Use `P` for `NtTraitItem`, `NtImplItem`, and `NtForeignItem`.

This commit reduces the size of `Nonterminal` from a whopping 240 bytes
to 72 bytes (on x86-64), which gets it below the `memcpy` threshold.

It also removes some impedance mismatches with `Annotatable`, which
already uses `P` for these variants.

3 files changed, 19 insertions, 15 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 5c64cc440ce..db4fd53fe16 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -2243,7 +2243,7 @@ pub struct Mod {
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct ForeignMod {
     pub abi: Option<StrLit>,
-    pub items: Vec<ForeignItem>,
+    pub items: Vec<P<ForeignItem>>,
 }
 
 /// Global inline assembly.
@@ -2605,7 +2605,7 @@ pub enum ItemKind {
     /// A trait declaration (`trait`).
     ///
     /// E.g., `trait Foo { .. }`, `trait Foo<T> { .. }` or `auto trait Foo {}`.
-    Trait(IsAuto, Unsafety, Generics, GenericBounds, Vec<AssocItem>),
+    Trait(IsAuto, Unsafety, Generics, GenericBounds, Vec<P<AssocItem>>),
     /// Trait alias
     ///
     /// E.g., `trait Foo = Bar + Quux;`.
@@ -2624,7 +2624,7 @@ pub enum ItemKind {
         of_trait: Option<TraitRef>,
 
         self_ty: P<Ty>,
-        items: Vec<AssocItem>,
+        items: Vec<P<AssocItem>>,
     },
     /// A macro invocation.
     ///
diff --git a/src/libsyntax/mut_visit.rs b/src/libsyntax/mut_visit.rs
index 4a460c5d7b2..e9e1675b9b0 100644
--- a/src/libsyntax/mut_visit.rs
+++ b/src/libsyntax/mut_visit.rs
@@ -82,7 +82,7 @@ pub trait MutVisitor: Sized {
         noop_visit_use_tree(use_tree, self);
     }
 
-    fn flat_map_foreign_item(&mut self, ni: ForeignItem) -> SmallVec<[ForeignItem; 1]> {
+    fn flat_map_foreign_item(&mut self, ni: P<ForeignItem>) -> SmallVec<[P<ForeignItem>; 1]> {
         noop_flat_map_foreign_item(ni, self)
     }
 
@@ -102,11 +102,11 @@ pub trait MutVisitor: Sized {
         noop_visit_item_kind(i, self);
     }
 
-    fn flat_map_trait_item(&mut self, i: AssocItem) -> SmallVec<[AssocItem; 1]> {
+    fn flat_map_trait_item(&mut self, i: P<AssocItem>) -> SmallVec<[P<AssocItem>; 1]> {
         noop_flat_map_assoc_item(i, self)
     }
 
-    fn flat_map_impl_item(&mut self, i: AssocItem) -> SmallVec<[AssocItem; 1]> {
+    fn flat_map_impl_item(&mut self, i: P<AssocItem>) -> SmallVec<[P<AssocItem>; 1]> {
         noop_flat_map_assoc_item(i, self)
     }
 
@@ -947,11 +947,11 @@ pub fn noop_visit_item_kind<T: MutVisitor>(kind: &mut ItemKind, vis: &mut T) {
 }
 
 pub fn noop_flat_map_assoc_item<T: MutVisitor>(
-    mut item: AssocItem,
+    mut item: P<AssocItem>,
     visitor: &mut T,
-) -> SmallVec<[AssocItem; 1]> {
+) -> SmallVec<[P<AssocItem>; 1]> {
     let AssocItem { id, ident, vis, defaultness: _, attrs, generics, kind, span, tokens: _ } =
-        &mut item;
+        item.deref_mut();
     visitor.visit_id(id);
     visitor.visit_ident(ident);
     visitor.visit_vis(vis);
@@ -1036,10 +1036,10 @@ pub fn noop_flat_map_item<T: MutVisitor>(
 }
 
 pub fn noop_flat_map_foreign_item<T: MutVisitor>(
-    mut item: ForeignItem,
+    mut item: P<ForeignItem>,
     visitor: &mut T,
-) -> SmallVec<[ForeignItem; 1]> {
-    let ForeignItem { ident, attrs, id, kind, vis, span, tokens: _ } = &mut item;
+) -> SmallVec<[P<ForeignItem>; 1]> {
+    let ForeignItem { ident, attrs, id, kind, vis, span, tokens: _ } = item.deref_mut();
     visitor.visit_ident(ident);
     visit_attrs(attrs, visitor);
     match kind {
diff --git a/src/libsyntax/token.rs b/src/libsyntax/token.rs
index 14279561cbb..c826b728f80 100644
--- a/src/libsyntax/token.rs
+++ b/src/libsyntax/token.rs
@@ -680,11 +680,15 @@ pub enum Nonterminal {
     // Used only for passing items to proc macro attributes (they are not
     // strictly necessary for that, `Annotatable` can be converted into
     // tokens directly, but doing that naively regresses pretty-printing).
-    NtTraitItem(ast::AssocItem),
-    NtImplItem(ast::AssocItem),
-    NtForeignItem(ast::ForeignItem),
+    NtTraitItem(P<ast::AssocItem>),
+    NtImplItem(P<ast::AssocItem>),
+    NtForeignItem(P<ast::ForeignItem>),
 }
 
+// `Nonterminal` is used a lot. Make sure it doesn't unintentionally get bigger.
+#[cfg(target_arch = "x86_64")]
+rustc_data_structures::static_assert_size!(Nonterminal, 72);
+
 impl PartialEq for Nonterminal {
     fn eq(&self, rhs: &Self) -> bool {
         match (self, rhs) {