Document usage of babel.config.js files

[novemberborn]

As of #1798 we support Babel 7 beta 48. This supports a new babel.config.js file.

We need to update our Babel recipe with examples of babel.config.js files. I think we may even be able to remove .babelrc examples, as I'm under the impression that this is the desired new config format for Babel 7.

We need to update our Babel integration tests (in test/api.js) so we're also testing babel.config.js files. We should change our default behavior so that both babelrc and config files are considered when compiling test & helper files. See:

ava/lib/babel-pipeline.js

Line 28 in a5de369

const defaultOptions = {babelrc: true};

ava/lib/babel-pipeline.js

Line 125 in a5de369

configFile: false,

[danny-andrews]

Just for clarification, does ava currently support babel.config.js? i.e., is this simply a documentation/test issue?

[kevva]

@danny-andrews, yes, if you add something like this to your ava config:

"babel": {
	"testOptions": {
		"configFile": "./babel.config.js"
	}
}

[novemberborn]

We need to auto-detect it though, like we do .babelrc files. That's not implemented yet. We also need tests for that implementation, including what happens when both files are present.

Then, I'd like to update our documentation to use babel.config.js rather than .babelrc.

[kevva]

@novemberborn, wouldn't just providing configFile: true in defaultOptions work? Then it'd fallback to Babels own behaviour. And yeah, needs some tests too.

[novemberborn]

@kevva yup, I just didn't want to do that without having tests and an understanding of how it all behaves.

[novemberborn]

master now supports babel.config.js files, but we still need to update the documentation.