perf(es/parser): Add initial capacitity for some vectors (#10361)

Author: bvanjoi

crates/swc_ecma_parser/src/lexer/mod.rs

@@ -910,7 +910,7 @@ impl Lexer<'_> {
  fn read_unicode_escape(&mut self) -> LexResult<Vec<Char>> {
  debug_assert_eq!(self.cur(), Some('u'));
 
- let mut chars = Vec::new();
+ let mut chars = Vec::with_capacity(4);
  let mut is_curly = false;
 
  self.bump(); // 'u'

crates/swc_ecma_parser/src/parser/class_and_fn.rs

@@ -124,7 +124,7 @@ impl<I: Tokens> Parser<I> {
  let implements = if p.input.syntax().typescript() && eat!(p, "implements") {
  p.parse_ts_heritage_clause()?
  } else {
- Vec::new()
+ Vec::with_capacity(4)
  };
 
  {
@@ -333,7 +333,7 @@ impl<I: Tokens> Parser<I> {
  }
 
  fn parse_class_body(&mut self) -> PResult<Vec<ClassMember>> {
- let mut elems = Vec::new();
+ let mut elems = Vec::with_capacity(32);
  let mut has_constructor_with_body = false;
  while !eof!(self) && !is!(self, '}') {
  if eat_exact!(self, ';') {

crates/swc_ecma_parser/src/parser/expr.rs

@@ -499,7 +499,7 @@ impl<I: Tokens> Parser<I> {
  let start = cur_pos!(self);
 
  assert_and_bump!(self, '[');
- let mut elems = Vec::new();
+ let mut elems = Vec::with_capacity(8);
 
  while !eof!(self) && !is!(self, ']') {
  if is!(self, ',') {

crates/swc_ecma_parser/src/parser/object.rs

@@ -22,7 +22,7 @@ impl<I: Tokens> Parser<I> {
  let mut trailing_comma = None;
  assert_and_bump!(p, '{');
 
- let mut props = Vec::new();
+ let mut props = Vec::with_capacity(8);
 
  while !eat!(p, '}') {
  props.push(p.parse_object_prop()?);

crates/swc_ecma_parser/src/parser/stmt.rs

@@ -904,7 +904,7 @@ impl<'a, I: Tokens> Parser<I> {
  }
  }
 
- let mut decls = Vec::new();
+ let mut decls = Vec::with_capacity(4);
  let mut first = true;
  while first || eat!(self, ',') {
  if first {

crates/swc_ecma_parser/src/parser/stmt/module_item.rs

@@ -79,7 +79,7 @@ impl<I: Tokens> Parser<I> {
 
  let mut type_only = false;
  let mut phase = ImportPhase::Evaluation;
- let mut specifiers = Vec::new();
+ let mut specifiers = Vec::with_capacity(4);
 
  'import_maybe_ident: {
  if is!(self, BindingIdent) {

crates/swc_ecma_parser/src/parser/typescript.rs

@@ -79,7 +79,7 @@ impl<I: Tokens> Parser<I> {
  {
  debug_assert!(self.input.syntax().typescript());
 
- let mut buf = Vec::new();
+ let mut buf = Vec::with_capacity(8);
  while !self.is_ts_list_terminator(kind)? {
  // Skipping "parseListElement" from the TS source since that's just for error
  // handling.
@@ -1980,7 +1980,7 @@ impl<I: Tokens> Parser<I> {
  debug_assert!(self.input.syntax().typescript());
 
  let params = self.parse_formal_params()?;
- let mut list = Vec::new();
+ let mut list = Vec::with_capacity(4);
 
  for param in params {
  let item = match param.pat {