rustc: Fix reachability with cross-crate generators

Same solution as in f2df185

Closes #44181

Author: alexcrichton

src/librustc_privacy/lib.rs

@@ -446,6 +446,7 @@ impl<'b, 'a, 'tcx> TypeVisitor<'tcx> for ReachEverythingInTheInterfaceVisitor<'b
             ty::TyProjection(ref proj) => Some(proj.item_def_id),
             ty::TyFnDef(def_id, ..) |
             ty::TyClosure(def_id, ..) |
+            ty::TyGenerator(def_id, ..) |
             ty::TyAnon(def_id, _) => Some(def_id),
             _ => None
         };

src/test/run-pass/generator/auxiliary/xcrate-reachable.rs

@@ -0,0 +1,24 @@
+// Copyright 2017 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.
+
+#![feature(conservative_impl_trait, generators, generator_trait)]
+
+use std::ops::Generator;
+
+fn msg() -> u32 {
+    0
+}
+
+pub fn foo() -> impl Generator<Yield=(), Return=u32> {
+    || {
+        yield;
+        return msg();
+    }
+}

src/test/run-pass/generator/xcrate-reachable.rs

@@ -0,0 +1,21 @@
+// Copyright 2017 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.
+
+// aux-build:xcrate-reachable.rs
+
+#![feature(conservative_impl_trait, generator_trait)]
+
+extern crate xcrate_reachable as foo;
+
+use std::ops::Generator;
+
+fn main() {
+    foo::foo().resume();
+}