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This PR implements a configuration option in `next.config.js` to support
for rust-based MDX compiler (https://github.com/wooorm/mdxjs-rs).
Currently it is marked as experimental, as mdx-rs and loader both may
need some iteration to fix regressions.
When a new experimental flag is set (`mdxRs: true`), instead of using
`@mdx/js` loader `next/mdx` loads a new webpack loader instead.
Internally, it mostly mimics mdx/js's loader behavior, however actual
compilation will be delegated into next/swc's binding to call mdx-rs's
compiler instead.
I choose to use next-swc to expose its binding function, as mdx-rs
internally uses swc already and creating new binary can double up
bytesize (with all the complex processes of publishing new package).
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
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