Rewrite Bun in Rust has been merged

Blog post with details coming soon.

It passes Bun's pre-existing test suite on all platforms (and fixes several memory leaks and flaky tests), the binary size shrinks by 3 MB - 8 MB, the benchmarks are between neutral and faster - and most importantly, we now have compiler-assisted tools for catching & preventing memory bugs, which have costed the team an enormous amount of development & debugging time over the years.

The codebase is otherwise largely the same. The same architecture, the same data structures. Bun still uses few 3rd party libraries. No async rust.

To try this, run:

bun upgrade --canary

Please do file issues if you run into any. If this thread gets crazy I will lock it.

Note:

• Still some optimization work to do before this lands in non-canary version.
• Still some cleanup work to do (which will come in a series of follow-up PRs)