Rollup merge of #53801 - GuillaumeGomez:duplicated-foreign-type-impls, r=QuietMisdreavus

Prevent duplicated impl on foreign types

Fixes #53689.

r? @QuietMisdreavus

src/librustdoc/html/render.rs

@@ -2956,14 +2956,18 @@ fn item_trait(
                 </h2>
             ")?;
 
+            let mut foreign_cache = FxHashSet();
             for implementor in foreign {
+                if foreign_cache.insert(implementor.inner_impl().to_string()) {
                     let assoc_link = AssocItemLink::GotoSource(
-                    implementor.impl_item.def_id, &implementor.inner_impl().provided_trait_methods
+                        implementor.impl_item.def_id,
+                        &implementor.inner_impl().provided_trait_methods
                     );
                     render_impl(w, cx, &implementor, assoc_link,
                                 RenderMode::Normal, implementor.impl_item.stable_since(), false)?;
                 }
             }
+        }
 
         write!(w, "{}", impl_header)?;
         for implementor in concrete {