rustc_typeck to rustc_hir_analysis

compiler/rustc_hir_analysis/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();
+                }
+            }
+        }
+    }
+}