rustdoc: Skip types in impls in search index

For a trait *implementation* there are typedefs which are the types for
that particular trait and implementor. Skip these in the search index.

There were lots of dud items in the search index due to this (search for
Item, Iterator's associated type).

Add a boolean to clean::TypedefItem so that it tracks whether the it is
a type alias on its own, or if it's a `type` item in a trait impl.

Fixes #22442

src/librustdoc/clean/inline.rs

@@ -216,7 +216,7 @@ fn build_type(cx: &DocContext, tcx: &ty::ctxt, did: ast::DefId) -> clean::ItemEn
     clean::TypedefItem(clean::Typedef {
         type_: t.ty.clean(cx),
         generics: (&t.generics, &predicates, subst::TypeSpace).clean(cx),
-    })
+    }, false)
 }
 
 pub fn build_impls(cx: &DocContext, tcx: &ty::ctxt,
@@ -368,7 +368,7 @@ pub fn build_impl(cx: &DocContext,
                                subst::ParamSpace::TypeSpace).clean(cx);
                 Some(clean::Item {
                     name: Some(assoc_ty.name.clean(cx)),
-                    inner: clean::TypedefItem(typedef),
+                    inner: clean::TypedefItem(typedef, true),
                     source: clean::Span::empty(),
                     attrs: vec![],
                     visibility: None,

src/librustdoc/clean/mod.rs

@@ -343,7 +343,7 @@ pub enum ItemEnum {
     EnumItem(Enum),
     FunctionItem(Function),
     ModuleItem(Module),
-    TypedefItem(Typedef),
+    TypedefItem(Typedef, bool /* is associated type */),
     StaticItem(Static),
     ConstantItem(Constant),
     TraitItem(Trait),
@@ -1282,7 +1282,7 @@ impl Clean<Item> for ast::ImplItem {
                     type_params: Vec::new(),
                     where_predicates: Vec::new()
                 },
-            }),
+            }, true),
             ast::MacImplItem(_) => {
                 MacroItem(Macro {
                     source: self.span.to_src(cx),
@@ -2078,7 +2078,7 @@ impl Clean<Item> for doctree::Typedef {
             inner: TypedefItem(Typedef {
                 type_: self.ty.clean(cx),
                 generics: self.gen.clean(cx),
-            }),
+            }, false),
         }
     }
 }
@@ -2248,7 +2248,7 @@ fn build_deref_target_impls(cx: &DocContext,
 
     for item in items {
         let target = match item.inner {
-            TypedefItem(ref t) => &t.type_,
+            TypedefItem(ref t, true) => &t.type_,
             _ => continue,
         };
         let primitive = match *target {

src/librustdoc/html/render.rs

@@ -870,7 +870,7 @@ impl DocFolder for Cache {
             clean::StructItem(ref s)          => self.generics(&s.generics),
             clean::EnumItem(ref e)            => self.generics(&e.generics),
             clean::FunctionItem(ref f)        => self.generics(&f.generics),
-            clean::TypedefItem(ref t)         => self.generics(&t.generics),
+            clean::TypedefItem(ref t, _)      => self.generics(&t.generics),
             clean::TraitItem(ref t)           => self.generics(&t.generics),
             clean::ImplItem(ref i)            => self.generics(&i.generics),
             clean::TyMethodItem(ref i)        => self.generics(&i.generics),
@@ -936,6 +936,10 @@ impl DocFolder for Cache {
                         ((Some(*last), path), true)
                     }
                 }
+                clean::TypedefItem(_, true) => {
+                    // skip associated types in impls
+                    ((None, None), false)
+                }
                 _ => ((None, Some(&*self.stack)), false)
             };
             let hidden_field = match item.inner {
@@ -1497,7 +1501,7 @@ impl<'a> fmt::Display for Item<'a> {
             clean::TraitItem(ref t) => item_trait(fmt, self.cx, self.item, t),
             clean::StructItem(ref s) => item_struct(fmt, self.item, s),
             clean::EnumItem(ref e) => item_enum(fmt, self.item, e),
-            clean::TypedefItem(ref t) => item_typedef(fmt, self.item, t),
+            clean::TypedefItem(ref t, _) => item_typedef(fmt, self.item, t),
             clean::MacroItem(ref m) => item_macro(fmt, self.item, m),
             clean::PrimitiveItem(ref p) => item_primitive(fmt, self.item, p),
             clean::StaticItem(ref i) | clean::ForeignStaticItem(ref i) =>
@@ -2303,10 +2307,10 @@ fn render_deref_methods(w: &mut fmt::Formatter, impl_: &Impl) -> fmt::Result {
     let deref_type = impl_.impl_.trait_.as_ref().unwrap();
     let target = impl_.impl_.items.iter().filter_map(|item| {
         match item.inner {
-            clean::TypedefItem(ref t) => Some(&t.type_),
+            clean::TypedefItem(ref t, true) => Some(&t.type_),
             _ => None,
         }
-    }).next().unwrap();
+    }).next().expect("Expected associated type binding");
     let what = AssocItemRender::DerefFor { trait_: deref_type, type_: target };
     match *target {
         clean::ResolvedPath { did, .. } => render_assoc_items(w, did, what),
@@ -2350,7 +2354,7 @@ fn render_impl(w: &mut fmt::Formatter, i: &Impl, link: AssocItemLink,
                 try!(render_assoc_item(w, item, link));
                 try!(write!(w, "</code></h4>\n"));
             }
-            clean::TypedefItem(ref tydef) => {
+            clean::TypedefItem(ref tydef, _) => {
                 let name = item.name.as_ref().unwrap();
                 try!(write!(w, "<h4 id='assoc_type.{}' class='{}'><code>",
                             *name,

src/test/rustdoc/search-index.rs

@@ -10,6 +10,8 @@
 
 #![crate_name = "rustdoc_test"]
 
+use std::ops::Deref;
+
 // @has search-index.js Foo
 pub use private::Foo;
 
@@ -24,3 +26,11 @@ mod private {
         fn trait_method(&self) {} // @!has - priv_method
     }
 }
+
+pub struct Bar;
+
+impl Deref for Bar {
+    // @!has search-index.js Target
+    type Target = Bar;
+    fn deref(&self) -> &Bar { self }
+}