Add rustdoc test.

Author: cjgillot

src/test/rustdoc/macros.rs

@@ -8,3 +8,17 @@ macro_rules! my_macro {
     ($a:tt) => ();
     ($e:expr) => {};
 }
+
+// Check that exported macro defined in a module are shown at crate root.
+// @has macros/macro.my_sub_macro.html //pre 'macro_rules! my_sub_macro {'
+// @has - //pre '() => { ... };'
+// @has - //pre '($a:tt) => { ... };'
+// @has - //pre '($e:expr) => { ... };'
+mod sub {
+    #[macro_export]
+    macro_rules! my_sub_macro {
+        () => {};
+        ($a:tt) => {};
+        ($e:expr) => {};
+    }
+}