Add regression test for rust-lang#108231

Author: GuillaumeGomez

tests/rustdoc/issue-108231.rs

@@ -0,0 +1,23 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/108231>.
+// Macros with `#[macro_export]` attribute should be visible at the top level
+// even if they are inside a doc hidden item.
+
+#![crate_name = "foo"]
+
+// @has 'foo/index.html'
+// @count - '//*[@id="main-content"]//a[@class="macro"]' 1
+// @has - '//*[@id="main-content"]//a[@class="macro"]' 'foo'
+
+#[doc(hidden)]
+pub mod __internal {
+    /// This one should be visible.
+    #[macro_export]
+    macro_rules! foo {
+        () => {};
+    }
+
+    /// This one should be hidden.
+    macro_rules! bar {
+        () => {};
+    }
+}