perf: Optimize Input::reset_to (#10719)

Author: bvanjoi

.changeset/old-squids-greet.md

@@ -0,0 +1,6 @@
+---
+swc_common: patch
+swc_core: patch
+---
+
+refactor(es/lexer): unnecessary reset input

crates/swc_common/src/input.rs

@@ -180,6 +180,11 @@ impl<'a> Input<'a> for StringInput<'a> {
 
     #[inline]
     unsafe fn reset_to(&mut self, to: BytePos) {
+        if self.last_pos == to {
+            // No need to reset.
+            return;
+        }
+
         let orig = self.orig;
         let idx = (to - self.orig_start).0 as usize;
 

crates/swc_ecma_parser/src/parser/class_and_fn.rs

@@ -1,19 +1,13 @@
 #[cfg(test)]
-#[allow(unused)]
 mod tests {
 
     use swc_common::DUMMY_SP as span;
     use swc_ecma_ast::*;
-    use swc_ecma_lexer::{common::parser::expr::parse_lhs_expr, Syntax};
+    use swc_ecma_lexer::Syntax;
     use swc_ecma_visit::assert_eq_ignore_span;
 
-    use super::*;
     use crate::test_parser;
 
-    fn lhs(s: &'static str) -> Box<Expr> {
-        test_parser(s, Syntax::default(), |p| parse_lhs_expr::<_, false>(p))
-    }
-
     fn expr(s: &'static str) -> Box<Expr> {
         test_parser(s, Syntax::default(), |p| p.parse_expr())
     }