Auto merge of #116471 - notriddle:notriddle/js-trait-alias, r=GuillaumeGomez

rustdoc: use JS to inline target type impl docs into alias

Preview docs:

- https://notriddle.com/rustdoc-html-demo-5/js-trait-alias/std/io/type.Result.html

- https://notriddle.com/rustdoc-html-demo-5/js-trait-alias-compiler/rustc_middle/ty/type.PolyTraitRef.html

This pull request also includes a bug fix for trait alias inlining across crates. This means more documentation is generated, and is why ripgrep runs slower (it's a thin wrapper on top of the `grep` crate, so 5% of its docs are now the Result type).

- Before, built with rustdoc 1.75.0-nightly (aa1a71e9e 2023-10-26), Result type alias method docs are missing: http://notriddle.com/rustdoc-html-demo-5/ripgrep-js-nightly/rg/type.Result.html
- After, built with this branch, all the methods on Result are shown: http://notriddle.com/rustdoc-html-demo-5/ripgrep-js-trait-alias/rg/type.Result.html

*Review note: This is mostly just reverting https://github.com/rust-lang/rust/pull/115201. The last commit has the new work in it.*

Fixes #115718

This is an attempt to balance three problems, each of which would
be violated by a simpler implementation:

- A type alias should show all the `impl` blocks for the target
  type, and vice versa, if they're applicable. If nothing was
  done, and rustdoc continues to match them up in HIR, this
  would not work.

- Copying the target type's docs into its aliases' HTML pages
  directly causes far too much redundant HTML text to be generated
  when a crate has large numbers of methods and large numbers
  of type aliases.

- Using JavaScript exclusively for type alias impl docs would
  be a functional regression, and could make some docs very hard
  to find for non-JS readers.

- Making sure that only applicable docs are show in the
  resulting page requires a type checkers. Do not reimplement
  the type checker in JavaScript.

So, to make it work, rustdoc stashes these type-alias-inlined docs
in a JSONP "database-lite". The file is generated in `write_shared.rs`,
included in a `<script>` tag added in `print_item.rs`, and `main.js`
takes care of patching the additional docs into the DOM.

The format of `trait.impl` and `type.impl` JS files are superficially
similar. Each line, except the JSONP wrapper itself, belongs to a crate,
and they are otherwise separate (rustdoc should be idempotent). The
"meat" of the file is HTML strings, so the frontend code is very simple.
Links are relative to the doc root, though, so the frontend needs to fix
that up, and inlined docs can reuse these files.

However, there are a few differences, caused by the sophisticated
features that type aliases have. Consider this crate graph:

```text
 ---------------------------------
 | crate A: struct Foo<T>        |
 |          type Bar = Foo<i32>  |
 |          impl X for Foo<i8>   |
 |          impl Y for Foo<i32>  |
 ---------------------------------
     |
 ----------------------------------
 | crate B: type Baz = A::Foo<i8> |
 |          type Xyy = A::Foo<i8> |
 |          impl Z for Xyy        |
 ----------------------------------
```

The type.impl/A/struct.Foo.js JS file has a structure kinda like this:

```js
JSONP({
"A": [["impl Y for Foo<i32>", "Y", "A::Bar"]],
"B": [["impl X for Foo<i8>", "X", "B::Baz", "B::Xyy"], ["impl Z for Xyy", "Z", "B::Baz"]],
});
```

When the type.impl file is loaded, only the current crate's docs are
actually used. The main reason to bundle them together is that there's
enough duplication in them for DEFLATE to remove the redundancy.

The contents of a crate are a list of impl blocks, themselves
represented as lists. The first item in the sublist is the HTML block,
the second item is the name of the trait (which goes in the sidebar),
and all others are the names of type aliases that successfully match.

This way:

- There's no need to generate these files for types that have no aliases
  in the current crate. If a dependent crate makes a type alias, it'll
  take care of generating its own docs.
- There's no need to reimplement parts of the type checker in
  JavaScript. The Rust backend does the checking, and includes its
  results in the file.
- Docs defined directly on the type alias are dropped directly in the
  HTML by `render_assoc_items`, and are accessible without JavaScript.
  The JSONP file will not list impl items that are known to be part
  of the main HTML file already.

[JSONP]: https://en.wikipedia.org/wiki/JSONP

5 files changed, 424 insertions, 101 deletions

diff --git a/src/librustdoc/html/render/context.rs b/src/librustdoc/html/render/context.rs
index bf8d1a80337..6da9e45a1da 100644
--- a/src/librustdoc/html/render/context.rs
+++ b/src/librustdoc/html/render/context.rs
@@ -7,10 +7,8 @@ use std::sync::mpsc::{channel, Receiver};
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def_id::{DefIdMap, LOCAL_CRATE};
-use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
-use rustc_span::def_id::DefId;
 use rustc_span::edition::Edition;
 use rustc_span::source_map::FileName;
 use rustc_span::{sym, Symbol};
@@ -25,13 +23,13 @@ use super::{
     AllTypes, LinkFromSrc, StylePath,
 };
 use crate::clean::utils::has_doc_flag;
-use crate::clean::{self, types::ExternalLocation, ExternalCrate, TypeAliasItem};
+use crate::clean::{self, types::ExternalLocation, ExternalCrate};
 use crate::config::{ModuleSorting, RenderOptions};
 use crate::docfs::{DocFS, PathError};
 use crate::error::Error;
 use crate::formats::cache::Cache;
 use crate::formats::item_type::ItemType;
-use crate::formats::{self, FormatRenderer};
+use crate::formats::FormatRenderer;
 use crate::html::escape::Escape;
 use crate::html::format::{join_with_double_colon, Buffer};
 use crate::html::markdown::{self, plain_text_summary, ErrorCodes, IdMap};
@@ -150,53 +148,6 @@ impl SharedContext<'_> {
     pub(crate) fn edition(&self) -> Edition {
         self.tcx.sess.edition()
     }
-
-    /// Returns a list of impls on the given type, and, if it's a type alias,
-    /// other types that it aliases.
-    pub(crate) fn all_impls_for_item<'a>(
-        &'a self,
-        it: &clean::Item,
-        did: DefId,
-    ) -> Vec<&'a formats::Impl> {
-        let tcx = self.tcx;
-        let cache = &self.cache;
-        let mut saw_impls = FxHashSet::default();
-        let mut v: Vec<&formats::Impl> = cache
-            .impls
-            .get(&did)
-            .map(Vec::as_slice)
-            .unwrap_or(&[])
-            .iter()
-            .filter(|i| saw_impls.insert(i.def_id()))
-            .collect();
-        if let TypeAliasItem(ait) = &*it.kind &&
-            let aliased_clean_type = ait.item_type.as_ref().unwrap_or(&ait.type_) &&
-            let Some(aliased_type_defid) = aliased_clean_type.def_id(cache) &&
-            let Some(av) = cache.impls.get(&aliased_type_defid) &&
-            let Some(alias_def_id) = it.item_id.as_def_id()
-        {
-            // This branch of the compiler compares types structually, but does
-            // not check trait bounds. That's probably fine, since type aliases
-            // don't normally constrain on them anyway.
-            // https://github.com/rust-lang/rust/issues/21903
-            //
-            // FIXME(lazy_type_alias): Once the feature is complete or stable, rewrite this to use type unification.
-            // Be aware of `tests/rustdoc/issue-112515-impl-ty-alias.rs` which might regress.
-            let aliased_ty = tcx.type_of(alias_def_id).skip_binder();
-            let reject_cx = DeepRejectCtxt {
-                treat_obligation_params: TreatParams::AsCandidateKey,
-            };
-            v.extend(av.iter().filter(|impl_| {
-                if let Some(impl_def_id) = impl_.impl_item.item_id.as_def_id() {
-                    reject_cx.types_may_unify(aliased_ty, tcx.type_of(impl_def_id).skip_binder())
-                        && saw_impls.insert(impl_def_id)
-                } else {
-                    false
-                }
-            }));
-        }
-        v
-    }
 }
 
 impl<'tcx> Context<'tcx> {
diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index e01341acf43..d9086433608 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -1145,13 +1145,13 @@ pub(crate) fn render_all_impls(
 fn render_assoc_items<'a, 'cx: 'a>(
     cx: &'a mut Context<'cx>,
     containing_item: &'a clean::Item,
-    did: DefId,
+    it: DefId,
     what: AssocItemRender<'a>,
 ) -> impl fmt::Display + 'a + Captures<'cx> {
     let mut derefs = DefIdSet::default();
-    derefs.insert(did);
+    derefs.insert(it);
     display_fn(move |f| {
-        render_assoc_items_inner(f, cx, containing_item, did, what, &mut derefs);
+        render_assoc_items_inner(f, cx, containing_item, it, what, &mut derefs);
         Ok(())
     })
 }
@@ -1160,17 +1160,15 @@ fn render_assoc_items_inner(
     mut w: &mut dyn fmt::Write,
     cx: &mut Context<'_>,
     containing_item: &clean::Item,
-    did: DefId,
+    it: DefId,
     what: AssocItemRender<'_>,
     derefs: &mut DefIdSet,
 ) {
     info!("Documenting associated items of {:?}", containing_item.name);
     let shared = Rc::clone(&cx.shared);
-    let v = shared.all_impls_for_item(containing_item, did);
-    let v = v.as_slice();
-    let (non_trait, traits): (Vec<&Impl>, _) =
-        v.iter().partition(|i| i.inner_impl().trait_.is_none());
-    let mut saw_impls = FxHashSet::default();
+    let cache = &shared.cache;
+    let Some(v) = cache.impls.get(&it) else { return };
+    let (non_trait, traits): (Vec<_>, _) = v.iter().partition(|i| i.inner_impl().trait_.is_none());
     if !non_trait.is_empty() {
         let mut tmp_buf = Buffer::html();
         let (render_mode, id, class_html) = match what {
@@ -1199,9 +1197,6 @@ fn render_assoc_items_inner(
         };
         let mut impls_buf = Buffer::html();
         for i in &non_trait {
-            if !saw_impls.insert(i.def_id()) {
-                continue;
-            }
             render_impl(
                 &mut impls_buf,
                 cx,
@@ -1247,10 +1242,8 @@ fn render_assoc_items_inner(
 
         let (synthetic, concrete): (Vec<&Impl>, Vec<&Impl>) =
             traits.into_iter().partition(|t| t.inner_impl().kind.is_auto());
-        let (blanket_impl, concrete): (Vec<&Impl>, _) = concrete
-            .into_iter()
-            .filter(|t| saw_impls.insert(t.def_id()))
-            .partition(|t| t.inner_impl().kind.is_blanket());
+        let (blanket_impl, concrete): (Vec<&Impl>, _) =
+            concrete.into_iter().partition(|t| t.inner_impl().kind.is_blanket());
 
         render_all_impls(w, cx, containing_item, &concrete, &synthetic, &blanket_impl);
     }
diff --git a/src/librustdoc/html/render/print_item.rs b/src/librustdoc/html/render/print_item.rs
index f6432dc61ae..fdf45569061 100644
--- a/src/librustdoc/html/render/print_item.rs
+++ b/src/librustdoc/html/render/print_item.rs
@@ -1066,6 +1066,8 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
         }
     }
 
+    // [RUSTDOCIMPL] trait.impl
+    //
     // Include implementors in crates that depend on the current crate.
     //
     // This is complicated by the way rustdoc is invoked, which is basically
@@ -1101,7 +1103,7 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
     // ```
     //
     // Basically, we want `C::Baz` and `A::Foo` to show the same set of
-    // impls, which is easier if they both treat `/implementors/A/trait.Foo.js`
+    // impls, which is easier if they both treat `/trait.impl/A/trait.Foo.js`
     // as the Single Source of Truth.
     //
     // We also want the `impl Baz for Quux` to be written to
@@ -1110,7 +1112,7 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
     // because that'll load faster, and it's better for SEO. And we don't want
     // the same impl to show up twice on the same page.
     //
-    // To make this work, the implementors JS file has a structure kinda
+    // To make this work, the trait.impl/A/trait.Foo.js JS file has a structure kinda
     // like this:
     //
     // ```js
@@ -1127,7 +1129,7 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
     // So C's HTML will have something like this:
     //
     // ```html
-    // <script src="/implementors/A/trait.Foo.js"
+    // <script src="/trait.impl/A/trait.Foo.js"
     //     data-ignore-extern-crates="A,B" async></script>
     // ```
     //
@@ -1137,7 +1139,7 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
     // [JSONP]: https://en.wikipedia.org/wiki/JSONP
     let mut js_src_path: UrlPartsBuilder = std::iter::repeat("..")
         .take(cx.current.len())
-        .chain(std::iter::once("implementors"))
+        .chain(std::iter::once("trait.impl"))
         .collect();
     if let Some(did) = it.item_id.as_def_id() &&
         let get_extern = { || cache.external_paths.get(&did).map(|s| &s.0) } &&
@@ -1319,6 +1321,102 @@ fn item_type_alias(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &c
     // we need #14072 to make sense of the generics.
     write!(w, "{}", render_assoc_items(cx, it, def_id, AssocItemRender::All));
     write!(w, "{}", document_type_layout(cx, def_id));
+
+    // [RUSTDOCIMPL] type.impl
+    //
+    // Include type definitions from the alias target type.
+    //
+    // Earlier versions of this code worked by having `render_assoc_items`
+    // include this data directly. That generates *O*`(types*impls)` of HTML
+    // text, and some real crates have a lot of types and impls.
+    //
+    // To create the same UX without generating half a gigabyte of HTML for a
+    // crate that only contains 20 megabytes of actual documentation[^115718],
+    // rustdoc stashes these type-alias-inlined docs in a [JSONP]
+    // "database-lite". The file itself is generated in `write_shared.rs`,
+    // and hooks into functions provided by `main.js`.
+    //
+    // The format of `trait.impl` and `type.impl` JS files are superficially
+    // similar. Each line, except the JSONP wrapper itself, belongs to a crate,
+    // and they are otherwise separate (rustdoc should be idempotent). The
+    // "meat" of the file is HTML strings, so the frontend code is very simple.
+    // Links are relative to the doc root, though, so the frontend needs to fix
+    // that up, and inlined docs can reuse these files.
+    //
+    // However, there are a few differences, caused by the sophisticated
+    // features that type aliases have. Consider this crate graph:
+    //
+    // ```text
+    //  ---------------------------------
+    //  | crate A: struct Foo<T>        |
+    //  |          type Bar = Foo<i32>  |
+    //  |          impl X for Foo<i8>   |
+    //  |          impl Y for Foo<i32>  |
+    //  ---------------------------------
+    //      |
+    //  ----------------------------------
+    //  | crate B: type Baz = A::Foo<i8> |
+    //  |          type Xyy = A::Foo<i8> |
+    //  |          impl Z for Xyy        |
+    //  ----------------------------------
+    // ```
+    //
+    // The type.impl/A/struct.Foo.js JS file has a structure kinda like this:
+    //
+    // ```js
+    // JSONP({
+    // "A": [["impl Y for Foo<i32>", "Y", "A::Bar"]],
+    // "B": [["impl X for Foo<i8>", "X", "B::Baz", "B::Xyy"], ["impl Z for Xyy", "Z", "B::Baz"]],
+    // });
+    // ```
+    //
+    // When the type.impl file is loaded, only the current crate's docs are
+    // actually used. The main reason to bundle them together is that there's
+    // enough duplication in them for DEFLATE to remove the redundancy.
+    //
+    // The contents of a crate are a list of impl blocks, themselves
+    // represented as lists. The first item in the sublist is the HTML block,
+    // the second item is the name of the trait (which goes in the sidebar),
+    // and all others are the names of type aliases that successfully match.
+    //
+    // This way:
+    //
+    // - There's no need to generate these files for types that have no aliases
+    //   in the current crate. If a dependent crate makes a type alias, it'll
+    //   take care of generating its own docs.
+    // - There's no need to reimplement parts of the type checker in
+    //   JavaScript. The Rust backend does the checking, and includes its
+    //   results in the file.
+    // - Docs defined directly on the type alias are dropped directly in the
+    //   HTML by `render_assoc_items`, and are accessible without JavaScript.
+    //   The JSONP file will not list impl items that are known to be part
+    //   of the main HTML file already.
+    //
+    // [JSONP]: https://en.wikipedia.org/wiki/JSONP
+    // [^115718]: https://github.com/rust-lang/rust/issues/115718
+    let cloned_shared = Rc::clone(&cx.shared);
+    let cache = &cloned_shared.cache;
+    if let Some(target_did) = t.type_.def_id(cache) &&
+        let get_extern = { || cache.external_paths.get(&target_did) } &&
+        let Some(&(ref target_fqp, target_type)) = cache.paths.get(&target_did).or_else(get_extern) &&
+        target_type.is_adt() && // primitives cannot be inlined
+        let Some(self_did) = it.item_id.as_def_id() &&
+        let get_local = { || cache.paths.get(&self_did).map(|(p, _)| p) } &&
+        let Some(self_fqp) = cache.exact_paths.get(&self_did).or_else(get_local)
+    {
+        let mut js_src_path: UrlPartsBuilder = std::iter::repeat("..")
+            .take(cx.current.len())
+            .chain(std::iter::once("type.impl"))
+            .collect();
+        js_src_path.extend(target_fqp[..target_fqp.len() - 1].iter().copied());
+        js_src_path.push_fmt(format_args!("{target_type}.{}.js", target_fqp.last().unwrap()));
+        let self_path = self_fqp.iter().map(Symbol::as_str).collect::<Vec<&str>>().join("::");
+        write!(
+            w,
+            "<script src=\"{src}\" data-self-path=\"{self_path}\" async></script>",
+            src = js_src_path.finish(),
+        );
+    }
 }
 
 fn item_union(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, s: &clean::Union) {
diff --git a/src/librustdoc/html/render/sidebar.rs b/src/librustdoc/html/render/sidebar.rs
index fb429f237e3..4e8d88c55b6 100644
--- a/src/librustdoc/html/render/sidebar.rs
+++ b/src/librustdoc/html/render/sidebar.rs
@@ -38,18 +38,19 @@ pub(crate) struct LinkBlock<'a> {
     /// as well as the link to it, e.g. `#implementations`.
     /// Will be rendered inside an `<h3>` tag
     heading: Link<'a>,
+    class: &'static str,
     links: Vec<Link<'a>>,
     /// Render the heading even if there are no links
     force_render: bool,
 }
 
 impl<'a> LinkBlock<'a> {
-    pub fn new(heading: Link<'a>, links: Vec<Link<'a>>) -> Self {
-        Self { heading, links, force_render: false }
+    pub fn new(heading: Link<'a>, class: &'static str, links: Vec<Link<'a>>) -> Self {
+        Self { heading, links, class, force_render: false }
     }
 
-    pub fn forced(heading: Link<'a>) -> Self {
-        Self { heading, links: vec![], force_render: true }
+    pub fn forced(heading: Link<'a>, class: &'static str) -> Self {
+        Self { heading, links: vec![], class, force_render: true }
     }
 
     pub fn should_render(&self) -> bool {
@@ -157,7 +158,7 @@ fn sidebar_struct<'a>(
     };
     let mut items = vec![];
     if let Some(name) = field_name {
-        items.push(LinkBlock::new(Link::new("fields", name), fields));
+        items.push(LinkBlock::new(Link::new("fields", name), "structfield", fields));
     }
     sidebar_assoc_items(cx, it, &mut items);
     items
@@ -214,12 +215,15 @@ fn sidebar_trait<'a>(
         ("foreign-impls", "Implementations on Foreign Types", foreign_impls),
     ]
     .into_iter()
-    .map(|(id, title, items)| LinkBlock::new(Link::new(id, title), items))
+    .map(|(id, title, items)| LinkBlock::new(Link::new(id, title), "", items))
     .collect();
     sidebar_assoc_items(cx, it, &mut blocks);
-    blocks.push(LinkBlock::forced(Link::new("implementors", "Implementors")));
+    blocks.push(LinkBlock::forced(Link::new("implementors", "Implementors"), "impl"));
     if t.is_auto(cx.tcx()) {
-        blocks.push(LinkBlock::forced(Link::new("synthetic-implementors", "Auto Implementors")));
+        blocks.push(LinkBlock::forced(
+            Link::new("synthetic-implementors", "Auto Implementors"),
+            "impl-auto",
+        ));
     }
     blocks
 }
@@ -245,7 +249,7 @@ fn sidebar_type_alias<'a>(
 ) -> Vec<LinkBlock<'a>> {
     let mut items = vec![];
     if let Some(inner_type) = &t.inner_type {
-        items.push(LinkBlock::forced(Link::new("aliased-type", "Aliased type")));
+        items.push(LinkBlock::forced(Link::new("aliased-type", "Aliased type"), "type"));
         match inner_type {
             clean::TypeAliasInnerType::Enum { variants, is_non_exhaustive: _ } => {
                 let mut variants = variants
@@ -256,12 +260,12 @@ fn sidebar_type_alias<'a>(
                     .collect::<Vec<_>>();
                 variants.sort_unstable();
 
-                items.push(LinkBlock::new(Link::new("variants", "Variants"), variants));
+                items.push(LinkBlock::new(Link::new("variants", "Variants"), "variant", variants));
             }
             clean::TypeAliasInnerType::Union { fields }
             | clean::TypeAliasInnerType::Struct { ctor_kind: _, fields } => {
                 let fields = get_struct_fields_name(fields);
-                items.push(LinkBlock::new(Link::new("fields", "Fields"), fields));
+                items.push(LinkBlock::new(Link::new("fields", "Fields"), "field", fields));
             }
         }
     }
@@ -275,7 +279,7 @@ fn sidebar_union<'a>(
     u: &'a clean::Union,
 ) -> Vec<LinkBlock<'a>> {
     let fields = get_struct_fields_name(&u.fields);
-    let mut items = vec![LinkBlock::new(Link::new("fields", "Fields"), fields)];
+    let mut items = vec![LinkBlock::new(Link::new("fields", "Fields"), "structfield", fields)];
     sidebar_assoc_items(cx, it, &mut items);
     items
 }
@@ -287,12 +291,11 @@ fn sidebar_assoc_items<'a>(
     links: &mut Vec<LinkBlock<'a>>,
 ) {
     let did = it.item_id.expect_def_id();
-    let v = cx.shared.all_impls_for_item(it, it.item_id.expect_def_id());
-    let v = v.as_slice();
+    let cache = cx.cache();
 
     let mut assoc_consts = Vec::new();
     let mut methods = Vec::new();
-    if !v.is_empty() {
+    if let Some(v) = cache.impls.get(&did) {
         let mut used_links = FxHashSet::default();
         let mut id_map = IdMap::new();
 
@@ -328,7 +331,7 @@ fn sidebar_assoc_items<'a>(
                     cx,
                     &mut deref_methods,
                     impl_,
-                    v.iter().copied(),
+                    v,
                     &mut derefs,
                     &mut used_links,
                 );
@@ -341,12 +344,16 @@ fn sidebar_assoc_items<'a>(
 
             sidebar_render_assoc_items(cx, &mut id_map, concrete, synthetic, blanket_impl)
         } else {
-            std::array::from_fn(|_| LinkBlock::new(Link::empty(), vec![]))
+            std::array::from_fn(|_| LinkBlock::new(Link::empty(), "", vec![]))
         };
 
         let mut blocks = vec![
-            LinkBlock::new(Link::new("implementations", "Associated Constants"), assoc_consts),
-            LinkBlock::new(Link::new("implementations", "Methods"), methods),
+            LinkBlock::new(
+                Link::new("implementations", "Associated Constants"),
+                "associatedconstant",
+                assoc_consts,
+            ),
+            LinkBlock::new(Link::new("implementations", "Methods"), "method", methods),
         ];
         blocks.append(&mut deref_methods);
         blocks.extend([concrete, synthetic, blanket]);
@@ -358,7 +365,7 @@ fn sidebar_deref_methods<'a>(
     cx: &'a Context<'_>,
     out: &mut Vec<LinkBlock<'a>>,
     impl_: &Impl,
-    v: impl Iterator<Item = &'a Impl>,
+    v: &[Impl],
     derefs: &mut DefIdSet,
     used_links: &mut FxHashSet<String>,
 ) {
@@ -383,7 +390,7 @@ fn sidebar_deref_methods<'a>(
             // Avoid infinite cycles
             return;
         }
-        let deref_mut = { v }.any(|i| i.trait_did() == cx.tcx().lang_items().deref_mut_trait());
+        let deref_mut = v.iter().any(|i| i.trait_did() == cx.tcx().lang_items().deref_mut_trait());
         let inner_impl = target
             .def_id(c)
             .or_else(|| {
@@ -415,7 +422,7 @@ fn sidebar_deref_methods<'a>(
                 );
                 // We want links' order to be reproducible so we don't use unstable sort.
                 ret.sort();
-                out.push(LinkBlock::new(Link::new(id, title), ret));
+                out.push(LinkBlock::new(Link::new(id, title), "deref-methods", ret));
             }
         }
 
@@ -434,7 +441,7 @@ fn sidebar_deref_methods<'a>(
                 cx,
                 out,
                 target_deref_impl,
-                target_impls.iter(),
+                target_impls,
                 derefs,
                 used_links,
             );
@@ -454,7 +461,7 @@ fn sidebar_enum<'a>(
         .collect::<Vec<_>>();
     variants.sort_unstable();
 
-    let mut items = vec![LinkBlock::new(Link::new("variants", "Variants"), variants)];
+    let mut items = vec![LinkBlock::new(Link::new("variants", "Variants"), "variant", variants)];
     sidebar_assoc_items(cx, it, &mut items);
     items
 }
@@ -468,7 +475,7 @@ pub(crate) fn sidebar_module_like(
         .filter(|sec| item_sections_in_use.contains(sec))
         .map(|sec| Link::new(sec.id(), sec.name()))
         .collect();
-    LinkBlock::new(Link::empty(), item_sections)
+    LinkBlock::new(Link::empty(), "", item_sections)
 }
 
 fn sidebar_module(items: &[clean::Item]) -> LinkBlock<'static> {
@@ -529,12 +536,21 @@ fn sidebar_render_assoc_items(
     let synthetic = format_impls(synthetic, id_map);
     let blanket = format_impls(blanket_impl, id_map);
     [
-        LinkBlock::new(Link::new("trait-implementations", "Trait Implementations"), concrete),
+        LinkBlock::new(
+            Link::new("trait-implementations", "Trait Implementations"),
+            "trait-implementation",
+            concrete,
+        ),
         LinkBlock::new(
             Link::new("synthetic-implementations", "Auto Trait Implementations"),
+            "synthetic-implementation",
             synthetic,
         ),
-        LinkBlock::new(Link::new("blanket-implementations", "Blanket Implementations"), blanket),
+        LinkBlock::new(
+            Link::new("blanket-implementations", "Blanket Implementations"),
+            "blanket-implementation",
+            blanket,
+        ),
     ]
 }
 
diff --git a/src/librustdoc/html/render/write_shared.rs b/src/librustdoc/html/render/write_shared.rs
index e68d5ab2fbd..3e58dd96ed9 100644
--- a/src/librustdoc/html/render/write_shared.rs
+++ b/src/librustdoc/html/render/write_shared.rs
@@ -5,18 +5,28 @@ use std::io::{self, BufReader};
 use std::path::{Component, Path};
 use std::rc::{Rc, Weak};
 
+use indexmap::IndexMap;
 use itertools::Itertools;
 use rustc_data_structures::flock;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
+use rustc_span::def_id::DefId;
+use rustc_span::Symbol;
 use serde::ser::SerializeSeq;
 use serde::{Serialize, Serializer};
 
 use super::{collect_paths_for_type, ensure_trailing_slash, Context};
-use crate::clean::Crate;
+use crate::clean::{Crate, Item, ItemId, ItemKind};
 use crate::config::{EmitType, RenderOptions};
 use crate::docfs::PathError;
 use crate::error::Error;
+use crate::formats::cache::Cache;
+use crate::formats::item_type::ItemType;
+use crate::formats::{Impl, RenderMode};
+use crate::html::format::Buffer;
+use crate::html::render::{AssocItemLink, ImplRenderingParameters};
 use crate::html::{layout, static_files};
+use crate::visit::DocVisitor;
 use crate::{try_err, try_none};
 
 /// Rustdoc writes out two kinds of shared files:
@@ -361,9 +371,264 @@ if (typeof exports !== 'undefined') {exports.searchIndex = searchIndex};
         }
     }
 
+    let cloned_shared = Rc::clone(&cx.shared);
+    let cache = &cloned_shared.cache;
+
+    // Collect the list of aliased types and their aliases.
+    // <https://github.com/search?q=repo%3Arust-lang%2Frust+[RUSTDOCIMPL]+type.impl&type=code>
+    //
+    // The clean AST has type aliases that point at their types, but
+    // 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> {
+        // Map from DefId-of-aliased-type to its data.
+        aliased_types: IndexMap<DefId, AliasedType<'cache>>,
+        visited_aliases: FxHashSet<DefId>,
+        cache: &'cache Cache,
+        cx: &'cache mut Context<'cx>,
+    }
+    // Data for an aliased type.
+    //
+    // In the final file, the format will be roughly:
+    //
+    // ```json
+    // // type.impl/CRATE/TYPENAME.js
+    // JSONP(
+    // "CRATE": [
+    //   ["IMPL1 HTML", "ALIAS1", "ALIAS2", ...],
+    //   ["IMPL2 HTML", "ALIAS3", "ALIAS4", ...],
+    //    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ struct AliasedType
+    //   ...
+    // ]
+    // )
+    // ```
+    struct AliasedType<'cache> {
+        // 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>>,
+    }
+    // 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> {
+        impl_: &'cache Impl,
+        type_aliases: Vec<(&'cache [Symbol], Item)>,
+    }
+    impl<'cx, 'cache> DocVisitor for TypeImplCollector<'cx, 'cache> {
+        fn visit_item(&mut self, it: &Item) {
+            self.visit_item_recur(it);
+            let cache = self.cache;
+            let ItemKind::TypeAliasItem(ref t) = *it.kind else { return };
+            let Some(self_did) = it.item_id.as_def_id() else { return };
+            if !self.visited_aliases.insert(self_did) {
+                return;
+            }
+            let Some(target_did) = t.type_.def_id(cache) else { return };
+            let get_extern = { || cache.external_paths.get(&target_did) };
+            let Some(&(ref target_fqp, target_type)) =
+                cache.paths.get(&target_did).or_else(get_extern)
+            else {
+                return;
+            };
+            let aliased_type = self.aliased_types.entry(target_did).or_insert_with(|| {
+                let impl_ = cache
+                    .impls
+                    .get(&target_did)
+                    .map(|v| &v[..])
+                    .unwrap_or_default()
+                    .iter()
+                    .map(|impl_| {
+                        (
+                            impl_.impl_item.item_id,
+                            AliasedTypeImpl { impl_, type_aliases: Vec::new() },
+                        )
+                    })
+                    .collect();
+                AliasedType { target_fqp: &target_fqp[..], target_type, impl_ }
+            });
+            let get_local = { || cache.paths.get(&self_did).map(|(p, _)| p) };
+            let Some(self_fqp) = cache.exact_paths.get(&self_did).or_else(get_local) else {
+                return;
+            };
+            let aliased_ty = self.cx.tcx().type_of(self_did).skip_binder();
+            // Exclude impls that are directly on this type. They're already in the HTML.
+            // Some inlining scenarios can cause there to be two versions of the same
+            // impl: one on the type alias and one on the underlying target type.
+            let mut seen_impls: FxHashSet<ItemId> = cache
+                .impls
+                .get(&self_did)
+                .map(|s| &s[..])
+                .unwrap_or_default()
+                .iter()
+                .map(|i| i.impl_item.item_id)
+                .collect();
+            for (impl_item_id, aliased_type_impl) in &mut aliased_type.impl_ {
+                // Only include this impl if it actually unifies with this alias.
+                // Synthetic impls are not included; those are also included in the HTML.
+                //
+                // FIXME(lazy_type_alias): Once the feature is complete or stable, rewrite this
+                // to use type unification.
+                // Be aware of `tests/rustdoc/type-alias/deeply-nested-112515.rs` which might regress.
+                let Some(impl_did) = impl_item_id.as_def_id() else { continue };
+                let for_ty = self.cx.tcx().type_of(impl_did).skip_binder();
+                let reject_cx =
+                    DeepRejectCtxt { treat_obligation_params: TreatParams::AsCandidateKey };
+                if !reject_cx.types_may_unify(aliased_ty, for_ty) {
+                    continue;
+                }
+                // Avoid duplicates
+                if !seen_impls.insert(*impl_item_id) {
+                    continue;
+                }
+                // This impl was not found in the set of rejected impls
+                aliased_type_impl.type_aliases.push((&self_fqp[..], it.clone()));
+            }
+        }
+    }
+    let mut type_impl_collector = TypeImplCollector {
+        aliased_types: IndexMap::default(),
+        visited_aliases: FxHashSet::default(),
+        cache,
+        cx,
+    };
+    DocVisitor::visit_crate(&mut type_impl_collector, &krate);
+    // Final serialized form of the alias impl
+    struct AliasSerializableImpl {
+        text: String,
+        trait_: Option<String>,
+        aliases: Vec<String>,
+    }
+    impl Serialize for AliasSerializableImpl {
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: Serializer,
+        {
+            let mut seq = serializer.serialize_seq(None)?;
+            seq.serialize_element(&self.text)?;
+            if let Some(trait_) = &self.trait_ {
+                seq.serialize_element(trait_)?;
+            } else {
+                seq.serialize_element(&0)?;
+            }
+            for type_ in &self.aliases {
+                seq.serialize_element(type_)?;
+            }
+            seq.end()
+        }
+    }
+    let cx = type_impl_collector.cx;
+    let dst = cx.dst.join("type.impl");
+    let aliased_types = type_impl_collector.aliased_types;
+    for aliased_type in aliased_types.values() {
+        let impls = aliased_type
+            .impl_
+            .values()
+            .flat_map(|AliasedTypeImpl { impl_, type_aliases }| {
+                let mut ret = Vec::new();
+                let trait_ = impl_
+                    .inner_impl()
+                    .trait_
+                    .as_ref()
+                    .map(|trait_| format!("{:#}", trait_.print(cx)));
+                // render_impl will filter out "impossible-to-call" methods
+                // to make that functionality work here, it needs to be called with
+                // each type alias, and if it gives a different result, split the impl
+                for &(type_alias_fqp, ref type_alias_item) in type_aliases {
+                    let mut buf = Buffer::html();
+                    cx.id_map = Default::default();
+                    cx.deref_id_map = Default::default();
+                    let target_did = impl_
+                        .inner_impl()
+                        .trait_
+                        .as_ref()
+                        .map(|trait_| trait_.def_id())
+                        .or_else(|| impl_.inner_impl().for_.def_id(cache));
+                    let provided_methods;
+                    let assoc_link = if let Some(target_did) = target_did {
+                        provided_methods = impl_.inner_impl().provided_trait_methods(cx.tcx());
+                        AssocItemLink::GotoSource(ItemId::DefId(target_did), &provided_methods)
+                    } else {
+                        AssocItemLink::Anchor(None)
+                    };
+                    super::render_impl(
+                        &mut buf,
+                        cx,
+                        *impl_,
+                        &type_alias_item,
+                        assoc_link,
+                        RenderMode::Normal,
+                        None,
+                        &[],
+                        ImplRenderingParameters {
+                            show_def_docs: true,
+                            show_default_items: true,
+                            show_non_assoc_items: true,
+                            toggle_open_by_default: true,
+                        },
+                    );
+                    let text = buf.into_inner();
+                    let type_alias_fqp = (*type_alias_fqp).iter().join("::");
+                    if Some(&text) == ret.last().map(|s: &AliasSerializableImpl| &s.text) {
+                        ret.last_mut()
+                            .expect("already established that ret.last() is Some()")
+                            .aliases
+                            .push(type_alias_fqp);
+                    } else {
+                        ret.push(AliasSerializableImpl {
+                            text,
+                            trait_: trait_.clone(),
+                            aliases: vec![type_alias_fqp],
+                        })
+                    }
+                }
+                ret
+            })
+            .collect::<Vec<_>>();
+        let impls = format!(
+            r#""{}":{}"#,
+            krate.name(cx.tcx()),
+            serde_json::to_string(&impls).expect("failed serde conversion"),
+        );
+
+        let mut mydst = dst.clone();
+        for part in &aliased_type.target_fqp[..aliased_type.target_fqp.len() - 1] {
+            mydst.push(part.to_string());
+        }
+        cx.shared.ensure_dir(&mydst)?;
+        let aliased_item_type = aliased_type.target_type;
+        mydst.push(&format!(
+            "{aliased_item_type}.{}.js",
+            aliased_type.target_fqp[aliased_type.target_fqp.len() - 1]
+        ));
+
+        let (mut all_impls, _) = try_err!(collect(&mydst, krate.name(cx.tcx()).as_str()), &mydst);
+        all_impls.push(impls);
+        // Sort the implementors by crate so the file will be generated
+        // identically even with rustdoc running in parallel.
+        all_impls.sort();
+
+        let mut v = String::from("(function() {var type_impls = {\n");
+        v.push_str(&all_impls.join(",\n"));
+        v.push_str("\n};");
+        v.push_str(
+            "if (window.register_type_impls) {\
+                 window.register_type_impls(type_impls);\
+             } else {\
+                 window.pending_type_impls = type_impls;\
+             }",
+        );
+        v.push_str("})()");
+        cx.shared.fs.write(mydst, v)?;
+    }
+
     // Update the list of all implementors for traits
-    let dst = cx.dst.join("implementors");
-    let cache = cx.cache();
+    // <https://github.com/search?q=repo%3Arust-lang%2Frust+[RUSTDOCIMPL]+trait.impl&type=code>
+    let dst = cx.dst.join("trait.impl");
     for (&did, imps) in &cache.implementors {
         // Private modules can leak through to this phase of rustdoc, which
         // could contain implementations for otherwise private types. In some