auto merge of #16377 : pcwalton/rust/associated-items, r=nikomatsakis

This is waiting on an RFC, but this basic functionality should be
straightforward. The implementation essentially desugars during type
collection and AST type conversion time into the parameter scheme we
have now.

r? @nikomatsakis

src/doc/rust.md

@@ -2557,6 +2557,8 @@ The currently implemented features of the reference compiler are:
 
 * `tuple_indexing` - Allows use of tuple indexing (expressions like `expr.0`)
 
+* `associated_types` - Allows type aliases in traits. Experimental.
+
 If a feature is promoted to a language feature, then all existing programs will
 start to receive compilation warnings about #[feature] directives which enabled
 the new feature (because the directive is no longer necessary). However, if

src/librustc/lint/builtin.rs

@@ -844,6 +844,17 @@ fn method_context(cx: &Context, m: &ast::Method) -> MethodContext {
                         }
                     }
                 }
+                ty::TypeTraitItem(typedef) => {
+                    match typedef.container {
+                        ty::TraitContainer(..) => TraitDefaultImpl,
+                        ty::ImplContainer(cid) => {
+                            match ty::impl_trait_ref(cx.tcx, cid) {
+                                Some(..) => TraitImpl,
+                                None => PlainImpl
+                            }
+                        }
+                    }
+                }
             }
         }
     }
@@ -1511,13 +1522,9 @@ impl LintPass for Stability {
                                 method_num: index,
                                 ..
                             }) => {
-                                match ty::trait_item(cx.tcx,
-                                                     trait_ref.def_id,
-                                                     index) {
-                                    ty::MethodTraitItem(method) => {
-                                        method.def_id
-                                    }
-                                }
+                                ty::trait_item(cx.tcx,
+                                               trait_ref.def_id,
+                                               index).def_id()
                             }
                         }
                     }

src/librustc/lint/context.rs

@@ -25,6 +25,7 @@
 //! for all lint attributes.
 
 use middle::privacy::ExportedItems;
+use middle::subst;
 use middle::ty;
 use middle::typeck::astconv::AstConv;
 use middle::typeck::infer;
@@ -491,6 +492,26 @@ impl<'a, 'tcx> AstConv<'tcx> for Context<'a, 'tcx>{
     fn ty_infer(&self, _span: Span) -> ty::t {
         infer::new_infer_ctxt(self.tcx).next_ty_var()
     }
+
+    fn associated_types_of_trait_are_valid(&self, _: ty::t, _: ast::DefId)
+                                           -> bool {
+        // FIXME(pcwalton): This is wrong.
+        true
+    }
+
+    fn associated_type_binding(&self,
+                               _: Span,
+                               _: Option<ty::t>,
+                               trait_id: ast::DefId,
+                               associated_type_id: ast::DefId)
+                               -> ty::t {
+        // FIXME(pcwalton): This is wrong.
+        let trait_def = self.get_trait_def(trait_id);
+        let index = ty::associated_type_parameter_index(self.tcx,
+                                                        &*trait_def,
+                                                        associated_type_id);
+        ty::mk_param(self.tcx, subst::TypeSpace, index, associated_type_id)
+    }
 }
 
 impl<'a, 'tcx, 'v> Visitor<'v> for Context<'a, 'tcx> {

src/librustc/metadata/csearch.rs

@@ -349,3 +349,9 @@ pub fn get_stability(cstore: &cstore::CStore,
     let cdata = cstore.get_crate_data(def.krate);
     decoder::get_stability(&*cdata, def.node)
 }
+
+pub fn is_associated_type(cstore: &cstore::CStore, def: ast::DefId) -> bool {
+    let cdata = cstore.get_crate_data(def.krate);
+    decoder::is_associated_type(&*cdata, def.node)
+}
+

src/librustc/metadata/decoder.rs

@@ -23,7 +23,7 @@ use metadata::tydecode::{parse_ty_data, parse_region_data, parse_def_id,
                          parse_bare_fn_ty_data, parse_trait_ref_data};
 use middle::def;
 use middle::lang_items;
-use middle::resolve::TraitItemKind;
+use middle::resolve::{TraitItemKind, TypeTraitItemKind};
 use middle::subst;
 use middle::ty::{ImplContainer, TraitContainer};
 use middle::ty;
@@ -167,6 +167,8 @@ fn item_visibility(item: rbml::Doc) -> ast::Visibility {
 }
 
 fn item_sort(item: rbml::Doc) -> char {
+    // NB(pcwalton): The default of 'r' here is relied upon in
+    // `is_associated_type` below.
     let mut ret = 'r';
     reader::tagged_docs(item, tag_item_trait_item_sort, |doc| {
         ret = doc.as_str_slice().as_bytes()[0] as char;
@@ -714,6 +716,7 @@ pub fn get_impl_items(cdata: Cmd, impl_id: ast::NodeId)
         let def_id = item_def_id(doc, cdata);
         match item_sort(doc) {
             'r' | 'p' => impl_items.push(ty::MethodTraitItemId(def_id)),
+            't' => impl_items.push(ty::TypeTraitItemId(def_id)),
             _ => fail!("unknown impl item sort"),
         }
         true
@@ -733,6 +736,7 @@ pub fn get_trait_item_name_and_kind(intr: Rc<IdentInterner>,
             let explicit_self = get_explicit_self(doc);
             (name, TraitItemKind::from_explicit_self_category(explicit_self))
         }
+        't' => (name, TypeTraitItemKind),
         c => {
             fail!("get_trait_item_name_and_kind(): unknown trait item kind \
                    in metadata: `{}`", c)
@@ -758,13 +762,13 @@ pub fn get_impl_or_trait_item(intr: Rc<IdentInterner>,
     };
 
     let name = item_name(&*intr, method_doc);
+    let vis = item_visibility(method_doc);
 
     match item_sort(method_doc) {
         'r' | 'p' => {
             let generics = doc_generics(method_doc, tcx, cdata,
                                         tag_method_ty_generics);
             let fty = doc_method_fty(method_doc, tcx, cdata);
-            let vis = item_visibility(method_doc);
             let explicit_self = get_explicit_self(method_doc);
             let provided_source = get_provided_source(method_doc, cdata);
 
@@ -777,6 +781,14 @@ pub fn get_impl_or_trait_item(intr: Rc<IdentInterner>,
                                                         container,
                                                         provided_source)))
         }
+        't' => {
+            ty::TypeTraitItem(Rc::new(ty::AssociatedType {
+                ident: name,
+                vis: vis,
+                def_id: def_id,
+                container: container,
+            }))
+        }
         _ => fail!("unknown impl/trait item sort"),
     }
 }
@@ -790,6 +802,7 @@ pub fn get_trait_item_def_ids(cdata: Cmd, id: ast::NodeId)
         let def_id = item_def_id(mth, cdata);
         match item_sort(mth) {
             'r' | 'p' => result.push(ty::MethodTraitItemId(def_id)),
+            't' => result.push(ty::TypeTraitItemId(def_id)),
             _ => fail!("unknown trait item sort"),
         }
         true
@@ -827,6 +840,7 @@ pub fn get_provided_trait_methods(intr: Rc<IdentInterner>,
                 ty::MethodTraitItem(ref method) => {
                     result.push((*method).clone())
                 }
+                ty::TypeTraitItem(_) => {}
             }
         }
         true
@@ -1394,3 +1408,12 @@ fn doc_generics(base_doc: rbml::Doc,
 
     ty::Generics { types: types, regions: regions }
 }
+
+pub fn is_associated_type(cdata: Cmd, id: ast::NodeId) -> bool {
+    let items = reader::get_doc(rbml::Doc::new(cdata.data()), tag_items);
+    match maybe_find_item(id, items) {
+        None => false,
+        Some(item) => item_sort(item) == 't',
+    }
+}
+