Add regression test for re-export of doc hidden item inside private item not displayed

tests/rustdoc/reexport-doc-hidden-inside-private.rs

@@ -0,0 +1,16 @@
+// This test ensures that a re-export of  `#[doc(hidden)]` item inside a private
+// module will still be displayed (the re-export, not the item).
+
+#![crate_name = "foo"]
+
+mod private_module {
+    #[doc(hidden)]
+    pub struct Public;
+}
+
+// @has 'foo/index.html'
+// @has - '//*[@id="reexport.Foo"]/code' 'pub use crate::private_module::Public as Foo;'
+pub use crate::private_module::Public as Foo;
+// Glob re-exports with no visible items should not be displayed.
+// @count - '//*[@class="item-table"]/li' 1
+pub use crate::private_module::*;