de-rc external traits

Don't keep the `external_traits` as shared mutable data between the
`DocContext` and `clean::Crate`. Instead, move the data over when necessary.
This allows us to get rid of a borrowck hack in the `DocVisitor`.

Author: Lukas Markeffsky

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);
 }

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 {

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>(

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());

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

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

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
 }
 

src/librustdoc/visit.rs

@@ -61,11 +61,8 @@ pub(crate) trait DocVisitor: Sized {
     fn visit_crate(&mut self, c: &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));
         }
     }
 }