Use ThinVec in various AST types.

This commit changes the sequence parsers to produce `ThinVec`, which
triggers numerous conversions.

Author: nnethercote

Cargo.lock

@@ -3689,6 +3689,7 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "rustc_target",
+ "thin-vec",
  "tracing",
 ]
 
@@ -4072,6 +4073,7 @@ dependencies = [
  "rustc_trait_selection",
  "rustc_type_ir",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 
@@ -4128,6 +4130,7 @@ dependencies = [
  "rustc_serialize",
  "rustc_session",
  "rustc_span",
+ "thin-vec",
  "tracing",
 ]
 
@@ -4826,7 +4829,6 @@ dependencies = [
  "serde_json",
  "smallvec",
  "tempfile",
- "thin-vec",
  "tracing",
  "tracing-subscriber",
  "tracing-tree",

compiler/rustc_ast/src/ast.rs

@@ -253,7 +253,7 @@ pub struct ParenthesizedArgs {
     pub span: Span,
 
     /// `(A, B)`
-    pub inputs: Vec<P<Ty>>,
+    pub inputs: ThinVec<P<Ty>>,
 
     /// ```text
     /// Foo(A, B) -> C
@@ -503,7 +503,7 @@ pub enum MetaItemKind {
     /// List meta item.
     ///
     /// E.g., `#[derive(..)]`, where the field represents the `..`.
-    List(Vec<NestedMetaItem>),
+    List(ThinVec<NestedMetaItem>),
 
     /// Name value meta item.
     ///
@@ -581,7 +581,7 @@ impl Pat {
             // A tuple pattern `(P0, .., Pn)` can be reparsed as `(T0, .., Tn)`
             // assuming `T0` to `Tn` are all syntactically valid as types.
             PatKind::Tuple(pats) => {
-                let mut tys = Vec::with_capacity(pats.len());
+                let mut tys = ThinVec::with_capacity(pats.len());
                 // FIXME(#48994) - could just be collected into an Option<Vec>
                 for pat in pats {
                     tys.push(pat.to_ty()?);
@@ -725,11 +725,11 @@ pub enum PatKind {
     Struct(Option<P<QSelf>>, Path, Vec<PatField>, /* recovered */ bool),
 
     /// A tuple struct/variant pattern (`Variant(x, y, .., z)`).
-    TupleStruct(Option<P<QSelf>>, Path, Vec<P<Pat>>),
+    TupleStruct(Option<P<QSelf>>, Path, ThinVec<P<Pat>>),
 
     /// An or-pattern `A | B | C`.
     /// Invariant: `pats.len() >= 2`.
-    Or(Vec<P<Pat>>),
+    Or(ThinVec<P<Pat>>),
 
     /// A possibly qualified path pattern.
     /// Unqualified path patterns `A::B::C` can legally refer to variants, structs, constants
@@ -738,7 +738,7 @@ pub enum PatKind {
     Path(Option<P<QSelf>>, Path),
 
     /// A tuple pattern (`(a, b)`).
-    Tuple(Vec<P<Pat>>),
+    Tuple(ThinVec<P<Pat>>),
 
     /// A `box` pattern.
     Box(P<Pat>),
@@ -753,7 +753,7 @@ pub enum PatKind {
     Range(Option<P<Expr>>, Option<P<Expr>>, Spanned<RangeEnd>),
 
     /// A slice pattern `[a, b, c]`.
-    Slice(Vec<P<Pat>>),
+    Slice(ThinVec<P<Pat>>),
 
     /// A rest pattern `..`.
     ///
@@ -1204,7 +1204,7 @@ impl Expr {
             ExprKind::Array(exprs) if exprs.len() == 1 => exprs[0].to_ty().map(TyKind::Slice)?,
 
             ExprKind::Tup(exprs) => {
-                let tys = exprs.iter().map(|expr| expr.to_ty()).collect::<Option<Vec<_>>>()?;
+                let tys = exprs.iter().map(|expr| expr.to_ty()).collect::<Option<ThinVec<_>>>()?;
                 TyKind::Tup(tys)
             }
 
@@ -1337,7 +1337,7 @@ pub struct MethodCall {
     /// The receiver, e.g. `x`.
     pub receiver: P<Expr>,
     /// The arguments, e.g. `a, b, c`.
-    pub args: Vec<P<Expr>>,
+    pub args: ThinVec<P<Expr>>,
     /// The span of the function, without the dot and receiver e.g. `foo::<Bar,
     /// Baz>(a, b, c)`.
     pub span: Span,
@@ -1366,7 +1366,7 @@ pub enum ExprKind {
     /// A `box x` expression.
     Box(P<Expr>),
     /// An array (`[a, b, c, d]`)
-    Array(Vec<P<Expr>>),
+    Array(ThinVec<P<Expr>>),
     /// Allow anonymous constants from an inline `const` block
     ConstBlock(AnonConst),
     /// A function call
@@ -1375,11 +1375,11 @@ pub enum ExprKind {
     /// and the second field is the list of arguments.
     /// This also represents calling the constructor of
     /// tuple-like ADTs such as tuple structs and enum variants.
-    Call(P<Expr>, Vec<P<Expr>>),
+    Call(P<Expr>, ThinVec<P<Expr>>),
     /// A method call (e.g. `x.foo::<Bar, Baz>(a, b, c)`).
     MethodCall(Box<MethodCall>),
     /// A tuple (e.g., `(a, b, c, d)`).
-    Tup(Vec<P<Expr>>),
+    Tup(ThinVec<P<Expr>>),
     /// A binary operation (e.g., `a + b`, `a * b`).
     Binary(BinOp, P<Expr>, P<Expr>),
     /// A unary operation (e.g., `!x`, `*x`).
@@ -2078,7 +2078,7 @@ pub enum TyKind {
     /// The never type (`!`).
     Never,
     /// A tuple (`(A, B, C, D,...)`).
-    Tup(Vec<P<Ty>>),
+    Tup(ThinVec<P<Ty>>),
     /// A path (`module::module::...::Type`), optionally
     /// "qualified", e.g., `<Vec<T> as SomeTrait>::SomeType`.
     ///
@@ -2363,7 +2363,7 @@ impl Param {
 /// which contains metadata about function safety, asyncness, constness and ABI.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FnDecl {
-    pub inputs: Vec<Param>,
+    pub inputs: ThinVec<Param>,
     pub output: FnRetTy,
 }
 
@@ -2532,7 +2532,7 @@ pub enum UseTreeKind {
     /// `use prefix` or `use prefix as rename`
     Simple(Option<Ident>),
     /// `use prefix::{...}`
-    Nested(Vec<(UseTree, NodeId)>),
+    Nested(ThinVec<(UseTree, NodeId)>),
     /// `use prefix::*`
     Glob,
 }
@@ -2695,11 +2695,11 @@ pub enum VariantData {
     /// Struct variant.
     ///
     /// E.g., `Bar { .. }` as in `enum Foo { Bar { .. } }`.
-    Struct(Vec<FieldDef>, bool),
+    Struct(ThinVec<FieldDef>, bool),
     /// Tuple variant.
     ///
     /// E.g., `Bar(..)` as in `enum Foo { Bar(..) }`.
-    Tuple(Vec<FieldDef>, NodeId),
+    Tuple(ThinVec<FieldDef>, NodeId),
     /// Unit variant.
     ///
     /// E.g., `Bar = ..` as in `enum Foo { Bar = .. }`.
@@ -3122,8 +3122,8 @@ mod size_asserts {
     static_assert_size!(GenericBound, 56);
     static_assert_size!(Generics, 40);
     static_assert_size!(Impl, 136);
-    static_assert_size!(Item, 152);
-    static_assert_size!(ItemKind, 80);
+    static_assert_size!(Item, 144);
+    static_assert_size!(ItemKind, 72);
     static_assert_size!(LitKind, 24);
     static_assert_size!(Local, 72);
     static_assert_size!(MetaItemLit, 40);

compiler/rustc_ast/src/attr/mod.rs

@@ -20,7 +20,7 @@ use std::iter;
 use std::ops::BitXor;
 #[cfg(debug_assertions)]
 use std::sync::atomic::{AtomicU32, Ordering};
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 pub struct MarkedAttrs(GrowableBitSet<AttrId>);
 
@@ -135,7 +135,7 @@ impl Attribute {
         }
     }
 
-    pub fn meta_item_list(&self) -> Option<Vec<NestedMetaItem>> {
+    pub fn meta_item_list(&self) -> Option<ThinVec<NestedMetaItem>> {
         match &self.kind {
             AttrKind::Normal(normal) => normal.item.meta_item_list(),
             AttrKind::DocComment(..) => None,
@@ -216,7 +216,7 @@ impl AttrItem {
         self.args.span().map_or(self.path.span, |args_span| self.path.span.to(args_span))
     }
 
-    fn meta_item_list(&self) -> Option<Vec<NestedMetaItem>> {
+    fn meta_item_list(&self) -> Option<ThinVec<NestedMetaItem>> {
         match &self.args {
             AttrArgs::Delimited(args) if args.delim == MacDelimiter::Parenthesis => {
                 MetaItemKind::list_from_tokens(args.tokens.clone())
@@ -375,9 +375,9 @@ impl MetaItemKind {
         }
     }
 
-    fn list_from_tokens(tokens: TokenStream) -> Option<Vec<NestedMetaItem>> {
+    fn list_from_tokens(tokens: TokenStream) -> Option<ThinVec<NestedMetaItem>> {
         let mut tokens = tokens.into_trees().peekable();
-        let mut result = Vec::new();
+        let mut result = ThinVec::new();
         while tokens.peek().is_some() {
             let item = NestedMetaItem::from_tokens(&mut tokens)?;
             result.push(item);

compiler/rustc_ast/src/mut_visit.rs

@@ -369,6 +369,11 @@ pub fn visit_exprs<T: MutVisitor>(exprs: &mut Vec<P<Expr>>, vis: &mut T) {
     exprs.flat_map_in_place(|expr| vis.filter_map_expr(expr))
 }
 
+// No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
+pub fn visit_thin_exprs<T: MutVisitor>(exprs: &mut ThinVec<P<Expr>>, vis: &mut T) {
+    exprs.flat_map_in_place(|expr| vis.filter_map_expr(expr))
+}
+
 // No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
 pub fn visit_bounds<T: MutVisitor>(bounds: &mut GenericBounds, vis: &mut T) {
     visit_vec(bounds, |bound| vis.visit_param_bound(bound));
@@ -485,7 +490,7 @@ pub fn noop_visit_ty<T: MutVisitor>(ty: &mut P<Ty>, vis: &mut T) {
             vis.visit_fn_decl(decl);
             vis.visit_span(decl_span);
         }
-        TyKind::Tup(tys) => visit_vec(tys, |ty| vis.visit_ty(ty)),
+        TyKind::Tup(tys) => visit_thin_vec(tys, |ty| vis.visit_ty(ty)),
         TyKind::Paren(ty) => vis.visit_ty(ty),
         TyKind::Path(qself, path) => {
             vis.visit_qself(qself);
@@ -584,7 +589,7 @@ pub fn noop_visit_parenthesized_parameter_data<T: MutVisitor>(
     vis: &mut T,
 ) {
     let ParenthesizedArgs { inputs, output, span, .. } = args;
-    visit_vec(inputs, |input| vis.visit_ty(input));
+    visit_thin_vec(inputs, |input| vis.visit_ty(input));
     noop_visit_fn_ret_ty(output, vis);
     vis.visit_span(span);
 }
@@ -647,7 +652,7 @@ pub fn noop_visit_meta_item<T: MutVisitor>(mi: &mut MetaItem, vis: &mut T) {
     let MetaItem { path: _, kind, span } = mi;
     match kind {
         MetaItemKind::Word => {}
-        MetaItemKind::List(mis) => visit_vec(mis, |mi| vis.visit_meta_list_item(mi)),
+        MetaItemKind::List(mis) => visit_thin_vec(mis, |mi| vis.visit_meta_list_item(mi)),
         MetaItemKind::NameValue(_s) => {}
     }
     vis.visit_span(span);
@@ -1236,7 +1241,7 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
         PatKind::TupleStruct(qself, path, elems) => {
             vis.visit_qself(qself);
             vis.visit_path(path);
-            visit_vec(elems, |elem| vis.visit_pat(elem));
+            visit_thin_vec(elems, |elem| vis.visit_pat(elem));
         }
         PatKind::Path(qself, path) => {
             vis.visit_qself(qself);
@@ -1255,7 +1260,7 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
             vis.visit_span(span);
         }
         PatKind::Tuple(elems) | PatKind::Slice(elems) | PatKind::Or(elems) => {
-            visit_vec(elems, |elem| vis.visit_pat(elem))
+            visit_thin_vec(elems, |elem| vis.visit_pat(elem))
         }
         PatKind::Paren(inner) => vis.visit_pat(inner),
         PatKind::MacCall(mac) => vis.visit_mac_call(mac),
@@ -1312,18 +1317,18 @@ pub fn noop_visit_expr<T: MutVisitor>(
 ) {
     match kind {
         ExprKind::Box(expr) => vis.visit_expr(expr),
-        ExprKind::Array(exprs) => visit_exprs(exprs, vis),
+        ExprKind::Array(exprs) => visit_thin_exprs(exprs, vis),
         ExprKind::ConstBlock(anon_const) => {
             vis.visit_anon_const(anon_const);
         }
         ExprKind::Repeat(expr, count) => {
             vis.visit_expr(expr);
             vis.visit_anon_const(count);
         }
-        ExprKind::Tup(exprs) => visit_exprs(exprs, vis),
+        ExprKind::Tup(exprs) => visit_thin_exprs(exprs, vis),
         ExprKind::Call(f, args) => {
             vis.visit_expr(f);
-            visit_exprs(args, vis);
+            visit_thin_exprs(args, vis);
         }
         ExprKind::MethodCall(box MethodCall {
             seg: PathSegment { ident, id, args: seg_args },
@@ -1335,7 +1340,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
             vis.visit_id(id);
             visit_opt(seg_args, |args| vis.visit_generic_args(args));
             vis.visit_method_receiver_expr(receiver);
-            visit_exprs(call_args, vis);
+            visit_thin_exprs(call_args, vis);
             vis.visit_span(span);
         }
         ExprKind::Binary(_binop, lhs, rhs) => {

compiler/rustc_ast_lowering/src/expr.rs

@@ -18,7 +18,7 @@ use rustc_session::errors::report_lit_error;
 use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned};
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::DUMMY_SP;
-use thin_vec::thin_vec;
+use thin_vec::{thin_vec, ThinVec};
 
 impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
@@ -367,7 +367,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_legacy_const_generics(
         &mut self,
         mut f: Expr,
-        args: Vec<AstP<Expr>>,
+        args: ThinVec<AstP<Expr>>,
         legacy_args_idx: &[usize],
     ) -> hir::ExprKind<'hir> {
         let ExprKind::Path(None, path) = &mut f.kind else {

compiler/rustc_ast_passes/Cargo.toml

@@ -5,7 +5,7 @@ edition = "2021"
 
 [dependencies]
 itertools = "0.10.1"
-tracing = "0.1"
+rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_attr = { path = "../rustc_attr" }
 rustc_data_structures = { path = "../rustc_data_structures" }
@@ -16,4 +16,5 @@ rustc_parse = { path = "../rustc_parse" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
-rustc_ast = { path = "../rustc_ast" }
+thin-vec = "0.2.12"
+tracing = "0.1"

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -10,6 +10,8 @@ use rustc_span::source_map::Spanned;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_target::spec::abi;
+use thin_vec::ThinVec;
+use tracing::debug;
 
 use crate::errors::ForbiddenLifetimeBound;
 
@@ -250,7 +252,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
             ast::ItemKind::Struct(..) => {
                 for attr in self.sess.filter_by_name(&i.attrs, sym::repr) {
-                    for item in attr.meta_item_list().unwrap_or_else(Vec::new) {
+                    for item in attr.meta_item_list().unwrap_or_else(ThinVec::new) {
                         if item.has_name(sym::simd) {
                             gate_feature_post!(
                                 &self,

compiler/rustc_ast_passes/src/lib.rs

@@ -11,9 +11,6 @@
 #![feature(let_chains)]
 #![recursion_limit = "256"]
 
-#[macro_use]
-extern crate tracing;
-
 pub mod ast_validation;
 mod errors;
 pub mod feature_gate;

compiler/rustc_ast_pretty/src/pprust/tests.rs

@@ -3,6 +3,7 @@ use super::*;
 use rustc_ast as ast;
 use rustc_span::create_default_session_globals_then;
 use rustc_span::symbol::Ident;
+use thin_vec::ThinVec;
 
 fn fun_to_string(
     decl: &ast::FnDecl,
@@ -27,8 +28,10 @@ fn test_fun_to_string() {
     create_default_session_globals_then(|| {
         let abba_ident = Ident::from_str("abba");
 
-        let decl =
-            ast::FnDecl { inputs: Vec::new(), output: ast::FnRetTy::Default(rustc_span::DUMMY_SP) };
+        let decl = ast::FnDecl {
+            inputs: ThinVec::new(),
+            output: ast::FnRetTy::Default(rustc_span::DUMMY_SP),
+        };
         let generics = ast::Generics::default();
         assert_eq!(
             fun_to_string(&decl, ast::FnHeader::default(), abba_ident, &generics),