rustdoc: Remove unnecessary `StripItem` wrapper

src/librustdoc/fold.rs

 use crate::clean::*;
 
-crate struct StripItem(pub Item);
-
-impl StripItem {
-    crate fn strip(self) -> Item {
-        match self.0 {
-            Item { kind: box StrippedItem(..), .. } => self.0,
-            mut i => {
-                i.kind = box StrippedItem(i.kind);
-                i
-            }
-        }
+crate fn strip_item(mut item: Item) -> Item {
+    if !matches!(*item.kind, StrippedItem(..)) {
+        item.kind = box StrippedItem(item.kind);
     }
+    item
 }
 
 crate trait DocFolder: Sized {

src/librustdoc/passes/strip_hidden.rs

@@ -4,7 +4,7 @@
 use crate::clean;
 use crate::clean::{FakeDefIdSet, Item, NestedAttributesExt};
 use crate::core::DocContext;
-use crate::fold::{DocFolder, StripItem};
+use crate::fold::{strip_item, DocFolder};
 use crate::passes::{ImplStripper, Pass};
 
 crate const STRIP_HIDDEN: Pass = Pass {
@@ -44,7 +44,7 @@ fn fold_item(&mut self, i: Item) -> Option<Item> {
                     // strip things like impl methods but when doing so
                     // we must not add any items to the `retained` set.
                     let old = mem::replace(&mut self.update_retained, false);
-                    let ret = StripItem(self.fold_item_recur(i)).strip();
+                    let ret = strip_item(self.fold_item_recur(i));
                     self.update_retained = old;
                     return Some(ret);
                 }

src/librustdoc/passes/stripper.rs

@@ -3,7 +3,7 @@
 use std::mem;
 
 use crate::clean::{self, FakeDefIdSet, GetDefId, Item};
-use crate::fold::{DocFolder, StripItem};
+use crate::fold::{strip_item, DocFolder};
 
 crate struct Stripper<'a> {
     crate retained: &'a mut FakeDefIdSet,
@@ -51,7 +51,7 @@ fn fold_item(&mut self, i: Item) -> Option<Item> {
 
             clean::StructFieldItem(..) => {
                 if !i.visibility.is_public() {
-                    return Some(StripItem(i).strip());
+                    return Some(strip_item(i));
                 }
             }
 
@@ -59,7 +59,7 @@ fn fold_item(&mut self, i: Item) -> Option<Item> {
                 if i.def_id.is_local() && !i.visibility.is_public() {
                     debug!("Stripper: stripping module {:?}", i.name);
                     let old = mem::replace(&mut self.update_retained, false);
-                    let ret = StripItem(self.fold_item_recur(i)).strip();
+                    let ret = strip_item(self.fold_item_recur(i));
                     self.update_retained = old;
                     return Some(ret);
                 }