Add trait alias support in rustdoc

src/librustdoc/clean/mod.rs

@@ -517,6 +517,7 @@ pub enum ItemEnum {
     StaticItem(Static),
     ConstantItem(Constant),
     TraitItem(Trait),
+    TraitAliasItem(TraitAlias),
     ImplItem(Impl),
     /// A method signature only. Used for required methods in traits (ie,
     /// non-default-methods).
@@ -554,6 +555,7 @@ impl ItemEnum {
             ItemEnum::TyMethodItem(ref i) => &i.generics,
             ItemEnum::MethodItem(ref i) => &i.generics,
             ItemEnum::ForeignFunctionItem(ref f) => &f.generics,
+            ItemEnum::TraitAliasItem(ref ta) => &ta.generics,
             _ => return None,
         })
     }
@@ -603,6 +605,7 @@ impl Clean<Item> for doctree::Module {
         items.extend(self.impls.iter().flat_map(|x| x.clean(cx)));
         items.extend(self.macros.iter().map(|x| x.clean(cx)));
         items.extend(self.proc_macros.iter().map(|x| x.clean(cx)));
+        items.extend(self.trait_aliases.iter().map(|x| x.clean(cx)));
 
         // determine if we should display the inner contents or
         // the outer `mod` item for the source code.
@@ -1885,13 +1888,41 @@ impl Clean<Item> for doctree::Trait {
                 items: self.items.clean(cx),
                 generics: self.generics.clean(cx),
                 bounds: self.bounds.clean(cx),
-                is_spotlight: is_spotlight,
+                is_spotlight,
                 is_auto: self.is_auto.clean(cx),
             }),
         }
     }
 }
 
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
+pub struct TraitAlias {
+    pub generics: Generics,
+    pub bounds: Vec<GenericBound>,
+    pub is_spotlight: bool,
+}
+
+impl Clean<Item> for doctree::TraitAlias {
+    fn clean(&self, cx: &DocContext) -> Item {
+        let attrs = self.attrs.clean(cx);
+        let is_spotlight = attrs.has_doc_flag("spotlight");
+        Item {
+            name: Some(self.name.clean(cx)),
+            attrs,
+            source: self.whence.clean(cx),
+            def_id: cx.tcx.hir().local_def_id(self.id),
+            visibility: self.vis.clean(cx),
+            stability: self.stab.clean(cx),
+            deprecation: self.depr.clean(cx),
+            inner: TraitAliasItem(TraitAlias {
+                generics: self.generics.clean(cx),
+                bounds: self.bounds.clean(cx),
+                is_spotlight,
+            }),
+        }
+    }
+}
+
 impl Clean<bool> for hir::IsAuto {
     fn clean(&self, _: &DocContext) -> bool {
         match *self {
@@ -2223,6 +2254,7 @@ pub enum TypeKind {
     Macro,
     Attr,
     Derive,
+    TraitAlias,
 }
 
 pub trait GetDefId {
@@ -3819,10 +3851,9 @@ pub fn register_def(cx: &DocContext, def: Def) -> DefId {
             MacroKind::Derive => (i, TypeKind::Derive),
             MacroKind::ProcMacroStub => unreachable!(),
         },
+        Def::TraitAlias(i) => (i, TypeKind::TraitAlias),
         Def::SelfTy(Some(def_id), _) => (def_id, TypeKind::Trait),
-        Def::SelfTy(_, Some(impl_def_id)) => {
-            return impl_def_id
-        }
+        Def::SelfTy(_, Some(impl_def_id)) => return impl_def_id,
         _ => return def.def_id()
     };
     if did.is_local() { return did }

src/librustdoc/doctree.rs

@@ -38,6 +38,7 @@ pub struct Module {
     pub foreigns: Vec<hir::ForeignMod>,
     pub macros: Vec<Macro>,
     pub proc_macros: Vec<ProcMacro>,
+    pub trait_aliases: Vec<TraitAlias>,
     pub is_crate: bool,
 }
 
@@ -53,21 +54,22 @@ impl Module {
             where_inner: syntax_pos::DUMMY_SP,
             attrs      : hir::HirVec::new(),
             extern_crates: Vec::new(),
-            imports    : Vec::new(),
-            structs    : Vec::new(),
-            unions     : Vec::new(),
-            enums      : Vec::new(),
-            fns        : Vec::new(),
-            mods       : Vec::new(),
-            typedefs   : Vec::new(),
-            existentials: Vec::new(),
-            statics    : Vec::new(),
-            constants  : Vec::new(),
-            traits     : Vec::new(),
-            impls      : Vec::new(),
-            foreigns   : Vec::new(),
-            macros     : Vec::new(),
-            proc_macros: Vec::new(),
+            imports    :   Vec::new(),
+            structs    :   Vec::new(),
+            unions     :   Vec::new(),
+            enums      :   Vec::new(),
+            fns        :   Vec::new(),
+            mods       :   Vec::new(),
+            typedefs   :   Vec::new(),
+            existentials:  Vec::new(),
+            statics    :   Vec::new(),
+            constants  :   Vec::new(),
+            traits     :   Vec::new(),
+            impls      :   Vec::new(),
+            foreigns   :   Vec::new(),
+            macros     :   Vec::new(),
+            proc_macros:   Vec::new(),
+            trait_aliases: Vec::new(),
             is_crate   : false,
         }
     }
@@ -208,6 +210,18 @@ pub struct Trait {
     pub depr: Option<attr::Deprecation>,
 }
 
+pub struct TraitAlias {
+    pub name: Name,
+    pub generics: hir::Generics,
+    pub bounds: hir::HirVec<hir::GenericBound>,
+    pub attrs: hir::HirVec<ast::Attribute>,
+    pub id: ast::NodeId,
+    pub whence: Span,
+    pub vis: hir::Visibility,
+    pub stab: Option<attr::Stability>,
+    pub depr: Option<attr::Deprecation>,
+}
+
 #[derive(Debug)]
 pub struct Impl {
     pub unsafety: hir::Unsafety,

src/librustdoc/html/item_type.rs

@@ -42,6 +42,7 @@ pub enum ItemType {
     Existential     = 22,
     ProcAttribute   = 23,
     ProcDerive      = 24,
+    TraitAlias      = 25,
 }
 
 
@@ -86,6 +87,7 @@ impl<'a> From<&'a clean::Item> for ItemType {
             clean::AssociatedTypeItem(..)  => ItemType::AssociatedType,
             clean::ForeignTypeItem         => ItemType::ForeignType,
             clean::KeywordItem(..)         => ItemType::Keyword,
+            clean::TraitAliasItem(..)      => ItemType::TraitAlias,
             clean::ProcMacroItem(ref mac)  => match mac.kind {
                 MacroKind::Bang            => ItemType::Macro,
                 MacroKind::Attr            => ItemType::ProcAttribute,
@@ -100,20 +102,21 @@ impl<'a> From<&'a clean::Item> for ItemType {
 impl From<clean::TypeKind> for ItemType {
     fn from(kind: clean::TypeKind) -> ItemType {
         match kind {
-            clean::TypeKind::Struct   => ItemType::Struct,
-            clean::TypeKind::Union    => ItemType::Union,
-            clean::TypeKind::Enum     => ItemType::Enum,
-            clean::TypeKind::Function => ItemType::Function,
-            clean::TypeKind::Trait    => ItemType::Trait,
-            clean::TypeKind::Module   => ItemType::Module,
-            clean::TypeKind::Static   => ItemType::Static,
-            clean::TypeKind::Const    => ItemType::Constant,
-            clean::TypeKind::Variant  => ItemType::Variant,
-            clean::TypeKind::Typedef  => ItemType::Typedef,
-            clean::TypeKind::Foreign  => ItemType::ForeignType,
-            clean::TypeKind::Macro    => ItemType::Macro,
-            clean::TypeKind::Attr     => ItemType::ProcAttribute,
-            clean::TypeKind::Derive   => ItemType::ProcDerive,
+            clean::TypeKind::Struct     => ItemType::Struct,
+            clean::TypeKind::Union      => ItemType::Union,
+            clean::TypeKind::Enum       => ItemType::Enum,
+            clean::TypeKind::Function   => ItemType::Function,
+            clean::TypeKind::Trait      => ItemType::Trait,
+            clean::TypeKind::Module     => ItemType::Module,
+            clean::TypeKind::Static     => ItemType::Static,
+            clean::TypeKind::Const      => ItemType::Constant,
+            clean::TypeKind::Variant    => ItemType::Variant,
+            clean::TypeKind::Typedef    => ItemType::Typedef,
+            clean::TypeKind::Foreign    => ItemType::ForeignType,
+            clean::TypeKind::Macro      => ItemType::Macro,
+            clean::TypeKind::Attr       => ItemType::ProcAttribute,
+            clean::TypeKind::Derive     => ItemType::ProcDerive,
+            clean::TypeKind::TraitAlias => ItemType::TraitAlias,
         }
     }
 }
@@ -146,6 +149,7 @@ impl ItemType {
             ItemType::Existential     => "existential",
             ItemType::ProcAttribute   => "attr",
             ItemType::ProcDerive      => "derive",
+            ItemType::TraitAlias      => "traitalias",
         }
     }
 
@@ -160,6 +164,7 @@ impl ItemType {
             ItemType::Primitive |
             ItemType::AssociatedType |
             ItemType::Existential |
+            ItemType::TraitAlias |
             ItemType::ForeignType => NameSpace::Type,
 
             ItemType::ExternCrate |

src/librustdoc/html/render.rs

@@ -1836,6 +1836,7 @@ struct AllTypes {
     keywords: FxHashSet<ItemEntry>,
     attributes: FxHashSet<ItemEntry>,
     derives: FxHashSet<ItemEntry>,
+    trait_aliases: FxHashSet<ItemEntry>,
 }
 
 impl AllTypes {
@@ -1856,6 +1857,7 @@ impl AllTypes {
             keywords: new_set(100),
             attributes: new_set(100),
             derives: new_set(100),
+            trait_aliases: new_set(100),
         }
     }
 
@@ -1879,6 +1881,7 @@ impl AllTypes {
                 ItemType::Constant => self.constants.insert(ItemEntry::new(new_url, name)),
                 ItemType::ProcAttribute => self.attributes.insert(ItemEntry::new(new_url, name)),
                 ItemType::ProcDerive => self.derives.insert(ItemEntry::new(new_url, name)),
+                ItemType::TraitAlias => self.trait_aliases.insert(ItemEntry::new(new_url, name)),
                 _ => true,
             };
         }
@@ -1922,6 +1925,7 @@ impl fmt::Display for AllTypes {
         print_entries(f, &self.derives, "Derive Macros", "derives")?;
         print_entries(f, &self.functions, "Functions", "functions")?;
         print_entries(f, &self.typedefs, "Typedefs", "typedefs")?;
+        print_entries(f, &self.trait_aliases, "Trait Aliases", "trait-alias")?;
         print_entries(f, &self.existentials, "Existentials", "existentials")?;
         print_entries(f, &self.statics, "Statics", "statics")?;
         print_entries(f, &self.constants, "Constants", "constants")
@@ -2419,6 +2423,7 @@ impl<'a> fmt::Display for Item<'a> {
             clean::ForeignTypeItem => write!(fmt, "Foreign Type ")?,
             clean::KeywordItem(..) => write!(fmt, "Keyword ")?,
             clean::ExistentialItem(..) => write!(fmt, "Existential Type ")?,
+            clean::TraitAliasItem(..) => write!(fmt, "Trait Alias ")?,
             _ => {
                 // We don't generate pages for any other type.
                 unreachable!();
@@ -2457,6 +2462,7 @@ impl<'a> fmt::Display for Item<'a> {
             clean::ForeignTypeItem => item_foreign_type(fmt, self.cx, self.item),
             clean::KeywordItem(ref k) => item_keyword(fmt, self.cx, self.item, k),
             clean::ExistentialItem(ref e, _) => item_existential(fmt, self.cx, self.item, e),
+            clean::TraitAliasItem(ref ta) => item_trait_alias(fmt, self.cx, self.item, ta),
             _ => {
                 // We don't generate pages for any other type.
                 unreachable!();
@@ -3014,23 +3020,17 @@ fn render_impls(cx: &Context, w: &mut fmt::Formatter,
     Ok(())
 }
 
-fn bounds(t_bounds: &[clean::GenericBound]) -> String {
+fn bounds(t_bounds: &[clean::GenericBound], trait_alias: bool) -> String {
     let mut bounds = String::new();
-    let mut bounds_plain = String::new();
     if !t_bounds.is_empty() {
-        if !bounds.is_empty() {
-            bounds.push(' ');
-            bounds_plain.push(' ');
+        if !trait_alias {
+            bounds.push_str(": ");
         }
-        bounds.push_str(": ");
-        bounds_plain.push_str(": ");
         for (i, p) in t_bounds.iter().enumerate() {
             if i > 0 {
                 bounds.push_str(" + ");
-                bounds_plain.push_str(" + ");
             }
             bounds.push_str(&(*p).to_string());
-            bounds_plain.push_str(&format!("{:#}", *p));
         }
     }
     bounds
@@ -3050,7 +3050,7 @@ fn item_trait(
     it: &clean::Item,
     t: &clean::Trait,
 ) -> fmt::Result {
-    let bounds = bounds(&t.bounds);
+    let bounds = bounds(&t.bounds, false);
     let types = t.items.iter().filter(|m| m.is_associated_type()).collect::<Vec<_>>();
     let consts = t.items.iter().filter(|m| m.is_associated_const()).collect::<Vec<_>>();
     let required = t.items.iter().filter(|m| m.is_ty_method()).collect::<Vec<_>>();
@@ -4280,7 +4280,26 @@ fn item_existential(
            it.name.as_ref().unwrap(),
            t.generics,
            where_clause = WhereClause { gens: &t.generics, indent: 0, end_newline: true },
-           bounds = bounds(&t.bounds))?;
+           bounds = bounds(&t.bounds, false))?;
+
+    document(w, cx, it)?;
+
+    // Render any items associated directly to this alias, as otherwise they
+    // won't be visible anywhere in the docs. It would be nice to also show
+    // associated items from the aliased type (see discussion in #32077), but
+    // we need #14072 to make sense of the generics.
+    render_assoc_items(w, cx, it, it.def_id, AssocItemRender::All)
+}
+
+fn item_trait_alias(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
+                    t: &clean::TraitAlias) -> fmt::Result {
+    write!(w, "<pre class='rust trait-alias'>")?;
+    render_attributes(w, it)?;
+    write!(w, "trait {}{}{} = {};</pre>",
+           it.name.as_ref().unwrap(),
+           t.generics,
+           WhereClause { gens: &t.generics, indent: 0, end_newline: true },
+           bounds(&t.bounds, true))?;
 
     document(w, cx, it)?;
 
@@ -4844,6 +4863,7 @@ fn item_ty_to_strs(ty: &ItemType) -> (&'static str, &'static str) {
         ItemType::Existential     => ("existentials", "Existentials"),
         ItemType::ProcAttribute   => ("attributes", "Attribute Macros"),
         ItemType::ProcDerive      => ("derives", "Derive Macros"),
+        ItemType::TraitAlias      => ("trait-alias", "Trait aliases"),
     }
 }
 

src/librustdoc/passes/mod.rs

@@ -224,6 +224,7 @@ impl<'a> fold::DocFolder for Stripper<'a> {
             | clean::ConstantItem(..)
             | clean::UnionItem(..)
             | clean::AssociatedConstItem(..)
+            | clean::TraitAliasItem(..)
             | clean::ForeignTypeItem => {
                 if i.def_id.is_local() {
                     if !self.access_levels.is_exported(i.def_id) {

src/librustdoc/visit_ast.rs

@@ -547,8 +547,19 @@ impl<'a, 'tcx, 'rcx> RustdocVisitor<'a, 'tcx, 'rcx> {
                 };
                 om.traits.push(t);
             },
-            hir::ItemKind::TraitAlias(..) => {
-                unimplemented!("trait objects are not yet implemented")
+            hir::ItemKind::TraitAlias(ref gen, ref b) => {
+                let t = TraitAlias {
+                    name: ident.name,
+                    generics: gen.clone(),
+                    bounds: b.iter().cloned().collect(),
+                    id: item.id,
+                    attrs: item.attrs.clone(),
+                    whence: item.span,
+                    vis: item.vis.clone(),
+                    stab: self.stability(item.id),
+                    depr: self.deprecation(item.id),
+                };
+                om.trait_aliases.push(t);
             },
 
             hir::ItemKind::Impl(unsafety,

src/test/rustdoc/trait_alias.rs

@@ -0,0 +1,21 @@
+#![feature(trait_alias)]
+
+#![crate_name = "foo"]
+
+use std::fmt::Debug;
+
+// @has foo/all.html '//a[@href="traitalias.CopyAlias.html"]' 'CopyAlias'
+// @has foo/all.html '//a[@href="traitalias.Alias2.html"]' 'Alias2'
+// @has foo/all.html '//a[@href="traitalias.Foo.html"]' 'Foo'
+
+// @has foo/index.html '//h2[@id="trait-alias"]' 'Trait aliases'
+// @has foo/index.html '//a[@class="traitalias"]' 'CopyAlias'
+// @has foo/index.html '//a[@class="traitalias"]' 'Alias2'
+// @has foo/index.html '//a[@class="traitalias"]' 'Foo'
+
+// @has foo/traitalias.CopyAlias.html '//section[@id="main"]/pre' 'trait CopyAlias = Copy;'
+pub trait CopyAlias = Copy;
+// @has foo/traitalias.Alias2.html '//section[@id="main"]/pre' 'trait Alias2 = Copy + Debug;'
+pub trait Alias2 = Copy + Debug;
+// @has foo/traitalias.Foo.html '//section[@id="main"]/pre' 'trait Foo<T> = Into<T> + Debug;'
+pub trait Foo<T> = Into<T> + Debug;