transformed generator code doesn't work for 'break' in 'while' and 'switch'

[Justin-ZS]

Bug Report

My generator code didn't work correctly after upgrade to babel 7

Original code

function* transform_generator_issue(input) {
  const id = i => i;
  while (true) {
    const a = 1;
    const f = x => id(x, a);
    switch (input) {
      default: {
        yield 1;
        break;
      }
    }
  }
}

this generator should create an infinite iterator.

Transformed code

function transform_generator_issue(input) {
  var id, _loop, _ret;

  return regeneratorRuntime.wrap(function transform_generator_issue$(_context3) {
    while (1) {
      switch (_context3.prev = _context3.next) {
        case 0:
          id = function id(i) {
            return i;
          };

          _loop =
          /*#__PURE__*/
          regeneratorRuntime.mark(function _loop() {
            var a, f;
            return regeneratorRuntime.wrap(function _loop$(_context2) {
              while (1) {
                switch (_context2.prev = _context2.next) {
                  case 0:
                    a = 1;

                    f = function f(x) {
                      return id(x, a);
                    };

                    _context2.t0 = input;
                    _context2.next = 5;
                    break;

                  case 5:
                    _context2.next = 7;
                    return 1;

                  case 7:
                    return _context2.abrupt("return", "break"); // should be _context2.abrupt("break", 8)

                  case 8:
                  case "end":
                    return _context2.stop();
                }
              }
            }, _loop, this);
          });

        case 2:
          if (false) {}

          return _context3.delegateYield(_loop(), "t0", 4);

        case 4:
          _ret = _context3.t0;

          if (!(_ret === "break")) {
            _context3.next = 7;
            break;
          }

          return _context3.abrupt("break", 9);

        case 7:
          _context3.next = 2;
          break;

        case 9:
        case "end":
          return _context3.stop();
      }
    }
  }, _marked2, this);
}

With the wrong _context2.abrupt("return", "break"), the iterator will jump out the while statement.

Useless effort

1. If i remove some code in the sample, it will produce correct code.

// every function below will give me correct code.
function* transform_generator_issue(input) {
  const id = i => i;
  while (true) {
    // const a = 1;
    const f = x => id(x);
    switch (input) {
      default: {
        yield 1;
        break;
      }
    }
  }
}
// or
function* transform_generator_issue(input) {
  const id = i => i;
  while (true) {
    const a = 1;
    // const f = x => id(x, a);
    switch (input) {
      default: {
        yield 1;
        break;
      }
    }
  }
}
// or a infinite loop
function* transform_generator_issue(input) {
  const id = i => i;
  while (true) {
    const a = 1;
    const f = x => id(x, a);
    switch (input) {
      default: {
        // yield 1;
        break;
      }
    }
  }
}

2. I can't reproduce this bug in offical repl

3. I can't reproduce this bug in babel cli too
   I try to install @babel/cli@7.1.2 @babel/core@7.1.2 @babel/plugin-transform-regenerator@7.0.0.
   run npx babel --plugins @babel/plugin-transform-regenerator code.js.
   the output is:

var _marked =
/*#__PURE__*/
regeneratorRuntime.mark(transform_generator_issue);

function transform_generator_issue(input) {
  var id, a, f;
  return regeneratorRuntime.wrap(function transform_generator_issue$(_context) {
    while (1) switch (_context.prev = _context.next) {
      case 0:
        id = i => i;

      case 1:
        if (!true) {
          _context.next = 12;
          break;
        }

        a = 1;

        f = x => id(x, a);

        _context.t0 = input;
        _context.next = 7;
        break;

      case 7:
        _context.next = 9;
        return 1;

      case 9:
        return _context.abrupt("break", 10);

      case 10:
        _context.next = 1;
        break;

      case 12:
      case "end":
        return _context.stop();
    }
  }, _marked, this);
}

Environment

• Babel version(s): 7.1.2
• Node/npm version: Node 11.1.0/npm 6.4.1
• OS: OSX 10.12.6
• Monorepo: yes
• How you are using Babel: loader with webpack

[babel-bot]

Hey @Justin-ZS! 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.

[nicolo-ribaudo]

This should be fixed by #8914. Can you try version 7.1.5?

[Justin-ZS]

@nicolo-ribaudo
Hi! this bug has been fixed after upgrading @babel/preset-env to ^7.1.5.
👍