Bug: switch statements containing closures are broken

[mbostock]

Bug Report

Current behavior
Switch statements containing closures are generating broken code causing adjacent cases to run. See this minimal reproduction with the default settings:

https://babeljs.io/en/repl#?browsers=defaults&build=&builtIns=false&spec=false&loose=false&code_lz=GYewTgBAFAxiB2BnALhAhhEwIG0CMAugJQQDeAUBBIgO4CWyMAFtMmAK4CmJFVVMaRJwhsuALjKU-_BCggAjCAF4IeANxTpUEkoB8CjdKp1sUUdwVhOaANaGjceMjrwu9qgF9NEAUIjA0ABshCV4jZCYwEBoIeE4YgFEwKLAoACJ2eCs0ZjR5QM40oncIL09yLyA&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=7.10.4&externalPlugins=

Input Code

for (const a of [1]) {
  switch (true) {
    case true: {
      const b = 1;
      () => b;
      if (true) break;
      continue;
    }
    case false: {
      throw new Error("unreachable");
    }
  }
}

Output Code

for (var _i = 0, _arr = [1]; _i < _arr.length; _i++) {
  var a = _arr[_i];

  switch (true) {
    case true:
      {
        var _ret = function () {
          var b = 1;

          (function () {
            return b;
          });

          if (true) return "break";
          return "continue";
        }();

        switch (_ret) {
          case "break":
            break;

          case "continue":
            continue;
        }
      }

    case false:
      {
        throw new Error("unreachable");
      }
  }
}

Expected behavior
No error is thrown (the break statement functions as intended, and the false case does not run).

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)
Defaults. See the REPL.

Environment
Defaults. See the REPL.

Possible Solution
If you want to use a break statement here, it needs to be a labeled break to break the outer loop.

switch (_ret) {
  case "break":
    break outer;

  case "continue":
    continue;
}

Alternatively, use an if instead of a nested switch.

if (_ret === "break") break;
if (_ret === "continue") continue;

[babel-bot]

Hey @mbostock! 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."

[Andarist]

Thanks for the report! I'm marking this as "help wanted" - maybe some volunteer will jump into fixing this before the core team manages to do it. I believe the solution using if statements seems like the easier one.

[JLHwung]

Duplicate of #11690

[hzoo]

Thanks for the report and suggested fix @mbostock!