Support assignability for struct fields. r=pcwalton

src/librustc/middle/typeck/check/mod.rs

@@ -1679,9 +1679,11 @@ fn check_expr_with_unifier(fcx: @fn_ctxt,
                     let expected_field_type =
                         ty::lookup_field_type(
                             tcx, class_id, field_id, substitutions);
-                    bot |= check_expr(fcx,
+                    bot |=
+                        check_expr_with_assignability(
+                            fcx,
                             field.node.expr,
-                                      Some(expected_field_type));
+                            expected_field_type);
                     class_field_map.insert(
                         field.node.ident, (field_id, true));
                     fields_found += 1;

src/test/run-pass/struct-field-assignability.rs

@@ -0,0 +1,9 @@
+struct Foo {
+    x: &int
+}
+
+fn main() {
+    let f = Foo { x: @3 };
+    assert *f.x == 3;
+}
+