Allow some resources to be considered const.

Author: eholk

src/rustc/middle/ty.rs

@@ -1526,7 +1526,10 @@ fn type_kind(cx: ctxt, ty: t) -> kind {
         }
         lowest
       }
-      ty_res(did, inner, tps) { kind_send_only() }
+      ty_res(did, inner, tps) {
+        let inner = subst(cx, tps, inner);
+        (kind_const() & type_kind(cx, inner)) | kind_send_only()
+      }
       ty_param(_, did) {
         // FIXME: type params shouldn't be implicitly copyable (#2449)
         let k = param_bounds_to_kind(cx.ty_param_bounds.get(did.node));

src/test/compile-fail/non-const.rs

@@ -3,6 +3,7 @@
 fn foo<T: const>(_x: T) { }
 
 resource r(_x: int) {}
+resource r2(_x: @mut int) {}
 
 fn main() {
     foo({f: 3});
@@ -13,7 +14,8 @@ fn main() {
     foo(~mut 1); //! ERROR missing `const`
     foo(@1);
     foo(@mut 1); //! ERROR missing `const`
-    foo(r(1)); //! ERROR missing `const`
+    foo(r(1)); // this is okay now.
+    foo(r2(@mut 1)); //! ERROR missing `const`
     foo("123");
     foo({f: {mut f: 1}}); //! ERROR missing `const`
 }