newline-after-var rule is broken with babel-eslint >= 9

[brokenmass]

Tell us about your environment

• ESLint Version: 5.16.0
• Node Version: 10
• npm Version: 6.10

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

Please show your full configuration:

Configuration

module.exports = {
  env: {
    browser: true,
    es6: true,
    node: true
  },
  parser: 'babel-eslint',
  parserOptions: {
    ecmaFeatures: {
      globalReturn: false,
      impliedStrict: true,
      jsx: true
    },
    ecmaVersion: 2017,
    sourceType: 'module'
  },
  plugins: [
    'babel'
  ],
  "rules": {
    "newline-after-var": [
      "error",
      "always"
    ]
  }
}

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 const1 = 1;
let variable1 = 1;
let variable2 = 1;
let variable3 = 1;

eslint --ignore-path .gitignore '**/*.js'

What did you expect to happen?
expected eslint to not return any error

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

eslint-newline-after-var-bug/index.js
  1:1  error  Expected blank line after variable declarations  newline-after-var
  2:1  error  Expected blank line after variable declarations  newline-after-var
  3:1  error  Expected blank line after variable declarations  newline-after-var

Explanation
Since version 9.0.0, babel-eslint broke the eslint rule newline-after-var. the reason is that since that version they have been using @babel/parser@^7 and that changed how the code AST is generated. In the specific let token does not have Keyword type anymore but instead has type Identifier (this is probably because of this so this problem is also loosely correlated to #11830)

This change affect the newline-after-var rule as it use the following check to group together chunks of variable declaration (link to actual code):

if (nextToken.type === "Keyword" && isVar(nextToken.value)) {
  return;
}

while the second part of the if is still valid the first now fails for let variables (this bug does not affects const or var)

Related babel-eslint issue
babel/babel-eslint#771

Are you willing to submit a pull request to fix this bug?
yes if we can agree on a solution and where to implement it (eslint@newline-after-var rule or babel-eslint@babylon-to-espree code)

[g-plane]

Hey @brokenmass , thanks for the issue.

This rule has been deprecated.

[brokenmass]

@g-plane thanks for the quick response. I totally missed the fact that the rule had been deprecated.