Faster tokenizer lookahead (#13341)

* refactor: simplify token context structure

* add benchmark

* perf: return a sub-state on tokenizer lookahead

* Update packages/babel-parser/src/tokenizer/index.js

Co-authored-by: Brian Ng <bng412@gmail.com>

* Update packages/babel-parser/src/tokenizer/index.js

Co-authored-by: Brian Ng <bng412@gmail.com>

* remove irrelevant comment

* fix: guard curPosition with isLookahead

* add test cases

Co-authored-by: Brian Ng <bng412@gmail.com>

packages/babel-parser/src/plugins/flow/index.js

@@ -9,7 +9,6 @@ import type Parser from "../../parser";
 import { types as tt, type TokenType } from "../../tokenizer/types";
 import * as N from "../../types";
 import type { Pos, Position } from "../../util/location";
-import type State from "../../tokenizer/state";
 import { types as tc } from "../../tokenizer/context";
 import * as charCodes from "charcodes";
 import { isIteratorStart, isKeyword } from "../../util/identifier";
@@ -154,7 +153,7 @@ function hasTypeImportKind(node: N.Node): boolean {
   return node.importKind === "type" || node.importKind === "typeof";
 }
 
-function isMaybeDefaultImport(state: State): boolean {
+function isMaybeDefaultImport(state: { type: TokenType, value: any }): boolean {
   return (
     (state.type === tt.name || !!state.type.keyword) && state.value !== "from"
   );

packages/babel-parser/src/plugins/jsx/index.js

@@ -15,6 +15,10 @@ import { isIdentifierChar, isIdentifierStart } from "../../util/identifier";
 import type { Position } from "../../util/location";
 import { isNewLine } from "../../util/whitespace";
 import { Errors, makeErrorTemplates, ErrorCodes } from "../../parser/error";
+import type { LookaheadState } from "../../tokenizer/state";
+import State from "../../tokenizer/state";
+
+type JSXLookaheadState = LookaheadState & { inPropertyName: boolean };
 
 const HEX_NUMBER = /^[\da-fA-F]+$/;
 const DECIMAL_NUMBER = /^\d+$/;
@@ -573,6 +577,14 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       }
     }
 
+    createLookaheadState(state: State): JSXLookaheadState {
+      const lookaheadState = ((super.createLookaheadState(
+        state,
+      ): any): JSXLookaheadState);
+      lookaheadState.inPropertyName = state.inPropertyName;
+      return lookaheadState;
+    }
+
     getTokenFromCode(code: number): void {
       if (this.state.inPropertyName) return super.getTokenFromCode(code);