"async" identifier is wrongly reported as a parsing error

[ashwinbaliga]

Steps to reproduce

Call the following API for the given piece of code:
esprima.parseModule(sourceCode, { loc: true, tolerant: true });

class MyClass {
    async;
    foo() {
    }
}

Expected output

The parsing goes through fine

Actual output

Error
description: "Unexpected token ;"
index: 28
lineNumber: 2
column: 10
stack: "Error: Line 2: Unexpected token ;\n    at ErrorHandler.constructError (http://localhost:8000/esprima-next/esprima-next.js:1482:17)
    at ErrorHandler.createError (http://localhost:8000/esprima-next/esprima-next.js:1495:25)
    at Parser.unexpectedTokenError (http://localhost:8000/esprima-next/esprima-next.js:2890:32)
    at Parser.throwUnexpectedToken (http://localhost:8000/esprima-next/esprima-next.js:2899:16)
    at Parser.parseObjectPropertyKey (http://localhost:8000/esprima-next/esprima-next.js:3403:22)
    at Parser.parseClassElement (http://localhost:8000/esprima-next/esprima-next.js:5696:24)
    at Parser.parseClassElementList (http://localhost:8000/esprima-next/esprima-next.js:5797:24)
    at Parser.parseClassBody (http://localhost:8000/esprima-next/esprima-next.js:5805:30)
    at Parser.parseClassDeclaration (http://localhost:8000/esprima-next/esprima-next.js:5821:28)
    at Parser.parseStatementListItem (http://localhost:8000/esprima-next/esprima-next.js:4405:28)"

Relevant references

"async" is a valid identifier. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar

Some keywords are reserved, meaning that they cannot be used as an identifier for variable declarations, function declarations, etc. They are often called reserved words. A list of these reserved words is provided below. Not all keywords are reserved — for example, async can be used as an identifier anywhere.