Auto merge of #57428 - alexreg:associated_type_bounds, r=nikomatsakis…

…,Centril

Implementation of RFC 2289 (associated_type_bounds)

This PR implements the [`asociated_type_bounds` feature](https://github.com/rust-lang/rfcs/blob/master/text/2289-associated-type-bounds.md).

Associated type bounds are implemented in:
   - function/method arguments and return types
   - structs, enums, unions
   - associated items in traits
   - type aliases
   - type parameter defaults
   - trait objects
   - let bindings

CC @nikomatsakis @Centril

src/libcore/cell.rs

@@ -1351,7 +1351,7 @@ impl<'b> BorrowRefMut<'b> {
         }
     }
 
-    // Clone a `BorrowRefMut`.
+    // Clones a `BorrowRefMut`.
     //
     // This is only valid if each `BorrowRefMut` is used to track a mutable
     // reference to a distinct, nonoverlapping range of the original object.

src/libcore/ops/unsize.rs

@@ -71,7 +71,7 @@ impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}
 
 /// This is used for object safety, to check that a method's receiver type can be dispatched on.
 ///
-/// example impl:
+/// An example implementation of the trait:
 ///
 /// ```
 /// # #![feature(dispatch_from_dyn, unsize)]

src/librustc/hir/intravisit.rs

@@ -674,7 +674,14 @@ pub fn walk_assoc_type_binding<'v, V: Visitor<'v>>(visitor: &mut V,
                                                    type_binding: &'v TypeBinding) {
     visitor.visit_id(type_binding.hir_id);
     visitor.visit_ident(type_binding.ident);
-    visitor.visit_ty(&type_binding.ty);
+    match type_binding.kind {
+        TypeBindingKind::Equality { ref ty } => {
+            visitor.visit_ty(ty);
+        }
+        TypeBindingKind::Constraint { ref bounds } => {
+            walk_list!(visitor, visit_param_bound, bounds);
+        }
+    }
 }
 
 pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat) {
@@ -934,7 +941,6 @@ pub fn walk_impl_item_ref<'v, V: Visitor<'v>>(visitor: &mut V, impl_item_ref: &'
     visitor.visit_defaultness(defaultness);
 }
 
-
 pub fn walk_struct_def<'v, V: Visitor<'v>>(visitor: &mut V, struct_definition: &'v VariantData) {
     if let Some(ctor_hir_id) = struct_definition.ctor_hir_id() {
         visitor.visit_id(ctor_hir_id);

src/librustc/hir/map/collector.rs

@@ -19,7 +19,7 @@ use std::iter::repeat;
 use crate::ich::StableHashingContext;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableHasherResult};
 
-/// A Visitor that walks over the HIR and collects Nodes into a HIR map
+/// A visitor that walks over the HIR and collects `Node`s into a HIR map.
 pub(super) struct NodeCollector<'a, 'hir> {
     /// The crate
     krate: &'hir Crate,
@@ -45,7 +45,7 @@ pub(super) struct NodeCollector<'a, 'hir> {
 
     hcx: StableHashingContext<'a>,
 
-    // We are collecting DepNode::HirBody hashes here so we can compute the
+    // We are collecting `DepNode::HirBody` hashes here so we can compute the
     // crate hash from then later on.
     hir_body_nodes: Vec<(DefPathHash, Fingerprint)>,
 }
@@ -109,7 +109,7 @@ impl<'a, 'hir> NodeCollector<'a, 'hir> {
 
         let mut hir_body_nodes = Vec::new();
 
-        // Allocate DepNodes for the root module
+        // Allocate `DepNode`s for the root module.
         let (root_mod_sig_dep_index, root_mod_full_dep_index) = {
             let Crate {
                 ref module,

src/librustc/hir/map/definitions.rs

@@ -239,7 +239,7 @@ impl DefPath {
                        "{}[{}]",
                        component.data.as_interned_str(),
                        component.disambiguator)
-                    .unwrap();
+                       .unwrap();
             }
         }
 
@@ -263,7 +263,7 @@ impl DefPath {
                        "{}[{}]",
                        component.data.as_interned_str(),
                        component.disambiguator)
-                    .unwrap();
+                       .unwrap();
             }
         }
         s
@@ -276,7 +276,7 @@ pub enum DefPathData {
     // they are treated specially by the `def_path` function.
     /// The crate root (marker)
     CrateRoot,
-    // Catch-all for random DefId things like DUMMY_NODE_ID
+    // Catch-all for random DefId things like `DUMMY_NODE_ID`
     Misc,
     // Different kinds of items and item-like things:
     /// An impl
@@ -298,9 +298,9 @@ pub enum DefPathData {
     AnonConst,
     /// An `impl Trait` type node
     ImplTrait,
-    /// 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.
+    /// 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),
 }
 
@@ -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]
@@ -442,7 +447,7 @@ impl Definitions {
         root_index
     }
 
-    /// Add a definition with a parent definition.
+    /// Adds a definition with a parent definition.
     pub fn create_def_with_parent(&mut self,
                                   parent: DefIndex,
                                   node_id: ast::NodeId,
@@ -559,7 +564,7 @@ impl DefPathData {
             GlobalMetaData(name) => {
                 return name
             }
-            // note that this does not show up in user printouts
+            // Note that this does not show up in user print-outs.
             CrateRoot => sym::double_braced_crate,
             Impl => sym::double_braced_impl,
             Misc => sym::double_braced_misc,