YOLO: https://phabricator.babeljs.io/T1633 . It seems that babelrc: false should have the same effect. Would you mind trying that instead?

Yeah, I tried to use it, but it's not working. The purpose of babelrc has been changed in Babel 6.

Babel 5:

babelrc (default value = null) Specify a custom file path to load a .babelrc config from.

Babel 6:

babelrc (default value = true) Specify whether or not to use .babelrc and .babelignore files.

Uh :-/ It looked like it should work because of this check:

    // resolve all .babelrc files
    if (opts.babelrc !== false) {
      this.findConfigs(opts.filename);
    }

But OK, breakConfig is basically doing the same thing a few lines above.

Well, opts.babelrc is undefined... I did very simple thing:

function setup(tr, babel) {
  if (babel === 'babel') {
    require('babel-core/register')({ babelrc: false });
  }
  transform = require(tr);
}

console.log('opts:', opts);
// resolve all .babelrc files
if (opts.babelrc !== false) {
  this.findConfigs(opts.filename);
}

Output: opts: { filename: '<my-transformation>.js' }.
And they taking breakConfig not from opts but from this.options...

Ah I see. The options object passed to the function (transformOpts) is not passed passed to init, but added separately:

  var optsManager = new OptionManager;
  optsManager.mergeOptions(transformOpts);
  opts = optsManager.init(opts);

that's why opts.babelrc doesn't work but this.options.breakConfig does.

Released with v0.3.13.

Awesome, thanks!