Implemented for function bounds, type bounds, and named existential types.

Author: Alexander Regueiro

src/librustc/hir/lowering.rs

@@ -69,7 +69,7 @@ use syntax::symbol::{kw, sym, Symbol};
 use syntax::tokenstream::{TokenStream, TokenTree};
 use syntax::parse::token::Token;
 use syntax::visit::{self, Visitor};
-use syntax_pos::{edition, Span};
+use syntax_pos::{DUMMY_SP, edition, Span};
 
 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
 
@@ -191,9 +191,9 @@ enum ImplTraitContext<'a> {
     /// equivalent to a fresh existential parameter like `existential type T; fn foo() -> T`.
     ///
     /// We optionally store a `DefId` for the parent item here so we can look up necessary
-    /// information later. It is `None` when no information about the context should be stored,
-    /// e.g., for consts and statics.
-    Existential(Option<DefId>),
+    /// information later. It is `None` when no information about the context should be stored
+    /// (e.g., for consts and statics).
+    Existential(Option<DefId> /* fn def-ID */),
 
     /// `impl Trait` is not accepted in this position.
     Disallowed(ImplTraitPosition),
@@ -216,7 +216,7 @@ impl<'a> ImplTraitContext<'a> {
         use self::ImplTraitContext::*;
         match self {
             Universal(params) => Universal(params),
-            Existential(did) => Existential(*did),
+            Existential(fn_def_id) => Existential(*fn_def_id),
             Disallowed(pos) => Disallowed(*pos),
         }
     }
@@ -1342,13 +1342,36 @@ impl<'a> LoweringContext<'a> {
         }
     }
 
-    fn lower_ty_binding(&mut self, b: &TypeBinding,
-                        itctx: ImplTraitContext<'_>) -> hir::TypeBinding {
+    fn lower_assoc_ty_constraint(&mut self,
+                                 c: &AssocTyConstraint,
+                                 itctx: ImplTraitContext<'_>)
+                                 -> hir::TypeBinding {
+        let ty = match c.kind {
+            AssocTyConstraintKind::Equality { ref ty } => self.lower_ty(ty, itctx),
+            AssocTyConstraintKind::Bound { ref bounds } => {
+                // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`.
+                let impl_ty_node_id = self.sess.next_node_id();
+                let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
+                self.resolver.definitions().create_def_with_parent(
+                    parent_def_index,
+                    impl_ty_node_id,
+                    DefPathData::Misc,
+                    DefIndexAddressSpace::High,
+                    Mark::root(),
+                    DUMMY_SP);
+                self.lower_ty(&Ty {
+                    id: self.sess.next_node_id(),
+                    node: TyKind::ImplTrait(impl_ty_node_id, bounds.clone()),
+                    span: DUMMY_SP,
+                }, itctx)
+            }
+        };
+
         hir::TypeBinding {
-            hir_id: self.lower_node_id(b.id),
-            ident: b.ident,
-            ty: self.lower_ty(&b.ty, itctx),
-            span: b.span,
+            hir_id: self.lower_node_id(c.id),
+            ident: c.ident,
+            ty
+            span: c.span,
         }
     }
 
@@ -1604,7 +1627,7 @@ impl<'a> LoweringContext<'a> {
                 origin: hir::ExistTyOrigin::ReturnImplTrait,
             };
 
-            trace!("exist ty from impl trait def index: {:#?}", exist_ty_def_index);
+            trace!("exist ty from impl trait def-index: {:#?}", exist_ty_def_index);
             let exist_ty_id = lctx.generate_existential_type(
                 exist_ty_node_id,
                 exist_ty_item,
@@ -1617,7 +1640,7 @@ impl<'a> LoweringContext<'a> {
         })
     }
 
-    /// Registers a new existential type with the proper NodeIds and
+    /// Registers a new existential type with the proper `NodeId`ss and
     /// returns the lowered node ID for the existential type.
     fn generate_existential_type(
         &mut self,
@@ -2195,15 +2218,16 @@ impl<'a> LoweringContext<'a> {
         param_mode: ParamMode,
         mut itctx: ImplTraitContext<'_>,
     ) -> (hir::GenericArgs, bool) {
-        let &AngleBracketedArgs { ref args, ref bindings, .. } = data;
+        let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
         let has_types = args.iter().any(|arg| match arg {
             ast::GenericArg::Type(_) => true,
             _ => false,
         });
         (
             hir::GenericArgs {
                 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
-                bindings: bindings.iter().map(|b| self.lower_ty_binding(b, itctx.reborrow())).collect(),
+                bindings: constraints.iter().map(
+                    |b| self.lower_assoc_ty_constraint(b, itctx.reborrow())).collect(),
                 parenthesized: false,
             },
             !has_types && param_mode == ParamMode::Optional
@@ -3236,12 +3260,14 @@ impl<'a> LoweringContext<'a> {
                 self.lower_ty(t, ImplTraitContext::disallowed()),
                 self.lower_generics(generics, ImplTraitContext::disallowed()),
             ),
-            ItemKind::Existential(ref b, ref generics) => hir::ItemKind::Existential(hir::ExistTy {
-                generics: self.lower_generics(generics, ImplTraitContext::disallowed()),
-                bounds: self.lower_param_bounds(b, ImplTraitContext::disallowed()),
-                impl_trait_fn: None,
-                origin: hir::ExistTyOrigin::ExistentialType,
-            }),
+            ItemKind::Existential(ref b, ref generics) => hir::ItemKind::Existential(
+                hir::ExistTy {
+                    generics: self.lower_generics(generics, ImplTraitContext::disallowed()),
+                    bounds: self.lower_param_bounds(b, ImplTraitContext::Existential(None)),
+                    impl_trait_fn: None,
+                    origin: hir::ExistTyOrigin::ExistentialType,
+                },
+            ),
             ItemKind::Enum(ref enum_definition, ref generics) => hir::ItemKind::Enum(
                 hir::EnumDef {
                     variants: enum_definition

src/librustc/hir/map/definitions.rs

@@ -397,6 +397,11 @@ impl Definitions {
         self.node_to_hir_id[node_id]
     }
 
+    #[inline]
+    pub fn def_index_to_node_id(&self, def_index: DefIndex) -> ast::NodeId {
+        self.as_local_node_id(DefId::local(def_index)).unwrap()
+    }
+
     /// Retrieves the span of the given `DefId` if `DefId` is in the local crate, the span exists
     /// and it's not `DUMMY_SP`.
     #[inline]

src/librustc/hir/map/mod.rs

@@ -288,7 +288,7 @@ impl<'hir> Map<'hir> {
 
     #[inline]
     pub fn def_index_to_node_id(&self, def_index: DefIndex) -> NodeId {
-        self.definitions.as_local_node_id(DefId::local(def_index)).unwrap()
+        self.definitions.def_index_to_node_id(def_index)
     }
 
     #[inline]
@@ -649,16 +649,16 @@ impl<'hir> Map<'hir> {
         result
     }
 
-    /// Similar to `get_parent`; returns the parent node-id, or own `id` if there is
-    /// no parent. Note that the parent may be `CRATE_NODE_ID`, which is not itself
-    /// present in the map -- so passing the return value of get_parent_node to
-    /// get may actually panic.
-    /// This function returns the immediate parent in the AST, whereas get_parent
+    /// Similar to `get_parent`; returns the parent node-ID, or just `hir_id` if there
+    /// is no parent. Note that the parent may be `CRATE_NODE_ID`, which is not itself
+    /// present in the map, so passing the return value of `get_parent_node` to
+    /// `get` may in fact panic.
+    /// This function returns the immediate parent in the AST, whereas `get_parent`
     /// returns the enclosing item. Note that this might not be the actual parent
-    /// node in the AST - some kinds of nodes are not in the map and these will
-    /// never appear as the parent_node. So you can always walk the `parent_nodes`
-    /// from a node to the root of the ast (unless you get the same ID back here
-    /// that can happen if the ID is not in the map itself or is just weird).
+    /// node in the AST -- some kinds of nodes are not in the map and these will
+    /// never appear as the parent node. Thus, you can always walk the parent nodes
+    /// from a node to the root of the AST (unless you get back the same ID here,
+    /// which can happen if the ID is not in the map itself or is just weird).
     pub fn get_parent_node(&self, id: NodeId) -> NodeId {
         let hir_id = self.node_to_hir_id(id);
         let parent_hir_id = self.get_parent_node_by_hir_id(hir_id);
@@ -841,21 +841,66 @@ impl<'hir> Map<'hir> {
         }
     }
 
-    /// Returns the nearest enclosing scope. A scope is an item or block.
-    /// FIXME: it is not clear to me that all items qualify as scopes -- statics
-    /// and associated types probably shouldn't, for example. Behavior in this
-    /// regard should be expected to be highly unstable.
-    pub fn get_enclosing_scope(&self, hir_id: HirId) -> Option<HirId> {
+    /// Returns the nearest enclosing scope. A scope is roughly an item or block.
+    pub fn get_enclosing_scope(&self, id: HirId) -> Option<HirId> {
         self.walk_parent_nodes(hir_id, |node| match *node {
-            Node::Item(_) |
-            Node::ForeignItem(_) |
-            Node::TraitItem(_) |
-            Node::ImplItem(_) |
+            Node::Item(i) => {
+                match i.node {
+                    ItemKind::Fn(..)
+                    | ItemKind::Mod(..)
+                    | ItemKind::Enum(..)
+                    | ItemKind::Struct(..)
+                    | ItemKind::Union(..)
+                    | ItemKind::Trait(..)
+                    | ItemKind::Impl(..) => true,
+                    _ => false,
+                }
+            },
+            Node::ForeignItem(fi) => {
+                match fi.node {
+                    ForeignItemKind::Fn(..) => true,
+                    _ => false,
+                }
+            },
+            Node::TraitItem(ti) => {
+                match ti.node {
+                    TraitItemKind::Method(..) => true,
+                    _ => false,
+                }
+            },
+            Node::ImplItem(ii) => {
+                match ii.node {
+                    ImplItemKind::Method(..) => true,
+                    _ => false,
+                }
+            },
             Node::Block(_) => true,
             _ => false,
         }, |_| false).ok()
     }
 
+    /// Returns the defining scope for an existential type definition.
+    pub fn get_defining_scope(&self, id: NodeId) -> Option<NodeId> {
+        let mut scope = id;
+        loop {
+            scope = self.get_enclosing_scope(scope)?;
+            if scope == CRATE_NODE_ID {
+                return Some(CRATE_NODE_ID);
+            }
+            match self.get(scope) {
+                Node::Item(i) => {
+                    match i.node {
+                        ItemKind::Existential(ExistTy { impl_trait_fn: None, .. }) => {}
+                        _ => break,
+                    }
+                }
+                Node::Block(_) => {}
+                _ => break,
+            }
+        }
+        Some(scope)
+    }
+
     pub fn get_parent_did(&self, id: NodeId) -> DefId {
         let hir_id = self.node_to_hir_id(id);
         self.get_parent_did_by_hir_id(hir_id)

src/librustc/infer/opaque_types/mod.rs

@@ -786,13 +786,13 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
                             match tcx.hir().find_by_hir_id(opaque_hir_id)
                         {
                             Some(Node::Item(item)) => match item.node {
-                                // impl trait
+                                // Anonymous `impl Trait`
                                 hir::ItemKind::Existential(hir::ExistTy {
                                     impl_trait_fn: Some(parent),
                                     origin,
                                     ..
                                 }) => (parent == self.parent_def_id, origin),
-                                // named existential types
+                                // Named `existential type`
                                 hir::ItemKind::Existential(hir::ExistTy {
                                     impl_trait_fn: None,
                                     origin,
@@ -868,7 +868,7 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
 
         let predicates_of = tcx.predicates_of(def_id);
         debug!(
-            "instantiate_opaque_types: predicates: {:#?}",
+            "instantiate_opaque_types: predicates={:#?}",
             predicates_of,
         );
         let bounds = predicates_of.instantiate(tcx, substs);
@@ -884,11 +884,11 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
         // (e.g., `existential type Foo<T: Bound>: Bar;` needs to be
         // defined by a function like `fn foo<T: Bound>() -> Foo<T>`).
         debug!(
-            "instantiate_opaque_types: param_env: {:#?}",
+            "instantiate_opaque_types: param_env={:#?}",
             self.param_env,
         );
         debug!(
-            "instantiate_opaque_types: generics: {:#?}",
+            "instantiate_opaque_types: generics={:#?}",
             tcx.generics_of(def_id),
         );
 
@@ -922,8 +922,9 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
     }
 }
 
-/// Returns `true` if `opaque_node_id` is a sibling or a child of a sibling of `def_id`.
+/// Returns `true` if `opaque_hir_id` is a sibling or a child of a sibling of `def_id`.
 ///
+/// Example:
 /// ```rust
 /// pub mod foo {
 ///     pub mod bar {
@@ -936,24 +937,28 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
 /// }
 /// ```
 ///
-/// Here, `def_id` is the `DefId` of the existential type `Baz` and `opaque_node_id` is the
-/// `NodeId` of the reference to `Baz` (i.e., the return type of both `f1` and `f2`).
-/// We return `true` if the reference is within the same module as the existential type
-/// (i.e., `true` for `f1`, `false` for `f2`).
+/// Here, `def_id` is the `DefId` of the defining use of the existential type (e.g., `f1` or `f2`),
+/// and `opaque_hir_id` is the `HirId` of the definition of the existential type `Baz`.
+/// For the above example, this function returns `true` for `f1` and `false` for `f2`.
 pub fn may_define_existential_type(
     tcx: TyCtxt<'_, '_, '_>,
     def_id: DefId,
     opaque_hir_id: hir::HirId,
 ) -> bool {
     let mut hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
-    // Named existential types can be defined by any siblings or
-    // children of siblings.
-    let mod_id = tcx.hir().get_parent_item(opaque_hir_id);
-    // We walk up the node tree until we hit the root or the parent
-    // of the opaque type.
-    while hir_id != mod_id && node_id != ast::CRATE_HIR_ID {
+    trace!(
+        "may_define_existential_type(def={:?}, opaque_node={:?})",
+        tcx.hir().get(hir_id),
+        tcx.hir().get(opaque_hir_id)
+    );
+
+    // Named existential types can be defined by any siblings or children of siblings.
+    let scope_id = tcx.hir().get_defining_scope(opaque_hir_id)
+                            .expect("could not get defining scope");
+    // We walk up the node tree until we hit the root or the scope of the opaque type.
+    while hir_id != scope_id && hir_id != ast::CRATE_hir_ID {
         hir_id = tcx.hir().get_parent_item(hir_id);
     }
-    // Syntactically we are allowed to define the concrete type.
-    hir_id == mod_id
+    // Syntactically, we are allowed to define the concrete type if:
+    hir_id == scope_id
 }

src/librustc/traits/select.rs

@@ -1848,8 +1848,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             .iter()
             .filter_map(|o| o.to_opt_poly_trait_ref());
 
-        // micro-optimization: filter out predicates relating to different
-        // traits.
+        // Micro-optimization: filter out predicates relating to different traits.
         let matching_bounds =
             all_bounds.filter(|p| p.def_id() == stack.obligation.predicate.def_id());
 

src/librustc_interface/util.rs

@@ -716,8 +716,22 @@ impl<'a> ReplaceBodyWithLoop<'a> {
                                     ast::GenericArg::Type(ty) => Some(ty),
                                     _ => None,
                                 });
+                                let any_assoc_ty_bounds = data.constraints.iter().any(|c| {
+                                    if let ast::AssocTyConstraintKind::Bound { .. } = c.kind {
+                                        true
+                                    } else {
+                                        false
+                                    }
+                                });
+                                any_assoc_ty_bounds ||
                                 any_involves_impl_trait(types.into_iter()) ||
-                                any_involves_impl_trait(data.bindings.iter().map(|b| &b.ty))
+                                any_involves_impl_trait(data.constraints.iter().filter_map(|c| {
+                                    if let ast::AssocTyConstraintKind::Equality { ref ty } = c.kind {
+                                        Some(ty)
+                                    } else {
+                                        None
+                                    }
+                                }))
                             },
                             Some(&ast::GenericArgs::Parenthesized(ref data)) => {
                                 any_involves_impl_trait(data.inputs.iter()) ||