diff options
Diffstat (limited to 'compiler/rustc_typeck/src/coherence/mod.rs')
| -rw-r--r-- | compiler/rustc_typeck/src/coherence/mod.rs | 237 |
1 files changed, 237 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/coherence/mod.rs b/compiler/rustc_typeck/src/coherence/mod.rs new file mode 100644 index 000000000..ae9ebe590 --- /dev/null +++ b/compiler/rustc_typeck/src/coherence/mod.rs @@ -0,0 +1,237 @@ +// Coherence phase +// +// The job of the coherence phase of typechecking is to ensure that +// each trait has at most one implementation for each type. This is +// done by the orphan and overlap modules. Then we build up various +// mappings. That mapping code resides here. + +use rustc_errors::struct_span_err; +use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_middle::ty::query::Providers; +use rustc_middle::ty::{self, TyCtxt, TypeVisitable}; +use rustc_trait_selection::traits; + +mod builtin; +mod inherent_impls; +mod inherent_impls_overlap; +mod orphan; +mod unsafety; + +fn check_impl(tcx: TyCtxt<'_>, impl_def_id: LocalDefId, trait_ref: ty::TraitRef<'_>) { + debug!( + "(checking implementation) adding impl for trait '{:?}', item '{}'", + trait_ref, + tcx.def_path_str(impl_def_id.to_def_id()) + ); + + // Skip impls where one of the self type is an error type. + // This occurs with e.g., resolve failures (#30589). + if trait_ref.references_error() { + return; + } + + enforce_trait_manually_implementable(tcx, impl_def_id, trait_ref.def_id); + enforce_empty_impls_for_marker_traits(tcx, impl_def_id, trait_ref.def_id); +} + +fn enforce_trait_manually_implementable( + tcx: TyCtxt<'_>, + impl_def_id: LocalDefId, + trait_def_id: DefId, +) { + let did = Some(trait_def_id); + let li = tcx.lang_items(); + let impl_header_span = tcx.def_span(impl_def_id); + + // Disallow *all* explicit impls of `Pointee`, `DiscriminantKind`, `Sized` and `Unsize` for now. + if did == li.pointee_trait() { + struct_span_err!( + tcx.sess, + impl_header_span, + E0322, + "explicit impls for the `Pointee` trait are not permitted" + ) + .span_label(impl_header_span, "impl of `Pointee` not allowed") + .emit(); + return; + } + + if did == li.discriminant_kind_trait() { + struct_span_err!( + tcx.sess, + impl_header_span, + E0322, + "explicit impls for the `DiscriminantKind` trait are not permitted" + ) + .span_label(impl_header_span, "impl of `DiscriminantKind` not allowed") + .emit(); + return; + } + + if did == li.sized_trait() { + struct_span_err!( + tcx.sess, + impl_header_span, + E0322, + "explicit impls for the `Sized` trait are not permitted" + ) + .span_label(impl_header_span, "impl of `Sized` not allowed") + .emit(); + return; + } + + if did == li.unsize_trait() { + struct_span_err!( + tcx.sess, + impl_header_span, + E0328, + "explicit impls for the `Unsize` trait are not permitted" + ) + .span_label(impl_header_span, "impl of `Unsize` not allowed") + .emit(); + return; + } + + if tcx.features().unboxed_closures { + // the feature gate allows all Fn traits + return; + } + + if let ty::trait_def::TraitSpecializationKind::AlwaysApplicable = + tcx.trait_def(trait_def_id).specialization_kind + { + if !tcx.features().specialization && !tcx.features().min_specialization { + tcx.sess + .struct_span_err( + impl_header_span, + "implementing `rustc_specialization_trait` traits is unstable", + ) + .help("add `#![feature(min_specialization)]` to the crate attributes to enable") + .emit(); + return; + } + } +} + +/// We allow impls of marker traits to overlap, so they can't override impls +/// as that could make it ambiguous which associated item to use. +fn enforce_empty_impls_for_marker_traits( + tcx: TyCtxt<'_>, + impl_def_id: LocalDefId, + trait_def_id: DefId, +) { + if !tcx.trait_def(trait_def_id).is_marker { + return; + } + + if tcx.associated_item_def_ids(trait_def_id).is_empty() { + return; + } + + struct_span_err!( + tcx.sess, + tcx.def_span(impl_def_id), + E0715, + "impls for marker traits cannot contain items" + ) + .emit(); +} + +pub fn provide(providers: &mut Providers) { + use self::builtin::coerce_unsized_info; + use self::inherent_impls::{crate_incoherent_impls, crate_inherent_impls, inherent_impls}; + use self::inherent_impls_overlap::crate_inherent_impls_overlap_check; + use self::orphan::orphan_check_impl; + + *providers = Providers { + coherent_trait, + crate_inherent_impls, + crate_incoherent_impls, + inherent_impls, + crate_inherent_impls_overlap_check, + coerce_unsized_info, + orphan_check_impl, + ..*providers + }; +} + +fn coherent_trait(tcx: TyCtxt<'_>, def_id: DefId) { + // Trigger building the specialization graph for the trait. This will detect and report any + // overlap errors. + tcx.ensure().specialization_graph_of(def_id); + + let impls = tcx.hir().trait_impls(def_id); + for &impl_def_id in impls { + let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); + + check_impl(tcx, impl_def_id, trait_ref); + check_object_overlap(tcx, impl_def_id, trait_ref); + + tcx.sess.time("unsafety_checking", || unsafety::check_item(tcx, impl_def_id)); + tcx.sess.time("orphan_checking", || tcx.ensure().orphan_check_impl(impl_def_id)); + } + + builtin::check_trait(tcx, def_id); +} + +/// Checks whether an impl overlaps with the automatic `impl Trait for dyn Trait`. +fn check_object_overlap<'tcx>( + tcx: TyCtxt<'tcx>, + impl_def_id: LocalDefId, + trait_ref: ty::TraitRef<'tcx>, +) { + let trait_def_id = trait_ref.def_id; + + if trait_ref.references_error() { + debug!("coherence: skipping impl {:?} with error {:?}", impl_def_id, trait_ref); + return; + } + + // check for overlap with the automatic `impl Trait for dyn Trait` + if let ty::Dynamic(data, ..) = trait_ref.self_ty().kind() { + // This is something like impl Trait1 for Trait2. Illegal + // if Trait1 is a supertrait of Trait2 or Trait2 is not object safe. + + let component_def_ids = data.iter().flat_map(|predicate| { + match predicate.skip_binder() { + ty::ExistentialPredicate::Trait(tr) => Some(tr.def_id), + ty::ExistentialPredicate::AutoTrait(def_id) => Some(def_id), + // An associated type projection necessarily comes with + // an additional `Trait` requirement. + ty::ExistentialPredicate::Projection(..) => None, + } + }); + + for component_def_id in component_def_ids { + if !tcx.is_object_safe(component_def_id) { + // Without the 'object_safe_for_dispatch' feature this is an error + // which will be reported by wfcheck. Ignore it here. + // This is tested by `coherence-impl-trait-for-trait-object-safe.rs`. + // With the feature enabled, the trait is not implemented automatically, + // so this is valid. + } else { + let mut supertrait_def_ids = traits::supertrait_def_ids(tcx, component_def_id); + if supertrait_def_ids.any(|d| d == trait_def_id) { + let span = tcx.def_span(impl_def_id); + struct_span_err!( + tcx.sess, + span, + E0371, + "the object type `{}` automatically implements the trait `{}`", + trait_ref.self_ty(), + tcx.def_path_str(trait_def_id) + ) + .span_label( + span, + format!( + "`{}` automatically implements trait `{}`", + trait_ref.self_ty(), + tcx.def_path_str(trait_def_id) + ), + ) + .emit(); + } + } + } + } +} |