Addressed points raised in review.

src/librustc/hir/lowering.rs

@@ -1382,12 +1382,12 @@ impl<'a> LoweringContext<'a> {
                 if existential_desugaring {
                     // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`.
 
-                    let impl_ty_node_id = self.sess.next_node_id();
+                    let impl_trait_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,
+                        impl_trait_node_id,
+                        DefPathData::ImplTrait,
                         DefIndexAddressSpace::High,
                         Mark::root(),
                         DUMMY_SP
@@ -1397,7 +1397,7 @@ impl<'a> LoweringContext<'a> {
                         this.lower_ty(
                             &Ty {
                                 id: this.sess.next_node_id(),
-                                node: TyKind::ImplTrait(impl_ty_node_id, bounds.clone()),
+                                node: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
                                 span: DUMMY_SP,
                             },
                             itctx,
@@ -1410,9 +1410,8 @@ impl<'a> LoweringContext<'a> {
                     let bounds = self.lower_param_bounds(bounds, itctx);
 
                     let id = self.sess.next_node_id();
-                    let LoweredNodeId { node_id: _, hir_id } = self.lower_node_id(id);
                     P(hir::Ty {
-                        hir_id,
+                        hir_id: self.lower_node_id(id),
                         node: hir::TyKind::AssocTyExistential(bounds),
                         span: DUMMY_SP,
                     })
@@ -1423,7 +1422,7 @@ impl<'a> LoweringContext<'a> {
         hir::TypeBinding {
             hir_id: self.lower_node_id(c.id),
             ident: c.ident,
-            ty
+            ty,
             span: c.span,
         }
     }
@@ -1647,7 +1646,7 @@ impl<'a> LoweringContext<'a> {
         // Not tracking it makes lints in rustc and clippy very fragile, as
         // frequently opened issues show.
         let exist_ty_span = self.mark_span_with_reason(
-            CompilerDesugaringKind::ExistentialReturnType,
+            CompilerDesugaringKind::ExistentialType,
             span,
             None,
         );

src/librustc/hir/map/definitions.rs

@@ -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),
 }
 

src/librustc/hir/map/mod.rs

@@ -842,7 +842,7 @@ impl<'hir> Map<'hir> {
     }
 
     /// Returns the nearest enclosing scope. A scope is roughly an item or block.
-    pub fn get_enclosing_scope(&self, id: HirId) -> Option<HirId> {
+    pub fn get_enclosing_scope(&self, hir_id: HirId) -> Option<HirId> {
         self.walk_parent_nodes(hir_id, |node| match *node {
             Node::Item(i) => {
                 match i.node {
@@ -880,14 +880,14 @@ impl<'hir> Map<'hir> {
     }
 
     /// Returns the defining scope for an existential type definition.
-    pub fn get_defining_scope(&self, id: NodeId) -> Option<NodeId> {
+    pub fn get_defining_scope(&self, id: HirId) -> Option<HirId> {
         let mut scope = id;
         loop {
             scope = self.get_enclosing_scope(scope)?;
-            if scope == CRATE_NODE_ID {
-                return Some(CRATE_NODE_ID);
+            if scope == CRATE_HIR_ID {
+                return Some(CRATE_HIR_ID);
             }
-            match self.get(scope) {
+            match self.get_by_hir_id(scope) {
                 Node::Item(i) => {
                     match i.node {
                         ItemKind::Existential(ExistTy { impl_trait_fn: None, .. }) => {}

src/librustc/hir/mod.rs

@@ -1780,7 +1780,7 @@ pub struct ImplItem {
     pub span: Span,
 }
 
-/// Represents different contents within `impl`s
+/// Represents different contents within `impl`s.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable)]
 pub enum ImplItemKind {
     /// An associated constant of the given type, set to the constant result
@@ -1794,7 +1794,7 @@ pub enum ImplItemKind {
     Existential(GenericBounds),
 }
 
-// Bind a type to an associated type: `A=Foo`.
+// Bind a type to an associated type (`A = Foo`).
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable)]
 pub struct TypeBinding {
     pub hir_id: HirId,

src/librustc/ich/impls_syntax.rs

@@ -408,7 +408,7 @@ impl_stable_hash_for!(enum ::syntax_pos::hygiene::CompilerDesugaringKind {
     Async,
     Await,
     QuestionMark,
-    ExistentialReturnType,
+    ExistentialType,
     ForLoop,
     TryBlock
 });

src/librustc/infer/opaque_types/mod.rs

@@ -953,14 +953,13 @@ pub fn may_define_existential_type(
     );
 
     // Named existential types can be defined by any siblings or children of siblings.
-    let scope_node_id = tcx.hir()
-        .get_defining_scope(tcx.hir().hir_to_node_id(opaque_hir_id))
+    let scope = tcx.hir()
+        .get_defining_scope(opaque_hir_id)
         .expect("could not get defining scope");
-    let scope_id = tcx.hir().node_to_hir_id(scope_node_id);
     // 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 != hir::CRATE_HIR_ID {
+    while hir_id != scope && hir_id != hir::CRATE_HIR_ID {
         hir_id = tcx.hir().get_parent_item(hir_id);
     }
     // Syntactically, we are allowed to define the concrete type if:
-    hir_id == scope_id
+    hir_id == scope
 }

src/librustc_interface/util.rs

@@ -716,23 +716,14 @@ 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.constraints.iter().filter_map(|c| {
-                                    if let ast::AssocTyConstraintKind::Equality { ref ty }
-                                            = c.kind {
-                                        Some(ty)
-                                    } else {
-                                        None
+                                data.constraints.iter().any(|c| {
+                                    match c.kind {
+                                        ast::AssocTyConstraintKind::Bound { .. } => true,
+                                        ast::AssocTyConstraintKind::Equality { ref ty } =>
+                                            involves_impl_trait(ty),
                                     }
-                                }))
+                                })
                             },
                             Some(&ast::GenericArgs::Parenthesized(ref data)) => {
                                 any_involves_impl_trait(data.inputs.iter()) ||

src/librustc_resolve/lib.rs

@@ -2533,7 +2533,7 @@ impl<'a> Resolver<'a> {
                 self.with_current_self_item(item, |this| {
                     this.with_generic_param_rib(HasGenericParams(generics, ItemRibKind), |this| {
                         let item_def_id = this.definitions.local_def_id(item.id);
-                        this.with_self_rib(Def::SelfTy(Some(item_def_id), None), |this| {
+                        this.with_self_rib(Res::SelfTy(Some(item_def_id), None), |this| {
                             visit::walk_item(this, item)
                         })
                     })

src/librustc_typeck/astconv.rs

@@ -764,7 +764,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
         let mut dup_bindings = FxHashMap::default();
         for binding in &assoc_bindings {
             // Specify type to assert that error was already reported in `Err` case.
-            let _ =
+            let _: Result<_, ErrorReported> =
                 self.add_predicates_for_ast_type_binding(
                     trait_ref.hir_ref_id,
                     poly_trait_ref,
@@ -933,8 +933,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
     }
 
     /// Translates the AST's notion of ty param bounds (which are an enum consisting of a newtyped
-    /// `Ty` or a region) to ty's notion of ty param bounds, which can either be user-defined traits
-    /// or the built-in trait `Send`.
+    /// `Ty` or a region) to ty's notion of ty param bounds (which can either be user-defined traits
+    /// or the built-in trait `Sized`).
     pub fn compute_bounds(&self,
         param_ty: Ty<'tcx>,
         ast_bounds: &[hir::GenericBound],

src/librustc_typeck/collect.rs

@@ -1650,24 +1650,23 @@ fn find_existential_constraints<'a, 'tcx>(
         }
     }
 
-    let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
-    let scope_node_id = tcx.hir()
-        .get_defining_scope(node_id)
+    let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
+    let scope = tcx.hir()
+        .get_defining_scope(hir_id)
         .expect("could not get defining scope");
-    let scope_id = tcx.hir().node_to_hir_id(scope_node_id);
     let mut locator = ConstraintLocator {
         def_id,
         tcx,
         found: None,
     };
 
-    debug!("find_existential_constraints: scope_id={:?}", scope_id);
+    debug!("find_existential_constraints: scope={:?}", scope);
 
-    if scope_id == hir::CRATE_HIR_ID {
+    if scope == hir::CRATE_HIR_ID {
         intravisit::walk_crate(&mut locator, tcx.hir().krate());
     } else {
-        debug!("find_existential_constraints: scope={:?}", tcx.hir().get_by_hir_id(scope_id));
-        match tcx.hir().get_by_hir_id(scope_id) {
+        debug!("find_existential_constraints: scope={:?}", tcx.hir().get_by_hir_id(scope));
+        match tcx.hir().get_by_hir_id(scope) {
             Node::Item(ref it) => intravisit::walk_item(&mut locator, it),
             Node::ImplItem(ref it) => intravisit::walk_impl_item(&mut locator, it),
             Node::TraitItem(ref it) => intravisit::walk_trait_item(&mut locator, it),

src/librustdoc/clean/mod.rs

@@ -2445,7 +2445,7 @@ pub struct PolyTrait {
 
 /// A representation of a type suitable for hyperlinking purposes. Ideally, one can get the original
 /// type out of the AST/`TyCtxt` given one of these, if more information is needed. Most
-/// importanntly, it does not preserve mutability or boxes.
+/// importantly, it does not preserve mutability or boxes.
 #[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Debug, Hash)]
 pub enum Type {
     /// Structs/enums/traits (most that would be an `hir::TyKind::Path`).

src/libsyntax_pos/hygiene.rs

@@ -714,7 +714,7 @@ pub enum CompilerDesugaringKind {
     /// Desugaring of an `impl Trait` in return type position
     /// to an `existential type Foo: Trait;` and replacing the
     /// `impl Trait` with `Foo`.
-    ExistentialReturnType,
+    ExistentialType,
     Async,
     Await,
     ForLoop,
@@ -728,7 +728,7 @@ impl CompilerDesugaringKind {
             CompilerDesugaringKind::Await => "await",
             CompilerDesugaringKind::QuestionMark => "?",
             CompilerDesugaringKind::TryBlock => "try block",
-            CompilerDesugaringKind::ExistentialReturnType => "existential type",
+            CompilerDesugaringKind::ExistentialType => "existential type",
             CompilerDesugaringKind::ForLoop => "for loop",
         })
     }

src/test/ui/associated-type-bounds/nested-lifetime-bounds.stderr

@@ -6,4 +6,3 @@ LL |     for<'a> <_2 as Iterator>::Item: for<'b> Lam<&'a &'b u8, App = _0>,
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0316`.

src/test/ui/associated-types/associated-types-path-2.stderr

@@ -49,7 +49,7 @@ error[E0308]: mismatched types
    |
 LL |     let _: i32 = f2(2i32);
    |                  ^^^^^^^^ expected i32, found u32
-help: you can convert an `u32` to `i32` and panic if the converted value wouldn't fit
+help: you can convert an `u32` to `i32` or panic if it the converted value wouldn't fit
    |
 LL |     let _: i32 = f2(2i32).try_into().unwrap();
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^