Auto merge of #28504 - Eljay:fix-trait-privacy, r=nrc

Fixes #16264 / #18241.

As far as I can tell, it should be impossible for a trait to be inaccessible if it's in scope, so this check is unnecessary. Are there any cases where this check is actually needed?

src/librustc_privacy/lib.rs

@@ -847,12 +847,8 @@ impl<'a, 'tcx> PrivacyVisitor<'a, 'tcx> {
             ty::ImplContainer(_) => {
                 self.check_static_method(span, method_def_id, name)
             }
-            // Trait methods are always all public. The only controlling factor
-            // is whether the trait itself is accessible or not.
-            ty::TraitContainer(trait_def_id) => {
-                self.report_error(self.ensure_public(span, trait_def_id,
-                                                     None, "source trait"));
-            }
+            // Trait methods are always accessible if the trait is in scope.
+            ty::TraitContainer(_) => {}
         }
     }
 }

src/test/compile-fail/privacy-ufcs.rs

@@ -0,0 +1,24 @@
+// Copyright 2015 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.
+
+// Test to ensure private traits are inaccessible with UFCS angle-bracket syntax.
+
+mod foo {
+    trait Bar {
+        fn baz() {}
+    }
+
+    impl Bar for i32 {}
+}
+
+fn main() {
+    <i32 as ::foo::Bar>::baz(); //~ERROR method `baz` is inaccessible
+                                //~^NOTE: trait `Bar` is private
+}

src/test/run-pass/issue-16264.rs

@@ -0,0 +1,27 @@
+// Copyright 2015 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 outer::Foo;
+
+mod outer {
+    pub use self::inner::Foo;
+
+    mod inner {
+        pub trait Foo {
+            fn bar(&self) {}
+        }
+        impl Foo for i32 {}
+    }
+}
+
+fn main() {
+    let x: i32 = 0;
+    x.bar();
+}