Auto merge of #84867 - pnkfelix:rustdoc-revert-deref-recur, r=jyn514

rustdoc: revert deref recur to resume inclusion of impl ExtTrait<Local> for ExtType

As discussed here: https://github.com/rust-lang/rust/issues/82465#issuecomment-829290384, Revert PR #80653 to resolve issue #82465.

Issue #82465 was we had stopped including certain trait implementations, namely implementations on an imported type of an imported trait *instantiated on a local type*. That bug was injected by PR #80653.

Reverting #80653 means we don't list all the methods that you have accessible via recursively applying `Deref`.

[Discussion in last week's rustc triage meeting](https://zulip-archive.rust-lang.org/238009tcompilermeetings/19557weekly2021042954818.html#236680594) led us to conclude that the bug was worse than the enhancement, and there was not an obvious fix for the bug itself. So for the short term we  remove the enhancement, while in the long term we will work on figuring out a way to have our imported trait implementation cake and eat it too.

3 files changed, 43 insertions, 89 deletions

diff --git a/src/librustdoc/html/render/context.rs b/src/librustdoc/html/render/context.rs
index d80b2db00ac..1898f5feed2 100644
--- a/src/librustdoc/html/render/context.rs
+++ b/src/librustdoc/html/render/context.rs
@@ -6,7 +6,7 @@ use std::rc::Rc;
 use std::sync::mpsc::{channel, Receiver};
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_hir::def_id::{DefId, LOCAL_CRATE};
+use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
 use rustc_span::edition::Edition;
@@ -51,9 +51,6 @@ crate struct Context<'tcx> {
     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][]
@@ -74,7 +71,7 @@ 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<'_>, 152);
+rustc_data_structures::static_assert_size!(Context<'_>, 112);
 
 /// Shared mutable state used in [`Context`] and elsewhere.
 crate struct SharedContext<'tcx> {
@@ -486,7 +483,6 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
             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),
         };
@@ -504,7 +500,6 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
             dst: self.dst.clone(),
             render_redirect_pages: self.render_redirect_pages,
             id_map: RefCell::new(IdMap::new()),
-            deref_id_map: RefCell::new(FxHashMap::default()),
             shared: Rc::clone(&self.shared),
             cache: Rc::clone(&self.cache),
         }
diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 2e940a31c2a..ebb4cfb7d48 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -1045,17 +1045,12 @@ fn render_assoc_items(
                 RenderMode::Normal
             }
             AssocItemRender::DerefFor { trait_, type_, deref_mut_ } => {
-                let id =
-                    cx.derive_id(small_url_encode(format!("deref-methods-{:#}", type_.print(cx))));
-                debug!("Adding {} to deref id map", type_.print(cx));
-                cx.deref_id_map.borrow_mut().insert(type_.def_id_full(cache).unwrap(), id.clone());
                 write!(
                     w,
-                    "<h2 id=\"{id}\" class=\"small-section-header\">\
+                    "<h2 id=\"deref-methods\" class=\"small-section-header\">\
                          Methods from {trait_}&lt;Target = {type_}&gt;\
-                         <a href=\"#{id}\" class=\"anchor\"></a>\
+                         <a href=\"#deref-methods\" class=\"anchor\"></a>\
                      </h2>",
-                    id = id,
                     trait_ = trait_.print(cx),
                     type_ = type_.print(cx),
                 );
@@ -1080,6 +1075,9 @@ fn render_assoc_items(
             );
         }
     }
+    if let AssocItemRender::DerefFor { .. } = what {
+        return;
+    }
     if !traits.is_empty() {
         let deref_impl = traits
             .iter()
@@ -1090,13 +1088,6 @@ fn render_assoc_items(
                 .any(|t| t.inner_impl().trait_.def_id_full(cache) == cx.cache.deref_mut_trait_did);
             render_deref_methods(w, cx, impl_, containing_item, has_deref_mut);
         }
-
-        // If we were already one level into rendering deref methods, we don't want to render
-        // anything after recursing into any further deref methods above.
-        if let AssocItemRender::DerefFor { .. } = what {
-            return;
-        }
-
         let (synthetic, concrete): (Vec<&&Impl>, Vec<&&Impl>) =
             traits.iter().partition(|t| t.inner_impl().synthetic);
         let (blanket_impl, concrete): (Vec<&&Impl>, _) =
@@ -2017,14 +2008,9 @@ 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.deref_id_map.borrow();
-                let id = deref_id_map
-                    .get(&real_target.def_id_full(c).unwrap())
-                    .expect("Deref section without derived id");
                 write!(
                     out,
-                    "<a class=\"sidebar-title\" href=\"#{}\">Methods from {}&lt;Target={}&gt;</a>",
-                    id,
+                    "<a class=\"sidebar-title\" href=\"#deref-methods\">Methods from {}&lt;Target={}&gt;</a>",
                     Escape(&format!("{:#}", impl_.inner_impl().trait_.as_ref().unwrap().print(cx))),
                     Escape(&format!("{:#}", real_target.print(cx))),
                 );
diff --git a/src/librustdoc/passes/collect_trait_impls.rs b/src/librustdoc/passes/collect_trait_impls.rs
index 4e621e100e3..6d7c45f6eea 100644
--- a/src/librustdoc/passes/collect_trait_impls.rs
+++ b/src/librustdoc/passes/collect_trait_impls.rs
@@ -3,8 +3,7 @@ use crate::clean::*;
 use crate::core::DocContext;
 use crate::fold::DocFolder;
 
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_hir::def_id::DefId;
+use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::ty::DefIdTree;
 use rustc_span::symbol::sym;
 
@@ -53,6 +52,39 @@ crate fn collect_trait_impls(krate: Crate, cx: &mut DocContext<'_>) -> Crate {
         }
     }
 
+    let mut cleaner = BadImplStripper { prims, items: crate_items };
+
+    // scan through included items ahead of time to splice in Deref targets to the "valid" sets
+    for it in &new_items {
+        if let ImplItem(Impl { ref for_, ref trait_, ref items, .. }) = *it.kind {
+            if cleaner.keep_impl(for_) && trait_.def_id() == cx.tcx.lang_items().deref_trait() {
+                let target = items
+                    .iter()
+                    .find_map(|item| match *item.kind {
+                        TypedefItem(ref t, true) => Some(&t.type_),
+                        _ => None,
+                    })
+                    .expect("Deref impl without Target type");
+
+                if let Some(prim) = target.primitive_type() {
+                    cleaner.prims.insert(prim);
+                } else if let Some(did) = target.def_id() {
+                    cleaner.items.insert(did.into());
+                }
+            }
+        }
+    }
+
+    new_items.retain(|it| {
+        if let ImplItem(Impl { ref for_, ref trait_, ref blanket_impl, .. }) = *it.kind {
+            cleaner.keep_impl(for_)
+                || trait_.as_ref().map_or(false, |t| cleaner.keep_impl(t))
+                || blanket_impl.is_some()
+        } else {
+            true
+        }
+    });
+
     // `tcx.crates()` doesn't include the local crate, and `tcx.all_trait_implementations`
     // doesn't work with it anyway, so pull them from the HIR map instead
     let mut extra_attrs = Vec::new();
@@ -84,53 +116,6 @@ crate fn collect_trait_impls(krate: Crate, cx: &mut DocContext<'_>) -> Crate {
         }
     }
 
-    let mut cleaner = BadImplStripper { prims, items: crate_items };
-
-    let mut type_did_to_deref_target: FxHashMap<DefId, &Type> = FxHashMap::default();
-    // Gather all type to `Deref` target edges.
-    for it in &new_items {
-        if let ImplItem(Impl { ref for_, ref trait_, ref items, .. }) = *it.kind {
-            if trait_.def_id() == cx.tcx.lang_items().deref_trait() {
-                let target = items.iter().find_map(|item| match *item.kind {
-                    TypedefItem(ref t, true) => Some(&t.type_),
-                    _ => None,
-                });
-                if let (Some(for_did), Some(target)) = (for_.def_id(), target) {
-                    type_did_to_deref_target.insert(for_did, target);
-                }
-            }
-        }
-    }
-    // Follow all `Deref` targets of included items and recursively add them as valid
-    fn add_deref_target(
-        map: &FxHashMap<DefId, &Type>,
-        cleaner: &mut BadImplStripper,
-        type_did: &DefId,
-    ) {
-        if let Some(target) = map.get(type_did) {
-            debug!("add_deref_target: type {:?}, target {:?}", type_did, target);
-            if let Some(target_prim) = target.primitive_type() {
-                cleaner.prims.insert(target_prim);
-            } else if let Some(target_did) = target.def_id() {
-                // `impl Deref<Target = S> for S`
-                if target_did == *type_did {
-                    // Avoid infinite cycles
-                    return;
-                }
-                cleaner.items.insert(target_did.into());
-                add_deref_target(map, cleaner, &target_did.into());
-            }
-        }
-    }
-    for type_did in type_did_to_deref_target.keys() {
-        // Since only the `DefId` portion of the `Type` instances is known to be same for both the
-        // `Deref` target type and the impl for type positions, this map of types is keyed by
-        // `DefId` and for convenience uses a special cleaner that accepts `DefId`s directly.
-        if cleaner.keep_impl_with_def_id(FakeDefId::Real(*type_did)) {
-            add_deref_target(&type_did_to_deref_target, &mut cleaner, type_did);
-        }
-    }
-
     let items = if let ModuleItem(Module { ref mut items, .. }) = *krate.module.kind {
         items
     } else {
@@ -138,19 +123,7 @@ crate fn collect_trait_impls(krate: Crate, cx: &mut DocContext<'_>) -> Crate {
     };
 
     items.extend(synth_impls);
-    for it in new_items.drain(..) {
-        if let ImplItem(Impl { ref for_, ref trait_, ref blanket_impl, .. }) = *it.kind {
-            if !(cleaner.keep_impl(for_)
-                || trait_.as_ref().map_or(false, |t| cleaner.keep_impl(t))
-                || blanket_impl.is_some())
-            {
-                continue;
-            }
-        }
-
-        items.push(it);
-    }
-
+    items.extend(new_items);
     krate
 }