Don't share `id_map` and `deref_id_map`

All the tests passed, so it doesn't seem they need to be shared.
Plus they should be item/page-specific.

I'm not sure why they were shared before. I think the reason `id_map`
worked as a shared value before is that it is cleared before rendering
each item (in `render_item`). And then I'm guessing `deref_id_map`
worked because it's a hashmap keyed by `DefId`, so there was no overlap
(though I'm guessing we could have had issues in the future).

Note that `id_map` currently still has to be cleared because otherwise
child items would inherit the `id_map` of their parent. I'm hoping to
figure out a way to stop cloning `Context`, but until then we have to
reset `id_map`.

src/librustdoc/html/render/context.rs

@@ -6,7 +6,7 @@ use std::rc::Rc;
 use std::sync::mpsc::channel;
 
 use rustc_data_structures::fx::FxHashMap;
-use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
 use rustc_span::edition::Edition;
@@ -30,7 +30,7 @@ use crate::formats::item_type::ItemType;
 use crate::formats::FormatRenderer;
 use crate::html::escape::Escape;
 use crate::html::format::Buffer;
-use crate::html::markdown::{self, plain_text_summary, ErrorCodes};
+use crate::html::markdown::{self, plain_text_summary, ErrorCodes, IdMap};
 use crate::html::{layout, sources};
 
 /// Major driving force in all rustdoc rendering. This contains information
@@ -52,6 +52,11 @@ crate struct Context<'tcx> {
     /// real location of an item. This is used to allow external links to
     /// publicly reused items to redirect to the right location.
     pub(super) render_redirect_pages: bool,
+    /// The map used to ensure all generated 'id=' attributes are unique.
+    pub(super) id_map: RefCell<IdMap>,
+    /// Tracks section IDs for `Deref` targets so they match in both the main
+    /// body and the sidebar.
+    pub(super) deref_id_map: RefCell<FxHashMap<DefId, String>>,
     /// Shared mutable state.
     ///
     /// Issue for improving the situation: [#82381][]
@@ -72,7 +77,7 @@ crate struct Context<'tcx> {
 
 // `Context` is cloned a lot, so we don't want the size to grow unexpectedly.
 #[cfg(target_arch = "x86_64")]
-rustc_data_structures::static_assert_size!(Context<'_>, 72);
+rustc_data_structures::static_assert_size!(Context<'_>, 152);
 
 impl<'tcx> Context<'tcx> {
     pub(super) fn path(&self, filename: &str) -> PathBuf {
@@ -95,7 +100,7 @@ impl<'tcx> Context<'tcx> {
     }
 
     pub(super) fn derive_id(&self, id: String) -> String {
-        let mut map = self.shared.id_map.borrow_mut();
+        let mut map = self.id_map.borrow_mut();
         map.derive(id)
     }
 
@@ -153,8 +158,8 @@ impl<'tcx> Context<'tcx> {
         };
 
         {
-            self.shared.id_map.borrow_mut().reset();
-            self.shared.id_map.borrow_mut().populate(&INITIAL_IDS);
+            self.id_map.borrow_mut().reset();
+            self.id_map.borrow_mut().populate(&INITIAL_IDS);
         }
 
         if !self.render_redirect_pages {
@@ -387,8 +392,6 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
             edition,
             codes: ErrorCodes::from(unstable_features.is_nightly_build()),
             playground,
-            id_map: RefCell::new(id_map),
-            deref_id_map: RefCell::new(FxHashMap::default()),
             all: RefCell::new(AllTypes::new()),
             errors: receiver,
             redirections: if generate_redirect_map { Some(Default::default()) } else { None },
@@ -418,6 +421,8 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
             current: Vec::new(),
             dst,
             render_redirect_pages: false,
+            id_map: RefCell::new(id_map),
+            deref_id_map: RefCell::new(FxHashMap::default()),
             shared: Rc::new(scx),
             cache: Rc::new(cache),
         };

src/librustdoc/html/render/mod.rs

@@ -70,7 +70,7 @@ use crate::html::format::{
     PrintWithSpace, WhereClause,
 };
 use crate::html::layout;
-use crate::html::markdown::{self, ErrorCodes, IdMap, Markdown, MarkdownHtml, MarkdownSummaryLine};
+use crate::html::markdown::{self, ErrorCodes, Markdown, MarkdownHtml, MarkdownSummaryLine};
 
 /// A pair of name and its optional document.
 crate type NameDoc = (String, Option<String>);
@@ -121,11 +121,6 @@ crate struct SharedContext<'tcx> {
     crate edition: Edition,
     codes: ErrorCodes,
     playground: Option<markdown::Playground>,
-    /// The map used to ensure all generated 'id=' attributes are unique.
-    id_map: RefCell<IdMap>,
-    /// Tracks section IDs for `Deref` targets so they match in both the main
-    /// body and the sidebar.
-    deref_id_map: RefCell<FxHashMap<DefId, String>>,
     all: RefCell<AllTypes>,
     /// Storage for the errors produced while generating documentation so they
     /// can be printed together at the end.
@@ -650,7 +645,7 @@ fn render_markdown(
     prefix: &str,
     is_hidden: bool,
 ) {
-    let mut ids = cx.shared.id_map.borrow_mut();
+    let mut ids = cx.id_map.borrow_mut();
     write!(
         w,
         "<div class=\"docblock{}\">{}{}</div>",
@@ -810,7 +805,7 @@ fn short_item_info(
 
         if let Some(note) = note {
             let note = note.as_str();
-            let mut ids = cx.shared.id_map.borrow_mut();
+            let mut ids = cx.id_map.borrow_mut();
             let html = MarkdownHtml(
                 &note,
                 &mut ids,
@@ -849,7 +844,7 @@ fn short_item_info(
         message.push_str(&format!(" ({})", feature));
 
         if let Some(unstable_reason) = reason {
-            let mut ids = cx.shared.id_map.borrow_mut();
+            let mut ids = cx.id_map.borrow_mut();
             message = format!(
                 "<details><summary>{}</summary>{}</details>",
                 message,
@@ -1189,8 +1184,7 @@ fn render_assoc_items(
                     type_.print(cx.cache())
                 )));
                 debug!("Adding {} to deref id map", type_.print(cx.cache()));
-                cx.shared
-                    .deref_id_map
+                cx.deref_id_map
                     .borrow_mut()
                     .insert(type_.def_id_full(cx.cache()).unwrap(), id.clone());
                 write!(
@@ -1497,7 +1491,7 @@ fn render_impl(
         }
 
         if let Some(ref dox) = cx.shared.maybe_collapsed_doc_value(&i.impl_item) {
-            let mut ids = cx.shared.id_map.borrow_mut();
+            let mut ids = cx.id_map.borrow_mut();
             write!(
                 w,
                 "<div class=\"docblock\">{}</div>",
@@ -2046,7 +2040,7 @@ fn sidebar_deref_methods(cx: &Context<'_>, out: &mut Buffer, impl_: &Impl, v: &V
                 .flat_map(|i| get_methods(i.inner_impl(), true, &mut used_links, deref_mut, c))
                 .collect::<Vec<_>>();
             if !ret.is_empty() {
-                let deref_id_map = cx.shared.deref_id_map.borrow();
+                let deref_id_map = cx.deref_id_map.borrow();
                 let id = deref_id_map
                     .get(&real_target.def_id_full(cx.cache()).unwrap())
                     .expect("Deref section without derived id");