Make sure type_use.rs doesn't get lost in recursive enums

Closes #2059

Author: marijnh

src/rustc/middle/trans/type_use.rs

@@ -18,6 +18,7 @@
 // invasive.)
 
 import std::map::hashmap;
+import std::list;
 import driver::session::session;
 import metadata::csearch;
 import syntax::ast::*, syntax::ast_util, syntax::visit;
@@ -91,21 +92,25 @@ fn type_needs(cx: ctx, use: uint, ty: ty::t) {
     let mut done = true;
     // Optimization -- don't descend type if all params already have this use
     for vec::each(cx.uses) {|u| if u & use != use { done = false } }
-    if !done { type_needs_inner(cx, use, ty); }
+    if !done { type_needs_inner(cx, use, ty, list::nil); }
 }
 
-fn type_needs_inner(cx: ctx, use: uint, ty: ty::t) {
+fn type_needs_inner(cx: ctx, use: uint, ty: ty::t,
+                    enums_seen: list::list<def_id>) {
     ty::maybe_walk_ty(ty) {|ty|
         if ty::type_has_params(ty) {
             alt ty::get(ty).struct {
               ty::ty_fn(_) | ty::ty_ptr(_) | ty::ty_rptr(_, _) |
               ty::ty_box(_) | ty::ty_iface(_, _) { false }
               ty::ty_enum(did, tps) {
-                for vec::each(*ty::enum_variants(cx.ccx.tcx, did)) {|v|
-                    for vec::each(v.args) {|aty|
-                        let t = ty::substitute_type_params(cx.ccx.tcx, tps,
-                                                           aty);
-                        type_needs_inner(cx, use, t);
+                if option::is_none(list::find(enums_seen, {|id| id == did})) {
+                    let seen = list::cons(did, @enums_seen);
+                    for vec::each(*ty::enum_variants(cx.ccx.tcx, did)) {|v|
+                        for vec::each(v.args) {|aty|
+                            let t = ty::substitute_type_params(cx.ccx.tcx,
+                                                               tps, aty);
+                            type_needs_inner(cx, use, t, seen);
+                        }
                     }
                 }
                 false