rustc: split GenericPredicates of a method from its parent predicates.

Author: eddyb

src/librustc/traits/select.rs

@@ -2897,20 +2897,18 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         // obligation will normalize to `<$0 as Iterator>::Item = $1` and
         // `$1: Copy`, so we must ensure the obligations are emitted in
         // that order.
-        let predicates = tcx
-            .lookup_predicates(def_id)
-            .predicates.iter()
-            .flat_map(|predicate| {
-                let predicate =
-                    normalize_with_depth(self, cause.clone(), recursion_depth,
-                                         &predicate.subst(tcx, substs));
-                predicate.obligations.into_iter().chain(
-                    Some(Obligation {
-                        cause: cause.clone(),
-                        recursion_depth: recursion_depth,
-                        predicate: predicate.value
-                    }))
-            }).collect();
+        let predicates = tcx.lookup_predicates(def_id);
+        assert_eq!(predicates.parent, None);
+        let predicates = predicates.predicates.iter().flat_map(|predicate| {
+            let predicate = normalize_with_depth(self, cause.clone(), recursion_depth,
+                                                 &predicate.subst(tcx, substs));
+            predicate.obligations.into_iter().chain(
+                Some(Obligation {
+                    cause: cause.clone(),
+                    recursion_depth: recursion_depth,
+                    predicate: predicate.value
+                }))
+        }).collect();
         self.infcx().plug_leaks(skol_map, snapshot, &predicates)
     }
 }

src/librustc/ty/mod.rs

@@ -768,27 +768,38 @@ pub struct Generics<'tcx> {
 /// Bounds on generics.
 #[derive(Clone)]
 pub struct GenericPredicates<'tcx> {
+    pub parent: Option<DefId>,
     pub predicates: Vec<Predicate<'tcx>>,
 }
 
 impl<'a, 'gcx, 'tcx> GenericPredicates<'tcx> {
-    pub fn empty() -> GenericPredicates<'tcx> {
-        GenericPredicates {
-            predicates: vec![]
-        }
-    }
-
     pub fn instantiate(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, substs: &Substs<'tcx>)
                        -> InstantiatedPredicates<'tcx> {
+        let mut instantiated = InstantiatedPredicates::empty();
+        self.instantiate_into(tcx, &mut instantiated, substs);
+        instantiated
+    }
+    pub fn instantiate_own(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, substs: &Substs<'tcx>)
+                           -> InstantiatedPredicates<'tcx> {
         InstantiatedPredicates {
-            predicates: self.predicates.subst(tcx, substs),
+            predicates: self.predicates.subst(tcx, substs)
+        }
+    }
+
+    fn instantiate_into(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
+                        instantiated: &mut InstantiatedPredicates<'tcx>,
+                        substs: &Substs<'tcx>) {
+        if let Some(def_id) = self.parent {
+            tcx.lookup_predicates(def_id).instantiate_into(tcx, instantiated, substs);
         }
+        instantiated.predicates.extend(self.predicates.iter().map(|p| p.subst(tcx, substs)))
     }
 
     pub fn instantiate_supertrait(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>,
                                   poly_trait_ref: &ty::PolyTraitRef<'tcx>)
                                   -> InstantiatedPredicates<'tcx>
     {
+        assert_eq!(self.parent, None);
         InstantiatedPredicates {
             predicates: self.predicates.iter().map(|pred| {
                 pred.subst_supertrait(tcx, poly_trait_ref)

src/librustc/ty/structural_impls.rs

@@ -832,18 +832,6 @@ impl<'tcx> TypeFoldable<'tcx> for ty::RegionParameterDef {
     }
 }
 
-impl<'tcx> TypeFoldable<'tcx> for ty::GenericPredicates<'tcx> {
-    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
-        ty::GenericPredicates {
-            predicates: self.predicates.fold_with(folder),
-        }
-    }
-
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
-        self.predicates.visit_with(visitor)
-    }
-}
-
 impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         match *self {

src/librustc_metadata/decoder.rs

@@ -1591,6 +1591,7 @@ fn doc_predicates<'a, 'tcx>(base_doc: rbml::Doc,
     let doc = reader::get_doc(base_doc, tag);
 
     ty::GenericPredicates {
+        parent: item_parent_item(cdata, doc),
         predicates: reader::tagged_docs(doc, tag_predicate).map(|predicate_doc| {
             doc_predicate(cdata, predicate_doc, tcx)
         }).collect()

src/librustc_metadata/encoder.rs

@@ -525,6 +525,9 @@ fn encode_predicates<'a,'tcx>(rbml_w: &mut Encoder,
                               tag: usize)
 {
     rbml_w.start_tag(tag);
+    if let Some(def_id) = predicates.parent {
+        rbml_w.wr_tagged_u64(tag_items_data_parent_item, def_to_u64(def_id));
+    }
     for predicate in &predicates.predicates {
         rbml_w.wr_tagged_u32(tag_predicate,
             index.add_xref(XRef::Predicate(predicate.clone())));

src/librustc_typeck/astconv.rs

@@ -1726,6 +1726,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                     let predicates = bounds.predicates(tcx, ty);
                     let predicates = tcx.lift_to_global(&predicates).unwrap();
                     tcx.predicates.borrow_mut().insert(def_id, ty::GenericPredicates {
+                        parent: None,
                         predicates: predicates
                     });
 

src/librustc_typeck/check/compare_method.rs

@@ -211,29 +211,18 @@ pub fn compare_impl_method<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
         return;
     }
 
-    // Depend on trait/impl predicates always being before method's own predicates,
-    // to be able to split method predicates into "inherited" and method-specific.
-    let trait_predicates = tcx.lookup_predicates(trait_m.container_id()).predicates;
-    let impl_predicates = tcx.lookup_predicates(impl_m.container_id()).predicates;
-    let trait_method_start = trait_predicates.len();
-    let impl_method_start = impl_predicates.len();
-    assert_eq!(&trait_predicates[..], &trait_m.predicates.predicates[..trait_method_start]);
-    assert_eq!(&impl_predicates[..], &impl_m.predicates.predicates[..impl_method_start]);
-
     tcx.infer_ctxt(None, None, Reveal::NotSpecializable).enter(|mut infcx| {
         let mut fulfillment_cx = traits::FulfillmentContext::new();
 
-        // Normalize the associated types in the trait_bounds.
-        let trait_bounds = trait_m.predicates.instantiate(tcx, trait_to_skol_substs);
-
         // Create obligations for each predicate declared by the impl
         // definition in the context of the trait's parameter
         // environment. We can't just use `impl_env.caller_bounds`,
         // however, because we want to replace all late-bound regions with
         // region variables.
-        let impl_bounds = impl_m.predicates.instantiate(tcx, impl_to_skol_substs);
+        let impl_predicates = tcx.lookup_predicates(impl_m.predicates.parent.unwrap());
+        let mut hybrid_preds = impl_predicates.instantiate(tcx, impl_to_skol_substs);
 
-        debug!("compare_impl_method: impl_bounds={:?}", impl_bounds);
+        debug!("compare_impl_method: impl_bounds={:?}", hybrid_preds);
 
         // This is the only tricky bit of the new way we check implementation methods
         // We need to build a set of predicates where only the FnSpace bounds
@@ -242,14 +231,14 @@ pub fn compare_impl_method<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
         //
         // We then register the obligations from the impl_m and check to see
         // if all constraints hold.
-        let hybrid_preds = impl_bounds.predicates[..impl_method_start].iter()
-                    .chain(trait_bounds.predicates[trait_method_start..].iter());
+        hybrid_preds.predicates.extend(
+            trait_m.predicates.instantiate_own(tcx, trait_to_skol_substs).predicates);
 
         // Construct trait parameter environment and then shift it into the skolemized viewpoint.
         // The key step here is to update the caller_bounds's predicates to be
         // the new hybrid bounds we computed.
         let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_body_id);
-        let trait_param_env = impl_param_env.with_caller_bounds(hybrid_preds.cloned().collect());
+        let trait_param_env = impl_param_env.with_caller_bounds(hybrid_preds.predicates);
         let trait_param_env = traits::normalize_param_env_or_error(tcx,
                                                                    trait_param_env,
                                                                    normalize_cause.clone());
@@ -261,12 +250,13 @@ pub fn compare_impl_method<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
 
         let mut selcx = traits::SelectionContext::new(&infcx);
 
-        let (impl_pred_fns, _) =
+        let impl_m_own_bounds = impl_m.predicates.instantiate_own(tcx, impl_to_skol_substs);
+        let (impl_m_own_bounds, _) =
             infcx.replace_late_bound_regions_with_fresh_var(
                 impl_m_span,
                 infer::HigherRankedType,
-                &ty::Binder(impl_bounds.predicates[impl_method_start..].to_vec()));
-        for predicate in impl_pred_fns {
+                &ty::Binder(impl_m_own_bounds.predicates));
+        for predicate in impl_m_own_bounds {
             let traits::Normalized { value: predicate, .. } =
                 traits::normalize(&mut selcx, normalize_cause.clone(), &predicate);
 

src/librustc_typeck/check/dropck.rs

@@ -184,6 +184,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'a, 'tcx>(
     // 'a:'b and T:'b into region inference constraints. It is simpler
     // just to look for all the predicates directly.
 
+    assert_eq!(dtor_predicates.parent, None);
     for predicate in &dtor_predicates.predicates {
         // (We do not need to worry about deep analysis of type
         // expressions etc because the Drop impls are already forced

src/librustc_typeck/check/mod.rs

@@ -1612,8 +1612,14 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                           bounds: &ty::GenericPredicates<'tcx>)
                           -> ty::InstantiatedPredicates<'tcx>
     {
+        let result = bounds.instantiate(self.tcx, substs);
+        let result = self.normalize_associated_types_in(span, &result.predicates);
+        debug!("instantiate_bounds(bounds={:?}, substs={:?}) = {:?}",
+               bounds,
+               substs,
+               result);
         ty::InstantiatedPredicates {
-            predicates: self.instantiate_type_scheme(span, substs, &bounds.predicates)
+            predicates: result
         }
     }
 
@@ -4210,8 +4216,6 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             }
             _ => {}
         }
-        let scheme = self.tcx.lookup_item_type(def.def_id());
-        let type_predicates = self.tcx.lookup_predicates(def.def_id());
 
         // Now we have to compare the types that the user *actually*
         // provided against the types that were *expected*. If the user
@@ -4296,6 +4300,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
         // The things we are substituting into the type should not contain
         // escaping late-bound regions, and nor should the base type scheme.
+        let scheme = self.tcx.lookup_item_type(def.def_id());
+        let type_predicates = self.tcx.lookup_predicates(def.def_id());
         assert!(!substs.has_escaping_regions());
         assert!(!scheme.ty.has_escaping_regions());
 

src/librustc_typeck/check/regionck.rs

@@ -1754,6 +1754,7 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
         //
         // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`.
         let trait_predicates = self.tcx.lookup_predicates(projection_ty.trait_ref.def_id);
+        assert_eq!(trait_predicates.parent, None);
         let predicates = trait_predicates.predicates.as_slice().to_vec();
         traits::elaborate_predicates(self.tcx, predicates)
             .filter_map(|predicate| {

src/librustc_typeck/check/wfcheck.rs

@@ -454,6 +454,7 @@ impl<'ccx, 'gcx> CheckTypeWellFormedVisitor<'ccx, 'gcx> {
 
         let item_def_id = self.tcx().map.local_def_id(item.id);
         let ty_predicates = self.tcx().lookup_predicates(item_def_id);
+        assert_eq!(ty_predicates.parent, None);
         let variances = self.tcx().item_variances(item_def_id);
 
         let mut constrained_parameters: HashSet<_> =