inherent_impls.rs

//! The code in this module gathers up all of the inherent impls in
//! the current crate and organizes them in a map. It winds up
//! touching the whole crate and thus must be recomputed completely
//! for any change, but it is very cheap to compute. In practice, most
//! code in the compiler never *directly* requests this map. Instead,
//! it requests the inherent impls specific to some type (via
//! `tcx.inherent_impls(def_id)`). That value, however,
//! is computed by selecting an idea from this table.

use rustc_errors::struct_span_err;
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::ty::fast_reject::{simplify_type, SimplifiedType, TreatParams};
use rustc_middle::ty::{self, CrateInherentImpls, Ty, TyCtxt};
use rustc_span::symbol::sym;

/// On-demand query: yields a map containing all types mapped to their inherent impls.
pub fn crate_inherent_impls(tcx: TyCtxt<'_>, (): ()) -> CrateInherentImpls {
    let mut collect = InherentCollect { tcx, impls_map: Default::default() };
    for id in tcx.hir().items() {
        collect.check_item(id);
    }
    collect.impls_map
}

pub fn crate_incoherent_impls(tcx: TyCtxt<'_>, simp: SimplifiedType) -> &[DefId] {
    let crate_map = tcx.crate_inherent_impls(());
    tcx.arena.alloc_from_iter(
        crate_map.incoherent_impls.get(&simp).unwrap_or(&Vec::new()).iter().map(|d| d.to_def_id()),
    )
}

/// On-demand query: yields a vector of the inherent impls for a specific type.
pub fn inherent_impls(tcx: TyCtxt<'_>, ty_def_id: LocalDefId) -> &[DefId] {
    let crate_map = tcx.crate_inherent_impls(());
    match crate_map.inherent_impls.get(&ty_def_id) {
        Some(v) => &v[..],
        None => &[],
    }
}

struct InherentCollect<'tcx> {
    tcx: TyCtxt<'tcx>,
    impls_map: CrateInherentImpls,
}

const INTO_CORE: &str = "consider moving this inherent impl into `core` if possible";
const INTO_DEFINING_CRATE: &str =
    "consider moving this inherent impl into the crate defining the type if possible";
const ADD_ATTR_TO_TY: &str = "alternatively add `#[rustc_has_incoherent_inherent_impls]` to the type \
     and `#[rustc_allow_incoherent_impl]` to the relevant impl items";
const ADD_ATTR: &str =
    "alternatively add `#[rustc_allow_incoherent_impl]` to the relevant impl items";

impl<'tcx> InherentCollect<'tcx> {
    fn check_def_id(&mut self, impl_def_id: LocalDefId, self_ty: Ty<'tcx>, ty_def_id: DefId) {
        if let Some(ty_def_id) = ty_def_id.as_local() {
            // Add the implementation to the mapping from implementation to base
            // type def ID, if there is a base type for this implementation and
            // the implementation does not have any associated traits.
            let vec = self.impls_map.inherent_impls.entry(ty_def_id).or_default();
            vec.push(impl_def_id.to_def_id());
            return;
        }

        if self.tcx.features().rustc_attrs {
            let items = self.tcx.associated_item_def_ids(impl_def_id);

            if !self.tcx.has_attr(ty_def_id, sym::rustc_has_incoherent_inherent_impls) {
                let impl_span = self.tcx.def_span(impl_def_id);
                struct_span_err!(
                    self.tcx.sess,
                    impl_span,
                    E0390,
                    "cannot define inherent `impl` for a type outside of the crate where the type is defined",
                )
                .help(INTO_DEFINING_CRATE)
                .span_help(impl_span, ADD_ATTR_TO_TY)
                .emit();
                return;
            }

            for &impl_item in items {
                if !self.tcx.has_attr(impl_item, sym::rustc_allow_incoherent_impl) {
                    let impl_span = self.tcx.def_span(impl_def_id);
                    struct_span_err!(
                        self.tcx.sess,
                        impl_span,
                        E0390,
                        "cannot define inherent `impl` for a type outside of the crate where the type is defined",
                    )
                    .help(INTO_DEFINING_CRATE)
                    .span_help(self.tcx.def_span(impl_item), ADD_ATTR)
                    .emit();
                    return;
                }
            }

            if let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsCandidateKey) {
                self.impls_map.incoherent_impls.entry(simp).or_default().push(impl_def_id);
            } else {
                bug!("unexpected self type: {:?}", self_ty);
            }
        } else {
            let impl_span = self.tcx.def_span(impl_def_id);
            struct_span_err!(
                self.tcx.sess,
                impl_span,
                E0116,
                "cannot define inherent `impl` for a type outside of the crate \
                              where the type is defined"
            )
            .span_label(impl_span, "impl for type defined outside of crate.")
            .note("define and implement a trait or new type instead")
            .emit();
        }
    }

    fn check_primitive_impl(&mut self, impl_def_id: LocalDefId, ty: Ty<'tcx>) {
        let items = self.tcx.associated_item_def_ids(impl_def_id);
        if !self.tcx.hir().rustc_coherence_is_core() {
            if self.tcx.features().rustc_attrs {
                for &impl_item in items {
                    if !self.tcx.has_attr(impl_item, sym::rustc_allow_incoherent_impl) {
                        let span = self.tcx.def_span(impl_def_id);
                        struct_span_err!(
                            self.tcx.sess,
                            span,
                            E0390,
                            "cannot define inherent `impl` for primitive types outside of `core`",
                        )
                        .help(INTO_CORE)
                        .span_help(self.tcx.def_span(impl_item), ADD_ATTR)
                        .emit();
                        return;
                    }
                }
            } else {
                let span = self.tcx.def_span(impl_def_id);
                let mut err = struct_span_err!(
                    self.tcx.sess,
                    span,
                    E0390,
                    "cannot define inherent `impl` for primitive types",
                );
                err.help("consider using an extension trait instead");
                if let ty::Ref(_, subty, _) = ty.kind() {
                    err.note(&format!(
                        "you could also try moving the reference to \
                            uses of `{}` (such as `self`) within the implementation",
                        subty
                    ));
                }
                err.emit();
                return;
            }
        }

        if let Some(simp) = simplify_type(self.tcx, ty, TreatParams::AsCandidateKey) {
            self.impls_map.incoherent_impls.entry(simp).or_default().push(impl_def_id);
        } else {
            bug!("unexpected primitive type: {:?}", ty);
        }
    }

    fn check_item(&mut self, id: hir::ItemId) {
        if !matches!(self.tcx.def_kind(id.owner_id), DefKind::Impl { of_trait: false }) {
            return;
        }

        let id = id.owner_id.def_id;
        let item_span = self.tcx.def_span(id);
        let self_ty = self.tcx.type_of(id).subst_identity();
        match *self_ty.kind() {
            ty::Adt(def, _) => self.check_def_id(id, self_ty, def.did()),
            ty::Foreign(did) => self.check_def_id(id, self_ty, did),
            ty::Dynamic(data, ..) if data.principal_def_id().is_some() => {
                self.check_def_id(id, self_ty, data.principal_def_id().unwrap());
            }
            ty::Dynamic(..) => {
                struct_span_err!(
                    self.tcx.sess,
                    item_span,
                    E0785,
                    "cannot define inherent `impl` for a dyn auto trait"
                )
                .span_label(item_span, "impl requires at least one non-auto trait")
                .note("define and implement a new trait or type instead")
                .emit();
            }
            ty::Bool
            | ty::Char
            | ty::Int(_)
            | ty::Uint(_)
            | ty::Float(_)
            | ty::Str
            | ty::Array(..)
            | ty::Slice(_)
            | ty::RawPtr(_)
            | ty::Ref(..)
            | ty::Never
            | ty::FnPtr(_)
            | ty::Tuple(..) => self.check_primitive_impl(id, self_ty),
            ty::Alias(..) | ty::Param(_) => {
                let mut err = struct_span_err!(
                    self.tcx.sess,
                    item_span,
                    E0118,
                    "no nominal type found for inherent implementation"
                );

                err.span_label(item_span, "impl requires a nominal type")
                    .note("either implement a trait on it or create a newtype to wrap it instead");

                err.emit();
            }
            ty::FnDef(..)
            | ty::Closure(..)
            | ty::Generator(..)
            | ty::GeneratorWitness(..)
            | ty::GeneratorWitnessMIR(..)
            | ty::Bound(..)
            | ty::Placeholder(_)
            | ty::Infer(_) => {
                bug!("unexpected impl self type of impl: {:?} {:?}", id, self_ty);
            }
            ty::Error(_) => {}
        }
    }
}