Auto merge of #22541 - Manishearth:rollup, r=Gankro 1.0.0-alpha.2

Continued from #22520

1 files changed, 14 insertions, 5 deletions

diff --git a/src/librustc/middle/traits/select.rs b/src/librustc/middle/traits/select.rs
index 027415de998..0e298920841 100644
--- a/src/librustc/middle/traits/select.rs
+++ b/src/librustc/middle/traits/select.rs
@@ -132,6 +132,7 @@ pub enum MethodMatchedData {
 /// parameters) that would have to be inferred from the impl.
 #[derive(PartialEq,Eq,Debug,Clone)]
 enum SelectionCandidate<'tcx> {
+    PhantomFnCandidate,
     BuiltinCandidate(ty::BuiltinBound),
     ParamCandidate(ty::PolyTraitRef<'tcx>),
     ImplCandidate(ast::DefId),
@@ -736,7 +737,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     {
         let cache = self.pick_candidate_cache();
         let hashmap = cache.hashmap.borrow();
-        hashmap.get(&cache_fresh_trait_pred.0.trait_ref).map(|c| (*c).clone())
+        hashmap.get(&cache_fresh_trait_pred.0.trait_ref).cloned()
     }
 
     fn insert_candidate_cache(&mut self,
@@ -793,8 +794,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                stack: &TraitObligationStack<'o, 'tcx>)
                                -> Result<SelectionCandidateSet<'tcx>, SelectionError<'tcx>>
     {
-        // Check for overflow.
-
         let TraitObligationStack { obligation, .. } = *stack;
 
         let mut candidates = SelectionCandidateSet {
@@ -802,6 +801,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             ambiguous: false
         };
 
+        // Check for the `PhantomFn` trait. This is really just a
+        // special annotation that is *always* considered to match, no
+        // matter what the type parameters are etc.
+        if self.tcx().lang_items.phantom_fn() == Some(obligation.predicate.def_id()) {
+            candidates.vec.push(PhantomFnCandidate);
+            return Ok(candidates);
+        }
+
         // Other bounds. Consider both in-scope bounds from fn decl
         // and applicable impls. There is a certain set of precedence rules here.
 
@@ -996,7 +1003,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let all_bounds =
             util::transitive_bounds(
-                self.tcx(), &caller_trait_refs[]);
+                self.tcx(), &caller_trait_refs[..]);
 
         let matching_bounds =
             all_bounds.filter(
@@ -1521,7 +1528,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     ty::substd_enum_variants(self.tcx(), def_id, substs)
                     .iter()
                     .flat_map(|variant| variant.args.iter())
-                    .map(|&ty| ty)
+                    .cloned()
                     .collect();
                 nominal(self, bound, def_id, types)
             }
@@ -1629,6 +1636,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     try!(self.confirm_builtin_candidate(obligation, builtin_bound))))
             }
 
+            PhantomFnCandidate |
             ErrorCandidate => {
                 Ok(VtableBuiltin(VtableBuiltinData { nested: VecPerParamSpace::empty() }))
             }
@@ -2295,6 +2303,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 impl<'tcx> Repr<'tcx> for SelectionCandidate<'tcx> {
     fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String {
         match *self {
+            PhantomFnCandidate => format!("PhantomFnCandidate"),
             ErrorCandidate => format!("ErrorCandidate"),
             BuiltinCandidate(b) => format!("BuiltinCandidate({:?})", b),
             ParamCandidate(ref a) => format!("ParamCandidate({})", a.repr(tcx)),