Same variables in switch/case is corrupts code

[mixalbl4-127]

BEFORE YOU SUBMIT please read the following:

I'm submitting a bug report

Webpack Version:
4.44.2 - latest

Babel Core Version:
7.11.6 - latest

Babel Loader Version:
8.1.0 - latest

Please tell us about your environment:
Linux Mint 18.3

Current behavior:
index.js

window.test = () => {
    const e = "TEST";
    switch (e) {
        case "TEST":
            const e = [];
            e.push('111');
            alert(e);
            break;
        default: alert('666'); break;
    }
};

converts to:
dist/out.js

    window.test = function () {
        switch (e) {
            case"TEST":
                var e = [];
                e.push("111"), alert(e);
                break;
            default:
                alert("666")
        }
    }

const e = "TEST"; was removed!

Expected/desired behavior:
since this variable is used in the switch, it should not be removed

webpack.config.js

const path = require("path");

module.exports = {
    entry: { main: './index.js' },
    module: {
        rules: [
            {
                oneOf: [
                    {
                        test: /\.js$/,
                        loader: require.resolve("babel-loader"),
                        options: {
                            presets: ['@babel/preset-env']
                        }
                    }
                ]
            }
        ]
    },
    output: {
        path: path.resolve(__dirname, 'dist'),
        filename: 'out.js'
    },
};

• What is the motivation / use case for changing the behavior?
  Same issue for terser: assignment in switch statement corrupts program terser/terser#445
  Same issue for vscode: Avoid shadowed variable declarations microsoft/vscode#80311

[nicolo-ribaudo]

I get this output: it's different, but still broken (it should be switch (e)):

window.test = function () {
  var e = "TEST";

  switch (_e) {
    case "TEST":
      var _e = [];

      _e.push('111');

      alert(_e);
      break;

    default:
      alert('666');
      break;
  }
};

[babel-bot]

Hey @mixalbl4-127! We really appreciate you taking the time to report an issue. The collaborators on this project attempt to help as many people as possible, but we're a limited number of volunteers, so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack community that typically always has someone willing to help. You can sign-up here for an invite."

[merceyz]

• Reproduces: https://babeljs.io/repl#?browsers=defaults&build=&builtIns=false&spec=false&loose=false&code_lz=O4SwdgJg9sB0AuBTAzvABAXjQCgJSYD40BvAKDQrQGMoxU1FM0AiAFQFEBlV5gbnMrJQ8KgAscifGUozqAQ2SM2XHgC4Bs2TTrpGWANoBdfps2JYABwCuyUdgDkARmf3cJ0zLkAbRACd42JLuHhQARr6IcgDWwbIQiABmclZe8Kpo3n4B9gBsea68aOGRMRpoAL6k5bxAA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=false&sourceType=module&lineWrap=true&presets=env%2Creact%2Cstage-2%2Cenv&prettier=false&targets=&version=7.11.6&externalPlugins=
• Doesn't reproduce: https://babeljs.io/repl#?browsers=defaults%2C%20not%20ie%2011&build=&builtIns=false&spec=false&loose=false&code_lz=O4SwdgJg9sB0AuBTAzvABAXjQCgJSYD40BvAKDQrQGMoxU1FM0AiAFQFEBlV5gbnMrJQ8KgAscifGUozqAQ2SM2XHgC4Bs2TTrpGWANoBdfps2JYABwCuyUdgDkARmf3cJ0zLkAbRACd42JLuHhQARr6IcgDWwbIQiABmclZe8Kpo3n4B9gBsea68aOGRMRpoAL6k5bxAA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=false&sourceType=module&lineWrap=true&presets=env%2Creact%2Cstage-2%2Cenv&prettier=false&targets=&version=7.11.6&externalPlugins=