Incorrect scope with @babel/preset-env due to plugin ordering #7557
Description
Choose one: is this a bug report or feature request? A bug report.
I couldn't tell if this was the same bug as other similar issues. Sorry for any duplication.
Input Code
for(let [a] of c) {
a=1;
()=>a;
}Babel/Babylon Configuration (.babelrc, package.json, cli command)
{
presets: [
[ '@babel/env', { debug: true } ]
]
}BROWSERSLIST='IE 11' npx babel --config-file ./.babelrc test.jsAdding in the destructuring plugin doesn't change anything.
Expected Behavior
Something like @babel/preset-es2015 produces (boilerplate omitted):
var _loop = function _loop() {
var _step$value = _slicedToArray(_step.value, 1),
a = _step$value[0];
a = 1;
(function () {
return a;
});
};
for (var _iterator = c[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
_loop();
}Current Behavior
var _loop = function _loop(_a) {
_a = 1;
(function () {
return _a;
});
a = _a;
};
var _iteratorNormalCompletion = true;
var _didIteratorError = false;
var _iteratorError = undefined;
try {
for (var _iterator = c[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
var _ref3 = _step.value;
var _ref2 = _slicedToArray(_ref3, 1);
var _a2 = _ref2[0];
_loop(_a2);
}The line a = _a assigns to a when no variable a is in scope.
It seems @babel/preset-env orders the relevant transforms like this:
transform-block-scoping { "ie":"11" }
transform-for-of { "ie":"11" }
when they really should be ordered like this:
transform-for-of { "ie":"11" }
transform-block-scoping { "ie":"11" }
or the relevant transformations should be insensitive to ordering.
You can run them by themselves to confirm:
npx babel --no-babelrc --plugins @babel/transform-for-of,@babel/transform-block-scoping test.js # works correctly
npx babel --no-babelrc --plugins @babel/transform-block-scoping,@babel/transform-for-of test.js # breaksContext
Our code had a more convoluted example, but basically captured a mutated loop variable within a lambda, and threw an exception at runtime because of the bogus assignment.
Your Environment
| software | version(s) |
|---|---|
| Babel | 7.0.0-beta.40 |
| node | 9.8.0 |
| npm | 5.6.0 |
| Operating System | macOS 10.13.3 |