The camelcase rule does not allow leading/trailing underscores for variable names

Tell us about your environment

• ESLint Version: v4.13.0
• Node Version: v8.9.3
• npm Version: v5.5.1

What parser (default, Babel-ESLint, etc.) are you using? default

Please show your full configuration:

Configuration

{
    "parserOptions": {
        "ecmaVersion": 8,
        "sourceType": "module",
        "ecmaFeatures": {}
    },
    "rules": {
        "camelcase": 2
    },
    "env": {}
}

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

Contents of test.js:

function shouldAllowUndercoreVars() {
	let { _value } = this;
	return _value;
}
shouldAllowUndercoreVars()

Shell command used:

eslint test.js

This is currently reproducible on the eslint demo site: https://eslint.org/demo/#eyJ0ZXh0IjoiZnVuY3Rpb24gc2hvdWxkQWxsb3dVbmRlcmNvcmVWYXJzKCkge1xuXHRsZXQgeyBfdmFsdWUgfSA9IHRoaXM7XG5cdHJldHVybiBfdmFsdWU7XG59XG5zaG91bGRBbGxvd1VuZGVyY29yZVZhcnMoKSIsIm9wdGlvbnMiOnsicGFyc2VyT3B0aW9ucyI6eyJlY21hVmVyc2lvbiI6OCwic291cmNlVHlwZSI6Im1vZHVsZSIsImVjbWFGZWF0dXJlcyI6e319LCJydWxlcyI6eyJjYW1lbGNhc2UiOjJ9LCJlbnYiOnt9fX0=

What did you expect to happen? I would have expected it to allow the variable name based on the camelcase docs docs quoted below:

It ignores leading and trailing underscores and only checks those in the middle of a variable name.

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

/Users/kyle/tmp/test.js
  2:8  error  Identifier '_value' is not in camel case  camelcase

✖ 1 problem (1 error, 0 warnings)

[platinumazure]

I’m hoping the team agrees that this should justify a patch release; if so, that patch release will probably occur sometime on Monday. Thanks for your patience and thank you also for testing the change!

[platinumazure]

Agreed, this seems to only apply to destructuring however.

No lint errors:

const _value = true;

Has lint errors (incorrectly):

const { _value } = obj;

@KylePDavis Does this occur in 4.12.x for you? Wondering if this was a side-effect of #9468.