Put negative trait implemtations behind a feature gate

src/libsyntax/feature_gate.rs

@@ -84,6 +84,9 @@ static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
     // A way to temporarily opt out of the new orphan rules. This will *never* be accepted.
     ("old_orphan_check", Deprecated),
 
+    // OIBIT specific features
+    ("optin_builtin_traits", Active),
+
     // These are used to test this portion of the compiler, they don't actually
     // mean anything
     ("test_accepted_feature", Accepted),
@@ -291,7 +294,17 @@ impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
                 }
             }
 
-            ast::ItemImpl(_, _, _, _, _, ref items) => {
+            ast::ItemImpl(_, polarity, _, _, _, ref items) => {
+                match polarity {
+                    ast::ImplPolarity::Negative => {
+                        self.gate_feature("optin_builtin_traits",
+                                          i.span,
+                                          "negative trait bounds are not yet fully implemented; \
+                                          use marker types for now");
+                    },
+                    _ => {}
+                }
+
                 if attr::contains_name(i.attrs[],
                                        "unsafe_destructor") {
                     self.gate_feature("unsafe_destructor",

src/test/compile-fail/syntax-trait-polarity-feature-gate.rs

@@ -0,0 +1,20 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::kinds::Send;
+
+struct TestType;
+
+trait TestTrait {}
+
+unsafe impl !Send for TestType {}
+//~^ ERROR negative trait bounds
+
+fn main() {}

src/test/compile-fail/syntax-trait-polarity.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(optin_builtin_traits)]
+
 use std::kinds::Send;
 
 struct TestType;

src/test/pretty/trait-polarity.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(optin_builtin_traits)]
+
 // pp-exact
 
 trait UnsafeTrait {

src/test/run-pass/syntax-trait-polarity.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(optin_builtin_traits)]
+
 use std::kinds::Send;
 
 struct TestType;