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 {