build_local_trait_impl: reuse memory

Co-authored-by: Joshua Nelson <[email protected]>

Author: bugadani

src/librustdoc/passes/collect_trait_impls.rs

@@ -56,11 +56,11 @@ crate fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
 
     // `tcx.crates()` doesn't include the local crate, and `tcx.all_trait_implementations`
     // doesn't work with it anyway, so pull them from the HIR map instead
+    let mut extra_attrs = Vec::new();
     for &trait_did in cx.tcx.all_traits(LOCAL_CRATE).iter() {
         for &impl_node in cx.tcx.hir().trait_impls(trait_did) {
             let impl_did = cx.tcx.hir().local_def_id(impl_node);
             cx.tcx.sess.prof.generic_activity("build_local_trait_impl").run(|| {
-                let mut extra_attrs = Vec::new();
                 let mut parent = cx.tcx.parent(impl_did.to_def_id());
                 while let Some(did) = parent {
                     extra_attrs.extend(
@@ -86,6 +86,7 @@ crate fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
                     Some(&extra_attrs),
                     &mut new_items,
                 );
+                extra_attrs.clear();
             });
         }
     }