compiler/rustc_middle/src/ty/trait_def.rs

   1 use crate::traits::specialization_graph;
   2 use crate::ty::fast_reject::{self, SimplifiedType, TreatParams};
   3 use crate::ty::fold::TypeFoldable;
   4 use crate::ty::{Ident, Ty, TyCtxt};
   5 use hir::def_id::LOCAL_CRATE;
   6 use rustc_hir as hir;
   7 use rustc_hir::def_id::DefId;
   8 use std::iter;
   9
  10 use rustc_data_structures::fx::FxIndexMap;
  11 use rustc_errors::ErrorGuaranteed;
  12 use rustc_macros::HashStable;
  13
  14 /// A trait's definition with type information.
  15 #[derive(HashStable, Encodable, Decodable)]
  16 pub struct TraitDef {
  17     pub def_id: DefId,
  18
  19     pub unsafety: hir::Unsafety,
  20
  21     /// If `true`, then this trait had the `#[rustc_paren_sugar]`
  22     /// attribute, indicating that it should be used with `Foo()`
  23     /// sugar. This is a temporary thing -- eventually any trait will
  24     /// be usable with the sugar (or without it).
  25     pub paren_sugar: bool,
  26
  27     pub has_auto_impl: bool,
  28
  29     /// If `true`, then this trait has the `#[marker]` attribute, indicating
  30     /// that all its associated items have defaults that cannot be overridden,
  31     /// and thus `impl`s of it are allowed to overlap.
  32     pub is_marker: bool,
  33
  34     /// If `true`, then this trait has the `#[rustc_skip_array_during_method_dispatch]`
  35     /// attribute, indicating that editions before 2021 should not consider this trait
  36     /// during method dispatch if the receiver is an array.
  37     pub skip_array_during_method_dispatch: bool,
  38
  39     /// Used to determine whether the standard library is allowed to specialize
  40     /// on this trait.
  41     pub specialization_kind: TraitSpecializationKind,
  42
  43     /// List of functions from `#[rustc_must_implement_one_of]` attribute one of which
  44     /// must be implemented.
  45     pub must_implement_one_of: Option<Box<[Ident]>>,
  46 }
  47
  48 /// Whether this trait is treated specially by the standard library
  49 /// specialization lint.
  50 #[derive(HashStable, PartialEq, Clone, Copy, Encodable, Decodable)]
  51 pub enum TraitSpecializationKind {
  52     /// The default. Specializing on this trait is not allowed.
  53     None,
  54     /// Specializing on this trait is allowed because it doesn't have any
  55     /// methods. For example `Sized` or `FusedIterator`.
  56     /// Applies to traits with the `rustc_unsafe_specialization_marker`
  57     /// attribute.
  58     Marker,
  59     /// Specializing on this trait is allowed because all of the impls of this
  60     /// trait are "always applicable". Always applicable means that if
  61     /// `X<'x>: T<'y>` for any lifetimes, then `for<'a, 'b> X<'a>: T<'b>`.
  62     /// Applies to traits with the `rustc_specialization_trait` attribute.
  63     AlwaysApplicable,
  64 }
  65
  66 #[derive(Default, Debug, HashStable)]
  67 pub struct TraitImpls {
  68     blanket_impls: Vec<DefId>,
  69     /// Impls indexed by their simplified self type, for fast lookup.
  70     non_blanket_impls: FxIndexMap<SimplifiedType, Vec<DefId>>,
  71 }
  72
  73 impl TraitImpls {
  74     pub fn blanket_impls(&self) -> &[DefId] {
  75         self.blanket_impls.as_slice()
  76     }
  77 }
  78
  79 impl<'tcx> TraitDef {
  80     pub fn new(
  81         def_id: DefId,
  82         unsafety: hir::Unsafety,
  83         paren_sugar: bool,
  84         has_auto_impl: bool,
  85         is_marker: bool,
  86         skip_array_during_method_dispatch: bool,
  87         specialization_kind: TraitSpecializationKind,
  88         must_implement_one_of: Option<Box<[Ident]>>,
  89     ) -> TraitDef {
  90         TraitDef {
  91             def_id,
  92             unsafety,
  93             paren_sugar,
  94             has_auto_impl,
  95             is_marker,
  96             skip_array_during_method_dispatch,
  97             specialization_kind,
  98             must_implement_one_of,
  99         }
 100     }
 101
 102     pub fn ancestors(
 103         &self,
 104         tcx: TyCtxt<'tcx>,
 105         of_impl: DefId,
 106     ) -> Result<specialization_graph::Ancestors<'tcx>, ErrorGuaranteed> {
 107         specialization_graph::ancestors(tcx, self.def_id, of_impl)
 108     }
 109 }
 110
 111 impl<'tcx> TyCtxt<'tcx> {
 112     pub fn for_each_impl<F: FnMut(DefId)>(self, def_id: DefId, mut f: F) {
 113         let impls = self.trait_impls_of(def_id);
 114
 115         for &impl_def_id in impls.blanket_impls.iter() {
 116             f(impl_def_id);
 117         }
 118
 119         for v in impls.non_blanket_impls.values() {
 120             for &impl_def_id in v {
 121                 f(impl_def_id);
 122             }
 123         }
 124     }
 125
 126     /// Iterate over every impl that could possibly match the
 127     /// self type `self_ty`.
 128     pub fn for_each_relevant_impl<F: FnMut(DefId)>(
 129         self,
 130         def_id: DefId,
 131         self_ty: Ty<'tcx>,
 132         mut f: F,
 133     ) {
 134         let _: Option<()> = self.find_map_relevant_impl(def_id, self_ty, |did| {
 135             f(did);
 136             None
 137         });
 138     }
 139
 140     pub fn non_blanket_impls_for_ty(
 141         self,
 142         def_id: DefId,
 143         self_ty: Ty<'tcx>,
 144     ) -> impl Iterator<Item = DefId> + 'tcx {
 145         let impls = self.trait_impls_of(def_id);
 146         if let Some(simp) = fast_reject::simplify_type(self, self_ty, TreatParams::AsInfer) {
 147             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
 148                 return impls.iter().copied();
 149             }
 150         }
 151
 152         [].iter().copied()
 153     }
 154
 155     /// Applies function to every impl that could possibly match the self type `self_ty` and returns
 156     /// the first non-none value.
 157     pub fn find_map_relevant_impl<T, F: FnMut(DefId) -> Option<T>>(
 158         self,
 159         def_id: DefId,
 160         self_ty: Ty<'tcx>,
 161         mut f: F,
 162     ) -> Option<T> {
 163         // FIXME: This depends on the set of all impls for the trait. That is
 164         // unfortunate wrt. incremental compilation.
 165         //
 166         // If we want to be faster, we could have separate queries for
 167         // blanket and non-blanket impls, and compare them separately.
 168         let impls = self.trait_impls_of(def_id);
 169
 170         for &impl_def_id in impls.blanket_impls.iter() {
 171             if let result @ Some(_) = f(impl_def_id) {
 172                 return result;
 173             }
 174         }
 175
 176         // Note that we're using `TreatParams::AsPlaceholder` to query `non_blanket_impls` while using
 177         // `TreatParams::AsInfer` while actually adding them.
 178         //
 179         // This way, when searching for some impl for `T: Trait`, we do not look at any impls
 180         // whose outer level is not a parameter or projection. Especially for things like
 181         // `T: Clone` this is incredibly useful as we would otherwise look at all the impls
 182         // of `Clone` for `Option<T>`, `Vec<T>`, `ConcreteType` and so on.
 183         if let Some(simp) = fast_reject::simplify_type(self, self_ty, TreatParams::AsPlaceholder) {
 184             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
 185                 for &impl_def_id in impls {
 186                     if let result @ Some(_) = f(impl_def_id) {
 187                         return result;
 188                     }
 189                 }
 190             }
 191         } else {
 192             for &impl_def_id in impls.non_blanket_impls.values().flatten() {
 193                 if let result @ Some(_) = f(impl_def_id) {
 194                     return result;
 195                 }
 196             }
 197         }
 198
 199         None
 200     }
 201
 202     /// Returns an iterator containing all impls
 203     pub fn all_impls(self, def_id: DefId) -> impl Iterator<Item = DefId> + 'tcx {
 204         let TraitImpls { blanket_impls, non_blanket_impls } = self.trait_impls_of(def_id);
 205
 206         blanket_impls.iter().chain(non_blanket_impls.iter().flat_map(|(_, v)| v)).cloned()
 207     }
 208 }
 209
 210 // Query provider for `trait_impls_of`.
 211 pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> TraitImpls {
 212     let mut impls = TraitImpls::default();
 213
 214     // Traits defined in the current crate can't have impls in upstream
 215     // crates, so we don't bother querying the cstore.
 216     if !trait_id.is_local() {
 217         for &cnum in tcx.crates(()).iter() {
 218             for &(impl_def_id, simplified_self_ty) in
 219                 tcx.implementations_of_trait((cnum, trait_id)).iter()
 220             {
 221                 if let Some(simplified_self_ty) = simplified_self_ty {
 222                     impls
 223                         .non_blanket_impls
 224                         .entry(simplified_self_ty)
 225                         .or_default()
 226                         .push(impl_def_id);
 227                 } else {
 228                     impls.blanket_impls.push(impl_def_id);
 229                 }
 230             }
 231         }
 232     }
 233
 234     for &impl_def_id in tcx.hir().trait_impls(trait_id) {
 235         let impl_def_id = impl_def_id.to_def_id();
 236
 237         let impl_self_ty = tcx.type_of(impl_def_id);
 238         if impl_self_ty.references_error() {
 239             continue;
 240         }
 241
 242         if let Some(simplified_self_ty) =
 243             fast_reject::simplify_type(tcx, impl_self_ty, TreatParams::AsInfer)
 244         {
 245             impls.non_blanket_impls.entry(simplified_self_ty).or_default().push(impl_def_id);
 246         } else {
 247             impls.blanket_impls.push(impl_def_id);
 248         }
 249     }
 250
 251     impls
 252 }
 253
 254 // Query provider for `incoherent_impls`.
 255 #[instrument(level = "debug", skip(tcx))]
 256 pub(super) fn incoherent_impls_provider(tcx: TyCtxt<'_>, simp: SimplifiedType) -> &[DefId] {
 257     let mut impls = Vec::new();
 258
 259     for cnum in iter::once(LOCAL_CRATE).chain(tcx.crates(()).iter().copied()) {
 260         for &impl_def_id in tcx.crate_incoherent_impls((cnum, simp)) {
 261             impls.push(impl_def_id)
 262         }
 263     }
 264
 265     debug!(?impls);
 266
 267     tcx.arena.alloc_slice(&impls)
 268 }