privacy: visit trait def id of projections

A refactoring in #117076 changed the `DefIdVisitorSkeleton` to avoid
calling `visit_projection_ty` for `ty::Projection` aliases, and instead
just iterate over the args - this makes sense, as `visit_projection_ty`
will indirectly visit all of the same args, but in doing so, will also
create a `TraitRef` containing the trait's `DefId`, which also gets
visited. The trait's `DefId` isn't visited when we only visit the
arguments without separating them into `TraitRef` and own args first.

Signed-off-by: David Wood <david@davidtw.co>

compiler/rustc_privacy/src/lib.rs

@@ -218,20 +218,21 @@ where
                     return ControlFlow::Continue(());
                 }
 
-                let kind = match kind {
-                    ty::Inherent | ty::Projection => "associated type",
-                    ty::Weak => "type alias",
-                    ty::Opaque => unreachable!(),
-                };
                 self.def_id_visitor.visit_def_id(
                     data.def_id,
-                    kind,
+                    match kind {
+                        ty::Inherent | ty::Projection => "associated type",
+                        ty::Weak => "type alias",
+                        ty::Opaque => unreachable!(),
+                    },
                     &LazyDefPathStr { def_id: data.def_id, tcx },
                 )?;
 
                 // This will also visit args if necessary, so we don't need to recurse.
                 return if V::SHALLOW {
                     ControlFlow::Continue(())
+                } else if kind == ty::Projection {
+                    self.visit_projection_ty(data)
                 } else {
                     data.args.iter().try_for_each(|subst| subst.visit_with(self))
                 };

tests/ui/privacy/auxiliary/issue-117997.rs

@@ -0,0 +1,35 @@
+// no-prefer-dynamic
+// compile-flags: --crate-type=rlib
+
+pub use impl_mod::TraitImplementer as Implementer;
+
+pub use trait_mod::get_assoc;
+
+mod impl_mod {
+    use crate::trait_mod::TraitWithAssocType;
+
+    pub struct TraitImplementer {}
+    pub struct AssociatedType {}
+
+    impl AssociatedType {
+        pub fn method_on_assoc(&self) -> i32 {
+            todo!()
+        }
+    }
+
+    impl TraitWithAssocType for TraitImplementer {
+        type AssocType = AssociatedType;
+    }
+}
+
+mod trait_mod {
+    use crate::Implementer;
+
+    pub fn get_assoc() -> <Implementer as TraitWithAssocType>::AssocType {
+        todo!()
+    }
+
+    pub trait TraitWithAssocType {
+        type AssocType;
+    }
+}

tests/ui/privacy/issue-117997.rs

@@ -0,0 +1,8 @@
+// aux-build:issue-117997.rs
+// build-pass
+
+extern crate issue_117997;
+
+pub fn main() {
+    issue_117997::get_assoc().method_on_assoc();
+}