Traverse types in reachability

Issue 2526 showed a test case where a library exported only a type
that was a synonym for a class. Because the class's destructor wasn't
getting marked as reachable, its linkage was wrongly getting set to
"internal". The solution is for reachability to traverse types.

Closes #2526.

src/rustc/middle/trans/reachable.rs

@@ -135,11 +135,37 @@ fn traverse_public_item(cx: ctx, item: @item) {
             }
         }
       }
-      item_const(*) | item_ty(*) |
+      item_ty(t, _, _) {
+        traverse_ty(t, cx, mk_ty_visitor());
+      }
+      item_const(*) |
       item_enum(*) | item_iface(*) {}
     }
 }
 
+fn mk_ty_visitor() -> visit::vt<ctx> {
+    visit::mk_vt(@{visit_ty: traverse_ty with *visit::default_visitor()})
+}
+
+fn traverse_ty(ty: @ty, cx: ctx, v: visit::vt<ctx>) {
+    if cx.rmap.contains_key(ty.id) { ret; }
+    cx.rmap.insert(ty.id, ());
+
+    alt ty.node {
+      ty_path(p, p_id) {
+        alt cx.tcx.def_map.find(p_id) {
+          // Kind of a hack to check this here, but I'm not sure what else
+          // to do
+          some(def_prim_ty(_)) { /* do nothing */ }
+          some(d) { traverse_def_id(cx, def_id_of_def(d)); }
+          none    { /* do nothing -- but should we fail here? */ }
+        }
+        for p.types.each {|t| v.visit_ty(t, cx, v); };
+      }
+      _ { visit::visit_ty(ty, cx, v); }
+    }
+}
+
 fn traverse_inline_body(cx: ctx, body: blk) {
     fn traverse_expr(e: @expr, cx: ctx, v: visit::vt<ctx>) {
         alt e.node {

src/test/auxiliary/issue-2526.rs

@@ -0,0 +1,32 @@
+#[link(name = "zmq",
+       vers = "0.2",
+       uuid = "54cc1bc9-02b8-447c-a227-75ebc923bc29")];
+#[crate_type = "lib"];
+
+use std;
+
+export context;
+
+resource arc_destruct<T: const>(_data: int) { }
+
+fn arc<T: const>(_data: T) -> arc_destruct<T> {
+    arc_destruct(0)
+}
+
+fn init() -> arc_destruct<context_res> unsafe {
+    arc(context_res())
+}
+
+class context_res {
+    let ctx : int;
+
+    new() { self.ctx = 0; }
+
+    drop { }
+}
+
+type context = arc_destruct<context_res>;
+
+impl context for context {
+    fn socket() { }
+}

src/test/run-pass/issue-2526-a.rs

@@ -0,0 +1,8 @@
+// xfail-fast
+// aux-build:issue-2526.rs
+
+use zmq;
+import zmq::*;
+
+fn main() {}
+