Metro minify changes code behavior

[yulanggong]

Do you want to request a feature or report a bug?

report a bug

What is the current behavior?

entry.js

function bnpInvDigit(b, DV) {
    if ((b & 1) == 0) {
        return 0;
    }
    var a = b & 3,
        a = (a * (2 - (b & 15) * a)) & 15,
        a = (a * (2 - (b & 255) * a)) & 255,
        a = (a * (2 - (((b & 65535) * a) & 65535))) & 65535,
        a = (a * (2 - ((b * a) % DV))) % DV;
    return a > 0 ? DV - a : -a;
}

console.log(bnpInvDigit(3, 3)); // 2
console.log(bnpInvDigit(3, 6)); // 5

metro build entry.js -O out.js

The codes passed to minifier in node_modules/metro/src/JSTransformer/worker.js:

__d(function (g, r, i, a, m, e, d) {
  "use strict";

  function bnpInvDigit(b, DV) {
    if ((b & 1) == 0) {
      return 0;
    }

    var _a3 = b & 3,
        // from here caused the bug
        a = _a3 * (2 - (b & 15) * _a3) & 15,
        a = _a3 * (2 - (b & 255) * _a3) & 255,
        a = _a3 * (2 - ((b & 65535) * _a3 & 65535)) & 65535,
        // end of the bug
        _a3 = _a3 * (2 - b * _a3 % DV) % DV;

    return _a3 > 0 ? DV - _a3 : -_a3;
  }

  console.log(bnpInvDigit(3, 3));
  console.log(bnpInvDigit(3, 6));
});

The primary part of the result:

function n(n, o) {
    if (0 == (1 & n)) return 0;
    var t;
    t = 3 & n;
    return (t = (t * (2 - ((n * t) % o))) % o) > 0 ? o - t : -t;
}
console.log(n(3, 3)), // -0
console.log(n(3, 6)); // 3

If the current behavior is a bug, please provide the steps to reproduce and a minimal repository on GitHub that we can yarn install and yarn test.

as above

What is the expected behavior?

do it right

Please provide your exact Metro configuration and mention your Metro, node, yarn/npm version and operating system.

• Metro 0.59.0

[yulanggong]

metro/packages/metro-transform-plugins/src/normalizePseudoGlobals.js

Line 84 in ccba71d

path.scope.rename(shortName, path.scope.generateUid(shortName));

This line caused the bug, maybe a babel bug babel/babel#11591.

Here is a workaround to avoid this bug:

module.exports = {
    transformer: {
        optimizationSizeLimit: 0
    }
};

[yulanggong]

bug fixed in babel v7.10.0
babel/babel#11595