src/librustc_middle/ty/trait_def.rs

   1 use crate::ich::{self, StableHashingContext};
   2 use crate::traits::specialization_graph;
   3 use crate::ty::fast_reject;
   4 use crate::ty::fold::TypeFoldable;
   5 use crate::ty::{Ty, TyCtxt};
   6 use rustc_hir as hir;
   7 use rustc_hir::def_id::{CrateNum, DefId};
   8 use rustc_hir::definitions::DefPathHash;
   9 use rustc_hir::HirId;
  10
  11 use rustc_data_structures::fx::FxHashMap;
  12 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
  13 use rustc_errors::ErrorReported;
  14 use rustc_macros::HashStable;
  15 use std::collections::BTreeMap;
  16
  17 /// A trait's definition with type information.
  18 #[derive(HashStable)]
  19 pub struct TraitDef {
  20     // We already have the def_path_hash below, no need to hash it twice
  21     #[stable_hasher(ignore)]
  22     pub def_id: DefId,
  23
  24     pub unsafety: hir::Unsafety,
  25
  26     /// If `true`, then this trait had the `#[rustc_paren_sugar]`
  27     /// attribute, indicating that it should be used with `Foo()`
  28     /// sugar. This is a temporary thing -- eventually any trait will
  29     /// be usable with the sugar (or without it).
  30     pub paren_sugar: bool,
  31
  32     pub has_auto_impl: bool,
  33
  34     /// If `true`, then this trait has the `#[marker]` attribute, indicating
  35     /// that all its associated items have defaults that cannot be overridden,
  36     /// and thus `impl`s of it are allowed to overlap.
  37     pub is_marker: 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     /// The ICH of this trait's DefPath, cached here so it doesn't have to be
  44     /// recomputed all the time.
  45     pub def_path_hash: DefPathHash,
  46 }
  47
  48 /// Whether this trait is treated specially by the standard library
  49 /// specialization lint.
  50 #[derive(HashStable, PartialEq, Clone, Copy, RustcEncodable, RustcDecodable)]
  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)]
  67 pub struct TraitImpls {
  68     blanket_impls: Vec<DefId>,
  69     /// Impls indexed by their simplified self type, for fast lookup.
  70     non_blanket_impls: FxHashMap<fast_reject::SimplifiedType, Vec<DefId>>,
  71 }
  72
  73 impl<'tcx> TraitDef {
  74     pub fn new(
  75         def_id: DefId,
  76         unsafety: hir::Unsafety,
  77         paren_sugar: bool,
  78         has_auto_impl: bool,
  79         is_marker: bool,
  80         specialization_kind: TraitSpecializationKind,
  81         def_path_hash: DefPathHash,
  82     ) -> TraitDef {
  83         TraitDef {
  84             def_id,
  85             unsafety,
  86             paren_sugar,
  87             has_auto_impl,
  88             is_marker,
  89             specialization_kind,
  90             def_path_hash,
  91         }
  92     }
  93
  94     pub fn ancestors(
  95         &self,
  96         tcx: TyCtxt<'tcx>,
  97         of_impl: DefId,
  98     ) -> Result<specialization_graph::Ancestors<'tcx>, ErrorReported> {
  99         specialization_graph::ancestors(tcx, self.def_id, of_impl)
 100     }
 101 }
 102
 103 impl<'tcx> TyCtxt<'tcx> {
 104     pub fn for_each_impl<F: FnMut(DefId)>(self, def_id: DefId, mut f: F) {
 105         let impls = self.trait_impls_of(def_id);
 106
 107         for &impl_def_id in impls.blanket_impls.iter() {
 108             f(impl_def_id);
 109         }
 110
 111         for v in impls.non_blanket_impls.values() {
 112             for &impl_def_id in v {
 113                 f(impl_def_id);
 114             }
 115         }
 116     }
 117
 118     /// Iterate over every impl that could possibly match the
 119     /// self type `self_ty`.
 120     pub fn for_each_relevant_impl<F: FnMut(DefId)>(
 121         self,
 122         def_id: DefId,
 123         self_ty: Ty<'tcx>,
 124         mut f: F,
 125     ) {
 126         let impls = self.trait_impls_of(def_id);
 127
 128         for &impl_def_id in impls.blanket_impls.iter() {
 129             f(impl_def_id);
 130         }
 131
 132         // simplify_type(.., false) basically replaces type parameters and
 133         // projections with infer-variables. This is, of course, done on
 134         // the impl trait-ref when it is instantiated, but not on the
 135         // predicate trait-ref which is passed here.
 136         //
 137         // for example, if we match `S: Copy` against an impl like
 138         // `impl<T:Copy> Copy for Option<T>`, we replace the type variable
 139         // in `Option<T>` with an infer variable, to `Option<_>` (this
 140         // doesn't actually change fast_reject output), but we don't
 141         // replace `S` with anything - this impl of course can't be
 142         // selected, and as there are hundreds of similar impls,
 143         // considering them would significantly harm performance.
 144
 145         // This depends on the set of all impls for the trait. That is
 146         // unfortunate. When we get red-green recompilation, we would like
 147         // to have a way of knowing whether the set of relevant impls
 148         // changed. The most naive
 149         // way would be to compute the Vec of relevant impls and see whether
 150         // it differs between compilations. That shouldn't be too slow by
 151         // itself - we do quite a bit of work for each relevant impl anyway.
 152         //
 153         // If we want to be faster, we could have separate queries for
 154         // blanket and non-blanket impls, and compare them separately.
 155         //
 156         // I think we'll cross that bridge when we get to it.
 157         if let Some(simp) = fast_reject::simplify_type(self, self_ty, true) {
 158             if let Some(impls) = impls.non_blanket_impls.get(&simp) {
 159                 for &impl_def_id in impls {
 160                     f(impl_def_id);
 161                 }
 162             }
 163         } else {
 164             for &impl_def_id in impls.non_blanket_impls.values().flatten() {
 165                 f(impl_def_id);
 166             }
 167         }
 168     }
 169
 170     /// Returns a vector containing all impls
 171     pub fn all_impls(self, def_id: DefId) -> impl Iterator<Item = DefId> + 'tcx {
 172         let TraitImpls { blanket_impls, non_blanket_impls } = self.trait_impls_of(def_id);
 173
 174         blanket_impls
 175             .into_iter()
 176             .chain(non_blanket_impls.into_iter().map(|(_, v)| v).flatten())
 177             .cloned()
 178     }
 179 }
 180
 181 // Query provider for `all_local_trait_impls`.
 182 pub(super) fn all_local_trait_impls<'tcx>(
 183     tcx: TyCtxt<'tcx>,
 184     krate: CrateNum,
 185 ) -> &'tcx BTreeMap<DefId, Vec<HirId>> {
 186     &tcx.hir_crate(krate).trait_impls
 187 }
 188
 189 // Query provider for `trait_impls_of`.
 190 pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> &TraitImpls {
 191     let mut impls = TraitImpls::default();
 192
 193     {
 194         let mut add_impl = |impl_def_id: DefId| {
 195             let impl_self_ty = tcx.type_of(impl_def_id);
 196             if impl_def_id.is_local() && impl_self_ty.references_error() {
 197                 return;
 198             }
 199
 200             if let Some(simplified_self_ty) = fast_reject::simplify_type(tcx, impl_self_ty, false) {
 201                 impls.non_blanket_impls.entry(simplified_self_ty).or_default().push(impl_def_id);
 202             } else {
 203                 impls.blanket_impls.push(impl_def_id);
 204             }
 205         };
 206
 207         // Traits defined in the current crate can't have impls in upstream
 208         // crates, so we don't bother querying the cstore.
 209         if !trait_id.is_local() {
 210             for &cnum in tcx.crates().iter() {
 211                 for &def_id in tcx.implementations_of_trait((cnum, trait_id)).iter() {
 212                     add_impl(def_id);
 213                 }
 214             }
 215         }
 216
 217         for &hir_id in tcx.hir().trait_impls(trait_id) {
 218             add_impl(tcx.hir().local_def_id(hir_id));
 219         }
 220     }
 221
 222     tcx.arena.alloc(impls)
 223 }
 224
 225 impl<'a> HashStable<StableHashingContext<'a>> for TraitImpls {
 226     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
 227         let TraitImpls { ref blanket_impls, ref non_blanket_impls } = *self;
 228
 229         ich::hash_stable_trait_impls(hcx, hasher, blanket_impls, non_blanket_impls);
 230     }
 231 }