Line breaks in block-level JSX create unexpected whitespace in the output

Subject of the issue

As we’re trying to improve Prettier’s support of MDX, I’m trying to understand its syntax better. So far it looked like block-level JSX is supposed to be 100% React-compatible for it to be possible to copy-paste React code from JS to MDX (also it would allow Prettier to use the same code for formatting JSX that it uses for JSX in JS). But I found an incompatibility that breaks this use case, namely: a line break between an element and text doesn’t create whitespace in the output in React but does in MDX. Posting here after asking on Spectrum.

Your environment

The official playground https://mdxjs.com/playground/

Steps to reproduce

<b>foo</b>
bar

Expected behaviour

Should be rendered as

foobar

https://codepen.io/thorn0/pen/NWWEaoo

Actual behaviour

Is rendered as

foo bar

[wooorm]

forgot to mention it here, but this landed for v2, on the next branch

[wooorm]

Hi all! I’m going to close this as it landed on the main, the (now default) branch we’re using to gear up to the MDX@2 release.

The reason is so that it’s more clear which issues still need to be solved already and don’t require further work.

Expect another next release soonish, which might include it, or maybe it’s already released as a beta!

For more info, see https://github.com/mdx-js/mdx/issues/1041.