Add regression test for cfg merging on re-exports

tests/rustdoc/reexport-cfg.rs

@@ -0,0 +1,30 @@
+// This test ensures that only the re-export `cfg` will be displayed and that it won't
+// include `cfg`s from the previous chained items.
+
+#![crate_name = "foo"]
+#![feature(doc_auto_cfg, doc_cfg)]
+
+mod foo {
+    #[cfg(not(feature = "foo"))]
+    pub struct Bar;
+
+    #[doc(cfg(not(feature = "bar")))]
+    pub struct Bar2;
+}
+
+// @has 'foo/index.html'
+// @has - '//*[@class="item-name"]' 'BabarNon-lie'
+#[cfg(not(feature = "lie"))]
+pub use crate::foo::Bar as Babar;
+
+// @has - '//*[@class="item-name"]' 'Babar2Non-cake'
+#[doc(cfg(not(feature = "cake")))]
+pub use crate::foo::Bar2 as Babar2;
+
+// @has - '//*[@class="item-table"]/li' 'pub use crate::Babar as Elephant;Non-robot'
+#[cfg(not(feature = "robot"))]
+pub use crate::Babar as Elephant;
+
+// @has - '//*[@class="item-table"]/li' 'pub use crate::Babar2 as Elephant2;Non-cat'
+#[doc(cfg(not(feature = "cat")))]
+pub use crate::Babar2 as Elephant2;