| // 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::traits; |
| use rustc::ty::query::Providers; |
| use rustc::ty::{self, TyCtxt, TypeFoldable}; |
| use rustc_errors::struct_span_err; |
| use rustc_hir::def_id::{DefId, LOCAL_CRATE}; |
| use rustc_hir::HirId; |
| |
| mod builtin; |
| mod inherent_impls; |
| mod inherent_impls_overlap; |
| mod orphan; |
| mod unsafety; |
| |
| fn check_impl(tcx: TyCtxt<'_>, hir_id: HirId) { |
| let impl_def_id = tcx.hir().local_def_id(hir_id); |
| |
| // If there are no traits, then this implementation must have a |
| // base type. |
| |
| if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) { |
| debug!( |
| "(checking implementation) adding impl for trait '{:?}', item '{}'", |
| trait_ref, |
| tcx.def_path_str(impl_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: DefId, trait_def_id: DefId) { |
| let did = Some(trait_def_id); |
| let li = tcx.lang_items(); |
| let span = tcx.sess.source_map().def_span(tcx.span_of_impl(impl_def_id).unwrap()); |
| |
| // Disallow *all* explicit impls of `Sized` and `Unsize` for now. |
| if did == li.sized_trait() { |
| struct_span_err!( |
| tcx.sess, |
| span, |
| E0322, |
| "explicit impls for the `Sized` trait are not permitted" |
| ) |
| .span_label(span, "impl of 'Sized' not allowed") |
| .emit(); |
| return; |
| } |
| |
| if did == li.unsize_trait() { |
| struct_span_err!( |
| tcx.sess, |
| span, |
| E0328, |
| "explicit impls for the `Unsize` trait are not permitted" |
| ) |
| .span_label(span, "impl of `Unsize` not allowed") |
| .emit(); |
| return; |
| } |
| |
| if tcx.features().unboxed_closures { |
| // the feature gate allows all Fn traits |
| return; |
| } |
| |
| let trait_name = if did == li.fn_trait() { |
| "Fn" |
| } else if did == li.fn_mut_trait() { |
| "FnMut" |
| } else if did == li.fn_once_trait() { |
| "FnOnce" |
| } else { |
| return; // everything OK |
| }; |
| struct_span_err!( |
| tcx.sess, |
| span, |
| E0183, |
| "manual implementations of `{}` are experimental", |
| trait_name |
| ) |
| .span_label(span, format!("manual implementations of `{}` are experimental", trait_name)) |
| .help("add `#![feature(unboxed_closures)]` to the crate attributes to enable") |
| .emit(); |
| } |
| |
| /// 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: DefId, 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; |
| } |
| |
| let span = tcx.sess.source_map().def_span(tcx.span_of_impl(impl_def_id).unwrap()); |
| struct_span_err!(tcx.sess, span, 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_inherent_impls, inherent_impls}; |
| use self::inherent_impls_overlap::crate_inherent_impls_overlap_check; |
| |
| *providers = Providers { |
| coherent_trait, |
| crate_inherent_impls, |
| inherent_impls, |
| crate_inherent_impls_overlap_check, |
| coerce_unsized_info, |
| ..*providers |
| }; |
| } |
| |
| fn coherent_trait(tcx: TyCtxt<'_>, def_id: DefId) { |
| let impls = tcx.hir().trait_impls(def_id); |
| for &impl_id in impls { |
| check_impl(tcx, impl_id); |
| } |
| for &impl_id in impls { |
| check_impl_overlap(tcx, impl_id); |
| } |
| builtin::check_trait(tcx, def_id); |
| } |
| |
| pub fn check_coherence(tcx: TyCtxt<'_>) { |
| for &trait_def_id in tcx.hir().krate().trait_impls.keys() { |
| tcx.ensure().coherent_trait(trait_def_id); |
| } |
| |
| tcx.sess.time("unsafety_checking", || unsafety::check(tcx)); |
| tcx.sess.time("orphan_checking", || orphan::check(tcx)); |
| |
| // these queries are executed for side-effects (error reporting): |
| tcx.ensure().crate_inherent_impls(LOCAL_CRATE); |
| tcx.ensure().crate_inherent_impls_overlap_check(LOCAL_CRATE); |
| } |
| |
| /// Overlap: no two impls for the same trait are implemented for the |
| /// same type. Likewise, no two inherent impls for a given type |
| /// constructor provide a method with the same name. |
| fn check_impl_overlap<'tcx>(tcx: TyCtxt<'tcx>, hir_id: HirId) { |
| let impl_def_id = tcx.hir().local_def_id(hir_id); |
| let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); |
| 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; |
| } |
| |
| // Trigger building the specialization graph for the trait of this impl. |
| // This will detect any overlap errors. |
| tcx.specialization_graph_of(trait_def_id); |
| |
| // check for overlap with the automatic `impl Trait for Trait` |
| if let ty::Dynamic(ref 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 sp = tcx.sess.source_map().def_span(tcx.span_of_impl(impl_def_id).unwrap()); |
| struct_span_err!( |
| tcx.sess, |
| sp, |
| E0371, |
| "the object type `{}` automatically implements the trait `{}`", |
| trait_ref.self_ty(), |
| tcx.def_path_str(trait_def_id) |
| ) |
| .span_label( |
| sp, |
| format!( |
| "`{}` automatically implements trait `{}`", |
| trait_ref.self_ty(), |
| tcx.def_path_str(trait_def_id) |
| ), |
| ) |
| .emit(); |
| } |
| } |
| } |
| } |
| } |