5 files changed, 78 insertions, 13 deletions

diff --git a/crates/hir_def/src/data.rs b/crates/hir_def/src/data.rs
index 0be868ba2..214bcc648 100644
--- a/crates/hir_def/src/data.rs
+++ b/crates/hir_def/src/data.rs
@@ -10,7 +10,7 @@ use crate::{
     body::Expander,
     db::DefDatabase,
     item_tree::{AssocItem, FunctionQualifier, ItemTreeId, ModItem, Param},
-    type_ref::{TypeBound, TypeRef},
+    type_ref::{TraitRef, TypeBound, TypeRef},
     visibility::RawVisibility,
     AssocContainerId, AssocItemId, ConstId, ConstLoc, FunctionId, FunctionLoc, HasModule, ImplId,
     Intern, Lookup, ModuleId, StaticId, TraitId, TypeAliasId, TypeAliasLoc,
@@ -156,8 +156,8 @@ impl TraitData {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ImplData {
-    pub target_trait: Option<TypeRef>,
-    pub target_type: TypeRef,
+    pub target_trait: Option<TraitRef>,
+    pub self_ty: TypeRef,
     pub items: Vec<AssocItemId>,
     pub is_negative: bool,
 }
@@ -170,7 +170,7 @@ impl ImplData {
         let item_tree = impl_loc.id.item_tree(db);
         let impl_def = &item_tree[impl_loc.id.value];
         let target_trait = impl_def.target_trait.map(|id| item_tree[id].clone());
-        let target_type = item_tree[impl_def.target_type].clone();
+        let self_ty = item_tree[impl_def.self_ty].clone();
         let is_negative = impl_def.is_negative;
         let module_id = impl_loc.container;
         let container = AssocContainerId::ImplId(id);
@@ -187,7 +187,7 @@ impl ImplData {
         );
         let items = items.into_iter().map(|(_, item)| item).collect();
 
-        Arc::new(ImplData { target_trait, target_type, items, is_negative })
+        Arc::new(ImplData { target_trait, self_ty, items, is_negative })
     }
 }
 
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index ca0048b16..5449bbf5d 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -31,7 +31,7 @@ use crate::{
     db::DefDatabase,
     generics::GenericParams,
     path::{path, AssociatedTypeBinding, GenericArgs, ImportAlias, ModPath, Path, PathKind},
-    type_ref::{Mutability, TypeBound, TypeRef},
+    type_ref::{Mutability, TraitRef, TypeBound, TypeRef},
     visibility::RawVisibility,
 };
 
@@ -147,6 +147,7 @@ impl ItemTree {
                 vis,
                 generics,
                 type_refs,
+                trait_refs,
                 inner_items,
             } = &mut **data;
 
@@ -173,6 +174,7 @@ impl ItemTree {
             generics.arena.shrink_to_fit();
             type_refs.arena.shrink_to_fit();
             type_refs.map.shrink_to_fit();
+            trait_refs.map.shrink_to_fit();
 
             inner_items.shrink_to_fit();
         }
@@ -295,6 +297,32 @@ impl TypeRefStorage {
     }
 }
 
+/// `TraitRef` interner.
+#[derive(Default, Debug, Eq, PartialEq)]
+struct TraitRefStorage {
+    arena: Arena<Arc<TraitRef>>,
+    map: FxHashMap<Arc<TraitRef>, Idx<Arc<TraitRef>>>,
+}
+
+impl TraitRefStorage {
+    // Note: We lie about the `Idx<TraitRef>` to hide the interner details.
+
+    fn intern(&mut self, ty: TraitRef) -> Idx<TraitRef> {
+        if let Some(id) = self.map.get(&ty) {
+            return Idx::from_raw(id.into_raw());
+        }
+
+        let ty = Arc::new(ty);
+        let idx = self.arena.alloc(ty.clone());
+        self.map.insert(ty, idx);
+        Idx::from_raw(idx.into_raw())
+    }
+
+    fn lookup(&self, id: Idx<TraitRef>) -> &TraitRef {
+        &self.arena[Idx::from_raw(id.into_raw())]
+    }
+}
+
 #[derive(Default, Debug, Eq, PartialEq)]
 struct ItemTreeData {
     imports: Arena<Import>,
@@ -319,6 +347,7 @@ struct ItemTreeData {
     vis: ItemVisibilities,
     generics: GenericParamsStorage,
     type_refs: TypeRefStorage,
+    trait_refs: TraitRefStorage,
 
     inner_items: FxHashMap<FileAstId<ast::BlockExpr>, SmallVec<[ModItem; 1]>>,
 }
@@ -556,6 +585,14 @@ impl Index<Idx<TypeRef>> for ItemTree {
     }
 }
 
+impl Index<Idx<TraitRef>> for ItemTree {
+    type Output = TraitRef;
+
+    fn index(&self, id: Idx<TraitRef>) -> &Self::Output {
+        self.data().trait_refs.lookup(id)
+    }
+}
+
 impl<N: ItemTreeNode> Index<FileItemTreeId<N>> for ItemTree {
     type Output = N;
     fn index(&self, id: FileItemTreeId<N>) -> &N {
@@ -692,8 +729,8 @@ pub struct Trait {
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct Impl {
     pub generic_params: GenericParamsId,
-    pub target_trait: Option<Idx<TypeRef>>,
-    pub target_type: Idx<TypeRef>,
+    pub target_trait: Option<Idx<TraitRef>>,
+    pub self_ty: Idx<TypeRef>,
     pub is_negative: bool,
     pub items: Box<[AssocItem]>,
     pub ast_id: FileAstId<ast::Impl>,
diff --git a/crates/hir_def/src/item_tree/lower.rs b/crates/hir_def/src/item_tree/lower.rs
index 3f558edd8..8d3862811 100644
--- a/crates/hir_def/src/item_tree/lower.rs
+++ b/crates/hir_def/src/item_tree/lower.rs
@@ -11,7 +11,7 @@ use syntax::{
 
 use crate::{
     generics::{GenericParams, TypeParamData, TypeParamProvenance},
-    type_ref::LifetimeRef,
+    type_ref::{LifetimeRef, TraitRef},
 };
 
 use super::*;
@@ -536,8 +536,11 @@ impl Ctx {
     fn lower_impl(&mut self, impl_def: &ast::Impl) -> Option<FileItemTreeId<Impl>> {
         let generic_params =
             self.lower_generic_params_and_inner_items(GenericsOwner::Impl, impl_def);
-        let target_trait = impl_def.trait_().map(|tr| self.lower_type_ref(&tr));
-        let target_type = self.lower_type_ref(&impl_def.self_ty()?);
+        // FIXME: If trait lowering fails, due to a non PathType for example, we treat this impl
+        // as if it was an non-trait impl. Ideally we want to create a unique missing ref that only
+        // equals itself.
+        let target_trait = impl_def.trait_().and_then(|tr| self.lower_trait_ref(&tr));
+        let self_ty = self.lower_type_ref(&impl_def.self_ty()?);
         let is_negative = impl_def.excl_token().is_some();
 
         // We cannot use `assoc_items()` here as that does not include macro calls.
@@ -554,7 +557,7 @@ impl Ctx {
             })
             .collect();
         let ast_id = self.source_ast_id_map.ast_id(impl_def);
-        let res = Impl { generic_params, target_trait, target_type, is_negative, items, ast_id };
+        let res = Impl { generic_params, target_trait, self_ty, is_negative, items, ast_id };
         Some(id(self.data().impls.alloc(res)))
     }
 
@@ -740,10 +743,16 @@ impl Ctx {
         self.data().vis.alloc(vis)
     }
 
+    fn lower_trait_ref(&mut self, trait_ref: &ast::Type) -> Option<Idx<TraitRef>> {
+        let trait_ref = TraitRef::from_ast(&self.body_ctx, trait_ref.clone())?;
+        Some(self.data().trait_refs.intern(trait_ref))
+    }
+
     fn lower_type_ref(&mut self, type_ref: &ast::Type) -> Idx<TypeRef> {
         let tyref = TypeRef::from_ast(&self.body_ctx, type_ref.clone());
         self.data().type_refs.intern(tyref)
     }
+
     fn lower_type_ref_opt(&mut self, type_ref: Option<ast::Type>) -> Idx<TypeRef> {
         match type_ref.map(|ty| self.lower_type_ref(&ty)) {
             Some(it) => it,
diff --git a/crates/hir_def/src/path/lower.rs b/crates/hir_def/src/path/lower.rs
index 505493a74..4de951fd3 100644
--- a/crates/hir_def/src/path/lower.rs
+++ b/crates/hir_def/src/path/lower.rs
@@ -74,6 +74,7 @@ pub(super) fn lower_path(mut path: ast::Path, hygiene: &Hygiene) -> Option<Path>
                     // <T as Trait<A>>::Foo desugars to Trait<Self=T, A>::Foo
                     Some(trait_ref) => {
                         let path = Path::from_src(trait_ref.path()?, hygiene)?;
+                        let num_segments = path.mod_path.segments.len();
                         kind = path.mod_path.kind;
 
                         let mut prefix_segments = path.mod_path.segments;
@@ -85,7 +86,8 @@ pub(super) fn lower_path(mut path: ast::Path, hygiene: &Hygiene) -> Option<Path>
                         generic_args.extend(prefix_args);
 
                         // Insert the type reference (T in the above example) as Self parameter for the trait
-                        let last_segment = generic_args.last_mut()?;
+                        let last_segment =
+                            generic_args.iter_mut().rev().nth(num_segments.saturating_sub(1))?;
                         if last_segment.is_none() {
                             *last_segment = Some(Arc::new(GenericArgs::empty()));
                         };
diff --git a/crates/hir_def/src/type_ref.rs b/crates/hir_def/src/type_ref.rs
index 049b2e462..4c24aae94 100644
--- a/crates/hir_def/src/type_ref.rs
+++ b/crates/hir_def/src/type_ref.rs
@@ -51,6 +51,23 @@ impl Rawness {
     }
 }
 
+#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+pub struct TraitRef {
+    pub path: Path,
+}
+
+impl TraitRef {
+    /// Converts an `ast::PathType` to a `hir::TraitRef`.
+    pub(crate) fn from_ast(ctx: &LowerCtx, node: ast::Type) -> Option<Self> {
+        // FIXME: Use `Path::from_src`
+        match node {
+            ast::Type::PathType(path) => {
+                path.path().and_then(|it| ctx.lower_path(it)).map(|path| TraitRef { path })
+            }
+            _ => None,
+        }
+    }
+}
 /// Compare ty::Ty
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub enum TypeRef {