rustdoc: correctly clean cross-crate opaque types

src/librustdoc/clean/mod.rs

@@ -2299,23 +2299,26 @@ fn clean_middle_opaque_bounds<'tcx>(
             let bindings: ThinVec<_> = bounds
                 .iter()
                 .filter_map(|bound| {
-                    if let ty::ClauseKind::Projection(proj) = bound.kind().skip_binder() {
-                        if proj.projection_ty.trait_ref(cx.tcx) == trait_ref.skip_binder() {
-                            Some(TypeBinding {
-                                assoc: projection_to_path_segment(
-                                    bound.kind().rebind(proj.projection_ty),
-                                    cx,
-                                ),
-                                kind: TypeBindingKind::Equality {
-                                    term: clean_middle_term(bound.kind().rebind(proj.term), cx),
-                                },
-                            })
-                        } else {
-                            None
-                        }
-                    } else {
-                        None
+                    let ty::ClauseKind::Projection(proj) = bound.kind().skip_binder() else {
+                        return None;
+                    };
+                    if !simplify::trait_is_same_or_supertrait2(
+                        cx,
+                        trait_ref.skip_binder(),
+                        proj.projection_ty.trait_ref(cx.tcx),
+                    ) {
+                        return None;
                     }
+
+                    Some(TypeBinding {
+                        assoc: projection_to_path_segment(
+                            bound.kind().rebind(proj.projection_ty),
+                            cx,
+                        ),
+                        kind: TypeBindingKind::Equality {
+                            term: clean_middle_term(bound.kind().rebind(proj.term), cx),
+                        },
+                    })
                 })
                 .collect();
 

src/librustdoc/clean/simplify.rs

@@ -68,6 +68,7 @@ pub(crate) fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> ThinVec<WP
     clauses
 }
 
+// NOTE(fmease): This basically does the same bound cleaning as `clean_middle_opaque_bounds`.
 pub(crate) fn merge_bounds(
     cx: &clean::DocContext<'_>,
     bounds: &mut Vec<clean::GenericBound>,
@@ -76,9 +77,8 @@ pub(crate) fn merge_bounds(
     rhs: &clean::Term,
 ) -> bool {
     !bounds.iter_mut().any(|b| {
-        let trait_ref = match *b {
-            clean::GenericBound::TraitBound(ref mut tr, _) => tr,
-            clean::GenericBound::Outlives(..) => return false,
+        let clean::GenericBound::TraitBound(trait_ref, _) = b else {
+            return false;
         };
         // If this QPath's trait `trait_did` is the same as, or a supertrait
         // of, the bound's trait `did` then we can keep going, otherwise
@@ -108,7 +108,21 @@ pub(crate) fn merge_bounds(
     })
 }
 
-fn trait_is_same_or_supertrait(cx: &DocContext<'_>, child: DefId, trait_: DefId) -> bool {
+// FIXME(fmease): This doesn't take into account the generic args of traits.
+//
+//                Get rid of this in favor of `trait_is_same_or_supertrait2`.
+//
+//                This is soft-blocked on `merge_bounds` and `where_clauses`
+//                operating on `rustc_middle` types directly instead of cleaned
+//                types (part of refactoring #115379).
+//                I suppose it's possible to not do that and to instead clean
+//                `ty::TraitRef`s in `trait_is_same_or_supertrait` as we go
+//                but that seems fragile and bad for perf.
+pub(crate) fn trait_is_same_or_supertrait(
+    cx: &DocContext<'_>,
+    child: DefId,
+    trait_: DefId,
+) -> bool {
     if child == trait_ {
         return true;
     }
@@ -128,6 +142,34 @@ fn trait_is_same_or_supertrait(cx: &DocContext<'_>, child: DefId, trait_: DefId)
         .any(|did| trait_is_same_or_supertrait(cx, did, trait_))
 }
 
+// FIXME(fmease): Add docs clarifying why we need to check the generics args for equality.
+// FIXME(fmease): Drop the `2` from the name.
+pub(crate) fn trait_is_same_or_supertrait2<'tcx>(
+    cx: &DocContext<'tcx>,
+    child: ty::TraitRef<'tcx>,
+    trait_: ty::TraitRef<'tcx>,
+) -> bool {
+    if child == trait_ {
+        return true;
+    }
+    let predicates = cx.tcx.super_predicates_of(child.def_id);
+    debug_assert!(cx.tcx.generics_of(child.def_id).has_self);
+    predicates
+        .predicates
+        .iter()
+        .filter_map(|(pred, _)| {
+            let ty::ClauseKind::Trait(pred) = pred.kind().skip_binder() else {
+                return None;
+            };
+            if pred.trait_ref.self_ty() != cx.tcx.types.self_param {
+                return None;
+            }
+
+            Some(ty::EarlyBinder::bind(pred.trait_ref).instantiate(cx.tcx, child.args))
+        })
+        .any(|child| trait_is_same_or_supertrait2(cx, child, trait_))
+}
+
 /// Move bounds that are (likely) directly attached to generic parameters from the where-clause to
 /// the respective parameter.
 ///

tests/rustdoc/inline_cross/auxiliary/impl_trait_aux.rs → tests/rustdoc/inline_cross/auxiliary/impl_trait.rs

@@ -1,5 +1,3 @@
-// edition:2018
-
 use std::ops::Deref;
 
 pub fn func<'a>(_x: impl Clone + Into<Vec<u8>> + 'a) {}
@@ -26,10 +24,22 @@ pub trait Auxiliary<'arena> {
     type Item<'input>;
 }
 
-pub async fn async_fn() {}
-
 pub struct Foo;
 
 impl Foo {
     pub fn method<'a>(_x: impl Clone + Into<Vec<u8>> + 'a) {}
 }
+
+// Regression test for issue #113015, subitem (1) / bevyengine/bevy#8898.
+// Check that we pick up on the return type of cross-crate opaque `Fn`s and
+// `FnMut`s (`FnOnce` already used to work fine).
+pub fn rpit_fn() -> impl Fn() -> bool {
+    || false
+}
+
+pub fn rpit_fn_mut() -> impl for<'a> FnMut(&'a str) -> &'a str {
+    |source| source
+}
+
+// FIXME(fmease): Add more tests that demonstrate the importance of checking the
+// generic args of supertrait bounds.

tests/rustdoc/inline_cross/impl_trait.rs

@@ -1,39 +1,46 @@
-// aux-build:impl_trait_aux.rs
+// aux-crate:impl_trait=impl_trait.rs
 // edition:2018
+#![crate_name = "user"]
 
-extern crate impl_trait_aux;
-
-// @has impl_trait/fn.func.html
+// @has user/fn.func.html
 // @has - '//pre[@class="rust item-decl"]' "pub fn func<'a>(_x: impl Clone + Into<Vec<u8, Global>> + 'a)"
 // @!has - '//pre[@class="rust item-decl"]' 'where'
-pub use impl_trait_aux::func;
+pub use impl_trait::func;
 
-// @has impl_trait/fn.func2.html
+// @has user/fn.func2.html
 // @has - '//pre[@class="rust item-decl"]' "func2<T>("
 // @has - '//pre[@class="rust item-decl"]' "_x: impl Deref<Target = Option<T>> + Iterator<Item = T>,"
 // @has - '//pre[@class="rust item-decl"]' "_y: impl Iterator<Item = u8> )"
 // @!has - '//pre[@class="rust item-decl"]' 'where'
-pub use impl_trait_aux::func2;
+pub use impl_trait::func2;
 
-// @has impl_trait/fn.func3.html
+// @has user/fn.func3.html
 // @has - '//pre[@class="rust item-decl"]' "func3("
 // @has - '//pre[@class="rust item-decl"]' "_x: impl Iterator<Item = impl Iterator<Item = u8>> + Clone)"
 // @!has - '//pre[@class="rust item-decl"]' 'where'
-pub use impl_trait_aux::func3;
+pub use impl_trait::func3;
 
-// @has impl_trait/fn.func4.html
+// @has user/fn.func4.html
 // @has - '//pre[@class="rust item-decl"]' "func4<T>("
 // @has - '//pre[@class="rust item-decl"]' "T: Iterator<Item = impl Clone>,"
-pub use impl_trait_aux::func4;
+pub use impl_trait::func4;
 
-// @has impl_trait/fn.func5.html
+// @has user/fn.func5.html
 // @has - '//pre[@class="rust item-decl"]' "func5("
 // @has - '//pre[@class="rust item-decl"]' "_f: impl for<'any> Fn(&'any str, &'any str) -> bool + for<'r> Other<T<'r> = ()>,"
 // @has - '//pre[@class="rust item-decl"]' "_a: impl for<'beta, 'alpha, '_gamma> Auxiliary<'alpha, Item<'beta> = fn(_: &'beta ())>"
 // @!has - '//pre[@class="rust item-decl"]' 'where'
-pub use impl_trait_aux::func5;
+pub use impl_trait::func5;
 
-// @has impl_trait/struct.Foo.html
+// @has user/struct.Foo.html
 // @has - '//*[@id="method.method"]//h4[@class="code-header"]' "pub fn method<'a>(_x: impl Clone + Into<Vec<u8, Global>> + 'a)"
 // @!has - '//*[@id="method.method"]//h4[@class="code-header"]' 'where'
-pub use impl_trait_aux::Foo;
+pub use impl_trait::Foo;
+
+// @has user/fn.rpit_fn.html
+// @has - '//pre[@class="rust item-decl"]' "rpit_fn() -> impl Fn() -> bool"
+pub use impl_trait::rpit_fn;
+
+// @has user/fn.rpit_fn_mut.html
+// @has - '//pre[@class="rust item-decl"]' "rpit_fn_mut() -> impl for<'a> FnMut(&'a str) -> &'a str"
+pub use impl_trait::rpit_fn_mut;