| //! Check properties that are required by built-in traits and set |
| //! up data structures required by type-checking/codegen. |
| |
| use crate::errors::{CopyImplOnNonAdt, CopyImplOnTypeWithDtor, DropImplOnWrongItem}; |
| use rustc_errors::{struct_span_err, MultiSpan}; |
| 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; |
| use rustc_infer::infer::outlives::env::OutlivesEnvironment; |
| use rustc_infer::infer::TyCtxtInferExt; |
| use rustc_middle::ty::adjustment::CoerceUnsizedInfo; |
| use rustc_middle::ty::{self, suggest_constraining_type_params, Ty, TyCtxt, TypeVisitable}; |
| use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt; |
| use rustc_trait_selection::traits::misc::{can_type_implement_copy, CopyImplementationError}; |
| use rustc_trait_selection::traits::predicate_for_trait_def; |
| use rustc_trait_selection::traits::{self, ObligationCause}; |
| use std::collections::BTreeMap; |
| |
| pub fn check_trait(tcx: TyCtxt<'_>, trait_def_id: DefId) { |
| let lang_items = tcx.lang_items(); |
| Checker { tcx, trait_def_id } |
| .check(lang_items.drop_trait(), visit_implementation_of_drop) |
| .check(lang_items.copy_trait(), visit_implementation_of_copy) |
| .check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized) |
| .check(lang_items.dispatch_from_dyn_trait(), visit_implementation_of_dispatch_from_dyn); |
| } |
| |
| struct Checker<'tcx> { |
| tcx: TyCtxt<'tcx>, |
| trait_def_id: DefId, |
| } |
| |
| impl<'tcx> Checker<'tcx> { |
| fn check<F>(&self, trait_def_id: Option<DefId>, mut f: F) -> &Self |
| where |
| F: FnMut(TyCtxt<'tcx>, LocalDefId), |
| { |
| if Some(self.trait_def_id) == trait_def_id { |
| for &impl_def_id in self.tcx.hir().trait_impls(self.trait_def_id) { |
| f(self.tcx, impl_def_id); |
| } |
| } |
| self |
| } |
| } |
| |
| fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: LocalDefId) { |
| // Destructors only work on local ADT types. |
| match tcx.type_of(impl_did).kind() { |
| ty::Adt(def, _) if def.did().is_local() => return, |
| ty::Error(_) => return, |
| _ => {} |
| } |
| |
| let sp = match tcx.hir().expect_item(impl_did).kind { |
| ItemKind::Impl(ref impl_) => impl_.self_ty.span, |
| _ => bug!("expected Drop impl item"), |
| }; |
| |
| tcx.sess.emit_err(DropImplOnWrongItem { span: sp }); |
| } |
| |
| fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) { |
| debug!("visit_implementation_of_copy: impl_did={:?}", impl_did); |
| |
| let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
| |
| let self_type = tcx.type_of(impl_did); |
| debug!("visit_implementation_of_copy: self_type={:?} (bound)", self_type); |
| |
| let param_env = tcx.param_env(impl_did); |
| assert!(!self_type.has_escaping_bound_vars()); |
| |
| debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type); |
| |
| let span = match tcx.hir().expect_item(impl_did).kind { |
| ItemKind::Impl(hir::Impl { polarity: hir::ImplPolarity::Negative(_), .. }) => return, |
| ItemKind::Impl(impl_) => impl_.self_ty.span, |
| _ => bug!("expected Copy impl item"), |
| }; |
| |
| let cause = traits::ObligationCause::misc(span, impl_hir_id); |
| match can_type_implement_copy(tcx, param_env, self_type, cause) { |
| Ok(()) => {} |
| Err(CopyImplementationError::InfrigingFields(fields)) => { |
| let mut err = struct_span_err!( |
| tcx.sess, |
| span, |
| E0204, |
| "the trait `Copy` may not be implemented for this type" |
| ); |
| |
| // We'll try to suggest constraining type parameters to fulfill the requirements of |
| // their `Copy` implementation. |
| let mut errors: BTreeMap<_, Vec<_>> = Default::default(); |
| let mut bounds = vec![]; |
| |
| for (field, ty) in fields { |
| let field_span = tcx.def_span(field.did); |
| let field_ty_span = match tcx.hir().get_if_local(field.did) { |
| Some(hir::Node::Field(field_def)) => field_def.ty.span, |
| _ => field_span, |
| }; |
| err.span_label(field_span, "this field does not implement `Copy`"); |
| // Spin up a new FulfillmentContext, so we can get the _precise_ reason |
| // why this field does not implement Copy. This is useful because sometimes |
| // it is not immediately clear why Copy is not implemented for a field, since |
| // all we point at is the field itself. |
| let infcx = tcx.infer_ctxt().ignoring_regions().build(); |
| for error in traits::fully_solve_bound( |
| &infcx, |
| traits::ObligationCause::dummy_with_span(field_ty_span), |
| param_env, |
| ty, |
| tcx.require_lang_item(LangItem::Copy, Some(span)), |
| ) { |
| let error_predicate = error.obligation.predicate; |
| // Only note if it's not the root obligation, otherwise it's trivial and |
| // should be self-explanatory (i.e. a field literally doesn't implement Copy). |
| |
| // FIXME: This error could be more descriptive, especially if the error_predicate |
| // contains a foreign type or if it's a deeply nested type... |
| if error_predicate != error.root_obligation.predicate { |
| errors |
| .entry((ty.to_string(), error_predicate.to_string())) |
| .or_default() |
| .push(error.obligation.cause.span); |
| } |
| if let ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate { |
| trait_ref, |
| polarity: ty::ImplPolarity::Positive, |
| .. |
| })) = error_predicate.kind().skip_binder() |
| { |
| let ty = trait_ref.self_ty(); |
| if let ty::Param(_) = ty.kind() { |
| bounds.push(( |
| format!("{ty}"), |
| trait_ref.print_only_trait_path().to_string(), |
| Some(trait_ref.def_id), |
| )); |
| } |
| } |
| } |
| } |
| for ((ty, error_predicate), spans) in errors { |
| let span: MultiSpan = spans.into(); |
| err.span_note( |
| span, |
| &format!("the `Copy` impl for `{}` requires that `{}`", ty, error_predicate), |
| ); |
| } |
| suggest_constraining_type_params( |
| tcx, |
| tcx.hir().get_generics(impl_did).expect("impls always have generics"), |
| &mut err, |
| bounds.iter().map(|(param, constraint, def_id)| { |
| (param.as_str(), constraint.as_str(), *def_id) |
| }), |
| ); |
| err.emit(); |
| } |
| Err(CopyImplementationError::NotAnAdt) => { |
| tcx.sess.emit_err(CopyImplOnNonAdt { span }); |
| } |
| Err(CopyImplementationError::HasDestructor) => { |
| tcx.sess.emit_err(CopyImplOnTypeWithDtor { span }); |
| } |
| } |
| } |
| |
| fn visit_implementation_of_coerce_unsized<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) { |
| debug!("visit_implementation_of_coerce_unsized: impl_did={:?}", impl_did); |
| |
| // Just compute this for the side-effects, in particular reporting |
| // errors; other parts of the code may demand it for the info of |
| // course. |
| let span = tcx.def_span(impl_did); |
| tcx.at(span).coerce_unsized_info(impl_did); |
| } |
| |
| fn visit_implementation_of_dispatch_from_dyn<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) { |
| debug!("visit_implementation_of_dispatch_from_dyn: impl_did={:?}", impl_did); |
| |
| let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
| let span = tcx.hir().span(impl_hir_id); |
| |
| let dispatch_from_dyn_trait = tcx.require_lang_item(LangItem::DispatchFromDyn, Some(span)); |
| |
| let source = tcx.type_of(impl_did); |
| assert!(!source.has_escaping_bound_vars()); |
| let target = { |
| let trait_ref = tcx.impl_trait_ref(impl_did).unwrap(); |
| assert_eq!(trait_ref.def_id, dispatch_from_dyn_trait); |
| |
| trait_ref.substs.type_at(1) |
| }; |
| |
| debug!("visit_implementation_of_dispatch_from_dyn: {:?} -> {:?}", source, target); |
| |
| let param_env = tcx.param_env(impl_did); |
| |
| let create_err = |msg: &str| struct_span_err!(tcx.sess, span, E0378, "{}", msg); |
| |
| let infcx = tcx.infer_ctxt().build(); |
| let cause = ObligationCause::misc(span, impl_hir_id); |
| |
| use rustc_type_ir::sty::TyKind::*; |
| match (source.kind(), target.kind()) { |
| (&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b)) |
| if infcx.at(&cause, param_env).eq(r_a, *r_b).is_ok() && mutbl_a == *mutbl_b => {} |
| (&RawPtr(tm_a), &RawPtr(tm_b)) if tm_a.mutbl == tm_b.mutbl => (), |
| (&Adt(def_a, substs_a), &Adt(def_b, substs_b)) |
| if def_a.is_struct() && def_b.is_struct() => |
| { |
| if def_a != def_b { |
| let source_path = tcx.def_path_str(def_a.did()); |
| let target_path = tcx.def_path_str(def_b.did()); |
| |
| create_err(&format!( |
| "the trait `DispatchFromDyn` may only be implemented \ |
| for a coercion between structures with the same \ |
| definition; expected `{}`, found `{}`", |
| source_path, target_path, |
| )) |
| .emit(); |
| |
| return; |
| } |
| |
| if def_a.repr().c() || def_a.repr().packed() { |
| create_err( |
| "structs implementing `DispatchFromDyn` may not have \ |
| `#[repr(packed)]` or `#[repr(C)]`", |
| ) |
| .emit(); |
| } |
| |
| let fields = &def_a.non_enum_variant().fields; |
| |
| let coerced_fields = fields |
| .iter() |
| .filter(|field| { |
| let ty_a = field.ty(tcx, substs_a); |
| let ty_b = field.ty(tcx, substs_b); |
| |
| if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) { |
| if layout.is_zst() && layout.align.abi.bytes() == 1 { |
| // ignore ZST fields with alignment of 1 byte |
| return false; |
| } |
| } |
| |
| if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) { |
| if ok.obligations.is_empty() { |
| create_err( |
| "the trait `DispatchFromDyn` may only be implemented \ |
| for structs containing the field being coerced, \ |
| ZST fields with 1 byte alignment, and nothing else", |
| ) |
| .note(&format!( |
| "extra field `{}` of type `{}` is not allowed", |
| field.name, ty_a, |
| )) |
| .emit(); |
| |
| return false; |
| } |
| } |
| |
| return true; |
| }) |
| .collect::<Vec<_>>(); |
| |
| if coerced_fields.is_empty() { |
| create_err( |
| "the trait `DispatchFromDyn` may only be implemented \ |
| for a coercion between structures with a single field \ |
| being coerced, none found", |
| ) |
| .emit(); |
| } else if coerced_fields.len() > 1 { |
| create_err("implementing the `DispatchFromDyn` trait requires multiple coercions") |
| .note( |
| "the trait `DispatchFromDyn` may only be implemented \ |
| for a coercion between structures with a single field \ |
| being coerced", |
| ) |
| .note(&format!( |
| "currently, {} fields need coercions: {}", |
| coerced_fields.len(), |
| coerced_fields |
| .iter() |
| .map(|field| { |
| format!( |
| "`{}` (`{}` to `{}`)", |
| field.name, |
| field.ty(tcx, substs_a), |
| field.ty(tcx, substs_b), |
| ) |
| }) |
| .collect::<Vec<_>>() |
| .join(", ") |
| )) |
| .emit(); |
| } else { |
| let errors = traits::fully_solve_obligations( |
| &infcx, |
| coerced_fields.into_iter().map(|field| { |
| predicate_for_trait_def( |
| tcx, |
| param_env, |
| cause.clone(), |
| dispatch_from_dyn_trait, |
| 0, |
| [field.ty(tcx, substs_a), field.ty(tcx, substs_b)], |
| ) |
| }), |
| ); |
| if !errors.is_empty() { |
| infcx.err_ctxt().report_fulfillment_errors(&errors, None); |
| } |
| |
| // Finally, resolve all regions. |
| let outlives_env = OutlivesEnvironment::new(param_env); |
| infcx.check_region_obligations_and_report_errors(impl_did, &outlives_env); |
| } |
| } |
| _ => { |
| create_err( |
| "the trait `DispatchFromDyn` may only be implemented \ |
| for a coercion between structures", |
| ) |
| .emit(); |
| } |
| } |
| } |
| |
| pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUnsizedInfo { |
| debug!("compute_coerce_unsized_info(impl_did={:?})", impl_did); |
| |
| // this provider should only get invoked for local def-ids |
| let impl_did = impl_did.expect_local(); |
| let span = tcx.def_span(impl_did); |
| |
| let coerce_unsized_trait = tcx.require_lang_item(LangItem::CoerceUnsized, Some(span)); |
| |
| let unsize_trait = tcx.lang_items().require(LangItem::Unsize).unwrap_or_else(|err| { |
| tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err.to_string())); |
| }); |
| |
| let source = tcx.type_of(impl_did); |
| let trait_ref = tcx.impl_trait_ref(impl_did).unwrap(); |
| assert_eq!(trait_ref.def_id, coerce_unsized_trait); |
| let target = trait_ref.substs.type_at(1); |
| debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)", source, target); |
| |
| let param_env = tcx.param_env(impl_did); |
| assert!(!source.has_escaping_bound_vars()); |
| |
| let err_info = CoerceUnsizedInfo { custom_kind: None }; |
| |
| debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)", source, target); |
| |
| let infcx = tcx.infer_ctxt().build(); |
| let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did); |
| let cause = ObligationCause::misc(span, impl_hir_id); |
| let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>, |
| mt_b: ty::TypeAndMut<'tcx>, |
| mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| { |
| if mt_a.mutbl < mt_b.mutbl { |
| infcx |
| .err_ctxt() |
| .report_mismatched_types( |
| &cause, |
| mk_ptr(mt_b.ty), |
| target, |
| ty::error::TypeError::Mutability, |
| ) |
| .emit(); |
| } |
| (mt_a.ty, mt_b.ty, unsize_trait, None) |
| }; |
| let (source, target, trait_def_id, kind) = match (source.kind(), target.kind()) { |
| (&ty::Ref(r_a, ty_a, mutbl_a), &ty::Ref(r_b, ty_b, mutbl_b)) => { |
| infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a); |
| let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a }; |
| let mt_b = ty::TypeAndMut { ty: ty_b, mutbl: mutbl_b }; |
| check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty)) |
| } |
| |
| (&ty::Ref(_, ty_a, mutbl_a), &ty::RawPtr(mt_b)) => { |
| let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a }; |
| check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty)) |
| } |
| |
| (&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty)), |
| |
| (&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b)) |
| if def_a.is_struct() && def_b.is_struct() => |
| { |
| if def_a != def_b { |
| let source_path = tcx.def_path_str(def_a.did()); |
| let target_path = tcx.def_path_str(def_b.did()); |
| struct_span_err!( |
| tcx.sess, |
| span, |
| E0377, |
| "the trait `CoerceUnsized` may only be implemented \ |
| for a coercion between structures with the same \ |
| definition; expected `{}`, found `{}`", |
| source_path, |
| target_path |
| ) |
| .emit(); |
| return err_info; |
| } |
| |
| // Here we are considering a case of converting |
| // `S<P0...Pn>` to S<Q0...Qn>`. As an example, let's imagine a struct `Foo<T, U>`, |
| // which acts like a pointer to `U`, but carries along some extra data of type `T`: |
| // |
| // struct Foo<T, U> { |
| // extra: T, |
| // ptr: *mut U, |
| // } |
| // |
| // We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized |
| // to `Foo<T, [i32]>`. That impl would look like: |
| // |
| // impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {} |
| // |
| // Here `U = [i32; 3]` and `V = [i32]`. At runtime, |
| // when this coercion occurs, we would be changing the |
| // field `ptr` from a thin pointer of type `*mut [i32; |
| // 3]` to a fat pointer of type `*mut [i32]` (with |
| // extra data `3`). **The purpose of this check is to |
| // make sure that we know how to do this conversion.** |
| // |
| // To check if this impl is legal, we would walk down |
| // the fields of `Foo` and consider their types with |
| // both substitutes. We are looking to find that |
| // exactly one (non-phantom) field has changed its |
| // type, which we will expect to be the pointer that |
| // is becoming fat (we could probably generalize this |
| // to multiple thin pointers of the same type becoming |
| // fat, but we don't). In this case: |
| // |
| // - `extra` has type `T` before and type `T` after |
| // - `ptr` has type `*mut U` before and type `*mut V` after |
| // |
| // Since just one field changed, we would then check |
| // that `*mut U: CoerceUnsized<*mut V>` is implemented |
| // (in other words, that we know how to do this |
| // conversion). This will work out because `U: |
| // Unsize<V>`, and we have a builtin rule that `*mut |
| // U` can be coerced to `*mut V` if `U: Unsize<V>`. |
| let fields = &def_a.non_enum_variant().fields; |
| let diff_fields = fields |
| .iter() |
| .enumerate() |
| .filter_map(|(i, f)| { |
| let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b)); |
| |
| if tcx.type_of(f.did).is_phantom_data() { |
| // Ignore PhantomData fields |
| return None; |
| } |
| |
| // Ignore fields that aren't changed; it may |
| // be that we could get away with subtyping or |
| // something more accepting, but we use |
| // equality because we want to be able to |
| // perform this check without computing |
| // variance where possible. (This is because |
| // we may have to evaluate constraint |
| // expressions in the course of execution.) |
| // See e.g., #41936. |
| if let Ok(ok) = infcx.at(&cause, param_env).eq(a, b) { |
| if ok.obligations.is_empty() { |
| return None; |
| } |
| } |
| |
| // Collect up all fields that were significantly changed |
| // i.e., those that contain T in coerce_unsized T -> U |
| Some((i, a, b)) |
| }) |
| .collect::<Vec<_>>(); |
| |
| if diff_fields.is_empty() { |
| struct_span_err!( |
| tcx.sess, |
| span, |
| E0374, |
| "the trait `CoerceUnsized` may only be implemented \ |
| for a coercion between structures with one field \ |
| being coerced, none found" |
| ) |
| .emit(); |
| return err_info; |
| } else if diff_fields.len() > 1 { |
| let item = tcx.hir().expect_item(impl_did); |
| let span = |
| if let ItemKind::Impl(hir::Impl { of_trait: Some(ref t), .. }) = item.kind { |
| t.path.span |
| } else { |
| tcx.def_span(impl_did) |
| }; |
| |
| struct_span_err!( |
| tcx.sess, |
| span, |
| E0375, |
| "implementing the trait \ |
| `CoerceUnsized` requires multiple \ |
| coercions" |
| ) |
| .note( |
| "`CoerceUnsized` may only be implemented for \ |
| a coercion between structures with one field being coerced", |
| ) |
| .note(&format!( |
| "currently, {} fields need coercions: {}", |
| diff_fields.len(), |
| diff_fields |
| .iter() |
| .map(|&(i, a, b)| { format!("`{}` (`{}` to `{}`)", fields[i].name, a, b) }) |
| .collect::<Vec<_>>() |
| .join(", ") |
| )) |
| .span_label(span, "requires multiple coercions") |
| .emit(); |
| return err_info; |
| } |
| |
| let (i, a, b) = diff_fields[0]; |
| let kind = ty::adjustment::CustomCoerceUnsized::Struct(i); |
| (a, b, coerce_unsized_trait, Some(kind)) |
| } |
| |
| _ => { |
| struct_span_err!( |
| tcx.sess, |
| span, |
| E0376, |
| "the trait `CoerceUnsized` may only be implemented \ |
| for a coercion between structures" |
| ) |
| .emit(); |
| return err_info; |
| } |
| }; |
| |
| // Register an obligation for `A: Trait<B>`. |
| let cause = traits::ObligationCause::misc(span, impl_hir_id); |
| let predicate = |
| predicate_for_trait_def(tcx, param_env, cause, trait_def_id, 0, [source, target]); |
| let errors = traits::fully_solve_obligation(&infcx, predicate); |
| if !errors.is_empty() { |
| infcx.err_ctxt().report_fulfillment_errors(&errors, None); |
| } |
| |
| // Finally, resolve all regions. |
| let outlives_env = OutlivesEnvironment::new(param_env); |
| infcx.check_region_obligations_and_report_errors(impl_did, &outlives_env); |
| |
| CoerceUnsizedInfo { custom_kind: kind } |
| } |
