perf(parser): improve perf of parse_template_lit (#11542)

camc314 · camc314 · commit f224585ae836 · 2025-06-09T10:20:35.000Z
diff --git a/crates/oxc_parser/src/js/expression.rs b/crates/oxc_parser/src/js/expression.rs
@@ -451,13 +451,16 @@ impl<'a> ParserImpl<'a> {
     ///     `SubstitutionTemplate`[?Yield, ?Await, ?Tagged]
     pub(crate) fn parse_template_literal(&mut self, tagged: bool) -> TemplateLiteral<'a> {
         let span = self.start_span();
-        let mut expressions = self.ast.vec();
-        let mut quasis = self.ast.vec();
-        match self.cur_kind() {
+
+        let (quasis, expressions) = match self.cur_kind() {
             Kind::NoSubstitutionTemplate => {
-                quasis.push(self.parse_template_element(tagged));
+                let quasis = self.ast.vec1(self.parse_template_element(tagged));
+                (quasis, self.ast.vec())
             }
             Kind::TemplateHead => {
+                let mut expressions = self.ast.vec_with_capacity(1);
+                let mut quasis = self.ast.vec_with_capacity(2);
+
                 quasis.push(self.parse_template_element(tagged));
                 // TemplateHead Expression[+In, ?Yield, ?Await]
                 let expr = self.context(Context::In, Context::empty(), Self::parse_expr);
@@ -483,9 +486,12 @@ impl<'a> ParserImpl<'a> {
                         }
                     }
                 }
+
+                (quasis, expressions)
             }
             _ => unreachable!("parse_template_literal"),
-        }
+        };
+
         self.ast.template_literal(self.end_span(span), quasis, expressions)
     }
 

Original file line number	Diff line number	Diff line change
`@@ -451,13 +451,16 @@ impl<'a> ParserImpl<'a> {`
`451`	`451`	/// `SubstitutionTemplate`[?Yield, ?Await, ?Tagged]
`452`	`452`	`pub(crate) fn parse_template_literal(&mut self, tagged: bool) -> TemplateLiteral<'a> {`
`453`	`453`	`let span = self.start_span();`
`454`		`- let mut expressions = self.ast.vec();`
`455`		`- let mut quasis = self.ast.vec();`
`456`		`- match self.cur_kind() {`
	`454`	`+`
	`455`	`+ let (quasis, expressions) = match self.cur_kind() {`
`457`	`456`	`Kind::NoSubstitutionTemplate => {`
`458`		`- quasis.push(self.parse_template_element(tagged));`
	`457`	`+ let quasis = self.ast.vec1(self.parse_template_element(tagged));`
	`458`	`+ (quasis, self.ast.vec())`
`459`	`459`	`}`
`460`	`460`	`Kind::TemplateHead => {`
	`461`	`+ let mut expressions = self.ast.vec_with_capacity(1);`
	`462`	`+ let mut quasis = self.ast.vec_with_capacity(2);`
	`463`	`+`
`461`	`464`	`quasis.push(self.parse_template_element(tagged));`
`462`	`465`	`// TemplateHead Expression[+In, ?Yield, ?Await]`
`463`	`466`	`let expr = self.context(Context::In, Context::empty(), Self::parse_expr);`
`@@ -483,9 +486,12 @@ impl<'a> ParserImpl<'a> {`
`483`	`486`	`}`
`484`	`487`	`}`
`485`	`488`	`}`
	`489`	`+`
	`490`	`+ (quasis, expressions)`
`486`	`491`	`}`
`487`	`492`	`_ => unreachable!("parse_template_literal"),`
`488`		`- }`
	`493`	`+ };`
	`494`	`+`
`489`	`495`	`self.ast.template_literal(self.end_span(span), quasis, expressions)`
`490`	`496`	`}`
`491`	`497`