1 use rustc_data_structures::fx::FxHashMap;
3 use rustc_hir::def_id::DefId;
4 use rustc_hir::itemlikevisit::ItemLikeVisitor;
5 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
6 use rustc_middle::ty::{self, Ty, TyCtxt};
9 use super::explicit::ExplicitPredicatesMap;
12 /// Infer predicates for the items in the crate.
14 /// `global_inferred_outlives`: this is initially the empty map that
15 /// was generated by walking the items in the crate. This will
16 /// now be filled with inferred predicates.
17 pub fn infer_predicates<'tcx>(
19 explicit_map: &mut ExplicitPredicatesMap<'tcx>,
20 ) -> FxHashMap<DefId, RequiredPredicates<'tcx>> {
21 debug!("infer_predicates");
23 let mut predicates_added = true;
25 let mut global_inferred_outlives = FxHashMap::default();
27 // If new predicates were added then we need to re-calculate
28 // all crates since there could be new implied predicates.
29 while predicates_added {
30 predicates_added = false;
32 let mut visitor = InferVisitor {
34 global_inferred_outlives: &mut global_inferred_outlives,
35 predicates_added: &mut predicates_added,
39 // Visit all the crates and infer predicates
40 tcx.hir().visit_all_item_likes(&mut visitor);
43 global_inferred_outlives
46 pub struct InferVisitor<'cx, 'tcx> {
48 global_inferred_outlives: &'cx mut FxHashMap<DefId, RequiredPredicates<'tcx>>,
49 predicates_added: &'cx mut bool,
50 explicit_map: &'cx mut ExplicitPredicatesMap<'tcx>,
53 impl<'cx, 'tcx> ItemLikeVisitor<'tcx> for InferVisitor<'cx, 'tcx> {
54 fn visit_item(&mut self, item: &hir::Item<'_>) {
55 let item_did = item.def_id;
57 debug!("InferVisitor::visit_item(item={:?})", item_did);
59 let mut item_required_predicates = RequiredPredicates::default();
61 hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) | hir::ItemKind::Struct(..) => {
62 let adt_def = self.tcx.adt_def(item_did.to_def_id());
64 // Iterate over all fields in item_did
65 for field_def in adt_def.all_fields() {
66 // Calculating the predicate requirements necessary
69 // For field of type &'a T (reference) or Adt
70 // (struct/enum/union) there will be outlive
71 // requirements for adt_def.
72 let field_ty = self.tcx.type_of(field_def.did);
73 let field_span = self.tcx.def_span(field_def.did);
74 insert_required_predicates_to_be_wf(
78 self.global_inferred_outlives,
79 &mut item_required_predicates,
80 &mut self.explicit_map,
88 // If new predicates were added (`local_predicate_map` has more
89 // predicates than the `global_inferred_outlives`), the new predicates
90 // might result in implied predicates for their parent types.
91 // Therefore mark `predicates_added` as true and which will ensure
92 // we walk the crates again and re-calculate predicates for all
94 let item_predicates_len: usize =
95 self.global_inferred_outlives.get(&item_did.to_def_id()).map_or(0, |p| p.len());
96 if item_required_predicates.len() > item_predicates_len {
97 *self.predicates_added = true;
98 self.global_inferred_outlives.insert(item_did.to_def_id(), item_required_predicates);
102 fn visit_trait_item(&mut self, _trait_item: &'tcx hir::TraitItem<'tcx>) {}
104 fn visit_impl_item(&mut self, _impl_item: &'tcx hir::ImplItem<'tcx>) {}
106 fn visit_foreign_item(&mut self, _foreign_item: &'tcx hir::ForeignItem<'tcx>) {}
109 fn insert_required_predicates_to_be_wf<'tcx>(
113 global_inferred_outlives: &FxHashMap<DefId, RequiredPredicates<'tcx>>,
114 required_predicates: &mut RequiredPredicates<'tcx>,
115 explicit_map: &mut ExplicitPredicatesMap<'tcx>,
117 for arg in field_ty.walk() {
118 let ty = match arg.unpack() {
119 GenericArgKind::Type(ty) => ty,
121 // No predicates from lifetimes or constants, except potentially
122 // constants' types, but `walk` will get to them as well.
123 GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => continue,
127 // The field is of type &'a T which means that we will have
128 // a predicate requirement of T: 'a (T outlives 'a).
130 // We also want to calculate potential predicates for the T
131 ty::Ref(region, rty, _) => {
133 insert_outlives_predicate(tcx, rty.into(), region, field_span, required_predicates);
136 // For each Adt (struct/enum/union) type `Foo<'a, T>`, we
137 // can load the current set of inferred and explicit
138 // predicates from `global_inferred_outlives` and filter the
139 // ones that are TypeOutlives.
140 ty::Adt(def, substs) => {
141 // First check the inferred predicates
145 // struct Foo<'a, T> {
146 // field1: Bar<'a, T>
149 // struct Bar<'b, U> {
153 // Here, when processing the type of `field1`, we would
154 // request the set of implicit predicates computed for `Bar`
155 // thus far. This will initially come back empty, but in next
156 // round we will get `U: 'b`. We then apply the substitution
157 // `['b => 'a, U => T]` and thus get the requirement that `T:
158 // 'a` holds for `Foo`.
160 if let Some(unsubstituted_predicates) = global_inferred_outlives.get(&def.did()) {
161 for (unsubstituted_predicate, &span) in unsubstituted_predicates {
162 // `unsubstituted_predicate` is `U: 'b` in the
163 // example above. So apply the substitution to
164 // get `T: 'a` (or `predicate`):
165 let predicate = unsubstituted_predicate.subst(tcx, substs);
166 insert_outlives_predicate(
176 // Check if the type has any explicit predicates that need
177 // to be added to `required_predicates`
178 // let _: () = substs.region_at(0);
179 check_explicit_predicates(
189 ty::Dynamic(obj, ..) => {
190 // This corresponds to `dyn Trait<..>`. In this case, we should
191 // use the explicit predicates as well.
194 debug!("field_ty = {}", &field_ty);
195 debug!("ty in field = {}", &ty);
196 if let Some(ex_trait_ref) = obj.principal() {
197 // Here, we are passing the type `usize` as a
198 // placeholder value with the function
199 // `with_self_ty`, since there is no concrete type
200 // `Self` for a `dyn Trait` at this
201 // stage. Therefore when checking explicit
202 // predicates in `check_explicit_predicates` we
203 // need to ignore checking the explicit_map for
206 ex_trait_ref.with_self_ty(tcx, tcx.types.usize).skip_binder().substs;
207 check_explicit_predicates(
209 ex_trait_ref.skip_binder().def_id,
213 Some(tcx.types.self_param),
218 ty::Projection(obj) => {
219 // This corresponds to `<T as Foo<'a>>::Bar`. In this case, we should use the
220 // explicit predicates as well.
221 debug!("Projection");
222 check_explicit_predicates(
224 tcx.associated_item(obj.item_def_id).container.id(),
237 /// We also have to check the explicit predicates
238 /// declared on the type.
240 /// struct Foo<'a, T> {
244 /// struct Bar<U> where U: 'static, U: Foo {
248 /// Here, we should fetch the explicit predicates, which
249 /// will give us `U: 'static` and `U: Foo`. The latter we
250 /// can ignore, but we will want to process `U: 'static`,
251 /// applying the substitution as above.
252 pub fn check_explicit_predicates<'tcx>(
255 substs: &[GenericArg<'tcx>],
256 required_predicates: &mut RequiredPredicates<'tcx>,
257 explicit_map: &mut ExplicitPredicatesMap<'tcx>,
258 ignored_self_ty: Option<Ty<'tcx>>,
261 "check_explicit_predicates(def_id={:?}, \
264 required_predicates={:?}, \
265 ignored_self_ty={:?})",
266 def_id, substs, explicit_map, required_predicates, ignored_self_ty,
268 let explicit_predicates = explicit_map.explicit_predicates_of(tcx, def_id);
270 for (outlives_predicate, &span) in explicit_predicates {
271 debug!("outlives_predicate = {:?}", &outlives_predicate);
273 // Careful: If we are inferring the effects of a `dyn Trait<..>`
274 // type, then when we look up the predicates for `Trait`,
275 // we may find some that reference `Self`. e.g., perhaps the
276 // definition of `Trait` was:
279 // trait Trait<'a, T> where Self: 'a { .. }
282 // we want to ignore such predicates here, because
283 // there is no type parameter for them to affect. Consider
284 // a struct containing `dyn Trait`:
287 // struct MyStruct<'x, X> { field: Box<dyn Trait<'x, X>> }
290 // The `where Self: 'a` predicate refers to the *existential, hidden type*
291 // that is represented by the `dyn Trait`, not to the `X` type parameter
292 // (or any other generic parameter) declared on `MyStruct`.
294 // Note that we do this check for self **before** applying `substs`. In the
295 // case that `substs` come from a `dyn Trait` type, our caller will have
296 // included `Self = usize` as the value for `Self`. If we were
297 // to apply the substs, and not filter this predicate, we might then falsely
298 // conclude that e.g., `X: 'x` was a reasonable inferred requirement.
300 // Another similar case is where we have an inferred
301 // requirement like `<Self as Trait>::Foo: 'b`. We presently
302 // ignore such requirements as well (cc #54467)-- though
303 // conceivably it might be better if we could extract the `Foo
304 // = X` binding from the object type (there must be such a
305 // binding) and thus infer an outlives requirement that `X:
307 if let Some(self_ty) = ignored_self_ty
308 && let GenericArgKind::Type(ty) = outlives_predicate.0.unpack()
309 && ty.walk().any(|arg| arg == self_ty.into())
311 debug!("skipping self ty = {:?}", &ty);
315 let predicate = outlives_predicate.subst(tcx, substs);
316 debug!("predicate = {:?}", &predicate);
317 insert_outlives_predicate(tcx, predicate.0, predicate.1, span, required_predicates);