Auto merge of #130857 - lukas-code:no-clones-allowed, r=notriddle

rustdoc perf: clone `clean::Item` less

In #130798, I caused a small perf regression for rustdoc (see #130807 (comment)), so here is a small improvement to make up for it 😺.

This change is actually unrelated to the minor perf regression in `Item::stability` and instead fixes a more relevant perf problem that I found while investigating: For certain crates with many impls on type aliases, we unnecessarily cloned large `clean::Item`s multiple times -- now we just borrow them.

Author: bors

Diff for: src/librustdoc/clean/inline.rs

@@ -837,8 +837,7 @@ pub(crate) fn record_extern_trait(cx: &mut DocContext<'_>, did: DefId) {
     }
 
     {
-        if cx.external_traits.borrow().contains_key(&did) || cx.active_extern_traits.contains(&did)
-        {
+        if cx.external_traits.contains_key(&did) || cx.active_extern_traits.contains(&did) {
             return;
         }
     }
@@ -850,6 +849,6 @@ pub(crate) fn record_extern_trait(cx: &mut DocContext<'_>, did: DefId) {
     debug!("record_extern_trait: {did:?}");
     let trait_ = build_external_trait(cx, did);
 
-    cx.external_traits.borrow_mut().insert(did, trait_);
+    cx.external_traits.insert(did, trait_);
     cx.active_extern_traits.remove(&did);
 }

Diff for: src/librustdoc/clean/types.rs

@@ -1,8 +1,6 @@
 use std::borrow::Cow;
-use std::cell::RefCell;
 use std::hash::Hash;
 use std::path::PathBuf;
-use std::rc::Rc;
 use std::sync::{Arc, OnceLock as OnceCell};
 use std::{fmt, iter};
 
@@ -115,7 +113,7 @@ impl From<DefId> for ItemId {
 pub(crate) struct Crate {
     pub(crate) module: Item,
     /// Only here so that they can be filtered through the rustdoc passes.
-    pub(crate) external_traits: Rc<RefCell<FxHashMap<DefId, Trait>>>,
+    pub(crate) external_traits: Box<FxHashMap<DefId, Trait>>,
 }
 
 impl Crate {

Diff for: src/librustdoc/clean/utils.rs

@@ -74,7 +74,7 @@ pub(crate) fn krate(cx: &mut DocContext<'_>) -> Crate {
         }));
     }
 
-    Crate { module, external_traits: cx.external_traits.clone() }
+    Crate { module, external_traits: Box::new(mem::take(&mut cx.external_traits)) }
 }
 
 pub(crate) fn clean_middle_generic_args<'tcx>(

Diff for: src/librustdoc/core.rs

@@ -1,5 +1,3 @@
-use std::cell::RefCell;
-use std::rc::Rc;
 use std::sync::atomic::AtomicBool;
 use std::sync::{Arc, LazyLock};
 use std::{io, mem};
@@ -41,7 +39,7 @@ pub(crate) struct DocContext<'tcx> {
     /// Most of this logic is copied from rustc_lint::late.
     pub(crate) param_env: ParamEnv<'tcx>,
     /// Later on moved through `clean::Crate` into `cache`
-    pub(crate) external_traits: Rc<RefCell<FxHashMap<DefId, clean::Trait>>>,
+    pub(crate) external_traits: FxHashMap<DefId, clean::Trait>,
     /// Used while populating `external_traits` to ensure we don't process the same trait twice at
     /// the same time.
     pub(crate) active_extern_traits: DefIdSet,
@@ -359,7 +357,7 @@ pub(crate) fn run_global_ctxt(
     // Note that in case of `#![no_core]`, the trait is not available.
     if let Some(sized_trait_did) = ctxt.tcx.lang_items().sized_trait() {
         let sized_trait = build_external_trait(&mut ctxt, sized_trait_did);
-        ctxt.external_traits.borrow_mut().insert(sized_trait_did, sized_trait);
+        ctxt.external_traits.insert(sized_trait_did, sized_trait);
     }
 
     debug!("crate: {:?}", tcx.hir().krate());

Diff for: src/librustdoc/fold.rs

@@ -1,3 +1,5 @@
+use std::mem;
+
 use crate::clean::*;
 
 pub(crate) fn strip_item(mut item: Item) -> Item {
@@ -116,10 +118,11 @@ pub(crate) trait DocFolder: Sized {
     fn fold_crate(&mut self, mut c: Crate) -> Crate {
         c.module = self.fold_item(c.module).unwrap();
 
-        let external_traits = { std::mem::take(&mut *c.external_traits.borrow_mut()) };
-        for (k, mut v) in external_traits {
-            v.items = v.items.into_iter().filter_map(|i| self.fold_item(i)).collect();
-            c.external_traits.borrow_mut().insert(k, v);
+        for trait_ in c.external_traits.values_mut() {
+            trait_.items = mem::take(&mut trait_.items)
+                .into_iter()
+                .filter_map(|i| self.fold_item(i))
+                .collect();
         }
 
         c

Diff for: src/librustdoc/formats/cache.rs

@@ -153,7 +153,8 @@ impl Cache {
 
         // Crawl the crate to build various caches used for the output
         debug!(?cx.cache.crate_version);
-        cx.cache.traits = krate.external_traits.take();
+        assert!(cx.external_traits.is_empty());
+        cx.cache.traits = mem::take(&mut krate.external_traits);
 
         // Cache where all our extern crates are located
         // FIXME: this part is specific to HTML so it'd be nice to remove it from the common code

Diff for: src/librustdoc/html/render/write_shared.rs

@@ -824,9 +824,9 @@ impl Serialize for Implementor {
 /// this visitor works to reverse that: `aliased_types` is a map
 /// from target to the aliases that reference it, and each one
 /// will generate one file.
-struct TypeImplCollector<'cx, 'cache> {
+struct TypeImplCollector<'cx, 'cache, 'item> {
     /// Map from DefId-of-aliased-type to its data.
-    aliased_types: IndexMap<DefId, AliasedType<'cache>>,
+    aliased_types: IndexMap<DefId, AliasedType<'cache, 'item>>,
     visited_aliases: FxHashSet<DefId>,
     cache: &'cache Cache,
     cx: &'cache mut Context<'cx>,
@@ -847,26 +847,26 @@ struct TypeImplCollector<'cx, 'cache> {
 /// ]
 /// )
 /// ```
-struct AliasedType<'cache> {
+struct AliasedType<'cache, 'item> {
     /// This is used to generate the actual filename of this aliased type.
     target_fqp: &'cache [Symbol],
     target_type: ItemType,
     /// This is the data stored inside the file.
     /// ItemId is used to deduplicate impls.
-    impl_: IndexMap<ItemId, AliasedTypeImpl<'cache>>,
+    impl_: IndexMap<ItemId, AliasedTypeImpl<'cache, 'item>>,
 }
 
 /// The `impl_` contains data that's used to figure out if an alias will work,
 /// and to generate the HTML at the end.
 ///
 /// The `type_aliases` list is built up with each type alias that matches.
-struct AliasedTypeImpl<'cache> {
+struct AliasedTypeImpl<'cache, 'item> {
     impl_: &'cache Impl,
-    type_aliases: Vec<(&'cache [Symbol], Item)>,
+    type_aliases: Vec<(&'cache [Symbol], &'item Item)>,
 }
 
-impl<'cx, 'cache> DocVisitor for TypeImplCollector<'cx, 'cache> {
-    fn visit_item(&mut self, it: &Item) {
+impl<'cx, 'cache, 'item> DocVisitor<'item> for TypeImplCollector<'cx, 'cache, 'item> {
+    fn visit_item(&mut self, it: &'item Item) {
         self.visit_item_recur(it);
         let cache = self.cache;
         let ItemKind::TypeAliasItem(ref t) = it.kind else { return };
@@ -927,7 +927,7 @@ impl<'cx, 'cache> DocVisitor for TypeImplCollector<'cx, 'cache> {
                 continue;
             }
             // This impl was not found in the set of rejected impls
-            aliased_type_impl.type_aliases.push((&self_fqp[..], it.clone()));
+            aliased_type_impl.type_aliases.push((&self_fqp[..], it));
         }
     }
 }

Diff for: src/librustdoc/html/sources.rs

@@ -103,7 +103,7 @@ impl LocalSourcesCollector<'_, '_> {
     }
 }
 
-impl DocVisitor for LocalSourcesCollector<'_, '_> {
+impl DocVisitor<'_> for LocalSourcesCollector<'_, '_> {
     fn visit_item(&mut self, item: &clean::Item) {
         self.add_local_source(item);
 
@@ -122,7 +122,7 @@ struct SourceCollector<'a, 'tcx> {
     crate_name: &'a str,
 }
 
-impl DocVisitor for SourceCollector<'_, '_> {
+impl DocVisitor<'_> for SourceCollector<'_, '_> {
     fn visit_item(&mut self, item: &clean::Item) {
         if !self.cx.include_sources {
             return;

Diff for: src/librustdoc/passes/calculate_doc_coverage.rs

@@ -187,7 +187,7 @@ impl<'a, 'b> CoverageCalculator<'a, 'b> {
     }
 }
 
-impl<'a, 'b> DocVisitor for CoverageCalculator<'a, 'b> {
+impl<'a, 'b> DocVisitor<'_> for CoverageCalculator<'a, 'b> {
     fn visit_item(&mut self, i: &clean::Item) {
         if !i.item_id.is_local() {
             // non-local items are skipped because they can be out of the users control,

Diff for: src/librustdoc/passes/check_doc_test_visibility.rs

@@ -34,7 +34,7 @@ pub(crate) fn check_doc_test_visibility(krate: Crate, cx: &mut DocContext<'_>) -
     krate
 }
 
-impl<'a, 'tcx> DocVisitor for DocTestVisibilityLinter<'a, 'tcx> {
+impl<'a, 'tcx> DocVisitor<'_> for DocTestVisibilityLinter<'a, 'tcx> {
     fn visit_item(&mut self, item: &Item) {
         look_for_tests(self.cx, &item.doc_value(), item);
 

Diff for: src/librustdoc/passes/collect_intra_doc_links.rs

@@ -816,7 +816,7 @@ fn is_derive_trait_collision<T>(ns: &PerNS<Result<Vec<(Res, T)>, ResolutionFailu
     }
 }
 
-impl<'a, 'tcx> DocVisitor for LinkCollector<'a, 'tcx> {
+impl<'a, 'tcx> DocVisitor<'_> for LinkCollector<'a, 'tcx> {
     fn visit_item(&mut self, item: &Item) {
         self.resolve_links(item);
         self.visit_item_recur(item)

Diff for: src/librustdoc/passes/collect_trait_impls.rs

@@ -219,6 +219,8 @@ pub(crate) fn collect_trait_impls(mut krate: Crate, cx: &mut DocContext<'_>) ->
         panic!("collect-trait-impls can't run");
     };
 
+    krate.external_traits.extend(cx.external_traits.drain());
+
     krate
 }
 
@@ -227,7 +229,7 @@ struct SyntheticImplCollector<'a, 'tcx> {
     impls: Vec<Item>,
 }
 
-impl<'a, 'tcx> DocVisitor for SyntheticImplCollector<'a, 'tcx> {
+impl<'a, 'tcx> DocVisitor<'_> for SyntheticImplCollector<'a, 'tcx> {
     fn visit_item(&mut self, i: &Item) {
         if i.is_struct() || i.is_enum() || i.is_union() {
             // FIXME(eddyb) is this `doc(hidden)` check needed?
@@ -254,7 +256,7 @@ impl<'cache> ItemAndAliasCollector<'cache> {
     }
 }
 
-impl<'cache> DocVisitor for ItemAndAliasCollector<'cache> {
+impl<'cache> DocVisitor<'_> for ItemAndAliasCollector<'cache> {
     fn visit_item(&mut self, i: &Item) {
         self.items.insert(i.item_id);
 

Diff for: src/librustdoc/passes/lint.rs

@@ -25,7 +25,7 @@ pub(crate) fn run_lints(krate: Crate, cx: &mut DocContext<'_>) -> Crate {
     krate
 }
 
-impl<'a, 'tcx> DocVisitor for Linter<'a, 'tcx> {
+impl<'a, 'tcx> DocVisitor<'_> for Linter<'a, 'tcx> {
     fn visit_item(&mut self, item: &Item) {
         let Some(hir_id) = DocContext::as_local_hir_id(self.cx.tcx, item.item_id) else {
             // If non-local, no need to check anything.

Diff for: src/librustdoc/visit.rs

@@ -1,12 +1,12 @@
 use crate::clean::*;
 
-pub(crate) trait DocVisitor: Sized {
-    fn visit_item(&mut self, item: &Item) {
+pub(crate) trait DocVisitor<'a>: Sized {
+    fn visit_item(&mut self, item: &'a Item) {
         self.visit_item_recur(item)
     }
 
     /// don't override!
-    fn visit_inner_recur(&mut self, kind: &ItemKind) {
+    fn visit_inner_recur(&mut self, kind: &'a ItemKind) {
         match kind {
             StrippedItem(..) => unreachable!(),
             ModuleItem(i) => {
@@ -47,25 +47,22 @@ pub(crate) trait DocVisitor: Sized {
     }
 
     /// don't override!
-    fn visit_item_recur(&mut self, item: &Item) {
+    fn visit_item_recur(&mut self, item: &'a Item) {
         match &item.kind {
             StrippedItem(i) => self.visit_inner_recur(&*i),
             _ => self.visit_inner_recur(&item.kind),
         }
     }
 
-    fn visit_mod(&mut self, m: &Module) {
+    fn visit_mod(&mut self, m: &'a Module) {
         m.items.iter().for_each(|i| self.visit_item(i))
     }
 
-    fn visit_crate(&mut self, c: &Crate) {
+    fn visit_crate(&mut self, c: &'a Crate) {
         self.visit_item(&c.module);
 
-        // FIXME: make this a simple by-ref for loop once external_traits is cleaned up
-        let external_traits = { std::mem::take(&mut *c.external_traits.borrow_mut()) };
-        for (k, v) in external_traits {
-            v.items.iter().for_each(|i| self.visit_item(i));
-            c.external_traits.borrow_mut().insert(k, v);
+        for trait_ in c.external_traits.values() {
+            trait_.items.iter().for_each(|i| self.visit_item(i));
         }
     }
 }