missing parentheses in exponentiation with unary left side

[j4k0xb]

reproduction: https://stackblitz.com/edit/stackblitz-starters-9gkcmv?file=index.js&view=editor

const { parse, print, types } = require('recast');
const b = types.builders;

const { code } = print(
  b.binaryExpression(
    '**',
    b.unaryExpression('-', b.numericLiteral(1)),
    b.numericLiteral(2)
  )
);

console.log(code);
console.log(eval(code));

it prints -1 ** 2 which is invalid syntax:

Uncaught SyntaxError: Unary operator used immediately before exponentiation expression. Parenthesis must be used to disambiguate operator precedence

expected: (-1) ** 2

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_precedence#table 2.

related but not fixed by #363

[eventualbuddha]

Thanks for reporting this, @j4k0xb! Mind trying #1361 to see if that fixes it for you?

[j4k0xb]

yes that fixed it, thanks!

[j4k0xb]

a bit related but parsing (-1) ** 2 also fails

• https://github.com/jquery/esprima/pull/2070 will probably not get merged
• recast.parse('(-1) ** 2', { parser: acorn }) only allows es6 syntax, any idea why? https://github.com/benjamn/recast/blob/2bb3a4ffddf038138fefa8c49158ffcfe14515ea/lib/parser.ts#L32

[eventualbuddha]

I'm not sure why it's hardcoded to ecmaVersion: 6. I'm guessing it was added when that was the latest standard.