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::{Obligation, ObligationCause, PredicateObligation, SelectionContext};
12 use crate::infer::InferCtxtExt;
13 use rustc_infer::infer::InferOk;
14 pub use rustc_infer::traits::{self, util::*};
16 ///////////////////////////////////////////////////////////////////////////
17 // `TraitAliasExpander` iterator
18 ///////////////////////////////////////////////////////////////////////////
20 /// "Trait alias expansion" is the process of expanding a sequence of trait
21 /// references into another sequence by transitively following all trait
22 /// aliases. e.g. If you have bounds like `Foo + Send`, a trait alias
23 /// `trait Foo = Bar + Sync;`, and another trait alias
24 /// `trait Bar = Read + Write`, then the bounds would expand to
25 /// `Read + Write + Sync + Send`.
26 /// Expansion is done via a DFS (depth-first search), and the `visited` field
27 /// is used to avoid cycles.
28 pub struct TraitAliasExpander<'tcx> {
30 stack: Vec<TraitAliasExpansionInfo<'tcx>>,
33 /// Stores information about the expansion of a trait via a path of zero or more trait aliases.
34 #[derive(Debug, Clone)]
35 pub struct TraitAliasExpansionInfo<'tcx> {
36 pub path: SmallVec<[(ty::PolyTraitRef<'tcx>, Span); 4]>,
39 impl<'tcx> TraitAliasExpansionInfo<'tcx> {
40 fn new(trait_ref: ty::PolyTraitRef<'tcx>, span: Span) -> Self {
41 Self { path: smallvec![(trait_ref, span)] }
44 /// Adds diagnostic labels to `diag` for the expansion path of a trait through all intermediate
46 pub fn label_with_exp_info(&self, diag: &mut Diagnostic, top_label: &str, use_desc: &str) {
47 diag.span_label(self.top().1, top_label);
48 if self.path.len() > 1 {
49 for (_, sp) in self.path.iter().rev().skip(1).take(self.path.len() - 2) {
50 diag.span_label(*sp, format!("referenced here ({})", use_desc));
53 if self.top().1 != self.bottom().1 {
54 // When the trait object is in a return type these two spans match, we don't want
58 format!("trait alias used in trait object type ({})", use_desc),
63 pub fn trait_ref(&self) -> ty::PolyTraitRef<'tcx> {
67 pub fn top(&self) -> &(ty::PolyTraitRef<'tcx>, Span) {
68 self.path.last().unwrap()
71 pub fn bottom(&self) -> &(ty::PolyTraitRef<'tcx>, Span) {
72 self.path.first().unwrap()
75 fn clone_and_push(&self, trait_ref: ty::PolyTraitRef<'tcx>, span: Span) -> Self {
76 let mut path = self.path.clone();
77 path.push((trait_ref, span));
83 pub fn expand_trait_aliases<'tcx>(
85 trait_refs: impl Iterator<Item = (ty::PolyTraitRef<'tcx>, Span)>,
86 ) -> TraitAliasExpander<'tcx> {
88 trait_refs.map(|(trait_ref, span)| TraitAliasExpansionInfo::new(trait_ref, span)).collect();
89 TraitAliasExpander { tcx, stack: items }
92 impl<'tcx> TraitAliasExpander<'tcx> {
93 /// If `item` is a trait alias and its predicate has not yet been visited, then expands `item`
94 /// to the definition, pushes the resulting expansion onto `self.stack`, and returns `false`.
95 /// Otherwise, immediately returns `true` if `item` is a regular trait, or `false` if it is a
97 /// The return value indicates whether `item` should be yielded to the user.
98 fn expand(&mut self, item: &TraitAliasExpansionInfo<'tcx>) -> bool {
100 let trait_ref = item.trait_ref();
101 let pred = trait_ref.without_const().to_predicate(tcx);
103 debug!("expand_trait_aliases: trait_ref={:?}", trait_ref);
105 // Don't recurse if this bound is not a trait alias.
106 let is_alias = tcx.is_trait_alias(trait_ref.def_id());
111 // Don't recurse if this trait alias is already on the stack for the DFS search.
112 let anon_pred = anonymize_predicate(tcx, pred);
113 if item.path.iter().rev().skip(1).any(|&(tr, _)| {
114 anonymize_predicate(tcx, tr.without_const().to_predicate(tcx)) == anon_pred
119 // Get components of trait alias.
120 let predicates = tcx.super_predicates_of(trait_ref.def_id());
123 let items = predicates.predicates.iter().rev().filter_map(|(pred, span)| {
124 pred.subst_supertrait(tcx, &trait_ref)
125 .to_opt_poly_trait_pred()
126 .map(|trait_ref| item.clone_and_push(trait_ref.map_bound(|t| t.trait_ref), *span))
128 debug!("expand_trait_aliases: items={:?}", items.clone().collect::<Vec<_>>());
130 self.stack.extend(items);
136 impl<'tcx> Iterator for TraitAliasExpander<'tcx> {
137 type Item = TraitAliasExpansionInfo<'tcx>;
139 fn size_hint(&self) -> (usize, Option<usize>) {
140 (self.stack.len(), None)
143 fn next(&mut self) -> Option<TraitAliasExpansionInfo<'tcx>> {
144 while let Some(item) = self.stack.pop() {
145 if self.expand(&item) {
153 ///////////////////////////////////////////////////////////////////////////
154 // Iterator over def-IDs of supertraits
155 ///////////////////////////////////////////////////////////////////////////
157 pub struct SupertraitDefIds<'tcx> {
160 visited: FxHashSet<DefId>,
163 pub fn supertrait_def_ids(tcx: TyCtxt<'_>, trait_def_id: DefId) -> SupertraitDefIds<'_> {
166 stack: vec![trait_def_id],
167 visited: Some(trait_def_id).into_iter().collect(),
171 impl Iterator for SupertraitDefIds<'_> {
174 fn next(&mut self) -> Option<DefId> {
175 let def_id = self.stack.pop()?;
176 let predicates = self.tcx.super_predicates_of(def_id);
177 let visited = &mut self.visited;
182 .filter_map(|(pred, _)| pred.to_opt_poly_trait_pred())
183 .map(|trait_ref| trait_ref.def_id())
184 .filter(|&super_def_id| visited.insert(super_def_id)),
190 ///////////////////////////////////////////////////////////////////////////
192 ///////////////////////////////////////////////////////////////////////////
194 /// Instantiate all bound parameters of the impl subject with the given substs,
195 /// returning the resulting subject and all obligations that arise.
196 /// The obligations are closed under normalization.
197 pub fn impl_subject_and_oblig<'a, 'tcx>(
198 selcx: &mut SelectionContext<'a, 'tcx>,
199 param_env: ty::ParamEnv<'tcx>,
201 impl_substs: SubstsRef<'tcx>,
202 ) -> (ImplSubject<'tcx>, impl Iterator<Item = PredicateObligation<'tcx>>) {
203 let subject = selcx.tcx().bound_impl_subject(impl_def_id);
204 let subject = subject.subst(selcx.tcx(), impl_substs);
205 let InferOk { value: subject, obligations: normalization_obligations1 } = selcx
207 .partially_normalize_associated_types_in(ObligationCause::dummy(), param_env, subject);
209 let predicates = selcx.tcx().predicates_of(impl_def_id);
210 let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
211 let InferOk { value: predicates, obligations: normalization_obligations2 } = selcx
213 .partially_normalize_associated_types_in(ObligationCause::dummy(), param_env, predicates);
214 let impl_obligations =
215 super::predicates_for_generics(|_, _| ObligationCause::dummy(), param_env, predicates);
217 let impl_obligations = impl_obligations
218 .chain(normalization_obligations1.into_iter())
219 .chain(normalization_obligations2.into_iter());
221 (subject, impl_obligations)
224 pub fn predicate_for_trait_ref<'tcx>(
226 cause: ObligationCause<'tcx>,
227 param_env: ty::ParamEnv<'tcx>,
228 trait_ref: ty::TraitRef<'tcx>,
229 recursion_depth: usize,
230 ) -> PredicateObligation<'tcx> {
235 predicate: ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
239 pub fn predicate_for_trait_def<'tcx>(
241 param_env: ty::ParamEnv<'tcx>,
242 cause: ObligationCause<'tcx>,
244 recursion_depth: usize,
245 params: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
246 ) -> PredicateObligation<'tcx> {
247 let trait_ref = tcx.mk_trait_ref(trait_def_id, params);
248 predicate_for_trait_ref(tcx, cause, param_env, trait_ref, recursion_depth)
251 /// Casts a trait reference into a reference to one of its super
252 /// traits; returns `None` if `target_trait_def_id` is not a
254 pub fn upcast_choices<'tcx>(
256 source_trait_ref: ty::PolyTraitRef<'tcx>,
257 target_trait_def_id: DefId,
258 ) -> Vec<ty::PolyTraitRef<'tcx>> {
259 if source_trait_ref.def_id() == target_trait_def_id {
260 return vec![source_trait_ref]; // Shortcut the most common case.
263 supertraits(tcx, source_trait_ref).filter(|r| r.def_id() == target_trait_def_id).collect()
266 /// Given a trait `trait_ref`, returns the number of vtable entries
267 /// that come from `trait_ref`, excluding its supertraits. Used in
268 /// computing the vtable base for an upcast trait of a trait object.
269 pub fn count_own_vtable_entries<'tcx>(
271 trait_ref: ty::PolyTraitRef<'tcx>,
273 tcx.own_existential_vtable_entries(trait_ref.def_id()).len()
276 /// Given an upcast trait object described by `object`, returns the
277 /// index of the method `method_def_id` (which should be part of
278 /// `object.upcast_trait_ref`) within the vtable for `object`.
279 pub fn get_vtable_index_of_object_method<'tcx, N>(
281 object: &super::ImplSourceObjectData<'tcx, N>,
282 method_def_id: DefId,
284 // Count number of methods preceding the one we are selecting and
285 // add them to the total offset.
286 if let Some(index) = tcx
287 .own_existential_vtable_entries(object.upcast_trait_ref.def_id())
290 .position(|def_id| def_id == method_def_id)
292 Some(object.vtable_base + index)
298 pub fn closure_trait_ref_and_return_type<'tcx>(
300 fn_trait_def_id: DefId,
302 sig: ty::PolyFnSig<'tcx>,
303 tuple_arguments: TupleArgumentsFlag,
304 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
305 assert!(!self_ty.has_escaping_bound_vars());
306 let arguments_tuple = match tuple_arguments {
307 TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
308 TupleArgumentsFlag::Yes => tcx.intern_tup(sig.skip_binder().inputs()),
310 let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty, arguments_tuple]);
311 sig.map_bound(|sig| (trait_ref, sig.output()))
314 pub fn generator_trait_ref_and_outputs<'tcx>(
316 fn_trait_def_id: DefId,
318 sig: ty::PolyGenSig<'tcx>,
319 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>, Ty<'tcx>)> {
320 assert!(!self_ty.has_escaping_bound_vars());
321 let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty, sig.skip_binder().resume_ty]);
322 sig.map_bound(|sig| (trait_ref, sig.yield_ty, sig.return_ty))
325 pub fn future_trait_ref_and_outputs<'tcx>(
327 fn_trait_def_id: DefId,
329 sig: ty::PolyGenSig<'tcx>,
330 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
331 assert!(!self_ty.has_escaping_bound_vars());
332 let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty]);
333 sig.map_bound(|sig| (trait_ref, sig.return_ty))
336 pub fn impl_item_is_final(tcx: TyCtxt<'_>, assoc_item: &ty::AssocItem) -> bool {
337 assoc_item.defaultness(tcx).is_final()
338 && tcx.impl_defaultness(assoc_item.container_id(tcx)).is_final()
341 pub enum TupleArgumentsFlag {