Fix rustdoc infinitely recursing when an external crate reexports itself

Previously, rustdoc's LibEmbargoVisitor unconditionally visited the
child modules of an external crate. If a module re-exported its parent
via 'pub use super::*', rustdoc would re-walk the parent, leading to
infinite recursion.

This commit makes LibEmbargoVisitor store already visited modules in an
FxHashSet, ensuring that each module is only walked once.

Fixes #40936

2 files changed, 31 insertions, 0 deletions

diff --git a/src/test/rustdoc/auxiliary/issue-40936.rs b/src/test/rustdoc/auxiliary/issue-40936.rs
new file mode 100644
index 00000000000..54cc18cca23
--- /dev/null
+++ b/src/test/rustdoc/auxiliary/issue-40936.rs
@@ -0,0 +1,15 @@
+// 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.
+
+pub mod outermod {
+    pub mod innermod {
+        pub use super::*;
+    }
+}
diff --git a/src/test/rustdoc/issue-40936.rs b/src/test/rustdoc/issue-40936.rs
new file mode 100644
index 00000000000..3e02eec1b9c
--- /dev/null
+++ b/src/test/rustdoc/issue-40936.rs
@@ -0,0 +1,16 @@
+// 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:issue-40936.rs
+// build-aux-docs
+
+#![crate_name = "foo"]
+
+extern crate issue_40936;