Improve handing of missing_docs for macros

Author: inquisitivecrystal

compiler/rustc_lint/src/builtin.rs

@@ -571,8 +571,9 @@ impl<'tcx> LateLintPass<'tcx> for MissingDoc {
         self.check_missing_docs_attrs(cx, hir::CRATE_HIR_ID, krate.item.inner, "the", "crate");
 
         for macro_def in krate.exported_macros {
-            // Non exported MBE 2.0 macros should be skipped
-            if !macro_def.ast.macro_rules && !cx.access_levels.is_exported(macro_def.hir_id()) {
+            // Non exported macros should be skipped, since `missing_docs` only
+            // applies to externally visible items.
+            if !cx.access_levels.is_exported(macro_def.hir_id()) {
                 continue;
             }