Bug Report

This is about an internal API to detect TDZ : _guessExecutionStatusRelativeTo

Current Behavior

• When used with preset-env, the method _guessExecutionStatusRelativeTo predicts the execution result and is the opposite of when used without preset-env

Input Code

Minimal Reproduction in this repo -

https://github.com/boopathi/babel-exec-status-bug-1

const x = 1, {y} = x;

Plugin Code

module.exports = function(babel) {
  const { types: t } = babel;

  return {
    visitor: {
      ReferencedIdentifier(path) {
        if (path.isBindingIdentifier()) return;
        const binding = path.scope.getBinding(path.node.name);

        if (!binding) return;

        const execStatus = binding.path._guessExecutionStatusRelativeTo(path);

        if (execStatus === "before") {
          const evalResult = path.evaluate();

          if (evalResult.confident) {
            path.replaceWith(t.valueToNode(evalResult.value));
          }
        } else if (execStatus === "after") {
          //
          // This happens when `block scoped vars` are converted to vars
          // i.e. the execStatus computes to `after` even though it actually is `before`
          //
          path.replaceWith(t.valueToNode(undefined));
        }
      }
    }
  };
};

Expected behavior/code:

With (or) without preset-env, the behavior is expected to be the same - when the preset-env does not change the meaning of the code in this context.

Babel Configuration (.babelrc, package.json, cli command)

{
  "presets": [
    { plugins: ["the above plugin"] },
    "@babel/preset-env"
  ]
}

Environment

• Babel version(s): 7.0.0-beta.47
• How you are using Babel: Node API

Possible Solution

Not sure. Without the preset-env it works as expected.

I'm not sure which one to look - preset-env plugins or the _guessExecutionStatus function. Maybe preset-env misses registration of the newly created items that _guessExecutionStatus isn't able to figure it out. I'll try to look and debug at the _guessExecutionStatusRelativeTo function more.

Additional context/Screenshots

The current TDZ evaluation is based on a custom implementation in babel-minify. I'm trying to use this API in babel-minify to get TDZ.