Box ItemKind to reduce the size of `Item`

This brings the size of `Item` from

```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 680
```

to

```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 280
```

5 files changed, 11 insertions, 11 deletions

diff --git a/src/librustdoc/passes/calculate_doc_coverage.rs b/src/librustdoc/passes/calculate_doc_coverage.rs
index 52f6a97089b..6951b01e03d 100644
--- a/src/librustdoc/passes/calculate_doc_coverage.rs
+++ b/src/librustdoc/passes/calculate_doc_coverage.rs
@@ -187,7 +187,7 @@ impl<'a, 'b> CoverageCalculator<'a, 'b> {
 
 impl<'a, 'b> fold::DocFolder for CoverageCalculator<'a, 'b> {
     fn fold_item(&mut self, i: clean::Item) -> Option<clean::Item> {
-        match i.kind {
+        match *i.kind {
             _ if !i.def_id.is_local() => {
                 // non-local items are skipped because they can be out of the users control,
                 // especially in the case of trait impls, which rustdoc eagerly inlines
diff --git a/src/librustdoc/passes/collect_trait_impls.rs b/src/librustdoc/passes/collect_trait_impls.rs
index 60fcbe74872..9b0ae09cb3f 100644
--- a/src/librustdoc/passes/collect_trait_impls.rs
+++ b/src/librustdoc/passes/collect_trait_impls.rs
@@ -58,11 +58,11 @@ crate fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
 
     // scan through included items ahead of time to splice in Deref targets to the "valid" sets
     for it in &new_items {
-        if let ImplItem(Impl { ref for_, ref trait_, ref items, .. }) = it.kind {
+        if let ImplItem(Impl { ref for_, ref trait_, ref items, .. }) = *it.kind {
             if cleaner.keep_item(for_) && trait_.def_id() == cx.tcx.lang_items().deref_trait() {
                 let target = items
                     .iter()
-                    .find_map(|item| match item.kind {
+                    .find_map(|item| match *item.kind {
                         TypedefItem(ref t, true) => Some(&t.type_),
                         _ => None,
                     })
@@ -78,7 +78,7 @@ crate fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
     }
 
     new_items.retain(|it| {
-        if let ImplItem(Impl { ref for_, ref trait_, ref blanket_impl, .. }) = it.kind {
+        if let ImplItem(Impl { ref for_, ref trait_, ref blanket_impl, .. }) = *it.kind {
             cleaner.keep_item(for_)
                 || trait_.as_ref().map_or(false, |t| cleaner.keep_item(t))
                 || blanket_impl.is_some()
@@ -124,7 +124,7 @@ crate fn collect_trait_impls(krate: Crate, cx: &DocContext<'_>) -> Crate {
     }
 
     if let Some(ref mut it) = krate.module {
-        if let ModuleItem(Module { ref mut items, .. }) = it.kind {
+        if let ModuleItem(Module { ref mut items, .. }) = *it.kind {
             items.extend(synth.impls);
             items.extend(new_items);
         } else {
diff --git a/src/librustdoc/passes/doc_test_lints.rs b/src/librustdoc/passes/doc_test_lints.rs
index 1c1141e7c81..68ce73f944b 100644
--- a/src/librustdoc/passes/doc_test_lints.rs
+++ b/src/librustdoc/passes/doc_test_lints.rs
@@ -59,7 +59,7 @@ impl crate::doctest::Tester for Tests {
 
 crate fn should_have_doc_example(cx: &DocContext<'_>, item: &clean::Item) -> bool {
     if matches!(
-        item.kind,
+        *item.kind,
         clean::StructFieldItem(_)
             | clean::VariantItem(_)
             | clean::AssocConstItem(_, _)
diff --git a/src/librustdoc/passes/strip_hidden.rs b/src/librustdoc/passes/strip_hidden.rs
index 6b59eb8cf28..5694ce27de8 100644
--- a/src/librustdoc/passes/strip_hidden.rs
+++ b/src/librustdoc/passes/strip_hidden.rs
@@ -41,7 +41,7 @@ impl<'a> DocFolder for Stripper<'a> {
         if i.attrs.lists(sym::doc).has_word(sym::hidden) {
             debug!("strip_hidden: stripping {:?} {:?}", i.type_(), i.name);
             // use a dedicated hidden item for given item type if any
-            match i.kind {
+            match *i.kind {
                 clean::StructFieldItem(..) | clean::ModuleItem(..) => {
                     // We need to recurse into stripped modules to
                     // strip things like impl methods but when doing so
diff --git a/src/librustdoc/passes/stripper.rs b/src/librustdoc/passes/stripper.rs
index 444fd593ec9..f872e403ab0 100644
--- a/src/librustdoc/passes/stripper.rs
+++ b/src/librustdoc/passes/stripper.rs
@@ -13,7 +13,7 @@ crate struct Stripper<'a> {
 
 impl<'a> DocFolder for Stripper<'a> {
     fn fold_item(&mut self, i: Item) -> Option<Item> {
-        match i.kind {
+        match *i.kind {
             clean::StrippedItem(..) => {
                 // We need to recurse into stripped modules to strip things
                 // like impl methods but when doing so we must not add any
@@ -86,7 +86,7 @@ impl<'a> DocFolder for Stripper<'a> {
             clean::KeywordItem(..) => {}
         }
 
-        let fastreturn = match i.kind {
+        let fastreturn = match *i.kind {
             // nothing left to do for traits (don't want to filter their
             // methods out, visibility controlled by the trait)
             clean::TraitItem(..) => true,
@@ -121,7 +121,7 @@ crate struct ImplStripper<'a> {
 
 impl<'a> DocFolder for ImplStripper<'a> {
     fn fold_item(&mut self, i: Item) -> Option<Item> {
-        if let clean::ImplItem(ref imp) = i.kind {
+        if let clean::ImplItem(ref imp) = *i.kind {
             // emptied none trait impls can be stripped
             if imp.trait_.is_none() && imp.items.is_empty() {
                 return None;
@@ -160,7 +160,7 @@ crate struct ImportStripper;
 
 impl DocFolder for ImportStripper {
     fn fold_item(&mut self, i: Item) -> Option<Item> {
-        match i.kind {
+        match *i.kind {
             clean::ExternCrateItem(..) | clean::ImportItem(..) if !i.visibility.is_public() => None,
             _ => Some(self.fold_item_recur(i)),
         }