3 files changed, 60 insertions, 17 deletions
diff --git a/src/librustdoc/html/render/mod.rs b/src/librustdoc/html/render/mod.rs
index 3e671a64b54..b0ce475850c 100644
--- a/src/librustdoc/html/render/mod.rs
+++ b/src/librustdoc/html/render/mod.rs
@@ -54,7 +54,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def_id::{DefId, DefIdSet};
 use rustc_hir::Mutability;
 use rustc_middle::middle::stability;
-use rustc_middle::ty::TyCtxt;
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::{
     symbol::{sym, Symbol},
     BytePos, FileName, RealFileName,
@@ -102,6 +102,7 @@ pub(crate) struct IndexItem {
     pub(crate) desc: String,
     pub(crate) parent: Option<DefId>,
     pub(crate) parent_idx: Option<isize>,
+    pub(crate) impl_id: Option<DefId>,
     pub(crate) search_type: Option<IndexItemFunctionType>,
     pub(crate) aliases: Box<[Symbol]>,
     pub(crate) deprecation: Option<Deprecation>,
@@ -1877,7 +1878,7 @@ pub(crate) fn render_impl_summary(
     aliases: &[String],
 ) {
     let inner_impl = i.inner_impl();
-    let id = cx.derive_id(get_id_for_impl(&inner_impl.for_, inner_impl.trait_.as_ref(), cx));
+    let id = cx.derive_id(get_id_for_impl(cx.tcx(), i.impl_item.item_id));
     let aliases = if aliases.is_empty() {
         String::new()
     } else {
@@ -1994,21 +1995,35 @@ pub(crate) fn small_url_encode(s: String) -> String {
     }
 }
 
-fn get_id_for_impl(for_: &clean::Type, trait_: Option<&clean::Path>, cx: &Context<'_>) -> String {
-    match trait_ {
-        Some(t) => small_url_encode(format!("impl-{:#}-for-{:#}", t.print(cx), for_.print(cx))),
-        None => small_url_encode(format!("impl-{:#}", for_.print(cx))),
-    }
+fn get_id_for_impl<'tcx>(tcx: TyCtxt<'tcx>, impl_id: ItemId) -> String {
+    use rustc_middle::ty::print::with_forced_trimmed_paths;
+    let (type_, trait_) = match impl_id {
+        ItemId::Auto { trait_, for_ } => {
+            let ty = tcx.type_of(for_).skip_binder();
+            (ty, Some(ty::TraitRef::new(tcx, trait_, [ty])))
+        }
+        ItemId::Blanket { impl_id, .. } | ItemId::DefId(impl_id) => {
+            match tcx.impl_subject(impl_id).skip_binder() {
+                ty::ImplSubject::Trait(trait_ref) => {
+                    (trait_ref.args[0].expect_ty(), Some(trait_ref))
+                }
+                ty::ImplSubject::Inherent(ty) => (ty, None),
+            }
+        }
+    };
+    with_forced_trimmed_paths!(small_url_encode(if let Some(trait_) = trait_ {
+        format!("impl-{trait_}-for-{type_}", trait_ = trait_.print_only_trait_path())
+    } else {
+        format!("impl-{type_}")
+    }))
 }
 
 fn extract_for_impl_name(item: &clean::Item, cx: &Context<'_>) -> Option<(String, String)> {
     match *item.kind {
-        clean::ItemKind::ImplItem(ref i) => {
-            i.trait_.as_ref().map(|trait_| {
-                // Alternative format produces no URLs,
-                // so this parameter does nothing.
-                (format!("{:#}", i.for_.print(cx)), get_id_for_impl(&i.for_, Some(trait_), cx))
-            })
+        clean::ItemKind::ImplItem(ref i) if i.trait_.is_some() => {
+            // Alternative format produces no URLs,
+            // so this parameter does nothing.
+            Some((format!("{:#}", i.for_.print(cx)), get_id_for_impl(cx.tcx(), item.item_id)))
         }
         _ => None,
     }
diff --git a/src/librustdoc/html/render/search_index.rs b/src/librustdoc/html/render/search_index.rs
index 78c443b2257..af1dab59496 100644
--- a/src/librustdoc/html/render/search_index.rs
+++ b/src/librustdoc/html/render/search_index.rs
@@ -12,7 +12,7 @@ use crate::formats::cache::{Cache, OrphanImplItem};
 use crate::formats::item_type::ItemType;
 use crate::html::format::join_with_double_colon;
 use crate::html::markdown::short_markdown_summary;
-use crate::html::render::{IndexItem, IndexItemFunctionType, RenderType, RenderTypeId};
+use crate::html::render::{self, IndexItem, IndexItemFunctionType, RenderType, RenderTypeId};
 
 /// Builds the search index from the collected metadata
 pub(crate) fn build_index<'tcx>(
@@ -26,7 +26,8 @@ pub(crate) fn build_index<'tcx>(
 
     // Attach all orphan items to the type's definition if the type
     // has since been learned.
-    for &OrphanImplItem { parent, ref item, ref impl_generics } in &cache.orphan_impl_items {
+    for &OrphanImplItem { impl_id, parent, ref item, ref impl_generics } in &cache.orphan_impl_items
+    {
         if let Some((fqp, _)) = cache.paths.get(&parent) {
             let desc = short_markdown_summary(&item.doc_value(), &item.link_names(cache));
             cache.search_index.push(IndexItem {
@@ -36,6 +37,7 @@ pub(crate) fn build_index<'tcx>(
                 desc,
                 parent: Some(parent),
                 parent_idx: None,
+                impl_id,
                 search_type: get_function_type_for_search(item, tcx, impl_generics.as_ref(), cache),
                 aliases: item.attrs.get_doc_aliases(),
                 deprecation: item.deprecation(tcx),
@@ -222,6 +224,29 @@ pub(crate) fn build_index<'tcx>(
         })
         .collect();
 
+    // Find associated items that need disambiguators
+    let mut associated_item_duplicates = FxHashMap::<(isize, ItemType, Symbol), usize>::default();
+
+    for &item in &crate_items {
+        if item.impl_id.is_some() && let Some(parent_idx) = item.parent_idx {
+            let count = associated_item_duplicates
+                .entry((parent_idx, item.ty, item.name))
+                .or_insert(0);
+            *count += 1;
+        }
+    }
+
+    let associated_item_disambiguators = crate_items
+        .iter()
+        .enumerate()
+        .filter_map(|(index, item)| {
+            let impl_id = ItemId::DefId(item.impl_id?);
+            let parent_idx = item.parent_idx?;
+            let count = *associated_item_duplicates.get(&(parent_idx, item.ty, item.name))?;
+            if count > 1 { Some((index, render::get_id_for_impl(tcx, impl_id))) } else { None }
+        })
+        .collect::<Vec<_>>();
+
     struct CrateData<'a> {
         doc: String,
         items: Vec<&'a IndexItem>,
@@ -230,6 +255,8 @@ pub(crate) fn build_index<'tcx>(
         //
         // To be noted: the `usize` elements are indexes to `items`.
         aliases: &'a BTreeMap<String, Vec<usize>>,
+        // Used when a type has more than one impl with an associated item with the same name.
+        associated_item_disambiguators: &'a Vec<(usize, String)>,
     }
 
     struct Paths {
@@ -382,6 +409,7 @@ pub(crate) fn build_index<'tcx>(
             crate_data.serialize_field("f", &functions)?;
             crate_data.serialize_field("c", &deprecated)?;
             crate_data.serialize_field("p", &paths)?;
+            crate_data.serialize_field("b", &self.associated_item_disambiguators)?;
             if has_aliases {
                 crate_data.serialize_field("a", &self.aliases)?;
             }
@@ -398,6 +426,7 @@ pub(crate) fn build_index<'tcx>(
             items: crate_items,
             paths: crate_paths,
             aliases: &aliases,
+            associated_item_disambiguators: &associated_item_disambiguators,
         })
         .expect("failed serde conversion")
         // All these `replace` calls are because we have to go through JS string for JSON content.
diff --git a/src/librustdoc/html/render/sidebar.rs b/src/librustdoc/html/render/sidebar.rs
index 76f63c6f63e..3f8b22050c8 100644
--- a/src/librustdoc/html/render/sidebar.rs
+++ b/src/librustdoc/html/render/sidebar.rs
@@ -503,8 +503,7 @@ fn sidebar_render_assoc_items(
             .iter()
             .filter_map(|it| {
                 let trait_ = it.inner_impl().trait_.as_ref()?;
-                let encoded =
-                    id_map.derive(super::get_id_for_impl(&it.inner_impl().for_, Some(trait_), cx));
+                let encoded = id_map.derive(super::get_id_for_impl(cx.tcx(), it.impl_item.item_id));
 
                 let prefix = match it.inner_impl().polarity {
                     ty::ImplPolarity::Positive | ty::ImplPolarity::Reservation => "",