rustdoc: render bounds of cross-crate GAT params

src/librustdoc/clean/mod.rs

@@ -1201,21 +1201,19 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
             }
 
             if let ty::TraitContainer = assoc_item.container {
-                // FIXME(fmease): `tcx.explicit_item_bounds` does not contain the bounds of GATs,
-                //                e.g. the bounds `Copy`, `Display` & (implicitly) `Sized` in
-                //                `type Assoc<T: Copy> where T: Display`. This also means that we
-                //                later incorrectly render `where T: ?Sized`.
-                //
-                //                The result of `tcx.explicit_predicates_of` *does* contain them but
-                //                it does not contain the other bounds / predicates we need.
-                //                Either merge those two interned lists somehow or refactor
-                //                `clean_ty_generics` to call `explicit_item_bounds` by itself.
                 let bounds = tcx.explicit_item_bounds(assoc_item.def_id);
-                let predicates = ty::GenericPredicates { parent: None, predicates: bounds };
-                let mut generics =
-                    clean_ty_generics(cx, tcx.generics_of(assoc_item.def_id), predicates);
-                // Filter out the bounds that are (likely?) directly attached to the associated type,
-                // as opposed to being located in the where clause.
+                let predicates = tcx.explicit_predicates_of(assoc_item.def_id).predicates;
+                let predicates =
+                    tcx.arena.alloc_from_iter(bounds.into_iter().chain(predicates).copied());
+                let mut generics = clean_ty_generics(
+                    cx,
+                    tcx.generics_of(assoc_item.def_id),
+                    ty::GenericPredicates { parent: None, predicates },
+                );
+                // Move bounds that are (likely) directly attached to the associated type
+                // from the where clause to the associated type.
+                // There is no guarantee that this is what the user actually wrote but we have
+                // no way of knowing.
                 let mut bounds = generics
                     .where_predicates
                     .drain_filter(|pred| match *pred {
@@ -1273,6 +1271,24 @@ pub(crate) fn clean_middle_assoc_item<'tcx>(
                     }
                     None => bounds.push(GenericBound::maybe_sized(cx)),
                 }
+                // Move bounds that are (likely) directly attached to the parameters of the
+                // (generic) associated type from the where clause to the respective parameter.
+                // There is no guarantee that this is what the user actually wrote but we have
+                // no way of knowing.
+                let mut where_predicates = Vec::new();
+                for mut pred in generics.where_predicates {
+                    if let WherePredicate::BoundPredicate { ty: Generic(arg), bounds, .. } = &mut pred
+                    && let Some(GenericParamDef {
+                        kind: GenericParamDefKind::Type { bounds: param_bounds, .. },
+                        ..
+                    }) = generics.params.iter_mut().find(|param| &param.name == arg)
+                    {
+                        param_bounds.extend(mem::take(bounds));
+                    } else {
+                        where_predicates.push(pred);
+                    }
+                }
+                generics.where_predicates = where_predicates;
 
                 if tcx.impl_defaultness(assoc_item.def_id).has_value() {
                     AssocTypeItem(

src/test/rustdoc/inline_cross/assoc_item_trait_bounds.out0.html

@@ -0,0 +1 @@
+<h4 class="code-header">type <a href="#associatedtype.Out0" class="associatedtype">Out0</a>: <a class="trait" href="../assoc_item_trait_bounds/trait.Support.html" title="trait assoc_item_trait_bounds::Support">Support</a>&lt;Item = <a class="primitive" href="{{channel}}/std/primitive.unit.html">()</a>&gt;</h4>

src/test/rustdoc/inline_cross/assoc_item_trait_bounds.out2.html

@@ -0,0 +1 @@
+<h4 class="code-header">type <a href="#associatedtype.Out2" class="associatedtype">Out2</a>&lt;T&gt;: <a class="trait" href="../assoc_item_trait_bounds/trait.Support.html" title="trait assoc_item_trait_bounds::Support">Support</a>&lt;Item = T&gt;</h4>

src/test/rustdoc/inline_cross/assoc_item_trait_bounds.rs

@@ -1,13 +1,10 @@
 // Regression test for issues #77763, #84579 and #102142.
 #![crate_name = "main"]
 
-// aux-build:assoc_item_trait_bounds_with_bindings.rs
+// aux-build:assoc_item_trait_bounds.rs
 // build-aux-docs
 // ignore-cross-compile
-extern crate assoc_item_trait_bounds_with_bindings as aux;
-
-// FIXME(fmease): Don't render an incorrect `T: ?Sized` where-clause for parameters
-//                of GATs like `Main::Out{2,4}`. Add a snapshot test once it's fixed.
+extern crate assoc_item_trait_bounds as aux;
 
 // @has main/trait.Main.html
 // @has - '//*[@id="associatedtype.Out0"]' 'type Out0: Support<Item = ()>'
@@ -24,11 +21,15 @@ extern crate assoc_item_trait_bounds_with_bindings as aux;
 // @has - '//*[@id="associatedtype.Out11"]' "type Out11: for<'r, 's> Helper<A<'s> = &'s (), B<'r> = ()>"
 // @has - '//*[@id="associatedtype.Out12"]' "type Out12: for<'w> Helper<B<'w> = Cow<'w, str>, A<'w> = bool>"
 // @has - '//*[@id="associatedtype.Out13"]' "type Out13: for<'fst, 'snd> Aid<'snd, Result<'fst> = &'fst mut str>"
+// @has - '//*[@id="associatedtype.Out14"]' "type Out14<P: Copy + Eq, Q: ?Sized>"
 //
-// Snapshots: Check that we do not render any where-clauses for those associated types since all of
-// the trait bounds contained within were moved to the bounds of the respective item.
+// Snapshots:
+// Check that we don't render any where-clauses for the following associated types since
+// all corresponding projection equality predicates should have already been re-sugared
+// to associated type bindings:
 //
 // @snapshot out0 - '//*[@id="associatedtype.Out0"]/*[@class="code-header"]'
+// @snapshot out2 - '//*[@id="associatedtype.Out2"]/*[@class="code-header"]'
 // @snapshot out9 - '//*[@id="associatedtype.Out9"]/*[@class="code-header"]'
 //
 // @has - '//*[@id="tymethod.make"]' \

src/test/rustdoc/inline_cross/assoc_item_trait_bounds_with_bindings.out0.html

@@ -1 +0,0 @@
-<h4 class="code-header">type <a href="#associatedtype.Out0" class="associatedtype">Out0</a>: <a class="trait" href="../assoc_item_trait_bounds_with_bindings/trait.Support.html" title="trait assoc_item_trait_bounds_with_bindings::Support">Support</a>&lt;Item = <a class="primitive" href="{{channel}}/std/primitive.unit.html">()</a>&gt;</h4>

src/test/rustdoc/inline_cross/auxiliary/assoc_item_trait_bounds.rs

@@ -15,6 +15,7 @@ pub trait Main {
     type Out11: for<'r, 's> Helper<A<'s> = &'s (), B<'r> = ()>;
     type Out12: for<'w> Helper<B<'w> = std::borrow::Cow<'w, str>, A<'w> = bool>;
     type Out13: for<'fst, 'snd> Aid<'snd, Result<'fst> = &'fst mut str>;
+    type Out14<P: Copy + Eq, Q: ?Sized>;
 
     fn make<F>(_: F, _: impl FnMut(&str) -> bool)
     where