Don't warn on pub fields of pub(restricted) structs

Author: Urgau

compiler/rustc_lint/src/builtin.rs

@@ -1424,8 +1424,24 @@ impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
     }
 
     fn check_field_def(&mut self, cx: &LateContext<'_>, field: &hir::FieldDef<'_>) {
-        if matches!(cx.tcx.parent_hir_node(field.hir_id), Node::Variant(_)) {
-            return;
+        match cx.tcx.parent_hir_node(field.hir_id) {
+            Node::Variant(_) => return,
+            // We don't want to lint on struct/union fields whose parent def is
+            // not public. We therefore check if the parent is a struct/union and
+            // if it `pub` we ignore the field.
+            //
+            // ```
+            // pub(crate) struct Hydrogen {
+            //     pub neutrons: usize, // should not lint
+            // }
+            // ```
+            Node::Item(item)
+                if item.is_struct_or_union()
+                    && !cx.tcx.visibility(item.owner_id.def_id).is_public() =>
+            {
+                return;
+            }
+            _ => {}
         }
         self.perform_lint(cx, "field", field.def_id, field.vis_span, false);
     }

tests/ui/lint/unreachable_pub.rs

@@ -15,6 +15,10 @@ mod private_mod {
         // (... but not more-restricted fields)
         pub(crate) electrons: usize
     }
+    pub(crate) struct Hydrogen {
+        pub neutrons: usize, // the visibility is clearly defined by the struct above
+                             // no need to cluter the field definition
+    }
     impl Hydrogen {
         // impls, too
         pub fn count_neutrons(&self) -> usize { self.neutrons } //~ WARNING unreachable_pub