From 4623d51573b22c95ec25c2041aa43221a9e61597 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Le=C3=B3n=20Orell=20Valerian=20Liehr?=
 <liehr.exchange@gmx.net>
Date: Thu, 7 Apr 2022 16:50:51 +0200
Subject: [PATCH] Hide cross-crate doc-hidden assoc items in trait impls

---
 src/librustdoc/clean/inline.rs                | 21 +++++++++++++----
 .../cross-crate-hidden-assoc-trait-items.rs   | 19 +++++++++++++++
 .../cross-crate-hidden-assoc-trait-items.rs   | 23 +++++++++++++++++++
 3 files changed, 59 insertions(+), 4 deletions(-)
 create mode 100644 src/test/rustdoc/auxiliary/cross-crate-hidden-assoc-trait-items.rs
 create mode 100644 src/test/rustdoc/cross-crate-hidden-assoc-trait-items.rs

diff --git a/src/librustdoc/clean/inline.rs b/src/librustdoc/clean/inline.rs
index 8c19cf973fc86..d06e4fa1cc2f5 100644
--- a/src/librustdoc/clean/inline.rs
+++ b/src/librustdoc/clean/inline.rs
@@ -425,13 +425,26 @@ crate fn build_impl(
         None => (
             tcx.associated_items(did)
                 .in_definition_order()
-                .filter_map(|item| {
-                    if associated_trait.is_some() || item.vis.is_public() {
-                        Some(item.clean(cx))
+                .filter(|item| {
+                    // If this is a trait impl, filter out associated items whose corresponding item
+                    // in the associated trait is marked `doc(hidden)`.
+                    // If this is an inherent impl, filter out private associated items.
+                    if let Some(associated_trait) = associated_trait {
+                        let trait_item = tcx
+                            .associated_items(associated_trait.def_id)
+                            .find_by_name_and_kind(
+                                tcx,
+                                item.ident(tcx),
+                                item.kind,
+                                associated_trait.def_id,
+                            )
+                            .unwrap(); // corresponding associated item has to exist
+                        !tcx.is_doc_hidden(trait_item.def_id)
                     } else {
-                        None
+                        item.vis.is_public()
                     }
                 })
+                .map(|item| item.clean(cx))
                 .collect::<Vec<_>>(),
             clean::enter_impl_trait(cx, |cx| {
                 clean_ty_generics(cx, tcx.generics_of(did), predicates)
diff --git a/src/test/rustdoc/auxiliary/cross-crate-hidden-assoc-trait-items.rs b/src/test/rustdoc/auxiliary/cross-crate-hidden-assoc-trait-items.rs
new file mode 100644
index 0000000000000..3baf8a6c07ee8
--- /dev/null
+++ b/src/test/rustdoc/auxiliary/cross-crate-hidden-assoc-trait-items.rs
@@ -0,0 +1,19 @@
+pub trait Tr {
+    type VisibleAssoc;
+    #[doc(hidden)]
+    type HiddenAssoc;
+
+    const VISIBLE_ASSOC: ();
+    #[doc(hidden)]
+    const HIDDEN_ASSOC: ();
+}
+
+pub struct Ty;
+
+impl Tr for Ty {
+    type VisibleAssoc = ();
+    type HiddenAssoc = ();
+
+    const VISIBLE_ASSOC: () = ();
+    const HIDDEN_ASSOC: () = ();
+}
diff --git a/src/test/rustdoc/cross-crate-hidden-assoc-trait-items.rs b/src/test/rustdoc/cross-crate-hidden-assoc-trait-items.rs
new file mode 100644
index 0000000000000..d02bc4fe71250
--- /dev/null
+++ b/src/test/rustdoc/cross-crate-hidden-assoc-trait-items.rs
@@ -0,0 +1,23 @@
+// Regression test for issue #95717
+// Hide cross-crate `#[doc(hidden)]` associated items in trait impls.
+
+#![crate_name = "dependent"]
+// edition:2021
+// aux-crate:dependency=cross-crate-hidden-assoc-trait-items.rs
+
+// The trait `Tr` contains 2 hidden and 2 visisible associated items.
+// Instead of checking for the absence of the hidden items, check for the presence of the
+// visible items instead and assert that there are *exactly two* associated items
+// (by counting the number of `section`s). This is more robust and future-proof.
+
+// @has dependent/struct.Ty.html
+// @has - '//*[@id="associatedtype.VisibleAssoc"]' 'type VisibleAssoc = ()'
+// @has - '//*[@id="associatedconstant.VISIBLE_ASSOC"]' 'const VISIBLE_ASSOC: ()'
+// @count - '//*[@class="impl-items"]/section' 2
+
+// @has dependent/trait.Tr.html
+// @has - '//*[@id="associatedtype.VisibleAssoc-1"]' 'type VisibleAssoc = ()'
+// @has - '//*[@id="associatedconstant.VISIBLE_ASSOC-1"]' 'const VISIBLE_ASSOC: ()'
+// @count - '//*[@class="impl-items"]/section' 2
+
+pub use dependency::{Tr, Ty};