1 use rustc_errors::Diagnostic;
3 use smallvec::smallvec;
4 use smallvec::SmallVec;
6 use rustc_data_structures::fx::FxHashSet;
7 use rustc_hir::def_id::DefId;
8 use rustc_middle::ty::{self, ImplSubject, ToPredicate, Ty, TyCtxt, TypeVisitable};
9 use rustc_middle::ty::{GenericArg, SubstsRef};
11 use super::{Normalized, Obligation, ObligationCause, PredicateObligation, SelectionContext};
12 pub use rustc_infer::traits::{self, util::*};
14 ///////////////////////////////////////////////////////////////////////////
15 // `TraitAliasExpander` iterator
16 ///////////////////////////////////////////////////////////////////////////
18 /// "Trait alias expansion" is the process of expanding a sequence of trait
19 /// references into another sequence by transitively following all trait
20 /// aliases. e.g. If you have bounds like `Foo + Send`, a trait alias
21 /// `trait Foo = Bar + Sync;`, and another trait alias
22 /// `trait Bar = Read + Write`, then the bounds would expand to
23 /// `Read + Write + Sync + Send`.
24 /// Expansion is done via a DFS (depth-first search), and the `visited` field
25 /// is used to avoid cycles.
26 pub struct TraitAliasExpander<'tcx> {
28 stack: Vec<TraitAliasExpansionInfo<'tcx>>,
31 /// Stores information about the expansion of a trait via a path of zero or more trait aliases.
32 #[derive(Debug, Clone)]
33 pub struct TraitAliasExpansionInfo<'tcx> {
34 pub path: SmallVec<[(ty::PolyTraitRef<'tcx>, Span); 4]>,
37 impl<'tcx> TraitAliasExpansionInfo<'tcx> {
38 fn new(trait_ref: ty::PolyTraitRef<'tcx>, span: Span) -> Self {
39 Self { path: smallvec![(trait_ref, span)] }
42 /// Adds diagnostic labels to `diag` for the expansion path of a trait through all intermediate
44 pub fn label_with_exp_info(&self, diag: &mut Diagnostic, top_label: &str, use_desc: &str) {
45 diag.span_label(self.top().1, top_label);
46 if self.path.len() > 1 {
47 for (_, sp) in self.path.iter().rev().skip(1).take(self.path.len() - 2) {
48 diag.span_label(*sp, format!("referenced here ({})", use_desc));
51 if self.top().1 != self.bottom().1 {
52 // When the trait object is in a return type these two spans match, we don't want
56 format!("trait alias used in trait object type ({})", use_desc),
61 pub fn trait_ref(&self) -> ty::PolyTraitRef<'tcx> {
65 pub fn top(&self) -> &(ty::PolyTraitRef<'tcx>, Span) {
66 self.path.last().unwrap()
69 pub fn bottom(&self) -> &(ty::PolyTraitRef<'tcx>, Span) {
70 self.path.first().unwrap()
73 fn clone_and_push(&self, trait_ref: ty::PolyTraitRef<'tcx>, span: Span) -> Self {
74 let mut path = self.path.clone();
75 path.push((trait_ref, span));
81 pub fn expand_trait_aliases<'tcx>(
83 trait_refs: impl Iterator<Item = (ty::PolyTraitRef<'tcx>, Span)>,
84 ) -> TraitAliasExpander<'tcx> {
86 trait_refs.map(|(trait_ref, span)| TraitAliasExpansionInfo::new(trait_ref, span)).collect();
87 TraitAliasExpander { tcx, stack: items }
90 impl<'tcx> TraitAliasExpander<'tcx> {
91 /// If `item` is a trait alias and its predicate has not yet been visited, then expands `item`
92 /// to the definition, pushes the resulting expansion onto `self.stack`, and returns `false`.
93 /// Otherwise, immediately returns `true` if `item` is a regular trait, or `false` if it is a
95 /// The return value indicates whether `item` should be yielded to the user.
96 fn expand(&mut self, item: &TraitAliasExpansionInfo<'tcx>) -> bool {
98 let trait_ref = item.trait_ref();
99 let pred = trait_ref.without_const().to_predicate(tcx);
101 debug!("expand_trait_aliases: trait_ref={:?}", trait_ref);
103 // Don't recurse if this bound is not a trait alias.
104 let is_alias = tcx.is_trait_alias(trait_ref.def_id());
109 // Don't recurse if this trait alias is already on the stack for the DFS search.
110 let anon_pred = anonymize_predicate(tcx, pred);
111 if item.path.iter().rev().skip(1).any(|&(tr, _)| {
112 anonymize_predicate(tcx, tr.without_const().to_predicate(tcx)) == anon_pred
117 // Get components of trait alias.
118 let predicates = tcx.super_predicates_of(trait_ref.def_id());
121 let items = predicates.predicates.iter().rev().filter_map(|(pred, span)| {
122 pred.subst_supertrait(tcx, &trait_ref)
123 .to_opt_poly_trait_pred()
124 .map(|trait_ref| item.clone_and_push(trait_ref.map_bound(|t| t.trait_ref), *span))
126 debug!("expand_trait_aliases: items={:?}", items.clone().collect::<Vec<_>>());
128 self.stack.extend(items);
134 impl<'tcx> Iterator for TraitAliasExpander<'tcx> {
135 type Item = TraitAliasExpansionInfo<'tcx>;
137 fn size_hint(&self) -> (usize, Option<usize>) {
138 (self.stack.len(), None)
141 fn next(&mut self) -> Option<TraitAliasExpansionInfo<'tcx>> {
142 while let Some(item) = self.stack.pop() {
143 if self.expand(&item) {
151 ///////////////////////////////////////////////////////////////////////////
152 // Iterator over def-IDs of supertraits
153 ///////////////////////////////////////////////////////////////////////////
155 pub struct SupertraitDefIds<'tcx> {
158 visited: FxHashSet<DefId>,
161 pub fn supertrait_def_ids(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SupertraitDefIds<'_> {
164 stack: vec![trait_def_id],
165 visited: Some(trait_def_id).into_iter().collect(),
169 impl Iterator for SupertraitDefIds<'_> {
172 fn next(&mut self) -> Option<DefId> {
173 let def_id = self.stack.pop()?;
174 let predicates = self.tcx.super_predicates_of(def_id);
175 let visited = &mut self.visited;
180 .filter_map(|(pred, _)| pred.to_opt_poly_trait_pred())
181 .map(|trait_ref| trait_ref.def_id())
182 .filter(|&super_def_id| visited.insert(super_def_id)),
188 ///////////////////////////////////////////////////////////////////////////
190 ///////////////////////////////////////////////////////////////////////////
192 /// Instantiate all bound parameters of the impl subject with the given substs,
193 /// returning the resulting subject and all obligations that arise.
194 /// The obligations are closed under normalization.
195 pub fn impl_subject_and_oblig<'a, 'tcx>(
196 selcx: &mut SelectionContext<'a, 'tcx>,
197 param_env: ty::ParamEnv<'tcx>,
199 impl_substs: SubstsRef<'tcx>,
200 ) -> (ImplSubject<'tcx>, impl Iterator<Item = PredicateObligation<'tcx>>) {
201 let subject = selcx.tcx().bound_impl_subject(impl_def_id);
202 let subject = subject.subst(selcx.tcx(), impl_substs);
203 let Normalized { value: subject, obligations: normalization_obligations1 } =
204 super::normalize(selcx, param_env, ObligationCause::dummy(), subject);
206 let predicates = selcx.tcx().predicates_of(impl_def_id);
207 let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
208 let Normalized { value: predicates, obligations: normalization_obligations2 } =
209 super::normalize(selcx, param_env, ObligationCause::dummy(), predicates);
210 let impl_obligations =
211 super::predicates_for_generics(|_, _| ObligationCause::dummy(), param_env, predicates);
213 let impl_obligations = impl_obligations
214 .chain(normalization_obligations1.into_iter())
215 .chain(normalization_obligations2.into_iter());
217 (subject, impl_obligations)
220 pub fn predicate_for_trait_ref<'tcx>(
222 cause: ObligationCause<'tcx>,
223 param_env: ty::ParamEnv<'tcx>,
224 trait_ref: ty::TraitRef<'tcx>,
225 recursion_depth: usize,
226 ) -> PredicateObligation<'tcx> {
231 predicate: ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
235 pub fn predicate_for_trait_def<'tcx>(
237 param_env: ty::ParamEnv<'tcx>,
238 cause: ObligationCause<'tcx>,
240 recursion_depth: usize,
241 params: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
242 ) -> PredicateObligation<'tcx> {
243 let trait_ref = tcx.mk_trait_ref(trait_def_id, params);
244 predicate_for_trait_ref(tcx, cause, param_env, trait_ref, recursion_depth)
247 /// Casts a trait reference into a reference to one of its super
248 /// traits; returns `None` if `target_trait_def_id` is not a
250 pub fn upcast_choices<'tcx>(
252 source_trait_ref: ty::PolyTraitRef<'tcx>,
253 target_trait_def_id: DefId,
254 ) -> Vec<ty::PolyTraitRef<'tcx>> {
255 if source_trait_ref.def_id() == target_trait_def_id {
256 return vec![source_trait_ref]; // Shortcut the most common case.
259 supertraits(tcx, source_trait_ref).filter(|r| r.def_id() == target_trait_def_id).collect()
262 /// Given a trait `trait_ref`, returns the number of vtable entries
263 /// that come from `trait_ref`, excluding its supertraits. Used in
264 /// computing the vtable base for an upcast trait of a trait object.
265 pub fn count_own_vtable_entries<'tcx>(
267 trait_ref: ty::PolyTraitRef<'tcx>,
269 tcx.own_existential_vtable_entries(trait_ref.def_id()).len()
272 /// Given an upcast trait object described by `object`, returns the
273 /// index of the method `method_def_id` (which should be part of
274 /// `object.upcast_trait_ref`) within the vtable for `object`.
275 pub fn get_vtable_index_of_object_method<'tcx, N>(
277 object: &super::ImplSourceObjectData<'tcx, N>,
278 method_def_id: DefId,
280 // Count number of methods preceding the one we are selecting and
281 // add them to the total offset.
282 if let Some(index) = tcx
283 .own_existential_vtable_entries(object.upcast_trait_ref.def_id())
286 .position(|def_id| def_id == method_def_id)
288 Some(object.vtable_base + index)
294 pub fn closure_trait_ref_and_return_type<'tcx>(
296 fn_trait_def_id: DefId,
298 sig: ty::PolyFnSig<'tcx>,
299 tuple_arguments: TupleArgumentsFlag,
300 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
301 let arguments_tuple = match tuple_arguments {
302 TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
303 TupleArgumentsFlag::Yes => tcx.intern_tup(sig.skip_binder().inputs()),
305 debug_assert!(!self_ty.has_escaping_bound_vars());
306 let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty, arguments_tuple]);
307 sig.map_bound(|sig| (trait_ref, sig.output()))
310 pub fn generator_trait_ref_and_outputs<'tcx>(
312 fn_trait_def_id: DefId,
314 sig: ty::PolyGenSig<'tcx>,
315 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>, Ty<'tcx>)> {
316 debug_assert!(!self_ty.has_escaping_bound_vars());
317 let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty, sig.skip_binder().resume_ty]);
318 sig.map_bound(|sig| (trait_ref, sig.yield_ty, sig.return_ty))
321 pub fn impl_item_is_final(tcx: TyCtxt<'_>, assoc_item: &ty::AssocItem) -> bool {
322 assoc_item.defaultness(tcx).is_final()
323 && tcx.impl_defaultness(assoc_item.container_id(tcx)).is_final()
326 pub enum TupleArgumentsFlag {