move the implementation under check_def_field

Author: quangcito

clippy_lints/src/missing_doc.rs

@@ -91,14 +91,6 @@ impl MissingDoc {
         article: &'static str,
         desc: &'static str,
     ) {
-        // Skip checking if the item starts with underscore and allow_unused is enabled
-        if self.allow_unused {
-            if let Some(name) = cx.tcx.opt_item_name(def_id.to_def_id()) {
-                if name.as_str().starts_with('_') {
-                    return;
-                }
-            }
-        }
         // If we're building a test harness, then warning about
         // documentation is probably not really relevant right now.
         if cx.sess().opts.test {
@@ -272,6 +264,12 @@ impl<'tcx> LateLintPass<'tcx> for MissingDoc {
 
     fn check_field_def(&mut self, cx: &LateContext<'tcx>, sf: &'tcx hir::FieldDef<'_>) {
         if !sf.is_positional() {
+            // Skip checking if the field starts with underscore and allow_unused is enabled
+            if self.allow_unused && sf.ident.as_str().starts_with('_') {
+                self.prev_span = Some(sf.span);
+                return;
+            }
+
             let attrs = cx.tcx.hir_attrs(sf.hir_id);
             if !is_from_proc_macro(cx, sf) {
                 self.check_missing_docs_attrs(cx, sf.def_id, attrs, sf.span, "a", "struct field");