Don't unnecessarily clone some fields in `Context`

There was no need to clone `id_map` because it was reset before each
item was rendered. `deref_id_map` was not reset, but it was keyed by
`DefId` and thus was unlikely to have collisions (at least for now).

Now we just clone the fields that need to be cloned, and instead create
fresh versions of the others.

1 files changed, 15 insertions, 6 deletions

diff --git a/src/librustdoc/html/render/context.rs b/src/librustdoc/html/render/context.rs
index 23c2a925105..41d4aef7c7a 100644
--- a/src/librustdoc/html/render/context.rs
+++ b/src/librustdoc/html/render/context.rs
@@ -40,7 +40,6 @@ use crate::html::{layout, sources};
 /// It is intended that this context is a lightweight object which can be fairly
 /// easily cloned because it is cloned per work-job (about once per item in the
 /// rustdoc tree).
-#[derive(Clone)]
 crate struct Context<'tcx> {
     /// Current hierarchy of components leading down to what's currently being
     /// rendered
@@ -157,11 +156,6 @@ impl<'tcx> Context<'tcx> {
             static_extra_scripts: &[],
         };
 
-        {
-            self.id_map.borrow_mut().reset();
-            self.id_map.borrow_mut().populate(&INITIAL_IDS);
-        }
-
         if !self.render_redirect_pages {
             layout::render(
                 &self.shared.layout,
@@ -436,6 +430,21 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
         Ok((cx, krate))
     }
 
+    fn make_child_renderer(&self) -> Self {
+        let mut id_map = IdMap::new();
+        id_map.populate(&INITIAL_IDS);
+
+        Self {
+            current: self.current.clone(),
+            dst: self.dst.clone(),
+            render_redirect_pages: self.render_redirect_pages,
+            id_map: Box::new(RefCell::new(id_map)),
+            deref_id_map: Box::new(RefCell::new(FxHashMap::default())),
+            shared: Rc::clone(&self.shared),
+            cache: Rc::clone(&self.cache),
+        }
+    }
+
     fn after_krate(
         &mut self,
         krate: &clean::Crate,