Auto merge of #86385 - JohnTitor:use-attrvec, r=davidtwco

Use `AttrVec` for `Arm`, `FieldDef`, and `Variant`

Uses `AttrVec` for `Arm`, `FieldDef`, and `Variant`, i.e., where the size of the vector can be empty often.
Skips `Crate` and `Item` because I think they may have the attributes on common cases and need more work outside of `rustc_ast` (e.g. rustc_expand needs a lot of tweaks). But if it's reasonable to change, I'm happy to do so.

Fixes #77662

Author: bors

compiler/rustc_ast/src/ast.rs

@@ -1017,7 +1017,7 @@ pub struct Local {
 /// ```
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct Arm {
-    pub attrs: Vec<Attribute>,
+    pub attrs: AttrVec,
     /// Match arm pattern, e.g. `10` in `match foo { 10 => {}, _ => {} }`
     pub pat: P<Pat>,
     /// Match arm guard, e.g. `n > 10` in `match foo { n if n > 10 => {}, _ => {} }`
@@ -2293,7 +2293,7 @@ pub struct EnumDef {
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct Variant {
     /// Attributes of the variant.
-    pub attrs: Vec<Attribute>,
+    pub attrs: AttrVec,
     /// Id of the variant (not the constructor, see `VariantData::ctor_id()`).
     pub id: NodeId,
     /// Span
@@ -2474,7 +2474,7 @@ impl VisibilityKind {
 /// E.g., `bar: usize` as in `struct Foo { bar: usize }`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FieldDef {
-    pub attrs: Vec<Attribute>,
+    pub attrs: AttrVec,
     pub id: NodeId,
     pub span: Span,
     pub vis: Visibility,

compiler/rustc_ast/src/mut_visit.rs

@@ -420,7 +420,7 @@ pub fn noop_visit_use_tree<T: MutVisitor>(use_tree: &mut UseTree, vis: &mut T) {
 
 pub fn noop_flat_map_arm<T: MutVisitor>(mut arm: Arm, vis: &mut T) -> SmallVec<[Arm; 1]> {
     let Arm { attrs, pat, guard, body, span, id, is_placeholder: _ } = &mut arm;
-    visit_attrs(attrs, vis);
+    visit_thin_attrs(attrs, vis);
     vis.visit_id(id);
     vis.visit_pat(pat);
     visit_opt(guard, |guard| vis.visit_expr(guard));
@@ -504,7 +504,7 @@ pub fn noop_flat_map_variant<T: MutVisitor>(
     let Variant { ident, vis, attrs, id, data, disr_expr, span, is_placeholder: _ } = &mut variant;
     visitor.visit_ident(ident);
     visitor.visit_vis(vis);
-    visit_attrs(attrs, visitor);
+    visit_thin_attrs(attrs, visitor);
     visitor.visit_id(id);
     visitor.visit_variant_data(data);
     visit_opt(disr_expr, |disr_expr| visitor.visit_anon_const(disr_expr));
@@ -918,7 +918,7 @@ pub fn noop_flat_map_field_def<T: MutVisitor>(
     visitor.visit_vis(vis);
     visitor.visit_id(id);
     visitor.visit_ty(ty);
-    visit_attrs(attrs, visitor);
+    visit_thin_attrs(attrs, visitor);
     smallvec![fd]
 }
 

compiler/rustc_ast_pretty/src/pprust/tests.rs

@@ -49,7 +49,7 @@ fn test_variant_to_string() {
                 kind: ast::VisibilityKind::Inherited,
                 tokens: None,
             },
-            attrs: Vec::new(),
+            attrs: ast::AttrVec::new(),
             id: ast::DUMMY_NODE_ID,
             data: ast::VariantData::Unit(ast::DUMMY_NODE_ID),
             disr_expr: None,

compiler/rustc_expand/src/build.rs

@@ -432,7 +432,7 @@ impl<'a> ExtCtxt<'a> {
 
     pub fn arm(&self, span: Span, pat: P<ast::Pat>, expr: P<ast::Expr>) -> ast::Arm {
         ast::Arm {
-            attrs: vec![],
+            attrs: AttrVec::new(),
             pat,
             guard: None,
             body: expr,

compiler/rustc_parse/src/parser/expr.rs

@@ -2116,7 +2116,7 @@ impl<'a> Parser<'a> {
                     let span = body.span;
                     return Ok((
                         ast::Arm {
-                            attrs,
+                            attrs: attrs.into(),
                             pat,
                             guard,
                             body,
@@ -2170,7 +2170,7 @@ impl<'a> Parser<'a> {
 
             Ok((
                 ast::Arm {
-                    attrs,
+                    attrs: attrs.into(),
                     pat,
                     guard,
                     body: expr,

compiler/rustc_parse/src/parser/item.rs

@@ -1143,7 +1143,7 @@ impl<'a> Parser<'a> {
                     ident,
                     vis,
                     id: DUMMY_NODE_ID,
-                    attrs: variant_attrs,
+                    attrs: variant_attrs.into(),
                     data: struct_def,
                     disr_expr,
                     span: vlo.to(this.prev_token.span),
@@ -1286,7 +1286,7 @@ impl<'a> Parser<'a> {
                         ident: None,
                         id: DUMMY_NODE_ID,
                         ty,
-                        attrs,
+                        attrs: attrs.into(),
                         is_placeholder: false,
                     },
                     TrailingToken::MaybeComma,
@@ -1460,7 +1460,7 @@ impl<'a> Parser<'a> {
             vis,
             id: DUMMY_NODE_ID,
             ty,
-            attrs,
+            attrs: attrs.into(),
             is_placeholder: false,
         })
     }

src/tools/rustfmt/src/types.rs

@@ -1,7 +1,7 @@
 use std::iter::ExactSizeIterator;
 use std::ops::Deref;
 
-use rustc_ast::ast::{self, FnRetTy, Mutability};
+use rustc_ast::ast::{self, AttrVec, FnRetTy, Mutability};
 use rustc_span::{symbol::kw, symbol::Ident, BytePos, Pos, Span};
 
 use crate::config::lists::*;
@@ -776,7 +776,7 @@ impl Rewrite for ast::Ty {
                 );
                 let data = ast::VariantData::Struct(fields.clone(), recovered);
                 let variant = ast::Variant {
-                    attrs: vec![],
+                    attrs: AttrVec::new(),
                     id: self.id,
                     span: self.span,
                     vis: DEFAULT_VISIBILITY,
@@ -800,7 +800,7 @@ impl Rewrite for ast::Ty {
                 );
                 let data = ast::VariantData::Struct(fields.clone(), recovered);
                 let variant = ast::Variant {
-                    attrs: vec![],
+                    attrs: AttrVec::new(),
                     id: self.id,
                     span: self.span,
                     vis: DEFAULT_VISIBILITY,