rustdoc: avoid cleaning modules with duplicate names

src/librustdoc/clean/mod.rs

@@ -55,9 +55,11 @@ pub(crate) fn clean_doc_module<'tcx>(doc: &DocModule<'tcx>, cx: &mut DocContext<
         }
         item
     }));
-    items.extend(doc.mods.iter().map(|x| {
-        inserted.insert((ItemType::Module, x.name));
-        clean_doc_module(x, cx)
+    items.extend(doc.mods.iter().filter_map(|x| {
+        if !inserted.insert((ItemType::Module, x.name)) {
+            return None;
+        }
+        Some(clean_doc_module(x, cx))
     }));
 
     // Split up imports from all other items.

src/test/rustdoc/issue-83375-multiple-mods-w-same-name-doc-inline.rs

@@ -0,0 +1,15 @@
+#![crate_name = "foo"]
+
+pub mod sub {
+    pub struct Item;
+
+    pub mod prelude {
+        pub use super::Item;
+    }
+}
+
+// @count foo/index.html '//a[@class="mod"][@title="foo::prelude mod"]' 1
+pub mod prelude {}
+
+#[doc(inline)]
+pub use sub::*;