Don't generate "Impls on Foreign Types" for std

Hack: many traits and types in std are re-exported from core or alloc. In
general, rustdoc is capable of recognizing these implementations as being
on local types. However, in at least one case, rustdoc gets confused and
labels an implementation as being on a foreign type. To make sure that
confusion doesn't pass on to the reader, consider all implementations in
std, core, and alloc to be on local types.

Author: jsha

src/librustdoc/formats/mod.rs

@@ -7,7 +7,7 @@ use rustc_hir::def_id::DefId;
 pub(crate) use renderer::{run_format, FormatRenderer};
 
 use crate::clean::{self, ItemId};
-use cache::Cache;
+use crate::html::render::Context;
 
 /// Specifies whether rendering directly implemented trait items or ones from a certain Deref
 /// impl.
@@ -65,7 +65,8 @@ impl Impl {
     // Returns true if this is an implementation on a "local" type, meaning:
     // the type is in the current crate, or the type and the trait are both
     // re-exported by the current crate.
-    pub(crate) fn is_on_local_type(&self, cache: &Cache) -> bool {
+    pub(crate) fn is_on_local_type(&self, cx: &Context<'_>) -> bool {
+        let cache = cx.cache();
         let for_type = &self.inner_impl().for_;
         if let Some(for_type_did) = for_type.def_id(cache) {
             // The "for" type is local if it's in the paths for the current crate.
@@ -80,6 +81,18 @@ impl Impl {
                 if for_type_did.krate == trait_did.krate {
                     return true;
                 }
+                // Hack: many traits and types in std are re-exported from
+                // core or alloc. In general, rustdoc is capable of recognizing
+                // these implementations as being on local types. However, in at
+                // least one case (https://github.com/rust-lang/rust/issues/97610),
+                // rustdoc gets confused and labels an implementation as being on
+                // a foreign type. To make sure that confusion doesn't pass on to
+                // the reader, consider all implementations in std, core, and alloc
+                // to be on local types.
+                let crate_name = cx.tcx().crate_name(trait_did.krate);
+                if matches!(crate_name.as_str(), "std" | "core" | "alloc") {
+                    return true;
+                }
             }
             return false;
         };

src/librustdoc/html/render/mod.rs

@@ -2281,11 +2281,10 @@ fn sidebar_trait(cx: &Context<'_>, buf: &mut Buffer, it: &clean::Item, t: &clean
         |sym| format!("<a href=\"#{1}.{0}\">{0}</a>", sym, ItemType::Method),
     );
 
-    let cache = cx.cache();
-    if let Some(implementors) = cache.implementors.get(&it.item_id.expect_def_id()) {
+    if let Some(implementors) = cx.cache().implementors.get(&it.item_id.expect_def_id()) {
         let mut res = implementors
             .iter()
-            .filter(|i| !i.is_on_local_type(cache))
+            .filter(|i| !i.is_on_local_type(cx))
             .filter_map(|i| extract_for_impl_name(&i.impl_item, cx))
             .collect::<Vec<_>>();
 

src/librustdoc/html/render/print_item.rs

@@ -823,7 +823,7 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
         }
 
         let (local, foreign) =
-            implementors.iter().partition::<Vec<_>, _>(|i| i.is_on_local_type(cache));
+            implementors.iter().partition::<Vec<_>, _>(|i| i.is_on_local_type(cx));
 
         let (mut synthetic, mut concrete): (Vec<&&Impl>, Vec<&&Impl>) =
             local.iter().partition(|i| i.inner_impl().kind.is_auto());