integrate trait aliases into def-paths / metadata

Co-authored-by: Alexander Regueiro <alexreg@me.com>

13 files changed, 82 insertions, 39 deletions

diff --git a/src/librustc/hir/map/def_collector.rs b/src/librustc/hir/map/def_collector.rs
index bc0a64ae7c5..c9b4b2bb997 100644
--- a/src/librustc/hir/map/def_collector.rs
+++ b/src/librustc/hir/map/def_collector.rs
@@ -120,10 +120,10 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
         let def_data = match i.node {
             ItemKind::Impl(..) => DefPathData::Impl,
             ItemKind::Trait(..) => DefPathData::Trait(i.ident.as_interned_str()),
+            ItemKind::TraitAlias(..) => DefPathData::TraitAlias(i.ident.as_interned_str()),
             ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) |
-            ItemKind::TraitAlias(..) | ItemKind::Existential(..) |
-            ItemKind::ExternCrate(..) | ItemKind::ForeignMod(..) | ItemKind::Ty(..) =>
-                DefPathData::TypeNs(i.ident.as_interned_str()),
+            ItemKind::Existential(..) | ItemKind::ExternCrate(..) | ItemKind::ForeignMod(..) |
+            ItemKind::Ty(..) => DefPathData::TypeNs(i.ident.as_interned_str()),
             ItemKind::Mod(..) if i.ident == keywords::Invalid.ident() => {
                 return visit::walk_item(self, i);
             }
diff --git a/src/librustc/hir/map/definitions.rs b/src/librustc/hir/map/definitions.rs
index 6b707dd2dcc..1b744519947 100644
--- a/src/librustc/hir/map/definitions.rs
+++ b/src/librustc/hir/map/definitions.rs
@@ -373,7 +373,9 @@ pub enum DefPathData {
     /// GlobalMetaData identifies a piece of crate metadata that is global to
     /// a whole crate (as opposed to just one item). GlobalMetaData components
     /// are only supposed to show up right below the crate root.
-    GlobalMetaData(InternedString)
+    GlobalMetaData(InternedString),
+    /// A trait alias.
+    TraitAlias(InternedString),
 }
 
 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug,
@@ -615,6 +617,7 @@ impl DefPathData {
         match *self {
             TypeNs(name) |
             Trait(name) |
+            TraitAlias(name) |
             AssocTypeInTrait(name) |
             AssocTypeInImpl(name) |
             AssocExistentialInImpl(name) |
@@ -642,6 +645,7 @@ impl DefPathData {
         let s = match *self {
             TypeNs(name) |
             Trait(name) |
+            TraitAlias(name) |
             AssocTypeInTrait(name) |
             AssocTypeInImpl(name) |
             AssocExistentialInImpl(name) |
diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs
index 6db6fe31fba..4d478365e72 100644
--- a/src/librustc/traits/select.rs
+++ b/src/librustc/traits/select.rs
@@ -2154,7 +2154,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
 
         let def_id = obligation.predicate.def_id();
 
-        if ty::is_trait_alias(self.tcx(), def_id) {
+        if self.tcx().is_trait_alias(def_id) {
             candidates.vec.push(TraitAliasCandidate(def_id.clone()));
         }
 
diff --git a/src/librustc/ty/item_path.rs b/src/librustc/ty/item_path.rs
index 417e14054d2..9328de4f6a0 100644
--- a/src/librustc/ty/item_path.rs
+++ b/src/librustc/ty/item_path.rs
@@ -311,6 +311,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             data @ DefPathData::Misc |
             data @ DefPathData::TypeNs(..) |
             data @ DefPathData::Trait(..) |
+            data @ DefPathData::TraitAlias(..) |
             data @ DefPathData::AssocTypeInTrait(..) |
             data @ DefPathData::AssocTypeInImpl(..) |
             data @ DefPathData::AssocExistentialInImpl(..) |
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index a2c96e7cf9f..e2f696b0974 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -3178,18 +3178,6 @@ pub fn is_impl_trait_defn(tcx: TyCtxt<'_, '_, '_>, def_id: DefId) -> Option<DefI
     None
 }
 
-/// Returns `true` if `def_id` is a trait alias.
-pub fn is_trait_alias(tcx: TyCtxt<'_, '_, '_>, def_id: DefId) -> bool {
-    if let Some(node_id) = tcx.hir().as_local_node_id(def_id) {
-        if let Node::Item(item) = tcx.hir().get(node_id) {
-            if let hir::ItemKind::TraitAlias(..) = item.node {
-                return true;
-            }
-        }
-    }
-    false
-}
-
 /// See `ParamEnv` struct definition for details.
 fn param_env<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                        def_id: DefId)
diff --git a/src/librustc/ty/util.rs b/src/librustc/ty/util.rs
index e989ef823e9..75fc0f716a2 100644
--- a/src/librustc/ty/util.rs
+++ b/src/librustc/ty/util.rs
@@ -526,6 +526,15 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
+    /// True if `def_id` refers to a trait alias (i.e., `trait Foo = ...;`).
+    pub fn is_trait_alias(self, def_id: DefId) -> bool {
+        if let DefPathData::TraitAlias(_) = self.def_key(def_id).disambiguated_data.data {
+            true
+        } else {
+            false
+        }
+    }
+
     /// True if this def-id refers to the implicit constructor for
     /// a tuple struct like `struct Foo(u32)`.
     pub fn is_struct_constructor(self, def_id: DefId) -> bool {
diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs
index 04e571863d4..51e9192cd29 100644
--- a/src/librustc/util/ppaux.rs
+++ b/src/librustc/util/ppaux.rs
@@ -409,6 +409,7 @@ impl PrintContext {
                     DefPathData::AssocTypeInImpl(_) |
                     DefPathData::AssocExistentialInImpl(_) |
                     DefPathData::Trait(_) |
+                    DefPathData::TraitAlias(_) |
                     DefPathData::Impl |
                     DefPathData::TypeNs(_) => {
                         break;
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index dc8db5be582..1f07e8f478b 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -418,6 +418,7 @@ impl<'tcx> EntryKind<'tcx> {
             EntryKind::Mod(_) => Def::Mod(did),
             EntryKind::Variant(_) => Def::Variant(did),
             EntryKind::Trait(_) => Def::Trait(did),
+            EntryKind::TraitAlias(_) => Def::TraitAlias(did),
             EntryKind::Enum(..) => Def::Enum(did),
             EntryKind::MacroDef(_) => Def::Macro(did, MacroKind::Bang),
             EntryKind::ForeignType => Def::ForeignTy(did),
@@ -520,17 +521,26 @@ impl<'a, 'tcx> CrateMetadata {
     }
 
     pub fn get_trait_def(&self, item_id: DefIndex, sess: &Session) -> ty::TraitDef {
-        let data = match self.entry(item_id).kind {
-            EntryKind::Trait(data) => data.decode((self, sess)),
-            _ => bug!(),
-        };
-
-        ty::TraitDef::new(self.local_def_id(item_id),
-                          data.unsafety,
-                          data.paren_sugar,
-                          data.has_auto_impl,
-                          data.is_marker,
-                          self.def_path_table.def_path_hash(item_id))
+        match self.entry(item_id).kind {
+            EntryKind::Trait(data) => {
+                let data = data.decode((self, sess));
+                ty::TraitDef::new(self.local_def_id(item_id),
+                                  data.unsafety,
+                                  data.paren_sugar,
+                                  data.has_auto_impl,
+                                  data.is_marker,
+                                  self.def_path_table.def_path_hash(item_id))
+            },
+            EntryKind::TraitAlias(_) => {
+                ty::TraitDef::new(self.local_def_id(item_id),
+                                  hir::Unsafety::Normal,
+                                  false,
+                                  false,
+                                  false,
+                                  self.def_path_table.def_path_hash(item_id))
+            },
+            _ => bug!("def-index does not refer to trait or trait alias"),
+        }
     }
 
     fn get_variant(&self,
@@ -615,10 +625,13 @@ impl<'a, 'tcx> CrateMetadata {
                                 item_id: DefIndex,
                                 tcx: TyCtxt<'a, 'tcx, 'tcx>)
                                 -> ty::GenericPredicates<'tcx> {
-        match self.entry(item_id).kind {
-            EntryKind::Trait(data) => data.decode(self).super_predicates.decode((self, tcx)),
-            _ => bug!(),
-        }
+        let super_predicates = match self.entry(item_id).kind {
+            EntryKind::Trait(data) => data.decode(self).super_predicates,
+            EntryKind::TraitAlias(data) => data.decode(self).super_predicates,
+            _ => bug!("def-index does not refer to trait or trait alias"),
+        };
+
+        super_predicates.decode((self, tcx))
     }
 
     pub fn get_generics(&self,
@@ -1014,7 +1027,8 @@ impl<'a, 'tcx> CrateMetadata {
         }
         def_key.parent.and_then(|parent_index| {
             match self.entry(parent_index).kind {
-                EntryKind::Trait(_) => Some(self.local_def_id(parent_index)),
+                EntryKind::Trait(_) |
+                EntryKind::TraitAlias(_) => Some(self.local_def_id(parent_index)),
                 _ => None,
             }
         })
diff --git a/src/librustc_metadata/encoder.rs b/src/librustc_metadata/encoder.rs
index 032a4656efc..2522469086f 100644
--- a/src/librustc_metadata/encoder.rs
+++ b/src/librustc_metadata/encoder.rs
@@ -1131,8 +1131,7 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
 
                 EntryKind::Impl(self.lazy(&data))
             }
-            hir::ItemKind::Trait(..) |
-            hir::ItemKind::TraitAlias(..) => {
+            hir::ItemKind::Trait(..) => {
                 let trait_def = tcx.trait_def(def_id);
                 let data = TraitData {
                     unsafety: trait_def.unsafety,
@@ -1144,6 +1143,13 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
 
                 EntryKind::Trait(self.lazy(&data))
             }
+            hir::ItemKind::TraitAlias(..) => {
+                let data = TraitAliasData {
+                    super_predicates: self.lazy(&tcx.super_predicates_of(def_id)),
+                };
+
+                EntryKind::TraitAlias(self.lazy(&data))
+            }
             hir::ItemKind::ExternCrate(_) |
             hir::ItemKind::Use(..) => bug!("cannot encode info for item {:?}", item),
         };
@@ -1217,6 +1223,7 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
                 hir::ItemKind::Impl(..) |
                 hir::ItemKind::Existential(..) |
                 hir::ItemKind::Trait(..) => Some(self.encode_generics(def_id)),
+                hir::ItemKind::TraitAlias(..) => Some(self.encode_generics(def_id)),
                 _ => None,
             },
             predicates: match item.node {
@@ -1229,7 +1236,8 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
                 hir::ItemKind::Union(..) |
                 hir::ItemKind::Impl(..) |
                 hir::ItemKind::Existential(..) |
-                hir::ItemKind::Trait(..) => Some(self.encode_predicates(def_id)),
+                hir::ItemKind::Trait(..) |
+                hir::ItemKind::TraitAlias(..) => Some(self.encode_predicates(def_id)),
                 _ => None,
             },
 
@@ -1239,7 +1247,8 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
             // hack. (No reason not to expand it in the future if
             // necessary.)
             predicates_defined_on: match item.node {
-                hir::ItemKind::Trait(..) => Some(self.encode_predicates_defined_on(def_id)),
+                hir::ItemKind::Trait(..) |
+                hir::ItemKind::TraitAlias(..) => Some(self.encode_predicates_defined_on(def_id)),
                 _ => None, // not *wrong* for other kinds of items, but not needed
             },
 
diff --git a/src/librustc_metadata/schema.rs b/src/librustc_metadata/schema.rs
index 25f499bc319..f3ff9747625 100644
--- a/src/librustc_metadata/schema.rs
+++ b/src/librustc_metadata/schema.rs
@@ -316,6 +316,7 @@ pub enum EntryKind<'tcx> {
     AssociatedType(AssociatedContainer),
     AssociatedExistential(AssociatedContainer),
     AssociatedConst(AssociatedContainer, ConstQualif, Lazy<RenderedConst>),
+    TraitAlias(Lazy<TraitAliasData<'tcx>>),
 }
 
 impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for EntryKind<'gcx> {
@@ -370,6 +371,9 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for EntryKind<'gcx> {
             EntryKind::Trait(ref trait_data) => {
                 trait_data.hash_stable(hcx, hasher);
             }
+            EntryKind::TraitAlias(ref trait_alias_data) => {
+                trait_alias_data.hash_stable(hcx, hasher);
+            }
             EntryKind::Impl(ref impl_data) => {
                 impl_data.hash_stable(hcx, hasher);
             }
@@ -475,6 +479,15 @@ impl_stable_hash_for!(struct TraitData<'tcx> {
 });
 
 #[derive(RustcEncodable, RustcDecodable)]
+pub struct TraitAliasData<'tcx> {
+    pub super_predicates: Lazy<ty::GenericPredicates<'tcx>>,
+}
+
+impl_stable_hash_for!(struct TraitAliasData<'tcx> {
+    super_predicates
+});
+
+#[derive(RustcEncodable, RustcDecodable)]
 pub struct ImplData<'tcx> {
     pub polarity: hir::ImplPolarity,
     pub defaultness: hir::Defaultness,
diff --git a/src/librustc_resolve/build_reduced_graph.rs b/src/librustc_resolve/build_reduced_graph.rs
index a452bbf0c9d..28b80fe3aaf 100644
--- a/src/librustc_resolve/build_reduced_graph.rs
+++ b/src/librustc_resolve/build_reduced_graph.rs
@@ -673,6 +673,9 @@ impl<'a> Resolver<'a> {
                 }
                 module.populated.set(true);
             }
+            Def::TraitAlias(..) => {
+                self.define(parent, ident, TypeNS, (def, vis, DUMMY_SP, expansion));
+            }
             Def::Struct(..) | Def::Union(..) => {
                 self.define(parent, ident, TypeNS, (def, vis, DUMMY_SP, expansion));
 
diff --git a/src/librustc_traits/lowering/mod.rs b/src/librustc_traits/lowering/mod.rs
index 5502a1d186e..9bdef3051e5 100644
--- a/src/librustc_traits/lowering/mod.rs
+++ b/src/librustc_traits/lowering/mod.rs
@@ -158,7 +158,8 @@ crate fn program_clauses_for<'a, 'tcx>(
     def_id: DefId,
 ) -> Clauses<'tcx> {
     match tcx.def_key(def_id).disambiguated_data.data {
-        DefPathData::Trait(_) => program_clauses_for_trait(tcx, def_id),
+        DefPathData::Trait(_) |
+        DefPathData::TraitAlias(_) => program_clauses_for_trait(tcx, def_id),
         DefPathData::Impl => program_clauses_for_impl(tcx, def_id),
         DefPathData::AssocTypeInImpl(..) => program_clauses_for_associated_type_value(tcx, def_id),
         DefPathData::AssocTypeInTrait(..) => program_clauses_for_associated_type_def(tcx, def_id),
diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index e0e173901ef..66b2443af41 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -706,7 +706,7 @@ fn super_predicates_of<'a, 'tcx>(
     // In the case of trait aliases, however, we include all bounds in the where clause,
     // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
     // as one of its "superpredicates".
-    let is_trait_alias = ty::is_trait_alias(tcx, trait_def_id);
+    let is_trait_alias = tcx.is_trait_alias(trait_def_id);
     let superbounds2 = icx.type_parameter_bounds_in_generics(
         generics, item.id, self_param_ty, OnlySelfBounds(!is_trait_alias));