perf(es/parser): Move found_module_item to Parser (#10388)

This may reduce the cost of creating `State`(72 bytes -> 64 bytes) in `parse_fn_body`.

Author: CPunisher

Diff for: .changeset/selfish-pears-shake.md

@@ -0,0 +1,6 @@
+---
+swc_ecma_parser: patch
+swc_core: patch
+---
+
+perf(es/parser): move `found_module_item` to `Parser`

Diff for: crates/swc_ecma_parser/src/parser/class_and_fn.rs

@@ -1397,12 +1397,8 @@ impl<I: Tokens> Parser<I> {
             },
         );
 
-        let state = State {
-            labels: Vec::new(),
-            ..Default::default()
-        };
         self.with_ctx(ctx)
-            .with_state(state)
+            .with_state(State::default())
             .parse_fn_body_inner(is_simple_parameter_list)
     }
 }

Diff for: crates/swc_ecma_parser/src/parser/expr.rs

@@ -2069,7 +2069,7 @@ impl<I: Tokens> Parser<I> {
         no_call: bool,
     ) -> PResult<Box<Expr>> {
         if eat!(self, '.') {
-            self.state.found_module_item = true;
+            self.found_module_item = true;
 
             let ident = self.parse_ident_name()?;
 

Diff for: crates/swc_ecma_parser/src/parser/expr/ops.rs

@@ -399,7 +399,7 @@ impl<I: Tokens> Parser<I> {
 
         // This has been checked if start_of_await_token == true,
         if start_of_await_token.is_none() && ctx.contains(Context::TopLevel) {
-            self.state.found_module_item = true;
+            self.found_module_item = true;
             if !ctx.contains(Context::CanBeModule) {
                 self.emit_err(await_token, SyntaxError::TopLevelAwaitInScript);
             }

Diff for: crates/swc_ecma_parser/src/parser/mod.rs

@@ -48,15 +48,14 @@ pub type PResult<T> = Result<T, Error>;
 pub struct Parser<I: Tokens> {
     state: State,
     input: Buffer<I>,
+    found_module_item: bool,
 }
 
 #[derive(Clone, Default)]
 struct State {
     labels: Vec<Atom>,
     /// Start position of an assignment expression.
     potential_arrow_start: Option<BytePos>,
-
-    found_module_item: bool,
     /// Start position of an AST node and the span of its trailing comma.
     trailing_commas: FxHashMap<BytePos, Span>,
 }
@@ -83,6 +82,7 @@ impl<I: Tokens> Parser<I> {
         Parser {
             state: Default::default(),
             input: Buffer::new(input),
+            found_module_item: false,
         }
     }
 
@@ -142,7 +142,7 @@ impl<I: Tokens> Parser<I> {
         let ctx = self.ctx() | Context::CanBeModule | Context::TopLevel;
 
         let body: Vec<ModuleItem> = self.with_ctx(ctx).parse_block_body(true, None)?;
-        let has_module_item = self.state.found_module_item
+        let has_module_item = self.found_module_item
             || body
                 .iter()
                 .any(|item| matches!(item, ModuleItem::ModuleDecl(..)));

Diff for: crates/swc_ecma_parser/src/parser/stmt.rs

@@ -124,7 +124,7 @@ impl<'a, I: Tokens> Parser<I> {
         match cur!(self, true) {
             tok!("await") if include_decl || top_level => {
                 if top_level {
-                    self.state.found_module_item = true;
+                    self.found_module_item = true;
                     if !self.ctx().contains(Context::CanBeModule) {
                         self.emit_err(self.input.cur_span(), SyntaxError::TopLevelAwaitInScript);
                     }