Export syntax creates duplicate default exports

[jxnblk]

Using the following syntax for layouts causes a syntax error (SyntaxError: Only one default export allowed per module.):

export { default } from './Layout'

[silvenon]

Just to expand upon this a bit.

The code snippet above is a way to make a default export using named exports. There are other variants of this, like:

// exporting directly from a module
export { Layout as default } from './components'

// exporting a variable
import Layout from './components'
export { Layout as default }

// bundled with other exports
export { Layout as default, meta } from './post-components'

etc. AFAICT, this isn't a simple regex fix because we need convert things like this:

export { default } from './Layout'

into something like this:

import Layout from './Layout'

export default ({ components, ...props }) =>
  <MDXTag name="wrapper" layout={Layout} ...

which means that we need to pick a name which doesn't collide with existing variable names etc.

I think we need to bring in Babel parser for this.

[timneutkens]

I'm strongly against bringing Babel into mdx to solve just one issue.
The question would be if we really need to support all these edge cases and extra JS syntax if it can be achieved another way.

[silvenon]

As a maintainer I'm against it as well, but I can see why people would expect this to work. I can submit a PR which raises an error upon encountering this syntax.

[jxnblk]

I agree with keeping Babel out of mdx. I mostly just wanted to share that I noticed that that particular syntax doesn't seem to work