Rollup merge of rust-lang#34542 - jseyfried:fix_recursive_modules, r=nrc

Fix non-termination on recursive module re-exports in extern crates

Fixes rust-lang#33776.
r? @nrc

Author: Manishearth

src/librustc_resolve/lib.rs

@@ -3207,7 +3207,9 @@ impl<'a> Resolver<'a> {
                     if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
                         // add the module to the lookup
                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
-                        worklist.push((module, path_segments, is_extern));
+                        if !worklist.iter().any(|&(m, _, _)| m.def == module.def) {
+                            worklist.push((module, path_segments, is_extern));
+                        }
                     }
                 }
             })

src/test/compile-fail/auxiliary/recursive_reexports.rs

@@ -0,0 +1,13 @@
+// Copyright 2016 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.
+
+pub mod foo {
+    pub use foo;
+}

src/test/compile-fail/recursive-reexports.rs

@@ -0,0 +1,15 @@
+// Copyright 2016 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:recursive_reexports.rs
+
+fn f() -> recursive_reexports::S {} //~ ERROR undeclared
+
+fn main() {}