Adding parserOptions to babel-core transform result

[kesne]

Q	A
Patch: Bug Fix?	No
Major: Breaking Change?	No
Minor: New Feature?	Yes
Tests Added/Pass?	Not yet
Spec Compliancy?	N/A
License	MIT
Doc PR	No
Any Dependency Changes?	No

This adds parserOptions to the transform result from babel-core. The intent here is to be able to run a no-op through babel.transform() and get the resulting babylon options. These could then be used in something like babel-eslint to automatically have it configured based on the result of your babel plugins.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/5075/

[loganfsmyth]

I'm 100% behind enabling the usecase of resolving configs for babel-eslint, but I'd rather we expose a first-class option for it, rather than exposing it through a side-channel of a no-op transformation.

We currently expose loadOptions as part of the primary API, but I think we could pretty easily expose another function that had a similar behavior while exposing the parser options.

[kesne]

Yeah I'd love to expose a real way to do this, I can take that route, it just seemed a little difficult because we'd have to re-create some of the logic in the File class.

[ljharb]

cc @hzoo; this is related to the babel-eslint stuff we talked about this week :-)

[loganfsmyth]

I'm going to see if I can expose this in a better way with some refactoring, but I'll report back.

[loganfsmyth]

What should happen if you run try to lint a file that has been ignored either via .babelignore or .babelrc config? With the current config system, we bail out of config loading as soon as we see that a file is ignored, so there isn't a way to get the config options. We can add a way to do that, but I question how useful that would be.

[ljharb]

I would assume either, is treated the same as "env targets + no transforms", or falls back to the default parser, or falls back to ES5.

Ignoring that dir is definitely not that useful; eslintignore should be the only place files can be ignored.

[loganfsmyth]

Closing since this is making progress in babel/babel-eslint#594