look for default trait candidates

src/librustc/metadata/csearch.rs

@@ -410,3 +410,7 @@ pub fn is_associated_type(cstore: &cstore::CStore, def: ast::DefId) -> bool {
     decoder::is_associated_type(&*cdata, def.node)
 }
 
+pub fn is_default_trait(cstore: &cstore::CStore, def: ast::DefId) -> bool {
+    let cdata = cstore.get_crate_data(def.krate);
+    decoder::is_default_trait(&*cdata, def.node)
+}

src/librustc/metadata/decoder.rs

@@ -1563,3 +1563,12 @@ pub fn is_associated_type(cdata: Cmd, id: ast::NodeId) -> bool {
         Some(item) => item_sort(item) == 't',
     }
 }
+
+
+pub fn is_default_trait<'tcx>(cdata: Cmd, id: ast::NodeId) -> bool {
+    let item_doc = lookup_item(id, cdata.data());
+    match item_family(item_doc) {
+        Family::DefTrait => true,
+        _ => false
+    }
+}

src/librustc/middle/traits/mod.rs

@@ -221,6 +221,9 @@ pub enum Vtable<'tcx, N> {
     /// Vtable identifying a particular impl.
     VtableImpl(VtableImplData<'tcx, N>),
 
+    /// Vtable for default trait implementations
+    VtableDefaultTrait(ast::DefId),
+
     /// Successful resolution to an obligation provided by the caller
     /// for some type parameter. The `Vec<N>` represents the
     /// obligations incurred from normalizing the where-clause (if
@@ -513,17 +516,18 @@ impl<'tcx, N> Vtable<'tcx, N> {
     pub fn iter_nested(&self) -> Iter<N> {
         match *self {
             VtableImpl(ref i) => i.iter_nested(),
-            VtableFnPointer(..) => (&[]).iter(),
-            VtableClosure(..) => (&[]).iter(),
             VtableParam(ref n) => n.iter(),
-            VtableObject(_) => (&[]).iter(),
             VtableBuiltin(ref i) => i.iter_nested(),
+            VtableObject(_) |
+            VtableDefaultTrait(..) | VtableFnPointer(..) |
+            VtableClosure(..) => (&[]).iter(),
         }
     }
 
     pub fn map_nested<M, F>(&self, op: F) -> Vtable<'tcx, M> where F: FnMut(&N) -> M {
         match *self {
             VtableImpl(ref i) => VtableImpl(i.map_nested(op)),
+            VtableDefaultTrait(t) => VtableDefaultTrait(t),
             VtableFnPointer(ref sig) => VtableFnPointer((*sig).clone()),
             VtableClosure(d, ref s) => VtableClosure(d, s.clone()),
             VtableParam(ref n) => VtableParam(n.iter().map(op).collect()),
@@ -539,6 +543,7 @@ impl<'tcx, N> Vtable<'tcx, N> {
             VtableImpl(i) => VtableImpl(i.map_move_nested(op)),
             VtableFnPointer(sig) => VtableFnPointer(sig),
             VtableClosure(d, s) => VtableClosure(d, s),
+            VtableDefaultTrait(t) => VtableDefaultTrait(t),
             VtableParam(n) => VtableParam(n.into_iter().map(op).collect()),
             VtableObject(p) => VtableObject(p),
             VtableBuiltin(no) => VtableBuiltin(no.map_move_nested(op)),

src/librustc/middle/traits/project.rs

@@ -709,6 +709,7 @@ fn assemble_candidates_from_impls<'cx,'tcx>(
             // projection. And the projection where clause is handled
             // in `assemble_candidates_from_param_env`.
         }
+        super::VtableDefaultTrait(..) |
         super::VtableBuiltin(..) => {
             // These traits have no associated types.
             selcx.tcx().sess.span_bug(

src/librustc/middle/traits/select.rs

@@ -26,7 +26,7 @@ use super::{SelectionError, Unimplemented, Overflow, OutputTypeParameterMismatch
 use super::{Selection};
 use super::{SelectionResult};
 use super::{VtableBuiltin, VtableImpl, VtableParam, VtableClosure,
-            VtableFnPointer, VtableObject};
+            VtableFnPointer, VtableObject, VtableDefaultTrait};
 use super::{VtableImplData, VtableObjectData, VtableBuiltinData};
 use super::object_safety;
 use super::{util};
@@ -136,6 +136,7 @@ enum SelectionCandidate<'tcx> {
     BuiltinCandidate(ty::BuiltinBound),
     ParamCandidate(ty::PolyTraitRef<'tcx>),
     ImplCandidate(ast::DefId),
+    DefaultTraitCandidate(ast::DefId),
 
     /// This is a trait matching with a projected type as `Self`, and
     /// we found an applicable bound in the trait definition.
@@ -1130,7 +1131,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let self_ty = self.infcx.shallow_resolve(obligation.self_ty());
         debug!("assemble_candidates_from_impls(self_ty={})", self_ty.repr(self.tcx()));
 
-        let all_impls = self.all_impls(obligation.predicate.def_id());
+        let def_id = obligation.predicate.def_id();
+        let all_impls = self.all_impls(def_id);
         for &impl_def_id in &all_impls {
             self.infcx.probe(|snapshot| {
                 let (skol_obligation_trait_pred, skol_map) =
@@ -1144,6 +1146,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
             });
         }
+
+        if self.tcx().default_trait_impls.borrow().contains(&def_id) {
+            candidates.vec.push(DefaultTraitCandidate(def_id.clone()))
+        }
+
         Ok(())
     }
 
@@ -1646,6 +1653,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 Ok(VtableParam(obligations))
             }
 
+            DefaultTraitCandidate(trait_def_id) => {
+                Ok(VtableDefaultTrait(trait_def_id))
+            }
+
             ImplCandidate(impl_def_id) => {
                 let vtable_impl =
                     try!(self.confirm_impl_candidate(obligation, impl_def_id));
@@ -2308,6 +2319,7 @@ impl<'tcx> Repr<'tcx> for SelectionCandidate<'tcx> {
             BuiltinCandidate(b) => format!("BuiltinCandidate({:?})", b),
             ParamCandidate(ref a) => format!("ParamCandidate({})", a.repr(tcx)),
             ImplCandidate(a) => format!("ImplCandidate({})", a.repr(tcx)),
+            DefaultTraitCandidate(t) => format!("DefaultTraitCandidate({:?})", t),
             ProjectionCandidate => format!("ProjectionCandidate"),
             FnPointerCandidate => format!("FnPointerCandidate"),
             ObjectCandidate => {

src/librustc/middle/traits/util.rs

@@ -444,6 +444,9 @@ impl<'tcx, N:Repr<'tcx>> Repr<'tcx> for super::Vtable<'tcx, N> {
             super::VtableImpl(ref v) =>
                 v.repr(tcx),
 
+            super::VtableDefaultTrait(ref t) =>
+                format!("VtableDefaultTrait({:?})", t),
+
             super::VtableClosure(ref d, ref s) =>
                 format!("VtableClosure({},{})",
                         d.repr(tcx),

src/librustc/middle/ty.rs

@@ -757,6 +757,9 @@ pub struct ctxt<'tcx> {
     /// Maps a trait onto a list of impls of that trait.
     pub trait_impls: RefCell<DefIdMap<Rc<RefCell<Vec<ast::DefId>>>>>,
 
+    /// Maps a trait onto a list of *default* trait implementations
+    pub default_trait_impls: RefCell<DefIdSet>,
+
     /// Maps a DefId of a type to a list of its inherent impls.
     /// Contains implementations of methods that are inherent to a type.
     /// Methods in these implementations don't need to be exported.
@@ -2493,6 +2496,7 @@ pub fn mk_ctxt<'tcx>(s: Session,
         destructor_for_type: RefCell::new(DefIdMap()),
         destructors: RefCell::new(DefIdSet()),
         trait_impls: RefCell::new(DefIdMap()),
+        default_trait_impls: RefCell::new(DefIdSet()),
         inherent_impls: RefCell::new(DefIdMap()),
         impl_items: RefCell::new(DefIdMap()),
         used_unsafe: RefCell::new(NodeSet()),
@@ -5992,6 +5996,18 @@ pub fn item_variances(tcx: &ctxt, item_id: ast::DefId) -> Rc<ItemVariances> {
         || Rc::new(csearch::get_item_variances(&tcx.sess.cstore, item_id)))
 }
 
+/// Records a trait-to-implementation mapping.
+pub fn record_default_trait_implementation(tcx: &ctxt, trait_def_id: DefId) {
+
+    //assert!(did.krate != ast::LOCAL_CRATE);
+    if tcx.default_trait_impls.borrow().contains(&trait_def_id) {
+        return;
+    }
+
+    tcx.default_trait_impls.borrow_mut().insert(trait_def_id);
+}
+
+
 /// Records a trait-to-implementation mapping.
 pub fn record_trait_implementation(tcx: &ctxt,
                                    trait_def_id: DefId,
@@ -6074,11 +6090,21 @@ pub fn populate_implementations_for_trait_if_necessary(
     }
 
     csearch::each_implementation_for_trait(&tcx.sess.cstore, trait_id,
-            |implementation_def_id| {
+            |implementation_def_id|{
         let impl_items = csearch::get_impl_items(&tcx.sess.cstore, implementation_def_id);
 
-        // Record the trait->implementation mapping.
-        record_trait_implementation(tcx, trait_id, implementation_def_id);
+        if csearch::is_default_trait(&tcx.sess.cstore, implementation_def_id) {
+            record_default_trait_implementation(tcx, trait_id);
+            tcx.populated_external_traits.borrow_mut().insert(trait_id);
+
+            // Nothing else to do for default trait implementations since
+            // they are not allowed to have type parameters, methods, or any
+            // other item that could be associated to a trait implementation.
+            return;
+        } else {
+            // Record the trait->implementation mapping.
+            record_trait_implementation(tcx, trait_id, implementation_def_id);
+        }
 
         // For any methods that use a default implementation, add them to
         // the map. This is a bit unfortunate.

src/librustc/middle/ty_fold.rs

@@ -519,6 +519,7 @@ impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::Vtable<'tcx, N>
     fn fold_with<F:TypeFolder<'tcx>>(&self, folder: &mut F) -> traits::Vtable<'tcx, N> {
         match *self {
             traits::VtableImpl(ref v) => traits::VtableImpl(v.fold_with(folder)),
+            traits::VtableDefaultTrait(t) => traits::VtableDefaultTrait(t),
             traits::VtableClosure(d, ref s) => {
                 traits::VtableClosure(d, s.fold_with(folder))
             }

src/librustc_trans/trans/meth.rs

@@ -390,6 +390,7 @@ fn trans_monomorphized_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
             Callee { bcx: bcx, data: Fn(llfn) }
         }
         traits::VtableBuiltin(..) |
+        traits::VtableDefaultTrait(..) |
         traits::VtableParam(..) => {
             bcx.sess().bug(
                 &format!("resolved vtable bad vtable {} in trans",
@@ -714,6 +715,8 @@ pub fn get_vtable<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     let methods = traits::supertraits(tcx, trait_ref.clone()).flat_map(|trait_ref| {
         let vtable = fulfill_obligation(ccx, DUMMY_SP, trait_ref.clone());
         match vtable {
+            // Should default trait error here?
+            traits::VtableDefaultTrait(_) |
             traits::VtableBuiltin(_) => {
                 Vec::new().into_iter()
             }

src/librustc_typeck/collect.rs

@@ -649,7 +649,10 @@ fn convert_item(ccx: &CollectCtxt, it: &ast::Item) {
                                    &enum_definition.variants);
         },
         ast::ItemDefTrait(_, ref ast_trait_ref) => {
+            let trait_ref = astconv::instantiate_trait_ref(ccx, &ExplicitRscope,
+                                                           ast_trait_ref, None, None);
 
+            ty::record_default_trait_implementation(tcx, trait_ref.def_id)
         }
         ast::ItemImpl(_, _,
                       ref generics,