { + format!( + "consider removing `{}`, referring to it in a field, or using a marker such as `{}`", + param_name, + tcx.def_path_str(def_id), + ) + } else { + format!("consider removing `{param_name}` or referring to it in a field") + }; + err.help(&msg); + + if matches!(param.kind, hir::GenericParamKind::Type { .. }) && !has_explicit_bounds { + err.help(&format!( + "if you intended `{0}` to be a const parameter, use `const {0}: usize` instead", + param_name + )); + } + err.emit() +} + +impl<'tcx> WfCheckingCtxt<'_, 'tcx> { + /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that + /// aren't true. + #[instrument(level = "debug", skip(self))] + fn check_false_global_bounds(&mut self) { + let tcx = self.ocx.infcx.tcx; + let mut span = self.span; + let empty_env = ty::ParamEnv::empty(); + + let def_id = tcx.hir().local_def_id(self.body_id); + let predicates_with_span = tcx.predicates_of(def_id).predicates.iter().copied(); + // Check elaborated bounds. + let implied_obligations = traits::elaborate_predicates_with_span(tcx, predicates_with_span); + + for obligation in implied_obligations { + // We lower empty bounds like `Vec<dyn Copy>:` as + // `WellFormed(Vec<dyn Copy>)`, which will later get checked by + // regular WF checking + if let ty::PredicateKind::WellFormed(..) = obligation.predicate.kind().skip_binder() { + continue; + } + let pred = obligation.predicate; + // Match the existing behavior. + if pred.is_global() && !pred.has_late_bound_regions() { + let pred = self.normalize(span, None, pred); + let hir_node = tcx.hir().find(self.body_id); + + // only use the span of the predicate clause (#90869) + + if let Some(hir::Generics { predicates, .. }) = + hir_node.and_then(|node| node.generics()) + { + let obligation_span = obligation.cause.span(); + + span = predicates + .iter() + // There seems to be no better way to find out which predicate we are in + .find(|pred| pred.span().contains(obligation_span)) + .map(|pred| pred.span()) + .unwrap_or(obligation_span); + } + + let obligation = traits::Obligation::new( + traits::ObligationCause::new(span, self.body_id, traits::TrivialBound), + empty_env, + pred, + ); + self.ocx.register_obligation(obligation); + } + } + } +} + +fn check_mod_type_wf(tcx: TyCtxt<'_>, module: LocalDefId) { + let items = tcx.hir_module_items(module); + items.par_items(|item| tcx.ensure().check_well_formed(item.def_id)); + items.par_impl_items(|item| tcx.ensure().check_well_formed(item.def_id)); + items.par_trait_items(|item| tcx.ensure().check_well_formed(item.def_id)); + items.par_foreign_items(|item| tcx.ensure().check_well_formed(item.def_id)); +} + +/////////////////////////////////////////////////////////////////////////// +// ADT + +// FIXME(eddyb) replace this with getting fields/discriminants through `ty::AdtDef`. +struct AdtVariant<'tcx> { + /// Types of fields in the variant, that must be well-formed. + fields: Vec<AdtField<'tcx>>, + + /// Explicit discriminant of this variant (e.g. `A = 123`), + /// that must evaluate to a constant value. + explicit_discr: Option<LocalDefId>, +} + +struct AdtField<'tcx> { + ty: Ty<'tcx>, + def_id: LocalDefId, + span: Span, +} + +impl<'a, 'tcx> WfCheckingCtxt<'a, 'tcx> { + // FIXME(eddyb) replace this with getting fields through `ty::AdtDef`. + fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> { + let fields = struct_def + .fields() + .iter() + .map(|field| { + let def_id = self.tcx().hir().local_def_id(field.hir_id); + let field_ty = self.tcx().type_of(def_id); + let field_ty = self.normalize(field.ty.span, None, field_ty); + debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty); + AdtField { ty: field_ty, span: field.ty.span, def_id } + }) + .collect(); + AdtVariant { fields, explicit_discr: None } + } + + fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> { + enum_def + .variants + .iter() + .map(|variant| AdtVariant { + fields: self.non_enum_variant(&variant.data).fields, + explicit_discr: variant + .disr_expr + .map(|explicit_discr| self.tcx().hir().local_def_id(explicit_discr.hir_id)), + }) + .collect() + } +} + +fn error_392( + tcx: TyCtxt<'_>, + span: Span, + param_name: Symbol, +) -> DiagnosticBuilder<'_, ErrorGuaranteed> { + let mut err = struct_span_err!(tcx.sess, span, E0392, "parameter `{param_name}` is never used"); + err.span_label(span, "unused parameter"); + err +} + +pub fn provide(providers: &mut Providers) { + *providers = Providers { check_mod_type_wf, check_well_formed, ..*providers }; +} |