object-shorthand: autofix breaks first arrow function in default parameter

[nstepien]

Tell us about your environment

• ESLint Version: 5.12.1
• Node Version: 11.7.0
• npm Version: 6.5.0

What parser (default, Babel-ESLint, etc.) are you using?
babel-eslint, @typescript-eslint/parser, and the default parser.
Please show your full configuration:

Configuration

module.exports = {
  parserOptions: {
    "ecmaVersion": 6
  },
  rules: {
    'object-shorthand': [1, "always", { avoidExplicitReturnArrows: true }]
  }
};

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

var test = {
  key0: function(arg) {},
  key1: (arg) => {},
  key2: (arg = () => {}) => {},
  key3: (arg1 = () => {}, arg2 = () => {}) => {}
}

eslint --fix --ext js,jsx,ts,tsx --max-warnings 0 -f codeframe --cache --color src

What did you expect to happen?
Autofix should have been:

var test = {
  key0(arg) {},
  key1(arg) {},
  key2(arg = () => {}) {},
  key3(arg1 = () => {}, arg2 = () => {}) {}
}

What actually happened? Please include the actual, raw output from ESLint.
Autofix gives invalid syntax:

var test = {
  key0(arg) {},
  key1(arg) {},
  key2(arg = () {}) => {},
  key3(arg1 = () {}, arg2 = () => {}) => {}
}

Command output:

error: Parsing error: Unexpected token ) at src\file.js:4:15:
  2 |   key0(arg) {},
  3 |   key1(arg) {},
> 4 |   key2(arg = () {}) => {},
    |               ^
  5 |   key3(arg1 = () {}, arg2 = () => {}) => {}
  6 | }
  7 |


1 error found.

Are you willing to submit a pull request to fix this bug?
No, but @platinumazure might have some thoughts about this.

[platinumazure]

It looks like the issue is we find and remove the first arrow token in the object value, which could find an arrow token in a default parameter:

const arrowToken = sourceCode.getTokens(node.value).find(token => token.value === "=>");

Instead, I think we should be looking for the last arrow token before the body node. Something like:

// Note: We know we're in an ArrowFunctionExpression already
const arrowToken = sourceCode.getTokenBefore(node.value.body, { filter: token => token.value === "=>" });

There might be a bit more to it, but I'm hoping that will do the job for most cases.