[function-paren-newline] Missing support for async arrow functions

[mdziekon]

Tell us about your environment

• ESLint Version: 7.10.0
• Node Version: 14.7.0
• npm Version: 6.14.7

What parser (default, @babel/eslint-parser, @typescript-eslint/parser, etc.) are you using?

default

Please show your full configuration:

Configuration

module.exports = {
    rules: {
        'function-paren-newline': [
            'error',
            'multiline',
        ],
    },
};

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

const test = async (foo,
    bar) => {};

./node_modules/.bin/eslint src/test.js

What did you expect to happen?

ESLint should report the following problems:

  1:20  error  Expected newline after '('                             function-paren-newline
  2:8   error  Expected newline before ')'                            function-paren-newline

ESLint should be able to autofix this issue by inserting missing newlines.

What actually happened? Please include the actual, raw output from ESLint.

No errors were reported.

Are you willing to submit a pull request to fix this bug?

Yes

Cause of the problem

In this rule's getParenTokens function, when analysing ArrowFunctionExpression, the code wrongly assumes that any arrow function always starts with a parenthesis opening. Since the introduction of async / await syntax, this is no longer the case.

Scope of the problem

This issue affects all possible options, not only the multiline one as shown in my example.

[yeonjuan]

@mdziekon Hi :) Thanks for the report
It seems missing support for the async arrow function.

• online-demo

/* eslint function-paren-newline: ["error", "multiline"] */

function func(bar,	// error
               baz) {} // error

var arrow = (bar, // error
             baz) => {}  // error

var asyncArrow = async (bar, // no error
                  baz) => {} // no error