Exempt phantom fns from the object safety check

Author: nikomatsakis

src/librustc/middle/traits/object_safety.rs

@@ -138,10 +138,11 @@ fn supertraits_reference_self<'tcx>(tcx: &ty::ctxt<'tcx>,
             match predicate {
                 ty::Predicate::Trait(ref data) => {
                     // In the case of a trait predicate, we can skip the "self" type.
-                    data.0.trait_ref.substs.types.get_slice(TypeSpace)
-                                                 .iter()
-                                                 .cloned()
-                                                 .any(is_self)
+                    Some(data.def_id()) != tcx.lang_items.phantom_fn() &&
+                        data.0.trait_ref.substs.types.get_slice(TypeSpace)
+                                                     .iter()
+                                                     .cloned()
+                                                     .any(is_self)
                 }
                 ty::Predicate::Projection(..) |
                 ty::Predicate::TypeOutlives(..) |

src/test/compile-fail/object-safety-phantom-fn.rs

@@ -0,0 +1,28 @@
+// 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.
+
+// Check that `Self` appearing in a phantom fn does not make a trait not object safe.
+
+#![feature(rustc_attrs)]
+
+trait Baz : PhantomFn<Self> {
+}
+
+fn make_bar<T:Bar<u32>>(t: &T) -> &Bar<u32> {
+    t
+}
+
+fn make_baz<T:Baz>(t: &T) -> &Baz {
+    t
+}
+
+#[rustc_error]
+fn main() { //~ ERROR compilation successful
+}