stop feed vis when cant access for trait item

Author: bvanjoi

compiler/rustc_resolve/src/late.rs

@@ -3092,7 +3092,15 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
 
         let res = binding.res();
         let Res::Def(def_kind, id_in_trait) = res else { bug!() };
-        feed_visibility(self, id_in_trait);
+
+        if !self.r.is_accessible_from(binding.vis, self.parent_scope.module) {
+            self.r.dcx().span_delayed_bug(
+                span,
+                "privacy error should be emitted when a private trait is used",
+            );
+        } else {
+            feed_visibility(self, id_in_trait);
+        }
 
         match seen_trait_items.entry(id_in_trait) {
             Entry::Occupied(entry) => {

tests/ui/privacy/auxiliary/issue-119463-extern.rs

@@ -0,0 +1,3 @@
+trait PrivateTrait {
+    const FOO: usize;
+}

tests/ui/privacy/issue-119463.rs

@@ -0,0 +1,11 @@
+// aux-build:issue-119463-extern.rs
+
+extern crate issue_119463_extern;
+
+struct S;
+
+impl issue_119463_extern::PrivateTrait for S { //~ ERROR: trait `PrivateTrait` is private
+    const FOO: usize = 1;
+}
+
+fn main() {}

tests/ui/privacy/issue-119463.stderr

@@ -0,0 +1,15 @@
+error[E0603]: trait `PrivateTrait` is private
+  --> $DIR/issue-119463.rs:7:27
+   |
+LL | impl issue_119463_extern::PrivateTrait for S {
+   |                           ^^^^^^^^^^^^ private trait
+   |
+note: the trait `PrivateTrait` is defined here
+  --> $DIR/auxiliary/issue-119463-extern.rs:1:1
+   |
+LL | trait PrivateTrait {
+   | ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0603`.