Naming collision in mangle plugin when using transformFromAST

[kangax]

TLDR:

(traverse + block-scoping) → AST → traverse.clearCache() → (traverseFromAST + mangle) results in a naming conflict :)

The following code:

const babel = require('babel-core');
const traverse = require('babel-traverse').default;
const mangle = require('./packages/babel-plugin-minify-mangle-names/lib/index.js');

const srcTxt = `
  function f(x) {
    for (let i = 0; i; i++) {
      let n;
      if (n) return;
      g(() => n);
    }
  }
`;

const ast = babel.transform(srcTxt, {
  code: false,
  plugins: ['transform-es2015-block-scoping'],
}).ast;

traverse.clearCache();

const code = babel.transformFromAst(ast, null, {
  plugins: [mangle],
}).code;

console.log(code);

produces this output:

function f(a) {
  var b = function (c) {
    var b = void 0;
    if (b) return {
        v: void 0
      };
    g(() => b);
  };

  for (var c = 0; c; c++) {
    var a = b(c);
    if (typeof a === "object") return a.v;
  }
}

Notice conflict between a in arguments and a in a loop block. Removing clearCache fixes it BUT then mangling is incomplete:

function f(a) {
  var _loop = function (b) {
    var b = void 0;
    if (b) return {
        v: void 0
      };
    g(() => b);
  };

  for (var b = 0; b; b++) {
    var _ret = _loop(b);

    if (typeof _ret === "object") return _ret.v;
  }
}

[jamiebuilds]

Sidenote: @kittens Is there any reason that babel.transform* doesn't call traverse.clearCache() before or after it runs? Seems like you'd always want that unless I'm missing something

[kangax]

This is now fixed in a new mangler